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SpaceX Vehicles and Missions => SpaceX Super Heavy/Starship (BFR/BFS) - Earth to Deep Space => Topic started by: Nevyn72 on 02/15/2020 10:18 pm

Title: Starship On-orbit refueling - Options and Discussion
Post by: Nevyn72 on 02/15/2020 10:18 pm
Rather than clutter up the Off Earth modification and Assembly thread it's probably time that the In-orbit refueling concept gets it's own thread.

My own thoughts are that some concepts are getting a bit complicated and convoluted for their own good, especially at such an early stage in the process.

The first stage is and should be SS to SS refueling. This has the advantages of;
- simplest hardware
- you are only manufacturing one type of orbital hardware
- greatest flexibility (of mission profile)
- proof of concept with the most capable vehicle (ie. a fully maneuverable space ship)

In my opinion the second stage of development of the concept should be a permanently orbiting 'tank' which can be repositioned in orbit as required.
The prime candidate for this would be a modified SH which would be comparatively easily developed given it's an iteration of an existing design.

I envisige you would replace the SH thrust structure with a SS thrust structure. The SH (tank) could even supply fuel to the SH (launch) to help with the increased takeoff weight. You would then be using the proven SS attachment system for In-Orbit fuel transfers.

You could have a small nose section containing header tanks for the RCS system, batteries, avionics and even a deployable solar array. The existing SH design (with a SS thrust structure) is already devoid unnecessary external fittings found on the SS such as landing legs, flaps and thermal tiles.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Coastal Ron on 02/15/2020 10:33 pm
In my opinion the second stage of development of the concept should be a permanently orbiting 'tank' which can be repositioned in orbit as required.
The prime candidate for this would be a modified SH which would be comparatively easily developed given it's an iteration of an existing design.

I like the simplicity of this idea, and as you pointed out, it doesn't require any new hardware design.

Initially you might have to use a Super Heavy that is fairly new, but over time you could use older Super Heavies that need to be retired, and retiring them in space to use as a tanker might be an option.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: xvel on 02/15/2020 10:40 pm
the problem of too little thrust at lift off is not due to the fact that there is too little fuel, but to the physical limitations of the materials of which the engine is built, so there is a limit of maximum thrust per unit of surface area of the rocket base, which implies the maximum height of the rocket and the starship is already close to this limit, so adding more tanks on top makes t/w ratio worse not better
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 02/15/2020 10:46 pm
the problem of too little thrust at lift off is not due to the fact that there is too little fuel, but to the physical limitations of the materials of which the engine is built, so there is a limit of maximum thrust per unit of surface area of the rocket base, which implies the maximum height of the rocket and the starship is already close to this limit, so adding more tanks on top makes t/w ratio worse not better
My thought was to use a partly filled SH (tank) section, thus reducing total takeoff weight ratio to an amount similar to a SS+SH combo.

Using the connection between the SH components you could feed some additional fuel to the SH (launch) section to allow it to burn for a longer duration thus imparting a greater Delta V to the SH (tank) section.

I'm not a rocket engineer so this might just be a pointless thought bubble.....

EDIT: Clarity & grammar
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: fael097 on 02/15/2020 10:50 pm
You think the tanker variant will have just two huge fuel/ox tanks (plus header tanks) or separate regular tanks and storage tanks?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: xvel on 02/15/2020 10:54 pm
if super heavy had more dv and used it, it would cause problems with entering the atmosphere and landing
I'm not a rocket engineer either, I'm just an engineer  ;)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 02/15/2020 10:55 pm
You think the tanker variant will have just two huge fuel/ox tanks (plus header tanks) or separate regular tanks and storage tanks?

My concept is literally a standard SH with SS thrust structure and a small nosecone for support equipment.....
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 02/15/2020 10:56 pm
if super heavy had more dv and used it, it would cause problems with entering the atmosphere and landing
I'm not a rocket engineer either, I'm just an engineer  ;)

Would extra fuel for extra boost back help?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: fael097 on 02/15/2020 10:59 pm
You think the tanker variant will have just two huge fuel/ox tanks (plus header tanks) or separate regular tanks and storage tanks?

My concept is literally a standard SH with SS thrust structure and a small nosecone for support equipment.....

I guess I mean the SS tanker variant.
On that note, I don't think a SH could be a tanker, SH wouldn't survive orbital reentry, would it?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: xvel on 02/15/2020 11:00 pm
if super heavy had more dv and used it, it would cause problems with entering the atmosphere and landing
I'm not a rocket engineer either, I'm just an engineer  ;)

Would extra fuel for extra boost back help?

Yes, but you couldn't take it
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: xvel on 02/15/2020 11:08 pm
Current design of starship barely works on paper, there really is no room for modifications, and I don't see any need for the tanker to be bigger than a starship. Refueling anyway will probably be done with one tanker parked in orbit which will be refueled several times from Earth and then it will refuel the starship parked in orbit (thanks to this the starship will be fully refueled with one refueling which will increase safety)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: BrianPeterson on 02/15/2020 11:44 pm
Current design of starship barely works on paper, there really is no room for modifications, and I don't see any need for the tanker to be bigger than a starship. Refueling anyway will probably be done with one tanker parked in orbit which will be refueled several times from Earth and then it will refuel the starship parked in orbit (thanks to this the starship will be fully refueled with one refueling which will increase safety)

Musk hates the idea of an orbiting tanker. What has been stated is one Starship fueled up by an additional 3 to 4 other Starship launches.

Don't have any idea what lOX or Liquid methane weight, but payload bay converted to a tank is probably how this will work. .
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 02/16/2020 12:01 am
From what we've seen of the starship thrust structure, there is a single pipe from the CH4 header tank, to the engines, and down to  the skirt where it will presumably form the refueling system.

A single pipe means the connector will need to be androgonus.

I'm less familiar with airticht androgonus designs- any suggestions for the pipe cap?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: fael097 on 02/16/2020 12:19 am
How much propellant mass a tanker Starship could haul into LEO? Regular SS carries 1200 t of prop and 100 t of payload, so tanker SS would only carry 1300 t of prop? I mean, since it can carry more prop it can burn more prop, and it has internal space for carrying 2100 t of propellant without compromising fairing space for header tanks, batteries, actuators, etc. but could a booster even lift that up? and in the end, would a 2100 t prop tanker have more fuel left when it gets to LEO than say a 1300 t prop tanker?

This is a tanker with capacity for 2100 t:
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: joek on 02/16/2020 12:23 am
...
Musk hates the idea of an orbiting tanker. What has been stated is one Starship fueled up by an additional 3 to 4 other Starship launches.
...

"Hate" seems a bit strong; do you have a cite?  Pragmatic is likely a more appropriate description.  Not to mention that Musk appears to be trying to stay out of the "no depots" debate.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 02/16/2020 12:30 am
You think the tanker variant will have just two huge fuel/ox tanks (plus header tanks) or separate regular tanks and storage tanks?

My concept is literally a standard SH with SS thrust structure and a small nosecone for support equipment.....

I guess I mean the SS tanker variant.
On that note, I don't think a SH could be a tanker, SH wouldn't survive orbital reentry, would it?

It wouldn't need to survive re-entry, it stays up there.  ;)

When it finishes the current mission (could be multiple refueling events for a particular synod) it can reposition to new orbit as required/desired using the onboard SS thrust structure and surplus onboard fuel.

Note: this is all based on the concept that you don't a crewed SS sitting around waiting for multiple refueling events. You want a tanker up there waiting for it so refueling and departure can occur as quickly as possible. Having a SH based unit means you have surplus fuel available to top up the departing SS as much as possible.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 02/16/2020 12:32 am
if super heavy had more dv and used it, it would cause problems with entering the atmosphere and landing
I'm not a rocket engineer either, I'm just an engineer  ;)

Would extra fuel for extra boost back help?

Yes, but you couldn't take it

Well you could, the extra fuel for a longer boost back is part of the transfer from the SH (tank) being launched.

The only variable is how much fuel is left in the SH (tank) when it reaches the desired orbit.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 02/16/2020 12:38 am
if super heavy had more dv and used it, it would cause problems with entering the atmosphere and landing
I'm not a rocket engineer either, I'm just an engineer  ;)

Would extra fuel for extra boost back help?

Yes, but you couldn't take it

Well you could, the extra fuel for a longer boost back is part of the transfer from the SH (tank) being launched.

The only variable is how much fuel is left in the SH (tank) when it reaches the desired orbit.
are you trying to SSTO? Because that never works out as well as you think it does.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: BrianPeterson on 02/16/2020 12:39 am
"Hate" seems a bit strong; do you have a cite?  Pragmatic is likely a more appropriate description.  Not to mention that Musk appears to be trying to stay out of the "no depots" debate.

It was a video interview, where you could say he scoffed at the idea. Derided the idea. He doesn't like the idea much. I've watched so many interviews with him, finding the exact one is a needle in a haystack. 

I on the other hand think an orbital platform could be the best idea. What happens if one of the four launches required to refuel fails? Or weather suddenly makes it impossible to launch. You could have to scrub the mission or have a starship and crew hang out for days/weeks/months waiting for fueling. Having a platform that is constantly stocked up means you can launch knowing the required fuel is there and get the mission under way.

Musk has other ideas: this was easy to find.
<blockquote class="twitter-tweet"><p lang="en" dir="ltr">Orbital refilling is vital to humanity’s future in space. More likely spacecraft to spacecraft (as aircraft do aerial refueling), than a dedicated depot, at least at first.</p>&mdash; Elon Musk (@elonmusk) August 1, 2019 (https://twitter.com/elonmusk/status/1156970909258829824?ref_src=twsrc%5Etfw) <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 02/16/2020 12:43 am
...
Musk hates the idea of an orbiting tanker. What has been stated is one Starship fueled up by an additional 3 to 4 other Starship launches.
...

"Hate" seems a bit strong; do you have a cite?  Pragmatic is likely a more appropriate description.  Not to mention that Musk appears to be trying to stay out of the "no depots" debate.

I believe (my opinion, no citation) that the issue Musk has with an orbiting tanker is that it's located for where you need it initially but the desired location changes with each mission so quickly becomes useless.

My suggestion means that when needed you can reposition the unit to the next ideal staging orbit.

You will be leaving a SS in orbit in this role anyway but with the SS(tanker)-SS you are launching a whole lot of additional weight to allow the SS(tanker) to return to Earth, just so you can then re-launch the whole lot again to a different orbit for the next mission.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 02/16/2020 12:45 am
are you trying to SSTO? Because that never works out as well as you think it does.

Not at all, the SH (tank) is a second stage using a conventional SS thrust structure (you could even delete the Sea level Raptors).

You use a conventional SH for the first stage.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 02/16/2020 12:56 am
...
Musk hates the idea of an orbiting tanker. What has been stated is one Starship fueled up by an additional 3 to 4 other Starship launches.
...

"Hate" seems a bit strong; do you have a cite?  Pragmatic is likely a more appropriate description.  Not to mention that Musk appears to be trying to stay out of the "no depots" debate.

I believe (my opinion, no citation) that the issue Musk has with an orbiting tanker is that it's located for where you need it initially but the desired location changes with each mission so quickly becomes useless.

My suggestion means that when needed you can reposition the unit to the next ideal staging orbit.

You will be leaving a SS in orbit in this role anyway but with the SS(tanker)-SS you are launching a whole lot of additional weight to allow the SS(tanker) to return to Earth, just so you can then re-launch the whole lot again to a different orbit for the next mission.
the "extra weight" of a tanker let's you use Earth's atmosphere to adjust inclination and Earth's resources to reset the rocket equation for each mission.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: aero on 02/16/2020 01:01 am
I know that there is a very large, if not an infinite number of possible orbits for the tankers, but practically speaking, how many tankers would be needed to cover 90% of the orbits that would be used? For example, would the LEO parking orbit for all Mars-bound Starships be the same or does the parking orbit depend on the Earth/Mars locations so strongly that the Mars Transfer Orbit can't be efficiently adjusted during or after TMI? By efficiently adjusted, I mean "adjusted without serious impact to the payload or fuel reserves."
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 02/16/2020 01:05 am
I know that there is a very large, if not an infinite number of possible orbits for the tankers, but practically speaking, how many tankers would be needed to cover 90% of the orbits that would be used? For example, would the LEO parking orbit for all Mars-bound Starships be the same or does the parking orbit depend on the Earth/Mars locations so strongly that the Mars Transfer Orbit can't be efficiently adjusted after launch? By efficiently adjusted, I mean "adjusted without serious impact to the payload or fuel reserves."
I recall reading that Earth Mars cyclers could reasonably adjust their orbits to match the double flyby every 6 synods. That would imply six reasonable ejection angles for a Mars transfer.
But what about the moon? What about outer solar system destinations? What about different launch inclinations to Mars for that matter.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: xvel on 02/16/2020 01:10 am
How much propellant mass a tanker Starship could haul into LEO? Regular SS carries 1200 t of prop and 100 t of payload, so tanker SS would only carry 1300 t of prop? I mean, since it can carry more prop it can burn more prop, and it has internal space for carrying 2100 t of propellant without compromising fairing space for header tanks, batteries, actuators, etc. but could a booster even lift that up? and in the end, would a 2100 t prop tanker have more fuel left when it gets to LEO than say a 1300 t prop tanker?

This is a tanker with capacity for 2100 t:

A simple example with a tanker that takes 200t of fuel instead of 100t:

SH 280t dry, 3300t propellant
SS 220t dry (with payload), 1200t propellant
stack weight 5000t
final mass for SH 1700t

SH with SS assuming isp 350 (simplification, isp increases during flight when the ambient pressure drops) has dV 3,7km/s
SS assuming isp 380 has dV 6,95km/s

now with a tanker that has 200t of fuel as a load so it weighs 1520t
stack weight 5100t, final mass for SH 1800t

SH dV 3,57km/s (130m/s less and slightly more gravity drag)
tanker dV  must be 7,08km/s to compensate and you have to burn 1293t of fuel to do that, so you're left with 107t of fuel instead of 100t in orbit

and the more fuel you take, the more gravity drag (which is not taken into account in this calculation) eats

Orbital mechanics is brutal

Only real way to increase tanker capacity is to shave dry weight, or you need bigger booster (which MUST be larger diameter)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: 50_Caliber on 02/16/2020 02:00 am
A depot at EML-1 makes sense for Lunar missions, if they build a reusable Lunar lander with similar mass ratio to SS, then they can refuel at EML-1, go to the moon, land and come back ready to refuel for next mission. The SS has a 6km+ delta V, so a lander with similar delta V could be refueled with perhaps 3-4 tanker flights to EML-1 station to refuel the lander. It can make the trip to the moon, land and come back to EML-1 for around 5km/s delta V. If it uses methane\lox , then it's a pretty straightforward refueling exercise that meshes perfectly with the SS architecture. We bypass any need for ISRU mining on the moon and it fast-tracks lunar development.

This also gives us an excuse to make a legit 2001 space station at that point.  8)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 02/16/2020 04:48 am
Orbital mechanics is brutal

Only real way to increase tanker capacity is to shave dry weight, or you need bigger booster (which MUST be larger diameter)

Interesting, so you take the first phase of In-orbit refueling to be SS to SS with a goal of having a delivered weight of around 100t of fuel. We already believe this will be the case so can use it as a starting point.

Now in my speculated second phase where you have a dedicated, and movable, In-orbit refueling tanker/depot you now have a starting target weight.

The question then becomes how much would my postulated SH (tank) weigh?
Would it be more or less than a fully functional SS with 100t of fuel?

Alternatively, if you stripped the aero-surfaces, landing structures, thermal tiles and sea-level Raptors off a SS how much less would it weigh and hence how much extra fuel could it carry to orbit?
(This option wouldn't give you the additional capacity of the SH (tank) but would function in the same way)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: zodiacchris on 02/16/2020 05:20 am
Not quite sure where the SH as tanker second stage would be required. Wouldn’t it make more sense to simply build the tanker SS with extended tanks by fitting a few extra hoops in the tanks and deleting the payload bay? With the exception of flight relevant systems no fit out of the nose, no decks, air locks, life support, windows etc. That would be the most KISS solution and not change SS aerodynamics or mould line.

The weight savings of the reduced equipment plus the normal SS payload capacity would give you around 150 -200 tonnes of refuelling capacity. Send Tanker 1 up, refuel that from Tankers 2 -6, then launch the Mars SS last to take on the fuel from Tanker 1.

That avoids loiter time for the manned Mars SS in orbit and possible hang ups with bad weather.

Of course Elon did say a while ago that the tanker version would look weird, so yeah, what do we know? ???
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: libra on 02/16/2020 06:30 am
How much propellant mass a tanker Starship could haul into LEO? Regular SS carries 1200 t of prop and 100 t of payload, so tanker SS would only carry 1300 t of prop? I mean, since it can carry more prop it can burn more prop, and it has internal space for carrying 2100 t of propellant without compromising fairing space for header tanks, batteries, actuators, etc. but could a booster even lift that up? and in the end, would a 2100 t prop tanker have more fuel left when it gets to LEO than say a 1300 t prop tanker?

This is a tanker with capacity for 2100 t:

A simple example with a tanker that takes 200t of fuel instead of 100t:

SH 280t dry, 3300t propellant
SS 220t dry (with payload), 1200t propellant
stack weight 5000t
final mass for SH 1700t

SH with SS assuming isp 350 (simplification, isp increases during flight when the ambient pressure drops) has dV 3,7km/s
SS assuming isp 380 has dV 6,95km/s

now with a tanker that has 200t of fuel as a load so it weighs 1520t
stack weight 5100t, final mass for SH 1800t

SH dV 3,57km/s (130m/s less and slightly more gravity drag)
tanker dV  must be 7,08km/s to compensate and you have to burn 1293t of fuel to do that, so you're left with 107t of fuel instead of 100t in orbit

and the more fuel you take, the more gravity drag (which is not taken into account in this calculation) eats

Orbital mechanics is brutal

Only real way to increase tanker capacity is to shave dry weight, or you need bigger booster (which MUST be larger diameter)

Excellent post, really. Another way of putting it is as follow.

What is the tanker ?

Basically, it should be the usual Starship, its propellant mass, and its payload.

Then in the case of a tanker, the payload, obviously, should be the maximum amount of propellant you can haul into orbit by sacrificing everything but the kitchen sink, to rise payload.

That is, the cargo area becomes another fuel tank.

Then there is the problem of mass: what part of the "standard Starship"are you willing to sacrifice and turn into propellant mass, that is, useful tanker payload ?

Do you want a dumb prop tank inside the cargo area ? or do you start modifying or removing cargo area structure ?

There it depends of two things a) commonality with a "standard Starship" and b) reusability or not.

The more you sacrify commonality with the standard Starship, the more propellant raw mass you get into orbit, but of course tanker development costs rise...

An interesting historical exemple are the Boeing 707 innumerable variants, tankers included. While the KC-135 was a separate development of 707 from day one (different fuselage), there were also civilian 707s turned into makeshift, cheaper tankers - also far less efficient.
Well then the kerosene plumbery, the distribution of kerosene between the aircraft own tanks and the tanks dedicated to refueling, where vastly different.
Musk will face the same issues with tanker Starship.

Quote
Orbital mechanics is brutal

That's an understatement. The basic Starship has 1200 mt of propellant in the tanks when separating from SH, yet most of this vanishes during ascent. If it carries zero payload instead of 150 mt, then somewhat automatically, 150 mt of props remain in the tanks. That's a standard Starship. Then by scrounging whatever can be scrounged of structure and weight, maybe you can rise this to 200 mt. Maybe. Since Starship needs to be fully-fueled for Mars departure, then you need at least 6 and probably 7 tanker flights to fill that thing. Brutal numbers, sure.

How about starting from this number - 7 tankers - and start stockpiling 10 - 12 of them in orbit, docked to a dumb truss ? Would not be that expensive and would give margin.

But that's for 1 flight; Imagine for 1000 or more, the sheer number of tankers that will be needed...

As for different orbits with different inclinations - no panic. There is a simple formula to calculate plane changes delta-v
https://en.wikipedia.org/wiki/Orbital_inclination_change

Musk advantage here is the high specific impulse of his methalox engines. I can see "Starship depots" making reasonable plane changes by firing their engines.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Ultrafamicom on 02/16/2020 06:52 am
How much propellant mass a tanker Starship could haul into LEO? Regular SS carries 1200 t of prop and 100 t of payload, so tanker SS would only carry 1300 t of prop? I mean, since it can carry more prop it can burn more prop, and it has internal space for carrying 2100 t of propellant without compromising fairing space for header tanks, batteries, actuators, etc. but could a booster even lift that up? and in the end, would a 2100 t prop tanker have more fuel left when it gets to LEO than say a 1300 t prop tanker?

This is a tanker with capacity for 2100 t:

A simple example with a tanker that takes 200t of fuel instead of 100t:

SH 280t dry, 3300t propellant
SS 220t dry (with payload), 1200t propellant
stack weight 5000t
final mass for SH 1700t

SH with SS assuming isp 350 (simplification, isp increases during flight when the ambient pressure drops) has dV 3,7km/s
SS assuming isp 380 has dV 6,95km/s

now with a tanker that has 200t of fuel as a load so it weighs 1520t
stack weight 5100t, final mass for SH 1800t

SH dV 3,57km/s (130m/s less and slightly more gravity drag)
tanker dV  must be 7,08km/s to compensate and you have to burn 1293t of fuel to do that, so you're left with 107t of fuel instead of 100t in orbit

and the more fuel you take, the more gravity drag (which is not taken into account in this calculation) eats

Orbital mechanics is brutal

Only real way to increase tanker capacity is to shave dry weight, or you need bigger booster (which MUST be larger diameter)

On the other hand SH now needs 130m/s less dv for boostback and stages closer to launch pad, so more propellant can be used to boost SS, which gives a further increase in payloads.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 02/16/2020 10:14 am
I think there needs to be a distinction made between the tanker that remains in orbit and stockpiles fuel for the mission SS and the tanker that is used to transport fuel to the orbital stockpile.

The one that remains in orbit just needs to be delivered there (whether it is designed to return to Earth or not) and the amount of fuel it retains on arrival in orbit is largely academic. Design for the function becomes the priority.

The one(s) that deliver the fuel to orbit need to be optimised to maximise the fuel delivered and expedite launch cycle frequency, that becomes the design priority for these units.

The differing requirements mean that each unit are not necessarily identical in design.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Eka on 02/16/2020 11:46 am
I've never been able to pencil a scenario where an orbital fuel depot is better than just sending up the SS tankers. It all comes down to flexibility, the cost of putting that infrastructure into space, and how refueling is done. That last one, how refueling is done, is the killer. Once part or all of the propellants are available from outside Earth's gravity well, then the math may change, but not until then, and not always.

On how in orbit refueling is done. With the current Starship design, it MUST be done under acceleration. You must take that into account for any system you develop. Will that inflatable tank be able to handle the repeated accelerations and decelerations needed? Think of how much more mass you are accelerating and decelerating when you have a propellant load in that depot greater than than one SS can receive.
An fuel depot who can be one tanker or an dedicated tanker with an sort of sun shade, think an air mattress on an beam makes sense in that you can top it up during slow days and the Mars or Moon mission only need to refuel once.

Acceleration is needed to settle the fuel at the bottom of the tank, this does not to be an high acceleration, The dedicated fuel depot tanker will have pumps doing most of the work the trust is just to have the liquids settle at the bottom.
With a pump, you need enough acceleration and propellant head or tank pressure to keep the pump from cavitating.* Might as well just use a bit of acceleration, and tank pressure alone. Keep it as simple as possible. One thing to remember is both the source tank, and the receiving tank need the acceleration. The propellant must also be settled in the receiving tank to vent the gasses being displaced by the fuel. Want to transfer propellant without acceleration, one still needs the pressure, but another form of containment is needed. Fuel bladders in both source and destination tanks would work, but they add weight and can fail. Yes, many gotchas for fuel transfer in orbit. Gravity makes a lot of things easier here on earth.

* This is why 6 bar is the design goal for SS tanks. They need that pressure to keep the Raptor turbopumps from cavitating as they suck in huge amounts of fuel.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Ionmars on 02/16/2020 02:14 pm
To synthesize from previous posts, I agree that the tanker version of SS has the  function of delivering maximum feasible propellant to LEO. We should minimize structural mass and eliminate any feature that does not contribute to this function. It could be perceived in stages:

First, consider the standard SS with extra propellant tanks in the cargo area. We note that cargo SS features a large payload volume to accommodate a variety of payloads, such as equipment that occupies only part of the volume. In this case the mass carried in the cargo bay leaves some empty space in the cargo bay.  Liquid propellant, however, could occupy every cc of available cargo volume, provided propellant density allows propellant mass to be less than cargo mass capacity of 1100 tonnes. (I am no longer adept to calculate the excess volume.)

Second iteration, shorten tanker SS cargo bay. Determine the exact length required to carry the mass of propellant that is (edit:) to be transferred to another SS. The resulting mass savings allows propellant load to increase by an equal amount.

Third iteration, eliminate the cargo bay. Increase the length of main propellant tanks to accommodate both the fuel required to reach LEO and the fuel to be transferred.

Fourth iteration, increase diameter of fairing. Note that the most efficient shape to carry liquid is a sphere, which has less surface area than a cylinder for equal volume. In this step we would widen the nose section of tanker SS to be more like a sphere. It would be similar to the wide fairings used for some missions of Falcon 9, only more so. Tanker SS would assume the appearance of a Lollypop, which may be why Musk has said tanker SS would look kinda weird.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 02/16/2020 02:30 pm
To synthesize from previous posts, I agree that the tanker version of SS has the  function of delivering maximum feasible propellant to LEO. We should minimize structural mass and eliminate any feature that does not contribute to this function. It could be perceived in stages:

First, consider the standard SS with extra propellant tanks in the cargo area. We note that cargo SS features a large payload volume to accommodate a variety of payloads, such as equipment that occupies only part of the volume. In this case the mass carried in the cargo bay leaves some empty space in the cargo bay.  Liquid propellant, however, could occupy every cc of available cargo volume, provided propellant density allows propellant mass to be less than cargo mass capacity of 1100 tonnes. (I am no longer adept to calculate the excess volume.)

Second iteration, shorten tanker SS cargo bay. Determine the exact length required to carry the mass of propellant that is feasible to launch to LEO. The resulting mass savings allows propellant load to increase by an equal amount.

Third iteration, eliminate the cargo bay. Increase the length of main propellant tanks to accommodate both the fuel required to reach LEO and the fuel to be transferred to another SS.

Fourth iteration, increase diameter of fairing. Note that the most efficient shape to carry liquid is a sphere, which has less surface area than a cylinder for equal volume. In this step we would widen the nose section of tanker SS to be more like a sphere. It would be similar to the wide fairings used for some missions of Falcon 9, only more so. Tanker SS would assume the appearance of a Lollypop, which may be why Musk has said tanker SS would look kinda weird.
This all begs the question, why?

A tanker exists to refuel Starship. Therefore the most fuel it needs at any one time is enough to fully fuel one starship. Is there an existing ship with tanks that size, one you're already mass producing? Well, yes... Starship itself.

Any permanant depot must consider the trade between reentry mass, which allows the rocket to come home and resupply, and plane chance fuel, which must be lifted to orbit and docked to the existing depot in order to move the depot and any residual fuel to the new orbit.

If a plane change requires more than a mass ratio of 1- that is, if the mass of fuel needed for a useful "next plane" change of orbit is more than the (already reduced, by the removal of reentry mass) dry mass of the tanker, without fuel, it's easier to launch an entirely new tanker in the new orbit than move the old one.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Ionmars on 02/16/2020 03:07 pm
This all begs the question, why?
...
...
The reason that first comes to mind is an insurance policy. If there are unexpected fuel leaks during launch to orbit or minor spills during fuel transfers, we would still be able to deliver enough propellant over the planned number of launches to complete the mission.

Nevertheless, your point is well taken and SS tanker version is low priority.

Added: We may be addressing two different types of “tanker.” I am addressing the version of SS used to deliver propellant to orbit where it transfers fuel to another SS in orbit or to a “tanker-in-orbit,” which is a substitute for a propellant depot. I would call the tanker-in-orbit an SS Depot or some different name to avoid confusion.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: ZChris13 on 02/16/2020 03:19 pm
...
Musk hates the idea of an orbiting tanker. What has been stated is one Starship fueled up by an additional 3 to 4 other Starship launches.
...
"Hate" seems a bit strong; do you have a cite?  Pragmatic is likely a more appropriate description.  Not to mention that Musk appears to be trying to stay out of the "no depots" debate.
I believe (my opinion, no citation) that the issue Musk has with an orbiting tanker is that it's located for where you need it initially but the desired location changes with each mission so quickly becomes useless.
My suggestion means that when needed you can reposition the unit to the next ideal staging orbit.
You will be leaving a SS in orbit in this role anyway but with the SS(tanker)-SS you are launching a whole lot of additional weight to allow the SS(tanker) to return to Earth, just so you can then re-launch the whole lot again to a different orbit for the next mission.
Is that an issue?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: dnavas on 02/16/2020 03:52 pm
If a plane change requires more than a mass ratio of 1- that is, if the mass of fuel needed for a useful "next plane" change of orbit is more than the (already reduced, by the removal of reentry mass) dry mass of the tanker, without fuel, it's easier to launch an entirely new tanker in the new orbit than move the old one.

Just so.  In LEO there are a large number of possible waypoints, each of them mutually "inaccessible."  The question is whether there are a small enough "significant" set that the idea is tenable.  Because it's likewise a small iteration from fuel depot to electric LEO/GEO tug dock, but that iteration only makes sense if there are reasonable targets for LEO.  If only we had SST-lagrange point, but we don't.

Is there some way to determine, given a single SS tanker load of fuel, what LEO coverage exists for about 100mt of fuel?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: wannamoonbase on 02/16/2020 04:11 pm
Only real way to increase tanker capacity is to shave dry weight, or you need bigger booster (which MUST be larger diameter)

I would not be surprised to see SH have a larger diameter than SS. 

The engines under the 9 meter SH have been crammed in and little or no room for growth.

The number of refueling flights seem like they could be reduced with a larger booster or more staging (3rd stage or FH style.)

If these two vehicles are going to be so cheap to build then why not have a different diameter for each? 

Edit: If the vehicles can eventually be as cheap to build and easy to operate as projected then the cost of fuel for each launch drives cost then at some point there are more efficient ways to get 100 tons of fuel on orbit. 

I suppose there is a long way to go and there is plenty of time to optimize.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TrevorMonty on 02/16/2020 04:14 pm
If SS needs refuelling it is going to GEO, moon or mars. Which should reduce number of possible tanker/depot orbits.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: aero on 02/16/2020 04:40 pm
If SS needs refuelling it is going to GEO, moon or mars. Which should reduce number of possible tanker/depot orbits.

Remember, as pointed out above, plane change delta-V is linear with velocity. So if it is going beyond LEO then the plane change maneuver becomes cheaper the lower the velocity of the Starship. My orbital mechanics is beyond rusty but I think I recall that doing a plane change maneuver during the Mars transfer is the most economical. That means all this discussion of doing LEO maneuvers to calculate plane change delta-V is a sub-optimal topic.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: hkultala on 02/16/2020 05:30 pm
Only real way to increase tanker capacity is to shave dry weight, or you need bigger booster ....

yes.

Quote
(which MUST be larger diameter)

No, it does not have to, unless going to MUCH bigger.

The current specifications in SpaceX web site says "72 MN" for Superheavy thrust and 4600 tonnes total propellant + payload.

Assuming the spaceship + superheavy together have empty mass of  less than 400 tonnes, this means maximum of 5000 tonnes liftoff weight.

This is T/W ratio of 1.44. WHich is a lot

They can increase the first stage fuel tank size to something like 4000 tonnes, increasing the empty weight by only ~30-40 tonnes.

This would mean T/W ratio of 1.25, which is still enough. There would be more gravity losses, but payload would be greater.

There has also been talk about 250-tonne-thrust version of Raptor. The optimal nozzle size for that would be slightly bigger than the nozzle size of current raptor, but they can make it have the same nozzle and lose ~1% of isp, and fit the same number of those engines under the craft. And then they can increase the thrust from 7.2 MN to about 8.8 MN.

That would allow making the tanks much longer, adding considerable amount of propellant, while still keeping the T/W ratio very good.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TheRadicalModerate on 02/16/2020 06:01 pm
In my opinion the second stage of development of the concept should be a permanently orbiting 'tank' which can be repositioned in orbit as required.
The prime candidate for this would be a modified SH which would be comparatively easily developed given it's an iteration of an existing design.

I envisige you would replace the SH thrust structure with a SS thrust structure. The SH (tank) could even supply fuel to the SH (launch) to help with the increased takeoff weight. You would then be using the proven SS attachment system for In-Orbit fuel transfers.

This is similar to an idea that Twark_Main and I discussed (thread is here (https://forum.nasaspaceflight.com/index.php?topic=49134.msg2007579#msg2007579)).  I'd pretty much assumed that you just stretched the SS with a few extra tank rings and cannibalized some of the payload bay space, but you could probably start with a set of SH tanks as well.

The most demanding mission is getting a heavy cargo + crew to the lunar surface and back without lunar surface refueling.  You have to avoid refueling in HEEO to keep the crew out of the Van Allen Belts during refueling, and you have to carry all your prop with you for the return.  The "pusher/tanker" described in the link gets launched almost empty, uses regular tankers (whatever those are--likely just no-payload SSes) to acquire however much prop is needed, then docks nose-to-tail with the payload SS.  It transfers some of the prop to the payload SS, but then just acts as a first stage for most of the TLI delta-v.  Once in TLI, it either does a direct or free return to LEO, either aerobraking or propulsively inserting into whatever orbit the next mission needs.

The big deal here is risk reduction for crewed missions.  You only need one rendezvous/docking operation in the relatively low-radiation environment of LEO, and one jettison of the pusher/tanker.  Pusher/tanker isn't quite as prop-efficient as a series of refuelings in LEO and one refueling in HEEO, but prop efficiency probably isn't the most important criterion for a crewed mission.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Eer on 02/16/2020 06:36 pm
I look forward to the day when fuel is sourced from space itself - comets, asteroids, whatever. At that point, raising fuel from earth surface becomes unnecessary for most uses.

To begin with, though, “just in time” fuel supply can still benefit from “cross dock” delivery by filling an SS depot version (maybe never intended to land) so cruise SS with passengers can load and go just makes sense for many reasons (not least reducing suspense on part of passengers and crew whether all the tankers will arrive on schedule). That sort of risk reduction makes sense to me.

A small squadron of such depot SS versions can be deployed and filled in any number of orbits and gateway destinations, just like filling stations and recharging stations serve traffic where traffic regularly need services.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: xvel on 02/16/2020 06:43 pm
In my opinion the second stage of development of the concept should be a permanently orbiting 'tank' which can be repositioned in orbit as required.
The prime candidate for this would be a modified SH which would be comparatively easily developed given it's an iteration of an existing design.

I envisige you would replace the SH thrust structure with a SS thrust structure. The SH (tank) could even supply fuel to the SH (launch) to help with the increased takeoff weight. You would then be using the proven SS attachment system for In-Orbit fuel transfers.

This is similar to an idea that Twark_Main and I discussed (thread is here (https://forum.nasaspaceflight.com/index.php?topic=49134.msg2007579#msg2007579)).  I'd pretty much assumed that you just stretched the SS with a few extra tank rings and cannibalized some of the payload bay space, but you could probably start with a set of SH tanks as well.

The most demanding mission is getting a heavy cargo + crew to the lunar surface and back without lunar surface refueling.  You have to avoid refueling in HEEO to keep the crew out of the Van Allen Belts during refueling, and you have to carry all your prop with you for the return.  The "pusher/tanker" described in the link gets launched almost empty, uses regular tankers (whatever those are--likely just no-payload SSes) to acquire however much prop is needed, then docks nose-to-tail with the payload SS.  It transfers some of the prop to the payload SS, but then just acts as a first stage for most of the TLI delta-v.  Once in TLI, it either does a direct or free return to LEO, either aerobraking or propulsively inserting into whatever orbit the next mission needs.

The big deal here is risk reduction for crewed missions.  You only need one rendezvous/docking operation in the relatively low-radiation environment of LEO, and one jettison of the pusher/tanker.  Pusher/tanker isn't quite as prop-efficient as a series of refuelings in LEO and one refueling in HEEO, but prop efficiency probably isn't the most important criterion for a crewed mission.

Unnecessary complexity, such manoeuvres can be done with a simple starship tanker, fael097 calculated that the bulkhead shift alone will give a capacity of 2100t, so if it sends such a tanker with 1300t of fuel on the LEO will arrive with 100t, then it will be 20x refuelled to full. consumption of 700t gives dV 1.4km/s and in the tanker is 1200t to refuel the starship and 200t to return to the LEO (there would still be 100t left). when the starship enters the LEO it will be once refueled with another tanker which will give it dV 1.4km/s then both can meet in a higher orbit and the starship can be refueled to the full.

Instead of refuelling and docking, you have two refuellings and don't need a special tanker that can dock with its nose  ::)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 02/16/2020 06:57 pm
In my opinion the second stage of development of the concept should be a permanently orbiting 'tank' which can be repositioned in orbit as required.
The prime candidate for this would be a modified SH which would be comparatively easily developed given it's an iteration of an existing design.

I envisige you would replace the SH thrust structure with a SS thrust structure. The SH (tank) could even supply fuel to the SH (launch) to help with the increased takeoff weight. You would then be using the proven SS attachment system for In-Orbit fuel transfers.

This is similar to an idea that Twark_Main and I discussed (thread is here (https://forum.nasaspaceflight.com/index.php?topic=49134.msg2007579#msg2007579)).  I'd pretty much assumed that you just stretched the SS with a few extra tank rings and cannibalized some of the payload bay space, but you could probably start with a set of SH tanks as well.

The most demanding mission is getting a heavy cargo + crew to the lunar surface and back without lunar surface refueling.  You have to avoid refueling in HEEO to keep the crew out of the Van Allen Belts during refueling, and you have to carry all your prop with you for the return.  The "pusher/tanker" described in the link gets launched almost empty, uses regular tankers (whatever those are--likely just no-payload SSes) to acquire however much prop is needed, then docks nose-to-tail with the payload SS.  It transfers some of the prop to the payload SS, but then just acts as a first stage for most of the TLI delta-v.  Once in TLI, it either does a direct or free return to LEO, either aerobraking or propulsively inserting into whatever orbit the next mission needs.

The big deal here is risk reduction for crewed missions.  You only need one rendezvous/docking operation in the relatively low-radiation environment of LEO, and one jettison of the pusher/tanker.  Pusher/tanker isn't quite as prop-efficient as a series of refuelings in LEO and one refueling in HEEO, but prop efficiency probably isn't the most important criterion for a crewed mission.

Unnecessary complexity, such manoeuvres can be done with a simple starship tanker, fael097 calculated that the bulkhead shift alone will give a capacity of 2100t, so if it sends such a tanker with 1300t of fuel on the LEO will arrive with 100t, then it will be 20x refuelled to full. consumption of 700t gives dV 1.4km/s and in the tanker is 1200t to refuel the starship and 200t to return to the LEO (there would still be 100t left). when the starship enters the LEO it will be once refueled with another tanker which will give it dV 1.4km/s then both can meet in a higher orbit and the starship can be refueled to the full?

Instead of refuelling and docking, you have two refuellings and don't need a special tanker that can dock with its nose  ::)

This is all discussed in the thread, but briefly: the problem is that refueling in a higher orbit means multiple trips through the (edge of the) Van Allen belt. It also requires a greater number of rendezvous/docking events (ie more risk).

I'm also drawn to the Pusher Tanker architecture for the mission possibilities of an ultra-high delta-v "Starkicker." Starkicker only gets one chance for its escape burn, and Oberth says you want your engine firing to be as short a duration as possible. So there's no time to use re-fueling during the delta-v slam, and another approach (Pusher Tanker, or simply StarPusher (ie Pusher Tanker but with no propellant transfer to the departure stage)) is needed if you need/want more delta-v than Starkicker alone can deliver.

https://twitter.com/elonmusk/status/1111760133132947458
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: xvel on 02/16/2020 07:05 pm
In my opinion the second stage of development of the concept should be a permanently orbiting 'tank' which can be repositioned in orbit as required.
The prime candidate for this would be a modified SH which would be comparatively easily developed given it's an iteration of an existing design.

I envisige you would replace the SH thrust structure with a SS thrust structure. The SH (tank) could even supply fuel to the SH (launch) to help with the increased takeoff weight. You would then be using the proven SS attachment system for In-Orbit fuel transfers.

This is similar to an idea that Twark_Main and I discussed (thread is here (https://forum.nasaspaceflight.com/index.php?topic=49134.msg2007579#msg2007579)).  I'd pretty much assumed that you just stretched the SS with a few extra tank rings and cannibalized some of the payload bay space, but you could probably start with a set of SH tanks as well.

The most demanding mission is getting a heavy cargo + crew to the lunar surface and back without lunar surface refueling.  You have to avoid refueling in HEEO to keep the crew out of the Van Allen Belts during refueling, and you have to carry all your prop with you for the return.  The "pusher/tanker" described in the link gets launched almost empty, uses regular tankers (whatever those are--likely just no-payload SSes) to acquire however much prop is needed, then docks nose-to-tail with the payload SS.  It transfers some of the prop to the payload SS, but then just acts as a first stage for most of the TLI delta-v.  Once in TLI, it either does a direct or free return to LEO, either aerobraking or propulsively inserting into whatever orbit the next mission needs.

The big deal here is risk reduction for crewed missions.  You only need one rendezvous/docking operation in the relatively low-radiation environment of LEO, and one jettison of the pusher/tanker.  Pusher/tanker isn't quite as prop-efficient as a series of refuelings in LEO and one refueling in HEEO, but prop efficiency probably isn't the most important criterion for a crewed mission.

Unnecessary complexity, such manoeuvres can be done with a simple starship tanker, fael097 calculated that the bulkhead shift alone will give a capacity of 2100t, so if it sends such a tanker with 1300t of fuel on the LEO will arrive with 100t, then it will be 20x refuelled to full. consumption of 700t gives dV 1.4km/s and in the tanker is 1200t to refuel the starship and 200t to return to the LEO (there would still be 100t left). when the starship enters the LEO it will be once refueled with another tanker which will give it dV 1.4km/s then both can meet in a higher orbit and the starship can be refueled to the full?

Instead of refuelling and docking, you have two refuellings and don't need a special tanker that can dock with its nose  ::)

Problem is (and this is all discussed in the thread), refueling in a higher orbit means multiple trips through the Van Allen belt. It also requires a greater number of rendezvous/docking events (ie more risk).

I'm also drawn to Pusher Tanker for the mission possibilities of an ultra-high delta-v "Starkicker." Starkicker only gets one chance for its escape burn, and Oberth says you want your engine firing to be as short duration as possible. So there's no time to use re-fueling during the delta-v slam, and another approach is needed if you need/want more delta-v than Starkicker alone can deliver.

https://twitter.com/elonmusk/status/1111760133132947458

We don't know how long it will take to refuel, and since both the starship and the tanker can enter a higher orbit at the same time, Van Allen belts may not be such a problem if refueling will be fast.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 02/16/2020 07:17 pm
... don't need a special tanker that can dock with its nose  ::)

And as to the eye-rolling about docking with the nose, in this thread we seem to be all treating rockets like LEGO (lengthening, stacking two SH together, swapping SH interstage for a nose cone), so surely swapping SS's nose for SH's interstage adapter is fair game. 8)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 02/16/2020 07:22 pm
[snip]

We don't know how long it will take to refuel, and since both the starship and the tanker can enter a higher orbit at the same time, Van Allen belts may not be such a problem if refueling will be fast.

Both the apogee-raise burn to HEEO and the departure burn are optimally performed at perigee, because Oberth. There are large performance losses (ie you can't reach the Moon) if you do it any other way.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: xvel on 02/16/2020 07:45 pm
[snip]

We don't know how long it will take to refuel, and since both the starship and the tanker can enter a higher orbit at the same time, Van Allen belts may not be such a problem if refueling will be fast.

Both the apogee-raise burn to HEEO and the departure burn are optimally performed at perigee, because Oberth. There are large performance losses (ie you can't reach the Moon) if you do it any other way.

Yes, probably impossible to do faster than one full orbit
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TheRadicalModerate on 02/16/2020 08:33 pm
In my opinion the second stage of development of the concept should be a permanently orbiting 'tank' which can be repositioned in orbit as required.
The prime candidate for this would be a modified SH which would be comparatively easily developed given it's an iteration of an existing design.

I envisige you would replace the SH thrust structure with a SS thrust structure. The SH (tank) could even supply fuel to the SH (launch) to help with the increased takeoff weight. You would then be using the proven SS attachment system for In-Orbit fuel transfers.

This is similar to an idea that Twark_Main and I discussed (thread is here (https://forum.nasaspaceflight.com/index.php?topic=49134.msg2007579#msg2007579)).  I'd pretty much assumed that you just stretched the SS with a few extra tank rings and cannibalized some of the payload bay space, but you could probably start with a set of SH tanks as well.

The most demanding mission is getting a heavy cargo + crew to the lunar surface and back without lunar surface refueling.  You have to avoid refueling in HEEO to keep the crew out of the Van Allen Belts during refueling, and you have to carry all your prop with you for the return.  The "pusher/tanker" described in the link gets launched almost empty, uses regular tankers (whatever those are--likely just no-payload SSes) to acquire however much prop is needed, then docks nose-to-tail with the payload SS.  It transfers some of the prop to the payload SS, but then just acts as a first stage for most of the TLI delta-v.  Once in TLI, it either does a direct or free return to LEO, either aerobraking or propulsively inserting into whatever orbit the next mission needs.

The big deal here is risk reduction for crewed missions.  You only need one rendezvous/docking operation in the relatively low-radiation environment of LEO, and one jettison of the pusher/tanker.  Pusher/tanker isn't quite as prop-efficient as a series of refuelings in LEO and one refueling in HEEO, but prop efficiency probably isn't the most important criterion for a crewed mission.

Unnecessary complexity, such manoeuvres can be done with a simple starship tanker, fael097 calculated that the bulkhead shift alone will give a capacity of 2100t, so if it sends such a tanker with 1300t of fuel on the LEO will arrive with 100t, then it will be 20x refuelled to full. consumption of 700t gives dV 1.4km/s and in the tanker is 1200t to refuel the starship and 200t to return to the LEO (there would still be 100t left). when the starship enters the LEO it will be once refueled with another tanker which will give it dV 1.4km/s then both can meet in a higher orbit and the starship can be refueled to the full.

Instead of refuelling and docking, you have two refuellings and don't need a special tanker that can dock with its nose  ::)

Twark covered a lot of this, but:

1) Refueling in HEEO incurs an extra two passes through the VA belts, which is a big chunk of total radiation exposure, given average solar activity.  That won't quite double the total exposure for a lunar missions, but it'll come pretty close.

2) Whether this turns out to be "unnecessary complexity" depends in large part how much risk you incur with a docking/refueling operation.  P/T minimizes that.

An option to P/T that uses ordinary tankers (i.e., non-payload-carrying Starships) is to do the refueling rendezvous post-TLI.  That way, you don't incur the extra pair of VA belt transits.  The tanker then does a free return and reenters at TEI speeds.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 02/16/2020 08:54 pm
...

There has also been talk about 250-tonne-thrust version of Raptor. The optimal nozzle size for that would be slightly bigger than the nozzle size of current raptor, but they can make it have the same nozzle and lose ~1% of isp, and fit the same number of those engines under the craft. And then they can increase the thrust from 7.2 MN to about 8.8 MN.

I believe the 250 tonne version is simply a change of injectors. No throttling, but higher thrust.

In another thread I proposed a slightly more extreme version of this: cram the Raptor engines together in a honeycomb pattern as tight as the combustion chamber / plumbing will allow, and simply truncate the nozzle to a hexagonal profile (imagine taking a hexagon cookie cutter to the existing nozzle, without otherwise changing its shape). Bonus: the cut off nozzles will have a wicked "sawtooth" pattern when viewed from the side. :)





this means

Darn, they got to him...  :D
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: mikegi on 02/16/2020 09:03 pm
In my opinion the second stage of development of the concept should be a permanently orbiting 'tank' which can be repositioned in orbit as required.
The prime candidate for this would be a modified SH which would be comparatively easily developed given it's an iteration of an existing design.

I envisige you would replace the SH thrust structure with a SS thrust structure. The SH (tank) could even supply fuel to the SH (launch) to help with the increased takeoff weight. You would then be using the proven SS attachment system for In-Orbit fuel transfers.

This is similar to an idea that Twark_Main and I discussed (thread is here (https://forum.nasaspaceflight.com/index.php?topic=49134.msg2007579#msg2007579)).  I'd pretty much assumed that you just stretched the SS with a few extra tank rings and cannibalized some of the payload bay space, but you could probably start with a set of SH tanks as well.

The most demanding mission is getting a heavy cargo + crew to the lunar surface and back without lunar surface refueling.  You have to avoid refueling in HEEO to keep the crew out of the Van Allen Belts during refueling, and you have to carry all your prop with you for the return.  The "pusher/tanker" described in the link gets launched almost empty, uses regular tankers (whatever those are--likely just no-payload SSes) to acquire however much prop is needed, then docks nose-to-tail with the payload SS.  It transfers some of the prop to the payload SS, but then just acts as a first stage for most of the TLI delta-v.  Once in TLI, it either does a direct or free return to LEO, either aerobraking or propulsively inserting into whatever orbit the next mission needs.

The big deal here is risk reduction for crewed missions.  You only need one rendezvous/docking operation in the relatively low-radiation environment of LEO, and one jettison of the pusher/tanker.  Pusher/tanker isn't quite as prop-efficient as a series of refuelings in LEO and one refueling in HEEO, but prop efficiency probably isn't the most important criterion for a crewed mission.
I'm definitely no rocket scientist (understatement of the year!) but ... why not make the Pusher more of a large, reusable service module (LSM) for LEO->Moon->LEO? You attach a simple capsule and lunar lander to the front. The whole thing enters LLO, the lander does its thing, then the LSM returns them to Earth. The capsule detaches and reenters as the LSM passes by Earth. With no people onboard, the LSM can take as long as necessary to get back to a stable LEO (e.g. maybe multiple short passes through the atmosphere, make burns when optimal, etc.).
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 02/16/2020 09:24 pm
I on the other hand think an orbital platform could be the best idea. What happens if one of the four launches required to refuel fails? Or weather suddenly makes it impossible to launch. You could have to scrub the mission or have a starship and crew hang out for days/weeks/months waiting for fueling. Having a platform that is constantly stocked up means you can launch knowing the required fuel is there and get the mission under way.

You use one of the tankers as a pseudo-depot, you launch the mission ship itself last. If weather delays a fuel launch (or it fails), your crew are still on the ground. You only launch once the tanker-cum-depot has enough fuel for the mission. Then the tanker-depot lands and goes back into ordinary service.

That latter (ordinary service) is also why (IMO) the tankers wouldn't be modified from the standard cargo vehicles for a long time, even if in practice it meant launching 5 cargo-ships-as-fuel-tankers instead of 4 mass-optimised tankers. The additional cost of that one extra launch is not worth building a whole extra type of Starship that has such limited use.

[Aside: The same reasoning says that the first "passenger" Starships would just be cargo ships with a passenger pods. Different pods for different missions. Lets you do Shuttle-like missions with mixed cargo and personnel. Such as satellite recovery missions, service missions, mixed science missions, etc. And the latter lets researchers use Starships as single-purpose specialised space-stations, by swapping out mission pods.]

And the ease of using a cargo-ship-cum-tanker as a single-mission orbital depot is why you don't need an actual permanent depot for a long time.



Of course, I intend to contradict myself in my very next post:
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 02/16/2020 09:25 pm
If a plane change requires more than a mass ratio of 1- that is, if the mass of fuel needed for a useful "next plane" change of orbit is more than the (already reduced, by the removal of reentry mass) dry mass of the tanker, without fuel, it's easier to launch an entirely new tanker in the new orbit than move the old one.

If anyone's curious, assuming 380s Isp and 350nm LEO, that's a roughly 20 degrees plane change. (Maths below. You might be able to improve that with a Low/High/Low plane change, but I haven't worked that out.)

However, for the Moon or Mars, there's virtually no inclination requirement (Figures below). Hell, you can boost from polar orbit if you want, with barely a hit. So any LEO depot works for BEO missions. LEO-to-GEO is more restrictive, but low-inclination-LEO to equatorial-GEO hides most sins. So a general LEO depot for equatorial boost is likely to see a reasonable amount of use, IMO.

If there's enough traffic beyond GEO, a large general-purpose depot definitely make sense. And if there's enough traffic to a specific inclination of GEO (such as equatorial), then a depot for that makes sense.



Rocket equation: delta_V = Isp * 9.8 * ln(wet_mass/dry_mass)
Target is fuel_mass = dry_mass, so 2n/n, so 2.
dV = 380* 9.8 * ln(2) = ~2.5km/s.

Maximum plane change we can get from a 2.5km/s burn in a 7.5km/s orbit:
delta_V = 2*sin(phi/2)*Vc
:: sin(phi/2) = 2500 / (2*7500)
:: phi = ~19 degrees



For Mars/Moon/Eq_GEO, the effective plane-change is reduced by the distance of the target. Starting at, say 27 degree LEO, Equatorial GEO is around a 4.5 degree effective plane change. The Moon is a sub-half degree plane change. And Mars is so close to zero as to not be worth mentioning. (Mars' solar inclination relative to Earth's is vastly greater, and nothing done in Earth orbit changes that.)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TrevorMonty on 02/16/2020 09:28 pm
In my opinion the second stage of development of the concept should be a permanently orbiting 'tank' which can be repositioned in orbit as required.
The prime candidate for this would be a modified SH which would be comparatively easily developed given it's an iteration of an existing design.

I envisige you would replace the SH thrust structure with a SS thrust structure. The SH (tank) could even supply fuel to the SH (launch) to help with the increased takeoff weight. You would then be using the proven SS attachment system for In-Orbit fuel transfers.

This is similar to an idea that Twark_Main and I discussed (thread is here (https://forum.nasaspaceflight.com/index.php?topic=49134.msg2007579#msg2007579)).  I'd pretty much assumed that you just stretched the SS with a few extra tank rings and cannibalized some of the payload bay space, but you could probably start with a set of SH tanks as well.

The most demanding mission is getting a heavy cargo + crew to the lunar surface and back without lunar surface refueling.  You have to avoid refueling in HEEO to keep the crew out of the Van Allen Belts during refueling, and you have to carry all your prop with you for the return.  The "pusher/tanker" described in the link gets launched almost empty, uses regular tankers (whatever those are--likely just no-payload SSes) to acquire however much prop is needed, then docks nose-to-tail with the payload SS.  It transfers some of the prop to the payload SS, but then just acts as a first stage for most of the TLI delta-v.  Once in TLI, it either does a direct or free return to LEO, either aerobraking or propulsively inserting into whatever orbit the next mission needs.

The big deal here is risk reduction for crewed missions.  You only need one rendezvous/docking operation in the relatively low-radiation environment of LEO, and one jettison of the pusher/tanker.  Pusher/tanker isn't quite as prop-efficient as a series of refuelings in LEO and one refueling in HEEO, but prop efficiency probably isn't the most important criterion for a crewed mission.

Unnecessary complexity, such manoeuvres can be done with a simple starship tanker, fael097 calculated that the bulkhead shift alone will give a capacity of 2100t, so if it sends such a tanker with 1300t of fuel on the LEO will arrive with 100t, then it will be 20x refuelled to full. consumption of 700t gives dV 1.4km/s and in the tanker is 1200t to refuel the starship and 200t to return to the LEO (there would still be 100t left). when the starship enters the LEO it will be once refueled with another tanker which will give it dV 1.4km/s then both can meet in a higher orbit and the starship can be refueled to the full.

Instead of refuelling and docking, you have two refuellings and don't need a special tanker that can dock with its nose  ::)

Twark covered a lot of this, but:

1) Refueling in HEEO incurs an extra two passes through the VA belts, which is a big chunk of total radiation exposure, given average solar activity.  That won't quite double the total exposure for a lunar missions, but it'll come pretty close.

2) Whether this turns out to be "unnecessary complexity" depends in large part how much risk you incur with a docking/refueling operation.  P/T minimizes that.

An option to P/T that uses ordinary tankers (i.e., non-payload-carrying Starships) is to do the refueling rendezvous post-TLI.  That way, you don't incur the extra pair of VA belt transits.  The tanker then does a free return and reenters at TEI speeds.
Does the SS need to pass through VA belt twice?. If it is refuelled close earth before orbit hits belt, it can then do its earth departure burn, only passing through belt once.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 02/16/2020 09:43 pm
We shouldn't be too hysterical about the Van Allen belts. Apollo 14 (which came through near the thickest parts of both VA belts, both out and back) gave the crew a total dose of about 10 milligreys. (A CT scan is about 8mgr.)

The particles also aren't overly penetrating, compared to cosmic radiation, and secondary (shotgun) radiation from the skin isn't an issue. So combining the skin of Starship with a radiation shelter made from your water storage should protect the passengers for a good month of exposure, if they wanted to.

The VA belts are extremely dangerous for an unprotected human. But an "unprotected human" in space died before the airlock finished depressurising.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 02/16/2020 11:50 pm
In my opinion the second stage of development of the concept should be a permanently orbiting 'tank' which can be repositioned in orbit as required.
The prime candidate for this would be a modified SH which would be comparatively easily developed given it's an iteration of an existing design.

I envisige you would replace the SH thrust structure with a SS thrust structure. The SH (tank) could even supply fuel to the SH (launch) to help with the increased takeoff weight. You would then be using the proven SS attachment system for In-Orbit fuel transfers.

This is similar to an idea that Twark_Main and I discussed (thread is here (https://forum.nasaspaceflight.com/index.php?topic=49134.msg2007579#msg2007579)).  I'd pretty much assumed that you just stretched the SS with a few extra tank rings and cannibalized some of the payload bay space, but you could probably start with a set of SH tanks as well.

The most demanding mission is getting a heavy cargo + crew to the lunar surface and back without lunar surface refueling.  You have to avoid refueling in HEEO to keep the crew out of the Van Allen Belts during refueling, and you have to carry all your prop with you for the return.  The "pusher/tanker" described in the link gets launched almost empty, uses regular tankers (whatever those are--likely just no-payload SSes) to acquire however much prop is needed, then docks nose-to-tail with the payload SS.  It transfers some of the prop to the payload SS, but then just acts as a first stage for most of the TLI delta-v.  Once in TLI, it either does a direct or free return to LEO, either aerobraking or propulsively inserting into whatever orbit the next mission needs.

The big deal here is risk reduction for crewed missions.  You only need one rendezvous/docking operation in the relatively low-radiation environment of LEO, and one jettison of the pusher/tanker.  Pusher/tanker isn't quite as prop-efficient as a series of refuelings in LEO and one refueling in HEEO, but prop efficiency probably isn't the most important criterion for a crewed mission.

Unnecessary complexity, such manoeuvres can be done with a simple starship tanker, fael097 calculated that the bulkhead shift alone will give a capacity of 2100t, so if it sends such a tanker with 1300t of fuel on the LEO will arrive with 100t, then it will be 20x refuelled to full. consumption of 700t gives dV 1.4km/s and in the tanker is 1200t to refuel the starship and 200t to return to the LEO (there would still be 100t left). when the starship enters the LEO it will be once refueled with another tanker which will give it dV 1.4km/s then both can meet in a higher orbit and the starship can be refueled to the full.

Instead of refuelling and docking, you have two refuellings and don't need a special tanker that can dock with its nose  ::)

Twark covered a lot of this, but:

1) Refueling in HEEO incurs an extra two passes through the VA belts, which is a big chunk of total radiation exposure, given average solar activity.  That won't quite double the total exposure for a lunar missions, but it'll come pretty close.

2) Whether this turns out to be "unnecessary complexity" depends in large part how much risk you incur with a docking/refueling operation.  P/T minimizes that.

An option to P/T that uses ordinary tankers (i.e., non-payload-carrying Starships) is to do the refueling rendezvous post-TLI.  That way, you don't incur the extra pair of VA belt transits.  The tanker then does a free return and reenters at TEI speeds.
Does the SS need to pass through VA belt twice?. If it is refuelled close earth before orbit hits belt, it can then do its earth departure burn, only passing through belt once.

Sure, but that wouldn't be "refueling in HEEO," it would be refueling in LEO. And without HEEO refueling, Starship doesn't have the performance go to the Moon and back.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: joek on 02/17/2020 12:24 am
...
Musk has other ideas (https://arstechnica.com/science/2019/08/rocket-scientist-says-that-boeing-squelched-work-on-propellant-depots/)
...

Right.  That article (https://arstechnica.com/science/2019/08/rocket-scientist-says-that-boeing-squelched-work-on-propellant-depots/) is what I was referring to--and as I noted in a previous post in another thread at that time)--Musk wants to stay out of that fray.

Clearly Musk sees on-orbit refueling as a requirement (obvious from Starship conops).  However, Musk likely wants to stay out of the kerfuffle which would potentially put him at odds with certain major NASA programs-stakeholders (as articulated in Eric Berger's article):
Quote
But we were banned from even saying the 'd' word out loud.
...
Sowers' suggestion that "depots" should not be uttered in public is consistent with observations at the time that a US Senator from Alabama, Richard Shelby, had told NASA to stop talking about propellant depots. The NASA spaceflight center that manages the SLS rocket's development, Marshall Space Flight Center, is based in Alabama.

The operative question is: How to best achieve on-orbit refueling?  Musk's opinion is clearly "tankers"--at least in the near-term and for the missions SpaceX is considering.  Not to mention avoids the 'd' word.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: MATTBLAK on 02/17/2020 12:43 am
We shouldn't be too hysterical about the Van Allen belts. Apollo 14 (which came through near the thickest parts of both VA belts, both out and back) gave the crew a total dose of about 10 milligreys. (A CT scan is about 8mgr.)

The particles also aren't overly penetrating, compared to cosmic radiation, and secondary (shotgun) radiation from the skin isn't an issue. So combining the skin of Starship with a radiation shelter made from your water storage should protect the passengers for a good month of exposure, if they wanted to.

The VA belts are extremely dangerous for an unprotected human. But an "unprotected human" in space died before the airlock finished depressurising.
Didn't the Apollo 14 crew receive the highest overall dose of radiation of any Apollo crew? I'm sure I read that somewhere. EDIT: found table of dosage (see attachment) from bottom of this page - https://history.nasa.gov/SP-368/s2ch3.htm
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 02/17/2020 03:55 am
We shouldn't be too hysterical about the Van Allen belts. Apollo 14 (which came through near the thickest parts of both VA belts, both out and back) gave the crew a total dose of about 10 milligreys. (A CT scan is about 8mgr.)
Didn't the Apollo 14 crew receive the highest overall dose of radiation of any Apollo crew?

That's why I picked them as my example. (1rad is 10milligrays. Symptoms start in the low single digit grays, or low hundreds of rads.) They received the highest dose because of their trajectory, passing through the middle of the VA belts. The other missions were able to avoid most of the inner belt.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TheRadicalModerate on 02/17/2020 09:43 am
We shouldn't be too hysterical about the Van Allen belts. Apollo 14 (which came through near the thickest parts of both VA belts, both out and back) gave the crew a total dose of about 10 milligreys. (A CT scan is about 8mgr.)

The particles also aren't overly penetrating, compared to cosmic radiation, and secondary (shotgun) radiation from the skin isn't an issue. So combining the skin of Starship with a radiation shelter made from your water storage should protect the passengers for a good month of exposure, if they wanted to.

The VA belts are extremely dangerous for an unprotected human. But an "unprotected human" in space died before the airlock finished depressurising.

There's a lot of difference between a TLI trajectory, which transits both the inner and outer belts at something fairly close to maximum velocity, and, say, an LEO+2500 HEEO, which has a period of 11.5 hours and would likely spend a third of that deep in the outer belt.  I haven't done the time-of-flight computations, but my guess is that we're talking about several times the length of exposure that you get on a straight TLI burn.

Beyond that, what are the contingencies for a difficult rendezvous and docking?  You have close to 10 hours to achieve the R&D and transfer prop.  That should be plenty of time, but what if something goes wrong?  Do you abort the mission if you can't do a one-pass refueling?  Or do you expose the crew to still a third pair of passes through the VA belts?

Using either a TLI-based R&D for refueling or the pusher/tanker eliminates all of that risk, and incurs very little additional risk of a failed refueling, because both the tanker and the payload SS can always do a free-return around the Moon if they can't hook up.  Beyond that, the P/T guarantees a single R&D operation in LEO, where it's easiest to come fetch the crew if something goes wrong.

For cargo missions, none of this likely matters.  For crewed missions, it's a different story.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TheRadicalModerate on 02/17/2020 09:47 am
However, for the Moon or Mars, there's virtually no inclination requirement (Figures below). Hell, you can boost from polar orbit if you want, with barely a hit. So any LEO depot works for BEO missions. LEO-to-GEO is more restrictive, but low-inclination-LEO to equatorial-GEO hides most sins. So a general LEO depot for equatorial boost is likely to see a reasonable amount of use, IMO.

Two reasons you might want a high-inclination departure for the Moon:

1) It can minimize LLO insertion delta-v for lunar polar missions, which a likely to dominate the manifest.

2) High-inclination insertions avoid the thickest part of the VA belts, reducing radiation exposure.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: xvel on 02/17/2020 04:00 pm
If 250t thrust raptor will exists, SH will be able to raise the tanker with 2100t of fuel, which should provide 160t of fuel on LEO instead of 100t, from my calculations even bigger tankers works very well and are superior to multiple launches of smaller tankers. If SH has 250t engines, delta V is smaller and final angle is more vertical which makes landing easier, "only" problem is that this big tanker due to its weight and more vertical start has bigger gravitational losses so it should probably have more engines

I assume a dry weight of 120t, I don't think the tanker will be lighter, and I'm even afraid it may be heavier because it requires more 4mm rings.

(hkultala was right, you don't need a bigger booster if you equip SH with 250t engines)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TheRadicalModerate on 02/17/2020 04:49 pm
You use one of the tankers as a pseudo-depot, you launch the mission ship itself last. If weather delays a fuel launch (or it fails), your crew are still on the ground. You only launch once the tanker-cum-depot has enough fuel for the mission. Then the tanker-depot lands and goes back into ordinary service.

I've been calling this the "aggregation tanker".  It's no different from the vanilla-flavored tankers (unless you drink the Pusher/Tanker Kool-Aid); it's just the one that receives the prop from the other tankers to minimize the number of rendezvous/dock/refuel operations that have to be performed against the live payload.  You potentially need two aggregation tankers, one for LEO top-off and one for either HEEO or post-TLI top-off.  (Of course, if you use P/T, it is the agg tanker, and you only need one, and one rendezvous/dock/refuel.)

Quote
[Aside: The same reasoning says that the first "passenger" Starships would just be cargo ships with a passenger pods. Different pods for different missions. Lets you do Shuttle-like missions with mixed cargo and personnel. Such as satellite recovery missions, service missions, mixed science missions, etc. And the latter lets researchers use Starships as single-purpose specialised space-stations, by swapping out mission pods.]

And this because of its likely shape, needs to be called "StarKist".

I think this is no-brainer absolutely the way to engineer a Starship-based crew system, but it's surprisingly controversial.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: hkultala on 02/19/2020 03:55 am
[snip]

We don't know how long it will take to refuel, and since both the starship and the tanker can enter a higher orbit at the same time, Van Allen belts may not be such a problem if refueling will be fast.

Both the apogee-raise burn to HEEO and the departure burn are optimally performed at perigee, because Oberth. There are large performance losses (ie you can't reach the Moon) if you do it any other way.

There are much larger performance losses if you don't refuel at highly elliptic trajectory.

Argument that something should not be used unless it's perfect (when it's still much better than the alternatives) is stupid.

And there is no problem of raising the apogee at pegiree, then having the whole ~20-hour orbit time to transfer the fuel, then burning for the moon on the next pegiree.

Needs to go through the Van Allen belts three times, not a big deal.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Keldor on 02/19/2020 04:23 am
[snip]

We don't know how long it will take to refuel, and since both the starship and the tanker can enter a higher orbit at the same time, Van Allen belts may not be such a problem if refueling will be fast.

Both the apogee-raise burn to HEEO and the departure burn are optimally performed at perigee, because Oberth. There are large performance losses (ie you can't reach the Moon) if you do it any other way.

There are much larger performance losses if you don't refuel at highly elliptic trajectory.

Argument that something should not be used unless it's perfect (when it's still much better than the alternatives) is stupid.

And there is no problem of raising the apogee at pegiree, then having the whole ~20-hour orbit time to transfer the fuel, then burning for the moon on the next pegiree.

Needs to go through the Van Allen belts three times, not a big deal.

You could potentially use a high inclination orbit and avoid the Van Allen belts almost completely.  This should only cost DV during the initial launch to orbit, before refueling, since once you're in orbit, the rotation of the Earth doesn't effect you.  You'd have a slight loss of efficiency landing on the Moon, but it's rotation speed is so slow that it won't make much difference.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: kkattula on 02/19/2020 05:17 am
Or just use several micro-sats, with charged tethers, to drain the belts, and stop having to worry about it...
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TheRadicalModerate on 02/19/2020 08:20 am
[snip]

We don't know how long it will take to refuel, and since both the starship and the tanker can enter a higher orbit at the same time, Van Allen belts may not be such a problem if refueling will be fast.

Both the apogee-raise burn to HEEO and the departure burn are optimally performed at perigee, because Oberth. There are large performance losses (ie you can't reach the Moon) if you do it any other way.

There are much larger performance losses if you don't refuel at highly elliptic trajectory.

Argument that something should not be used unless it's perfect (when it's still much better than the alternatives) is stupid.

And there is no problem of raising the apogee at pegiree, then having the whole ~20-hour orbit time to transfer the fuel, then burning for the moon on the next pegiree.

Needs to go through the Van Allen belts three times, not a big deal.

I'm too lazy to do the math here, so correct me if I'm wrong:  You do better refueling at the highest energy possible, as long as you use the energy optimally.  For any EO, that means burning at the next perigee.  But TLI is the highest energy you'll need to get to the cis-lunar orbits, and it doesn't even need to do a second burn to complete the maneuver.  So refueling after TLI should be somewhat more efficient than refueling at HEEO.  (Technically, TLI is an HEEO...)

20 hours is likely enough time to do the rendezvous, dock, prop transfer, and undock.  But any glitch in the system leaves the crew in a dicey situation.  For example, if you had some problem that prevented you from doing the perigee burn with the main engines, you probably need to abort by chopping the perigee enough to reenter, using thrusters (it's not much delta-v).  Doing an indefinite number of passes through VAB would be bad.

You're in no worse shape refueling in TLI, and arguably in better shape because a free return will bring you back to reentry.

Of course, none of this is an issue with the pusher/tanker, since the P/T does one rendezvous in LEO and stages off, leaving the SS with enough prop to do the rest of TLI and everything needed to land and get home.  It's absolutely not as efficient as a tanker rendezvous in TLI, but it's fewer docking operations.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 02/19/2020 10:31 am
[snip]

We don't know how long it will take to refuel, and since both the starship and the tanker can enter a higher orbit at the same time, Van Allen belts may not be such a problem if refueling will be fast.

Both the apogee-raise burn to HEEO and the departure burn are optimally performed at perigee, because Oberth. There are large performance losses (ie you can't reach the Moon) if you do it any other way.

There are much larger performance losses if you don't refuel at highly elliptic trajectory.

So? No one is arguing for that.

Argument that something should not be used unless it's perfect (when it's still much better than the alternatives) is stupid.

No one is arguing for that either. Also, rude.

And there is no problem of raising the apogee at pegiree, then having the whole ~20-hour orbit time to transfer the fuel, then burning for the moon on the next pegiree.

Needs to go through the Van Allen belts three times...

That is exactly the problem.

...not a big deal.

That's a value judgement. TheRadicalModerate and I are just pointing out the trade-off.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 02/19/2020 10:38 am
(Technically, TLI is an HEEO...)

Technically it's hyperbolic, not elliptical. ;) But yes, your point about refilling post-TMI is a good one.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 02/19/2020 11:37 am
(Technically, TLI is an HEEO...)

Technically it's hyperbolic, not elliptical. ;) But yes, your point about refilling post-TMI is a good one.
it's only hyperbolic if the moon cuts off the orbit.

I've played enough kerbal to know you can have an orbit that wont inject to lunar SoI until the next time it goes around.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 02/19/2020 03:30 pm
(Technically, TLI is an HEEO...)

Technically it's hyperbolic, not elliptical. ;) But yes, your point about refilling post-TMI is a good one.
it's only hyperbolic if the moon cuts off the orbit.

I've played enough kerbal to know you can have an orbit that wont inject to lunar SoI until the next time it goes around.

Right, it's hyperbolic if it's moving at greater than Earth escape velocity (eg Apollo). An elliptical trajectory increases the trip time, but it doesn't really save that much propellant.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 02/19/2020 03:56 pm
Or just use several micro-sats, with charged tethers, to drain the belts, and stop having to worry about it...

"Don't you know that the Van Allen belts protect the Earth from solar storms? You corporate-lackey so-called 'scientists' only know how to destroy things." (Actual comments I've seen dominating the responses to articles about the VA belts on pop.sci sites.)

Isn't there also a way to drain at least the inner belt by injecting ELF from polar ground stations? (I might be misremembering, but I recall being amused by ELFs at the North Pole.)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TheRadicalModerate on 02/19/2020 05:55 pm
(Technically, TLI is an HEEO...)

Technically it's hyperbolic, not elliptical. ;) But yes, your point about refilling post-TMI is a good one.

TLI C3 is -2 km˛/s˛, more or less.  Model it as about 200 x 380,000 km and you'll be pretty close.

For TMI, things are a lot easier, because there's no hope of taking enough prop with you to return (even though the hope of doing Sabatier ISRU with some martian water and CO2 is much higher).  You can put an SS into a shorter-than-Hohmann TMI, direct from LEO, no problem.  All this HEEO stuff is a lunar idiosyncrasy.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: wannamoonbase on 02/19/2020 06:06 pm
….all this HEEO stuff is a lunar idiosyncrasy.

The HEEO and Lunar Gateway non-sense seems like NASA hedging itself.  That if lunar surface funds never arrived they would have a destination to use SLS and Orion.

If you're actually going to the Lunar surface then go to the surface.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TheRadicalModerate on 02/19/2020 08:16 pm
….all this HEEO stuff is a lunar idiosyncrasy.

The HEEO and Lunar Gateway non-sense seems like NASA hedging itself.  That if lunar surface funds never arrived they would have a destination to use SLS and Orion.

If you're actually going to the Lunar surface then go to the surface.

If nobody's ever going to the lunar surface, then this really doesn't matter.  Personally, I'm guessing that 90% of the revenue that SpaceX will earn from BEO missions in this decade will come from lunar surface and cis-lunar missions.

Note that HEEO or TLI-based refueling is a solution to a Starship-specific problem, and has nothing to do with the Gateway.  The Gateway, on the other hand, is a sorta-kinda solution to a set of SLS/Orion/HLS sorta-kinda problems, and has nothing to do with HEEO.  (Gateway is basically a risk reduction measure, to ease assembly of the HLS components.  If Boeing has its way with the "whole lander/ascender on a separate Block 1B" proposal, the Gateway will go away.)

FWIW (and O/T), I'm a big proponent of replacing the SLS/Orion method of getting to the Gateway and back with using Starship as an LEO-to-Gateway-back-to-LEO shuttle.  This:

1) Doesn't require launching a crew with SH/SS.  They can board from a separately-launched (and crew-qualified) F9/D2.

2) Doesn't require landing SS on the lunar surface.  They can use the HLS components to do that.

3) Doesn't require reentering and landing a crew on Earth with SS.  SS can propulsively return to LEO, then re-board the D2 for reentry.

4) Requires only refueling in LEO, and requires zero refuelings with the crew on board.  If you've got Isp=375s, then you can get to NRHO and back to (propulsive) LEO with 1190 t of prop.

This gets rid of the expensive SLS and Orion components ASAP, because crew-qualifying a Starship for only in-space use is a lot easier than crew-qualifying for launch, reentry, or landing on the Moon.  So you start with this, using the Gateway and HLS to land on the Moon, then qualify the lunar landing segment, then the earth reentry, and finally the launch.

Of course, the real problem is that getting rid of the expensive SLS and Orion is exactly what Congress wants to avoid...
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TrevorMonty on 02/19/2020 11:37 pm
….all this HEEO stuff is a lunar idiosyncrasy.

The HEEO and Lunar Gateway non-sense seems like NASA hedging itself.  That if lunar surface funds never arrived they would have a destination to use SLS and Orion.

If you're actually going to the Lunar surface then go to the surface.

If nobody's ever going to the lunar surface, then this really doesn't matter.  Personally, I'm guessing that 90% of the revenue that SpaceX will earn from BEO missions in this decade will come from lunar surface and cis-lunar missions.

Note that HEEO or TLI-based refueling is a solution to a Starship-specific problem, and has nothing to do with the Gateway.  The Gateway, on the other hand, is a sorta-kinda solution to a set of SLS/Orion/HLS sorta-kinda problems, and has nothing to do with HEEO.  (Gateway is basically a risk reduction measure, to ease assembly of the HLS components.  If Boeing has its way with the "whole lander/ascender on a separate Block 1B" proposal, the Gateway will go away.)

FWIW (and O/T), I'm a big proponent of replacing the SLS/Orion method of getting to the Gateway and back with using Starship as an LEO-to-Gateway-back-to-LEO shuttle.  This:

1) Doesn't require launching a crew with SH/SS.  They can board from a separately-launched (and crew-qualified) F9/D2.

2) Doesn't require landing SS on the lunar surface.  They can use the HLS components to do that.

3) Doesn't require reentering and landing a crew on Earth with SS.  SS can propulsively return to LEO, then re-board the D2 for reentry.

4) Requires only refueling in LEO, and requires zero refuelings with the crew on board.  If you've got Isp=375s, then you can get to NRHO and back to (propulsive) LEO with 1190 t of prop.

This gets rid of the expensive SLS and Orion components ASAP, because crew-qualifying a Starship for only in-space use is a lot easier than crew-qualifying for launch, reentry, or landing on the Moon.  So you start with this, using the Gateway and HLS to land on the Moon, then qualify the lunar landing segment, then the earth reentry, and finally the launch.

Of course, the real problem is that getting rid of the expensive SLS and Orion is exactly what Congress wants to avoid...
While I like idea of LEO-Gateway-LEO shuttle, SS is not best vehicle for this when only transferring few tons. Most of tanker missions fuel is used to move SS dry mass back and fore. A small purpose built shuttle could do round trip using 150 fuel, lot less if hydrolox.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Asteroza on 02/20/2020 02:43 am
Or just use several micro-sats, with charged tethers, to drain the belts, and stop having to worry about it...

There is the classic Tethers Unlimited paper showing they can drain the belts with 10 small sats with charged tethers in a few weeks or so. But, who pays for it, and why? Because everyone benefits from it whether they paid in or not, especially GEO birds that slowly spiral orbit up to GEO with electric thrusters (since they avoid roasting their solar panels). One of those tragedy of the commons moments, best fixed by a multinational Space Guard service charged with keeping the spacelanes clear (space junk included). Though I could easily see SpaceX doing just because it was incidental to their ops.

https://web.archive.org/web/20190213154045/http://www.tethers.com/papers/ES_Remediation_IEEE_Paper.pdf (https://web.archive.org/web/20190213154045/http://www.tethers.com/papers/ES_Remediation_IEEE_Paper.pdf)

For a fuel depot service though, maybe cheat with equatorial LEO as the baseline as that's the lowest exposure? Though that doesn't help for other orbits...
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TheRadicalModerate on 02/20/2020 05:40 am
….all this HEEO stuff is a lunar idiosyncrasy.

The HEEO and Lunar Gateway non-sense seems like NASA hedging itself.  That if lunar surface funds never arrived they would have a destination to use SLS and Orion.

If you're actually going to the Lunar surface then go to the surface.

If nobody's ever going to the lunar surface, then this really doesn't matter.  Personally, I'm guessing that 90% of the revenue that SpaceX will earn from BEO missions in this decade will come from lunar surface and cis-lunar missions.

Note that HEEO or TLI-based refueling is a solution to a Starship-specific problem, and has nothing to do with the Gateway.  The Gateway, on the other hand, is a sorta-kinda solution to a set of SLS/Orion/HLS sorta-kinda problems, and has nothing to do with HEEO.  (Gateway is basically a risk reduction measure, to ease assembly of the HLS components.  If Boeing has its way with the "whole lander/ascender on a separate Block 1B" proposal, the Gateway will go away.)

FWIW (and O/T), I'm a big proponent of replacing the SLS/Orion method of getting to the Gateway and back with using Starship as an LEO-to-Gateway-back-to-LEO shuttle.  This:

1) Doesn't require launching a crew with SH/SS.  They can board from a separately-launched (and crew-qualified) F9/D2.

2) Doesn't require landing SS on the lunar surface.  They can use the HLS components to do that.

3) Doesn't require reentering and landing a crew on Earth with SS.  SS can propulsively return to LEO, then re-board the D2 for reentry.

4) Requires only refueling in LEO, and requires zero refuelings with the crew on board.  If you've got Isp=375s, then you can get to NRHO and back to (propulsive) LEO with 1190 t of prop.

This gets rid of the expensive SLS and Orion components ASAP, because crew-qualifying a Starship for only in-space use is a lot easier than crew-qualifying for launch, reentry, or landing on the Moon.  So you start with this, using the Gateway and HLS to land on the Moon, then qualify the lunar landing segment, then the earth reentry, and finally the launch.

Of course, the real problem is that getting rid of the expensive SLS and Orion is exactly what Congress wants to avoid...
While I like idea of LEO-Gateway-LEO shuttle, SS is not best vehicle for this when only transferring few tons. Most of tanker missions fuel is used to move SS dry mass back and fore. A small purpose built shuttle could do round trip using 150 fuel, lot less if hydrolox.

If all Starship was ever going to do was an LEO-GW-LEO shuttle, I'd agree with you.  But the shuttle is merely the first capability, and the easiest one to get certified.  After that, SpaceX can bite off Earth EDL, followed by lunar landing/ascent, and finally launch from Earth with crew.  The order of these is up for debate, but the shuttle to and from NRHO is by far the lowest-hanging fruit.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: tbellman on 02/20/2020 09:39 am
While I like idea of LEO-Gateway-LEO shuttle, SS is not best vehicle for this when only transferring few tons. Most of tanker missions fuel is used to move SS dry mass back and fore. A small purpose built shuttle could do round trip using 150 fuel, lot less if hydrolox.

Question is then, which such purpose-built shuttle?  When will that be available?  And will it be significantly cheaper than a twice-refuelled Starship (even if I don't believe the $2M/launch figure Elon envisions will be reached within that timeframe)?

My understanding is that ACES is not currently being developed.  Will Blue Moon or some auxillary part of New Glenn be able to shuttle back and forth between LEO and lunar/cis-lunar?  Any other crafts in development?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TrevorMonty on 02/20/2020 12:24 pm
While I like idea of LEO-Gateway-LEO shuttle, SS is not best vehicle for this when only transferring few tons. Most of tanker missions fuel is used to move SS dry mass back and fore. A small purpose built shuttle could do round trip using 150 fuel, lot less if hydrolox.

Question is then, which such purpose-built shuttle?  When will that be available?  And will it be significantly cheaper than a twice-refuelled Starship (even if I don't believe the $2M/launch figure Elon envisions will be reached within that timeframe)?

My understanding is that ACES is not currently being developed.  Will Blue Moon or some auxillary part of New Glenn be able to shuttle back and forth between LEO and lunar/cis-lunar?  Any other crafts in development?
Blue are working OTV which is what BE7 is for besides lander. My guess is lander and OTV will be similar.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 02/20/2020 12:48 pm
Or just use several micro-sats, with charged tethers, to drain the belts, and stop having to worry about it...

There is the classic Tethers Unlimited paper showing they can drain the belts with 10 small sats with charged tethers in a few weeks or so. But, who pays for it, and why? Because everyone benefits from it whether they paid in or not, especially GEO birds that slowly spiral orbit up to GEO with electric thrusters (since they avoid roasting their solar panels). One of those tragedy of the commons moments, best fixed by a multinational Space Guard service charged with keeping the spacelanes clear (space junk included). Though I could easily see SpaceX doing just because it was incidental to their ops.

https://web.archive.org/web/20190213154045/http://www.tethers.com/papers/ES_Remediation_IEEE_Paper.pdf (https://web.archive.org/web/20190213154045/http://www.tethers.com/papers/ES_Remediation_IEEE_Paper.pdf)

For a fuel depot service though, maybe cheat with equatorial LEO as the baseline as that's the lowest exposure? Though that doesn't help for other orbits...
This particular TotC has a Gordian knot solution- One person does it for awhile, everyone gets used to benifiting, then the person announces they will stop doing it unless they receive donations to continue.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: dcengineering on 02/21/2020 07:56 pm

If all Starship was ever going to do was an LEO-GW-LEO shuttle, I'd agree with you.  But the shuttle is merely the first capability, and the easiest one to get certified.  After that, SpaceX can bite off Earth EDL, followed by lunar landing/ascent, and finally launch from Earth with crew.  The order of these is up for debate, but the shuttle to and from NRHO is by far the lowest-hanging fruit.

Might be a bit awkward when the "shuttle" has more living space than the Gateway does  ;D

I think you hit the nail on the head with your previous post. After reading through the whole thread, it seems a lot of the issues stem from the complexities and risk associated with these maneuvers while a crew is on board, when the likelihood of NASA crew certifying Starship anytime soon is almost zero. D2 has been in development for 6 years now and is still not certified even though Falcon 9 is a relatively simple rocket if you ignore the whole landing part (which is immaterial to its crew rating anyways).

What sort of insane timeline are we even looking at to crew certify Starship? While I am somewhat confident SpaceX can beat NASA's 2024 Moon landing goal, it would be little more than a capabilities demonstration when crew aren't allowed on board during this timeframe anyways.

In the short to medium term, we should probably assume that manned operations involving SS is going to require F9/D2 to get astronauts back and forth from orbit. 
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: xvel on 02/21/2020 08:08 pm
NASA can only certify for their missions, besides there is no such requirement as NASA certification for human flights
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 02/22/2020 01:35 am
NASA can only certify for their missions, besides there is no such requirement as NASA certification for human flights

FAA does.

Currently they are allowing suborbital (and presumably orbital) human rocket flight to classify vehicles as "experimental", passengers as "test crew", and exempt the operators from strict requirements of passenger aircraft. However, that's essentially a courtesy. It would take only a slightly more hostile Administration or a single anti-SpaceX senior senator to make the FAA adopt stricter airline-like rules.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: joek on 02/22/2020 01:58 am
NASA can only certify for their missions, besides there is no such requirement as NASA certification for human flights

Of course there is.  That is what CCP "certification" is all about (of which there are reams of documents).  In any case, this has nothing to do with this thread; take it elsewhere.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: joek on 02/22/2020 02:04 am
Currently they are allowing suborbital (and presumably orbital) human rocket flight to classify vehicles as "experimental", passengers as "test crew", and exempt the operators from strict requirements of passenger aircraft. However, that's essentially a courtesy. It would take only a slightly more hostile Administration or a single anti-SpaceX senior senator to make the FAA adopt stricter airline-like rules.

They are referred to as "participants" or "non-crew".  And yes, there have been pushes to institute FAA certification rules, which have been a work-in-progress for years, and resisted by the industry as a whole; SpaceX is not the only one with a stake in the game (and arguably less than some others).
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TheRadicalModerate on 02/22/2020 05:05 am
NASA can only certify for their missions, besides there is no such requirement as NASA certification for human flights

I'm much more interested in how Starship fits into--and eventually supplants--the Artemis architecture.  For that to happen, there is absolutely a requirement that NASA crew-rate Starship.

Could SpaceX do an all-private lunar surface mission?  I suppose so.  But it's a massive risk for very little reward.  There's not enough money to be made doing it, and an accident is a huge setback.  I'm betting that they'll be very, very conservative with lunar surface missions, and do them only under the aegis of Artemis.

They can likely get wilder and crazier with CLPS, and I'd expect CLPS missions to prove out a lot of the tech that will be used for crewed landings later on.  But that just gives something to feed to NASA to get the crew certification ball rolling for landings.  It's a lot easier to get the LEO-NRHO-LEO stuff up and running sooner.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: QuantumG on 02/22/2020 05:52 am
Could SpaceX do an all-private lunar surface mission?  I suppose so.  But it's a massive risk for very little reward.  There's not enough money to be made doing it, and an accident is a huge setback.  I'm betting that they'll be very, very conservative with lunar surface missions, and do them only under the aegis of Artemis.

I believe they're very interested in Artemis and I'd L O V E to see what they've submitted already.

I expect they'll do an automated lunar landing on their own dime.

Then I think they'll do a flight around the Moon with private astronauts (with an eccentric Japanese flight assignment officer!)

Around then NASA will look pretty silly if they don't put government astronauts on the next flight. NASA doesn't like to be put in these situations, so they've probably already secured a seat on the free-flyer.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: ThomasGadd on 02/22/2020 04:25 pm

While SpaceX is developing crewed Starship for NASA flights they can use Dragon as a transfer vehicle for non-NASA flights people could choose...
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TheRadicalModerate on 02/23/2020 07:44 pm

While SpaceX is developing crewed Starship for NASA flights they can use Dragon as a transfer vehicle for non-NASA flights people could choose...

Are you suggesting doing LEO to NRHO in a D2?  Not gonna happen; there's not enough delta-v and D2 only has consumables for 7 days.  But using an F9/D2 to get to LEO so that a crew can transfer to/from a Starship, which takes it to NRHO, is pretty easy, and the crew system for Starship isn't very challenging.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: GregTheGrumpy on 02/23/2020 08:44 pm

While SpaceX is developing crewed Starship for NASA flights they can use Dragon as a transfer vehicle for non-NASA flights people could choose...

NASA choosing to go this route **when** SpaceX has already sent and returned non-NASA individuals will be seen as churlish as the Russians seemed with DM-1 visited the ISS.  I just don't see that happening.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: docmordrid on 02/24/2020 12:14 pm

While SpaceX is developing crewed Starship for NASA flights they can use Dragon as a transfer vehicle for non-NASA flights people could choose...

Are you suggesting doing LEO to NRHO in a D2?  Not gonna happen; there's not enough delta-v and D2 only has consumables for 7 days.  But using an F9/D2 to get to LEO so that a crew can transfer to/from a Starship, which takes it to NRHO, is pretty easy, and the crew system for Starship isn't very challenging.

And a lot cheaper than doing it with Starliner or SLS/Orion.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: spacexfanatic on 04/15/2020 01:39 pm
Hi everyone, I did love the idea of Starship refueling another Starship but I was thinking about a simpler way to get extra fuel by mean of attaching external  tanks (cheap, disposable)  to  SS that will rendezvous somewhere ? think it simpler than later concept that still  has to be proven.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: SkyRate on 04/15/2020 02:26 pm
Hi everyone, I did love the idea of Starship refueling another Starship but I was thinking about a simpler way to get extra fuel by mean of attaching external  tanks (cheap, disposable)  to  SS that will rendezvous somewhere ? think it simpler than later concept that still  has to be proven.
Sure, the aft cargo pods could be made into tanks without hurting the ascent aerodynamics, but:

1. It's not that unproven. Progress tanker/cargo craft have auto-docked with Salyut-6, MIR and ISS 100+ times. Not to mention all the air-to-air refueling going on every day.

2. It's not that much simpler. Those tanks would each have to have connectors, valves, plumbing and sensors. The main tanks already have them (for being loaded via the SH). And if you transfer the tanks using a robotic arm, you have to add the weight and complexity of the arm. If not, it's a big, dangerous, time-consuming EVA job. "Best part is no part."

3. It's heavier. This is an upper stage. Every kg of structure is a kg less to orbit. Strap-on boosters are acceptable because they are dropped so early during the launch.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: spacexfanatic on 04/16/2020 10:01 am
Hi everyone, I did love the idea of Starship refueling another Starship but I was thinking about a simpler way to get extra fuel by mean of attaching external  tanks (cheap, disposable)  to  SS that will rendezvous somewhere ? think it simpler than later concept that still  has to be proven.

Sure, the aft cargo pods could be made into tanks without hurting the ascent aerodynamics, but:

1. It's not that unproven. Progress tanker/cargo craft have auto-docked with Salyut-6, MIR and ISS 100+ times. Not to mention all the air-to-air refueling going on every day.

2. It's not that much simpler. Those tanks would each have to have connectors, valves, plumbing and sensors. The main tanks already have them (for being loaded via the SH). And if you transfer the tanks using a robotic arm, you have to add the weight and complexity of the arm. If not, it's a big, dangerous, time-consuming EVA job. "Best part is no part."

3. It's heavier. This is an upper stage. Every kg of structure is a kg less to orbit. Strap-on boosters are acceptable because they are dropped so early during the launch.

My point is that it's more cost evective to only send the necessery to space which in our case is the fuel, sending the ship and get it back to earth is unessery if you could only send the fuel (and of course lightweight and cheap package) .

For the issue of rendezvous and connecting, I suggest the use of a flexible pipe like those used for air refueling which will use small thruster to move, once attached to the tank they will start suck the fuel or they will retract to connect the tank directly to straship. no plumbing needed just an orifice in the tank.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: RonM on 04/16/2020 12:49 pm
Hi everyone, I did love the idea of Starship refueling another Starship but I was thinking about a simpler way to get extra fuel by mean of attaching external  tanks (cheap, disposable)  to  SS that will rendezvous somewhere ? think it simpler than later concept that still  has to be proven.

Sure, the aft cargo pods could be made into tanks without hurting the ascent aerodynamics, but:

1. It's not that unproven. Progress tanker/cargo craft have auto-docked with Salyut-6, MIR and ISS 100+ times. Not to mention all the air-to-air refueling going on every day.

2. It's not that much simpler. Those tanks would each have to have connectors, valves, plumbing and sensors. The main tanks already have them (for being loaded via the SH). And if you transfer the tanks using a robotic arm, you have to add the weight and complexity of the arm. If not, it's a big, dangerous, time-consuming EVA job. "Best part is no part."

3. It's heavier. This is an upper stage. Every kg of structure is a kg less to orbit. Strap-on boosters are acceptable because they are dropped so early during the launch.

My point is that it's more cost evective to only send the necessery to space which in our case is the fuel, sending the ship and get it back to earth is unessery if you could only send the fuel (and of course lightweight and cheap package) .

For the issue of rendezvous and connecting, I suggest the use of a flexible pipe like those used for air refueling which will use small thruster to move, once attached to the tank they will start suck the fuel or they will retract to connect the tank directly to straship. no plumbing needed just an orifice in the tank.

Lightweight cheap packaging that can survive launch isn't possible for cryogenic propellants. This "package" will be the same construction as the SS propellant tanks, so why not skip the "middleman" and use SS tanks?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: spacexfanatic on 04/16/2020 01:33 pm
Hi everyone, I did love the idea of Starship refueling another Starship but I was thinking about a simpler way to get extra fuel by mean of attaching external  tanks (cheap, disposable)  to  SS that will rendezvous somewhere ? think it simpler than later concept that still  has to be proven.

Sure, the aft cargo pods could be made into tanks without hurting the ascent aerodynamics, but:

1. It's not that unproven. Progress tanker/cargo craft have auto-docked with Salyut-6, MIR and ISS 100+ times. Not to mention all the air-to-air refueling going on every day.

2. It's not that much simpler. Those tanks would each have to have connectors, valves, plumbing and sensors. The main tanks already have them (for being loaded via the SH). And if you transfer the tanks using a robotic arm, you have to add the weight and complexity of the arm. If not, it's a big, dangerous, time-consuming EVA job. "Best part is no part."

3. It's heavier. This is an upper stage. Every kg of structure is a kg less to orbit. Strap-on boosters are acceptable because they are dropped so early during the launch.

My point is that it's more cost evective to only send the necessery to space which in our case is the fuel, sending the ship and get it back to earth is unessery if you could only send the fuel (and of course lightweight and cheap package) .

For the issue of rendezvous and connecting, I suggest the use of a flexible pipe like those used for air refueling which will use small thruster to move, once attached to the tank they will start suck the fuel or they will retract to connect the tank directly to straship. no plumbing needed just an orifice in the tank.

Lightweight cheap packaging that can survive launch isn't possible for cryogenic propellants. This "package" will be the same construction as the SS propellant tanks, so why not skip the "middleman" and use SS tanks?

If Spacex envision to make reusable spacecrafts with 4mm thin stainless steel, it won't be that hard to imagine a fuel tank that goes to space with the same mensurations and with the same materials.skiping   the "middleman" may save weight and money.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Redclaws on 04/16/2020 01:39 pm
And now you’re discarding that item.  It has engines and avionics on it, doesn’t it?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: spacexfanatic on 04/16/2020 01:42 pm
And now you’re discarding that item.  It has engines and avionics on it, doesn’t it?

Engines and avionics like those in satellites.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: DistantTemple on 04/16/2020 05:27 pm
Two other points. Both questionable.
Those tanks you postulate have to then reenter and either burn up or splash down, as it would not be appropriate to leave them in orbit. So assuming SX does get sixSS's off to Mars, soon (2024 or 20260) that would be 5 x 6 = 30 reentry and spashdown (as stainless will not burn up, and CF is too expensive) events. And after a few more years, 100's of dropped tanks raining down, with practical, safety, environmental, and public comment concerns.

And two they all cost to make, in $, manpower, resources, and factory space.

The refuelling system is envisaged as one suitable for hundreds and then thousands of launches. It is supposed to moving towards airline-like operations, with only fuel as expendable. And driving the cost <$10M etc.... Mass manufacturing tanks, with navigation and propulsion doesn't marry easily with that. (I guess mass of tank+fuel/oxidiser ~150t )

And a second stage is still needed, which needs to be 100% reusable, else the tanks would become a second stage themselves!!!!!

ISTM EM called this right.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 04/17/2020 12:26 am
And now you’re discarding that item.  It has engines and avionics on it, doesn’t it?
Engines and avionics like those in satellites.

I can't picture what you are describing. How do these tanks, loaded with propellant, get into orbit?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: kkattula on 04/17/2020 09:03 am
And now you’re discarding that item.  It has engines and avionics on it, doesn’t it?
Engines and avionics like those in satellites.

I can't picture what you are describing. How do these tanks, loaded with propellant, get into orbit?

Yeah. Super Heavy by itself has about zero payload to LEO, expendable.  So you need a Starship second stage to get to orbit with payload. 

Sure, you could just have the propellant for transfer sitting in a disposable tank attached to a satellite bus, that gets dropped off in orbit.

But that costs a lot more and reduces payload per launch, compared to having it sit in Starship's own tanks, and let SS do all the maneuvering. 

Also, you can't just have an orifice in the tank and poke a hose in. The two vehicles need to be firmly connected, have thrust applied to settle the fluids, and have two pipes for each propellant. One for fluid and one for gas, so pressure differential will move the fluid one way and the gas the other.

Maybe you could do all that with a flexible 4-pipe and tether connector, but no need for thrusters. There are technologies for extending and guiding snake-like connectors.  (See Tesla auto-charger). Besides which, SS needs fueling pipes on the tail anyway, so it can be fueled through SH on the pad.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/27/2020 11:02 am
Hi,

Just wanted to start a thread discussing orbital refueling technology proposed by SX, this is (for me) a very critical technology for SS concept success in the future, very little is known about SX approah to the matter, so any insight on technologies existing or in R&D stages is welcome here to improve our understanding.

Quote
One of SpaceX's principal engineers behind the Starship project, Paul Wooster, has identified orbital refueling as one of most difficult technology challenges the company will have to overcome in order to realize its Mars ambitions.


Thanks.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/27/2020 11:47 am
The main issues to deal with are:

1-How to prevent cryogen from boiling-off (keep the fuel cool) for long duration.

2-How to transfert the cryogen from one container to the other.

NASA with Robotic Refueling Mission 3 (RRM3) has been trying to developpe the technology needed with relative success, but the scale needed for SX plans will require a complete review of the process for scaling up which may lead to using completly different technology.

The technology is at it early stages of maturation which means that time is still needed and this means that the technology (orbital refueling) most likely (IMHO) wont be ready for SS developement timeframe.

(https://www.nextbigfuture.com/wp-content/uploads/2017/11/a75bd7c23f0f273c52da444f936bedf3-730x430.jpg)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: sebk on 07/27/2020 12:04 pm
From the info extracted from Elon tweets and plugging holes with informed guesses we have rough general picture of how it would be done:

- Dock the vehicles bottom-to-bottom and obtain seal of the piping
- Vent receiving end to low internal tank pressure (probably well below atmospheric[*])
- Use thrusters (probably receiving end, see below why[*][**]) to produce ullage thrust in the same it's done before re-firing of any stage in orbit
- Open valves and let the transfer begin
- Pressure difference pushes the liquids while ullage thrust (in the order of milli-gee) keeps them settled
- Keep venting the receiving end. There's one possible difficulty here, see below [***]
- If the sending end is close full (for example transfer from accumulation tanker to receiving ship) you need also to keep it pressurized at the required level.
- Once liquid fuel is done pressure would equalize quickly. Possibly bubble detection would shut the valves before this happens as this would be a bit violent. Or maybe the system is made robust enough for it not to be a problem.
- Terminate the ullage thrust
- Purge & vent the piping between main valves on both vehicles.
- Undock

Notes:
*] Venting below atmospheric ensures the remaining fuel would be at a super-cooled temperature as intended.
**] Receiving end needs to be kept at low pressure so it has obvious source of gas for ullage thrusters
***] Receiving end may see liquid foaming and condensation foring in the ullage space. Venting liquid would be wasteful and could be a source of problems as liquid venting to vacuum will partly evaporate and partly freeze and frozen liquid may plug holes. So venting piping could use "cyclone" separator and possibly some mild heating.

From the above one could notice that we need some gas generating subsystem which could pressurize the vehicle without engines firing. So some burner, pump for it and heat exchanger to vaporize the liquid.


Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/27/2020 12:32 pm
From the info extracted from Elon tweets and plugging holes with informed guesses we have rough general picture of how it would be done:

- Dock the vehicles bottom-to-bottom and obtain seal of the piping
- Vent receiving end to low internal tank pressure (probably well below atmospheric[*])
- Use thrusters (probably receiving end, see below why[*][**]) to produce ullage thrust in the same it's done before re-firing of any stage in orbit
- Open valves and let the transfer begin
- Pressure difference pushes the liquids while ullage thrust (in the order of milli-gee) keeps them settled
- Keep venting the receiving end. There's one possible difficulty here, see below [***]
- If the sending end is close full (for example transfer from accumulation tanker to receiving ship) you need also to keep it pressurized at the required level.
- Once liquid fuel is done pressure would equalize quickly. Possibly bubble detection would shut the valves before this happens as this would be a bit violent. Or maybe the system is made robust enough for it not to be a problem.
- Terminate the ullage thrust
- Purge & vent the piping between main valves on both vehicles.
- Undock

Notes:
*] Venting below atmospheric ensures the remaining fuel would be at a super-cooled temperature as intended.
**] Receiving end needs to be kept at low pressure so it has obvious source of gas for ullage thrusters
***] Receiving end may see liquid foaming and condensation foring in the ullage space. Venting liquid would be wasteful and could be a source of problems as liquid venting to vacuum will partly evaporate and partly freeze and frozen liquid may plug holes. So venting piping could use "cyclone" separator and possibly some mild heating.

From the above one could notice that we need some gas generating subsystem which could pressurize the vehicle without engines firing. So some burner, pump for it and heat exchanger to vaporize the liquid.

Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?
(https://www.fourmilab.ch/autofile/e5/figures/external_tank.jpg)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Thunderscreech on 07/27/2020 12:52 pm
What's the benefit?  The fuel will still need to transfer out of the docked external tank into the engines, the system they envision has them doing that into existing tankage that's already present and used to get it into earth orbit (when it operates as the second stage) and the rest of the challenges aren't materially different in terms of timing for transferring fuel in during boost versus during the RCS-ullage+pressurization scenario another user shared above.

When adding new elements to a problem to solve it, it's useful to know why the added complexity is required and what unique problem it's solving, otherwise perhaps there's a better way.

In this instance, it's not clear what shipping up external tanks that will need to be plumbed solves that doing the ship-ship transfer doesn't.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/27/2020 01:05 pm
What's the benefit?  The fuel will still need to transfer out of the docked external tank into the engines, the system they envision has them doing that into existing tankage that's already present and used to get it into earth orbit (when it operates as the second stage) and the rest of the challenges aren't materially different in terms of timing for transferring fuel in during boost versus during the RCS-ullage+pressurization scenario another user shared above.

When adding new elements to a problem to solve it, it's useful to know why the added complexity is required and what unique problem it's solving, otherwise perhaps there's a better way.

In this instance, it's not clear what shipping up external tanks that will need to be plumbed solves that doing the ship-ship transfer doesn't.

May be because it's simpler to do so, just imagine space shuttle docking to her external tank and going all the way to Mars, no air drag issue, the tank is light weight, no time and energy waisted in fuel transfert, the external tank could also be imagined as a payload of a starship fairing.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Thunderscreech on 07/27/2020 01:12 pm
May be because it's simpler to do so, just imagine space shuttle docking to her external tank and going all the way to Mars, no air drag issue, the tank is light weight, no time and energy waisted in fuel transfert, the external tank could also be imagined as a payload of a starship fairing.
I think I might not have written my question clearly, please allow me to try again: What makes this simpler?  You're adding parts, you still have docking operations, you still have to transfer fuel into the vehicle (the only thing this changes is when it happens; the fuel needs to come in during the burn as opposed to during the fueling operation)....

What part of this is simpler?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: [email protected] on 07/27/2020 01:16 pm
We ofc want a thought experiment....

But at the end of the day it's up to SpaceX who actually does it. Remember that they have a very smart engineers, who knows everything they're doing = considerations of choosing this refueling method

They obviously already has NASA on supports, just to keep in mind
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/27/2020 01:23 pm
May be because it's simpler to do so, just imagine space shuttle docking to her external tank and going all the way to Mars, no air drag issue, the tank is light weight, no time and energy waisted in fuel transfert, the external tank could also be imagined as a payload of a starship fairing.
I think I might not have written my question clearly, please allow me to try again: What makes this simpler?  You're adding parts, you still have docking operations, you still have to transfer fuel into the vehicle (the only thing this changes is when it happens; the fuel needs to come in during the burn as opposed to during the fueling operation)....

What part of this is simpler?

I didn't add parts I just proposed a rethinking of the design, I also didn't suggest a fuel transfert but a direct fuel burn from external tank in SS engines, I think the proposed idea of mating two ends of SS is also hard to imagine, because it's not possible to get the fluid flow in a reversed direction without affecting all parts like pumps and turbines and you can't get extra plumbing in a place where it's already  congested (with engines).

We ofc want a thought experiment....

But at the end of the day it's up to SpaceX who actually does it. Remember that they have a very smart engineers, who knows everything they're doing = considerations of choosing this refueling method

They obviously already has NASA on supports, just to keep in mind

This a passive way to see things.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nomadd on 07/27/2020 01:26 pm
What's the benefit?  The fuel will still need to transfer out of the docked external tank into the engines, the system they envision has them doing that into existing tankage that's already present and used to get it into earth orbit (when it operates as the second stage) and the rest of the challenges aren't materially different in terms of timing for transferring fuel in during boost versus during the RCS-ullage+pressurization scenario another user shared above.

When adding new elements to a problem to solve it, it's useful to know why the added complexity is required and what unique problem it's solving, otherwise perhaps there's a better way.

In this instance, it's not clear what shipping up external tanks that will need to be plumbed solves that doing the ship-ship transfer doesn't.

May be because it's simpler to do so, just imagine space shuttle docking to her external tank and going all the way to Mars, no air drag issue, the tank is light weight, no time and energy waisted in fuel transfert, the external tank could also be imagined as a payload of a starship fairing.
You'd still have to transfer the fuel to the engines, which wouldn't be any simpler than transferring it to the SS tanks, and you'd be dragging an extra 30 or 40 tons of weight around.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: [email protected] on 07/27/2020 01:28 pm
because it's not possible to get the fluid flow in a reversed direction without affecting all parts like pumps and turbines...
What's make it not possible? It's not like they flow the propellant directly into the engine anyways


...and you can't get extra plumbing in a place where it's already  congested (with engines).
It still had quite enough space

With extra tanks, you will throw the full reusability right off the window, about as far as a billion light years away
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 07/27/2020 01:30 pm
May be because it's simpler to do so, just imagine space shuttle docking to her external tank and going all the way to Mars, no air drag issue, the tank is light weight, no time and energy waisted in fuel transfert, the external tank could also be imagined as a payload of a starship fairing.
I think I might not have written my question clearly, please allow me to try again: What makes this simpler?  You're adding parts, you still have docking operations, you still have to transfer fuel into the vehicle (the only thing this changes is when it happens; the fuel needs to come in during the burn as opposed to during the fueling operation)....

What part of this is simpler?

I didn't add parts I just proposed a rethinking of the design,
A rethinking that adds external tanks to the tanks used by starship to reach orbit in the first place.
Quote
I also didn't suggest a fuel transfert but a direct fuel burn from external tank in SS engines,
"Direct fuel burn" IS a fuel transfer.

Quote
I think the proposed idea of mating two ends of SS is also hard to imagine, because it's not possible to get the fluid flow in a reversed direction without affecting all parts like pumps and turbines and you can't get extra plumbing in a place where it's already  congested (with engines).
We're not talking the height-restricted SLS engine bay here- there's plenty of room for plumbing if it's needed to get the job done. The only question is how much mass it takes- and it is very easy to be less mass than a few external tanks.

Edit: You arnt thinking the fuel will be transferred from engine bell to engine bell, are you? because there are easier ways.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Thunderscreech on 07/27/2020 01:35 pm
Indeed, I think spitballing ideas is fun, for this one it just seems like it adds complexity without reducing it elsewhere.  More parts, different loading, etc yet the core problem of transferring the fuel in from another tank still exists, but now it exists under heavy thrust instead of being performed during an ullage-settled transfer between two Starships.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: guckyfan on 07/27/2020 01:35 pm
Starship gets fueled on the pad through internal connections from Superheavy, the first stage. Which means the connecting plumbing is already there.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/27/2020 01:37 pm
What's the benefit?  The fuel will still need to transfer out of the docked external tank into the engines, the system they envision has them doing that into existing tankage that's already present and used to get it into earth orbit (when it operates as the second stage) and the rest of the challenges aren't materially different in terms of timing for transferring fuel in during boost versus during the RCS-ullage+pressurization scenario another user shared above.

When adding new elements to a problem to solve it, it's useful to know why the added complexity is required and what unique problem it's solving, otherwise perhaps there's a better way.

In this instance, it's not clear what shipping up external tanks that will need to be plumbed solves that doing the ship-ship transfer doesn't.

May be because it's simpler to do so, just imagine space shuttle docking to her external tank and going all the way to Mars, no air drag issue, the tank is light weight, no time and energy waisted in fuel transfert, the external tank could also be imagined as a payload of a starship fairing.
You'd still have to transfer the fuel to the engines, which wouldn't be any simpler than transferring it to the SS tanks, and you'd be dragging an extra 30 or 40 tons of weight around.

Fuel transfert to engines is easy because turbopumps and vacuuem will take care of it, and for the weight you did mention space shuttle external tank weight which is true but the proposed concept may propose multiple external tanks jettisoned when empty.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: [email protected] on 07/27/2020 01:42 pm
What's the benefit?  The fuel will still need to transfer out of the docked external tank into the engines, the system they envision has them doing that into existing tankage that's already present and used to get it into earth orbit (when it operates as the second stage) and the rest of the challenges aren't materially different in terms of timing for transferring fuel in during boost versus during the RCS-ullage+pressurization scenario another user shared above.

When adding new elements to a problem to solve it, it's useful to know why the added complexity is required and what unique problem it's solving, otherwise perhaps there's a better way.

In this instance, it's not clear what shipping up external tanks that will need to be plumbed solves that doing the ship-ship transfer doesn't.

May be because it's simpler to do so, just imagine space shuttle docking to her external tank and going all the way to Mars, no air drag issue, the tank is light weight, no time and energy waisted in fuel transfert, the external tank could also be imagined as a payload of a starship fairing.
You'd still have to transfer the fuel to the engines, which wouldn't be any simpler than transferring it to the SS tanks, and you'd be dragging an extra 30 or 40 tons of weight around.

Fuel transfert to engines is easy because turbopumps and vacuuem will take care of it, and for the weight you did mention space shuttle external tank weight which is true but the proposed concept may propose multiple external tanks jettisoned when empty.
Hello, full & rapid reusability..
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 07/27/2020 01:48 pm
This is something that needs to be solved, but I consider it at least an order of magnitude easier than, say, reusable orbital reentry of the upper stage. You don’t need massive pumps or whatever. Just some light ullage thrust and a pressure differential.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: meekGee on 07/27/2020 02:15 pm




Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?
(https://www.fourmilab.ch/autofile/e5/figures/external_tank.jpg)

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Eer on 07/27/2020 02:17 pm
For me (IANARS or E) is the active cooling (and it's energy requirements) for sub-cooling the O2 and CH4.  Yes, the issue exists at the ISRU production for return, but it also seems likely to be required for the propellent accumulation before TMI.

Transfer is part of the issue, though the pressure gradient discussion in OP is enlightening.  But accomplishing and maintaining the subcooling densification will require something more than just venting gas, I would think.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: spacenut on 07/27/2020 02:27 pm
My idea is not to have a crew in an outbound for Mars Starship waiting and having to have 6 tankers dock and transfer fuel.

My idea is to put tankers in orbit with refrigeration equipment and some solar panels for power.  Then fill the tankers with other tankers.  Then the outbound crewed ship can dock only once to a full tanker and then go. 

So essentially orbital tankers will become fuel depots for only one stop and fill to go per Starship.  Orbital tankers can be filled at reasonable pace during the off synods.  Then you have several full orbital tankers that can be used for any outbound Starships to the moon or Mars.  SpaceX could also let others license their technology to fill tankers with their rockets for a mission they want to do in deep space. 

For massive flotillas of Starships bound for Mars colony during the 6 month synod when Mars is closest to earth, fuel depots of some sort is the only way to save time.  Using Starship tankers would be easy without building anything new.   Starship will be a do-all spacecraft.  Tanker, fuel depot, moon lander, Mars lander, satellite orbiter, cargo carrier.  Modified for whatever is needed. 
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: cdebuhr on 07/27/2020 02:37 pm
For me (IANARS or E) is the active cooling (and it's energy requirements) for sub-cooling the O2 and CH4.  Yes, the issue exists at the ISRU production for return, but it also seems likely to be required for the propellent accumulation before TMI.

Transfer is part of the issue, though the pressure gradient discussion in OP is enlightening.  But accomplishing and maintaining the subcooling densification will require something more than just venting gas, I would think.
As I understand it (if I understand it ...), the purpose of prop densification is to get more prop in the tanks to help with the very difficult task of getting out of the lower bits of Earth's relatively deep gravity well.  Do we really think they're going to be using densified props for TMI, or Mars ascent?  I had always assumed sub-cooling would be a getting-off-of-Earth thing, and otherwise props would be run of the mill (i.e., at the tank pressure determined  boiling point) cryogens.  Is Raptor so finely tuned that it requires sub-cooled prop, or is sub-cooling just used for a needed performance boost?  I had always assumed the latter.  My own (totally uninformed) speculation is that sub-cooling is a total non-issue for on-orbit prop transfer.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/27/2020 02:51 pm




Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...

You're right to point out to the vocabulary it might be deceiving, for me "Just" and "simply" means proven technology have been in use for a while.
"Complexe" means that it's at the early stages of concept has to be put in practice in reliable manner.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: meekGee on 07/27/2020 02:58 pm




Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...

You're right to point out to the vocabulary it might be deceiving, for me "Just" and "simply" means proven technology have been in use for a while.
"Complexe" means that it's at the early stages of concept has to be put in practice in reliable manner.
So..  it's proven to be prohibitively expensive?
 
Starship is anything but a Shuttle repeat.  It's the anti-shuttle.  Consider each element in isolation, fine, but certainly don't give it points just because it was used in shuttle..

Remember Starship has to land on Mars and take off again, then re-enter Earth.  Are you "just" going to keep docking with new tanks all the time and throwing them away afterwards?

Refueling is fundamental to any mode of transportation, and compared to other challenges like, say, launch and EDL, it's relatively easy.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: whitelancer64 on 07/27/2020 03:06 pm
My idea is not to have a crew in an outbound for Mars Starship waiting and having to have 6 tankers dock and transfer fuel.

My idea is to put tankers in orbit with refrigeration equipment and some solar panels for power.  Then fill the tankers with other tankers.  Then the outbound crewed ship can dock only once to a full tanker and then go. 

So essentially orbital tankers will become fuel depots for only one stop and fill to go per Starship.  Orbital tankers can be filled at reasonable pace during the off synods.  Then you have several full orbital tankers that can be used for any outbound Starships to the moon or Mars.  SpaceX could also let others license their technology to fill tankers with their rockets for a mission they want to do in deep space. 

For massive flotillas of Starships bound for Mars colony during the 6 month synod when Mars is closest to earth, fuel depots of some sort is the only way to save time.  Using Starship tankers would be easy without building anything new.   Starship will be a do-all spacecraft.  Tanker, fuel depot, moon lander, Mars lander, satellite orbiter, cargo carrier.  Modified for whatever is needed.

Was there someone suggesting they would launch crew first? That's entirely backwards.

I am pretty sure that using tankers as temporary fuel depots is already SpaceX's plan.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/27/2020 03:09 pm




Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...

You're right to point out to the vocabulary it might be deceiving, for me "Just" and "simply" means proven technology have been in use for a while.
"Complexe" means that it's at the early stages of concept has to be put in practice in reliable manner.
So..  it's proven to be prohibitively expensive?
 
Starship is anything but a Shuttle repeat.  It's the anti-shuttle.  Consider each element in isolation, fine, but certainly don't give it points just because it was used in shuttle..

Remember Starship has to land on Mars and take off again, then re-enter Earth.  Are you "just" going to keep docking with new tanks all the time and throwing them away afterwards?

Refueling is fundamental to any mode of transportation, and compared to other challenges like, say, launch and EDL, it's relatively easy.

I'm from those who consider Starship as a mean to get to Mars and beyond, the primary goal is to get to Mars, getting it cheap getting it reausable getting it through re-fueling or external tanks, this is for me a secondary issue that could be worked out, it must be some interim solution to get to Mars, but to get it in the 2030's IMHO we must get some compromises..
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 07/27/2020 03:10 pm
Just here to point out that the Shuttle External Tank cost $75 million, for a launch vehicle whose total payload is about 20-27 tonnes to LEO. And doesn’t last long in LEO due in part to popcorning of the insulation. Drop tanks are much too expensive except for maybe specialized missions. It’s not much different from just being totally expendable...
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: whitelancer64 on 07/27/2020 03:13 pm
Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...

You're right to point out to the vocabulary it might be deceiving, for me "Just" and "simply" means proven technology have been in use for a while.
"Complexe" means that it's at the early stages of concept has to be put in practice in reliable manner.
So..  it's proven to be prohibitively expensive?
 
Starship is anything but a Shuttle repeat.  It's the anti-shuttle.  Consider each element in isolation, fine, but certainly don't give it points just because it was used in shuttle..

Remember Starship has to land on Mars and take off again, then re-enter Earth.  Are you "just" going to keep docking with new tanks all the time and throwing them away afterwards?

Refueling is fundamental to any mode of transportation, and compared to other challenges like, say, launch and EDL, it's relatively easy.

I'm from those who consider Starship as a mean to get to Mars and beyond, the primary goal is to get to Mars, getting it cheap getting it reausable getting it through re-fueling or external tanks, this is for me a secondary issue that could be worked out, it must be some interim solution to get to Mars, but to get it in the 2030's IMHO we must get some compromises..

Why does there have to be an interim solution?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/27/2020 03:16 pm
Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...

You're right to point out to the vocabulary it might be deceiving, for me "Just" and "simply" means proven technology have been in use for a while.
"Complexe" means that it's at the early stages of concept has to be put in practice in reliable manner.
So..  it's proven to be prohibitively expensive?
 
Starship is anything but a Shuttle repeat.  It's the anti-shuttle.  Consider each element in isolation, fine, but certainly don't give it points just because it was used in shuttle..

Remember Starship has to land on Mars and take off again, then re-enter Earth.  Are you "just" going to keep docking with new tanks all the time and throwing them away afterwards?

Refueling is fundamental to any mode of transportation, and compared to other challenges like, say, launch and EDL, it's relatively easy.

I'm from those who consider Starship as a mean to get to Mars and beyond, the primary goal is to get to Mars, getting it cheap getting it reausable getting it through re-fueling or external tanks, this is for me a secondary issue that could be worked out, it must be some interim solution to get to Mars, but to get it in the 2030's IMHO we must get some compromises..

Why does there have to be an interim solution?

Because time is ticking and SX plans are too ambitiuos (IMHO) for the timeframe, and it's like a black hole money siphoning endeavor.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: meekGee on 07/27/2020 03:18 pm




Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...

You're right to point out to the vocabulary it might be deceiving, for me "Just" and "simply" means proven technology have been in use for a while.
"Complexe" means that it's at the early stages of concept has to be put in practice in reliable manner.
So..  it's proven to be prohibitively expensive?
 
Starship is anything but a Shuttle repeat.  It's the anti-shuttle.  Consider each element in isolation, fine, but certainly don't give it points just because it was used in shuttle..

Remember Starship has to land on Mars and take off again, then re-enter Earth.  Are you "just" going to keep docking with new tanks all the time and throwing them away afterwards?

Refueling is fundamental to any mode of transportation, and compared to other challenges like, say, launch and EDL, it's relatively easy.

I'm from those who consider Starship as a mean to get to Mars and beyond, the primary goal is to get to Mars, getting it cheap getting it reausable getting it through re-fueling or external tanks, this is for me a secondary issue that could be worked out, it must be some interim solution to get to Mars, but to get it in the 2030's IMHO we must get some compromises..
Why do you think that after figuring how to build a reusable heavy launcher, orbital fueling will be any sort of issue, or an issue big enough to warrant something as problematic for reuse as an external tank?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: [email protected] on 07/27/2020 03:24 pm
Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...

You're right to point out to the vocabulary it might be deceiving, for me "Just" and "simply" means proven technology have been in use for a while.
"Complexe" means that it's at the early stages of concept has to be put in practice in reliable manner.
So..  it's proven to be prohibitively expensive?
 
Starship is anything but a Shuttle repeat.  It's the anti-shuttle.  Consider each element in isolation, fine, but certainly don't give it points just because it was used in shuttle..

Remember Starship has to land on Mars and take off again, then re-enter Earth.  Are you "just" going to keep docking with new tanks all the time and throwing them away afterwards?

Refueling is fundamental to any mode of transportation, and compared to other challenges like, say, launch and EDL, it's relatively easy.

I'm from those who consider Starship as a mean to get to Mars and beyond, the primary goal is to get to Mars, getting it cheap getting it reausable getting it through re-fueling or external tanks, this is for me a secondary issue that could be worked out, it must be some interim solution to get to Mars, but to get it in the 2030's IMHO we must get some compromises..

Why does there have to be an interim solution?

Because time is ticking and SX plans are too ambitiuos (IMHO) for the timeframe, and it's like a black hole money siphoning endeavor.
Source? Or just for throwing shade at SpaceX instead of refueling technique discussion?

You are at it again, dedicated expensive lander, and now this?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/27/2020 03:27 pm




Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...

You're right to point out to the vocabulary it might be deceiving, for me "Just" and "simply" means proven technology have been in use for a while.
"Complexe" means that it's at the early stages of concept has to be put in practice in reliable manner.
So..  it's proven to be prohibitively expensive?
 
Starship is anything but a Shuttle repeat.  It's the anti-shuttle.  Consider each element in isolation, fine, but certainly don't give it points just because it was used in shuttle..

Remember Starship has to land on Mars and take off again, then re-enter Earth.  Are you "just" going to keep docking with new tanks all the time and throwing them away afterwards?

Refueling is fundamental to any mode of transportation, and compared to other challenges like, say, launch and EDL, it's relatively easy.

I'm from those who consider Starship as a mean to get to Mars and beyond, the primary goal is to get to Mars, getting it cheap getting it reausable getting it through re-fueling or external tanks, this is for me a secondary issue that could be worked out, it must be some interim solution to get to Mars, but to get it in the 2030's IMHO we must get some compromises..
Why do you think that after figuring how to build a reusable heavy launcher, orbital fueling will be any sort of issue, or an issue big enough to warrant something as problematic for reuse as an external tank?

You certainly mean theorically figuring how, but in practice and in a financially viable manner I dont think so.

[email protected]
Quote
Source? Or just for throwing shade at SpaceX instead of refueling technique discussion?

You are at it again

I made my point of view considering NASA R&D progress on the matter (orbital refuelling).
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: whitelancer64 on 07/27/2020 03:27 pm
Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...

You're right to point out to the vocabulary it might be deceiving, for me "Just" and "simply" means proven technology have been in use for a while.
"Complexe" means that it's at the early stages of concept has to be put in practice in reliable manner.
So..  it's proven to be prohibitively expensive?
 
Starship is anything but a Shuttle repeat.  It's the anti-shuttle.  Consider each element in isolation, fine, but certainly don't give it points just because it was used in shuttle..

Remember Starship has to land on Mars and take off again, then re-enter Earth.  Are you "just" going to keep docking with new tanks all the time and throwing them away afterwards?

Refueling is fundamental to any mode of transportation, and compared to other challenges like, say, launch and EDL, it's relatively easy.

I'm from those who consider Starship as a mean to get to Mars and beyond, the primary goal is to get to Mars, getting it cheap getting it reausable getting it through re-fueling or external tanks, this is for me a secondary issue that could be worked out, it must be some interim solution to get to Mars, but to get it in the 2030's IMHO we must get some compromises..

Why does there have to be an interim solution?

Because time is ticking and SX plans are too ambitiuos (IMHO) for the timeframe, and it's like a black hole money siphoning endeavor.

If "time is ticking" and money is short, then the last thing they'd want to be doing is working on a more complicated solution to the problem that also requires more money for development, hardware fabrication, tooling, etc.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 07/27/2020 03:54 pm
Starship already needs to be refueled on Mars for return.

If you want to get started and send equipment or even people to Mars one-way and you don’t care about the cost to do it, Red Dragon on falcon Heavy would work. They’d have to pay for finishing the powered landing capability development for Dragon plus probably a Dragon XL module for habitable space on the way there, but it’d work.

But it’s orders of magnitude more expensive per kg to Mars. It’s wasting precious capital (including human capital, which may be rarer than financial capital) and time on a dead end that nonetheless is risky.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: steveleach on 07/27/2020 03:58 pm
Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...

You're right to point out to the vocabulary it might be deceiving, for me "Just" and "simply" means proven technology have been in use for a while.
"Complexe" means that it's at the early stages of concept has to be put in practice in reliable manner.
So..  it's proven to be prohibitively expensive?
 
Starship is anything but a Shuttle repeat.  It's the anti-shuttle.  Consider each element in isolation, fine, but certainly don't give it points just because it was used in shuttle..

Remember Starship has to land on Mars and take off again, then re-enter Earth.  Are you "just" going to keep docking with new tanks all the time and throwing them away afterwards?

Refueling is fundamental to any mode of transportation, and compared to other challenges like, say, launch and EDL, it's relatively easy.

I'm from those who consider Starship as a mean to get to Mars and beyond, the primary goal is to get to Mars, getting it cheap getting it reausable getting it through re-fueling or external tanks, this is for me a secondary issue that could be worked out, it must be some interim solution to get to Mars, but to get it in the 2030's IMHO we must get some compromises..

Why does there have to be an interim solution?

Because time is ticking and SX plans are too ambitiuos (IMHO) for the timeframe, and it's like a black hole money siphoning endeavor.
I can't tell whether this is a troll, some strange sort of irony, or just a really uninformed but serious suggestion.

The idea is to launch a tank (pretty much a Starship with most bits thrown away somehow) and then dock with that, connect plumbing, and keep it attached for propellant transfer during the trans-Mars burn, yes?

And the justification is that it is simpler than launching another Starship, docking, connecting plumbing, transferring the propellant and then undocking?

Am I missing something here?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rsnellenberger on 07/27/2020 06:09 pm
Refueling Starship on orbit requires an automated/robotic umbilical connection mechanism. It can be more robustly built and complex than a “standard” rocket umbilical, since it’s going into a large, reusable vehicle. It also probably wants to be androgynous, since Starships will be refueling back-to-back.

My thought is - once they’ve developed that androgynous, automated refueling mechanism, why wouldn’t SpaceX use that same mechanism everywhere it applies?  Pad umbilicals & SH tanking umbilicals, SH-Starship tanking umbilicals, Starship-Starship refueling umbilicals, MarsPort pad umbilicals - the works. One added benefit would be that they’d be testing the bejeezus out of the mechanism every time they tanked or flew one of the vehicles.

Another benefit would be that they could move away from having time-critical T-0 umbilicals. Once the vehicle is in the final count and the tanks are pressurizing for flight (T-30-ish), disconnect and retract the umbilicals into a protective housing. If the launch is aborted, the umbilicals just hook themselves back up. 
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: philw1776 on 07/27/2020 07:05 pm
Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?

At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...

You're right to point out to the vocabulary it might be deceiving, for me "Just" and "simply" means proven technology have been in use for a while.
"Complexe" means that it's at the early stages of concept has to be put in practice in reliable manner.
So..  it's proven to be prohibitively expensive?
 
Starship is anything but a Shuttle repeat.  It's the anti-shuttle.  Consider each element in isolation, fine, but certainly don't give it points just because it was used in shuttle..

Remember Starship has to land on Mars and take off again, then re-enter Earth.  Are you "just" going to keep docking with new tanks all the time and throwing them away afterwards?

Refueling is fundamental to any mode of transportation, and compared to other challenges like, say, launch and EDL, it's relatively easy.

I'm from those who consider Starship as a mean to get to Mars and beyond, the primary goal is to get to Mars, getting it cheap getting it reausable getting it through re-fueling or external tanks, this is for me a secondary issue that could be worked out, it must be some interim solution to get to Mars, but to get it in the 2030's IMHO we must get some compromises..

Why does there have to be an interim solution?

Because time is ticking and SX plans are too ambitiuos (IMHO) for the timeframe, and it's like a black hole money siphoning endeavor.

Yet another thread disguised as SpaceX plans for X that is in reality "My alternative architecture because SpaceX is on a track to fail"
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Vanspace on 07/27/2020 08:33 pm
I have been wondering about the capabilities of the anti-boiloff systems. For Mars ISRU the last step is to condense the gases to liquid.

Can the anti-boiloff system on the now empty landed Starships be fed gaseous propellants and condense them down?

If it can, that saves a bunch of payload. If it can't is there a simple pre-stage like cooling or compressing that will help?

If the androgynous GSE adapter also has the vent lines can those be used to feed gaseous propellants to the anti-boiloff system?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: tbellman on 07/27/2020 10:22 pm
Can the anti-boiloff system on the now empty landed Starships be fed gaseous propellants and condense them down?

I can't recall hearing anything about cryocoolers being standard equipment on Starships, even on the Mars-bound Starships.  As far as I have heard, the only systems for preventing boiloff during the Earth-Mars and Mars-Earth transits, will be insulation (header tanks inside the main tanks; the empy main tanks then act as a giant thermos bottle), and minimize sunshine hitting the tanks by pointing them away from the Sun.  This will lower the amount boiloff enough that there will be propellant left when they arrive, but it will not entirely prevent boiloff.  And it is definitely not enough to chill down the propellant.

To actually chill down oxygen and methane to condense into liquids, you either need active cooling, i.e. cryocoolers, or get much further out in our solar system.

So they will need to bring cryocoolers to Mars as normal cargo.

(It would make sense to have cryocoolers on accumulation tankers in LEO, though.  It is much more difficult to keep the propellant cool in LEO, as A) you will fill the main tanks, so there is no thermos bottle protecting the propellant, and B) there is no direction to point the ship to minimize incoming heat radiation, as the Earth takes up almost half the surroundings, reflecting sunlight onto you from almost everywhere.)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Vanspace on 07/27/2020 10:30 pm
Can the anti-boiloff system on the now empty landed Starships be fed gaseous propellants and condense them down?

I can't recall hearing anything about cryocoolers being standard equipment on Starships, even on the Mars-bound Starships.  As far as I have heard, the only systems for preventing boiloff during the Earth-Mars and Mars-Earth transits, will be insulation (header tanks inside the main tanks; the empy main tanks then act as a giant thermos bottle), and minimize sunshine hitting the tanks by pointing them away from the Sun.  This will lower the amount boiloff enough that there will be propellant left when they arrive, but it will not entirely prevent boiloff.  And it is definitely not enough to chill down the propellant.

To actually chill down oxygen and methane to condense into liquids, you either need active cooling, i.e. cryocoolers, or get much further out in our solar system.

So they will need to bring cryocoolers to Mars as normal cargo.

(It would make sense to have cryocoolers on accumulation tankers in LEO, though.  It is much more difficult to keep the propellant cool in LEO, as A) you will fill the main tanks, so there is no thermos bottle protecting the propellant, and B) there is no direction to point the ship to minimize incoming heat radiation, as the Earth takes up almost half the surroundings, reflecting sunlight onto you from almost everywhere.)

Thank you!

If there needs to be cryocoolers on accumulation tankers, could they be added as part of the spec for mars bound ships? If you have to send it anyway, preassembled and already functioning might be better than as cargo.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Slarty1080 on 07/27/2020 10:54 pm
From the info extracted from Elon tweets and plugging holes with informed guesses we have rough general picture of how it would be done:

- Dock the vehicles bottom-to-bottom and obtain seal of the piping
- Vent receiving end to low internal tank pressure (probably well below atmospheric[*])
- Use thrusters (probably receiving end, see below why[*][**]) to produce ullage thrust in the same it's done before re-firing of any stage in orbit
- Open valves and let the transfer begin
- Pressure difference pushes the liquids while ullage thrust (in the order of milli-gee) keeps them settled
- Keep venting the receiving end. There's one possible difficulty here, see below [***]
- If the sending end is close full (for example transfer from accumulation tanker to receiving ship) you need also to keep it pressurized at the required level.
- Once liquid fuel is done pressure would equalize quickly. Possibly bubble detection would shut the valves before this happens as this would be a bit violent. Or maybe the system is made robust enough for it not to be a problem.
- Terminate the ullage thrust
- Purge & vent the piping between main valves on both vehicles.
- Undock

Notes:
*] Venting below atmospheric ensures the remaining fuel would be at a super-cooled temperature as intended.
**] Receiving end needs to be kept at low pressure so it has obvious source of gas for ullage thrusters
***] Receiving end may see liquid foaming and condensation foring in the ullage space. Venting liquid would be wasteful and could be a source of problems as liquid venting to vacuum will partly evaporate and partly freeze and frozen liquid may plug holes. So venting piping could use "cyclone" separator and possibly some mild heating.

From the above one could notice that we need some gas generating subsystem which could pressurize the vehicle without engines firing. So some burner, pump for it and heat exchanger to vaporize the liquid.

Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?
(https://www.fourmilab.ch/autofile/e5/figures/external_tank.jpg)
Sadly there is no way around the rocket equation. Adding a huge and heavy external tank will just slow it down (not to mention the design complexities). In fact more engines would be needed just to get it off the ground.

What SpaceX are doing with Starship in a crude sense is enabling a very fat rocket that would pose very difficult engineering problems to be launched in multiple thinner segments (if that makes sense).
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: envy887 on 07/28/2020 12:42 am
Can the anti-boiloff system on the now empty landed Starships be fed gaseous propellants and condense them down?

I can't recall hearing anything about cryocoolers being standard equipment on Starships, even on the Mars-bound Starships.  As far as I have heard, the only systems for preventing boiloff during the Earth-Mars and Mars-Earth transits, will be insulation (header tanks inside the main tanks; the empy main tanks then act as a giant thermos bottle), and minimize sunshine hitting the tanks by pointing them away from the Sun.  This will lower the amount boiloff enough that there will be propellant left when they arrive, but it will not entirely prevent boiloff.  And it is definitely not enough to chill down the propellant.

To actually chill down oxygen and methane to condense into liquids, you either need active cooling, i.e. cryocoolers, or get much further out in our solar system.

There's anther option. With a good sunshield you can freeze methane or oxygen solid, even at 1 AU.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: spacenut on 07/28/2020 03:26 am
Starship as said, will point engines toward sun traveling to and from Mars.  Then they will have fold out solar panels for power to and from Mars.  These will have a tendency to have some shade also since they will hing near the bottom and turn 90 degrees to the rocket toward the sun.  So the engines, which can take heat and the solar panels will shield the fuel and the crew from the sun.  They will have equipment on board to keep the fuel and lox liquid.  Also, lox and methane are only about 20 degrees different in liquid form.  They both would have far less boil-off than liquid hydrogen which is over twice as cold.  Space is already very cold in the shade.  Also, like someone up said, in LEO, you have more boil-off problems because of heat reflected off the earth. 
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Thrustpuzzle on 07/28/2020 04:20 am
Starship gets fueled on the pad through internal connections from Superheavy, the first stage. Which means the connecting plumbing is already there.
Starship's fueling has always been planned to be from the bottom, but is it for certain that SS's fuel on the Earth launch pad is delivered though Superheavy? The other alternative is a Starship specific GSE connection on the side of Superheavy's interstage, which has the small amount of plumbing to redirect the fuel and oxidizer to Starship's bottom fittings.

The SH interstage GSE connection plan has several tradeoffs, but the interstage method gives isolation between SH and SS plumbing systems and less weight and complexity (a lot of the plumbing and pumping is moved to GSE).  Downside is trickier GSE hardware design and operation, which may interfere with the fast (1-hour!) turnarounds Elon hopes for.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: tbellman on 07/28/2020 09:50 am
If there needs to be cryocoolers on accumulation tankers, could they be added as part of the spec for mars bound ships? If you have to send it anyway, preassembled and already functioning might be better than as cargo.

I don't think there are as much commonality as one might think between the two use cases.

The cryocoolers on an accumulation tanker (if they will have such coolers) will be designed to keep the already cold propellant cold, presumably thus handling liquids, and have radiators sized and designed for operation in vacuum, with significant influx of heat radiation from the Sun and Earth.  Cryocoolers for Mars ISRU will need to actually chill the propellants from maybe -60°C (if they are pre-cooled to ambient Mars temperatures) and in gas form, down to more than -180°C and liquid, and their radiators will want to be optimized for atmospheric use (thin though it may be).  I'm not sure how much difference this makes to their designs, though.

The normal tanking connections on Starship will be designed for liquids, and are basically straight pipes from the bottom of the ship up to the bottom of their respective tanks.  Cryocoolers on-board the ship will need to have a separate connector for receiving gas, and then either have their own pipes into the tanks for dumping their liquids into them, or have hoses that are connected to the normal tanking connectors.  (Having the cryocoolers sit inbetween the normal tanking connectors and the tanks, seems even more difficult: those connectors would then need to be able to handle both gas and liquid; there is limited space under the skirt; and the plumbing gets much more complicated.)

Later on (i.e, not the first few missions), SpaceX wants to be able to return ships within a couple of weeks from arriving at Mars, in order for them to be back on Earth to be reused every synod instead of every other synod.  Then you need to have cryocoolers on the ground, to cool the propellant as it is produced, as there won't be enough cryocooling capacity on the few ships that are landed.  Designing on-board cryocoolers to be used only for the first couple of missions would be a detour.


Those are the negatives.  On the other hand, for the first several missions, the ships themselves will need to act as tanks for the liquid propellants as it is produced, as there won't be enough room to bring separate tanks.  And you will need to keep that propellant cold for a long time, while the ships are surrounded by relatively warm atmosphere.  It seems unlikely that can be done efficiently without active cooling.  (Unless you build the tanks as large dewar flasks, but that will increase the dry mass of the ships significantly.)

But I think it still makes more sense to have the cryocoolers separate.  Then you can leave them on Mars, and have more space for other stuff on the next mission.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: tbellman on 07/28/2020 10:11 am
To actually chill down oxygen and methane to condense into liquids, you either need active cooling, i.e. cryocoolers, or get much further out in our solar system.

There's anther option. With a good sunshield you can freeze methane or oxygen solid, even at 1 AU.

Fairly difficult in LEO, though.  Half your viewfield has a warm planet which needs to be blocked, and the Sun shines in from some other direction.

And if the James Webb Space Telescope is anything to go by, a good sunshield is not cheap.  But possibly, if you stay away from LEO and LLO, it doesn't need to be quite as good and expensive. 8)

But yes, good point in general.  If one can be made simple and cheap, a sunshield could possibly be something for the HLS Starship waiting for the crew to arrive in NRHO at the Lunar Gateway.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/28/2020 10:45 am
From the info extracted from Elon tweets and plugging holes with informed guesses we have rough general picture of how it would be done:

- Dock the vehicles bottom-to-bottom and obtain seal of the piping
- Vent receiving end to low internal tank pressure (probably well below atmospheric[*])
- Use thrusters (probably receiving end, see below why[*][**]) to produce ullage thrust in the same it's done before re-firing of any stage in orbit
- Open valves and let the transfer begin
- Pressure difference pushes the liquids while ullage thrust (in the order of milli-gee) keeps them settled
- Keep venting the receiving end. There's one possible difficulty here, see below [***]
- If the sending end is close full (for example transfer from accumulation tanker to receiving ship) you need also to keep it pressurized at the required level.
- Once liquid fuel is done pressure would equalize quickly. Possibly bubble detection would shut the valves before this happens as this would be a bit violent. Or maybe the system is made robust enough for it not to be a problem.
- Terminate the ullage thrust
- Purge & vent the piping between main valves on both vehicles.
- Undock

Notes:
*] Venting below atmospheric ensures the remaining fuel would be at a super-cooled temperature as intended.
**] Receiving end needs to be kept at low pressure so it has obvious source of gas for ullage thrusters
***] Receiving end may see liquid foaming and condensation foring in the ullage space. Venting liquid would be wasteful and could be a source of problems as liquid venting to vacuum will partly evaporate and partly freeze and frozen liquid may plug holes. So venting piping could use "cyclone" separator and possibly some mild heating.

From the above one could notice that we need some gas generating subsystem which could pressurize the vehicle without engines firing. So some burner, pump for it and heat exchanger to vaporize the liquid.

Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?
(https://www.fourmilab.ch/autofile/e5/figures/external_tank.jpg)
Sadly there is no way around the rocket equation. Adding a huge and heavy external tank will just slow it down (not to mention the design complexities). In fact more engines would be needed just to get it off the ground.

What SpaceX are doing with Starship in a crude sense is enabling a very fat rocket that would pose very difficult engineering problems to be launched in multiple thinner segments (if that makes sense).

Orbital refueling/ISRU are technologies in the early stages of developpement this will require more time to be ready for SX planed timeframe and regarding the scale of requirement which is almost industriel to add to the diffucilty.

IMHO the external tank option seems to me the interim solution, I was also imagining putting those tanks in different positions like LEO, HEO, HTO, MO.............like gas stations. Those tanks may get some small thrusters, they dont have to travel with high velocity as is required for human travel.

Can someone give some data about fuel requirement for 100 tons dry mass SS round trip to Mars?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: tyrred on 07/28/2020 10:59 am
From the info extracted from Elon tweets and plugging holes with informed guesses we have rough general picture of how it would be done:

- Dock the vehicles bottom-to-bottom and obtain seal of the piping
- Vent receiving end to low internal tank pressure (probably well below atmospheric[*])
- Use thrusters (probably receiving end, see below why[*][**]) to produce ullage thrust in the same it's done before re-firing of any stage in orbit
- Open valves and let the transfer begin
- Pressure difference pushes the liquids while ullage thrust (in the order of milli-gee) keeps them settled
- Keep venting the receiving end. There's one possible difficulty here, see below [***]
- If the sending end is close full (for example transfer from accumulation tanker to receiving ship) you need also to keep it pressurized at the required level.
- Once liquid fuel is done pressure would equalize quickly. Possibly bubble detection would shut the valves before this happens as this would be a bit violent. Or maybe the system is made robust enough for it not to be a problem.
- Terminate the ullage thrust
- Purge & vent the piping between main valves on both vehicles.
- Undock

Notes:
*] Venting below atmospheric ensures the remaining fuel would be at a super-cooled temperature as intended.
**] Receiving end needs to be kept at low pressure so it has obvious source of gas for ullage thrusters
***] Receiving end may see liquid foaming and condensation foring in the ullage space. Venting liquid would be wasteful and could be a source of problems as liquid venting to vacuum will partly evaporate and partly freeze and frozen liquid may plug holes. So venting piping could use "cyclone" separator and possibly some mild heating.

From the above one could notice that we need some gas generating subsystem which could pressurize the vehicle without engines firing. So some burner, pump for it and heat exchanger to vaporize the liquid.

Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?
(https://www.fourmilab.ch/autofile/e5/figures/external_tank.jpg)
Sadly there is no way around the rocket equation. Adding a huge and heavy external tank will just slow it down (not to mention the design complexities). In fact more engines would be needed just to get it off the ground.

What SpaceX are doing with Starship in a crude sense is enabling a very fat rocket that would pose very difficult engineering problems to be launched in multiple thinner segments (if that makes sense).

Orbital refueling/ISRU are technologies in the early stages of developpement this will require more time to be ready for SX planed timeframe and regarding the scale of requirement which is almost industriel.

IMHO the external tank option seems to me the interim solution, I was also imagining putting those tanks in different positions like LEO, HEO, HTO, MO.............like gas stations. Those tanks may get some small thrusters, they dont have to travel with high velocity as is required for human travel.

Can someone give some data about fuel requirement for 100 tons dry mass SS round trip to Mars?

Orbital refueling is *not in early stages of development.

Orbital refueling has been standard operating  practice with the ISS for many years. It just doesn't *look like what orbital refueling for Starship will look like.

That is a completely separate topic from ISRU.

External tanks for Starship, as has been pointed out, are a pipe dream. The plan is for orbital refueling with tanker Starships. Stick to the plan, it's what the experts are doing.

Refueling airplanes in mid-air is nearly a century old. Rendezvous and docking in space is more than a half-century old. These are solved problems. Implementation is a different story.

Methinks you're making a mountain out of a molehill.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 07/28/2020 12:18 pm
Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?
(https://www.fourmilab.ch/autofile/e5/figures/external_tank.jpg)

I think you are missing two points that many others are trying to make, in different ways:

Point 1:

How do these tanks get into orbit?

These fully fuelled tanks, holding 5 launches worth of fuel.

Without refuelling.

Point 2:

What makes an external tank superior to the internal tanks already carried within each Starship?

An external tank that has to dock and be reliably attached and plumbed into the Mars-going Starship.

Versus the internal tanks of the same capacity already built into the Starship.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/28/2020 03:34 pm
Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?
(https://www.fourmilab.ch/autofile/e5/figures/external_tank.jpg)

I think you are missing two points that many others are trying to make, in different ways:

Point 1:

How do these tanks get into orbit?

These fully fuelled tanks, holding 5 launches worth of fuel.

Without refuelling.

Point 2:

What makes an external tank superior to the internal tanks already carried within each Starship?

An external tank that has to dock and be reliably attached and plumbed into the Mars-going Starship.

Versus the internal tanks of the same capacity already built into the Starship.

Just imagine the space shuttle without orbiter (only small engines on the external tank) how much fuel would be saved on the external tank?

-An external has not to do EDL or ascent again he could be jettisoned when empty.

-Imagine the fuel saved on getting rid of the extra weight of the tankers to get back to earth.

-Time saving on refueling.
-Saving on ullage fuel.
-Technologie available.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: wes_wilson on 07/28/2020 03:52 pm
Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?
(https://www.fourmilab.ch/autofile/e5/figures/external_tank.jpg)

I think you are missing two points that many others are trying to make, in different ways:

Point 1:

How do these tanks get into orbit?

These fully fuelled tanks, holding 5 launches worth of fuel.

Without refuelling.

Point 2:

What makes an external tank superior to the internal tanks already carried within each Starship?

An external tank that has to dock and be reliably attached and plumbed into the Mars-going Starship.

Versus the internal tanks of the same capacity already built into the Starship.

Just imagine the space shuttle without orbiter (only small engines on the external tank) how much fuel would be saved on the external tank?

-An external has not to do EDL or ascent again he could be jettisoned when empty.

-Imagine the fuel saved on getting rid of the extra weight of the tankers to get back to earth.

-Time saving on refueling.
-Saving on ullage fuel.
-Technologie available.

I get it, I've had ideas I was attached too that the group had to dissuade me from.  However, your idea is missing one single and totally not-negotiable item.  The system has to be 100% re-usable because that's what the company owner (Elon Musk) has set as a requirement.

So modify your concept of using the external fuel tank from a shuttle to include re-use.  Make whatever changes are needed for it to re-enter, be recovered, be refurbished, and then used a 2nd time and see where that leads you.  Eventually, it leads to something like Starship.

Any concept that isn't 100% re-usable isn't worth discussing because it doesn't meet the criteria required by the owner/operator of the project.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 07/28/2020 04:12 pm
[snip]

Just imagine the space shuttle without orbiter (only small engines on the external tank) how much fuel would be saved on the external tank?

Such a vehicle wouldn't be able to reach orbit. The Shuttle could only reach orbit because of the SSMEs, which you have replaced with "small engines."

-An external has not to do EDL or ascent again he could be jettisoned when empty.

-Imagine the fuel saved on getting rid of the extra weight of the tankers to get back to earth.

See wes_wilson's comments on reuse.

-Time saving on refueling.

-Saving on ullage fuel.

Extra structural mass because you're strapping a tank to the side which has to withstand the high-thrust TMI burn.

-Technologie available.

See SLS for an example of how that logic worked out.

And no, the technology isn't available. The Shuttle ET was never autonomously/telerobotically attached. It was never attached in orbit. Those are very different problems from attaching the ET on the ground in a purpose-built processing facility.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: SkyRate on 07/28/2020 04:13 pm
To actually chill down oxygen and methane to condense into liquids, you either need active cooling, i.e. cryocoolers, or get much further out in our solar system.
There's anther option. With a good sunshield you can freeze methane or oxygen solid, even at 1 AU.
Fairly difficult in LEO, though.  Half your viewfield has a warm planet which needs to be blocked, and the Sun shines in from some other direction.
You could borrow a trick from the lunar polar craters, and make a cylindrical sunshade with the open ends pointing out of the ecliptic.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: AC in NC on 07/28/2020 04:36 pm
I'd like to gently suggest that Star-Dust's solution-in-search-of-a-problem is so ill-formed as a concept that it deserves to be ignored and permitted a face-saving death on the vine.

These are a hodge-podge of internally inconsistent notions and it's unproductive to engage then with rational responses.

-  just imagine space shuttle docking to her external tank and going all the way to Mars

-  the external tank could also be imagined as a payload of a starship fairing.

-  I didn't add parts I just proposed a rethinking of the design, I also didn't suggest a fuel transfert but a direct fuel burn from external tank in SS engines

-  because it's not possible to get the fluid flow in a reversed direction without affecting all parts like pumps and turbines and you can't get extra plumbing in a place where it's already  congested (with engines).

-  and for the weight you did mention space shuttle external tank weight which is true but the proposed concept may propose multiple external tanks jettisoned when empty

-  Because time is ticking and SX plans are too ambitiuos (IMHO) for the timeframe, and it's like a black hole money siphoning endeavor.

-  I was also imagining putting those tanks in different positions like LEO, HEO, HTO, MO.............like gas stations.

-  Just imagine the space shuttle without orbiter (only small engines on the external tank) how much fuel would be saved on the external tank?

-  An external has not to do EDL or ascent again he could be jettisoned when empty.

-  Imagine the fuel saved on getting rid of the extra weight of the tankers to get back to earth.


Here we've got:

1.  Docking and fuel transfer from an external tank (Shuttle-style) solving (on an interim basis) the problem of docking and fuel transfer from an external tank (SS)
2.  Direct fuel burn from an externally mounted Shuttle-style tank not "adding parts" (which is a metaphor for resdesigning and adding complexity)
3.  An external tank as a payload inside a SS.
4.  The contention that it's not possible to reverse flow props though that's the central design principles of the aft GSE connects.
5.  Solving the time/energy/cost/complexity of multiple SS retankings with the obvious time/energy/cost/complexity savings of multiple external tanks jettisoned.
6.  The baseless black-hole siphoning nonsense.
7.  Boosting multiple expendable tanks as gas stations rather than direct burn tankage.
8.  Saving the expense of the the fuel to recover SS's at the cost of multiple expendable tanks.

Please.  Just let this die.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 07/28/2020 04:44 pm
To actually chill down oxygen and methane to condense into liquids, you either need active cooling, i.e. cryocoolers, or get much further out in our solar system.
There's anther option. With a good sunshield you can freeze methane or oxygen solid, even at 1 AU.
Fairly difficult in LEO, though.  Half your viewfield has a warm planet which needs to be blocked, and the Sun shines in from some other direction.

You could borrow a trick from the lunar polar craters, and make a cylindrical sunshade with the open ends pointing out of the ecliptic.
You'd need the sunshade to extend well past the ends of the tank to shade out heat from the Earth, and at that point your view solid angle is very small, so you wouldn't get much natural cooling.

Two cones that meet at the vehicle's "waist" would work better, since you'd get more solid angle for cooling. You'd want both cones to be angled so they point away from Earth, blocking out both the unidirectional Sun and the Earth hemisphere.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: matthewkantar on 07/28/2020 05:15 pm
It is so simple:

-Tanker to orbit.
-tanker to orbit, fill tanker in orbit,RTLS.
-repeat until prop requirement is met.
-Starship crew and gear to orbit.
-rendezvous, prop transfer, burn for Mars.

Any parts or steps added to this are dumb.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 07/28/2020 05:48 pm
It is so simple:

-Tanker to orbit.
-tanker to orbit, fill tanker in orbit,RTLS.
-repeat until prop requirement is met.
-Starship crew and gear to orbit.
-rendezvous, prop transfer, burn for Mars.

Any parts or steps added to this are dumb.

Adding drop tanks? Yeah, I agree that's dumb.

Adding sunshades and/or cryocoolers? I invite you to do the heat transfer calculation through a 4 mm stainless steel wall before calling it dumb. Even if we assume the heatshield is perfectly insulative, you're still getting a lot of Earthshine on the day side of your orbit.

Personally I think cryocoolers are most likely, considering the desire for full reuse and the complexity of "un-deploying" a large sunshade.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Lemurion on 07/28/2020 07:28 pm
Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?
(https://www.fourmilab.ch/autofile/e5/figures/external_tank.jpg)

I think you are missing two points that many others are trying to make, in different ways:

Point 1:

How do these tanks get into orbit?

These fully fuelled tanks, holding 5 launches worth of fuel.

Without refuelling.

Point 2:

What makes an external tank superior to the internal tanks already carried within each Starship?

An external tank that has to dock and be reliably attached and plumbed into the Mars-going Starship.

Versus the internal tanks of the same capacity already built into the Starship.

Just imagine the space shuttle without orbiter (only small engines on the external tank) how much fuel would be saved on the external tank?

-An external has not to do EDL or ascent again he could be jettisoned when empty.

-Imagine the fuel saved on getting rid of the extra weight of the tankers to get back to earth.

-Time saving on refueling.
-Saving on ullage fuel.
-Technologie available.

If you could actually get this tank to orbit with a full load of propellant, you'd also be able to get a fully fueled Starship to orbit so you wouldn't need the tank in the first place.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: aero on 07/28/2020 09:04 pm
It seems that using the heavy as a tanker doesn't work very well. I've calculated (using the rocket equation) that the heavy without a Starship could "probably" make it to orbit, there doesn't seem to be much leeway for residual prop upon reaching orbit. I do think that using more accurate data and math, some residual prop to orbit could be achieved but requiring an expendable heavy really precludes the approach.

The key factor in my calculation is that the heavy leaves the launch pad with a 2 to 1 thrust to weight ratio. High acceleration limits gravity losses tremendously. I calculate, using constant ISP = 340 seconds, that the heavy can achieve 8.5 km/sec delta-V. It should do better because ISP increases as the rocket leaves the sensible atmosphere and at ISP = 360 seconds, the heavy could achieve delta-V = 9.1 km/sec. A better estimate is somewhere between the two extremes.

The above still fails utterly as a tanker though, because the heavy reaches orbit with no residual prop and is incapable of returning to Earth.

It would work as a fuel depot if there were reasons to do so.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: CJ on 07/28/2020 09:23 pm
My working assumption is that the most efficient way to refuel a Starship in a high-energy orbit would be to refuel another Starship in LEO with several prop launches, and then have it transfer the fuel load to the actual mission Starship. (assuming the mission starship can't do the mission from LEO)

The reason I think this is that attempting to send tanker launches to a higher orbit means pushing a lot of mass though a lot of delta-v; the entire dry mass plus landing prop on each prop launch, pushed through the delta/v between LEO and the target orbit. 

Do I have this right?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Stan-1967 on 07/28/2020 09:34 pm
Do I have this right?

I would add that there should be more daily opportunities to launch propellant to an intermediate SS in LEO vs. the mission SS in HEO.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 07/28/2020 09:46 pm
My working assumption is that the most efficient way to refuel a Starship in a high-energy orbit would be to refuel another Starship in LEO with several prop launches, and then have it transfer the fuel load to the actual mission Starship. (assuming the mission starship can't do the mission from LEO)

The reason I think this is that attempting to send tanker launches to a higher orbit means pushing a lot of mass though a lot of delta-v; the entire dry mass plus landing prop on each prop launch, pushed through the delta/v between LEO and the target orbit.

Do I have this right?

Yes, I think that's correct.

Extrapolating a bit from this same logic, you should make sure that 1) you transfer all the fuel to the mission Starship (leaving just enough fuel left for the tanker to return and land) and 2) that transfer fully tops off the mission Starship's tanks.

If you violate condition 1 and the tanker has extra fuel left over, you could have used fewer tankers to fill it in LEO, or (if it's a fractional tanker load) you could have staged in a higher orbit and put more delta-v into the mission tanker.

If you violate condition 2 and the mission Starship tanks aren't completely filled, you could have staged in a lower orbit and wasted less propellant dragging the tanker to a higher orbit than necessary.

Incidentally, these two conditions (which can be expressed mathematically) give you enough "knowns" that you're able to calculate exactly the best elliptical orbit to use for a given mission. Of course you still need propellant margins so you won't hit it exactly, but at least we can figure out where the bullseye is. :)


One last thing: what if you want more delta-v than you can get from two fully fueled vehicles in LEO? The fuel optimal strategy is to start with three fully fueled vehicles, raise orbit until one tanker can use all its fuel to completely fill the other two, then proceed as before. And you still have enough information to calculate the (two) intermediate orbits.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Norm38 on 07/28/2020 10:48 pm
There's a cool 2001ish architecture that comes out of that.  Surface Tankers want to stop in LEO and drop their cargo.  Orbital Tankers want to move out of LEO full  (and establish a supply line and the tankers can use SEP orbit raising and lowering to get back to LEO)

So you get a LEO fuel depot.  That has regular service. Then you need to launch Starships, and launch cargo.  Maybe crew launches on Dragon for a while?

So Starships could launch to LEO, maybe dock to take on crew and cargo, fuel to reach the tanker orbit, then refuel and go.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 07/28/2020 11:19 pm
There's a cool 2001ish architecture that comes out of that.  Surface Tankers want to stop in LEO and drop their cargo.  Orbital Tankers want to move out of LEO full  (and establish a supply line and the tankers can use SEP orbit raising and lowering to get back to LEO)

So you get a LEO fuel depot.  That has regular service. Then you need to launch Starships, and launch cargo.  Maybe crew launches on Dragon for a while?

So Starships could launch to LEO, maybe dock to take on crew and cargo, fuel to reach the tanker orbit, then refuel and go.
The problem with that is that there is no singular LEO. A LEO with a given inclination can only be reached  twice a day from any given launch site, assuming no launch direction restrictions and the ability to turn the pad around for both launches.And an equitorial LEO is unreachable by ANY launch site without a course correction burn. (A polar orbit can be reached by any site twice a day, but loses all benifit from launching  with the rotation of the earth) It wouldnt be one fuel depot/station in orbit, it would need to be dozens, which pretty much eliminates the benifits from a unified depot/station.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: aero on 07/28/2020 11:38 pm
So does that mean they need 12 LEO depots to launch every hour? By how much time could the Depots be separated such that the needed course correction would be acceptable? 6 seconds? 6 minutes? 1 hour? 3 hours? 6 hours? I know that they use instantaneous launch windows quit a bit. Is that absolutely required for tanker launches?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 07/28/2020 11:52 pm
So does that mean they need 12 LEO depots to launch every hour? By how much time could the Depots be separated such that the needed course correction would be acceptable? 6 seconds? 6 minutes? 1 hour? 3 hours? 6 hours? I know that they use instantaneous launch windows quit a bit. Is that absolutely required for tanker launches?

I believe the ISS rendezvous window was only 4 minutes, but the recycle time was greater so they just launched instantaneously at the best point in the window.

The problem is the RAAN. If your launch site isn't under the orbital plane, you either need to burn a lot of fuel, or wait a long time while your orbit precesses around. Both are really painful if your goal is efficient tanker utilization.

TheRadicalModerate worked out that a circular 263 km orbit would give you one launch opportunity per day without the need for orbital phasing (this shortens rendezvous time substantially), so that would be a good candidate orbit for an accumulation tanker. A 555 km circular orbit gives two opportunities per day, but the debris risk is a lot higher, you're dragging the tanker dry mass higher so you get less propellant delivered per launch, and you lose some Oberth effect on your burn.

https://forum.nasaspaceflight.com/index.php?topic=50851.msg2080345#msg2080345
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Thunderscreech on 07/29/2020 03:19 am
A side-ish note on launch opportunities, there are potentially a lot more than one or two launch opportunities for a given depot orbit in LEO if there are more than one launchpads.  I know there's a lot (read: loooooooot) of skepticism about the E2E plans for Starship, but....  that _would_ mean there's a lot of potential places that can be chucking fueling tankers up to meet at depots. 

Even if E2E specifically doesn't happen, an active orbital site at Boca Chica, KSC, and then however many offshore launch pads they may or may not be working on right now might all contribute themselves to multiple launch opportunities each day.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/29/2020 08:25 am
Interesting but seems very very complexe,to add to the difficulty this will have to be done 5 times to get to Mars....................can't we just attach an external tank like for space shuttle?
(https://www.fourmilab.ch/autofile/e5/figures/external_tank.jpg)

I think you are missing two points that many others are trying to make, in different ways:

Point 1:

How do these tanks get into orbit?

These fully fuelled tanks, holding 5 launches worth of fuel.

Without refuelling.

Point 2:

What makes an external tank superior to the internal tanks already carried within each Starship?

An external tank that has to dock and be reliably attached and plumbed into the Mars-going Starship.

Versus the internal tanks of the same capacity already built into the Starship.

Just imagine the space shuttle without orbiter (only small engines on the external tank) how much fuel would be saved on the external tank?

-An external has not to do EDL or ascent again he could be jettisoned when empty.

-Imagine the fuel saved on getting rid of the extra weight of the tankers to get back to earth.

-Time saving on refueling.
-Saving on ullage fuel.
-Technologie available.

I get it, I've had ideas I was attached too that the group had to dissuade me from.  However, your idea is missing one single and totally not-negotiable item.  The system has to be 100% re-usable because that's what the company owner (Elon Musk) has set as a requirement.

So modify your concept of using the external fuel tank from a shuttle to include re-use.  Make whatever changes are needed for it to re-enter, be recovered, be refurbished, and then used a 2nd time and see where that leads you.  Eventually, it leads to something like Starship.

Any concept that isn't 100% re-usable isn't worth discussing because it doesn't meet the criteria required by the owner/operator of the project.

I was thinking that the primary goal for EM was to reach Mars in the 2024? so an interim solution is needed to keep the goal of 2024 credible.

The aim of reusability is to keep space flight cheap, I dont think aircrafts fuel drop tanks are that expensive, it must be some point where the cost of fuel to get 1kg of hardware to space will be equal (or more) to the cost of one kg of hardware, reaching that point is for me the objectif to keep costs relatively low, in the end a tank is only some sort of package.


Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: sebk on 07/29/2020 10:15 am
It seems that using the heavy as a tanker doesn't work very well. I've calculated (using the rocket equation) that the heavy without a Starship could "probably" make it to orbit, there doesn't seem to be much leeway for residual prop upon reaching orbit. I do think that using more accurate data and math, some residual prop to orbit could be achieved but requiring an expendable heavy really precludes the approach.

The key factor in my calculation is that the heavy leaves the launch pad with a 2 to 1 thrust to weight ratio. High acceleration limits gravity losses tremendously. I calculate, using constant ISP = 340 seconds, that the heavy can achieve 8.5 km/sec delta-V. It should do better because ISP increases as the rocket leaves the sensible atmosphere and at ISP = 360 seconds, the heavy could achieve delta-V = 9.1 km/sec. A better estimate is somewhere between the two extremes.

The above still fails utterly as a tanker though, because the heavy reaches orbit with no residual prop and is incapable of returning to Earth.

It would work as a fuel depot if there were reasons to do so.

What dry mass did you assume? Because my calc shows about 9.5km/s dV which should be plenty to reach orbit even witch much more moderate TWR.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 07/29/2020 11:15 am
It seems that using the heavy as a tanker doesn't work very well. I've calculated (using the rocket equation) that the heavy without a Starship could "probably" make it to orbit, there doesn't seem to be much leeway for residual prop upon reaching orbit. I do think that using more accurate data and math, some residual prop to orbit could be achieved but requiring an expendable heavy really precludes the approach.

The key factor in my calculation is that the heavy leaves the launch pad with a 2 to 1 thrust to weight ratio. High acceleration limits gravity losses tremendously. I calculate, using constant ISP = 340 seconds, that the heavy can achieve 8.5 km/sec delta-V. It should do better because ISP increases as the rocket leaves the sensible atmosphere and at ISP = 360 seconds, the heavy could achieve delta-V = 9.1 km/sec. A better estimate is somewhere between the two extremes.

The above still fails utterly as a tanker though, because the heavy reaches orbit with no residual prop and is incapable of returning to Earth.

It would work as a fuel depot if there were reasons to do so.

What dry mass did you assume? Because my calc shows about 9.5km/s dV which should be plenty to reach orbit even witch much more moderate TWR.
It can reach orbit as a massive depot, but it cant SSTO significant fuel mass the way Stardust wants.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: steveleach on 07/29/2020 11:52 am
I was thinking that the primary goal for EM was to reach Mars in the 2024? so an interim solution is needed to keep the goal of 2024 credible.
Do you have any evidence at all for this statement (an interim solution being needed)? Because if you don't, people will simply ignore it.

Quote
The aim of reusability is to keep space flight cheap, I dont think aircrafts fuel drop tanks are that expensive, it must be some point where the cost of fuel to get 1kg of hardware to space will be equal (or more) to the cost of one kg of hardware, reaching that point is for me the objectif to keep costs relatively low, in the end a tank is only some sort of package.
What on earth makes you think that the primary cost in your idea is the material cost of the tank?
Please, please re-read all the problems with your idea that people have pointed out above.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: sebk on 07/29/2020 11:54 am
It seems that using the heavy as a tanker doesn't work very well. I've calculated (using the rocket equation) that the heavy without a Starship could "probably" make it to orbit, there doesn't seem to be much leeway for residual prop upon reaching orbit. I do think that using more accurate data and math, some residual prop to orbit could be achieved but requiring an expendable heavy really precludes the approach.

The key factor in my calculation is that the heavy leaves the launch pad with a 2 to 1 thrust to weight ratio. High acceleration limits gravity losses tremendously. I calculate, using constant ISP = 340 seconds, that the heavy can achieve 8.5 km/sec delta-V. It should do better because ISP increases as the rocket leaves the sensible atmosphere and at ISP = 360 seconds, the heavy could achieve delta-V = 9.1 km/sec. A better estimate is somewhere between the two extremes.

The above still fails utterly as a tanker though, because the heavy reaches orbit with no residual prop and is incapable of returning to Earth.

It would work as a fuel depot if there were reasons to do so.

What dry mass did you assume? Because my calc shows about 9.5km/s dV which should be plenty to reach orbit even witch much more moderate TWR.
It can reach orbit as a massive depot, but it cant SSTO significant fuel mass the way Stardust wants.

That's for sure, no SSTO is good for bringing up significant mass in one go.

Stardust's proposal makes no sense whatsoever and we'd better let it die, but I don't think this subthread is related. I think it's rather about accumulation tanker or Starpusher stuff.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rsdavis9 on 07/29/2020 01:10 pm
So does that mean they need 12 LEO depots to launch every hour? By how much time could the Depots be separated such that the needed course correction would be acceptable? 6 seconds? 6 minutes? 1 hour? 3 hours? 6 hours? I know that they use instantaneous launch windows quit a bit. Is that absolutely required for tanker launches?

I believe the ISS rendezvous window was only 4 minutes, but the recycle time was greater so they just launched instantaneously at the best point in the window.

The problem is the RAAN. If your launch site isn't under the orbital plane, you either need to burn a lot of fuel, or wait a long time while your orbit precesses around. Both are really painful if your goal is efficient tanker utilization.

TheRadicalModerate worked out that a circular 263 km orbit would give you one launch opportunity per day without the need for orbital phasing (this shortens rendezvous time substantially), so that would be a good candidate orbit for an accumulation tanker. A 555 km circular orbit gives two opportunities per day, but the debris risk is a lot higher, you're dragging the tanker dry mass higher so you get less propellant delivered per launch, and you lose some Oberth effect on your burn.

https://forum.nasaspaceflight.com/index.php?topic=50851.msg2080345#msg2080345

Phasing requires VERY little fuel.
Phasing would tie up an orbiter for a longer time.
So either you have enough orbiters and don't worry about them being in orbit longer or you launch once per day.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: cdebuhr on 07/29/2020 01:30 pm
I was thinking that the primary goal for EM was to reach Mars in the 2024?
Nope - you're thinking here is just wrong.  EMs overarching goal is to safeguard the long-term future of human civilization.  A subordinate objective of this is to make human civilization multi-planetary.  Humans on Mars in 2024?  That would be great, but if its only flags-and-footprints (which is the very best you'll ever get with your idea), then Musk isn't interested.  Anything less than full colonization would be considered a failure.  Musk is in a hurry, but I think he'd much rather do it right than do it now.


so an interim solution is needed to keep the goal of 2024 credible.
Nope - see above.

The aim of reusability is to keep space flight cheap, I dont think aircrafts fuel drop tanks are that expensive, it must be some point where the cost of fuel to get 1kg of hardware to space will be equal (or more) to the cost of one kg of hardware, reaching that point is for me the objectif to keep costs relatively low, in the end a tank is only some sort of package.
As others have pointed out, your idea has been well and truly shredded here.  Please just let it go.  Your enthusiasm is commendable, but just as important as coming up with new ideas is knowing when to move on from an unworkable concept. 
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 07/29/2020 01:51 pm
I was thinking that the primary goal for EM was to reach Mars in the 2024? so an interim solution is needed to keep the goal of 2024 credible.
Do you have any evidence at all for this statement (an interim solution being needed)? Because if you don't, people will simply ignore it.

Quote
The aim of reusability is to keep space flight cheap, I dont think aircrafts fuel drop tanks are that expensive, it must be some point where the cost of fuel to get 1kg of hardware to space will be equal (or more) to the cost of one kg of hardware, reaching that point is for me the objectif to keep costs relatively low, in the end a tank is only some sort of package.
What on earth makes you think that the primary cost in your idea is the material cost of the tank?
Please, please re-read all the problems with your idea that people have pointed out above.

I have got one solid piece of evidence; refueling plans are gonna take a lot of time to be validated if ever financially viable option, regarding the cost of tankers fleet O&M costs, the engeering technical complexity.

A tank is by definition a large receptacle or storage chamber, it's all about materials (insulation, residtance, weight,........), I know there is some difficulties regarding boil-off, high pressure, rendevous, engines/thrusters but still there is no high value parts in it like engines/avionics/habitat.

When you travel light you will consume less fuel this is the idea, interim solution of course until we get advanced technologies that will allow ISRU, until we get  costs reduction per flights, which is still not in the foreseeable future.

I'm pretty sure if this option has been proposed by Elon a lot of educated experts here would have considered a genius idea and absolute truth but my name is not EM. ;D
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: t3kboi on 07/29/2020 02:36 pm
I can't do the math myself.  (Not lazy, just literally cannot do the math...)


Assumptions -
A Starship tanker has exactly the same configuration as SN5/6/8 we see being built now.
The Payload section has the same configuration as well.

There are two tanker types -
  Tanker 1 - delivery tanker.
   The Payload - additional cylindrical or spherical tankage up to the limits of either volume or mass.

  Tanker 2 - linger-on-orbit tanker (accepts deliveries, and performs final transfer to prime mission Starship)
   Tanker 1 Payload + cryo-coolers plumbed to both the Payload and main tankage.

*caveat - production Starships may ALL have the cryo-coolers, since that is part of operational necessity.  They may be removed from the delivery tankers to swap cryo-cooler mass for payload fuel mass.

Questions -

Given the known main tank volume and projected tankage volume available to the nose - how much can a tanker deliver to orbit? 

Total = (Main tank residuals - landing reserve) + Payload tank volume

How many refueling trips does it take to completely fill (assumed completely empty) prime mission Starship?

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: steveleach on 07/29/2020 04:57 pm
I was thinking that the primary goal for EM was to reach Mars in the 2024? so an interim solution is needed to keep the goal of 2024 credible.
Do you have any evidence at all for this statement (an interim solution being needed)? Because if you don't, people will simply ignore it.

Quote
The aim of reusability is to keep space flight cheap, I dont think aircrafts fuel drop tanks are that expensive, it must be some point where the cost of fuel to get 1kg of hardware to space will be equal (or more) to the cost of one kg of hardware, reaching that point is for me the objectif to keep costs relatively low, in the end a tank is only some sort of package.
What on earth makes you think that the primary cost in your idea is the material cost of the tank?
Please, please re-read all the problems with your idea that people have pointed out above.

I have got one solid piece of evidence; refueling plans are gonna take a lot of time to be validated if ever financially viable option, regarding the cost of tankers fleet O&M costs, the engeering technical complexity.

A tank is by definition a large receptacle or storage chamber, it's all about materials (insulation, residtance, weight,........), I know there is some difficulties regarding boil-off, high pressure, rendevous, engines/thrusters but still there is no high value parts in it like engines/avionics/habitat.

When you travel light you will consume less fuel this is the idea, interim solution of course until we get advanced technologies that will allow ISRU, until we get  costs reduction per flights, which is still not in the foreseeable future.

I'm pretty sure if this option has been proposed by Elon a lot of educated experts here would have considered a genius idea and absolute truth but my name is not EM. ;D
All you've done there is demonstrated that you don't understand what "evidence" means. Have a look at some other ideas being discussed on these forums and see how other people provide calculations or references to support their assertions, when they want them to be considered anything other than an opinion.  Suggesting that the objections are about you personally really isn't going to help your case, either.

Really, though, it's time to drop this now.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 07/29/2020 08:30 pm
So does that mean they need 12 LEO depots to launch every hour? By how much time could the Depots be separated such that the needed course correction would be acceptable? 6 seconds? 6 minutes? 1 hour? 3 hours? 6 hours? I know that they use instantaneous launch windows quit a bit. Is that absolutely required for tanker launches?

I believe the ISS rendezvous window was only 4 minutes, but the recycle time was greater so they just launched instantaneously at the best point in the window.

The problem is the RAAN. If your launch site isn't under the orbital plane, you either need to burn a lot of fuel, or wait a long time while your orbit precesses around. Both are really painful if your goal is efficient tanker utilization.

TheRadicalModerate worked out that a circular 263 km orbit would give you one launch opportunity per day without the need for orbital phasing (this shortens rendezvous time substantially), so that would be a good candidate orbit for an accumulation tanker. A 555 km circular orbit gives two opportunities per day, but the debris risk is a lot higher, you're dragging the tanker dry mass higher so you get less propellant delivered per launch, and you lose some Oberth effect on your burn.

https://forum.nasaspaceflight.com/index.php?topic=50851.msg2080345#msg2080345

Phasing requires VERY little fuel.
Phasing would tie up an orbiter for a longer time.

Indeed. "This shortens rendezvous time substantially." I conspicuously said nothing about fuel savings. ;)

So either you have enough orbiters and don't worry about them being in orbit longer or you launch once per day.

The implication, in other words, is that you can have multiple launches per day from the same launch pad rendezvousing with the same tanker, if you use orbital phasing.

This tripped my up at first too. However, it's not correct. :(

Again, the problem is RAAN. If your tankers aren't launching simultaneously, they'll be out-of-plane with the tanker. The only way it would work is if you launch those multiple tankers simultaneously, which would require multiple pads. So you still can't exceed 1 launch (or 2, if you use the problematic higher orbit) per pad per day to the same tanker.

You can certainly have multiple pads on the same launch site, of course. I expect SpaceX will do this.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rsdavis9 on 07/29/2020 08:38 pm
So does that mean they need 12 LEO depots to launch every hour? By how much time could the Depots be separated such that the needed course correction would be acceptable? 6 seconds? 6 minutes? 1 hour? 3 hours? 6 hours? I know that they use instantaneous launch windows quit a bit. Is that absolutely required for tanker launches?

I believe the ISS rendezvous window was only 4 minutes, but the recycle time was greater so they just launched instantaneously at the best point in the window.

The problem is the RAAN. If your launch site isn't under the orbital plane, you either need to burn a lot of fuel, or wait a long time while your orbit precesses around. Both are really painful if your goal is efficient tanker utilization.

TheRadicalModerate worked out that a circular 263 km orbit would give you one launch opportunity per day without the need for orbital phasing (this shortens rendezvous time substantially), so that would be a good candidate orbit for an accumulation tanker. A 555 km circular orbit gives two opportunities per day, but the debris risk is a lot higher, you're dragging the tanker dry mass higher so you get less propellant delivered per launch, and you lose some Oberth effect on your burn.

https://forum.nasaspaceflight.com/index.php?topic=50851.msg2080345#msg2080345

Phasing requires VERY little fuel.
Phasing would tie up an orbiter for a longer time.

Indeed. "This shortens rendezvous time substantially." I conspicuously said nothing about fuel savings. ;)

So either you have enough orbiters and don't worry about them being in orbit longer or you launch once per day.

The implication, in other words, is that you can have multiple launches per day from the same launch pad rendezvousing with the same tanker, if you use orbital phasing.

This tripped my up at first too. However, it's not correct. :(

Again, the problem is RAAN. If your tankers aren't launching simultaneously, they'll be out-of-plane with the tanker. The only way it would work is if you launch those multiple tankers simultaneously, which would require multiple pads. So you still can't exceed 1 launch per pad per day to the same tanker.

You can certainly have multiple pads on the same launch site, of course. I expect SpaceX will do this.

If the inclination of the orbit is greater than your latitude you can get 2 opportunities. One on the ascending node and one on the descending node. Not that I think it is worth it though. Better to keep inclination the same as latitude and keep the earth rotation benefit. You could always put 2 pads at one launch facility. Imagine dual SH/SS's launching at the same time from Boca Chica. :)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 07/29/2020 08:48 pm
[snip]

Phasing requires VERY little fuel.
Phasing would tie up an orbiter for a longer time.

Indeed. "This shortens rendezvous time substantially." I conspicuously said nothing about fuel savings. ;)

So either you have enough orbiters and don't worry about them being in orbit longer or you launch once per day.

The implication, in other words, is that you can have multiple launches per day from the same launch pad rendezvousing with the same tanker, if you use orbital phasing.

This tripped my up at first too. However, it's not correct. :(

Again, the problem is RAAN. If your tankers aren't launching simultaneously, they'll be out-of-plane with the tanker. The only way it would work is if you launch those multiple tankers simultaneously, which would require multiple pads. So you still can't exceed 1 launch per pad per day to the same tanker.

You can certainly have multiple pads on the same launch site, of course. I expect SpaceX will do this.

If the inclination of the orbit is greater than your latitude you can get 2 opportunities. One on the ascending node and one on the descending node. Not that I think it is worth it though. Better to keep inclination the same as latitude and keep the earth rotation benefit.

Yes, that's where you'd use the higher (555 km) orbit. But it has the aforementioned problems.

You could always put 2 pads at one launch facility. Imagine dual SH/SS's launching at the same time from Boca Chica. :)

Indeed. Didn't I say that?  8)  But since most of the expenses are per-pad instead of per-launch, there's not a lot of savings to be had. Non-zero, but not a lot.

Multiple pads on the same site might share payload processing facilities, but each pad needs its own foundation, flame trench, deluge system, propellant tank farm (or at least one farm with twice the capacity, "six of one half-dozen of the other"), GSE, etc.

Again I expect SpaceX will do it, but unfortunately it's not a buy-one-get-one-free situation.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 07/29/2020 11:11 pm
[snip]

Phasing requires VERY little fuel.
Phasing would tie up an orbiter for a longer time.

Indeed. "This shortens rendezvous time substantially." I conspicuously said nothing about fuel savings. ;)

So either you have enough orbiters and don't worry about them being in orbit longer or you launch once per day.

The implication, in other words, is that you can have multiple launches per day from the same launch pad rendezvousing with the same tanker, if you use orbital phasing.

This tripped my up at first too. However, it's not correct. :(

Again, the problem is RAAN. If your tankers aren't launching simultaneously, they'll be out-of-plane with the tanker. The only way it would work is if you launch those multiple tankers simultaneously, which would require multiple pads. So you still can't exceed 1 launch per pad per day to the same tanker.

You can certainly have multiple pads on the same launch site, of course. I expect SpaceX will do this.

If the inclination of the orbit is greater than your latitude you can get 2 opportunities. One on the ascending node and one on the descending node. Not that I think it is worth it though. Better to keep inclination the same as latitude and keep the earth rotation benefit.

Yes, that's where you'd use the higher (555 km) orbit. But it has the aforementioned problems.
Technically you can use both oppotunities even at the lower orbit. But only one opportunity would benefit from the perfect rendezvous- the other would require a predictable level of phasing to reach the accumulation tanker.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: john smith 19 on 08/02/2020 03:05 pm

The cryocoolers on an accumulation tanker (if they will have such coolers) will be designed to keep the already cold propellant cold, presumably thus handling liquids, and have radiators sized and designed for operation in vacuum, with significant influx of heat radiation from the Sun and Earth.  Cryocoolers for Mars ISRU will need to actually chill the propellants from maybe -60°C (if they are pre-cooled to ambient Mars temperatures) and in gas form, down to more than -180°C and liquid, and their radiators will want to be optimized for atmospheric use (thin though it may be).  I'm not sure how much difference this makes to their designs, though.
Quite a lot. What people normally call "radiators" are really "convectors." Gases are usually pretty poor conductors of heat and don't have much heat capacity but they can move quickly, extracting substantial heat from a surface. Vacuum OTOH leaves you solely with radiation and the stefan-boltzman law on black bodies. doubling the temperature increase radiator output by 16, but the size of the constants is so tiny the power per unit area is tiny. (IIRC the ISS radiators radiate 47w/Sq m. Improving radiator efficiency in vacuum could give serious mass savings) So a "radiator" on earth, or even on mars, can be quite small relative to one that has to operate in vacuum solely by actual radiation.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: john smith 19 on 08/02/2020 03:18 pm
A tank is by definition a large receptacle or storage chamber, it's all about materials (insulation, residtance, weight,........), I know there is some difficulties regarding boil-off, high pressure, rendevous, engines/thrusters but still there is no high value parts in it like engines/avionics/habitat.
Except it's not just a tank, is it?

It's a whole different mission architecture.

You're right that Musk would like to have something land on mars by 2024. However he does not expect it to be carrying crew and it doesn't have to be the full 150 tonne payload. 
Quote from: Star-Dust
I'm pretty sure if this option has been proposed by Elon a lot of educated experts here would have considered a genius idea and absolute truth but my name is not EM. ;D
I'm pretty sure people would be asking themselves what the hell happened to "Rapid and fully  reusable launch systems" and the goal of sustainable settlement.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: john smith 19 on 08/02/2020 03:25 pm
At work I outlawed the use of the words "just" and "simply" when proposing alternative ideas.

You're not allowed to grade your own work...
Excellent point.

I'd call it "Originator bias."

At best you could say it's probably simple to do if  you'd had a fair bit of experience doing something like it already. If they don't have that experience then it's just their (biased) opinion.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: DusanC on 08/03/2020 07:03 am

The cryocoolers on an accumulation tanker (if they will have such coolers) will be designed to keep the already cold propellant cold, presumably thus handling liquids, and have radiators sized and designed for operation in vacuum, with significant influx of heat radiation from the Sun and Earth.  Cryocoolers for Mars ISRU will need to actually chill the propellants from maybe -60°C (if they are pre-cooled to ambient Mars temperatures) and in gas form, down to more than -180°C and liquid, and their radiators will want to be optimized for atmospheric use (thin though it may be).  I'm not sure how much difference this makes to their designs, though.
Quite a lot. What people normally call "radiators" are really "convectors." Gases are usually pretty poor conductors of heat and don't have much heat capacity but they can move quickly, extracting substantial heat from a surface. Vacuum OTOH leaves you solely with radiation and the stefan-boltzman law on black bodies. doubling the temperature increase radiator output by 16, but the size of the constants is so tiny the power per unit area is tiny. (IIRC the ISS radiators radiate 47w/Sq m. Improving radiator efficiency in vacuum could give serious mass savings) So a "radiator" on earth, or even on mars, can be quite small relative to one that has to operate in vacuum solely by actual radiation.

Utilising Carnot cycle you could have much higher temperature at the radiator.

Selecting the working fluid would be a nice problem but IMHO if it could work in vacuum only employing radiation then on Mars with convection it's efficiency would just go up.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/09/2020 03:52 pm
Can the anti-boiloff system on the now empty landed Starships be fed gaseous propellants and condense them down?

I can't recall hearing anything about cryocoolers being standard equipment on Starships, even on the Mars-bound Starships.  As far as I have heard, the only systems for preventing boiloff during the Earth-Mars and Mars-Earth transits, will be insulation (header tanks inside the main tanks; the empy main tanks then act as a giant thermos bottle), and minimize sunshine hitting the tanks by pointing them away from the Sun.  This will lower the amount boiloff enough that there will be propellant left when they arrive, but it will not entirely prevent boiloff.  And it is definitely not enough to chill down the propellant.

To actually chill down oxygen and methane to condense into liquids, you either need active cooling, i.e. cryocoolers, or get much further out in our solar system.

So they will need to bring cryocoolers to Mars as normal cargo.

(It would make sense to have cryocoolers on accumulation tankers in LEO, though.  It is much more difficult to keep the propellant cool in LEO, as A) you will fill the main tanks, so there is no thermos bottle protecting the propellant, and B) there is no direction to point the ship to minimize incoming heat radiation, as the Earth takes up almost half the surroundings, reflecting sunlight onto you from almost everywhere.)

Thank you!

If there needs to be cryocoolers on accumulation tankers, could they be added as part of the spec for mars bound ships? If you have to send it anyway, preassembled and already functioning might be better than as cargo.
Poking my nose into a thread I haven't finished reading yet.


This is a good reason for dedicated accumulator/depot ships. Launch the cryocooler once and be done with it. Not the highest priority, but at some point the benefits outweigh the specialized build. A depot without boiloff = operational flexibility.


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/09/2020 08:04 pm
There's a cool 2001ish architecture that comes out of that.  Surface Tankers want to stop in LEO and drop their cargo.  Orbital Tankers want to move out of LEO full  (and establish a supply line and the tankers can use SEP orbit raising and lowering to get back to LEO)

So you get a LEO fuel depot.  That has regular service. Then you need to launch Starships, and launch cargo.  Maybe crew launches on Dragon for a while?

So Starships could launch to LEO, maybe dock to take on crew and cargo, fuel to reach the tanker orbit, then refuel and go.
The problem with that is that there is no singular LEO. A LEO with a given inclination can only be reached  twice a day from any given launch site, assuming no launch direction restrictions and the ability to turn the pad around for both launches.And an equitorial LEO is unreachable by ANY launch site without a course correction burn. (A polar orbit can be reached by any site twice a day, but loses all benifit from launching  with the rotation of the earth) It wouldnt be one fuel depot/station in orbit, it would need to be dozens, which pretty much eliminates the benifits from a unified depot/station.
True, there is no One LEO but is we're talking refueling we're talking about a payload destined for something other than LEO. I'm not a real orbital mechanic but from what I've worked out using vectors (ya gotta use what ya got) and from discussion on NSF, the higher you go the less energy needed for an orbital plane change.


If the payload ship is going to GEO, TLI or TMI launch to the orbital plane suggested by the launch site, which would most likely be the same plane as the depot. After tanking, boogie on in the same plane and change planes where it's cheap.


From discussion it sounds like a launch from BC needs a dog leg to avoid danger to population centers in case of abort so it sounds like there is a budget for maneuvering.


BC is 25.99 N, Kennedy is 28.39 N, a difference of 2.40 degrees. BC is further south and has a tad more energy from earth rotation plus it needs to dogleg anyway, so let it head out at 25.99 after the plane change.  AIUI from doing vectors, plane changes are cheap at small angles and increasingly expensive up to 90 or more deg. I could probably work up dV for any instantaneous plane change using vectors if I weren't so lazy.


Four fuel launches to LEO per day theoretically possible if I didn't trip over my pencil.


Phil


Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 08/09/2020 11:14 pm
There's a cool 2001ish architecture that comes out of that.  Surface Tankers want to stop in LEO and drop their cargo.  Orbital Tankers want to move out of LEO full  (and establish a supply line and the tankers can use SEP orbit raising and lowering to get back to LEO)

So you get a LEO fuel depot.  That has regular service. Then you need to launch Starships, and launch cargo.  Maybe crew launches on Dragon for a while?

So Starships could launch to LEO, maybe dock to take on crew and cargo, fuel to reach the tanker orbit, then refuel and go.
The problem with that is that there is no singular LEO. A LEO with a given inclination can only be reached  twice a day from any given launch site, assuming no launch direction restrictions and the ability to turn the pad around for both launches.And an equitorial LEO is unreachable by ANY launch site without a course correction burn. (A polar orbit can be reached by any site twice a day, but loses all benifit from launching  with the rotation of the earth) It wouldnt be one fuel depot/station in orbit, it would need to be dozens, which pretty much eliminates the benifits from a unified depot/station.
True, there is no One LEO but is we're talking refueling we're talking about a payload destined for something other than LEO. I'm not a real orbital mechanic but from what I've worked out using vectors (ya gotta use what ya got) and from discussion on NSF, the higher you go the less energy needed for an orbital plane change.


If the payload ship is going to GEO, TLI or TMI launch to the orbital plane suggested by the launch site, which would most likely be the same plane as the depot. After tanking, boogie on in the same plane and change planes where it's cheap.


From discussion it sounds like a launch from BC needs a dog leg to avoid danger to population centers in case of abort so it sounds like there is a budget for maneuvering.


BC is 25.99 N, Kennedy is 28.39 N, a difference of 2.40 degrees. BC is further south and has a tad more energy from earth rotation plus it needs to dogleg anyway, so let it head out at 25.99 after the plane change.  AIUI from doing vectors, plane changes are cheap at small angles and increasingly expensive up to 90 or more deg. I could probably work up dV for any instantaneous plane change using vectors if I weren't so lazy.


Four fuel launches to LEO per day theoretically possible if I didn't trip over my pencil.


Phil

This is a great point.

If you look carefully into the trajectories F9 has historically used to reach GTO, you'll see that after launch they're actually at a slightly lower inclination than the launch site latitude (<1 degree), implying a small amount of dogleg maneuvering. During the apogee raise burn there's also a small inclination correction, with the remainder being done by the upper stage during the GEO insertion burn. This may seem counterintuitive at first, but if you do the math you'll find it actually achieves slightly higher efficiency than doing the entire plane change during the GEO insertion burn.

So with Starship you could easily rendezvous first with a tanker or depot staged at inclination ~= launch site latitude, then perform the apogee raise and optional GEO insertion in a nearly identical manner to a standard F9 trajectory.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Greg Hullender on 08/09/2020 11:46 pm
For launches to the Moon and Mars, wouldn't you always want to use the ecliptic plane? That is, wouldn't you want orbits inclined 23.4 degrees to the equator and in the plane of the ecliptic?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 08/10/2020 12:09 am
For launches to the Moon and Mars, wouldn't you always want to use the ecliptic plane? That is, wouldn't you want orbits inclined 23.4 degrees to the equator and in the plane of the ecliptic?

You generally want to launch from a higher inclination to avoid passing through the worst of the van Allen belt post-TMI.

There's no need for your parking orbit to be right on the ecliptic from an orbital mechanics perspective. It doesn't matter if you're a little above or below the ecliptic plane with respect to Earth's center of mass, you just account for that in your trajectory calculations.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/10/2020 05:03 pm
For launches to the Moon and Mars, wouldn't you always want to use the ecliptic plane? That is, wouldn't you want orbits inclined 23.4 degrees to the equator and in the plane of the ecliptic?
I've a hunch Twark shot over your head so I'll throw in some detail. I'll go crawl under a rock if you got it.


For a moon shot the intent might be a polar orbit (example only) so coming in along the ecliptic would be of no help. If you want a lunar orbit over the ecliptic, where you do the maneuver putting yourself in that plane has different propellant costs.


The minimum propellant costs is where the ship is moving slowest. Using a launch profile that illustrates the point, picture the ship in circular LEO at an inclination of 26 deg. Where this orbit crossed the ecliptic is where the correction burn has to be.


Doing the plane change at LEO, ship has to kill all velocity taking it out of the ecliptic and add a bit along the ecliptic to stay at orbital velocity. Then it has to orbit until its roughly opposite the moon and do a burn to, in effect, raise its perigee up to L1 plus a little bit more so it coasts through and on to the moon.


Or, it can stay at 26 deg and do the burn that will pass it through L1. When it gets there it will be passing through the ecliptic and moving slow. Compared to the plane change in the first example it will just be a couple of puffs.


There are some refinement possible but I think these examples illustrate the core differences.


Mars transit can play a similar game but without that handy L1, I'm not sure exactly where the most fuel efficient plane change is. Maybe Mars/Sun L1?


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: LMT on 08/10/2020 05:25 pm
ELEO Starship

A LEO with a given inclination can only be reached  twice a day from any given launch site...

At Guiana Space Center you could launch efficiently to equatorial LEO ~ 15 times a day, if necessary.

Assuming SpaceX sublease, you could load 150 t cargo at GSC, or even hop that cargo from Boca Chica and then SH stack at GSC.  ELEO tankers would cycle from GSC.

Conceivably GSC and Alcântara Launch Center (http://www.parabolicarc.com/tag/alcantara-launch-center/) might compete for such a SpaceX sublease.

There are other benefits to ELEO, notably the potential for airliner-class radiation environment (https://forum.nasaspaceflight.com/index.php?topic=34036.msg1836275#msg1836275).  In ELEO, crews can undertake multiple long-duration missions without incurring career exposure penalty (https://www.nasa.gov/sites/default/files/atoms/files/space_radiation_ebook.pdf).

Image:  South Atlantic Anomaly.  ROSAT.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Asteroza on 08/11/2020 01:01 am
ELEO Starship

A LEO with a given inclination can only be reached  twice a day from any given launch site...

At Guiana Space Center you could launch efficiently to equatorial LEO ~ 15 times a day, if necessary.

Assuming SpaceX sublease, you could load 150 t cargo at GSC, or even hop that cargo from Boca Chica and then SH stack at GSC.  ELEO tankers would cycle from GSC.

Conceivably GSC and Alcântara Launch Center (http://www.parabolicarc.com/tag/alcantara-launch-center/) might compete for such a SpaceX sublease.

There are other benefits to ELEO, notably the potential for airliner-class radiation environment (https://forum.nasaspaceflight.com/index.php?topic=34036.msg1836275#msg1836275).  In ELEO, crews can undertake multiple long-duration missions without incurring career exposure penalty (https://www.nasa.gov/sites/default/files/atoms/files/space_radiation_ebook.pdf).

Image:  South Atlantic Anomaly.  ROSAT.


Alcantara might be more attractive for a US based company due to the technology protection agreement that was signed specifically for that spaceport.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/11/2020 01:04 am
Some thoughts on commercial refueling.


The SX refueling plan is innovative but idiosyncratic. I also think it can be made to work quite well. I also doubt any other launch provider could easily physically and operationally interface. They would have to latch on across 9m and have comparable fluid interconnects across what, eight meters? Then in the SX system the guest ship would have to provide ullage thrust. This is asking too much.


Commercial service would require an agnostic physical interface and maneuvering would most reasonably (opinion) be done by the depot.


New related thought: O2 is usually the more massive part of the propellant and it is common in all non hypergolics no matter what fuel they use. Tanking some O2 by itself would increase capabilities of other rockets.


Needing only one fluid connection, some creative engineering might find a way to dock asymmetrically without some gonzo structure being in the way of everything else. Obviously, I've got no idea how to do this.


Phil

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: AntiSanity on 08/11/2020 02:30 am
One thing that popped into mind is that most vehicles design their fuel and oxidizer tank ratios for their specific fuel mixture ratios. Vehicles would either have tanks with ratios that aren't optimized for non-orbit refueling or, more likely, they launch with less than the maximum possible oxidizer load and fill up on oxidizer in orbit.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/11/2020 03:01 am
One thing that popped into mind is that most vehicles design their fuel and oxidizer tank ratios for their specific fuel mixture ratios. Vehicles would either have tanks with ratios that aren't optimized for non-orbit refueling or, more likely, they launch with less than the maximum possible oxidizer load and fill up on oxidizer in orbit.
That's the idea. Second stage makes orbit with a lot more fuel than can be justified but then they top off the O2 and it all makes sense. Not as elegant and advantageous as complete refueling but better than none.


I doubt SX would ever stock anything but CH4 and O2 and there aren't that many rockets that use methane but that may change over the next decade.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TomH on 08/11/2020 03:47 am
IDK if this would simplify things or just make them more complex, but another possibility is to have two tanker variants: an O2 tanker and a CH4 tanker. Prop transfer on orbit might be simpler, but operational logistics on the ground would be more complicated.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: corpsband on 08/11/2020 12:04 pm
Seems to me the simplest solution is make a tanker/super heavy with enough payload capacity to fully refuel a single starship.  The eliminates all the complexity of multiple tanker launches, does not require the construction of depot, and fits the "less is more" principal.   Not sure exactly how large a stack would be necessary but surely it's less than 18m.  Once SS/SH is flying,  there is very little engineering required to upsize.  Most of the work now is (a) learning to manufacture a stainless steel ship as efficiently as possible (b) fine tuning the raptor design. 

A larger diameter tanker/SH neatly solves all the issues with refueling.  1 SS launch / 1 tanker launch / 1 rendezvous and you're on your way to wherever. 

Four or five launches and fuel transfers is fine to bootstrap the process but it is needlessly complex. 
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Slarty1080 on 08/11/2020 12:34 pm
Seems to me the simplest solution is make a tanker/super heavy with enough payload capacity to fully refuel a single starship.  The eliminates all the complexity of multiple tanker launches, does not require the construction of depot, and fits the "less is more" principal.   Not sure exactly how large a stack would be necessary but surely it's less than 18m.  Once SS/SH is flying,  there is very little engineering required to upsize.  Most of the work now is (a) learning to manufacture a stainless steel ship as efficiently as possible (b) fine tuning the raptor design. 

A larger diameter tanker/SH neatly solves all the issues with refueling.  1 SS launch / 1 tanker launch / 1 rendezvous and you're on your way to wherever. 

Four or five launches and fuel transfers is fine to bootstrap the process but it is needlessly complex.
No building an entirely new launch vehicle is needlessly complex. There would be a lot of issues at 18m diameter. Not necessary show stoppers but not insignificant. Whilst it might be inconvenient to have to make 4 or 5 launches, its a lot less inconvenient than designing a new rocket. I may be wrong - we shall see what SpaceX decides to do, they are the experts here.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: [email protected] on 08/11/2020 12:43 pm
Seems to me the simplest solution is make a tanker/super heavy with enough payload capacity to fully refuel a single starship.  The eliminates all the complexity of multiple tanker launches, does not require the construction of depot, and fits the "less is more" principal.   Not sure exactly how large a stack would be necessary but surely it's less than 18m.  Once SS/SH is flying,  there is very little engineering required to upsize.  Most of the work now is (a) learning to manufacture a stainless steel ship as efficiently as possible (b) fine tuning the raptor design. 

A larger diameter tanker/SH neatly solves all the issues with refueling.  1 SS launch / 1 tanker launch / 1 rendezvous and you're on your way to wherever. 

Four or five launches and fuel transfers is fine to bootstrap the process but it is needlessly complex.
Don't forget that the fact that they're many launches for refueling is ACTUALLY a good thing! Why you might be asking? Well because it can proves reliability & bringing cost down per launch of the system

I think there's no substantial complexity of reviving a rapid launch cadences & very fast rendezvous like in the past on Gemini 11 & its Agena target vehicle. With that fast pace they can do all of the 6-8 refuelings in a matter of a single week
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/11/2020 02:48 pm
Seems to me the simplest solution is make a tanker/super heavy with enough payload capacity to fully refuel a single starship.

Why wouldn't you then use that superheavy architecture as the mission ship as well?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/11/2020 03:05 pm
I could probably work up dV for any instantaneous plane change using vectors if I weren't so lazy.

Already done:

Change in velocity required for a plane change of angle phi in a circular orbit:
delta_V = 2 * sin(phi/2) * sqrt(GM/r)
Vc = sqrt(GM/r)
Hence: delta_V = 2 * sin(phi/2) * Vc

So a 5 degree plane change requires nearly 9% of orbital velocity. (Using an arbitrary 7km/s, that's 610m/s.) A 10 degree plane change requires 17% (1.2km/s.) A 45 degree plane change requires over 75% (5.4km/s.) 60 degree plane change requires 100%. At some point, you might as well land and re-launch.

Speaking of which:

This is a good reason for dedicated accumulator/depot ships. Launch the cryocooler once and be done with it. Not the highest priority, but at some point the benefits outweigh the specialized build. A depot without boiloff = operational flexibility.

Since one ship, fully fuelled on orbit, holds enough propellant to fully fuel one ship, then you are going to have one accumulator for each mission ship. ISTM that the architecture for accumulator/depot ships would be to pre-launch them into the preferred orbital plane of the target mission for each ship going to that target.

After refuelling its mission-ship, then the accumulator returns to Earth to reset for its next missions.

This month (well, last month), it's an accumulator for Mars missions. Next month, after a quick refurbish, it goes back up as an accumulator for a future Jupiter/Europa mission, or subs out another accumulator in the Moon fleet that's due for refurb...

IMO, you don't need or want a permanent depot, just cheap reusable tanker-variants with some extra mods. Hence you aren't concerned about orbital planes not lining up with orbital transfer windows (the usual objection to depot architecture), because you launched the accumulator(s) into the window you wanted for each specific mission. And since you have one accumulator for each mission-ship (including cargo ships), these things are going to be as common as dirt.

This also fits in with SpaceX's iterative development cycle. Early accumulators can be made from superseded last-gen Starships while the depot technology is being proven. Doesn't matter if you lose a few in early experiments, since they were going to be scrapped anyway.

[I always find it amusing that SpaceX's take on reusability leaves them with a bunch of low cost expendable hardware available.]
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: tbellman on 08/11/2020 03:46 pm
Seems to me the simplest solution is make a tanker/super heavy with enough payload capacity to fully refuel a single starship.  The eliminates all the complexity of multiple tanker launches, does not require the construction of depot, and fits the "less is more" principal.   Not sure exactly how large a stack would be necessary but surely it's less than 18m.  Once SS/SH is flying,  there is very little engineering required to upsize.  Most of the work now is (a) learning to manufacture a stainless steel ship as efficiently as possible (b) fine tuning the raptor design. 

A larger diameter tanker/SH neatly solves all the issues with refueling.  1 SS launch / 1 tanker launch / 1 rendezvous and you're on your way to wherever. 

Four or five launches and fuel transfers is fine to bootstrap the process but it is needlessly complex.

If a normal 9m Starship can bring up 150 tonnes of propellant to orbit, then a special ship that can bring up 1200 tonnes would need to be 9m×sqrt(1200t/150t) ≈ 25.5 meter in diameter.  If you can increase thrust-per-engine-bell-area, you can make the rocket taller, and don't need to increase the diameter quite as much.

It might be possible to increase the amount of propellant to orbit by stretch the tanks into the nosecone, which should increase the tankage of the 9m Starship from 1200 tonnes to almost 2000 tonnes.  However, most of that 800 tonne increase would be consumed before reaching orbit.  Staging would need to happen some 20% earlier, and the second stage would need to make up the difference in Δv.  Not trivial to calculate how much more propellant you could bring to orbit, since that depends on gravity losses, which will increase when you increase the mass.  If you could get 300 tonnes of propellant to orbit with a tank-stretched 9m Starship, then a similar 18m ship could get 1200 tonnes to orbit.  But that to reach that, you likely need higher thrust density than the current SH/SS or Raptor (31 engines at 2MN each on SuperHeavy gives a thrust-to-weight ratio of 1.1 if you fill the Starship with 2000 tonnes of propellant, which is pretty bad).

"Surely less than 18m", no.  18 meter diameter is probably the minimum you can get away with.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rsdavis9 on 08/11/2020 04:01 pm
I may be stupid here.

Any orbit inclination in LEO should be able to inject into any orbit inclination on the moon, on mars, on etc.
What am I missing?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: sebk on 08/11/2020 04:27 pm
I may be stupid here.

Any orbit inclination in LEO should be able to inject into any orbit inclination on the moon, on mars, on etc.
What am I missing?

Nothing.

To elaborate, there'd by very very slight dV penalty from equatorial LEO to high inclination lunar orbit, but it's so slight it vanishes in necessary performance margins.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rsdavis9 on 08/11/2020 04:49 pm
I may be stupid here.

Any orbit inclination in LEO should be able to inject into any orbit inclination on the moon, on mars, on etc.
What am I missing?

Nothing.

To elaborate, there'd by very very slight dV penalty from equatorial LEO to high inclination lunar orbit, but it's so slight it vanishes in necessary performance margins.

So just use one LEO orbit and avoid any plane changes for interplanetary missions. Interplanetary includes the moon.

And while we are at it. A Mars mission is possible from LEO with a full tank?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/11/2020 05:34 pm
Any orbit inclination in LEO should be able to inject into any orbit inclination on the moon, on mars, on etc.
[yes]
So just use one LEO orbit and avoid any plane changes for interplanetary missions. Interplanetary includes the moon.

Yes. The inclination is close to irrelevant. Transfer from a polar Earth orbit to lunar equatorial orbit if you want (not that there's a reason to do that.) Or from ISS orbit. Or from equatorial orbit. Escape trajectories are very forgiving. So just pick the inclination that works best for the launch site, or has some other logistical advantage (like using ISS for check-out, fit-out, crew xfer, etc.)

With one small quibble:
The orbital plane is relatively fixed as Earth moves around the sun, hence it will move in and out of sync with the ecliptic. So the orbital plane of a a particular LEO orbit will have two opportunities per year to launch into an interplanetary trajectory without a massive plane-change manoeuvre. If the target requires a transfer window outside of those two opportunities, you can't use that plane. You therefore need to pick a plane such that it will line up for the intended mission window.

It's not a huge burden, the mission window will last days (or rather, dozens of windows per day, for several days). But it means you aren't going to have a single LEO orbit that can be used as a staging ground for many different mission types and targets. Even for the same target, a plane that works for one window (eg, 2020 Mars window) won't work for the next (eg, 2022.) Each mission will need its own orbit (barring happy coincidences.)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/11/2020 05:48 pm
Seems to me the simplest solution is make a tanker/super heavy with enough payload capacity to fully refuel a single starship.  The eliminates all the complexity of multiple tanker launches, does not require the construction of depot, and fits the "less is more" principal.   Not sure exactly how large a stack would be necessary but surely it's less than 18m.  Once SS/SH is flying,  there is very little engineering required to upsize.  Most of the work now is (a) learning to manufacture a stainless steel ship as efficiently as possible (b) fine tuning the raptor design. 

A larger diameter tanker/SH neatly solves all the issues with refueling.  1 SS launch / 1 tanker launch / 1 rendezvous and you're on your way to wherever. 

Four or five launches and fuel transfers is fine to bootstrap the process but it is needlessly complex.
Well, if this is based on a larger diameter SH it's not going to happen any time in the near future. Making a rocket longer is relatively easy. It's more of what you already have. Making it fatter is way more difficult. It's closer to a new rocket than a redesign.


If it's based on a longer SS, it's unclear that it could make orbit with any appreciable propellant payload. IIRC, somebody that knows how ran a calculation on this. It would also be a throw away. It'll never make it back.


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TomH on 08/11/2020 10:23 pm
Making a rocket longer is relatively easy. It's more of what you already have. Making it fatter is way more difficult. It's closer to a new rocket than a redesign.

If you make a rocket longer while maintaining the same diameter you are increasing mass while maintaining the same planar area for engine thrust. You either have to increase engine thrust or take a hit to your T/W (thrust to weight ratio). Any T/W has to be > 1 to attain liftoff. The lower the T/W, the greater your gravity losses. If you can cram in more engines, that's fine. If not, you have to increase prop flow rate and combustion chamber pressure. Sometimes that is possible, sometimes not. And when it is possible, it is not necessarily easy. Instead of a new rocket you may wind up with a new engine.

Having substantial T/W is critical on a S1. It is far less important on upper stages where iSP is a more significant factor.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: spacenut on 08/11/2020 10:53 pm
Haven't they already stretched the Starship and Superheavy and packed as many engines in the Superheavy as possible?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: wila on 08/11/2020 11:57 pm
To anyone/everyone talking about doing one shot refueling with 18m+ diameter tanker to refuel a SS, why even make a tanker to carry up 1200+ tonnes of propellant when you could just make a slightly larger vehicle that could orbit the full 1500 tonnes of a fully fueled starship [1200t propellant, 150t dry, 150t payload] ???  - therefore not even bothering at all these "risky" docking and propellant transfer operations you are afraid of?

I thought the whole purpose of in space refueling is to not need to build a something that is over 75% of the way to just doing it directly.

Please explain your logic to me, because as I see it,as an individual vehicle it would then be an even simpler design without all the rendezvous/docking/propellant hardware.

[EDIT taker to tanker :)]
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Redclaws on 08/12/2020 01:00 am
Because refueling is not primarily about LEO payload.  It’s about getting a rocket full of fuel in orbit, to carry that payload to high energy orbits.  If you build an extremely large rocket as your solution, you lose out hugely on mass fraction - it’s mostly empty, so there’s a huge amount of wasted tank and engine (etc) mass.

Build moderate sized rockets and refuel and you can both avoid a larger rocket - which is hard for a lot of reasons - and you get far, far better results to high energy trajectories.  (eg, fast Mars transfers)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: corpsband on 08/12/2020 03:42 am
Interesting to read the replies.  They fall into a couple of categories:

1) Multi-flight refueling is best. 

This ignores all the points I made about a specialized large tanker is more efficient.


2) Increasing the diameter mean starting from scratch on a new rocket design


Perhaps so but the number of tankers needed would be *far* smaller than the number of starships.   I'm also a bit skeptical that this is simply hand-waving.  SpaceX is learning to build in stainless but that knowledge doesn't evaporate when scaling up.  It may be a new design but the construction practices will already be in place.  A lot of the iteration in Boca Chica right now presumably centers on lowering manufacturing cost and maximizing manufacturing efficiency.  For a large fuel tanker neither of those need apply. 



3) If you have a system with that much payload,  why not just scrap the 9m design and use that for everything?

Because Starship is being optimized for MASS PRODUCTION.  In Elon's vision, SS's will be everywhere:  flying P2P , flying to the Moon, launching other payloads,  making trips to Mars.

The tankers could be a low volume, relatively high cost design very different from SS.  But the very fact that the design in NOT versatile (like SS) means simplifying a lot of things.  You basically get a second stage which is all tanks.  No provisions for adaptability.  No ECLSS.  No cargo doors.

Getting fuel to orbit efficiently is going to be a reality for a long time -- realistically until some sort of fusion engine is flown or perhaps space elevators become a reality.  Getting things out of Earth's gravity well will always be expensive in the foreseeable future. 

Oil supertankers are excessively large.  Yet we keep building them larger because they're efficient even if they are expensive to design and build.  The same applies to transporting fuel to LEO. Bigger is better.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/12/2020 03:47 am
Because refueling is not primarily about LEO payload.  It’s about getting a rocket full of fuel in orbit, to carry that payload to high energy orbits.  If you build an extremely large rocket as your solution, you lose out hugely on mass fraction - it’s mostly empty, so there’s a huge amount of wasted tank and engine (etc) mass.

Build moderate sized rockets and refuel and you can both avoid a larger rocket - which is hard for a lot of reasons - and you get far, far better results to high energy trajectories.  (eg, fast Mars transfers)
The "why dont you just" is about making 9m starship a 3rd stage, lifted to LEO fully fueled by a hypothetical 20m super-starship, with no orbital rendevus, docking or refueling needed.

If you're building a new rocket anyway, what does "launch 9m starship + launch 18m full fuel load" have over "Launch 9m starship+ Launch 9m fuel+ launch 9m fuel+ launch 9m fuel..." that isnt done even better by "Launch 20m starship and full fuel load for 9m 3rd stage in one launch."
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: alang on 08/12/2020 04:13 am
If it's a given that cryogenic fuels are more difficult to manage due to 'boil off' which will be ameliorated during the cruise to Mars by having a 'tank within a tank', then would there be any advantage in having some large sun/earth shades parked in a few earth orbits so that initial earth orbit refuelling can be slower?
This is based on the assumption that such a solution would be relatively 'dumb' from a technical point of view compared to having fuel depots or dedicated tankers.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/12/2020 04:25 am
Well, maybe we need the 36m. Maximo Supremo booster lofting the 18m Semi Maximo second stage with the 12m Maximo Simpatico tanker. Launch the whole sucker To Mars on a rail gun and do away with ISRU. With some small operational modifications it could stop off in LEO and refuel SS.  :o
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TomH on 08/12/2020 10:12 pm
Interesting to read the replies.  They fall into a couple of categories:

1) Multi-flight refueling is best. 

This ignores all the points I made about a specialized large tanker is more efficient.

Sorry, but you are the one ignoring all the evidence that you are incorrect. With all factors considered, it just is not.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: corpsband on 08/12/2020 11:34 pm
Interesting to read the replies.  They fall into a couple of categories:

1) Multi-flight refueling is best. 

This ignores all the points I made about a specialized large tanker is more efficient.

Sorry, but you are the one ignoring all the evidence that you are incorrect. With all factors considered, it just is not.
Re-read the thread and that "evidence" is missing.  It amounts to "this is the ship we have" so it's the best we can do.   If you read my original post, this is a given at the start of real
 SS missions and for some period of time thereafter.  But it's not evidence that fueling up by 1/5th of a tank at a time is superior to fueling by "fill-er-up please" .   In fact I fully expect the multi-flight refueling to target a place-holder tanker (with regen equipment on board)  which will then fill the "mission" SS all at once.   So full-tank fueling will still be used. 

In any case,  I humbly request that you re-post or quote this additional evidence.  Saying "no it's not" is just a rebuttal without supporting arguments.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: r8ix on 08/13/2020 01:18 am
Interesting to read the replies.  They fall into a couple of categories:

1) Multi-flight refueling is best. 

This ignores all the points I made about a specialized large tanker is more efficient.

Sorry, but you are the one ignoring all the evidence that you are incorrect. With all factors considered, it just is not.
Re-read the thread and that "evidence" is missing.  It amounts to "this is the ship we have" so it's the best we can do.   If you read my original post, this is a given at the start of real
 SS missions and for some period of time thereafter.  But it's not evidence that fueling up by 1/5th of a tank at a time is superior to fueling by "fill-er-up please" .   In fact I fully expect the multi-flight refueling to target a place-holder tanker (with regen equipment on board)  which will then fill the "mission" SS all at once.   So full-tank fueling will still be used. 

In any case,  I humbly request that you re-post or quote this additional evidence.  Saying "no it's not" is just a rebuttal without supporting arguments.

Well, they’ve already mentioned depots, so yes, full tank refueling would seem to be on the agenda.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/13/2020 01:35 am
Interesting to read the replies.  They fall into a couple of categories:

1) Multi-flight refueling is best. 

This ignores all the points I made about a specialized large tanker is more efficient.

Sorry, but you are the one ignoring all the evidence that you are incorrect. With all factors considered, it just is not.
Re-read the thread and that "evidence" is missing.  It amounts to "this is the ship we have" so it's the best we can do.   If you read my original post, this is a given at the start of real
 SS missions and for some period of time thereafter.  But it's not evidence that fueling up by 1/5th of a tank at a time is superior to fueling by "fill-er-up please" .   In fact I fully expect the multi-flight refueling to target a place-holder tanker (with regen equipment on board)  which will then fill the "mission" SS all at once.   So full-tank fueling will still be used. 

In any case,  I humbly request that you re-post or quote this additional evidence.  Saying "no it's not" is just a rebuttal without supporting arguments.
How is a 18m single launch refueling of a 9m starship better than a 20m 3 stage rocket that puts a fully fueled 9m starship into orbit without any refueling at all?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Lars-J on 08/13/2020 01:44 am
Interesting to read the replies.  They fall into a couple of categories:

1) Multi-flight refueling is best. 

This ignores all the points I made about a specialized large tanker is more efficient.

Sorry, but you are the one ignoring all the evidence that you are incorrect. With all factors considered, it just is not.
Re-read the thread and that "evidence" is missing.  It amounts to "this is the ship we have" so it's the best we can do.   If you read my original post, this is a given at the start of real
 SS missions and for some period of time thereafter.  But it's not evidence that fueling up by 1/5th of a tank at a time is superior to fueling by "fill-er-up please" .   In fact I fully expect the multi-flight refueling to target a place-holder tanker (with regen equipment on board)  which will then fill the "mission" SS all at once.   So full-tank fueling will still be used. 

In any case,  I humbly request that you re-post or quote this additional evidence.  Saying "no it's not" is just a rebuttal without supporting arguments.
How is a 18m single launch refueling of a 9m starship better than a 20m 3 stage rocket that puts a fully fueled 9m starship into orbit without any refueling at all?

A smaller rocket is cheaper. Fewer stages are cheaper. Flying more often makes each flight cheaper. It seems rather obvious, but perhaps you are judging "better" by another metric than cost? What metric do you use for "better"?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/13/2020 01:50 am
Interesting to read the replies.  They fall into a couple of categories:

1) Multi-flight refueling is best. 

This ignores all the points I made about a specialized large tanker is more efficient.

Sorry, but you are the one ignoring all the evidence that you are incorrect. With all factors considered, it just is not.
Re-read the thread and that "evidence" is missing.  It amounts to "this is the ship we have" so it's the best we can do.   If you read my original post, this is a given at the start of real
 SS missions and for some period of time thereafter.  But it's not evidence that fueling up by 1/5th of a tank at a time is superior to fueling by "fill-er-up please" .   In fact I fully expect the multi-flight refueling to target a place-holder tanker (with regen equipment on board)  which will then fill the "mission" SS all at once.   So full-tank fueling will still be used. 

In any case,  I humbly request that you re-post or quote this additional evidence.  Saying "no it's not" is just a rebuttal without supporting arguments.
How is a 18m single launch refueling of a 9m starship better than a 20m 3 stage rocket that puts a fully fueled 9m starship into orbit without any refueling at all?

A smaller rocket is cheaper. Fewer stages are cheaper. Flying more often makes each flight cheaper. It seems rather obvious, but perhaps you are judging "better" by another metric than cost? What metric do you use for "better"?
Are those the only reasons? Because the program of record (9m tanker spam) has the 18m supertanker handilly beat, by that metric.

And the 3 stage design has the supertanker beat in all the ways the supertanker is better than the program or record, for only small increases in problems the supertanker already needs to solve.

So what exactly is the supertanker design best at, compared to both designs at once? (9m tanker spam, and 3 stage tankerless)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Lars-J on 08/13/2020 02:02 am
How is a 18m single launch refueling of a 9m starship better than a 20m 3 stage rocket that puts a fully fueled 9m starship into orbit without any refueling at all?

A smaller rocket is cheaper. Fewer stages are cheaper. Flying more often makes each flight cheaper. It seems rather obvious, but perhaps you are judging "better" by another metric than cost? What metric do you use for "better"?
Are those the only reasons? Because the program of record (9m tanker spam) has the 18m supertanker handilly beat, by that metric.

Indeed it does. Which is why don't expect to see an 18m supertanker for a veeeery long time. I'm not advocating for a 18m+ design, on the contrary. But perhaps you are confusing me for someone else.

And the 3 stage design has the supertanker beat in all the ways the supertanker is better than the program or record, for only small increases in problems the supertanker already needs to solve.

None of them are better than the program of record. And you just asserted that your "3 stage design" is better without anything to back it up with. So I ask again - By what metric? How is it better? Other than being like Apollo...
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: corpsband on 08/13/2020 02:15 am
How is a 18m single launch refueling of a 9m starship better than a 20m 3 stage rocket that puts a fully fueled 9m starship into orbit without any refueling at all?
The supertanker is being proposed as the next logical step in increasing the efficiency of the 1000's of SS already on the drawing board.  SS is being designed to be mass-produced.  Supertanker is a higher cost,  low volume vehicle.   

If you want to go hypothetical,  SS is the Jeep.  It's tough, adaptable, and very useful.  It's also available in large numbers.   Tanker semi's are more efficient at carrying useful loads of fuel but they are specialized vehicles.  You don't go the grocery store, do some off-roading at the beach, and take the kids to school in the tanker truck.  Specific vehicles for specific use cases.

Bringing fuel to orbit is expensive and SSTO will never (at least with current fuels) get around it.  So long as you have lots of jeeps sitting around,  it makes sense being able to efficiently fuel them up.  Does that logical chain lead to fuel depots?  Perhaps it does.  Or maybe  a load and go tanker is more efficient than an on-orbit depot. 

But even if they aren't, fuel depots want tanker trucks to deliver fuel,  not jeeps. 

In the case of your super super heavy,  why not use that first stage to get a much larger vehicle to LEO and then refuel it with multiple flights.   The circle goes round and round until you literally can't build any larger.

To me at least it seems very rational to build fuel delivery vehicles which are much larger than the rest of your fleet.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/13/2020 02:41 am
I've been noodling SS based depots and was wondering if anybody has WAGS on some weights. This might fit better in the engineering thread but it's directly related to refueling so I ask some indulgence.


Here's numbers I've been working with but don't have that tight a feel for some of them. Ideas most welcome.
-Final leg design: 12t (we haven't seen them yet so this number is crude)
-Heatshield: 10t (I've seen this number within the last few months but new detail is emerging)
-Fins, mechanism, hull reinforcement: 18 t (a total WAG and probably too low)
-Cargo bay stringers: .75t/ring. (A WAG)
-Landing propellant: ??  (I have no idea)
-Top and bottom dome volumes: 1 ring equivalent (A stab in the dark)


Here's a couple of hard ones. A preliminary guesstimate allows a tank stretch of two rings. The top three rings could go away and save 7 tons which isn't worth trying to convert into another rings worth of tankage.


What sort of sun shade and deployment mechanism can be done for seven tons?
How much cryo cooler, PV, batteries and radiators, can 7t buy? What would average power consumption be?
Is there some combination of cooler and shade that would do a better job than either individually within a 7t budget?


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: r8ix on 08/13/2020 02:57 am
Not now. Eventually, perhaps; but as you noted, building the supertanker implies a heavier lift capacity, which means even cheaper $/kg to orbit, making larger vessels useful which would require multiple refueling trips…

For now, we will have 4-5 variations on a single basic design. Later, we may add an 18m version, with 3-4 variations. As a space ecosystem develops, and as those initial efforts reduce the cost of gettin to LEO (and higher) there will be greater opportunity and need for specialization. If Musk is right about StarShip launch costs, and if Supertanker development cost $1 billion, you’d have to eliminate 400 launches just to pay for the development costs. Full fuel-up in orbit under the current scenario would cost $15-20 million. If each supertanker launch got that down to $10 million, you’re looking at in the neighborhood of 1000 tanker launches (to be replaced by 125 supertanker launches) to break even, assuming no time cost of money, and no time loss to develop the supertanker…

So, like I said, maybe someday. But it doesn’t make sense now.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/13/2020 03:10 am
How is a 18m single launch refueling of a 9m starship better than a 20m 3 stage rocket that puts a fully fueled 9m starship into orbit without any refueling at all?
The supertanker is being proposed as the next logical step in increasing the efficiency of the 1000's of SS already on the drawing board.  SS is being designed to be mass-produced.  Supertanker is a higher cost,  low volume vehicle.   

If you want to go hypothetical,  SS is the Jeep.  It's tough, adaptable, and very useful.  It's also available in large numbers.   Tanker semi's are more efficient at carrying useful loads of fuel but they are specialized vehicles.  You don't go the grocery store, do some off-roading at the beach, and take the kids to school in the tanker truck.  Specific vehicles for specific use cases.

Bringing fuel to orbit is expensive and SSTO will never (at least with current fuels) get around it.  So long as you have lots of jeeps sitting around,  it makes sense being able to efficiently fuel them up.  Does that logical chain lead to fuel depots?  Perhaps it does.  Or maybe  a load and go tanker is more efficient than an on-orbit depot. 

But even if they aren't, fuel depots want tanker trucks to deliver fuel,  not jeeps. 

In the case of your super super heavy,  why not use that first stage to get a much larger vehicle to LEO and then refuel it with multiple flights.   The circle goes round and round until you literally can't build any larger.


To me at least it seems very rational to build fuel delivery vehicles which are much larger than the rest of your fleet.
But it ISNT significantly bigger than your 18m supertanker. it's literally 1200 tons payload vs 1470 tons payload, a difference of only 22%. This is in comparison with your existing jump of 800% to go from 150 tons payload to 1200 tons of payload.

A rocket that's only 22% larger removes all orbital docking and refueling events, compared to reducing the rendevus and refueling events to 1.

This is where comparisons to jeeps and such break down. When literally 90% of the vehical is propellant, bringing the extra 10% of non-propellant is nothing in comparison.

The advantage of the program of record is that everything is common- that tankers and cargo flights and crew flights can all use the same pads, the same boosters. That you maximize your benifits from mass production.

But if you are making the jump to a larger size, you might as well bring the whole thing, instead of just the fuel.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: corpsband on 08/13/2020 03:23 am
Not now. Eventually, perhaps; but as you noted, building the supertanker implies a heavier lift capacity, which means even cheaper $/kg to orbit, making larger vessels useful which would require multiple refueling trips…
...
So, like I said, maybe someday. But it doesn’t make sense now.
I agree and never suggested that a supertanker program be undertaken until after the 9m SS ecosystem is fully operational. 

Getting fuel to orbit is always going to be a major bottleneck until some significant breakthrough in propulsion technology occurs.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TomH on 08/13/2020 03:49 am
I humbly request that you re-post or quote this additional evidence.  Saying "no it's not" is just a rebuttal without supporting arguments.

I don't need to. The last few pages are full of evidence that rebut your ultra-tanker notion. You are the one ignoring evidence and reality.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/13/2020 04:13 am
How is a 18m single launch refueling of a 9m starship better than a 20m 3 stage rocket that puts a fully fueled 9m starship into orbit without any refueling at all?
The supertanker is being proposed as the next logical step in increasing the efficiency of the 1000's of SS already on the drawing board.  SS is being designed to be mass-produced.  Supertanker is a higher cost,  low volume vehicle.   

If you want to go hypothetical,  SS is the Jeep.  It's tough, adaptable, and very useful.  It's also available in large numbers.   Tanker semi's are more efficient at carrying useful loads of fuel but they are specialized vehicles.  You don't go the grocery store, do some off-roading at the beach, and take the kids to school in the tanker truck.  Specific vehicles for specific use cases.

Bringing fuel to orbit is expensive and SSTO will never (at least with current fuels) get around it.  So long as you have lots of jeeps sitting around,  it makes sense being able to efficiently fuel them up.  Does that logical chain lead to fuel depots?  Perhaps it does.  Or maybe  a load and go tanker is more efficient than an on-orbit depot. 

But even if they aren't, fuel depots want tanker trucks to deliver fuel,  not jeeps. 

In the case of your super super heavy,  why not use that first stage to get a much larger vehicle to LEO and then refuel it with multiple flights.   The circle goes round and round until you literally can't build any larger.

To me at least it seems very rational to build fuel delivery vehicles which are much larger than the rest of your fleet.
I see the logic in your position and will offer a practical reason it will not happen real soon.


SX has been working 11 months to get a nine meter rocket to hop. They need to develop a heat shield, refueling, a booster... I think you underestimate the difficulty of building a bigger rocket. Despite the fact it would probably be the same material and share construction techniques, it is very difficult. Big things do not scale linearly. Every aspect needs new calculations and trade off analysis. It's about as straight forward as figuring out SS.


Nothing now at BC is scaled to it, from the tents to the pads, the to the road between the build and launch site. There is barely room for doing the SS at BC. It would have to be another complete facility somewhere else. Started from scratch. Money is not infinite. Indeed what has already been done has been done on a shoestring by aerospace standards. Elon has to watch the purse very carefully.


The last announced intention was to build 100 rockets a year for 10 years. After two or three years of refueling experience Elon might say "Ok, enough of this crap. Let's build a big tanker." If this happens it will be because the pressure of immediate needs is gone and cash flow (from Starlink?) is improved. But he is a business man and he makes decisions based on cost effectiveness.


The super tanked is to be built in limited numbers. An equivalent of BC has to be built but bigger, and the R&D has to be done. Divide this by the number to be built (10?) and you have a base unit cost before any metal is bent. There will be little savings  through volume purchasing except for stainless and welding wire. Where the SS might cost 20 million each (including all R&D and capital outlay amortized over the fleet) the super tanker might be as high as three or four hundred million each. The big nut at the front end is spread over fewer ships.


Then the next question is, how much will it save? Even a launch facility substantially larger than any in existence, has to be built. What will it cost per launch? What is it's lifetime?


Only if it can do substantially more than a break even would it be considered.


Nobody here on NSF, including you and those who disagree, have these numbers. Elon probably has enough in his plate to keep him from putting much energy into the question but if he does decide to look at it, it is these numbers that will influence his decision.


For now Elon has to get SS running, launch some starlinks, go to mars and maybe go to the moon.


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: r8ix on 08/13/2020 05:08 am
Another point for consideration (given the ship analogy above), is that container ships, bulk cargo ships, and cruise ships are not significantly smaller than oil tankers. But they don’t have the “used fuel is 80-90% of total mass” issue.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: corpsband on 08/13/2020 12:25 pm

I see the logic in your position and will offer a practical reason it will not happen real soon.
...
Nobody here on NSF, including you and those who disagree, have these numbers. Elon probably has enough in his plate to keep him from putting much energy into the question but if he does decide to look at it, it is these numbers that will influence his decision.


For now Elon has to get SS running, launch some starlinks, go to mars and maybe go to the moon.


Phil
Well the very title of the thread invites speculation :)   We only recently have grain silo's hopping and we're discussing on-orbit refueling options!   In any case thanks for at least seeing the logic of my argument.   Getting fuel out of the gravity well is a huge barrier to putting a lot of mass on Mars (or the Moon). And it doesn't really take very many Mars-bound Starships to logistically overwhelm the current plan. 

If we're really going to have a self-supporting colony on Mars, a handful of SS's isn't going to cut it.  You need to ship a LOT of infrastructure-building cargo before that first 100 settlers arrive. 

Otherwise you're not doing much besides planting a flag. 

Personally I want to see the settlement not 10 guys in a tent camping on Mars. 
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: corpsband on 08/13/2020 12:30 pm
Another point for consideration (given the ship analogy above), is that container ships, bulk cargo ships, and cruise ships are not significantly smaller than oil tankers. But they don’t have the “used fuel is 80-90% of total mass” issue.
Indeed (although cruise ships are not really transportation per se -- they're floating resorts). Huge cargo ships will probably have an analog,  but a little further down the road.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: spacenut on 08/13/2020 01:09 pm
Sea Dragon was to be about 70'-75' in diameter or about 23m in diameter.  It was to be built at a shipyard that builds submarines. 

Anything over about 12m would require an entirely new infrastructure and launched at sea and land at sea.  Shear size and sonic boom wouldn't allow anything much bigger than 12m to be launched from any existing facilities.  Pads 39A and B were built to launch a Nova size (12m) rocket, nothing larger. 

I don't forsee an 18m ship for a long time.  Maybe a 12m.  12m is almost double the volume of a 9m Starship.  So almost double the payload.  An 18m Starship would give 4 times the capacity of a 9m starship. 

Reusing existing Starships (9m version) would allow for more launches for tanking a fuel depot (modified Starship tanker) to fill during the 18 month off synod between Starship flotillas going to Mars during the 6 month synod.  That way Starships going to Mars would only have to make one stop and fill up before going to Mars or the moon. 

Starship/Superheavy will be like Falcon 9 once fully operational.  Lots of launches and reuse.  Then SpaceX could work on a larger Starship/Superheavy, maybe a 12m-14m diameter.  18m seems a bit of a stretch. 
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/13/2020 02:17 pm
Interesting to read the replies.  They fall into a couple of categories:
1) Multi-flight refueling is best. 
This ignores all the points I made about a specialized large tanker is more efficient.

Based on emphasising the wrong kind of "efficiency".

3) If you have a system with that much payload,  why not just scrap the 9m design and use that for everything?
Because Starship is being optimized for MASS PRODUCTION.  In Elon's vision, SS's will be everywhere: [...]
The tankers could be a low volume, relatively high cost design very different from SS.  But the very fact that the design in NOT versatile (like SS) means simplifying a lot of things.  You basically get a second stage which is all tanks.  No provisions for adaptability.  No ECLSS.  No cargo doors.

Those things you list for the tanker are all bad things. It's more expensive to make (both per-unit and per-program), it launches less often (making it also much more expensive to operate), and it can't be used for anything else by design.

The whole business case for low cost Earth launch is based on flexible, rapidly launched, reusable ships that you use for everything. There might be a reason to replace Starship with a larger version, 12m, 16m, 18m, whatever SpaceX decides makes sense, but there's no good reason to have a single-purpose vehicle that is much more expensive than their work-horse.

"Expensive and rarely used" is the mindset that SpaceX was founded to get away from.

That said: There might be brief periods where SpaceX is building a larger Starship, where the basic launcher is flying, but not yet proven, where it is used as a fuel tanker and treated as essentially disposable, while SpaceX is iterating its design. But even then, a big tanker fuelling a previous generation Starship won't be the point of the design, and it won't be optimised for it. It's just a handy test mission. The moment the larger hardware is proven, it replaces that previous generation entirely as the general purpose workhorse launcher. They are not "jeeps", they are mass produced, standardised commercial trucks.

(Semi-trailer tankers are similarly based on standard general purpose semis. Designed to use standard infrastructure (roads). Even the trailer chassis are mostly standard, only the tanks themselves (and fuel handling equipment) are specialised. They are more like Starship tankers, a variant on the standard workhorse cargo vehicle.)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: r8ix on 08/13/2020 02:27 pm
Another point for consideration (given the ship analogy above), is that container ships, bulk cargo ships, and cruise ships are not significantly smaller than oil tankers. But they don’t have the “used fuel is 80-90% of total mass” issue.
Indeed (although cruise ships are not really transportation per se -- they're floating resorts). Huge cargo ships will probably have an analog,  but a little further down the road.
Because we don't use ships for "transportation" any more. But the Queen Mary 2 was about the same size (345m), and the Harmony of the Seas is 362m. Long-term crewed vessels will have to be a little more "resort-like" than the ISS, and once we move past leading-edge exploration, resort vessels are not out of the question. Avenue 5, anyone?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: wila on 08/16/2020 05:58 am
Firstly, just to clarify, I have never "advocated" a 3 stage Star Ship, I personally think that is a expensive Bad Idea.
But...
I do think it makes more sense than making a dedicated 20-22m diameter 1200t capacity SuperTanker AND the UltraSuperHeavy booster needed to loft it AND the launch site/GSE for all of it (which would likely have to be far out at sea [is it still GSE when at sea, not on the ground?]). And all that for the sole purpose of reducing what, by then, should be standard, well practiced and reliable rendezvous/docking/fuel transfer events from 5 or 6 down to 1, about an 80% risk reduction to this one part of the overall mission. If instead, by making this system 23m diameter and treat a fully fueled StarShip as cargo you eliminate the need for them all-together, giving a 100% risk reduction? (Okay, maybe 99.9% due to added stage seperation event, but that has got to be a lot less risky than even one rendezvous/docking/fuel transfer/undocking event.)

As I said though, I do not view it as a good idea, just better than a dedicated single purpose SuperTanker/UltraSuperHeavy setup.

Warning and disclaimer - all numbers used in the rest of this post are derived by very detailed arm waving, and then simplified to nicely rounded numbers - this is fully justifiable as even the great Elon himself knows not yet what these the numbers may come to be ;)

I do not believe an 18m diameter tanker could get 1200t propellant to orbit. As is, Raptor has an almost unbeatable thrust to nozzle area ratio.  As has be discussed to death several times  across multiple NSF forums, doubling the diameter only increases the area four time, so with the same thrust per area, you are only getting 4 times the thrust and therefor can only lift 4 times as much meaning your payload only increases by ~4 times, all else being equal (ISP, full-burnout mass ratio, etc.).   StarShip as described needs ~1200t propellant to fully refuel when empty.  The cargo version is to have ~150t cargo capacity.  The Tanker version has to be able to carry over 200t propellant to fully refuel a StarShip in 6 tanker runs, and over 240t to do it in 5 runs - the over bit being whatever amount is needed to compensate for boil-off. At the best value of 240t, 4 times that is only 960t, 240t short of a full load, so you'll need a second tanker run and associated rendezvous/docking/transfer/undocking event to fully fuel, and unless you can use the excess ~720t left in that second tanker to dock with and top off two or three more Starships it is a waste and you are still doing multiple rendezvous/docking/fuel transfer/undocking events.  So you need a SuperTanker larger than 18m.  Over 20m diameter if the ratios of a 240+t 5 run tanker are scaled, and almost 22m diameter if the 200+t 6 run tanker ratios are scaled, in order for the SuperTanker to be able to refuel a 9 m StarShip in just one rendezvous/docking/fuel transfer/undocking event.  And unless you've developed a new 5-6 times bigger engine, you are talking 155-186 or more current Raptors on that booster alone  :P .

Musk has said that 9m StarShip is what he considers to be the minimum needed to start setting up and populating a sizable (10,000 person plus) Mars BASE, but to get to the 1 million person colony level WILL need a bigger vehicle.  Mars trips will be the vast majority of flights that will need fully refueled StarShips in LEO.  The realistic need for fully refueled starships for GTO/DirectGEO/Lunar/DeepSpace  trips is only going to be in the few tens per year at very best for the next decade plus.  So these possibly 22m SuperTankers and associated facilities are going to be super busy 3 or 4 out of every 26 month Mars synodoic period, then just sit around almost unused till the next synod?  This is going to jack the cost of StarShip flights thru the roof in order to cover the costs of developing and maintaining such massive and overall seldom used system (shades of SLS).

By the time 9m SS and SH can't keep up with trips to mars, new bigger StarShip and associated booster will be needed anyway, and it will be sized to its needs, whether 12, 18 or 20+m diameter.

And if this specifically designed just to fill a 9m StarShip in one go SuperTanker/UltraHeavyBooster isn't usefull to it, said SuperTanker/UltraHeavy/GSE/Pad will just be a very expensive one trick pony.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/16/2020 05:06 pm
Firstly, just to clarify, I have never "advocated" a 3 stage Star Ship, I personally think that is a expensive Bad Idea.
But...
I do think it makes more sense than making a dedicated 20-22m diameter 1200t capacity SuperTanker AND the UltraSuperHeavy booster needed to loft it AND the launch site/GSE for all of it (which would likely have to be far out at sea [is it still GSE when at sea, not on the ground?]). And all that for the sole purpose of reducing what, by then, should be standard, well practiced and reliable rendezvous/docking/fuel transfer events from 5 or 6 down to 1, about an 80% risk reduction to this one part of the overall mission. If instead, by making this system 23m diameter and treat a fully fueled StarShip as cargo you eliminate the need for them all-together, giving a 100% risk reduction? (Okay, maybe 99.9% due to added stage seperation event, but that has got to be a lot less risky than even one rendezvous/docking/fuel transfer/undocking event.)

As I said though, I do not view it as a good idea, just better than a dedicated single purpose SuperTanker/UltraSuperHeavy setup.

Warning and disclaimer - all numbers used in the rest of this post are derived by very detailed arm waving, and then simplified to nicely rounded numbers - this is fully justifiable as even the great Elon himself knows not yet what these the numbers may come to be ;)

I do not believe an 18m diameter tanker could get 1200t propellant to orbit. As is, Raptor has an almost unbeatable thrust to nozzle area ratio.  As has be discussed to death several times  across multiple NSF forums, doubling the diameter only increases the area four time, so with the same thrust per area, you are only getting 4 times the thrust and therefor can only lift 4 times as much meaning your payload only increases by ~4 times, all else being equal (ISP, full-burnout mass ratio, etc.).   StarShip as described needs ~1200t propellant to fully refuel when empty.  The cargo version is to have ~150t cargo capacity.  The Tanker version has to be able to carry over 200t propellant to fully refuel a StarShip in 6 tanker runs, and over 240t to do it in 5 runs - the over bit being whatever amount is needed to compensate for boil-off. At the best value of 240t, 4 times that is only 960t, 240t short of a full load, so you'll need a second tanker run and associated rendezvous/docking/transfer/undocking event to fully fuel, and unless you can use the excess ~720t left in that second tanker to dock with and top off two or three more Starships it is a waste and you are still doing multiple rendezvous/docking/fuel transfer/undocking events.  So you need a SuperTanker larger than 18m.  Over 20m diameter if the ratios of a 240+t 5 run tanker are scaled, and almost 22m diameter if the 200+t 6 run tanker ratios are scaled, in order for the SuperTanker to be able to refuel a 9 m StarShip in just one rendezvous/docking/fuel transfer/undocking event.  And unless you've developed a new 5-6 times bigger engine, you are talking 155-186 or more current Raptors on that booster alone  :P .

Musk has said that 9m StarShip is what he considers to be the minimum needed to start setting up and populating a sizable (10,000 person plus) Mars BASE, but to get to the 1 million person colony level WILL need a bigger vehicle.  Mars trips will be the vast majority of flights that will need fully refueled StarShips in LEO.  The realistic need for fully refueled starships for GTO/DirectGEO/Lunar/DeepSpace  trips is only going to be in the few tens per year at very best for the next decade plus.  So these possibly 22m SuperTankers and associated facilities are going to be super busy 3 or 4 out of every 26 month Mars synodoic period, then just sit around almost unused till the next synod?  This is going to jack the cost of StarShip flights thru the roof in order to cover the costs of developing and maintaining such massive and overall seldom used system (shades of SLS).

By the time 9m SS and SH can't keep up with trips to mars, new bigger StarShip and associated booster will be needed anyway, and it will be sized to its needs, whether 12, 18 or 20+m diameter.

And if this specifically designed just to fill a 9m StarShip in one go SuperTanker/UltraHeavyBooster isn't usefull to it, said SuperTanker/UltraHeavy/GSE/Pad will just be a very expensive one trick pony.
Wow! Arm waving for sure, but half the trick to arm waving is finding the right numbers to wave over. I think ya dun good.


IMO, once refueling is proven and reliable, and the need is established, a custom built depot makes sense. It allows a steady tempo of launches over time instead of a flurry all at once. Between a sun shade and PV powered cryo cooling losses should be acceptable. A steady tempo with dedicated SS based tankers takes a lot of stress off launch and supply operations.


Keeping a Depot orbit at the inclination of BC or Kennedy (only ~2deg different) gives an opportunity to refuel missions to any location beyond LEO and with the correct mission profile, at minimum dV for a plane change. All without a massive one off SuperDuper booster.


Once there is a depot established for general, rather than mission specific use, the
small size might become an issue. Figure on a mars mission with two crewed and 10 cargo ships and a lot of refueling has to happen. Throw in a few GEO and lunar launches and it's a problem.


Down the road (2-3 mars missions?) there might be reason for a custom 12m hammerhead tank perched atop an SH with only enough propellant to make LEO. Total mass the same as SS but with no cargo, heatshield, fins or legs. Figure a nominal 100 tons dry mass for a standard SS and a guesstimate of 190 tons savings that can become dry mass and that tank can hold quite a bit of propellant.


I have no pencil or paper handy so my arm waving does not cover structural feasibility through launch. Probably not very good. Still, it can shrink back to 9m, include a cryo cooler, PV and a sunshade and some starter propellant and still be quite large. And a lot less hassle than mega launchers. A total WAG, 2-3 SS refueling.


Phil


Edit: I was editing for clarity and sanity when by battery quit, so here goes.
- the 190t savings came from legs, heatshield and fins: 40t estimate. No cargo =150t. These numbers are provisional.
- following that number in the main body where I spoke of the depot holding quite a bit of propellant I meant once on orbit. It would launch dry except for propellant to reach LEO.
-Converting the 190t savings into 1.6t rings allows 118 additional 9m rings with no launch mass change. Give it 33% penalty for additional structure and it's 79 additional rings. Make the depot 12m and it gets 52 rings. No way this is going to happen.
- The current SS HAS 9+ propellant rings. For every nine+ additional rings an SS can be topped off. What might be the longest it can be  safely stretched? Even with reinforcing and maybe greater ullage pressure. Would 12m make it easier? I doubt the engineering effort is worth it.
- Even with any reasonable stretch, more than one would be needed to refuel a modest Mars fleet. Does a long term depots impact on launch cadence justify its existence?




Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Slarty1080 on 08/16/2020 10:58 pm
Firstly, just to clarify, I have never "advocated" a 3 stage Star Ship, I personally think that is a expensive Bad Idea.
But...
I do think it makes more sense than making a dedicated 20-22m diameter 1200t capacity SuperTanker AND the UltraSuperHeavy booster needed to loft it AND the launch site/GSE for all of it (which would likely have to be far out at sea [is it still GSE when at sea, not on the ground?]). And all that for the sole purpose of reducing what, by then, should be standard, well practiced and reliable rendezvous/docking/fuel transfer events from 5 or 6 down to 1, about an 80% risk reduction to this one part of the overall mission. If instead, by making this system 23m diameter and treat a fully fueled StarShip as cargo you eliminate the need for them all-together, giving a 100% risk reduction? (Okay, maybe 99.9% due to added stage seperation event, but that has got to be a lot less risky than even one rendezvous/docking/fuel transfer/undocking event.)

As I said though, I do not view it as a good idea, just better than a dedicated single purpose SuperTanker/UltraSuperHeavy setup.

Warning and disclaimer - all numbers used in the rest of this post are derived by very detailed arm waving, and then simplified to nicely rounded numbers - this is fully justifiable as even the great Elon himself knows not yet what these the numbers may come to be ;)

I do not believe an 18m diameter tanker could get 1200t propellant to orbit. As is, Raptor has an almost unbeatable thrust to nozzle area ratio.  As has be discussed to death several times  across multiple NSF forums, doubling the diameter only increases the area four time, so with the same thrust per area, you are only getting 4 times the thrust and therefor can only lift 4 times as much meaning your payload only increases by ~4 times, all else being equal (ISP, full-burnout mass ratio, etc.).   StarShip as described needs ~1200t propellant to fully refuel when empty.  The cargo version is to have ~150t cargo capacity.  The Tanker version has to be able to carry over 200t propellant to fully refuel a StarShip in 6 tanker runs, and over 240t to do it in 5 runs - the over bit being whatever amount is needed to compensate for boil-off. At the best value of 240t, 4 times that is only 960t, 240t short of a full load, so you'll need a second tanker run and associated rendezvous/docking/transfer/undocking event to fully fuel, and unless you can use the excess ~720t left in that second tanker to dock with and top off two or three more Starships it is a waste and you are still doing multiple rendezvous/docking/fuel transfer/undocking events.  So you need a SuperTanker larger than 18m.  Over 20m diameter if the ratios of a 240+t 5 run tanker are scaled, and almost 22m diameter if the 200+t 6 run tanker ratios are scaled, in order for the SuperTanker to be able to refuel a 9 m StarShip in just one rendezvous/docking/fuel transfer/undocking event.  And unless you've developed a new 5-6 times bigger engine, you are talking 155-186 or more current Raptors on that booster alone  :P .

Musk has said that 9m StarShip is what he considers to be the minimum needed to start setting up and populating a sizable (10,000 person plus) Mars BASE, but to get to the 1 million person colony level WILL need a bigger vehicle.  Mars trips will be the vast majority of flights that will need fully refueled StarShips in LEO.  The realistic need for fully refueled starships for GTO/DirectGEO/Lunar/DeepSpace  trips is only going to be in the few tens per year at very best for the next decade plus.  So these possibly 22m SuperTankers and associated facilities are going to be super busy 3 or 4 out of every 26 month Mars synodoic period, then just sit around almost unused till the next synod?  This is going to jack the cost of StarShip flights thru the roof in order to cover the costs of developing and maintaining such massive and overall seldom used system (shades of SLS).

By the time 9m SS and SH can't keep up with trips to mars, new bigger StarShip and associated booster will be needed anyway, and it will be sized to its needs, whether 12, 18 or 20+m diameter.

And if this specifically designed just to fill a 9m StarShip in one go SuperTanker/UltraHeavyBooster isn't usefull to it, said SuperTanker/UltraHeavy/GSE/Pad will just be a very expensive one trick pony.
Wow! Arm waving for sure, but half the trick to arm waving is finding the right numbers to wave over. I think ya dun good.


IMO, once refueling is proven and reliable, and the need is established, a custom built depot makes sense. It allows a steady tempo of launches over time instead of a flurry all at once. Between a sun shade and PV powered cryo cooling losses should be acceptable. A steady tempo with dedicated SS based tankers takes a lot of stress off launch and supply operations.


Keeping a Depot orbit at the inclination of BC or Kennedy (only ~2deg different) gives an opportunity to refuel missions to any location beyond LEO and with the correct mission profile, at minimum dV for a plane change. All without a massive one off SuperDuper booster.


Once there is a depot established for general, rather than mission specific use, the
small size might become an issue. Figure on a mars mission with two crewed and 10 cargo ships and a lot of refueling has to happen. Throw in a few GEO and lunar launches and it's a problem.


Down the road (2-3 mars missions?) there might be reason for a custom 12m hammerhead tank perched atop an SH with only enough propellant to make LEO. Total mass the same as SS but with no cargo, heatshield, fins or legs. Figure a nominal 100 tons dry mass for a standard SS and a guesstimate of 190 tons savings that can become dry mass and that tank can hold quite a bit of propellant.


I have no pencil or paper handy so my arm waving does not cover structural feasibility through launch. Probably not very good. Still, it can shrink back to 9m, include a cryo cooler, PV and a sunshade and some starter propellant and still be quite large. And a lot less hassle than mega launchers. A total WAG, 2-3 SS refueling.


Phil


Edit: I was editing for clarity and sanity when by battery quit, so here goes.
- the 190t savings came from legs, heatshield and fins: 40t estimate. No cargo =150t. These numbers are provisional.
- following that number in the main body where I spoke of the depot holding quite a bit of propellant I meant once on orbit. It would launch dry except for propellant to reach LEO.
-Converting the 190t savings into 1.6t rings allows 118 additional 9m rings with no launch mass change. Give it 33% penalty for additional structure and it's 79 additional rings. Make the depot 12m and it gets 52 rings. No way this is going to happen.
- The current SS HAS 9+ propellant rings. For every nine+ additional rings an SS can be topped off. What might be the longest it can be  safely stretched? Even with reinforcing and maybe greater ullage pressure. Would 12m make it easier? I doubt the engineering effort is worth it.
- Even with any reasonable stretch, more than one would be needed to refuel a modest Mars fleet. Does a long term depots impact on launch cadence justify its existence?
Best bet is to remove the heat shield, legs, fins and header tanks. Launch that and if greater capacity is required launch more of them and link them together in orbit. Perhaps a multi tank docking node with sun shield and cryocooler could also be put up into orbit to round it off (although this would require a bit of additional work).
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/18/2020 02:24 pm
Yep. I got the first 40t stripping that stuff off. Another 150t by ditching payload. You get a LOT of extra 1.6t rings for that savings.


ISTM that joining depots together just isn't worth the hassle. Just have more in the same local. Keep one for routine GEO and lunar stuff and the additional ones for surges like Mars. But this still begs the core question. Is creating depot capacity to meet surge needs worth doing? I'm looking at ~10 year window after refueling is proven.


Pro: A steady predictable tanker launch cadence instead of a flurry of launches competing for launch capacity. This assumes it will be quite a while before any launch site can support even one launch a day.


Con: A super stretch depot based on SS can probably add only ~10 rings (18m+) of propellant storage - a total top off capacity of 2 SS. This is based on unwieldiness at launch, not mass. An SS based depot without any tank stretch can top off 1 SS.


Is a halving the total number of depots for a mars fleet worth it? ISTM to depend on things we don't know and can't know until SS is much more mature.


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/18/2020 03:04 pm
Firstly, just to clarify, I have never "advocated" a 3 stage Star Ship, I personally think that is a expensive Bad Idea.
But...
I do think it makes more sense than making a dedicated 20-22m diameter 1200t capacity SuperTanker AND the UltraSuperHeavy booster needed to loft it AND the launch site/GSE for all of it (which would likely have to be far out at sea [is it still GSE when at sea, not on the ground?]). And all that for the sole purpose of reducing what, by then, should be standard, well practiced and reliable rendezvous/docking/fuel transfer events from 5 or 6 down to 1, about an 80% risk reduction to this one part of the overall mission. If instead, by making this system 23m diameter and treat a fully fueled StarShip as cargo you eliminate the need for them all-together, giving a 100% risk reduction? (Okay, maybe 99.9% due to added stage seperation event, but that has got to be a lot less risky than even one rendezvous/docking/fuel transfer/undocking event.)

As I said though, I do not view it as a good idea, just better than a dedicated single purpose SuperTanker/UltraSuperHeavy setup.

Warning and disclaimer - all numbers used in the rest of this post are derived by very detailed arm waving, and then simplified to nicely rounded numbers - this is fully justifiable as even the great Elon himself knows not yet what these the numbers may come to be ;)

I do not believe an 18m diameter tanker could get 1200t propellant to orbit. As is, Raptor has an almost unbeatable thrust to nozzle area ratio.  As has be discussed to death several times  across multiple NSF forums, doubling the diameter only increases the area four time, so with the same thrust per area, you are only getting 4 times the thrust and therefor can only lift 4 times as much meaning your payload only increases by ~4 times, all else being equal (ISP, full-burnout mass ratio, etc.).   StarShip as described needs ~1200t propellant to fully refuel when empty.  The cargo version is to have ~150t cargo capacity.  The Tanker version has to be able to carry over 200t propellant to fully refuel a StarShip in 6 tanker runs, and over 240t to do it in 5 runs - the over bit being whatever amount is needed to compensate for boil-off. At the best value of 240t, 4 times that is only 960t, 240t short of a full load, so you'll need a second tanker run and associated rendezvous/docking/transfer/undocking event to fully fuel, and unless you can use the excess ~720t left in that second tanker to dock with and top off two or three more Starships it is a waste and you are still doing multiple rendezvous/docking/fuel transfer/undocking events.  So you need a SuperTanker larger than 18m.  Over 20m diameter if the ratios of a 240+t 5 run tanker are scaled, and almost 22m diameter if the 200+t 6 run tanker ratios are scaled, in order for the SuperTanker to be able to refuel a 9 m StarShip in just one rendezvous/docking/fuel transfer/undocking event.  And unless you've developed a new 5-6 times bigger engine, you are talking 155-186 or more current Raptors on that booster alone  :P .

Musk has said that 9m StarShip is what he considers to be the minimum needed to start setting up and populating a sizable (10,000 person plus) Mars BASE, but to get to the 1 million person colony level WILL need a bigger vehicle.  Mars trips will be the vast majority of flights that will need fully refueled StarShips in LEO.  The realistic need for fully refueled starships for GTO/DirectGEO/Lunar/DeepSpace  trips is only going to be in the few tens per year at very best for the next decade plus.  So these possibly 22m SuperTankers and associated facilities are going to be super busy 3 or 4 out of every 26 month Mars synodoic period, then just sit around almost unused till the next synod?  This is going to jack the cost of StarShip flights thru the roof in order to cover the costs of developing and maintaining such massive and overall seldom used system (shades of SLS).

By the time 9m SS and SH can't keep up with trips to mars, new bigger StarShip and associated booster will be needed anyway, and it will be sized to its needs, whether 12, 18 or 20+m diameter.

And if this specifically designed just to fill a 9m StarShip in one go SuperTanker/UltraHeavyBooster isn't usefull to it, said SuperTanker/UltraHeavy/GSE/Pad will just be a very expensive one trick pony.
Wow! Arm waving for sure, but half the trick to arm waving is finding the right numbers to wave over. I think ya dun good.


IMO, once refueling is proven and reliable, and the need is established, a custom built depot makes sense. It allows a steady tempo of launches over time instead of a flurry all at once. Between a sun shade and PV powered cryo cooling losses should be acceptable. A steady tempo with dedicated SS based tankers takes a lot of stress off launch and supply operations.


Keeping a Depot orbit at the inclination of BC or Kennedy (only ~2deg different) gives an opportunity to refuel missions to any location beyond LEO and with the correct mission profile, at minimum dV for a plane change. All without a massive one off SuperDuper booster.


Once there is a depot established for general, rather than mission specific use, the
small size might become an issue. Figure on a mars mission with two crewed and 10 cargo ships and a lot of refueling has to happen. Throw in a few GEO and lunar launches and it's a problem.


Down the road (2-3 mars missions?) there might be reason for a custom 12m hammerhead tank perched atop an SH with only enough propellant to make LEO. Total mass the same as SS but with no cargo, heatshield, fins or legs. Figure a nominal 100 tons dry mass for a standard SS and a guesstimate of 190 tons savings that can become dry mass and that tank can hold quite a bit of propellant.


I have no pencil or paper handy so my arm waving does not cover structural feasibility through launch. Probably not very good. Still, it can shrink back to 9m, include a cryo cooler, PV and a sunshade and some starter propellant and still be quite large. And a lot less hassle than mega launchers. A total WAG, 2-3 SS refueling.


Phil


Edit: I was editing for clarity and sanity when by battery quit, so here goes.
- the 190t savings came from legs, heatshield and fins: 40t estimate. No cargo =150t. These numbers are provisional.
- following that number in the main body where I spoke of the depot holding quite a bit of propellant I meant once on orbit. It would launch dry except for propellant to reach LEO.
-Converting the 190t savings into 1.6t rings allows 118 additional 9m rings with no launch mass change. Give it 33% penalty for additional structure and it's 79 additional rings. Make the depot 12m and it gets 52 rings. No way this is going to happen.
- The current SS HAS 9+ propellant rings. For every nine+ additional rings an SS can be topped off. What might be the longest it can be  safely stretched? Even with reinforcing and maybe greater ullage pressure. Would 12m make it easier? I doubt the engineering effort is worth it.
- Even with any reasonable stretch, more than one would be needed to refuel a modest Mars fleet. Does a long term depots impact on launch cadence justify its existence?
Best bet is to remove the heat shield, legs, fins and header tanks. Launch that and if greater capacity is required launch more of them and link them together in orbit. Perhaps a multi tank docking node with sun shield and cryocooler could also be put up into orbit to round it off (although this would require a bit of additional work).

I do love the idea, ISTM more practical  in the mid term than the back to back SS refueling, we may also send this multi tank docking node with some sort of propulsion system to Mars orbit, this could reduce the requirement for back home journey and such allowing more cargo.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/18/2020 10:49 pm

You might be misunderstanding. There is nothing in a depot, one tank or multiple, that precludes butt to butt refueling. Two entirely separate issues.


As for sending a depot to Mars, there has been discussion in this. First you need to understand that it does not remove the SS need to refuel before leaving earth. It's an alternative to having ISRU propellant production on mars. However, it's always seen as a supplement for early missions until reliable ISRU is on line, and not a replacement. Mars will never be more than a base if it depends on earth for its very ability to return.


Phil

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: mikelepage on 08/19/2020 08:10 am
The orbital plane is relatively fixed as Earth moves around the sun, hence it will move in and out of sync with the ecliptic. So the orbital plane of a a particular LEO orbit will have two opportunities per year to launch into an interplanetary trajectory without a massive plane-change manoeuvre. If the target requires a transfer window outside of those two opportunities, you can't use that plane. You therefore need to pick a plane such that it will line up for the intended mission window.

It's not a huge burden, the mission window will last days (or rather, dozens of windows per day, for several days). But it means you aren't going to have a single LEO orbit that can be used as a staging ground for many different mission types and targets. Even for the same target, a plane that works for one window (eg, 2020 Mars window) won't work for the next (eg, 2022.) Each mission will need its own orbit (barring happy coincidences.)

Somewhat off-topic, but this particular quirk of orbital mechanics is why I doubt Phobos or Deimos will ever (?) be used as way-stations/depots on the way to Mars surface.  Only twice per Martian year would it be possible to arrive at Mars and capture into an orbital plane aligned with the moons... and how often would those arrival windows synchronise with the Earth-Mars synodic cycle?  You might be able to get around this by performing multiple plane change maneuvers whilst aero-capturing into Martian orbit, but there would have to be an upper limit to how great a plane change you could perform that way.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/19/2020 08:21 am

You might be misunderstanding. There is nothing in a depot, one tank or multiple, that precludes butt to butt refueling. Two entirely separate issues.


As for sending a depot to Mars, there has been discussion in this. First you need to understand that it does not remove the SS need to refuel before leaving earth. It's an alternative to having ISRU propellant production on mars. However, it's always seen as a supplement for early missions until reliable ISRU is on line, and not a replacement. Mars will never be more than a base if it depends on earth for its very ability to return.


Phil

I keep my opinion on  Mars colonisation prospect for me, but getting first human and first permanent settlement on the red planet will require a step by step approach. If we want to get a real plan to do so we can't bet on future developement of new technologies that does not exist yet. this is why interim solutions is required you improve the process while you achieve what can be achieved in a timely manner, the air travel didn't await for the modern jet reaction airliners to be a reality, it took years and years and many accidents to get to what is now air travel.

The above mentioned idea of a multiple disposable tanks that will be joint to a nodal comprtment as is the case for ISS, seems to me practicle for multiple reasons:

-No need for a fleet of tankers and subsequent logistic issues.
-No time waisted for SS departing to Mars.
-Depot could be positioned in any strategic position.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: tyrred on 08/19/2020 09:44 am
There is a need for tankers. Logistics of tankers is a solved problem Earth-side, and must be solved space-side anyway.

Tanking has to be done before the optimal TMI window anyway, tanking operations just need to have enough certainty and margin built in to compensate for delays.

Depots can be placed strategically, but the strategies get very convoluted considering orbital mechanics.

Step by step approach should always consider reusability and sustainability.

Break away from the disposable past when building a new planet, for Bahphomet's sake.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/19/2020 10:22 am
There is a need for tankers. Logistics of tankers is a solved problem Earth-side, and must be solved space-side anyway.

Tanking has to be done before the optimal TMI window anyway, tanking operations just need to have enough certainty and margin built in to compensate for delays.

Depots can be placed strategically, but the strategies get very convoluted considering orbital mechanics.

Step by step approach should always consider reusability and sustainability.

Break away from the disposable past when building a new planet, for Bahphomet's sake.

Reusability is meant for keeping launching cost low, you reuse what is expensive, you dont reuse what is cheap or at least does not worth the reuse, if SH/SS building cost will get cheaper considering staineless steel use and others consideration, the reusability wont affect costs that much, so I think that going to Mars should considers this advices:

-Travel light.
-Have a plan B
-Simple is beautiful.
-Cheap is wonderful.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Thunderscreech on 08/19/2020 12:23 pm

Reusability is meant for keeping launching cost low, you reuse what is expensive, you dont reuse what is cheap or at least does not worth the reuse, if SH/SS building cost will get cheaper considering staineless steel use and others consideration, the reusability wont affect costs that much, so I think that going to Mars should considers this advices:

-Travel light.
-Have a plan B
-Simple is beautiful.
-Cheap is wonderful.
There are persistent, deeply unsolved problems with your proposal that you cannot seem to explain which contradict almost every point you make.  You still haven't explained how fully fueled large tanks arrive in LEO, how they're cheaper, how they're simpler, or how they enable you to 'travel light'.  The skepticism you're encountering is not 'the old guard versus John Houbolt, it's curiosity that's evolved into a little bit of exasperation because you seem to have either chosen not to answer or cannot answer the questions posed to you that seem to undercut the entire basis of your argument. 

And this is all before we get to the point where developing an entirely new, complicated hardware system with its own undefined capabilities and challenges is 'easier' than solving free-fall refueling of cryogenics. 

The skepticism is not assuaged by breezy, 'it's no big deal to disregard everything being done and start a brand new plan, my plan' summary like the bullet points you end with above.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/19/2020 01:03 pm

I keep my opinion on  Mars colonisation prospect for me, but getting first human and first permanent settlement on the red planet will require a step by step approach.
Who made that claim, and when do they expect to reach Mars?

Because under even the most pessimistic projections, SpaceX is going "before the decade is out," while if all goes well, they will be sending the first unmanned ships in 2 years.

You have repeatedly waved away the cheaper approach claiming that it can be made cheaper later. That's not how the world works. Time IS Money. Cheaper is faster.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/19/2020 01:06 pm

Reusability is meant for keeping launching cost low, you reuse what is expensive, you dont reuse what is cheap or at least does not worth the reuse, if SH/SS building cost will get cheaper considering staineless steel use and others consideration, the reusability wont affect costs that much, so I think that going to Mars should considers this advices:

-Travel light.
-Have a plan B
-Simple is beautiful.
-Cheap is wonderful.
There are persistent, deeply unsolved problems with your proposal that you cannot seem to explain which contradict almost every point you make.  You still haven't explained how fully fueled large tanks arrive in LEO, how they're cheaper, how they're simpler, or how they enable you to 'travel light'.  The skepticism you're encountering is not 'the old guard versus John Houbolt, it's curiosity that's evolved into a little bit of exasperation because you seem to have either chosen not to answer or cannot answer the questions posed to you that seem to undercut the entire basis of your argument. 

And this is all before we get to the point where developing an entirely new, complicated hardware system with its own undefined capabilities and challenges is 'easier' than solving free-fall refueling of cryogenics. 

The skepticism is not assuaged by breezy, 'it's no big deal to disregard everything being done and start a brand new plan, my plan' summary like the bullet points you end with above.

I thought it was obvious but let put thing clear:

-Send fuel tanks to LEO atop of a SH.
-Make tanks rendezvous with a multi tank docking node .
-When all tanks are in place send StarShip bound for Mars, make rendezvous transfert and launch.
-Travel lighter: if SS can get her fuel for the journey back home in Mars orbit it wont have to have the burden fuel for leaving Mars gravity.
-Cheap: because the switch to stainless steel will significantlly reduce the cost of the hardware (starship/SH), so even in the case of disposable vehicles that wont be affecting the costs that much.


I keep my opinion on  Mars colonisation prospect for me, but getting first human and first permanent settlement on the red planet will require a step by step approach.
Who made that claim, and when do they expect to reach Mars?

Because under even the most pessimistic projections, SpaceX is going "before the decade is out," while if all goes well, they will be sending the first unmanned ships in 2 years.

You have repeatedly waved away the cheaper approach claiming that it can be made cheaper later. That's not how the world works. Time IS Money. Cheaper is faster.

My point  is that a lot of enthousiasts here think that when StarShip will reach Mars, people will flock as in the west gold rush, IMHO things wont works like this, we could imagine NASA paying 15/20 billions a ride ticket for first step for man on the red planet, may be the fare will get lower for coming 10 to 20 years for scientists for a permanent base (200 to 400 millions ticket), for beyond I can't predict anything it's too far for me, its pure speculation.

But your unmanned SS for Mars in 2 years is overly optimistic.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: [email protected] on 08/19/2020 01:17 pm

Reusability is meant for keeping launching cost low, you reuse what is expensive, you dont reuse what is cheap or at least does not worth the reuse, if SH/SS building cost will get cheaper considering staineless steel use and others consideration, the reusability wont affect costs that much, so I think that going to Mars should considers this advices:

-Travel light.
-Have a plan B
-Simple is beautiful.
-Cheap is wonderful.
There are persistent, deeply unsolved problems with your proposal that you cannot seem to explain which contradict almost every point you make.  You still haven't explained how fully fueled large tanks arrive in LEO, how they're cheaper, how they're simpler, or how they enable you to 'travel light'.  The skepticism you're encountering is not 'the old guard versus John Houbolt, it's curiosity that's evolved into a little bit of exasperation because you seem to have either chosen not to answer or cannot answer the questions posed to you that seem to undercut the entire basis of your argument. 

And this is all before we get to the point where developing an entirely new, complicated hardware system with its own undefined capabilities and challenges is 'easier' than solving free-fall refueling of cryogenics. 

The skepticism is not assuaged by breezy, 'it's no big deal to disregard everything being done and start a brand new plan, my plan' summary like the bullet points you end with above.

I thought it was obvious but let put thing clear:

-Send fuel tanks to LEO atop of a SH.
-Make tanks rendezvous with a multi tank docking node .
-When all tanks are in place send StarShip bound for Mars, make rendezvous transfert and launch.
-Travel lighter: if SS can get her fuel for the journey back home in Mars orbit it wont have to have the burden fuel for leaving Mars gravity.
-Cheap: because the switch to stainless steel will significantlly reduce the cost of the hardware (starship/SH), so even in the case of disposable vehicles that wont be affecting the costs that much.
Did you already in your company's office doing the design work?

I imagine in your office there will be a poster saying "Beat SpaceX, because they didn't used or bother at all with my plan, which is so much better the world is super stupid for not implementing it. I'm a rocket engineering prophet!"
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: cdebuhr on 08/19/2020 01:33 pm

Reusability is meant for keeping launching cost low, you reuse what is expensive, you dont reuse what is cheap or at least does not worth the reuse, if SH/SS building cost will get cheaper considering staineless steel use and others consideration, the reusability wont affect costs that much, so I think that going to Mars should considers this advices:

-Travel light.
-Have a plan B
-Simple is beautiful.
-Cheap is wonderful.
There are persistent, deeply unsolved problems with your proposal that you cannot seem to explain which contradict almost every point you make.  You still haven't explained how fully fueled large tanks arrive in LEO, how they're cheaper, how they're simpler, or how they enable you to 'travel light'.  The skepticism you're encountering is not 'the old guard versus John Houbolt, it's curiosity that's evolved into a little bit of exasperation because you seem to have either chosen not to answer or cannot answer the questions posed to you that seem to undercut the entire basis of your argument. 

And this is all before we get to the point where developing an entirely new, complicated hardware system with its own undefined capabilities and challenges is 'easier' than solving free-fall refueling of cryogenics. 

The skepticism is not assuaged by breezy, 'it's no big deal to disregard everything being done and start a brand new plan, my plan' summary like the bullet points you end with above.

I thought it was obvious but let put thing clear:

-Send fuel tanks to LEO atop of a SH.
-Make tanks rendezvous with a multi tank docking node .
-When all tanks are in place send StarShip bound for Mars, make rendezvous transfert and launch.
-Travel lighter: if SS can get her fuel for the journey back home in Mars orbit it wont have to have the burden fuel for leaving Mars gravity.
-Cheap: because the switch to stainless steel will significantlly reduce the cost of the hardware (starship/SH), so even in the case of disposable vehicles that wont be affecting the costs that much.

[ ... snip ...]
This feels like "drop tanks" all over again ...

If you want to be taken seriously, you're going to have to back these notions up with numbers, because without that they don't seen to make much sense (to those who have looked at the numbers).

Here are some of the most obvious issues I see on casual examination of this plan ... I'm sure others here can (and have) picked this idea apart in somewhat more detail:

* How big are these fuel tanks you propose to launch?  How many will you need?  Do the math!
* Will these fuel tank be launched full (small tanks) or empty (allowing bigger tanks)?  If empty, you're going to need  ... tankers.
* How is you "multi tank docking node" simpler that tail-to-tail fuel transfer?  Be specific!
* If you're taking not just SS to mars but all the return fuel as well, your're going to need a MUCH more capable propulsion system to do it.  Please provide details.  Be specific, and do the math!

If you can't do this, then please, please try to listen and learn from those here who can.  If you can do this and just won't then you're just trolling, and I ask you to please stop.  If you can do this and are willing to put in the effort, then I think you will find this forum a wonderful place for fruitful discussions.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/19/2020 01:35 pm
-Send fuel tanks to LEO atop of a SH.
That doesnt work. Superheavy  cannot put any significant mass into orbit. If you add starship (and yes, reusable starship is significantly cheaper  per ton of fuel than expendable upperstage, even figuring in the reduced lift) then you have starship refueling starship, which is the program of record.
Quote
-Make tanks rendezvous with a multi tank docking node .
Instead of plumbing each tank through a heavy structure designed to keep multiple large tanks aligned  under thrust while rocket fuel goes through said plumbing... just plumb two starships together under 0g, transfer the fuel at a safe rate, and unplug.

Quote
-Travel lighter: if SS can get her fuel for the journey back home in Mars orbit it wont have to have the burden fuel for leaving Mars gravity.
a wagon train of return fuel coming from earth is not "Light travel" compared to going over the pass for supplies. when you need it. Starship is Spec'd for  single stage earth return, so adding a refueling stop there isnt saving anything.
Quote
-Cheap: because the switch to stainless steel will significantlly reduce the cost of the hardware (starship/SH), so even in the case of disposable vehicles that wont be affecting the costs that much.
Plastic knives are $3.50 for a box of 100. Stainless steel cutlery (40 pieces) is 30 dollars. Breakeven would be around 20-25 uses, and that's with a cheaper material being used.
Stainless vs stainless, expendable doesnt save you nearly enough to be worthwhile.

Quote

I keep my opinion on  Mars colonisation prospect for me, but getting first human and first permanent settlement on the red planet will require a step by step approach.
Who made that claim, and when do they expect to reach Mars?

Because under even the most pessimistic projections, SpaceX is going "before the decade is out," while if all goes well, they will be sending the first unmanned ships in 2 years.

You have repeatedly waved away the cheaper approach claiming that it can be made cheaper later. That's not how the world works. Time IS Money. Cheaper is faster.
(...)
But your unmanned SS for Mars in 2 years is overly optimistic.
Even if it's 4 years instead of 2, that's faster than a multi-billion nasa program can possibly be. Doing things "like NASA" would only slow them down.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Thunderscreech on 08/19/2020 01:36 pm
-Send fuel tanks to LEO atop of a SH.
SH can't bring anything to orbit, the 'tanks' would need to propel themselves the rest of the way after a couple minutes of boost.  So what you call 'tanks' are Starship tanker spacecraft without landing legs or heat shield but everything else.

-Make tanks rendezvous with a multi tank docking node .
-When all tanks are in place send StarShip bound for Mars, make rendezvous transfert and launch.
So they're docking with a depot instead of a mars-bound Starship?  Then the Starship docks with the depot?  If it is going to use the fuel from these mostly expended tanks (and all the deadweight from the tankage and engines needed to carry it to orbit after separating from the first stage) then they will need to transfer, all you're doing is switching this complicated cryogenic transfer to the worst possible method because you're transferring it during the trans-martian injection burn and carrying a hundred tons or more of extra tanks instead of doing the fuel transfer into your existing tank.

-Travel lighter: if SS can get her fuel for the journey back home in Mars orbit it wont have to have the burden fuel for leaving Mars gravity.
There is no source of fuel in Mars orbit unless you're ALSO shipping kilotons of propellant to Mars and elaborately and expensively aerobraking them into an orbit where they're out of reach of thirsty spacecraft stuck on the surface.

-Cheap: because the switch to stainless steel will significantlly reduce the cost of the hardware (starship/SH), so even in the case of disposable vehicles that wont be affecting the costs that much.
This is perplexing, the spacecraft are already stainless and nothing you do lowers costs; in fact you increase costs at every single possible step from the development of new spacecraft to requiring more fuel launches (to make up for all the extra disposable mass you're carrying during your TMI burn) to making everything disposable and throwing away raptors and avionics instead of re-using them....

There are deep, load bearing structural weaknesses in your proposal and that's usually fine, that's a normal part of spitballing different ideas and usually those are either worked out or used to decide 'hey, this won't work', but there's this element of repeating the same problems without recognizing them that probably some in your audience deeply skeptical about how much thought you've put into this and whether or not you're participating in a back and forth conversation or just repeating the same points without recognizing or addressing the problems others have identified.  I can't speak for anyone else, but this is where I am.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/19/2020 02:04 pm
Just to answer  : cdebuhr, rakaydos and Thunderscreech as your post are pretty the same:

-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? if you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.

-In terms of costs we must put the cost of building and maintaining a fleet of tankers into consideration, achieving full and rapid reusability will take some time so while awaiting for that moment expandable would be a better option as an interim solution.

-I evocked Stainless steel in term of cost reduction for hardware building costs not only in terms of overall material cost but also in term of building process simplification.

-Lowering costs with reusability will require using hardware multiple times and the later is not for near future so expandable option is best sueted coming years.

-No viable business plan for Mars bound missions will make you depend on governement spending and this one wont require large scale use planned by Elon Musk.


In the end there is still a lot of shadow area for EM Mars projections that makes his assumptions in difficult position.






Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/19/2020 02:11 pm
The orbital plane is relatively fixed as Earth moves around the sun, hence it will move in and out of sync with the ecliptic. So the orbital plane of a a particular LEO orbit will have two opportunities per year to launch into an interplanetary trajectory without a massive plane-change manoeuvre. If the target requires a transfer window outside of those two opportunities, you can't use that plane. You therefore need to pick a plane such that it will line up for the intended mission window.

It's not a huge burden, the mission window will last days (or rather, dozens of windows per day, for several days). But it means you aren't going to have a single LEO orbit that can be used as a staging ground for many different mission types and targets. Even for the same target, a plane that works for one window (eg, 2020 Mars window) won't work for the next (eg, 2022.) Each mission will need its own orbit (barring happy coincidences.)

Somewhat off-topic, but this particular quirk of orbital mechanics is why I doubt Phobos or Deimos will ever (?) be used as way-stations/depots on the way to Mars surface.  Only twice per Martian year would it be possible to arrive at Mars and capture into an orbital plane aligned with the moons... and how often would those arrival windows synchronise with the Earth-Mars synodic cycle?  You might be able to get around this by performing multiple plane change maneuvers whilst aero-capturing into Martian orbit, but there would have to be an upper limit to how great a plane change you could perform that way.
Well, I'm going to wander OT with you into orbital mechanics but for on topic reasons. This has very much to do with refueling strategies and budgets for plane changes.


Changing planes is considered to be a high energy maneuver and they can be, but they can also be done with much lower energy at the cost of time. Let's look at the worst possible example; turning around and going the other way.


Let's assume the universe is only earth and the orbiting ship and all maneuvers are instantaneous. The ship is in LEO at 7.75kps. It needs go in the opposite direction. The brute force approach is a retro burn of 7.75kps to bring it to a halt, then 7.75kps in the new direction. Total budget is 15.5kps.


Escape velocity is 11.2kps. So for a deltaV of under 3.45kps the ship can raise itself to an apogee of any arbitrary height and then upon return to perigee apply the same dV to circularize it's orbit. Total budget is 6.9kps.


At apogee the ship is moving slow and, using a highly technical term, one 'puff' will stop it dead in its tracks. A second puff will send it back the way it came. Total budget for the most radical possible plane change possible is 6.9kps +2 puffs. Total savings is 8.6kps less two puffs. The higher the apogee, the smaller the puffs.


This applies directly to refueling operations and mission profiles. Canaveral is at 28.5N latitude and the natural orbit inclination from there is the same. With a depot placed at this inclination and a lunar mission launched the same, refueling is, orbitally speaking, straight forward.


The refueled ship then does a burn for TLI at the same inclination and when passing through L1 (I think) will be at its lowest velocity. This is where a plane change is most economical. Want a polar orbit? This is where to do it.


The same principal applies to plane changes on a mars mission. The difference is that the ideal place to change planes will be the Mars-Sun L1 (I think). It might work out to be cheaper heading to lunar L1 and picking a plane change that slings the ship around Luna and off to Mars awaiting further refinement later on, but the numbers are beyond me.


The upshot is settling into co-orbit with Phobos or Demos should not be especially expensive. There will probably be a plane change of some sort anyway.


Phil



Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/19/2020 02:32 pm
Just to answer  : cdebuhr, rakaydos and Thunderscreech as your post are pretty the same:

-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? if you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.
The number being thrown around in the Lunar Starship thread is 40 tons for reuse equipment. No idea how accurate that is, but it's a starting point. With the same tanks, engines, and booster, that would increase payload from 150 to 190 tons... Less than a 33% increase. A SINGLE tanker reuse more than breaks even, putting more fuel into orbit than an expendable stage.

Quote
-In terms of costs we must put the cost of building and maintaining a fleet of tankers into consideration, achieving full and rapid reusability will take some time so while awaiting for that moment expandable would be a better option as an interim solution.
Why a fleet? Just use one or two tankers, and fully reuse, even if it isnt rapid yet? Expendable is NOT a better option.

Quote
-Lowering costs with reusability will require using hardware multiple times and the later is not for near future so expandable option is best sueted coming years.
Why is this "not for the near future?" Using hardware multiple times is already happening- hopper flew twice, SN5 and SN6 will be trading off flights, SN8 will bemaking multiple hops... Your premice is ungrounded in reality.

Quote
-No viable business plan for Mars bound missions will make you depend on governement spending and this one wont require large scale use planned by Elon Musk.
Only if it's too expensive for a billionare to self-fund. The wealth gap in America is unbelievable.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/19/2020 02:47 pm

You might be misunderstanding. There is nothing in a depot, one tank or multiple, that precludes butt to butt refueling. Two entirely separate issues.


As for sending a depot to Mars, there has been discussion in this. First you need to understand that it does not remove the SS need to refuel before leaving earth. It's an alternative to having ISRU propellant production on mars. However, it's always seen as a supplement for early missions until reliable ISRU is on line, and not a replacement. Mars will never be more than a base if it depends on earth for its very ability to return.


Phil

I keep my opinion on  Mars colonisation prospect for me, but getting first human and first permanent settlement on the red planet will require a step by step approach. If we want to get a real plan to do so we can't bet on future developement of new technologies that does not exist yet. this is why interim solutions is required you improve the process while you achieve what can be achieved in a timely manner, the air travel didn't await for the modern jet reaction airliners to be a reality, it took years and years and many accidents to get to what is now air travel.

The above mentioned idea of a multiple disposable tanks that will be joint to a nodal comprtment as is the case for ISS, seems to me practicle for multiple reasons:

-No need for a fleet of tankers and subsequent logistic issues.
-No time waisted for SS departing to Mars.
-Depot could be positioned in any strategic position.
Ahhh. I think I see the problem. It's a matter of religious doctrine and not amenable to reasoned argument - from either side of the question.


Stardust, from what I'm picking up, you are skeptical of the entire approach. This is observation, not criticism.


For the majority of us, we are skeptical of the traditional approach. Again, an observation and not an endorsement.


The two religions are so diametrically at odds that they can never be reconciled no matter how much technical argument is presented. So let's stop this bickering over detail and agree to disagree. THERE IS NOTHING HERE TO GET frakked ABOUT!!


I learned a long time ago that all logic based arguments have at least one predicate - an assumption. What we have here is a conflict of assumptions.


Stardust, the only fault I can assign you is that you have stepped into a den of new spacers and are espousing the doctrine of old space or something close to it. In another time that would get you burned at the stake or an invitation to make love with the Iron Maiden. I promise, we won't do that.


What I would suggest is that you start another discussion with those who share your beliefs. I'd like to believe that we are collectively mature enough to allow others to discuss that which we disagree with although we might want to draw the line at flat earthers 8)


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rsdavis9 on 08/19/2020 03:00 pm
Well, I'm going to wander OT with you into orbital mechanics but for on topic reasons. This has very much to do with refueling strategies and budgets for plane changes.


Changing planes is considered to be a high energy maneuver and they can be, but they can also be done with much lower energy at the cost of time. Let's look at the worst possible example; turning around and going the other way.


Let's assume the universe is only earth and the orbiting ship and all maneuvers are instantaneous. The ship is in LEO at 7.75kps. It needs go in the opposite direction. The brute force approach is a retro burn of 7.75kps to bring it to a halt, then 7.75kps in the new direction. Total budget is 15.5kps.


Escape velocity is 11.2kps. So for a deltaV of under 3.45kps the ship can raise itself to an apogee of any arbitrary height and then upon return to perigee apply the same dV to circularize it's orbit. Total budget is 6.9kps.


At apogee the ship is moving slow and, using a highly technical term, one 'puff' will stop it dead in its tracks. A second puff will send it back the way it came. Total budget for the most radical possible plane change possible is 6.9kps +2 puffs. Total savings is 8.6kps less two puffs. The higher the apogee, the smaller the puffs.


This applies directly to refueling operations and mission profiles. Canaveral is at 28.5N latitude and the natural orbit inclination from there is the same. With a depot placed at this inclination and a lunar mission launched the same, refueling is, orbitally speaking, straight forward.


The refueled ship then does a burn for TLI at the same inclination and when passing through L1 (I think) will be at its lowest velocity. This is where a plane change is most economical. Want a polar orbit? This is where to do it.


The same principal applies to plane changes on a mars mission. The difference is that the ideal place to change planes will be the Mars-Sun L1 (I think). It might work out to be cheaper heading to lunar L1 and picking a plane change that slings the ship around Luna and off to Mars awaiting further refinement later on, but the numbers are beyond me.


The upshot is settling into co-orbit with Phobos or Demos should not be especially expensive. There will probably be a plane change of some sort anyway.


Phil

Why bother with a plane change if you don't have to. The only orbital depot you need is the one in LEO with enough fuel for all the ships going to wherever. Fill them up when the plan is made.

There really isn't a plane change when going interplanetary. As you approach escape velocity the tangential  component drops to zero. The tangential component is what the "plane change" changes.

A depot is simply a collection of ships held together by positioning, ropes, struts whatever. Each individual depot ship will fill one destination ship with butt to butt refueling.

Now if a depot was located in a very high orbit. l1, l2, l3, l4, l5 etc. then the tangential component is low so any plane change is less expensive. But for mars and most destinations this high orbit refueling isn't needed.

EDIT: spelling
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/19/2020 03:19 pm

You might be misunderstanding. There is nothing in a depot, one tank or multiple, that precludes butt to butt refueling. Two entirely separate issues.


As for sending a depot to Mars, there has been discussion in this. First you need to understand that it does not remove the SS need to refuel before leaving earth. It's an alternative to having ISRU propellant production on mars. However, it's always seen as a supplement for early missions until reliable ISRU is on line, and not a replacement. Mars will never be more than a base if it depends on earth for its very ability to return.


Phil

I keep my opinion on  Mars colonisation prospect for me, but getting first human and first permanent settlement on the red planet will require a step by step approach. If we want to get a real plan to do so we can't bet on future developement of new technologies that does not exist yet. this is why interim solutions is required you improve the process while you achieve what can be achieved in a timely manner, the air travel didn't await for the modern jet reaction airliners to be a reality, it took years and years and many accidents to get to what is now air travel.

The above mentioned idea of a multiple disposable tanks that will be joint to a nodal comprtment as is the case for ISS, seems to me practicle for multiple reasons:

-No need for a fleet of tankers and subsequent logistic issues.
-No time waisted for SS departing to Mars.
-Depot could be positioned in any strategic position.
Ahhh. I think I see the problem. It's a matter of religious doctrine and not amenable to reasoned argument - from either side of the question.


Stardust, from what I'm picking up, you are skeptical of the entire approach. This is observation, not criticism.


For the majority of us, we are skeptical of the traditional approach. Again, an observation and not an endorsement.


The two religions are so diametrically at odds that they can never be reconciled no matter how much technical argument is presented. So let's stop this bickering over detail and agree to disagree. THERE IS NOTHING HERE TO GET frakked ABOUT!!


I learned a long time ago that all logic based arguments have at least one predicate - an assumption. What we have here is a conflict of assumptions.


Stardust, the only fault I can assign you is that you have stepped into a den of new spacers and are espousing the doctrine of old space or something close to it. In another time that would get you burned at the stake or an invitation to make love with the Iron Maiden. I promise, we won't do that.


What I would suggest is that you start another discussion with those who share your beliefs. I'd like to believe that we are collectively mature enough to allow others to discuss that which we disagree with although we might want to draw the line at flat earthers 8)


Phil

I got a lot of things that make me skeptical from low maturity technology to financial plan lacking realism and no sustainable viable business plan. :-\
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: wes_wilson on 08/19/2020 03:35 pm

You might be misunderstanding. There is nothing in a depot, one tank or multiple, that precludes butt to butt refueling. Two entirely separate issues.


As for sending a depot to Mars, there has been discussion in this. First you need to understand that it does not remove the SS need to refuel before leaving earth. It's an alternative to having ISRU propellant production on mars. However, it's always seen as a supplement for early missions until reliable ISRU is on line, and not a replacement. Mars will never be more than a base if it depends on earth for its very ability to return.


Phil

I keep my opinion on  Mars colonisation prospect for me, but getting first human and first permanent settlement on the red planet will require a step by step approach. If we want to get a real plan to do so we can't bet on future developement of new technologies that does not exist yet. this is why interim solutions is required you improve the process while you achieve what can be achieved in a timely manner, the air travel didn't await for the modern jet reaction airliners to be a reality, it took years and years and many accidents to get to what is now air travel.

The above mentioned idea of a multiple disposable tanks that will be joint to a nodal comprtment as is the case for ISS, seems to me practicle for multiple reasons:

-No need for a fleet of tankers and subsequent logistic issues.
-No time waisted for SS departing to Mars.
-Depot could be positioned in any strategic position.
Ahhh. I think I see the problem. It's a matter of religious doctrine and not amenable to reasoned argument - from either side of the question.


Stardust, from what I'm picking up, you are skeptical of the entire approach. This is observation, not criticism.


For the majority of us, we are skeptical of the traditional approach. Again, an observation and not an endorsement.


The two religions are so diametrically at odds that they can never be reconciled no matter how much technical argument is presented. So let's stop this bickering over detail and agree to disagree. THERE IS NOTHING HERE TO GET frakked ABOUT!!


I learned a long time ago that all logic based arguments have at least one predicate - an assumption. What we have here is a conflict of assumptions.


Stardust, the only fault I can assign you is that you have stepped into a den of new spacers and are espousing the doctrine of old space or something close to it. In another time that would get you burned at the stake or an invitation to make love with the Iron Maiden. I promise, we won't do that.


What I would suggest is that you start another discussion with those who share your beliefs. I'd like to believe that we are collectively mature enough to allow others to discuss that which we disagree with although we might want to draw the line at flat earthers 8)


Phil

I got a lot of things that make me skeptical from low maturity technology to financial plan lacking realism and no sustainable viable business plan. :-\

That's glass half empty, or some people might say more realistic lol.  I prefer to think they're the team who finally have a real plan for doing this with re-use, powered landing, and funding from starlink.  If they've got it, they're building a new era in human travel.  If they fail, then they'll have advanced the state of the art a long way and eventually someone will take their successes and build on them. 

Either way, spending time on approaches they've clearly discarded is wasteful.  Same reason we're no longer dissecting the nuances of large scale composite construction; they discarded that approach.  Likewise, they long ago discarded the notion of expendable rocketry.  Right, wrong?  Only history will decide, but burning up the forum advocating SpaceX go disposable isn't a great use of page space.

If you really like the expendable idea you should explore the habitat threads.  There's a lot of supportive discussion for the  concept there in terms of leaving them at Mars and using as permanent habitats.  Musk's even hinted that may be the fate of early flights.  You're not wrong that there may be some expendable parts  in the architecture for some time; but you're really misplaced thinking it's going to be their plan in earth orbit since they've clearly stated the opposite.

Just my $0.02,  I think your idea would generate more healthy debate in the habitats thread where people are eager to only fly them once ;)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/19/2020 05:03 pm
Well, I'm going to wander OT with you into orbital mechanics but for on topic reasons. This has very much to do with refueling strategies and budgets for plane changes.


Changing planes is considered to be a high energy maneuver and they can be, but they can also be done with much lower energy at the cost of time. Let's look at the worst possible example; turning around and going the other way.


Let's assume the universe is only earth and the orbiting ship and all maneuvers are instantaneous. The ship is in LEO at 7.75kps. It needs go in the opposite direction. The brute force approach is a retro burn of 7.75kps to bring it to a halt, then 7.75kps in the new direction. Total budget is 15.5kps.


Escape velocity is 11.2kps. So for a deltaV of under 3.45kps the ship can raise itself to an apogee of any arbitrary height and then upon return to perigee apply the same dV to circularize it's orbit. Total budget is 6.9kps.


At apogee the ship is moving slow and, using a highly technical term, one 'puff' will stop it dead in its tracks. A second puff will send it back the way it came. Total budget for the most radical possible plane change possible is 6.9kps +2 puffs. Total savings is 8.6kps less two puffs. The higher the apogee, the smaller the puffs.


This applies directly to refueling operations and mission profiles. Canaveral is at 28.5N latitude and the natural orbit inclination from there is the same. With a depot placed at this inclination and a lunar mission launched the same, refueling is, orbitally speaking, straight forward.


The refueled ship then does a burn for TLI at the same inclination and when passing through L1 (I think) will be at its lowest velocity. This is where a plane change is most economical. Want a polar orbit? This is where to do it.


The same principal applies to plane changes on a mars mission. The difference is that the ideal place to change planes will be the Mars-Sun L1 (I think). It might work out to be cheaper heading to lunar L1 and picking a plane change that slings the ship around Luna and off to Mars awaiting further refinement later on, but the numbers are beyond me.


The upshot is settling into co-orbit with Phobos or Demos should not be especially expensive. There will probably be a plane change of some sort anyway.


Phil

Why bother with a plane change if you don't have to. The only orbital depot you need is the one in LEO with enough fuel for all the ships going to wherever. Fill them up when the plan is made.

There really isn't a plane change when going interplanetary. As you approach escape velocity the tangential  component drops to zero. The tangential component is what the "plane change" changes.

A depot is simply a collection of ships held together by positioning, ropes, struts whatever. Each individual depot ship will fill one destination ship with butt to butt refueling.

Now if a depot was located in a very high orbit. l1, l2, l3, l4, l5 etc. then the tangential component is low so any plane change is less expensive. But for mars and most destinations this high orbit refueling isn't needed.

EDIT: spelling
I see your point on interplanetary. Which also negates the concern about Phobos & Demos.


Plane change is still needed for lunar and GEO. My point that a general purpose depot doing fine in any convenient LEO still holds.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rsdavis9 on 08/19/2020 05:05 pm

I see your point on interplanetary. Which also negates the concern about Phobos & Demos.


Plane change is still needed for lunar and GEO. My point that a general purpose depot doing fine in any convenient LEO still holds.

Moon is basically/almost interplanetary.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: AJW on 08/19/2020 11:32 pm
-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? If you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.

-In terms of costs we must put the cost of building and maintaining a fleet of tankers into consideration, achieving full and rapid reusability will take some time so while awaiting for that moment expandable would be a better option as an interim solution.
 

Star-Dust, you have aspirations of sending rockets to Mars, that is admirable, and if rockets were fueled with persistence, you might already be in orbit.  My unsolicited advice to you is that like early aviators, take one step at a time and develop a firm grasp of the fundamentals before taking that giant leap. 

A great example is your lack of understanding that SH can’t deliver your proposed depot to orbit.  This is an easy mistake to make, but as a result of this error, you have been now forced to fabricate this new expendable stage.  You deride the cost of maintaining tankers, but now somehow building expendable second stages comes without a tremendous cost?  That cost comes in many forms, not just in dollars, but also in manufacturing time and a workforce that is now dedicated to building hardware that will be thrown away after every flight.  This is very inefficient. 

If you have paid attention to the work at BC, you can see that constructing a SS is a multi-month process.  How is SS minus wings and the payload section any different from your proposed second stage?  Are you really willing to wait months between depot launches?  Have you done any analysis of the cost to dispose of five stages vs. maintenance of a single tanker?  Now work the other side of the problem.  You have your depot, but without the stage you just threw away, you can’t change orbits or dock with other depots.  You will need power to keep the fuels at the proper pressure.  Where will this come from?  Are you now going to add solar arrays and compressors that you also dispose of along with communications equipment, RCS, batteries, fuel pumps, etc.?  How will you de-orbit your empty depot?

My recommendation is to stick with this first step.  Perhaps spend some time studying the capabilities of SH and SS so you can avoid further simple errors.  Look at necessary capabilities for that second stage you are proposing compared to a SS Tanker/Depot concept. Again, before you can convince us that you have a viable vision for how to get to Mars and back, at least do the minimum legwork and develop a viable plan for how to get just a single Starship worth of fuel to LEO without one year required to build your five expendable second stages, along with 30 or more Raptors that you plan to dispose of.  Yes, this will take some discipline, and you just might succeed in this first step and either make a compelling case for your depots, or garner the knowledge and understanding as to why so many who have studied this problem, some for decades, disagree with you.  Best of luck.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: envy887 on 08/20/2020 12:51 am
...
Escape velocity is 11.2kps. So for a deltaV of under 3.45kps the ship can raise itself to an apogee of any arbitrary height and then upon return to perigee apply the same dV to circularize it's orbit. Total budget is 6.9kps.
There really isn't a plane change when going interplanetary. As you approach escape velocity the tangential  component drops to zero. The tangential component is what the "plane change" changes.
...

That's not accurate. All departure burns accelerate the vehicle prograde relative to Earth, increasing only the tangential component of the velocity. If your LEO orbit plane is parallel to the Sun-Earth line, you have a problem, because you need to go in the direction the Earth is travelling around the Sun, which is 90 degrees to the Earth-Sun line. That requires a plane change because at no point in the orbit does your velocity vector point in that direction.

But you don't need to raise the entire depot far from Earth to change planes. Just let nodal precession do that for you, changing altitude slightly to take advantage of different precession rates.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/20/2020 02:00 am
-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? If you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.

-In terms of costs we must put the cost of building and maintaining a fleet of tankers into consideration, achieving full and rapid reusability will take some time so while awaiting for that moment expandable would be a better option as an interim solution.
 

Star-Dust, you have aspirations of sending rockets to Mars, that is admirable, and if rockets were fueled with persistence, you might already be in orbit.  My unsolicited advice to you is that like early aviators, take one step at a time and develop a firm grasp of the fundamentals before taking that giant leap. 

A great example is your lack of understanding that SH can’t deliver your proposed depot to orbit.  This is an easy mistake to make, but as a result of this error, you have been now forced to fabricate this new expendable stage.  You deride the cost of maintaining tankers, but now somehow building expendable second stages comes without a tremendous cost?  That cost comes in many forms, not just in dollars, but also in manufacturing time and a workforce that is now dedicated to building hardware that will be thrown away after every flight.  This is very inefficient. 

If you have paid attention to the work at BC, you can see that constructing a SS is a multi-month process.  How is SS minus wings and the payload section any different from your proposed second stage?  Are you really willing to wait months between depot launches?  Have you done any analysis of the cost to dispose of five stages vs. maintenance of a single tanker?  Now work the other side of the problem.  You have your depot, but without the stage you just threw away, you can’t change orbits or dock with other depots.  You will need power to keep the fuels at the proper pressure.  Where will this come from?  Are you now going to add solar arrays and compressors that you also dispose of along with communications equipment, RCS, batteries, fuel pumps, etc.?  How will you de-orbit your empty depot?

My recommendation is to stick with this first step.  Perhaps spend some time studying the capabilities of SH and SS so you can avoid further simple errors.  Look at necessary capabilities for that second stage you are proposing compared to a SS Tanker/Depot concept. Again, before you can convince us that you have a viable vision for how to get to Mars and back, at least do the minimum legwork and develop a viable plan for how to get just a single Starship worth of fuel to LEO without one year required to build your five expendable second stages, along with 30 or more Raptors that you plan to dispose of.  Yes, this will take some discipline, and you just might succeed in this first step and either make a compelling case for your depots, or garner the knowledge and understanding as to why so many who have studied this problem, some for decades, disagree with you.  Best of luck.
This is good advice. The best way I can think of educating yourself is to go back to the earliest SS thread and start reading. Sounds like quite a task but it is only if you let it. Best damn Science Fiction Fact I've read in a long time.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Pahimarus on 08/20/2020 02:32 am
...
Escape velocity is 11.2kps. So for a deltaV of under 3.45kps the ship can raise itself to an apogee of any arbitrary height and then upon return to perigee apply the same dV to circularize it's orbit. Total budget is 6.9kps.
There really isn't a plane change when going interplanetary. As you approach escape velocity the tangential  component drops to zero. The tangential component is what the "plane change" changes.
...

That's not accurate. All departure burns accelerate the vehicle prograde relative to Earth, increasing only the tangential component of the velocity. If your LEO orbit plane is parallel to the Sun-Earth line, you have a problem, because you need to go in the direction the Earth is travelling around the Sun, which is 90 degrees to the Earth-Sun line. That requires a plane change because at no point in the orbit does your velocity vector point in that direction.

But you don't need to raise the entire depot far from Earth to change planes. Just let nodal precession do that for you, changing altitude slightly to take advantage of different precession rates.

So I've been lurking on this thread for awhile and this is a critical point that has come up several times around the depot concept.

The key question is does launching from an inclined orbit have a meaningful effect on interplanetary transfers?

If no, then you can have a general purpose depot in LEO. If yes, then you can only have mission specific depots. I'm not sure I've seen a clear consensus in this thread and I've been doing some noodling and reading so I'm going to take a stab at it.

Caveat: I am entirely kerbal trained plus I work in the soft sciences and math makes me slightly nauseated (insert Luke walking into the cantina gif here) so take this for what it is worth.

I think the answer is yes and no. Obviously you can launch to Mars from an inclined orbit. Three vehicles just did it last month. I highly doubt they spent the dv to plane change into equatorial orbits.

However I think your inclined orbit has to be pointed in the right direction (AN and DN aligned in a certain way relative to your intended ejection angle).

This is no big deal for a specific mission. Do some maths and launch your ships at the right time of day basically (though as previously discussed you'd have limited launch windows). But I really do think it means you can't easily have a depot in an inclined orbit to service multiple different interplanetary transfers.

You also want it in LEO for oberth.

However, despair not general purpose depot proponents.

It occurs to me that the problem fundamentally is inclined orbits which occur because KSC is not on the equator and can't easily be moved there.

But if one was an ambitious billionaire planning on turning an oil rig into a launch platform... Well now...<stokes beard thoughtfully>...
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: armchairfan on 08/20/2020 02:38 am
-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? if you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.
I think that you'll gain more insight if you run such what-if exercises yourself.

I suggest Silverbird Astronautics Launch Vehicle Performance Calculator (http://www.silverbirdastronautics.com/LVperform.html). Unfortunately, the SS/SH stack isn't listed so you'll have to use the "User-defined" option.

Here are some reasonable suggestions to get you going but they are by no means definitive.

Number of Stages: 2
Strap-on Boosters? No
Dry Mass (kg) 1st stage: 220000 , 2nd stage 135000 (both #s include landing propellant)
Propellant (kg) 1st stage 3400000 , 2nd stage 1200000
Thrust (KN) 1st stage 56000, 2nd stage 11000
Isp (s) 1st stage 330, 2nd stage 350
Default Propellant Residuals? Yes
Restartable Upper Stage? Yes
Payload Fairing: 0 and 0
Launch Site: Cape Canaveral (USA)
Destination:
Earth Orbit
Apogee (km): 300
Perigee (km): 300
Inclination (deg): 28.4
Trajectory: Optimal

"Calculate" yields an estimated payload of about 100 tonnes. SpaceX hopes to get that to 150 tonnes by various improvements (and unlike me, they don't have to guesstimate what the vehicle specs are). Leave off the second stage and see what SH can do by itself. You won't be impressed.

The web-page will even estimate the payload for an escape trajectory (try Moon @ C3=-2 or Mars @ C3=13 km^2/s^2). Spoiler alert: it's 0. As everyone knows, you need to refuel Starship to go beyond Earth orbit and that means lifting up to 1200 tonnes of propellant into LEO. So what's the best way to do that?

You could use expendable tankers which would gain you back the landing propellant (15 tonnes) and the various other items needed for landing (probably around 25 tonnes). So expendable tankers might carry 40% more propellant than reusable ones. Even ignoring the significant cost of expending the tankers, do you really think that you can build two expendable tankers in less time than you can launch a single tanker three times?

Quote
I got a lot of things that make me skeptical from low maturity technology to financial plan lacking realism and no sustainable viable business plan. :-\

[rant]
Fortunately for SpaceX, they don't have to convince you. They've already got investors who see the value in developing Starship and other technologies even if the motivation might not be for Mars. And, they've got the world's 4th richest person who calls the shots and is motivated to make it happen. Perhaps you've noticed that there's a lot going on in Boca Chica and elsewhere these days. Maybe cities on Mars don't pan out but Elon's giving it a shot and I for one wouldn't bet against him.

And as a Space advocate *and* US taxpayer, the bang for the buck of SpaceX's vision is off-scale high.
[/rant]
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: armchairfan on 08/20/2020 05:08 am
But you don't need to raise the entire depot far from Earth to change planes. Just let nodal precession do that for you, changing altitude slightly to take advantage of different precession rates.

However I think your inclined orbit has to be pointed in the right direction (AN and DN aligned in a certain way relative to your intended ejection angle).

As an exercise and if I've done the math right -- a big ask -- a 340 km circular orbit at 28.4 inclination (Cape Canaveral) will precess at such a rate as to be aligned toward Mars every 26 months; i.e. when the next launch window rolls around. While that's a fairly low orbit, (I'm guessing that) you can probably keep it going with just the propellant that you'd otherwise lose to boil-off.

This probably only makes sense if you're going to use an entire synod sending tankers to a depot(s) in preparation for a vast fleet of starships leaving all at once.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Slarty1080 on 08/20/2020 09:28 am
-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? If you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.

-In terms of costs we must put the cost of building and maintaining a fleet of tankers into consideration, achieving full and rapid reusability will take some time so while awaiting for that moment expandable would be a better option as an interim solution.
 

Star-Dust, you have aspirations of sending rockets to Mars, that is admirable, and if rockets were fueled with persistence, you might already be in orbit.  My unsolicited advice to you is that like early aviators, take one step at a time and develop a firm grasp of the fundamentals before taking that giant leap. 

A great example is your lack of understanding that SH can’t deliver your proposed depot to orbit.  This is an easy mistake to make, but as a result of this error, you have been now forced to fabricate this new expendable stage.  You deride the cost of maintaining tankers, but now somehow building expendable second stages comes without a tremendous cost?  That cost comes in many forms, not just in dollars, but also in manufacturing time and a workforce that is now dedicated to building hardware that will be thrown away after every flight.  This is very inefficient. 

If you have paid attention to the work at BC, you can see that constructing a SS is a multi-month process.  How is SS minus wings and the payload section any different from your proposed second stage?  Are you really willing to wait months between depot launches?  Have you done any analysis of the cost to dispose of five stages vs. maintenance of a single tanker?  Now work the other side of the problem.  You have your depot, but without the stage you just threw away, you can’t change orbits or dock with other depots.  You will need power to keep the fuels at the proper pressure.  Where will this come from?  Are you now going to add solar arrays and compressors that you also dispose of along with communications equipment, RCS, batteries, fuel pumps, etc.?  How will you de-orbit your empty depot?

My recommendation is to stick with this first step.  Perhaps spend some time studying the capabilities of SH and SS so you can avoid further simple errors.  Look at necessary capabilities for that second stage you are proposing compared to a SS Tanker/Depot concept. Again, before you can convince us that you have a viable vision for how to get to Mars and back, at least do the minimum legwork and develop a viable plan for how to get just a single Starship worth of fuel to LEO without one year required to build your five expendable second stages, along with 30 or more Raptors that you plan to dispose of.  Yes, this will take some discipline, and you just might succeed in this first step and either make a compelling case for your depots, or garner the knowledge and understanding as to why so many who have studied this problem, some for decades, disagree with you.  Best of luck.
This is good advice. The best way I can think of educating yourself is to go back to the earliest SS thread and start reading. Sounds like quite a task but it is only if you let it. Best damn Science Fiction Fact I've read in a long time.
It is not immediately clear to me what Stardust meant here. Expandable or expendable?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: armchairfan on 08/20/2020 10:20 am
It is not immediately clear to me what Stardust meant here. Expandable or expendable?
Good point. I read it as "expendable" ("spell-checked" to "expandable") based on the earlier "drop-tank" idea. However, re-reading, I think that expandable actually is the intended meeting. So ...

If the Starship tanker uses the same outer mold line as the other Starship variants, it's pretty much expandable as is. Just relocate the tank bulkheads upward into the otherwise unused payload section. That might not even require more mass. Elon recently tweeted that there's 1000 cubic meters of useable volume in the fairing. That'd be 1000 tonnes of additional propellant capacity, which is *way* more than Starship could lift.

Or create a single tanker variant by removing three rings from the payload section and adding two of them to the LOX tank and one to the LCH4 tank. That's more than 300 tons of additional propellant capacity. Then only fill the tanks with as much propellant as you can take to the destination orbit. An optimized tanker, which Elon tweeted about a while back, would remove more rings from the nose section and look stubbier.

BTW, this isn't a new idea; it's been discussed many times. There's an incredible amount of information on NSF though it can take a while to wade through it if you're just getting started.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Pahimarus on 08/20/2020 11:57 am
Quote from: armchairfan

As an exercise and if I've done the math right -- a big ask -- a 340 km circular orbit at 28.4 inclination (Cape Canaveral) will precess at such a rate as to be aligned toward Mars every 26 months; i.e. when the next launch window rolls around. While that's a fairly low orbit, (I'm guessing that) you can probably keep it going with just the propellant that you'd otherwise lose to boil-off.

This probably only makes sense if you're going to use an entire synod sending tankers to a depot(s) in preparation for a vast fleet of starships leaving all at once.

Thanks. I was trying to understand if such an orbit existed or not.

This was discussed earlier in the thread and I realized that I missed the page where it came to a conclusion. So I won't continue necro'ing the discussion beyond to offer my own $0.02. Initially it will make more sense to just launch a train of tanker starships (say 1 every 12-24 hr based on your twice daily launch window and presumably some time to do refueling ops for each tanker) to rendezvous with the mission starship shortly before the intended launch. So you'd only spend a few days to a week on orbit refueling.

However, when sending many many starships that launch cadence doesn't seem sustainable to me over a short mars transfer window even with ksc, bc, and maybe an offshore platform or two pitching in. So an accumulation tanker in a carefully selected orbit like you calculated would make sense to allow you to preposition fuel for a launch window. By this time the use case will be existent not theoretical and launch costs would have been massively reduced so one could justify the added costs of on orbit construction for a dedicated facility.

That said it may prove out that a rapid reuse and launch cadence is easier to solve than in space depot construction. It will certainly need to be if point to point is going to be a serious proposition.

Either way holy smokes are you looking at a lot of launches for a mars bound fleet.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rsdavis9 on 08/20/2020 12:08 pm
...
Escape velocity is 11.2kps. So for a deltaV of under 3.45kps the ship can raise itself to an apogee of any arbitrary height and then upon return to perigee apply the same dV to circularize it's orbit. Total budget is 6.9kps.
There really isn't a plane change when going interplanetary. As you approach escape velocity the tangential  component drops to zero. The tangential component is what the "plane change" changes.
...

That's not accurate. All departure burns accelerate the vehicle prograde relative to Earth, increasing only the tangential component of the velocity. If your LEO orbit plane is parallel to the Sun-Earth line, you have a problem, because you need to go in the direction the Earth is travelling around the Sun, which is 90 degrees to the Earth-Sun line. That requires a plane change because at no point in the orbit does your velocity vector point in that direction.

But you don't need to raise the entire depot far from Earth to change planes. Just let nodal precession do that for you, changing altitude slightly to take advantage of different precession rates.

Trying to understand what you said...

I should have said as you leave the gravity well tangential velocity approaches zero.
What do you mean as parallel?
As I understand it the plane of LEO orbit should have intersecting nodes in the direction of the interplanetary object.
This is hard to explain!
We have the plane of LEO orbit.
We have the direction of where we want to go.
The direction we want to go should be in the plane of the LEO orbit.

EDIT:

Another way to understand this. Take an extreme example(not efficient).
A polar orbit done at the equinox. It is perpendicular to the sun earth plane. Twice per year the plane will align with where you want to go (the direction will be in the plane). So this plane will not be correct for many 2 year launch oppurtunities to mars because this plane is more or less fixed in space.

Now of course LEO orbits precess relative to the stars. What we want for mars is a orbit that precesses just enough every 2 years.

Or just launch the depot in the correct orbital plane for the upcoming departure window.   
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/20/2020 02:32 pm
This might be useful.

https://en.m.wikipedia.org/wiki/File:Orbit1.svg

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rsdavis9 on 08/20/2020 03:07 pm
This might be useful.

https://en.m.wikipedia.org/wiki/File:Orbit1.svg

Thats fine but I didn't want to use those terms because they are relative to earths orbit and the first point of ares.

Various destinations depart dramatically from this coordinate system.
I.E. moon, pluto
The rest of the them the destination direction pretty much resides in the ecliptic plane.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/20/2020 06:19 pm
-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? if you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.
I think that you'll gain more insight if you run such what-if exercises yourself.

I suggest Silverbird Astronautics Launch Vehicle Performance Calculator (http://www.silverbirdastronautics.com/LVperform.html). Unfortunately, the SS/SH stack isn't listed so you'll have to use the "User-defined" option.

Here are some reasonable suggestions to get you going but they are by no means definitive.

Number of Stages: 2
Strap-on Boosters? No
Dry Mass (kg) 1st stage: 220000 , 2nd stage 135000 (both #s include landing propellant)
Propellant (kg) 1st stage 3400000 , 2nd stage 1200000
Thrust (KN) 1st stage 56000, 2nd stage 11000
Isp (s) 1st stage 330, 2nd stage 350
Default Propellant Residuals? Yes
Restartable Upper Stage? Yes
Payload Fairing: 0 and 0
Launch Site: Cape Canaveral (USA)
Destination:
Earth Orbit
Apogee (km): 300
Perigee (km): 300
Inclination (deg): 28.4
Trajectory: Optimal

"Calculate" yields an estimated payload of about 100 tonnes. SpaceX hopes to get that to 150 tonnes by various improvements (and unlike me, they don't have to guesstimate what the vehicle specs are). Leave off the second stage and see what SH can do by itself. You won't be impressed.

The web-page will even estimate the payload for an escape trajectory (try Moon @ C3=-2 or Mars @ C3=13 km^2/s^2). Spoiler alert: it's 0. As everyone knows, you need to refuel Starship to go beyond Earth orbit and that means lifting up to 1200 tonnes of propellant into LEO. So what's the best way to do that?

You could use expendable tankers which would gain you back the landing propellant (15 tonnes) and the various other items needed for landing (probably around 25 tonnes). So expendable tankers might carry 40% more propellant than reusable ones. Even ignoring the significant cost of expending the tankers, do you really think that you can build two expendable tankers in less time than you can launch a single tanker three times?

Quote
I got a lot of things that make me skeptical from low maturity technology to financial plan lacking realism and no sustainable viable business plan. :-\

[rant]
Fortunately for SpaceX, they don't have to convince you. They've already got investors who see the value in developing Starship and other technologies even if the motivation might not be for Mars. And, they've got the world's 4th richest person who calls the shots and is motivated to make it happen. Perhaps you've noticed that there's a lot going on in Boca Chica and elsewhere these days. Maybe cities on Mars don't pan out but Elon's giving it a shot and I for one wouldn't bet against him.

And as a Space advocate *and* US taxpayer, the bang for the buck of SpaceX's vision is off-scale high.
[/rant]
A useful metric I've come up with is the increase in tank volume allowed by one ton of mass savings. One ton of propellant, O2 and CH4 at 3.6:1, allows a consolidated tank stretch of 0.016m. Using this saves a lot of math.


So, when discussing a tanker intended to become a no return depot, every ton of heatshield, fins & mechanism and landing legs saved allow a 0.016m tank stretch while  allowing maximum propellant on board and keeping mass constant. Reducing propellant load allows greater depot tank volume at the cost of less propellant delivered on that launch.


All the other variables, max mass to LEO and  using different orbits being a couple biggies, are still there but this helps give an easily calculated apples to apples baseline.


I don't exactly hate math, but I do struggle.


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: yg1968 on 08/20/2020 06:22 pm
I am highly skeptical of this information but there is a guy on Twitter that says that lunar Starship requires 12 refueling flights in order to get to the NRHO. He says that he got this information from someone involved in the HLS program at MSFC.

I would expect only one or two refueling flights would be required, not 12. What is a realistic number of re-fueling missions required for lunar Starship to get to NRHO?

https://twitter.com/Kerb2024/status/1296485561306419203
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/20/2020 06:52 pm
there is a guy on Twitter that says that lunar Starship requires 12 refueling flights in order to get to the NRHO. He says that he got this information from someone involved in the HLS program at MSFC.

I assume they just went: Starship holds 1,200 tonnes of propellant. If one Starship can launch 100t into LEO, then 1200/100=12 launches. There's no analysis of NRHO, or delta-v, or anything deeper than that.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/20/2020 06:55 pm
Quote from: armchairfan

As an exercise and if I've done the math right -- a big ask -- a 340 km circular orbit at 28.4 inclination (Cape Canaveral) will precess at such a rate as to be aligned toward Mars every 26 months; i.e. when the next launch window rolls around. While that's a fairly low orbit, (I'm guessing that) you can probably keep it going with just the propellant that you'd otherwise lose to boil-off.

This probably only makes sense if you're going to use an entire synod sending tankers to a depot(s) in preparation for a vast fleet of starships leaving all at once.

Thanks. I was trying to understand if such an orbit existed or not.

This was discussed earlier in the thread and I realized that I missed the page where it came to a conclusion. So I won't continue necro'ing the discussion beyond to offer my own $0.02. Initially it will make more sense to just launch a train of tanker starships (say 1 every 12-24 hr based on your twice daily launch window and presumably some time to do refueling ops for each tanker) to rendezvous with the mission starship shortly before the intended launch. So you'd only spend a few days to a week on orbit refueling.

However, when sending many many starships that launch cadence doesn't seem sustainable to me over a short mars transfer window even with ksc, bc, and maybe an offshore platform or two pitching in. So an accumulation tanker in a carefully selected orbit like you calculated would make sense to allow you to preposition fuel for a launch window. By this time the use case will be existent not theoretical and launch costs would have been massively reduced so one could justify the added costs of on orbit construction for a dedicated facility.

That said it may prove out that a rapid reuse and launch cadence is easier to solve than in space depot construction. It will certainly need to be if point to point is going to be a serious proposition.

Either way holy smokes are you looking at a lot of launches for a mars bound fleet.
Yup, a buttload of launches. But a depot(s) doesn't have to involve in space construction.


A standard SS in LEO for example, when filled by tankers would hold enough propellant to support one SS going to Mars. If the mars fleet is 10 ships, use 10 SS's accumulating fuel, which can then return to earth.


For another example, strip everything unnecessary and increase capacity for a permanent no return depot.  My very rough calculation shows this could fill 1.2 mars bound SS's. If it is structurally possible to use the three remaining rings as tankage and stretch an SS by an estimate five additional rings the depot could tank up two mars bound ships. Of course it could not launch with all this tankage filled with propellant.


This does not change the number of tankers to orbit but it does add safety by limiting each mars bound ship to one refueling and it avoids the difficulty of on orbit construction.


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: eriblo on 08/20/2020 07:17 pm
I am highly skeptical of this information but there is a guy on Twitter that says that lunar Starship requires 12 refueling flights in order to get to the NRHO. He says that he got this information from someone involved in the HLS program at MSFC.

I would expect only one or two refueling flights would be required, not 12. What is a realistic number of re-fueling missions required for lunar Starship to get to NRHO?

https://twitter.com/Kerb2024/status/1296485561306419203
Quick check on wikipedia: 3.2km/s TLI from LEO, 0.43km/s powered flyby and insertion into NRHO. Lets say standard Starship is 120t empty with 100t payload to LEO and that payload mass can be traded for residual fuel 1:1. Lets use 365 for average in space Isp.

Maths:
Empty Starship from LEO to Gateway and back to reentry/aerobreaking is 3.2+2*0.43=4.06km/s.
Rocket equation gives initial mass as 373t, so 253t of fuel or 100t residual from initial launch and two refuelings with 100t and 53t respectively. Full refueling of 200t to initial mass of 420t gives 15t of payload to Gateway and back or 17t payload and empty back.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/20/2020 07:56 pm
...
Escape velocity is 11.2kps. So for a deltaV of under 3.45kps the ship can raise itself to an apogee of any arbitrary height and then upon return to perigee apply the same dV to circularize it's orbit. Total budget is 6.9kps.
There really isn't a plane change when going interplanetary. As you approach escape velocity the tangential  component drops to zero. The tangential component is what the "plane change" changes.
...

That's not accurate. All departure burns accelerate the vehicle prograde relative to Earth, increasing only the tangential component of the velocity. If your LEO orbit plane is parallel to the Sun-Earth line, you have a problem, because you need to go in the direction the Earth is travelling around the Sun, which is 90 degrees to the Earth-Sun line. That requires a plane change because at no point in the orbit does your velocity vector point in that direction.

But you don't need to raise the entire depot far from Earth to change planes. Just let nodal precession do that for you, changing altitude slightly to take advantage of different precession rates.

So I've been lurking on this thread for awhile and this is a critical point that has come up several times around the depot concept.

The key question is does launching from an inclined orbit have a meaningful effect on interplanetary transfers?

If no, then you can have a general purpose depot in LEO. If yes, then you can only have mission specific depots. I'm not sure I've seen a clear consensus in this thread and I've been doing some noodling and reading so I'm going to take a stab at it.

Caveat: I am entirely kerbal trained plus I work in the soft sciences and math makes me slightly nauseated (insert Luke walking into the cantina gif here) so take this for what it is worth.

I think the answer is yes and no. Obviously you can launch to Mars from an inclined orbit. Three vehicles just did it last month. I highly doubt they spent the dv to plane change into equatorial orbits.

However I think your inclined orbit has to be pointed in the right direction (AN and DN aligned in a certain way relative to your intended ejection angle).

This is no big deal for a specific mission. Do some maths and launch your ships at the right time of day basically (though as previously discussed you'd have limited launch windows). But I really do think it means you can't easily have a depot in an inclined orbit to service multiple different interplanetary transfers.

You also want it in LEO for oberth.

However, despair not general purpose depot proponents.

It occurs to me that the problem fundamentally is inclined orbits which occur because KSC is not on the equator and can't easily be moved there.

But if one was an ambitious billionaire planning on turning an oil rig into a launch platform... Well now...<stokes beard thoughtfully>...
An extra point to consider. Earth is tipped 23.5 deg to our orbital plane so an equatorial launch faces the same limitations of node alignment with the ecliptic.


I don't think there is any place on earth without this problem. It's something we have to live with until we can afford to take it to the shop for an axis alignment


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/20/2020 08:04 pm
The orbital plane is relatively fixed as Earth moves around the sun, hence it will move in and out of sync with the ecliptic. So the orbital plane of a a particular LEO orbit will have two opportunities per year to launch into an interplanetary trajectory without a massive plane-change manoeuvre.
this particular quirk of orbital mechanics is why I doubt Phobos or Deimos will ever (?) be used as way-stations/depots on the way to Mars surface.  Only twice per Martian year would it be possible to arrive at Mars and capture into an orbital plane aligned with the moons... and how often would those arrival windows synchronise with the Earth-Mars synodic cycle?  You might be able to get around this by performing multiple plane change maneuvers whilst aero-capturing into Martian orbit, but there would have to be an upper limit to how great a plane change you could perform that way.

Just one plane change.

You aero-capture into a very high Mars orbit, putting apoapsis right on the edge of the Hill Sphere (or even fractionally beyond), then do a plane change at apoapsis to match the destination orbital plane. At this distance, the delta-v cost of even a 90 degree plane change is in the low hundreds of m/s. On the next pass, do a second smaller aero-capture to lower apoapsis to match the altitude of the target orbit. (Then do your circularisation burn when the orbital phasing catches up to the target.) Adds about two weeks or so of additional travel for the passengers. Not a deal-breaker if the ship has sustained months-long interplanetary flight.

You might be able to perform a plane change during the aero-capture, but it's not necessary. And with Mars' variable atmosphere, doing a high plane-change is probably less risky.

If Phobos or Deimos have tethers, you can get away with one aero-capture. There's a point on the tethers that matches hyperbolic velocity, so capturing at near-hyperbolic velocity is possible.

(Note that this also applied to docking with Mars space elevators, only with the added fun of oscillating the elevator to avoid Phobos crashing into it. The space elevator is in Mars' equatorial plane (roughly), which is at 25 degrees to its solar orbital plane. You need at least one plane change manoeuvre.)



You can do the same thing when returning to Earth. Do a burn from Phobos (say) to the edge of the Hill Sphere. Do a plane-change burn at apoapsis, where it costs virtually nothing. Then on periapsis, do the interplanetary burn. You preserve the velocity from your boost into high-orbit as excess velocity when you swing back near the planet, so Mr. Oberth is happy. And your interplanetary burn also happens while low, so he's even happier.

Earth orbit is a little more complex because you want to minimise passes through the Van Allen belts. But in theory, you can do the same when leaving Earth from a 28 degree inclination "universal depot" that is even 90 degrees out-of-sync with the exit plane. Costs you two extra passes through the belts, but you have a "storm shelter" on any interplanetary ship, use it.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: eriblo on 08/20/2020 08:09 pm
Some smart people with names you might recognize have put some relevant musings on paper.

Selinanboondocks blog post. (https://selenianboondocks.com/2018/02/aas-paper-review-practical-methodologies-for-low-delta-v-penalty-on-time-departures-to-arbitrary-interplanetary-destinations-from-a-medium-inclination-low-earth-orbit-depot/)

https://selenianboondocks.com/wp-content/uploads/2018/02/AAS-17-696-1.pdf

https://selenianboondocks.com/wp-content/uploads/2018/09/RAAN-Agnostic_3-BurnPaperV2_AAS-18-447-1.pdf

:)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/20/2020 08:14 pm
However I think your inclined orbit has to be pointed in the right direction (AN and DN aligned in a certain way relative to your intended ejection angle).
This is no big deal for a specific mission. Do some maths and launch your ships at the right time of day basically (though as previously discussed you'd have limited launch windows). But I really do think it means you can't easily have a depot in an inclined orbit to service multiple different interplanetary transfers.
An extra point to consider. Earth is tipped 23.5 deg to our orbital plane so an equatorial launch faces the same limitations of node alignment with the ecliptic.
I don't think there is any place on earth without this problem. It's something we have to live with until we can afford to take it to the shop for an axis alignment

As Pahimarus correctly notes, a launch site effectively rotates its orbital plane 360 degrees every day. Therefore there's a launch window every day (or two) that can put you into an orbit that matches your desired exit plane.

The issue with permanent depots is changing that orbital plane after it's in orbit.

But if "propellant is cheap", then doing the low-high-low manoeuvre gives you a cheap plane-change, provided you can handle the two extra passes through the VA belts.

[edit: eriblo - Yeah, it was either Jon Goff or Hollister David where I first read about low-high-low plane-changes.]
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: yg1968 on 08/20/2020 08:57 pm
I am highly skeptical of this information but there is a guy on Twitter that says that lunar Starship requires 12 refueling flights in order to get to the NRHO. He says that he got this information from someone involved in the HLS program at MSFC.

I would expect only one or two refueling flights would be required, not 12. What is a realistic number of re-fueling missions required for lunar Starship to get to NRHO?

https://twitter.com/Kerb2024/status/1296485561306419203
Quick check on wikipedia: 3.2km/s TLI from LEO, 0.43km/s powered flyby and insertion into NRHO. Lets say standard Starship is 120t empty with 100t payload to LEO and that payload mass can be traded for residual fuel 1:1. Lets use 365 for average in space Isp.

Maths:
Empty Starship from LEO to Gateway and back to reentry/aerobreaking is 3.2+2*0.43=4.06km/s.
Rocket equation gives initial mass as 373t, so 253t of fuel or 100t residual from initial launch and two refuelings with 100t and 53t respectively. Full refueling of 200t to initial mass of 420t gives 15t of payload to Gateway and back or 17t payload and empty back.

Thanks! I am not engineer, so I am not sure that I fully understand, you are saying that two refueling missions should be enough to deliver 15mt to the Moon and back (or 17mt one way to the Moon)?

Would it be possible for lunar Starship to get to the Moon (through NRHO) and back to LEO (through NRHO) without any re-fueling?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: LMT on 08/20/2020 09:18 pm
If Phobos or Deimos have tethers, you can get away with one aero-capture. There's a point on the tethers that matches hyperbolic velocity, so capturing at near-hyperbolic velocity is possible.

Capture orbit lacks hyperbolic trajectory velocity, by definition.  State your goal, terms and steps more clearly, if you want to claim something.  You made an untrue tether claim (https://forum.nasaspaceflight.com/index.php?topic=51387.msg2120985#msg2120985) recently.

this also applied to docking with Mars space elevators, only with the added fun of oscillating the elevator to avoid Phobos crashing into it.

No, the MSE-oscillation notion is outdated.  As you've seen, Dr. Lades' Mars Lift (http://www.lakematthew.com/press/press-release-september-18-2017/) calculation demonstrated that an MSE can float off the equatorial plane, never touching it.  No oscillation is required, which is good, because no engineer knows how to manage the merely notional Phobos oscillation.  1 (https://forum.nasaspaceflight.com/index.php?topic=37667.msg1951870#msg1951870) 2 (https://forum.nasaspaceflight.com/index.php?topic=37667.msg1952008#msg1952008) 3 (https://forum.nasaspaceflight.com/index.php?topic=37667.msg1952021#msg1952021)

Image:  Numerical solutions for "Mars Lift" MSE tether curve.  High specific strength in green, low in purple.  Phobos orbit range in brown.  Dr. Martin Lades, ISEC.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: eriblo on 08/20/2020 11:28 pm
I am highly skeptical of this information but there is a guy on Twitter that says that lunar Starship requires 12 refueling flights in order to get to the NRHO. He says that he got this information from someone involved in the HLS program at MSFC.

I would expect only one or two refueling flights would be required, not 12. What is a realistic number of re-fueling missions required for lunar Starship to get to NRHO?

[tweet]
Quick check on wikipedia: 3.2km/s TLI from LEO, 0.43km/s powered flyby and insertion into NRHO. Lets say standard Starship is 120t empty with 100t payload to LEO and that payload mass can be traded for residual fuel 1:1. Lets use 365 for average in space Isp.

Maths:
Empty Starship from LEO to Gateway and back to reentry/aerobreaking is 3.2+2*0.43=4.06km/s.
Rocket equation gives initial mass as 373t, so 253t of fuel or 100t residual from initial launch and two refuelings with 100t and 53t respectively. Full refueling of 200t to initial mass of 420t gives 15t of payload to Gateway and back or 17t payload and empty back.

Thanks! I am not engineer, so I am not sure that I fully understand, you are saying that two refueling missions should be enough to deliver 15mt to the Moon and back (or 17mt one way to the Moon)?

Would it be possible for lunar Starship to get to the Moon (through NRHO) and back to LEO (through NRHO) without any re-fueling?
Not quite - you pass by the Moon going to NRHO but staying there (i.e. entering low lunar orbit) is harder and getting to the surface is much harder. I will also mention that the tweet said Moonship while I was talking about a standard Starship with a heat shield useful at lunar return velocities (and forgot about landing propellant, so payload a bit less). Moonship lacks heat shield and can not get back to LEO as easily.
To summarize for Starships/Moonships at 120t empty, up to 100t payload to LEO and 1200t of propellant capacity:
 
If capable of cislunar travel a standard Starship can service the Gateway from LEO with two refuelings and return.

A Moonship in LEO can not quite get to the Gateway with a single refueling (unless it is below 115t or so) but can easily get there with plenty of payload with two.

A fully refueled Moonship in LEO (i.e. the 12 refueling flights) should be able to get the full 100t payload to the Gateway :P and back to LEO propulsively (empty). With no payload it is right at the limit for getting to Gateway, down to the surface and back to the Gateway again.

This is all very simplistic, highly sensitive to performance numbers and totally ignores things like boil off or the feasibility of actually docking to the Gateway.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: CJ on 08/21/2020 12:06 am
Quote from: armchairfan

As an exercise and if I've done the math right -- a big ask -- a 340 km circular orbit at 28.4 inclination (Cape Canaveral) will precess at such a rate as to be aligned toward Mars every 26 months; i.e. when the next launch window rolls around. While that's a fairly low orbit, (I'm guessing that) you can probably keep it going with just the propellant that you'd otherwise lose to boil-off.

This probably only makes sense if you're going to use an entire synod sending tankers to a depot(s) in preparation for a vast fleet of starships leaving all at once.

Thanks. I was trying to understand if such an orbit existed or not.

This was discussed earlier in the thread and I realized that I missed the page where it came to a conclusion. So I won't continue necro'ing the discussion beyond to offer my own $0.02. Initially it will make more sense to just launch a train of tanker starships (say 1 every 12-24 hr based on your twice daily launch window and presumably some time to do refueling ops for each tanker) to rendezvous with the mission starship shortly before the intended launch. So you'd only spend a few days to a week on orbit refueling.

However, when sending many many starships that launch cadence doesn't seem sustainable to me over a short mars transfer window even with ksc, bc, and maybe an offshore platform or two pitching in. So an accumulation tanker in a carefully selected orbit like you calculated would make sense to allow you to preposition fuel for a launch window. By this time the use case will be existent not theoretical and launch costs would have been massively reduced so one could justify the added costs of on orbit construction for a dedicated facility.

That said it may prove out that a rapid reuse and launch cadence is easier to solve than in space depot construction. It will certainly need to be if point to point is going to be a serious proposition.

Either way holy smokes are you looking at a lot of launches for a mars bound fleet.
Yup, a buttload of launches. But a depot(s) doesn't have to involve in space construction.


A standard SS in LEO for example, when filled by tankers would hold enough propellant to support one SS going to Mars. If the mars fleet is 10 ships, use 10 SS's accumulating fuel, which can then return to earth.


For another example, strip everything unnecessary and increase capacity for a permanent no return depot.  My very rough calculation shows this could fill 1.2 mars bound SS's. If it is structurally possible to use the three remaining rings as tankage and stretch an SS by an estimate five additional rings the depot could tank up two mars bound ships. Of course it could not launch with all this tankage filled with propellant.


This does not change the number of tankers to orbit but it does add safety by limiting each mars bound ship to one refueling and it avoids the difficulty of on orbit construction.


Phil

I keep wondering if having a depot (enough to refuel, say, 3 Starships) might be a viable future development.

Would it be plausible (and viable) to use a Superheavy near the end of its service life as a depot? It'd need a few modifications, such as refueling compatibility with Starships (both ways, of course, seeing as the prop has to get there somehow). It would also need something akin to IVF (Integrated Vehicle Fluids, basically a tiny internal combustion engine to provide power for temp, pressurization, station keeping, etc).

This, of course, assumes you can get a stripped-down (no recovery hardware, no fins, fewer Raptors, etc) Superheavy to do SSTO. It appears possible, assuming an aggressive launch profile, and assuming (yeah, lots of assumptions here, not good) that projected dry mass is in the ballpark. It would need a nosecone of some sort, as light as possible, perhaps modeled on the FH side booster nosecones.

It would, I think, require a sunshade before adding prop. Seeing as this notional Superheavy would arrive in LEO with  no payload and essentially no remaining prop, the sunshade could be added later, by a Starship. For a sunshade, I'm thinking something roughly akin to the Echo2 satalite, which was essentially a giant Mylar spherical balloon (self-rigidizing, so no need to keep it pressurized). It would require very little gas to inflate it in orbit (perhaps tank residual?). I can't find a figure for Echo 2, except a mention of "a few pounds" of gas. Echo 2 was a 40 meter diameter sphere, weighing  256 kg (including other hardware, like the inflation tank). Deflated, it fit inside the payload fairing of a Thor-Agena (looks like a 65 inch diameter fairing). A couple of 40 meter spheres might be sub-optimum for a sunshade for a Superheavy, so why not make it a tube?  A tube with a 10 meter internal diameter and a 12 meter external diameter would fit around SH. Even if several times the mass of Echo2, this is still under a tonne. It would also provide micrometeorite and small orbital debris protection for the depot. (and, something similar but smaller might be useful for Starship on a Mars voyage). As for how to emplace it once inflated, I'm not sure (unless cargo Starships will have a RMS). Perhaps add a cold gas thruster pack from a F9 or a fairing, nudge it into position, then hold it in place with a few extendable rods (like old-style extending car radio antennas - maybe literally use those).   

Might this concept be a way to create an orbital depot (capable of holding 3400 tons of prop) if such a depot would be useful? Perhaps, if sufficient end-of-life Superheavies are available, deploy one in each of, say, 3 inclinations?

Many things could make this non-viable; cost, the refueling system or IVF system might require too many modifications to SH, SH's systems might be incompatible with this purpose, the "sunshade" might be inadequate to reduce thermal influx to manageable levels, etc, . (and, if a stripped down SH can't do SSTO). Or, of course, this whole concept might be more trouble and expense than just using Starships as temporary depots.  There's also the fact that it would require a Superheavy at the end of its service life, and around 20 Raptors likewise at the end of their service life. I have no doubt that I am failing to see  some other potential dealkillers.

A couple of links; Integrated Vehicle Fluids
https://arc.aiaa.org/doi/abs/10.2514/6.2012-5302
(I know this is for HydroLox, but a similar system for MethLox ought to be possible)

Echo 2
http://www.astronautix.com/e/echo2.html

     
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/21/2020 12:33 am
However I think your inclined orbit has to be pointed in the right direction (AN and DN aligned in a certain way relative to your intended ejection angle).
This is no big deal for a specific mission. Do some maths and launch your ships at the right time of day basically (though as previously discussed you'd have limited launch windows). But I really do think it means you can't easily have a depot in an inclined orbit to service multiple different interplanetary transfers.
An extra point to consider. Earth is tipped 23.5 deg to our orbital plane so an equatorial launch faces the same limitations of node alignment with the ecliptic.
I don't think there is any place on earth without this problem. It's something we have to live with until we can afford to take it to the shop for an axis alignment

As Pahimarus correctly notes, a launch site effectively rotates its orbital plane 360 degrees every day. Therefore there's a launch window every day (or two) that can put you into an orbit that matches your desired exit plane.

The issue with permanent depots is changing that orbital plane after it's in orbit.

But if "propellant is cheap", then doing the low-high-low manoeuvre gives you a cheap plane-change, provided you can handle the two extra passes through the VA belts.

[edit: eriblo - Yeah, it was either Jon Goff or Hollister David where I first read about low-high-low plane-changes.]
Agree. I was just pointing out that equatorial launch doesn't make much difference for this problem.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: yg1968 on 08/21/2020 12:56 am
I am highly skeptical of this information but there is a guy on Twitter that says that lunar Starship requires 12 refueling flights in order to get to the NRHO. He says that he got this information from someone involved in the HLS program at MSFC.

I would expect only one or two refueling flights would be required, not 12. What is a realistic number of re-fueling missions required for lunar Starship to get to NRHO?

[tweet]
Quick check on wikipedia: 3.2km/s TLI from LEO, 0.43km/s powered flyby and insertion into NRHO. Lets say standard Starship is 120t empty with 100t payload to LEO and that payload mass can be traded for residual fuel 1:1. Lets use 365 for average in space Isp.

Maths:
Empty Starship from LEO to Gateway and back to reentry/aerobreaking is 3.2+2*0.43=4.06km/s.
Rocket equation gives initial mass as 373t, so 253t of fuel or 100t residual from initial launch and two refuelings with 100t and 53t respectively. Full refueling of 200t to initial mass of 420t gives 15t of payload to Gateway and back or 17t payload and empty back.

Thanks! I am not engineer, so I am not sure that I fully understand, you are saying that two refueling missions should be enough to deliver 15mt to the Moon and back (or 17mt one way to the Moon)?

Would it be possible for lunar Starship to get to the Moon (through NRHO) and back to LEO (through NRHO) without any re-fueling?
Not quite - you pass by the Moon going to NRHO but staying there (i.e. entering low lunar orbit) is harder and getting to the surface is much harder. I will also mention that the tweet said Moonship while I was talking about a standard Starship with a heat shield useful at lunar return velocities (and forgot about landing propellant, so payload a bit less). Moonship lacks heat shield and can not get back to LEO as easily.
To summarize for Starships/Moonships at 120t empty, up to 100t payload to LEO and 1200t of propellant capacity:
 
If capable of cislunar travel a standard Starship can service the Gateway from LEO with two refuelings and return.

A Moonship in LEO can not quite get to the Gateway with a single refueling (unless it is below 115t or so) but can easily get there with plenty of payload with two.

A fully refueled Moonship in LEO (i.e. the 12 refueling flights) should be able to get the full 100t payload to the Gateway :P and back to LEO propulsively (empty). With no payload it is right at the limit for getting to Gateway, down to the surface and back to the Gateway again.

This is all very simplistic, highly sensitive to performance numbers and totally ignores things like boil off or the feasibility of actually docking to the Gateway.

I think that the tweet meant lunar Starship would pick up the astronauts at NRHO and then continue to the Moon since that is what lunar Starship is meant to do. Lunar Starship isn't meant for ferrying cargo to Gateway (that should be Dragon XL's job).

My question is what is the minimum amount of refueling missions which will be necessary in order for lunar Starhip to bring 2 astronauts to the Moon (through NRHO) with a minimum amount of cargo and then come back from the Moon to LEO (through NRHO).

I believe that is the itinerary for lunar Starship. It will travel from Earth to the Moon (through NRHO) and it will come back from the Moon to LEO through NRHO. My understanding of lunar Starship is that it will be re-fueled in LEO, not in NRHO. 

In any event, thanks for your answers. I have asked this question before but it's been hard to get an answer. It's possible that this question has been answered elsewhere but I haven't seen it.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/21/2020 12:59 am
Quote from: armchairfan

As an exercise and if I've done the math right -- a big ask -- a 340 km circular orbit at 28.4 inclination (Cape Canaveral) will precess at such a rate as to be aligned toward Mars every 26 months; i.e. when the next launch window rolls around. While that's a fairly low orbit, (I'm guessing that) you can probably keep it going with just the propellant that you'd otherwise lose to boil-off.

This probably only makes sense if you're going to use an entire synod sending tankers to a depot(s) in preparation for a vast fleet of starships leaving all at once.

Thanks. I was trying to understand if such an orbit existed or not.

This was discussed earlier in the thread and I realized that I missed the page where it came to a conclusion. So I won't continue necro'ing the discussion beyond to offer my own $0.02. Initially it will make more sense to just launch a train of tanker starships (say 1 every 12-24 hr based on your twice daily launch window and presumably some time to do refueling ops for each tanker) to rendezvous with the mission starship shortly before the intended launch. So you'd only spend a few days to a week on orbit refueling.

However, when sending many many starships that launch cadence doesn't seem sustainable to me over a short mars transfer window even with ksc, bc, and maybe an offshore platform or two pitching in. So an accumulation tanker in a carefully selected orbit like you calculated would make sense to allow you to preposition fuel for a launch window. By this time the use case will be existent not theoretical and launch costs would have been massively reduced so one could justify the added costs of on orbit construction for a dedicated facility.

That said it may prove out that a rapid reuse and launch cadence is easier to solve than in space depot construction. It will certainly need to be if point to point is going to be a serious proposition.

Either way holy smokes are you looking at a lot of launches for a mars bound fleet.
Yup, a buttload of launches. But a depot(s) doesn't have to involve in space construction.


A standard SS in LEO for example, when filled by tankers would hold enough propellant to support one SS going to Mars. If the mars fleet is 10 ships, use 10 SS's accumulating fuel, which can then return to earth.


For another example, strip everything unnecessary and increase capacity for a permanent no return depot.  My very rough calculation shows this could fill 1.2 mars bound SS's. If it is structurally possible to use the three remaining rings as tankage and stretch an SS by an estimate five additional rings the depot could tank up two mars bound ships. Of course it could not launch with all this tankage filled with propellant.


This does not change the number of tankers to orbit but it does add safety by limiting each mars bound ship to one refueling and it avoids the difficulty of on orbit construction.


Phil

I keep wondering if having a depot (enough to refuel, say, 3 Starships) might be a viable future development.

Would it be plausible (and viable) to use a Superheavy near the end of its service life as a depot? It'd need a few modifications, such as refueling compatibility with Starships (both ways, of course, seeing as the prop has to get there somehow). It would also need something akin to IVF (Integrated Vehicle Fluids, basically a tiny internal combustion engine to provide power for temp, pressurization, station keeping, etc).

This, of course, assumes you can get a stripped-down (no recovery hardware, no fins, fewer Raptors, etc) Superheavy to do SSTO. It appears possible, assuming an aggressive launch profile, and assuming (yeah, lots of assumptions here, not good) that projected dry mass is in the ballpark. It would need a nosecone of some sort, as light as possible, perhaps modeled on the FH side booster nosecones.

It would, I think, require a sunshade before adding prop. Seeing as this notional Superheavy would arrive in LEO with  no payload and essentially no remaining prop, the sunshade could be added later, by a Starship. For a sunshade, I'm thinking something roughly akin to the Echo2 satalite, which was essentially a giant Mylar spherical balloon (self-rigidizing, so no need to keep it pressurized). It would require very little gas to inflate it in orbit (perhaps tank residual?). I can't find a figure for Echo 2, except a mention of "a few pounds" of gas. Echo 2 was a 40 meter diameter sphere, weighing  256 kg (including other hardware, like the inflation tank). Deflated, it fit inside the payload fairing of a Thor-Agena (looks like a 65 inch diameter fairing). A couple of 40 meter spheres might be sub-optimum for a sunshade for a Superheavy, so why not make it a tube?  A tube with a 10 meter internal diameter and a 12 meter external diameter would fit around SH. Even if several times the mass of Echo2, this is still under a tonne. It would also provide micrometeorite and small orbital debris protection for the depot. (and, something similar but smaller might be useful for Starship on a Mars voyage). As for how to emplace it once inflated, I'm not sure (unless cargo Starships will have a RMS). Perhaps add a cold gas thruster pack from a F9 or a fairing, nudge it into position, then hold it in place with a few extendable rods (like old-style extending car radio antennas - maybe literally use those).   

Might this concept be a way to create an orbital depot (capable of holding 3400 tons of prop) if such a depot would be useful? Perhaps, if sufficient end-of-life Superheavies are available, deploy one in each of, say, 3 inclinations?

Many things could make this non-viable; cost, the refueling system or IVF system might require too many modifications to SH, SH's systems might be incompatible with this purpose, the "sunshade" might be inadequate to reduce thermal influx to manageable levels, etc, . (and, if a stripped down SH can't do SSTO). Or, of course, this whole concept might be more trouble and expense than just using Starships as temporary depots.  There's also the fact that it would require a Superheavy at the end of its service life, and around 20 Raptors likewise at the end of their service life. I have no doubt that I am failing to see  some other potential dealkillers.

A couple of links; Integrated Vehicle Fluids
https://arc.aiaa.org/doi/abs/10.2514/6.2012-5302 (https://arc.aiaa.org/doi/abs/10.2514/6.2012-5302)
(I know this is for HydroLox, but a similar system for MethLox ought to be possible)

Echo 2
http://www.astronautix.com/e/echo2.html (http://www.astronautix.com/e/echo2.html)

     
I've been noodling an SSTO SH and don't know if it's possible, but if it is, a reasonable way to go - but not an early priority.


The SH has no heatshield or fins so that's a job that's not needed. It's already designed to interface with SS plumbing - the same plumbing SS will use to refuel. No extra work there. It will need a sun shade, maybe an earth shade, a fuel fridge and a radiator. The fuel fridge can be PV powered but I don't have a feel for power needs.


The big Q is getting SH to orbit SSTO. Beyond my skills.



Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: yg1968 on 08/21/2020 01:46 am
Here is another tweets that says lunar Starship needs a lot of re-fueling flights:

https://twitter.com/joe_mckirdy/status/1296563733519577090

Quote
Starship is estimated to have a dry mass of 100 metric tons. To refuel it is LEO to fly to the Gateway with its payload of 100 tons would require 300 tons of liquid oxygen and methane (LOx/CH4) propellant. This could be supported with three tanker Starship flights to LEO. But then to land on the moon, discharge its cargo, and return to the Gateway would require a further 400 tons of propellant delivered to the Gateway, or four trans-lunar tankers. Each of these would need to be enabled for flight from LEO to the gateway by three further tanker flights, for a total of 20 Starship launches for each piloted lunar mission. That doesn’t make sense.

https://spacenews.com/op-ed-toward-a-coherent-artemis-plan/
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/21/2020 01:51 am
It occurred to me that thermal shields will necessarily be reflective and might cause a reaction from the astronomical community. No nearly as numerous as Starlinks but the good neighbor thing...


The shields need to run interference from the sun and earth which implies constant repositioning of the shades and maybe the whole depot. the ISS used Control Moment Gyros (CMG) instead of reaction jets. Would they be justified for a depot?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: envy887 on 08/21/2020 02:09 am
Here is a couple of other tweets that says lunar Starship needs a lot of re-fueling flights:

Those tweets are complete garbageposts and demonstrate a total lack of even the most basic understanding of any of the mechanics needed to optimize a refueling solution.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: yg1968 on 08/21/2020 02:22 am
Here is a couple of other tweets that says lunar Starship needs a lot of re-fueling flights:

Those tweets are complete garbageposts and demonstrate a total lack of even the most basic understanding of any of the mechanics needed to optimize a refueling solution.

I think that they are based on Zubrin's article but his article assumed a 100mt payload to the Moon.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: yg1968 on 08/21/2020 03:17 am
I was reading comments to a couple of posts to some Space News articles and some of the posters say 8 to 12 missions for a lunar landing.

Quote from: gunsandrockets
To land that much cargo as a one way expendable cargo mission requires the support of 6 tanker Starship missions to LEO. To land that much cargo as a reusable lander, each HLS Starship mission will require the support of a minimum of 11 tanker Starship missions plus 1 cargo Starship mission, more likely 12 tankers plus 2 cargo Starships.

http://disq.us/p/292z8r9

Quote from: envy
A single Starship tanker would be refueled in LEO with a total of about 8 launches. This single tanker would make 1 flight to the Gateway and deliver about 400 tons of propellant to the HLS Starship lander, which is enough for the HLS Starship lander to make the round trip to the surface and return to Gateway. The tanker would return to Earth, and participate in the next set of about 8 launches needed to again send it to gateway to refill the HLS lander.

So only about 8 Starship/SuperHeavy launches, and not 20 (!!!), are needed for each landing.

http://disq.us/p/29c9ih2
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: LMT on 08/21/2020 04:02 am
It will need a sun shade, maybe an earth shade, a fuel fridge and a radiator. The fuel fridge can be PV powered but I don't have a feel for power needs.

Gravlee et al. 2012 anticipates a 2 W Stirling cooler to refrigerate 71 kg of LH2.

Image:  CRYOTE Grande.  Gravlee et al. 2012, Fig. 10.

Refs.

Gravlee, M., Kutter, B., McLean, C. and Marquardt, J., 2012. Cryogenic Orbital Testbed (CRYOTE) Development Status. (https://www.ulalaunch.com/docs/default-source/extended-duration/cryogenic-orbital-test-bed-development.pdf) Cryogenics, 52(4-6), pp.231-235.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: kkattula on 08/21/2020 06:55 am

I keep wondering if having a depot (enough to refuel, say, 3 Starships) might be a viable future development.

Would it be plausible (and viable) to use a Superheavy near the end of its service life as a depot? It'd need a few modifications, such as refueling compatibility with Starships (both ways, of course, seeing as the prop has to get there somehow). It would also need something akin to IVF (Integrated Vehicle Fluids, basically a tiny internal combustion engine to provide power for temp, pressurization, station keeping, etc).
...
I've been noodling an SSTO SH and don't know if it's possible, but if it is, a reasonable way to go - but not an early priority.

The SH has no heatshield or fins so that's a job that's not needed. It's already designed to interface with SS plumbing - the same plumbing SS will use to refuel. No extra work there. It will need a sun shade, maybe an earth shade, a fuel fridge and a radiator. The fuel fridge can be PV powered but I don't have a feel for power needs.

The big Q is getting SH to orbit SSTO. Beyond my skills.

Why would you want a Super Heavy with all those extra engines as a depot?

A modified Starship with no legs, fins, heat-shield or header tanks, and the main tanks extended to almost full height should hold close to 2000 t of propellant in orbit. It would have to launch with partially filled tanks, getting to LEO with maybe 200 t remaining.
Or a little less if some of that mass is replaced by a cryo-cooler, solar panels and a sun-shield.

Other options include an extra long version, or maybe a 12 m diameter version, holding 3500+ t.  Not needing an EDL capability opens up a lot of options.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: SoTOP on 08/21/2020 07:29 am
Why would you want a Super Heavy with all those extra engines as a depot?

A modified Starship with no legs, fins, heat-shield or header tanks, and the main tanks extended to almost full height should hold close to 2000 t of propellant in orbit. It would have to launch with partially filled tanks, getting to LEO with maybe 200 t remaining.
Or a little less if some of that mass is replaced by a cryo-cooler, solar panels and a sun-shield.

Other options include an extra long version, or maybe a 12 m diameter version, holding 3500+ t.  Not needing an EDL capability opens up a lot of options.
You can modify SH the same way you suggest to modify Starship. For example, have just enough engines to get into orbit.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: mikelepage on 08/21/2020 07:45 am
The orbital plane is relatively fixed as Earth moves around the sun, hence it will move in and out of sync with the ecliptic. So the orbital plane of a a particular LEO orbit will have two opportunities per year to launch into an interplanetary trajectory without a massive plane-change manoeuvre.
this particular quirk of orbital mechanics is why I doubt Phobos or Deimos will ever (?) be used as way-stations/depots on the way to Mars surface.  Only twice per Martian year would it be possible to arrive at Mars and capture into an orbital plane aligned with the moons... and how often would those arrival windows synchronise with the Earth-Mars synodic cycle?  You might be able to get around this by performing multiple plane change maneuvers whilst aero-capturing into Martian orbit, but there would have to be an upper limit to how great a plane change you could perform that way.

Just one plane change.

You aero-capture into a very high Mars orbit, putting apoapsis right on the edge of the Hill Sphere (or even fractionally beyond), then do a plane change at apoapsis to match the destination orbital plane. At this distance, the delta-v cost of even a 90 degree plane change is in the low hundreds of m/s. On the next pass, do a second smaller aero-capture to lower apoapsis to match the altitude of the target orbit. (Then do your circularisation burn when the orbital phasing catches up to the target.) Adds about two weeks or so of additional travel for the passengers. Not a deal-breaker if the ship has sustained months-long interplanetary flight.


I don't want to derail this thread any further, so I went back and found the "Station on Phobos" thread where Hop_David put the problem that I was getting at into technical terms.  Also helped me refresh my memory on how I came to that thinking.  Never got my final question answered though, so maybe those of us interested can continue the discussion there?

https://forum.nasaspaceflight.com/index.php?topic=40176.100

TLDR: Assuming you've aerobraked into high martian orbit, the plane change to become co-orbital with Phobos/Deimos is easy at apoapsis, *if* the longitude of ascending node of your HMO (which is constrained by your original approach vector/timing) is aligned with that of Phobos/Deimos equatorial orbit.  Also, because the moons' orbits are more-or-less equatorial, you would have to make yet another plane change maneuver to get to/from the moons to any higher inclination site on Mars' surface - hence why I said I doubt they will be used "way-stations" (though I could still see them eventually becoming destinations in their own right).
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Thunderscreech on 08/21/2020 12:38 pm
You can modify SH the same way you suggest to modify Starship. For example, have just enough engines to get into orbit.
So you go from 31 engines to...  25 engines?  20 engines?  You're still going to be throwing away millions of dollars in engines to gain an unclear advantage over using recoverable (or even expendable) Starships in exchange for something like 20% more storage volume on-orbit and even then, you have razor thin margins for hardware like insulation & coolers to maintain the propellants so it's an expensive, capital-rich expenditure for a difficult to quantify benefit, isn't it?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: envy887 on 08/21/2020 03:07 pm
Here is a couple of other tweets that says lunar Starship needs a lot of re-fueling flights:

Those tweets are complete garbageposts and demonstrate a total lack of even the most basic understanding of any of the mechanics needed to optimize a refueling solution.

I think that they are based on Zubrin's article but his article assumed a 100mt payload to the Moon.

Unless we're landing hundreds of people at a time, there's no reason to assume that 100 tonnes come back. Coming back is the hard part.

For 100 t down and 5 t up, as one might expect for a heavy cargo lander with minimalist crew return, then the HLS Starship lander only needs about 400 t of propellant delivered to NRHO per landing. A single tanker can bring this from LEO.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: sebk on 08/21/2020 03:29 pm
The orbital plane is relatively fixed as Earth moves around the sun, hence it will move in and out of sync with the ecliptic. So the orbital plane of a a particular LEO orbit will have two opportunities per year to launch into an interplanetary trajectory without a massive plane-change manoeuvre.
this particular quirk of orbital mechanics is why I doubt Phobos or Deimos will ever (?) be used as way-stations/depots on the way to Mars surface.  Only twice per Martian year would it be possible to arrive at Mars and capture into an orbital plane aligned with the moons... and how often would those arrival windows synchronise with the Earth-Mars synodic cycle?  You might be able to get around this by performing multiple plane change maneuvers whilst aero-capturing into Martian orbit, but there would have to be an upper limit to how great a plane change you could perform that way.

Just one plane change.

You aero-capture into a very high Mars orbit, putting apoapsis right on the edge of the Hill Sphere (or even fractionally beyond), then do a plane change at apoapsis to match the destination orbital plane. At this distance, the delta-v cost of even a 90 degree plane change is in the low hundreds of m/s. On the next pass, do a second smaller aero-capture to lower apoapsis to match the altitude of the target orbit. (Then do your circularisation burn when the orbital phasing catches up to the target.) Adds about two weeks or so of additional travel for the passengers. Not a deal-breaker if the ship has sustained months-long interplanetary flight.


I don't want to derail this thread any further, so I went back and found the "Station on Phobos" thread where Hop_David put the problem that I was getting at into technical terms.  Also helped me refresh my memory on how I came to that thinking.  Never got my final question answered though, so maybe those of us interested can continue the discussion there?

https://forum.nasaspaceflight.com/index.php?topic=40176.100

TLDR: Assuming you've aerobraked into high martian orbit, the plane change to become co-orbital with Phobos/Deimos is easy at apoapsis, *if* the longitude of ascending node of your HMO (which is constrained by your original approach vector/timing) is aligned with that of Phobos/Deimos equatorial orbit.  Also, because the moons' orbits are more-or-less equatorial, you would have to make yet another plane change maneuver to get to/from the moons to any higher inclination site on Mars' surface - hence why I said I doubt they will be used "way-stations" (though I could still see them eventually becoming destinations in their own right).

Just a note: equatorial orbit doesn't have a longtitude of ascending node. It's like dividing 0 by 0.

Phobos is not exactly equatorial, but it's inclination is so low (~1°) that even if you miss it's ascending node by 180° dV to it would be small.

I don't see a point of making Phobos a waystation, as getting to higher latitudes from it is costly, but capturing to its orbit is not the reason why not.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/21/2020 03:50 pm
I was reading comments to a couple of posts to some Space News articles and some of the posters say 8 to 12 missions for a lunar landing.

Quote from: gunsandrockets
To land that much cargo as a one way expendable cargo mission requires the support of 6 tanker Starship missions to LEO. To land that much cargo as a reusable lander, each HLS Starship mission will require the support of a minimum of 11 tanker Starship missions plus 1 cargo Starship mission, more likely 12 tankers plus 2 cargo Starships.

http://disq.us/p/292z8r9 (http://disq.us/p/292z8r9)

Quote from: envy
A single Starship tanker would be refueled in LEO with a total of about 8 launches. This single tanker would make 1 flight to the Gateway and deliver about 400 tons of propellant to the HLS Starship lander, which is enough for the HLS Starship lander to make the round trip to the surface and return to Gateway. The tanker would return to Earth, and participate in the next set of about 8 launches needed to again send it to gateway to refill the HLS lander.

So only about 8 Starship/SuperHeavy launches, and not 20 (!!!), are needed for each landing.

http://disq.us/p/29c9ih2 (http://disq.us/p/29c9ih2)
ISTM the number of tanker loads is irrelevant. Cost per mission or $/kilo delivered seems more to the point.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: brainbit on 08/21/2020 04:18 pm
Could not a fuel depot in space be used to store any excess fuel from a SH, for example if SH had to spend some time in orbit saving any boil off as am assuming depot has fuel management built in. Also for SH which has to have enough fuel to land it must save fuel to be able to unload this fuel onto depot and when ready to return to earth recover said fuel. When SH needs to orbit a heavy load and cannot carry enough fuel for a landing as well, then it should be able to use fuel depot to re-fuel enough for a landing, same for SH returning from higher orbits. I like the fuel depot.  ;D   
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: philw1776 on 08/21/2020 04:30 pm
Could not a fuel depot in space be used to store any excess fuel from a SH, for example if SH had to spend some time in orbit saving any boil off as am assuming depot has fuel management built in. Also for SH which has to have enough fuel to land it must save fuel to be able to unload this fuel onto depot and when ready to return to earth recover said fuel. When SH needs to orbit a heavy load and cannot carry enough fuel for a landing as well, then it should be able to use fuel depot to re-fuel enough for a landing, same for SH returning from higher orbits. I like the fuel depot.  ;D

A SH can't land period.  It has no TPS.  It cannot re-enter at orbital speeds.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: cdebuhr on 08/21/2020 04:39 pm
Could not a fuel depot in space be used to store any excess fuel from a SH, for example if SH had to spend some time in orbit saving any boil off as am assuming depot has fuel management built in. Also for SH which has to have enough fuel to land it must save fuel to be able to unload this fuel onto depot and when ready to return to earth recover said fuel. When SH needs to orbit a heavy load and cannot carry enough fuel for a landing as well, then it should be able to use fuel depot to re-fuel enough for a landing, same for SH returning from higher orbits. I like the fuel depot.  ;D

A SH can't land period.  It has no TPS.  It cannot re-enter at orbital speeds.
I think I know what you're getting at ... but for the benefit of brainbit, SH will be able to land - that's sort of the whole point of reusable rockets.  But it will not be able to:
1) Achieve anything even remotely close to orbital velocity, particularly when boosting SS.  This precludes entering orbit and rendezvousing with the notional depot.
2) As you point out, if it did somehow enter orbit, it would never be coming back.  At least not in one piece.  Without TPS, orbital re-entry would be possible, but very ... traumatic.  (Re-entry is always possible - you just might not like it very much!)

So the flight profile is like a big F9 (more or less) - boost, then re-enter and land, either RTLS, or downrange, presumably on a floating platform.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/21/2020 04:42 pm

I keep wondering if having a depot (enough to refuel, say, 3 Starships) might be a viable future development.

Would it be plausible (and viable) to use a Superheavy near the end of its service life as a depot? It'd need a few modifications, such as refueling compatibility with Starships (both ways, of course, seeing as the prop has to get there somehow). It would also need something akin to IVF (Integrated Vehicle Fluids, basically a tiny internal combustion engine to provide power for temp, pressurization, station keeping, etc).
...
I've been noodling an SSTO SH and don't know if it's possible, but if it is, a reasonable way to go - but not an early priority.

The SH has no heatshield or fins so that's a job that's not needed. It's already designed to interface with SS plumbing - the same plumbing SS will use to refuel. No extra work there. It will need a sun shade, maybe an earth shade, a fuel fridge and a radiator. The fuel fridge can be PV powered but I don't have a feel for power needs.

The big Q is getting SH to orbit SSTO. Beyond my skills.

Why would you want a Super Heavy with all those extra engines as a depot?

A modified Starship with no legs, fins, heat-shield or header tanks, and the main tanks extended to almost full height should hold close to 2000 t of propellant in orbit. It would have to launch with partially filled tanks, getting to LEO with maybe 200 t remaining.
Or a little less if some of that mass is replaced by a cryo-cooler, solar panels and a sun-shield.

Other options include an extra long version, or maybe a 12 m diameter version, holding 3500+ t.  Not needing an EDL capability opens up a lot of options.
I agree. The exact numbers can be quibbled but the concept is sound. There are unknowns like the exact mass of the removed items and the dry mass of SS. And how much of a stretch that can launch safely.


My crude BOE sez that adding 5, maybe 6 more rings and turning it all into tankage gives capacity to top off two SS's. Then there is the possibility of a 12m tank expansion but this would entail some serious engineering and R&D. My gut says this would be a late development and would be a precursor to the next generation of ships.


The loss of a set of raptors on each SSTO SH is not to be sneezed at but also has to be balanced against development costs for an outsized SS. A five ring stretch, IMO, would be minimal development cost and possibly the most cost effective solution in the mid term. One issue thrown into the trade off matrix is each SS based depot of any size eats six raptors.


Bigger is better. Ideally one depot would be adequate for one Mars fleet. Without numbers in front of me I guesstimate one SH worth of tankage could refuel 3-4 SS's. Good, but not ideal. I have no idea where this fits into the trade offs but it 'feels' like it's close enough to the ballpark that it deserves a close look before dismissal.


Unfortunately there are enough unknowns that the best we can do is look at possibilities and as the unknowns resolve, narrow things down a bit.


Phil





Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/21/2020 04:50 pm
The orbital plane is relatively fixed as Earth moves around the sun, hence it will move in and out of sync with the ecliptic. So the orbital plane of a a particular LEO orbit will have two opportunities per year to launch into an interplanetary trajectory without a massive plane-change manoeuvre.
this particular quirk of orbital mechanics is why I doubt Phobos or Deimos will ever (?) be used as way-stations/depots on the way to Mars surface.  Only twice per Martian year would it be possible to arrive at Mars and capture into an orbital plane aligned with the moons... and how often would those arrival windows synchronise with the Earth-Mars synodic cycle?  You might be able to get around this by performing multiple plane change maneuvers whilst aero-capturing into Martian orbit, but there would have to be an upper limit to how great a plane change you could perform that way.

Just one plane change.

You aero-capture into a very high Mars orbit, putting apoapsis right on the edge of the Hill Sphere (or even fractionally beyond), then do a plane change at apoapsis to match the destination orbital plane. At this distance, the delta-v cost of even a 90 degree plane change is in the low hundreds of m/s. On the next pass, do a second smaller aero-capture to lower apoapsis to match the altitude of the target orbit. (Then do your circularisation burn when the orbital phasing catches up to the target.) Adds about two weeks or so of additional travel for the passengers. Not a deal-breaker if the ship has sustained months-long interplanetary flight.


I don't want to derail this thread any further, so I went back and found the "Station on Phobos" thread where Hop_David put the problem that I was getting at into technical terms.  Also helped me refresh my memory on how I came to that thinking.  Never got my final question answered though, so maybe those of us interested can continue the discussion there?

https://forum.nasaspaceflight.com/index.php?topic=40176.100 (https://forum.nasaspaceflight.com/index.php?topic=40176.100)

TLDR: Assuming you've aerobraked into high martian orbit, the plane change to become co-orbital with Phobos/Deimos is easy at apoapsis, *if* the longitude of ascending node of your HMO (which is constrained by your original approach vector/timing) is aligned with that of Phobos/Deimos equatorial orbit.  Also, because the moons' orbits are more-or-less equatorial, you would have to make yet another plane change maneuver to get to/from the moons to any higher inclination site on Mars' surface - hence why I said I doubt they will be used "way-stations" (though I could still see them eventually becoming destinations in their own right).

Just a note: equatorial orbit doesn't have a longtitude of ascending node. It's like dividing 0 by 0.

Phobos is not exactly equatorial, but it's inclination is so low (~1°) that even if you miss it's ascending node by 180° dV to it would be small.

I don't see a point of making Phobos a waystation, as getting to higher latitudes from it is costly, but capturing to its orbit is not the reason why not.
Ignoring the purpose of the maneuver and looking only at the orbital mechanics; the mars axis of rotation is tilted to the plane of its orbit. An entry from the local ecliptic to an equatorial orbit needs a plane change.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/21/2020 05:08 pm
Could not a fuel depot in space be used to store any excess fuel from a SH, for example if SH had to spend some time in orbit saving any boil off as am assuming depot has fuel management built in. Also for SH which has to have enough fuel to land it must save fuel to be able to unload this fuel onto depot and when ready to return to earth recover said fuel. When SH needs to orbit a heavy load and cannot carry enough fuel for a landing as well, then it should be able to use fuel depot to re-fuel enough for a landing, same for SH returning from higher orbits. I like the fuel depot.  ;D
As philw1776 points out, SH can't do reentry from orbit. Indeed, the only reason it might ever go to orbit would be without SS and only to become a fuel depot - not a done deal.
As for a depot collecting residual propellant from other launches, the devil is in the details. The residuals would have to be more than what it takes to match orbit with the depot. If the SS is needed for a fast turnaround the lost time for orbit matching, approach and transfer might not be worth it.


All in all, probably better to keep tighter control of propellant loading unless it's a very light launch to a convenient orbit allowing enough residuals to be worthwhile.


As for how much residuals might be enough to make it worthwhile, I'm drawing a blank. Maybe 200 tons? Just a guess.


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 08/21/2020 05:36 pm
Super Heavy (with a nose fairing) would make a heck of a Mars launch vehicle. Like, for launching stuff to low Mars orbit. Thousands of tons to LMO per launch. Maybe around 10,000 tons if it were lengthened (lower Mars gravity would mean the same engine thrust could allow almost triple the take-off mass). Low Mars orbit reentry is pretty modest, 3.3-3.5km/s or so. Comparable to a Falcon Heavy center core booster reentry. Might not need much (any?) TPS since it's made of stainless.

This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: ach1000 on 08/21/2020 05:59 pm
This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.

If I'm reading this chart correctly, deltaV requirement is 6.3 km/s for Mars to Earth orbit, v. 9.4 km/s for Earth surface to Earth orbit.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: LMT on 08/21/2020 08:21 pm
most of the propellant for trips to Mars might actually come *from* Mars.

If Deimos' very low density (https://solarsystem.nasa.gov/moons/mars-moons/deimos/by-the-numbers/) truly indicates volatiles, propellant for both Mars launch and LEO launch (https://forum.nasaspaceflight.com/index.php?topic=45299.msg1802366#msg1802366) could be produced more efficiently on Deimos than on Mars.  At scale, there'd be no need for Mars ISRU propellant (https://forum.nasaspaceflight.com/index.php?topic=45299.msg1802366#msg1802366), or for a tanker SH fleet - apart from the possibility of a small Earth-orbit depot fleet.

Various Earth-Moon-Mars propellant scenarios could be calculated with the network flow modeling method for optimized logistics in Ishimatsu et al. 2016.  Note their particular interest in Deimos:

Quote from: Ishimatsu et al. 2016
...it is interesting that part of the resources produced on Deimos are delivered back to GTO and LEO, and wait to be used for the crew and cargo outbound trip. Though it seems strange and non-intuitive at first, this is true at least computationally because in terms of ∆V, LEO is closer to Deimos than to the lunar surface and even Earth’s surface.

Image:  Network graph featuring Deimos ISRU propellant.  Ishimatsu et al. 2016, Fig. 10e.

Refs.

Ishimatsu, T., de Weck, O.L., Hoffman, J.A., Ohkami, Y. and Shishko, R., 2016. Generalized multicommodity network flow model for the earth–moon–mars logistics system. (https://dspace.mit.edu/bitstream/handle/1721.1/99360/JSR_Final_Manuscript_Ishimatsu.pdf?sequence=1&isAllowed=y) Journal of Spacecraft and Rockets, 53(1), pp.25-38.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/21/2020 08:35 pm
Super Heavy (with a nose fairing) would make a heck of a Mars launch vehicle. Like, for launching stuff to low Mars orbit. Thousands of tons to LMO per launch. Maybe around 10,000 tons if it were lengthened (lower Mars gravity would mean the same engine thrust could allow almost triple the take-off mass). Low Mars orbit reentry is pretty modest, 3.3-3.5km/s or so. Comparable to a Falcon Heavy center core booster reentry. Might not need much (any?) TPS since it's made of stainless.

This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.
Interesting concept. As a variation, might it be better to launch CO2 and water from Mars and process en route to take advantage of increasing solar power? A big argument against would be novel tank requirements.


On the pro side, fewer PV's to trip over on Mars. The return could be more about filling a pipeline than immediate deliverables so the slowest most economical return can be a great advantage in reducing the size of PV.


There are a class of trajectories that allow a low energy, long elapsed time, approach to mars orbit. The essence is aiming ahead of mars and slightly further outside mars orbit or behind mars and slightly inside mars orbit. In either case the craft is eventually swept up by mars into a highly elliptical orbit using aerobraking to circularize. The investigators claim up to 25% propellant savings.
https://www.scientificamerican.com/article/a-new-way-to-reach-mars-safely-anytime-and-on-the-cheap/ (https://www.scientificamerican.com/article/a-new-way-to-reach-mars-safely-anytime-and-on-the-cheap/)


I'm not sure but I think this might be adaptable to earth return of a depot or cargo.


So, once one of these depots returns to earth and refuels part of a mars fleet, what do you do with it? Could it carry enough dV for a useful propellant delivery AND a return to mars for another load? Oh, my brain hurts. So many variables.


Phil
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: LMT on 08/21/2020 09:29 pm
once one of these depots returns to earth and refuels part of a mars fleet, what do you do with it? Could it carry enough dV for a useful propellant delivery AND a return to mars for another load?

Why build dedicated Earth-Mars tankers?  Just cycle the existing cargo ships, using them as tankers when inbound.  This saves all the cost of a redundant Earth-Mars tanker fleet, which is cut.  E.g., Omaha Trail (http://www.lakematthew.com/press/press-release-november-7-2017/) cargo.   
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/21/2020 09:53 pm
The biggest problem with filling LEO tankers with non-terran methane, is that departure burns from LEO put the exaust in a suborbital trajectory. And we have enough problems with co2 on earth without importing martian Co2.

Terran methane would just be recycled back to earth, but martian methane would be a pure import.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: cdebuhr on 08/22/2020 12:07 am
The biggest problem with filling LEO tankers with non-terran methane, is that departure burns from LEO put the exaust in a suborbital trajectory. And we have enough problems with co2 on earth without importing martian Co2.

Terran methane would just be recycled back to earth, but martian methane would be a pure import.
I take the problem of excess CO2 in Earth's atmosphere as seriously as anyone.  We must halt and begin to revers this sooner rhater than later.  That said ...

Compared to current and reasonably foreseeable terrestrial emissions, Star ship exhaust, even in full, heavy colonization mode, won''t even be a rounding error.   If it ever does become a concern, build a few more air-capture plants.  We're likely going to need plenty of those anyway.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: CJ on 08/22/2020 01:10 am
The biggest problem with filling LEO tankers with non-terran methane, is that departure burns from LEO put the exaust in a suborbital trajectory. And we have enough problems with co2 on earth without importing martian Co2.

Terran methane would just be recycled back to earth, but martian methane would be a pure import.

IMHO, you may be overlooking something - the net. Regardless of the source of the methane's combustion byproducts, it's going to enter Earth's carbon cycle if suborbital. Viewed alone, there's no difference. However, if Martian, it would be replacing Terran methane - and Terran methane has to get to orbit somehow. That somehow is going to use many times the orbital fuel's mass to get it to orbit. All of that will be going into the atmosphere. This is not true for Martian methane. So, utilizing Martian methane is actually a very large net reduction in byproducts ending up in the Earth's atmosphere. And that's not even counting the lower total delta/v to LEO from the surface of Mars vs. the surface of Earth. 

IMHO, that lower delta/v to LEO makes getting prop from Mars (or an asteroid, or a martian moon) for use in LEO very attractive, though of course very long-term. Likewise, other consumables for LEO infrastructure. 

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Pahimarus on 08/22/2020 01:45 am
Quote
An extra point to consider. Earth is tipped 23.5 deg to our orbital plane so an equatorial launch faces the same limitations of node alignment with the ecliptic.


I don't think there is any place on earth without this problem. It's something we have to live with until we can afford to take it to the shop for an axis alignment


Phil

You are right of course. I thought about that after I posted.

That is the problem with being kerbal trained without the realism mods.  ;) :-[

I do think the the offshore platforms could help by allowing you more launch sites within the desired latitude range but it would make more sense to align them with bc and ksc than to put them on the equator though you do get a touch more effiency with you launch.

The idea of using a modified or just empty ss as a depot makes sense. At least as you say you only have to tank once instead of 5 times with the mission starship which significantly reduces risk of a problem you don't have time to recover from during the transfer window. Really what you described with 10 ss depots is just a distributed depot. In fact as I think about it there are a number of advantages to doing it that way. Namely that an accident only takes out 1/10th of your depot. Unless there is some major advantage to sharing equipment across multiple, a larger mega depot like I was envisioning probably wouldn't make sense.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/22/2020 02:00 am
The biggest problem with filling LEO tankers with non-terran methane, is that departure burns from LEO put the exaust in a suborbital trajectory. And we have enough problems with co2 on earth without importing martian Co2.

Terran methane would just be recycled back to earth, but martian methane would be a pure import.

IMHO, you may be overlooking something - the net. Regardless of the source of the methane's combustion byproducts, it's going to enter Earth's carbon cycle if suborbital. Viewed alone, there's no difference. However, if Martian, it would be replacing Terran methane - and Terran methane has to get to orbit somehow. That somehow is going to use many times the orbital fuel's mass to get it to orbit. All of that will be going into the atmosphere. This is not true for Martian methane. So, utilizing Martian methane is actually a very large net reduction in byproducts ending up in the Earth's atmosphere. And that's not even counting the lower total delta/v to LEO from the surface of Mars vs. the surface of Earth. 

IMHO, that lower delta/v to LEO makes getting prop from Mars (or an asteroid, or a martian moon) for use in LEO very attractive, though of course very long-term. Likewise, other consumables for LEO infrastructure.
I am assuming all terran methane is made the same way martian methane is- with water, CO2 and electricity. That makes any and all terran methane net carbon neutral, for launch as well as for departure burns. Martian landing burns are an export of terran methane, landing burns of starships returning from mars are an import, but the balance is net earth export. (Pretty much all lunar operations are net export as well.)

But bringing martian methane to earth orbit to burn upsets that "trade balance."
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Pahimarus on 08/22/2020 05:04 pm
Quote from: rakaydos
I am assuming all terran methane is made the same way martian methane is- with water, CO2 and electricity. That makes any and all terran methane net carbon neutral, for launch as well as for departure burns.

Except it isn't.

Terran methane is dug up from underground sequestered areas and burned.

As pointed out previously the amount of carbon is trivial compared to the amount in the Earth's overall carbon cycle. So what you really have to concern yourself with is the immediate emissions impact (if that is even significant which I doubt WAG each ss launch is 0.0000004% of annual emissions but for the sake of argument).

If that is the case you must consider the whole life cycle analysis of your methane/co2.

From earth's perspective martian sourced fuel appears in the atmosphere as CO2. So does Terran methane. If anything more emissions are generated drilling for and processing the earth methane than vice versa.

Until the majority of earth methane is synthesized from atmospheric CO2 using renewable power this will continue to be true so you can't write it off as net neutral.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/22/2020 05:12 pm
AIUI, gasses in the upper atmosphere get banged around quite a bit by UV. Is this enough to disassociate CH4? Any ideas on what the half life would be at different altitudes if this happens?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/22/2020 06:30 pm
Quote from: rakaydos
I am assuming all terran methane is made the same way martian methane is- with water, CO2 and electricity. That makes any and all terran methane net carbon neutral, for launch as well as for departure burns.
Until the majority of earth methane is synthesized from atmospheric CO2 using renewable power this will continue to be true so you can't write it off as net neutral.
Not to put too fine a point on it, but we dont have an orbital class methane rocket yet, let alone martian methane to fill it up with.

By the time a martian colony is developed enough to export methane, earth had BETTER have moved to non-fossil methane, or we will have bigger problems than supplying a martian base.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Slarty1080 on 08/22/2020 08:55 pm
The biggest problem with filling LEO tankers with non-terran methane, is that departure burns from LEO put the exaust in a suborbital trajectory. And we have enough problems with co2 on earth without importing martian Co2.

Terran methane would just be recycled back to earth, but martian methane would be a pure import.

IMHO, you may be overlooking something - the net. Regardless of the source of the methane's combustion byproducts, it's going to enter Earth's carbon cycle if suborbital. Viewed alone, there's no difference. However, if Martian, it would be replacing Terran methane - and Terran methane has to get to orbit somehow. That somehow is going to use many times the orbital fuel's mass to get it to orbit. All of that will be going into the atmosphere. This is not true for Martian methane. So, utilizing Martian methane is actually a very large net reduction in byproducts ending up in the Earth's atmosphere. And that's not even counting the lower total delta/v to LEO from the surface of Mars vs. the surface of Earth. 

IMHO, that lower delta/v to LEO makes getting prop from Mars (or an asteroid, or a martian moon) for use in LEO very attractive, though of course very long-term. Likewise, other consumables for LEO infrastructure.
I am assuming all terran methane is made the same way martian methane is- with water, CO2 and electricity. That makes any and all terran methane net carbon neutral, for launch as well as for departure burns. Martian landing burns are an export of terran methane, landing burns of starships returning from mars are an import, but the balance is net earth export. (Pretty much all lunar operations are net export as well.)

But bringing martian methane to earth orbit to burn upsets that "trade balance."
Unfortunately Terran methane is currently derived from fossil sources and likely to remain that way for many years . It will not be energy efficient to generate methane from the sabatier process on Earth until all fossil power stations have been replaced. Because it will always be more efficient to plug a new solar or wind farm into the grid and switch off a fossil fuel plant than using the solar/wind electricity to unscramble the CO2 egg after it has been burnt.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/22/2020 09:02 pm
AIUI, gasses in the upper atmosphere get banged around quite a bit by UV. Is this enough to disassociate CH4?

Burning it in oxygen sure would.

(Rockets are releasing combustion products, not raw fuel.)

[Also, what Rakaydos said. Should we be concerned about the accumulation of re-entry heat? Changes to Earth's rotational inertia due to mass loss to deep space missions? Yes. Yes we should. Once we're a K1+ civilisation, there are many such things we'll need to manage. Should we be concerned now? No.]
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: spacenut on 08/22/2020 09:22 pm
For some of you guys information, the US has a 200 year supply of natural gas drilled, tapped, and capped, without drilling another well.  Producing methane from CO2 and water on earth costs more than just buying existing natural gas.  Unless Musk wants to make it anyways, the first methane rockets for several years, will be extracted from the existing 95% methane natural gas.  Coal, oil, and gasoline, produce far far more CO2 per year than natural gas.  Rockets will be a minor use, even at high flight rates. 
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: CJ on 08/22/2020 11:20 pm
Do we have a ballpark estimate of the G needed for Starship-to-Starship refueling, and how long it would need to be applied for?

As I recall, the plan was to use thrusters to impart some G to settle the prop in order to transfer it. I was wondering how much prop would need to be used for said thrusters for each transfer. (which could be calculated if we knew the G and the time).

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: TomH on 08/23/2020 12:12 am
Do we have a ballpark estimate of the G needed for Starship-to-Starship refueling, and how long it would need to be applied for?

As I recall, the plan was to use thrusters to impart some G to settle the prop in order to transfer it. I was wondering how much prop would need to be used for said thrusters for each transfer. (which could be calculated if we knew the G and the time).

I don't think they intend for the flow to be induced by gravity. You need some G to keep the prop settled, but as soon as settling begins, pumps would be used to transfer the liquids. Waiting for artificial gravity alone to induce the transfer would take a long time. The transfer rate will depend upon pump capacity. Does anyone have any specs re. the pumps they intend to use? Pipe diameter and flow resistance related to coefficient of friction in relation to material type, temperature, etc. are also factors in the flow rate, but the pump capacity is the main thing.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/23/2020 12:15 am
AIUI, gasses in the upper atmosphere get banged around quite a bit by UV. Is this enough to disassociate CH4?

Burning it in oxygen sure would.

(Rockets are releasing combustion products, not raw fuel.)

[Also, what Rakaydos said. Should we be concerned about the accumulation of re-entry heat? Changes to Earth's rotational inertia due to mass loss to deep space missions? Yes. Yes we should. Once we're a K1+ civilisation, there are many such things we'll need to manage. Should we be concerned now? No.]
My bad. Change the Q to CO2.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/23/2020 12:26 am
Do we have a ballpark estimate of the G needed for Starship-to-Starship refueling, and how long it would need to be applied for?

As I recall, the plan was to use thrusters to impart some G to settle the prop in order to transfer it. I was wondering how much prop would need to be used for said thrusters for each transfer. (which could be calculated if we knew the G and the time).
Literally micro G's. Think if it as the tank sliding 'up' around the propellant. It would take a while to settle. More G, faster settling but still probably a fraction of a G. Once settled, back to micro G.


Playing with this to find optimum will be high priority once they start doing it.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/23/2020 12:28 am
Do we have a ballpark estimate of the G needed for Starship-to-Starship refueling, and how long it would need to be applied for?

As I recall, the plan was to use thrusters to impart some G to settle the prop in order to transfer it. I was wondering how much prop would need to be used for said thrusters for each transfer. (which could be calculated if we knew the G and the time).

I don't think they intend for the flow to be induced by gravity. You need some G to keep the prop settled, but as soon as settling begins, pumps would be used to transfer the liquids. Waiting for artificial gravity alone to induce the transfer would take a long time. The transfer rate will depend upon pump capacity. Does anyone have any specs re. the pumps they intend to use? Pipe diameter and flow resistance related to coefficient of friction in relation to material type, temperature, etc. are also factors in the flow rate, but the pump capacity is the main thing.
Could it be done with pressure?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Redclaws on 08/23/2020 01:05 am
So if you pulled a mild vacuum in the empty tank, then topped the other up with ... whatever is going to fill it...  that might work.  I don’t think you could pull much vacuum, though, without collapsing the tank.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: SkyRate on 08/23/2020 01:20 am
So if you pulled a mild vacuum in the empty tank, then topped the other up with ... whatever is going to fill it...  that might work.  I don’t think you could pull much vacuum, though, without collapsing the tank.
What pressure would collapse the tank?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: envy887 on 08/23/2020 01:21 am
So if you pulled a mild vacuum in the empty tank, then topped the other up with ... whatever is going to fill it...  that might work.  I don’t think you could pull much vacuum, though, without collapsing the tank.

A ship in LEO is sitting in a hard vacuum. You don't need to "pull" to get a vacuum, and you certainly won't be collapsing anything.

They will probably pressurize the tanker and vent the tankee to make a pressure differential. If they pump anything, it will be compressing boiloff in COPVs to be used to press the tanker. This can be done with solar electric over a period of time between refueling flights, so it doesn't require high powered pumps.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: ericgu on 08/23/2020 03:01 am
Quote from: rakaydos
I am assuming all terran methane is made the same way martian methane is- with water, CO2 and electricity. That makes any and all terran methane net carbon neutral, for launch as well as for departure burns.

Except it isn't.

Terran methane is dug up from underground sequestered areas and burned.


This is an interesting question; I found a paper https://www.sciencedirect.com/science/article/pii/S0306261919312681 (https://www.sciencedirect.com/science/article/pii/S0306261919312681) that looked at the economics.

There could be reasons that would push you towards wanting to create your own methane...

* Maybe there isn't a big enough pipeline the area where you want to operate.
* Maybe the refining is problematic  - you can't easily do it, you can't dispose of the fractions you don't want, etc.
* Maybe you have an excess of renewable power at certain times of the day (like Texas has too much wind power at night) that you can economically use.
* Maybe there are carbon taxes that make fossil fuel more expensive.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: livingjw on 08/23/2020 03:49 am
Do we have a ballpark estimate of the G needed for Starship-to-Starship refueling, and how long it would need to be applied for?

As I recall, the plan was to use thrusters to impart some G to settle the prop in order to transfer it. I was wondering how much prop would need to be used for said thrusters for each transfer. (which could be calculated if we knew the G and the time).

I don't think they intend for the flow to be induced by gravity. You need some G to keep the prop settled, but as soon as settling begins, pumps would be used to transfer the liquids. Waiting for artificial gravity alone to induce the transfer would take a long time. The transfer rate will depend upon pump capacity. Does anyone have any specs re. the pumps they intend to use? Pipe diameter and flow resistance related to coefficient of friction in relation to material type, temperature, etc. are also factors in the flow rate, but the pump capacity is the main thing.
Could it be done with pressure?

- Yes, you can do it with low pressure pumps and as a benefit, you don't have to vent any gases.

- You could also do it with pressure differential, but you would have to vent some gases.

John
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Thrustpuzzle on 08/23/2020 07:18 am
- You could also do it with pressure differential, but you would have to vent some gases.
There may be little or no venting needed since we're dealing with cryogenic fluids, not water or kerosene. The receiving tanks will have their ullage space filled with gas, and the incoming liquids will displace some of that volume, compressing that gas to higher pressure, requiring venting. But these are cryo liquids, by definition at temperatures lower than (perhaps much lower than) the boiling point of the gas, so in fact that ullage gas will be cooled by the incoming cryogenic rain at the same time it's compressed. Depending on the temperature of the incoming liquid, and the efficiency of heat transfer between the rain and the gas, the ullage gas pressure could even lower as the tank is filled, increasing the pressure differential between source and destination tanks. It depends on the temperature balance and mixing efficiency.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Slarty1080 on 08/23/2020 08:08 am
Quote from: rakaydos
I am assuming all terran methane is made the same way martian methane is- with water, CO2 and electricity. That makes any and all terran methane net carbon neutral, for launch as well as for departure burns.

Except it isn't.

Terran methane is dug up from underground sequestered areas and burned.


This is an interesting question; I found a paper https://www.sciencedirect.com/science/article/pii/S0306261919312681 (https://www.sciencedirect.com/science/article/pii/S0306261919312681) that looked at the economics.

There could be reasons that would push you towards wanting to create your own methane...

* Maybe there isn't a big enough pipeline the area where you want to operate.
* Maybe the refining is problematic  - you can't easily do it, you can't dispose of the fractions you don't want, etc.
* Maybe you have an excess of renewable power at certain times of the day (like Texas has too much wind power at night) that you can economically use.
* Maybe there are carbon taxes that make fossil fuel more expensive.
This is a good point. There are certainly cases where you would want to create methane, if the nearest supply is far enough away to make delivery impractical and you need large quantities (and you really do need it) and you have a lot of renewable power available. Having an accessible source of CO2 would also be beneficial.

The most obvious place where these condition hold is Mars. It could happen on Earth but the conditions would have to be  very unusual.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 08/23/2020 10:11 am
[SNIP]

- Yes, you can do it with low pressure pumps and as a benefit, you don't have to vent any gases.

This.

You pump the gas from the empty ship into the tanker, this pushes the liquid into the empty ship.
(or the other way around if that's your preference ie, pump the liquid which pushes the gas)

It would be a roughly equal volumetric exchange so no need to vent or compress anything.  :)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/23/2020 11:34 am
-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? If you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.

-In terms of costs we must put the cost of building and maintaining a fleet of tankers into consideration, achieving full and rapid reusability will take some time so while awaiting for that moment expandable would be a better option as an interim solution.
 

Star-Dust, you have aspirations of sending rockets to Mars, that is admirable, and if rockets were fueled with persistence, you might already be in orbit.  My unsolicited advice to you is that like early aviators, take one step at a time and develop a firm grasp of the fundamentals before taking that giant leap. 

A great example is your lack of understanding that SH can’t deliver your proposed depot to orbit.  This is an easy mistake to make, but as a result of this error, you have been now forced to fabricate this new expendable stage.  You deride the cost of maintaining tankers, but now somehow building expendable second stages comes without a tremendous cost?  That cost comes in many forms, not just in dollars, but also in manufacturing time and a workforce that is now dedicated to building hardware that will be thrown away after every flight.  This is very inefficient. 

If you have paid attention to the work at BC, you can see that constructing a SS is a multi-month process.  How is SS minus wings and the payload section any different from your proposed second stage?  Are you really willing to wait months between depot launches?  Have you done any analysis of the cost to dispose of five stages vs. maintenance of a single tanker?  Now work the other side of the problem.  You have your depot, but without the stage you just threw away, you can’t change orbits or dock with other depots.  You will need power to keep the fuels at the proper pressure.  Where will this come from?  Are you now going to add solar arrays and compressors that you also dispose of along with communications equipment, RCS, batteries, fuel pumps, etc.?  How will you de-orbit your empty depot?

My recommendation is to stick with this first step.  Perhaps spend some time studying the capabilities of SH and SS so you can avoid further simple errors.  Look at necessary capabilities for that second stage you are proposing compared to a SS Tanker/Depot concept. Again, before you can convince us that you have a viable vision for how to get to Mars and back, at least do the minimum legwork and develop a viable plan for how to get just a single Starship worth of fuel to LEO without one year required to build your five expendable second stages, along with 30 or more Raptors that you plan to dispose of.  Yes, this will take some discipline, and you just might succeed in this first step and either make a compelling case for your depots, or garner the knowledge and understanding as to why so many who have studied this problem, some for decades, disagree with you.  Best of luck.

1- I have calculated (online calculator) a 200 tons  payload to LEO with a second stage on top of SH, this is if the figures available are correct twice as much as a reusable SS capability in term of payload (100 tons) , and by definition will require twice less the number of flights, no need to remind  that SH on each flight require a 3400 tons of fuel+ 1200 tons SS ( 2.5 millions$ saved on fuel rough calculation based on 600$/ton LCH4, 200$/ton LOX).

2-A second stage by definition is a basic rocket which mean engines + fuel tank, I dont think that a stainless steel tank coupled with six raptors engines will weigh that much in the overall balance of a $/per ton of payload (no heat shield, no legs/no extra fuel,.........etc.).

3-The option of depot will mitigate the need for rapid  launch of tankers, SS bound for Mars will only be launched when all tanks are in place, this allowing time for further developement of rapid reuse of SH/SH while not delaying first mission to Mars (interim solution).

4-No extra spending on O&M for tankers and less expensive 2S than a tanker.

5- Fuel depot could be sent to Mars orbit.


Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/23/2020 12:43 pm

You might be misunderstanding. There is nothing in a depot, one tank or multiple, that precludes butt to butt refueling. Two entirely separate issues.


As for sending a depot to Mars, there has been discussion in this. First you need to understand that it does not remove the SS need to refuel before leaving earth. It's an alternative to having ISRU propellant production on mars. However, it's always seen as a supplement for early missions until reliable ISRU is on line, and not a replacement. Mars will never be more than a base if it depends on earth for its very ability to return.


Phil

I keep my opinion on  Mars colonisation prospect for me, but getting first human and first permanent settlement on the red planet will require a step by step approach. If we want to get a real plan to do so we can't bet on future developement of new technologies that does not exist yet. this is why interim solutions is required you improve the process while you achieve what can be achieved in a timely manner, the air travel didn't await for the modern jet reaction airliners to be a reality, it took years and years and many accidents to get to what is now air travel.

The above mentioned idea of a multiple disposable tanks that will be joint to a nodal comprtment as is the case for ISS, seems to me practicle for multiple reasons:

-No need for a fleet of tankers and subsequent logistic issues.
-No time waisted for SS departing to Mars.
-Depot could be positioned in any strategic position.
Ahhh. I think I see the problem. It's a matter of religious doctrine and not amenable to reasoned argument - from either side of the question.


Stardust, from what I'm picking up, you are skeptical of the entire approach. This is observation, not criticism.


For the majority of us, we are skeptical of the traditional approach. Again, an observation and not an endorsement.


The two religions are so diametrically at odds that they can never be reconciled no matter how much technical argument is presented. So let's stop this bickering over detail and agree to disagree. THERE IS NOTHING HERE TO GET frakked ABOUT!!


I learned a long time ago that all logic based arguments have at least one predicate - an assumption. What we have here is a conflict of assumptions.


Stardust, the only fault I can assign you is that you have stepped into a den of new spacers and are espousing the doctrine of old space or something close to it. In another time that would get you burned at the stake or an invitation to make love with the Iron Maiden. I promise, we won't do that.


What I would suggest is that you start another discussion with those who share your beliefs. I'd like to believe that we are collectively mature enough to allow others to discuss that which we disagree with although we might want to draw the line at flat earthers 8)


Phil

I got a lot of things that make me skeptical from low maturity technology to financial plan lacking realism and no sustainable viable business plan. :-\

That's glass half empty, or some people might say more realistic lol.  I prefer to think they're the team who finally have a real plan for doing this with re-use, powered landing, and funding from starlink.  If they've got it, they're building a new era in human travel.  If they fail, then they'll have advanced the state of the art a long way and eventually someone will take their successes and build on them. 

Either way, spending time on approaches they've clearly discarded is wasteful.  Same reason we're no longer dissecting the nuances of large scale composite construction; they discarded that approach.  Likewise, they long ago discarded the notion of expendable rocketry.  Right, wrong?  Only history will decide, but burning up the forum advocating SpaceX go disposable isn't a great use of page space.

If you really like the expendable idea you should explore the habitat threads.  There's a lot of supportive discussion for the  concept there in terms of leaving them at Mars and using as permanent habitats.  Musk's even hinted that may be the fate of early flights.  You're not wrong that there may be some expendable parts  in the architecture for some time; but you're really misplaced thinking it's going to be their plan in earth orbit since they've clearly stated the opposite.

Just my $0.02,  I think your idea would generate more healthy debate in the habitats thread where people are eager to only fly them once ;)

For me it's more about technology maturation time requirement than affinity.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: livingjw on 08/23/2020 12:55 pm
[SNIP]

- Yes, you can do it with low pressure pumps and as a benefit, you don't have to vent any gases.

This.

You pump the gas from the empty ship into the tanker, this pushes the liquid into the empty ship.
(or the other way around if that's your preference ie, pump the liquid which pushes the gas)

It would be a roughly equal volumetric exchange so no need to vent or compress anything.  :)

No, if you are using a pressure difference, the gas from the tank being filled is lower than the tank doing the filling, so the gas has to be either condensed or vented.

John
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Keldor on 08/23/2020 02:43 pm
-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? If you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.

-In terms of costs we must put the cost of building and maintaining a fleet of tankers into consideration, achieving full and rapid reusability will take some time so while awaiting for that moment expandable would be a better option as an interim solution.
 

Star-Dust, you have aspirations of sending rockets to Mars, that is admirable, and if rockets were fueled with persistence, you might already be in orbit.  My unsolicited advice to you is that like early aviators, take one step at a time and develop a firm grasp of the fundamentals before taking that giant leap. 

A great example is your lack of understanding that SH can’t deliver your proposed depot to orbit.  This is an easy mistake to make, but as a result of this error, you have been now forced to fabricate this new expendable stage.  You deride the cost of maintaining tankers, but now somehow building expendable second stages comes without a tremendous cost?  That cost comes in many forms, not just in dollars, but also in manufacturing time and a workforce that is now dedicated to building hardware that will be thrown away after every flight.  This is very inefficient. 

If you have paid attention to the work at BC, you can see that constructing a SS is a multi-month process.  How is SS minus wings and the payload section any different from your proposed second stage?  Are you really willing to wait months between depot launches?  Have you done any analysis of the cost to dispose of five stages vs. maintenance of a single tanker?  Now work the other side of the problem.  You have your depot, but without the stage you just threw away, you can’t change orbits or dock with other depots.  You will need power to keep the fuels at the proper pressure.  Where will this come from?  Are you now going to add solar arrays and compressors that you also dispose of along with communications equipment, RCS, batteries, fuel pumps, etc.?  How will you de-orbit your empty depot?

My recommendation is to stick with this first step.  Perhaps spend some time studying the capabilities of SH and SS so you can avoid further simple errors.  Look at necessary capabilities for that second stage you are proposing compared to a SS Tanker/Depot concept. Again, before you can convince us that you have a viable vision for how to get to Mars and back, at least do the minimum legwork and develop a viable plan for how to get just a single Starship worth of fuel to LEO without one year required to build your five expendable second stages, along with 30 or more Raptors that you plan to dispose of.  Yes, this will take some discipline, and you just might succeed in this first step and either make a compelling case for your depots, or garner the knowledge and understanding as to why so many who have studied this problem, some for decades, disagree with you.  Best of luck.

1- I have calculated (online calculator) a 200 tons  payload to LEO with a second stage on top of SH, this is if the figures available are correct twice as much as a reusable SS capability in term of payload (100 tons) , and by definition will require twice less the number of flights, no need to remind  that SH on each flight require a 3400 tons of fuel+ 1200 tons SS ( 2.5 millions$ saved on fuel rough calculation based on 600$/ton LCH4, 200$/ton LOX).

2-A second stage by definition is a basic rocket which mean engines + fuel tank, I dont think that a stainless steel tank coupled with six raptors engines will weigh that much in the overall balance of a $/per ton of payload (no heat shield, no legs/no extra fuel,.........etc.).

3-The option of depot will mitigate the need for rapid  launch of tankers, SS bound for Mars will only be launched when all tanks are in place, this allowing time for further developement of rapid reuse of SH/SH while not delaying first mission to Mars (interim solution).

4-No extra spending on O&M for tankers and less expensive 2S than a tanker.

5- Fuel depot could be sent to Mars orbit.

There are a few reasons I doubt the practicality of a fueling deopt.

First, orbital mechanics.  The problem is that orbits have to be properly aligned for the rocket to be able to rendevous with the depot and then proceed to Mars.  With a depot in low orbit, this might not be a problem, but something on a high eccentric orbit (such as needed for landing on the Moon) will rarely be in the right alignment.  You can imagine the oblong shape of the orbit being like an arrow, pointing the direction the vehicle has to depart in.  Most of the time, it will be pointing the wrong way.  Also, once the depot is in this orbit, it takes a lot of fuel and/or time to change this orbit, so you're largely stuck with whatever direction it happens to point.


Low orbits have a different problem, namely heat.  Cryogenic fuel must be kept very cold to stay liquid.  If it boils into a gas state, your tank will explode from the pressure much like a giant steam boiler that has been overheated.  But the environment in low earth orbit is very hot.  A good comparason would be to Death Valley or somewhere in the middle of the Sahara.  Except in orbit, there's no wind blowing in from cooler places to moderate temperatures.  The same problem happens in high orbits or interplanetary transit, but here the vehicle can do things like pointing the engines toward the sun to shade the rest of the vehicle.  But there's no escaping the reflection off Earth when you're in low orbit.  It's difficult to shed heat in space, since again, there's no air flow to conduct it away, it all has to leave in the form of infrared radiation.  This is a slow process, requiring huge radiators, which again, need to somehow be shaded from both the Earth and the Sun or else they'll become heaters.  Also, since they need to reject enough heat to cool the tanks down to cryogenic temperatures, they'll have to be well below the temperature of the propellant, or else you'll need a heat pump system much like air conditioning, but this generates a lot of waste heat which now must be dealt with as well...

It's simply very difficult to store propellant in orbit for long periods of time in any practical fashion.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/23/2020 03:27 pm
-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? If you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.

-In terms of costs we must put the cost of building and maintaining a fleet of tankers into consideration, achieving full and rapid reusability will take some time so while awaiting for that moment expandable would be a better option as an interim solution.
 

Star-Dust, you have aspirations of sending rockets to Mars, that is admirable, and if rockets were fueled with persistence, you might already be in orbit.  My unsolicited advice to you is that like early aviators, take one step at a time and develop a firm grasp of the fundamentals before taking that giant leap. 

A great example is your lack of understanding that SH can’t deliver your proposed depot to orbit.  This is an easy mistake to make, but as a result of this error, you have been now forced to fabricate this new expendable stage.  You deride the cost of maintaining tankers, but now somehow building expendable second stages comes without a tremendous cost?  That cost comes in many forms, not just in dollars, but also in manufacturing time and a workforce that is now dedicated to building hardware that will be thrown away after every flight.  This is very inefficient. 

If you have paid attention to the work at BC, you can see that constructing a SS is a multi-month process.  How is SS minus wings and the payload section any different from your proposed second stage?  Are you really willing to wait months between depot launches?  Have you done any analysis of the cost to dispose of five stages vs. maintenance of a single tanker?  Now work the other side of the problem.  You have your depot, but without the stage you just threw away, you can’t change orbits or dock with other depots.  You will need power to keep the fuels at the proper pressure.  Where will this come from?  Are you now going to add solar arrays and compressors that you also dispose of along with communications equipment, RCS, batteries, fuel pumps, etc.?  How will you de-orbit your empty depot?

My recommendation is to stick with this first step.  Perhaps spend some time studying the capabilities of SH and SS so you can avoid further simple errors.  Look at necessary capabilities for that second stage you are proposing compared to a SS Tanker/Depot concept. Again, before you can convince us that you have a viable vision for how to get to Mars and back, at least do the minimum legwork and develop a viable plan for how to get just a single Starship worth of fuel to LEO without one year required to build your five expendable second stages, along with 30 or more Raptors that you plan to dispose of.  Yes, this will take some discipline, and you just might succeed in this first step and either make a compelling case for your depots, or garner the knowledge and understanding as to why so many who have studied this problem, some for decades, disagree with you.  Best of luck.

1- I have calculated (online calculator) a 200 tons  payload to LEO with a second stage on top of SH, this is if the figures available are correct twice as much as a reusable SS capability in term of payload (100 tons) , and by definition will require twice less the number of flights, no need to remind  that SH on each flight require a 3400 tons of fuel+ 1200 tons SS ( 2.5 millions$ saved on fuel rough calculation based on 600$/ton LCH4, 200$/ton LOX).

2-A second stage by definition is a basic rocket which mean engines + fuel tank, I dont think that a stainless steel tank coupled with six raptors engines will weigh that much in the overall balance of a $/per ton of payload (no heat shield, no legs/no extra fuel,.........etc.).

3-The option of depot will mitigate the need for rapid  launch of tankers, SS bound for Mars will only be launched when all tanks are in place, this allowing time for further developement of rapid reuse of SH/SH while not delaying first mission to Mars (interim solution).

4-No extra spending on O&M for tankers and less expensive 2S than a tanker.

5- Fuel depot could be sent to Mars orbit.

There are a few reasons I doubt the practicality of a fueling deopt.

First, orbital mechanics.  The problem is that orbits have to be properly aligned for the rocket to be able to rendevous with the depot and then proceed to Mars.  With a depot in low orbit, this might not be a problem, but something on a high eccentric orbit (such as needed for landing on the Moon) will rarely be in the right alignment.  You can imagine the oblong shape of the orbit being like an arrow, pointing the direction the vehicle has to depart in.  Most of the time, it will be pointing the wrong way.  Also, once the depot is in this orbit, it takes a lot of fuel and/or time to change this orbit, so you're largely stuck with whatever direction it happens to point.


Low orbits have a different problem, namely heat.  Cryogenic fuel must be kept very cold to stay liquid.  If it boils into a gas state, your tank will explode from the pressure much like a giant steam boiler that has been overheated.  But the environment in low earth orbit is very hot.  A good comparason would be to Death Valley or somewhere in the middle of the Sahara.  Except in orbit, there's no wind blowing in from cooler places to moderate temperatures.  The same problem happens in high orbits or interplanetary transit, but here the vehicle can do things like pointing the engines toward the sun to shade the rest of the vehicle.  But there's no escaping the reflection off Earth when you're in low orbit.  It's difficult to shed heat in space, since again, there's no air flow to conduct it away, it all has to leave in the form of infrared radiation.  This is a slow process, requiring huge radiators, which again, need to somehow be shaded from both the Earth and the Sun or else they'll become heaters.  Also, since they need to reject enough heat to cool the tanks down to cryogenic temperatures, they'll have to be well below the temperature of the propellant, or else you'll need a heat pump system much like air conditioning, but this generates a lot of waste heat which now must be dealt with as well...

It's simply very difficult to store propellant in orbit for long periods of time in any practical fashion.

Fuel will certainly be the biggest challenge for Mars missions.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/23/2020 04:52 pm
-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? If you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.

-In terms of costs we must put the cost of building and maintaining a fleet of tankers into consideration, achieving full and rapid reusability will take some time so while awaiting for that moment expandable would be a better option as an interim solution.
 

Star-Dust, you have aspirations of sending rockets to Mars, that is admirable, and if rockets were fueled with persistence, you might already be in orbit.  My unsolicited advice to you is that like early aviators, take one step at a time and develop a firm grasp of the fundamentals before taking that giant leap. 

A great example is your lack of understanding that SH can’t deliver your proposed depot to orbit.  This is an easy mistake to make, but as a result of this error, you have been now forced to fabricate this new expendable stage.  You deride the cost of maintaining tankers, but now somehow building expendable second stages comes without a tremendous cost?  That cost comes in many forms, not just in dollars, but also in manufacturing time and a workforce that is now dedicated to building hardware that will be thrown away after every flight.  This is very inefficient. 

If you have paid attention to the work at BC, you can see that constructing a SS is a multi-month process.  How is SS minus wings and the payload section any different from your proposed second stage?  Are you really willing to wait months between depot launches?  Have you done any analysis of the cost to dispose of five stages vs. maintenance of a single tanker?  Now work the other side of the problem.  You have your depot, but without the stage you just threw away, you can’t change orbits or dock with other depots.  You will need power to keep the fuels at the proper pressure.  Where will this come from?  Are you now going to add solar arrays and compressors that you also dispose of along with communications equipment, RCS, batteries, fuel pumps, etc.?  How will you de-orbit your empty depot?

My recommendation is to stick with this first step.  Perhaps spend some time studying the capabilities of SH and SS so you can avoid further simple errors.  Look at necessary capabilities for that second stage you are proposing compared to a SS Tanker/Depot concept. Again, before you can convince us that you have a viable vision for how to get to Mars and back, at least do the minimum legwork and develop a viable plan for how to get just a single Starship worth of fuel to LEO without one year required to build your five expendable second stages, along with 30 or more Raptors that you plan to dispose of.  Yes, this will take some discipline, and you just might succeed in this first step and either make a compelling case for your depots, or garner the knowledge and understanding as to why so many who have studied this problem, some for decades, disagree with you.  Best of luck.

1- I have calculated (online calculator) a 200 tons  payload to LEO with a second stage on top of SH, this is if the figures available are correct twice as much as a reusable SS capability in term of payload (100 tons) , and by definition will require twice less the number of flights, no need to remind  that SH on each flight require a 3400 tons of fuel+ 1200 tons SS ( 2.5 millions$ saved on fuel rough calculation based on 600$/ton LCH4, 200$/ton LOX).

2-A second stage by definition is a basic rocket which mean engines + fuel tank, I dont think that a stainless steel tank coupled with six raptors engines will weigh that much in the overall balance of a $/per ton of payload (no heat shield, no legs/no extra fuel,.........etc.).

3-The option of depot will mitigate the need for rapid  launch of tankers, SS bound for Mars will only be launched when all tanks are in place, this allowing time for further developement of rapid reuse of SH/SH while not delaying first mission to Mars (interim solution).

4-No extra spending on O&M for tankers and less expensive 2S than a tanker.

5- Fuel depot could be sent to Mars orbit.

There are a few reasons I doubt the practicality of a fueling deopt.

First, orbital mechanics.  The problem is that orbits have to be properly aligned for the rocket to be able to rendevous with the depot and then proceed to Mars.  With a depot in low orbit, this might not be a problem, but something on a high eccentric orbit (such as needed for landing on the Moon) will rarely be in the right alignment.  You can imagine the oblong shape of the orbit being like an arrow, pointing the direction the vehicle has to depart in.  Most of the time, it will be pointing the wrong way.  Also, once the depot is in this orbit, it takes a lot of fuel and/or time to change this orbit, so you're largely stuck with whatever direction it happens to point.


Low orbits have a different problem, namely heat.  Cryogenic fuel must be kept very cold to stay liquid.  If it boils into a gas state, your tank will explode from the pressure much like a giant steam boiler that has been overheated.  But the environment in low earth orbit is very hot.  A good comparason would be to Death Valley or somewhere in the middle of the Sahara.  Except in orbit, there's no wind blowing in from cooler places to moderate temperatures.  The same problem happens in high orbits or interplanetary transit, but here the vehicle can do things like pointing the engines toward the sun to shade the rest of the vehicle.  But there's no escaping the reflection off Earth when you're in low orbit.  It's difficult to shed heat in space, since again, there's no air flow to conduct it away, it all has to leave in the form of infrared radiation.  This is a slow process, requiring huge radiators, which again, need to somehow be shaded from both the Earth and the Sun or else they'll become heaters.  Also, since they need to reject enough heat to cool the tanks down to cryogenic temperatures, they'll have to be well below the temperature of the propellant, or else you'll need a heat pump system much like air conditioning, but this generates a lot of waste heat which now must be dealt with as well...

It's simply very difficult to store propellant in orbit for long periods of time in any practical fashion.

Fuel will certainly be the biggest challenge for Mars missions.
Not really. Not if you can get replacement fuel up cheaply enough. But it's still better to fill in LEO immediately before departure.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/23/2020 04:56 pm
[SNIP]

- Yes, you can do it with low pressure pumps and as a benefit, you don't have to vent any gases.

This.

You pump the gas from the empty ship into the tanker, this pushes the liquid into the empty ship.
(or the other way around if that's your preference ie, pump the liquid which pushes the gas)

It would be a roughly equal volumetric exchange so no need to vent or compress anything.  :)

No, if you are using a pressure difference, the gas from the tank being filled is lower than the tank doing the filling, so the gas has to be either condensed or vented.

John
With autogenous pressurization, conceivably the pressure in the receiving tanks could be tapered off during the last burn, within operational limits. There is also a reasonable chance that autogenous gasses will distribute to high pressure tanks before distribution to lower pressure systems.


The Depot will have its own gas storage system that could be kept charged from boiloff or, save the boiloff for cryo cooler condensation and allow the receiving ship to recharge the depot high pressure gas system for general thruster use and tank press during refueling.


This could face some refinement but at first blush it seems to replenish consumables on the depot while minimizing propellant transfer wastage, at the cost of two more quick disconnects.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/23/2020 05:39 pm
-I dont know what is SH/SS payload to LEO, but let imagine some sort of expandable second stage on top of SH what would be the payload? If you have an answer then that is the weight of one single fuel tank bound for the mechanism (depot) put in space.

-In terms of costs we must put the cost of building and maintaining a fleet of tankers into consideration, achieving full and rapid reusability will take some time so while awaiting for that moment expandable would be a better option as an interim solution.
 

Star-Dust, you have aspirations of sending rockets to Mars, that is admirable, and if rockets were fueled with persistence, you might already be in orbit.  My unsolicited advice to you is that like early aviators, take one step at a time and develop a firm grasp of the fundamentals before taking that giant leap. 

A great example is your lack of understanding that SH can’t deliver your proposed depot to orbit.  This is an easy mistake to make, but as a result of this error, you have been now forced to fabricate this new expendable stage.  You deride the cost of maintaining tankers, but now somehow building expendable second stages comes without a tremendous cost?  That cost comes in many forms, not just in dollars, but also in manufacturing time and a workforce that is now dedicated to building hardware that will be thrown away after every flight.  This is very inefficient. 

If you have paid attention to the work at BC, you can see that constructing a SS is a multi-month process.  How is SS minus wings and the payload section any different from your proposed second stage?  Are you really willing to wait months between depot launches?  Have you done any analysis of the cost to dispose of five stages vs. maintenance of a single tanker?  Now work the other side of the problem.  You have your depot, but without the stage you just threw away, you can’t change orbits or dock with other depots.  You will need power to keep the fuels at the proper pressure.  Where will this come from?  Are you now going to add solar arrays and compressors that you also dispose of along with communications equipment, RCS, batteries, fuel pumps, etc.?  How will you de-orbit your empty depot?

My recommendation is to stick with this first step.  Perhaps spend some time studying the capabilities of SH and SS so you can avoid further simple errors.  Look at necessary capabilities for that second stage you are proposing compared to a SS Tanker/Depot concept. Again, before you can convince us that you have a viable vision for how to get to Mars and back, at least do the minimum legwork and develop a viable plan for how to get just a single Starship worth of fuel to LEO without one year required to build your five expendable second stages, along with 30 or more Raptors that you plan to dispose of.  Yes, this will take some discipline, and you just might succeed in this first step and either make a compelling case for your depots, or garner the knowledge and understanding as to why so many who have studied this problem, some for decades, disagree with you.  Best of luck.

1- I have calculated (online calculator) a 200 tons  payload to LEO with a second stage on top of SH, this is if the figures available are correct twice as much as a reusable SS capability in term of payload (100 tons) , and by definition will require twice less the number of flights, no need to remind  that SH on each flight require a 3400 tons of fuel+ 1200 tons SS ( 2.5 millions$ saved on fuel rough calculation based on 600$/ton LCH4, 200$/ton LOX).

2-A second stage by definition is a basic rocket which mean engines + fuel tank, I dont think that a stainless steel tank coupled with six raptors engines will weigh that much in the overall balance of a $/per ton of payload (no heat shield, no legs/no extra fuel,.........etc.).

3-The option of depot will mitigate the need for rapid  launch of tankers, SS bound for Mars will only be launched when all tanks are in place, this allowing time for further developement of rapid reuse of SH/SH while not delaying first mission to Mars (interim solution).

4-No extra spending on O&M for tankers and less expensive 2S than a tanker.

5- Fuel depot could be sent to Mars orbit.

There are a few reasons I doubt the practicality of a fueling deopt.

First, orbital mechanics.  The problem is that orbits have to be properly aligned for the rocket to be able to rendevous with the depot and then proceed to Mars.  With a depot in low orbit, this might not be a problem, but something on a high eccentric orbit (such as needed for landing on the Moon) will rarely be in the right alignment.  You can imagine the oblong shape of the orbit being like an arrow, pointing the direction the vehicle has to depart in.  Most of the time, it will be pointing the wrong way.  Also, once the depot is in this orbit, it takes a lot of fuel and/or time to change this orbit, so you're largely stuck with whatever direction it happens to point.


Low orbits have a different problem, namely heat.  Cryogenic fuel must be kept very cold to stay liquid.  If it boils into a gas state, your tank will explode from the pressure much like a giant steam boiler that has been overheated.  But the environment in low earth orbit is very hot.  A good comparason would be to Death Valley or somewhere in the middle of the Sahara.  Except in orbit, there's no wind blowing in from cooler places to moderate temperatures.  The same problem happens in high orbits or interplanetary transit, but here the vehicle can do things like pointing the engines toward the sun to shade the rest of the vehicle.  But there's no escaping the reflection off Earth when you're in low orbit.  It's difficult to shed heat in space, since again, there's no air flow to conduct it away, it all has to leave in the form of infrared radiation.  This is a slow process, requiring huge radiators, which again, need to somehow be shaded from both the Earth and the Sun or else they'll become heaters.  Also, since they need to reject enough heat to cool the tanks down to cryogenic temperatures, they'll have to be well below the temperature of the propellant, or else you'll need a heat pump system much like air conditioning, but this generates a lot of waste heat which now must be dealt with as well...

It's simply very difficult to store propellant in orbit for long periods of time in any practical fashion.
Cryo cooling is hard - not impossible.


One strategy would be a small fixed sun shield over the nose and keep that end aimed at the sun. Include a larger mobile shade to shield earth. Radiator panels would extend anti-earthward with the edge towards the sun and the faces towards open space. Use a cryo cooler. Fit in solar panels where appropriate.


The biggest operational issue is propellant use for keeping everything aligned. ISS uses Control Moment Gyros for this making it a watt issue, not a consumption issue. The problems with this are power consumption, mechanical longevity and 'saturation'.


PV can be as big as needed. Mechanical longevity seems to have improved post ISS failure mode analysis, and (I'm on weak ground here) I think the CMB's can desaturate (unwind) during the The night period. Multiple small CMB's for redundancy would be smarter than a few big ones.


All in all, much more complex than a simple tank in orbit. The ultimate question is not if it's doable, but does it give enough advantage to be justified. My gut says keep things simple at first and move in this direction as flight ops mature. Hmmm. Sounds almost like the SX mantra.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/23/2020 07:47 pm
An interesting paper on liquification and zero boiloff of martian ISRU propellant. Because it assumes gravity it is not directly applicable to depot boiloff. Assumption on tank dimensions, temperature and pressure both ambient and of the feed stock, are also different.


It's value is in a methodology for a preliminary assessment of different approaches and numbers that give a rough feel for the magnitude of the job.


What was looked at for a given delivery volume was mass, power consumption, power rejection, cost, maintainability, scaleability, reliability and what they call Volume-ility - the physical size and how much the hardware lends itself to physical distribution.


A methodology was developed to assign a weighting to these characteristics, and systems compared.

https://www.sciencedirect.com/science/article/pii/S0011227517302187 (https://www.sciencedirect.com/science/article/pii/S0011227517302187)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: vholub on 08/23/2020 11:12 pm
Hi there!
I created a somewhat in depth video about orbital debris, MMOD protection and related potential Starship issue that bothered for a while. I would appreciate your thoughts on both the aforementioned problems and the video.

https://youtu.be/2FrBEuAMHzw

TLDR: Starship needs to be at least several days in orbit for refueling and has no protection against any debris larger than 1 mm. Potentially high risk of mission failure.

Dear mods, I really did not know where to place this post, so please put it anywhere you think it belongs, or erase it if it goes against any rules.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Slarty1080 on 08/23/2020 11:27 pm
ISTM that either SpaceX will quickly get up to speed and will be able to launch a lot of propellant in a short period of time so that only modest cooling or shading is needed OR they will have to develop a proper orbital depot for the Mars mission with a larger shade, electric power, attitude control, cryo-coolers and radiators etc we will see.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/24/2020 12:46 am
1- I have calculated (online calculator) a 200 tons  payload to LEO with a second stage on top of SH

I bet you haven't, because...

I dont think that a stainless steel tank coupled with six raptors engines will weigh that much

...others have mentioned that the figures that estimate Starship's mass also estimate 40 tonnes for re-entry and landing. 25 tonnes for structure/heat-shield, and 15 tonnes for fuel.

Hence, if you're using a calculator that gives 100 tonnes payload (hence propellant) for the Starship tanker, then it will give 140 tonnes payload (prop) for the expendable version. If you got a higher figure, then you dropped the drymass to an unrealistic level.

3-The option of depot will mitigate the need for rapid  launch of tankers, SS bound for Mars will only be launched when all tanks are in place, this allowing time for further developement of rapid reuse of SH/SH while not delaying first mission to Mars (interim solution).

As mentioned repeatedly: Everything you require for your expendable tanks are the same as the tanker. You need to launch on SH, you need to be able to do docking manoeuvres in space, you need to connect up propellant lines (and gas-return lines for tank pressurisation), you need to be able to transfer propellant from the tanks to the engines on the main vehicle.

In addition, because you seem to have (finally!) accepted that you can't launch a single expendable fully fuelled tank into orbit, you now invent another whole structure, the docking node that holds a bunch of tanks as a depot. The depot then has to transfer fuel to the main Mars vehicle... kind of like... you know... a tanker.

You have all the requirements of building tankers, plus you need a depot before it's usable. It's not an "interim" solution.

The only technology you are trying to skip is reusability, which only requires re-entry and landing. But if Starship can land on Mars, then the technology for reusable tankers has already been developed. If the technology to land tankers isn't ready, Starship can't go to Mars.

So again, there's no "interim" where the Mars Starship exists but the tankers don't. Either the landing technology is ready, making tankers viable, or you can't land on Mars.

5- Fuel depot could be sent to Mars orbit.

Having fuel in Mars orbit doesn't replace ISRU production for a manned Starship mission: Starship can't land while fully fuelled, hence can't launch back into Mars orbit without ISRU propellant on the ground. If they have that, then your proposal isn't needed. If they don't, then you can't send humans to Mars. Again, there's no "interim".
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 08/24/2020 02:22 am
[SNIP]

- Yes, you can do it with low pressure pumps and as a benefit, you don't have to vent any gases.

This.

You pump the gas from the empty ship into the tanker, this pushes the liquid into the empty ship.
(or the other way around if that's your preference ie, pump the liquid which pushes the gas)

It would be a roughly equal volumetric exchange so no need to vent or compress anything.  :)

No, if you are using a pressure difference, the gas from the tank being filled is lower than the tank doing the filling, so the gas has to be either condensed or vented.

John

Sorry, perhaps I wasn't being clear, I'm talking about displacement exchange to negate the need to compress or vent gas.

When liquid is transferred from the tanker to the recipient, the tanker pressure drops and the recipient pressure increases. The excess recipient pressure needs to be reduced (either by venting or compression) and the tanker pressure needs to be maintained to aid pumping.

I'm saying solve two problems at once by transferring the excess pressure, in the form of gas, from the recipient to the tanker.

The pumping can occur either by pumping gas into the tanker to push the liquid through or by pumping liquid into the recipient and allow excess pressure gas to flow into the tanker. Either way you're not wasting energy compressing gas or wasting gas by venting.

Microgravity can be used to assist the flow from one to the other.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/24/2020 02:51 am
This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.

It isn't just delta-v. Producing enough propellant to launch enough propellant as cargo to Earth, to fully fuel its own return plus one SS flight puts a burden on the ISRU production that puts disproportionate burdens on a Mars settlement that it doesn't on a few extra Earth launches.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 08/24/2020 02:51 am
The biggest problem with filling LEO tankers with non-terran methane, is that departure burns from LEO put the exaust in a suborbital trajectory. And we have enough problems with co2 on earth without importing martian Co2.

Terran methane would just be recycled back to earth, but martian methane would be a pure import.
This is an interesting idea. I don't think whether it's martian or terran methane makes a big difference, tho, to the outcome.

It's worth considering that long-lived water vapor is a really powerful greenhouse gas. So you want to minimize Earth launches and consider alternate propellants. Ironically, CO/O2 is a better propellant from this perspective as the CO2 is a MUCH less powerful greenhouse gas than water vapor and CO2 already has a really long life in the atmosphere (~200 years), so adding another 5 years or so makes little difference (just install more direct air capture capacity on the ground). Additionally, you could go for Solar Electric Propulsion and use inert (and infrared-transparent) gases like Argon (which Mars has plenty of) for Earth departure. SpaceX has been also proving super cheap SEP using Starlink. In either case, getting the propellant from Mars reduces the number of Earth launches required for a given Mars trip and would reduce the greenhouse gas impact. Also, it might be cheaper in the long-run.

And the flip side (to water vapor being a really powerful greenhouse gas if placed in the upper atmosphere where its lifetime is much greater) is that using Mars to launch a whole bunch of stuff to Earth would actually help *terraform* Mars as a side effect!
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 08/24/2020 02:52 am
most of the propellant for trips to Mars might actually come *from* Mars.

If Deimos' very low density (https://solarsystem.nasa.gov/moons/mars-moons/deimos/by-the-numbers/) truly indicates volatiles, propellant for both Mars launch and LEO launch (https://forum.nasaspaceflight.com/index.php?topic=45299.msg1802366#msg1802366) could be produced more efficiently on Deimos than on Mars.  At scale, there'd be no need for Mars ISRU propellant (https://forum.nasaspaceflight.com/index.php?topic=45299.msg1802366#msg1802366), or for a tanker SH fleet - apart from the possibility of a small Earth-orbit depot fleet.

Various Earth-Moon-Mars propellant scenarios could be calculated with the network flow modeling method for optimized logistics in Ishimatsu et al. 2016.  Note their particular interest in Deimos:

Quote from: Ishimatsu et al. 2016
...it is interesting that part of the resources produced on Deimos are delivered back to GTO and LEO, and wait to be used for the crew and cargo outbound trip. Though it seems strange and non-intuitive at first, this is true at least computationally because in terms of ∆V, LEO is closer to Deimos than to the lunar surface and even Earth’s surface.

Image:  Network graph featuring Deimos ISRU propellant.  Ishimatsu et al. 2016, Fig. 10e.

Refs.

Ishimatsu, T., de Weck, O.L., Hoffman, J.A., Ohkami, Y. and Shishko, R., 2016. Generalized multicommodity network flow model for the earth–moon–mars logistics system. (https://dspace.mit.edu/bitstream/handle/1721.1/99360/JSR_Final_Manuscript_Ishimatsu.pdf?sequence=1&isAllowed=y) Journal of Spacecraft and Rockets, 53(1), pp.25-38.

I'm skeptical about the Martian moons for direct ISRU. But using them for a delta-v assist using a modest tether IS interesting and could help a lot without requiring magic materials (for Earth elevator) or super long transit times (in the case of a lunar elevator).
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 08/24/2020 02:56 am
For some of you guys information, the US has a 200 year supply of natural gas drilled, tapped, and capped, without drilling another well.  Producing methane from CO2 and water on earth costs more than just buying existing natural gas.  Unless Musk wants to make it anyways, the first methane rockets for several years, will be extracted from the existing 95% methane natural gas.  Coal, oil, and gasoline, produce far far more CO2 per year than natural gas.  Rockets will be a minor use, even at high flight rates.
Do the math on the 100 Megatons-per-year tweet that Musk mentioned earlier. It's something like a third of the entire world's natural gas production. It's not a rounding error. Particularly since it's putting water vapor (a strong greenhous gas) in the stratosphere (and upward) where the lifetime is years, not days like it is in the troposphere. That's like 10 times a bigger problem than the CO2 alone.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 08/24/2020 02:59 am
ISTM that either SpaceX will quickly get up to speed and will be able to launch a lot of propellant in a short period of time so that only modest cooling or shading is needed OR they will have to develop a proper orbital depot for the Mars mission with a larger shade, electric power, attitude control, cryo-coolers and radiators etc we will see.
SpaceX already mentioned a depot variant of Starship for their lunar mission.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 08/24/2020 02:59 am
This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.

It isn't just delta-v. Producing enough propellant to launch enough propellant as cargo to Earth, to fully fuel its own return plus one SS flight puts a burden on the ISRU production that puts disproportionate burdens on a Mars settlement that it doesn't on a few extra Earth launches.
Moving that industrial burden off of the Earth and on to Mars is a net-plus for the biosphere of Earth, long-term. And gives a Mars settlement a legitimate revenue stream. And helps terraform Mars through side effects of a really high launch rate.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 08/24/2020 03:15 am
AIUI, gasses in the upper atmosphere get banged around quite a bit by UV. Is this enough to disassociate CH4?

Burning it in oxygen sure would.

(Rockets are releasing combustion products, not raw fuel.)

[Also, what Rakaydos said. Should we be concerned about the accumulation of re-entry heat? Changes to Earth's rotational inertia due to mass loss to deep space missions? Yes. Yes we should. Once we're a K1+ civilisation, there are many such things we'll need to manage. Should we be concerned now? No.]
Reentry heat is not a major concern (it's basically just waste heat, which is a factor of ~100 less important than anthropogenic greenhouse gases in human-caused warming of the atmosphere) directly. But it CAN cause nitrogen oxides, which ARE a significant problem for various reasons. Something like 5% of reentered mass from LEO is converted into nitrogen oxides. Although this is highly non-linear, so I think you can reduce it by doing some more propulsive reentry. Might tip the scales toward more solar electric propulsion. And that amount of nitrogen oxides becomes a real problem at the flight levels SpaceX wants. But we CAN engineer around it, like I mentioned.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/24/2020 03:39 am
Microgravity can be used to assist the flow from one to the other.

For ullage, "milli" not "micro".

Not sure if it's enough to act as a steep enough hill to not need a dedicated pump. With 150 tonnes cargo-propellant plus 15% landing-propellant, the initial "pressure" is 3kN per milligee. (Assuming 3 milli-gee (typical ISS thruster burn), a half metre sump, and completely ignoring the fuel/ox ratio, you get around 19kPa / 2.8psi, dropping to 10kPa/1.5psi. Is that enough?)



This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.
[...] And gives a Mars settlement a legitimate revenue stream.

It's not a revenue stream. It's just paying for the cost of supporting a Mars settlement in a different way.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: kkattula on 08/24/2020 03:39 am
1- I have calculated (online calculator) a 200 tons  payload to LEO with a second stage on top of SH

I bet you haven't, because...

I dont think that a stainless steel tank coupled with six raptors engines will weigh that much

...others have mentioned that the figures that estimate Starship's mass also estimate 40 tonnes for re-entry and landing. 25 tonnes for structure/heat-shield, and 15 tonnes for fuel.

Hence, if you're using a calculator that gives 100 tonnes payload (hence propellant) for the Starship tanker, then it will give 140 tonnes payload (prop) for the expendable version. If you got a higher figure, then you dropped the drymass to an unrealistic level.


For the sake of argument, lets just assume that 200 tonnes payload second stage. It's really just an expendable Starship: no legs, fins, TPS & header tanks.  If it can do 200, a reusable tanker can do 150 tonnes.  Let's also ignore the mass of the drop tank, which would have to be close to 10 tonnes.

If a tanker Starship can be built for $5M (SpaceX stretch goal), then an expendable SS might be $3.5M and a drop tank $0.5M.  (Probably way more with all the extra fittings and equipment on the drop tank, but let's be extra charitable.)

To refill a Starship in orbit with 1200 tonnes of propellant, assuming only 8 lifetime uses of tanker, is: 8 x $2.5M + $5M = $25M

To launch the equivalent drop tanks using expendable stages is: 6 x ($2.5M + $4M) = $39M

If the number of reuses for a Starship goes up, the numbers get worse for drop tanks.
If the cost of a Starship is higher, the numbers get much worse for drop tanks.


Absurdly, on these numbers they could even launch completely expendable tanker Starships, carrying more payload propellant per launch than would be in drop tanks, for less cost than expendable stages with drop tanks:  6 x ($2.5M + $3.5M) = $36M
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 08/24/2020 03:45 am
...
This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.
[...] And gives a Mars settlement a legitimate revenue stream.

It's not a revenue stream. It's just paying for the cost of supporting a Mars settlement in a different way.
I imagine there are more users of cheap Mars volatiles in LEO than just the Mars settlement, but sure, valid. Point is that it gives the Mars settlement folks something to do while relieving Earth of some of the work. Exporting some of the economy and industrial capacity to Mars.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: kkattula on 08/24/2020 03:53 am
...
This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.
[...] And gives a Mars settlement a legitimate revenue stream.

It's not a revenue stream. It's just paying for the cost of supporting a Mars settlement in a different way.
I imagine there are more users of cheap Mars volatiles in LEO than just the Mars settlement, but sure, valid. Point is that it gives the Mars settlement folks something to do while relieving Earth of some of the work. Exporting some of the economy and industrial capacity to Mars.

I kind of think the Mars settlement folks will have quite a lot to do already.  Like trying to bootstrap an entire planetary industrialization.

Edit:  The cost of sending the resources to Mars to make the extra propellant to send back to LEO, would have to be less than the resources to just launch the prop to LEO in the first place.  What percentage of propellant made on Mars would reach LEO? 5%? 10%?

Edit 2:  I get 9% (112 tonnes) assuming aerocapture into LEO and no orbit adjustment burns. For a 120 tonne dry mass, 1200 tonne propellant, 370 ISP.  Of course that SS would then be stuck in LEO unless it reserved 15 tonnes for EDL, so 8%.   And how does the value of 120 tonnes of used SS on Mars compare to 97 tonnes of propellant in LEO?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: livingjw on 08/24/2020 04:13 am


No, if you are using a pressure difference, the gas from the tank being filled is lower than the tank doing the filling, so the gas has to be either condensed or vented.

John

Sorry, perhaps I wasn't being clear, I'm talking about displacement exchange to negate the need to compress or vent gas.

When liquid is transferred from the tanker to the recipient, the tanker pressure drops and the recipient pressure increases. The excess recipient pressure needs to be reduced (either by venting or compression) and the tanker pressure needs to be maintained to aid pumping.

I'm saying solve two problems at once by transferring the excess pressure, in the form of gas, from the recipient to the tanker.

The pumping can occur either by pumping gas into the tanker to push the liquid through or by pumping liquid into the recipient and allow excess pressure gas to flow into the tanker. Either way you're not wasting energy compressing gas or wasting gas by venting.

Microgravity can be used to assist the flow from one to the other.

- Pure displacement exchange will not be nearly fast enough without a pump to provide a few bar of pressure to speed it along.

- If you are using a pressure difference of a few bar, then you are introducing more gas into the tanks. For example:
 1) we have two tanks connected as shown, both at 1 bar, with all valves closed with propellants settled with micro g.
 2) if we open valves 1 and 5 on both vehicles fluid would slowly flow to the receiver while ullage gas flows to the tanker
 3) Not practical because it is too slow.
 4) If we introduce a 3-5 bar pump in the feed line we can speed up the transfer greatly and no venting required.
 5) Or we could provide a delta pressure using a high pressure gas source to introduce a 3-5 bar pressure difference but we would have to close off the receiving tank's valve 1. Fluid would flow until the ullage gas in the receiving tank reached a little over 3-5 bars, then no more flow. You can't finish transferring the fluid. You would have to vent the receiving tank using receiving valve 3.

John
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 08/24/2020 04:21 am
...
This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.
[...] And gives a Mars settlement a legitimate revenue stream.

It's not a revenue stream. It's just paying for the cost of supporting a Mars settlement in a different way.
I imagine there are more users of cheap Mars volatiles in LEO than just the Mars settlement, but sure, valid. Point is that it gives the Mars settlement folks something to do while relieving Earth of some of the work. Exporting some of the economy and industrial capacity to Mars.

I kind of think the Mars settlement folks will have quite a lot to do already.  Like trying to bootstrap an entire planetary industrialization.
I said at the very first it's a long-term thing. But rockets & propellant is something they better get REALLY good at REALLY fast.

Edit:  The cost of sending the resources to Mars to make the extra propellant to send back to LEO, would have to be less than the resources to just launch the prop to LEO in the first place.  What percentage of propellant made on Mars would reach LEO? 5%? 10%?

Edit 2:  I get 9% (112 tonnes) assuming aerocapture into LEO and no orbit adjustment burns. For a 120 tonne dry mass, 1200 tonne propellant, 370 ISP.  Of course that SS would then be stuck in LEO unless it reserved 15 tonnes for EDL, so 8%.   And how does the value of 120 tonnes of used SS on Mars compare to 97 tonnes of propellant in LEO?
About 30% using SEP and perhaps a Deimos tether (compare to about 3% for Earth's surface to LEO). But mass of propellant is less relevant than efficiency in this case. You could launch the propellant to LMO using CO/O2 rockets on Mars. The lower Isp is compensated nicely by the reduced energy cost per kg of propellant. Atmospheric ISRU on Mars may actually be easier than on Earth as direct air capture of CO2 is not cheap on Earth (but is easy on Mars).

Just the CH4 and O2 (or whatever propellant) would be needed to be delivered to LEO.

Also, you'd send it in large tanker variants of Starship fairly optimized for the trip. Not just regular versions of Starship. SpaceX already mentioned both tanker and depot variants of Starship. Most importantly: You wouldn't send the ship directly from mars to Earth but instead refuel a Starship tanker right at high Mars orbit, right before Earth injection burn. Dry mass-to-wet-mass would be reduced this way to around 0.1 instead of your 0.6 or so. (This makes an enormous difference.)

Secondly, you'd likely only put a small portion of the propellant in LEO. It makes sense to also refuel at HEO on the way to Mars, and if your propellant is coming from Mars anyway, might as well keep much of it in HEO to begin with as it gives you a greater benefit on the departure burn than the same amount of propellant in LEO. EDIT: Splitting the departure propellant between LEO and HEO like this almost halves the total amount of propellant needed for the same delta-v (say, 7.5km/s total starting in LEO), and the effect is significantly larger for faster transits than slower transit. I did NOT include that consideration below... If I did, the energy advantage for Mars over Earth would be about 15-20:1 instead of 10:1.

So again, I think you'd have roughly a 10:1 energy advantage (knocked down to, say, 4:1 by the lower sunlight intensity at Mars... which could be more-than-compensated-for, long-term, using areosynchronous orbital mirrors once you get to Terawatts of power... something you really shouldn't be doing at Earth... although this is all irrelevant if you use nuclear power which should be similar for Earth and Mars... tho the details get hairy).
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/24/2020 04:38 am
The pumping can occur either by pumping gas into the tanker to push the liquid through or by pumping liquid into the recipient and allow excess pressure gas to flow into the tanker. Either way you're not wasting energy compressing gas or wasting gas by venting.
- Pure displacement exchange will not be nearly fast enough without a pump

You keep misreading what he is saying.

Neyyn72 didn't say "without a pump". Quite the opposite, his point was that pumping the gas from receiver to tanker provides both pressure reduction in the receiver, and increased pressurant in the tanker. Exactly as in your diagram. He was responding to people concerned about a) the increasing pressure in the receiver-tank as it fills, requiring venting or cryo-cooling, and b) a lack of pressure in the tanker, and was simply saying "Uh, guys, you realise that one solves the other?"

I'm the one who speculated that the whole thing might work without a pump using just the pressure created by milli-gee ullage thrust. You should get a few PSI fluid pressure at the sump.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: kkattula on 08/24/2020 05:37 am
About 30% using SEP and perhaps a Deimos tether (compare to about 3% for Earth's surface to LEO). But mass of propellant is less relevant than efficiency in this case. You could launch the propellant to LMO using CO/O2 rockets on Mars. The lower Isp is compensated nicely by the reduced energy cost per kg of propellant. Atmospheric ISRU on Mars may actually be easier than on Earth as direct air capture of CO2 is not cheap on Earth (but is easy on Mars).

Just the CH4 and O2 (or whatever propellant) would be needed to be delivered to LEO.

Also, you'd send it in large tanker variants of Starship fairly optimized for the trip. Not just regular versions of Starship. SpaceX already mentioned both tanker and depot variants of Starship. Most importantly: You wouldn't send the ship directly from mars to Earth but instead refuel a Starship tanker right at high Mars orbit, right before Earth injection burn. Dry mass-to-wet-mass would be reduced this way to around 0.1 instead of your 0.6 or so. (This makes an enormous difference.)

Secondly, you'd likely only put a small portion of the propellant in LEO. It makes sense to also refuel at HEO on the way to Mars, and if your propellant is coming from Mars anyway, might as well keep much of it in HEO to begin with as it gives you a greater benefit on the departure burn than the same amount of propellant in LEO. EDIT: Splitting the departure propellant between LEO and HEO like this almost halves the total amount of propellant needed for the same delta-v (say, 7.5km/s total starting in LEO), and the effect is significantly larger for faster transits than slower transit. I did NOT include that consideration below... If I did, the energy advantage for Mars over Earth would be about 15-20:1 instead of 10:1.

So again, I think you'd have roughly a 10:1 energy advantage (knocked down to, say, 4:1 by the lower sunlight intensity at Mars... which could be more-than-compensated-for, long-term, using areosynchronous orbital mirrors once you get to Terawatts of power... something you really shouldn't be doing at Earth... although this is all irrelevant if you use nuclear power which should be similar for Earth and Mars... tho the details get hairy).

Ok, for something quite a bit more technically complex, (than just refueling a Starship on Mars then launching it), this makes a bit more sense. 

I hadn't factored in the 'staging' like advantages of depots in High Mars/Earth Orbit at each end which do reduce the delta v of each leg, so increase the overall efficiency.  I already think Starship storage tankers (depots) are going to end up being used at High & Low, Earth & Mars Orbits.

On the solar PV efficiency question, it might make sense to ship the 'raw feed-stock' as far down the logistics pipe as you can, before converting it to usable propellant.  Solar PV is more efficient in HMO than on the surface, and HEO more so than HMO.  Also liquid CO2 and H2O should be easier to store than LCH4 & LOX, let alone LH2.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Nevyn72 on 08/24/2020 06:31 am
The pumping can occur either by pumping gas into the tanker to push the liquid through or by pumping liquid into the recipient and allow excess pressure gas to flow into the tanker. Either way you're not wasting energy compressing gas or wasting gas by venting.
- Pure displacement exchange will not be nearly fast enough without a pump

You keep misreading what he is saying.

Neyyn72 didn't say "without a pump". Quite the opposite, his point was that pumping the gas from receiver to tanker provides both pressure reduction in the receiver, and increased pressurant in the tanker. Exactly as in your diagram. He was responding to people concerned about a) the increasing pressure in the receiver-tank as it fills, requiring venting or cryo-cooling, and b) a lack of pressure in the tanker, and was simply saying "Uh, guys, you realise that one solves the other?"

I'm the one who speculated that the whole thing might work without a pump using just the pressure created by milli-gee ullage thrust. You should get a few PSI fluid pressure at the sump.

Exactly!  :)
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: kkattula on 08/24/2020 07:22 am
Just for fun, I ran the numbers for percentage of Mars produced propellant reaching High Earth Orbit, using just standard methalox Starships as tankers, and depots in LMO and HMO:

I get 13% using propulsive capture into HEO, and 15% using aero-capture.

Eliminating legs, fins and heat-shield for the LMO-HMO & HMO-HEO legs makes negligible difference. (Except on the return leg).

Switching to hydrolox for LMO-HMO & HMO-HEO gives 15% (assuming same MR, which would be worse in reality, due to larger tanks)

Switching to hydrolox for every leg gives 19% (assuming same MR, which would be a lot worse in reality, due to EDL for larger tanks)


Everything else being equal, which it isn't, fully Hydrolox makes 50% more propellant available in HEO, which because you need less, enables 75% more payload than methalox.  More like 40% and 70% with propellant density factored in, and who know with ISRU production & storage factored in.


Using methalox for Mars to LMO, then SEP, I got 21% to 24% (1800 to 3000 Isp).

Using CO2/LOX, for Mars to LMO, then SEP, I got 14% to 15% (1800 to 3000 Isp).

Using CO2/LOX, for Mars to LMO, then hydrolox, I got 10%.

Using CO2/LOX, for Mars to LMO, then methalox , I got 8%. Might as well just send a Starship direct from the surface.


NOTE: All these trips are one-way. When you need to send an empty tanker back to HMO or LMO, it requires about 16% of the propellant just delivered for methalox, and 21% for hydrolox (lower density -> higher empty mass). Around 12% for SEP.

Edit: fix return %
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/24/2020 10:31 am
1- I have calculated (online calculator) a 200 tons  payload to LEO with a second stage on top of SH

I bet you haven't, because...

I dont think that a stainless steel tank coupled with six raptors engines will weigh that much

...others have mentioned that the figures that estimate Starship's mass also estimate 40 tonnes for re-entry and landing. 25 tonnes for structure/heat-shield, and 15 tonnes for fuel.

Hence, if you're using a calculator that gives 100 tonnes payload (hence propellant) for the Starship tanker, then it will give 140 tonnes payload (prop) for the expendable version. If you got a higher figure, then you dropped the drymass to an unrealistic level.

3-The option of depot will mitigate the need for rapid  launch of tankers, SS bound for Mars will only be launched when all tanks are in place, this allowing time for further developement of rapid reuse of SH/SH while not delaying first mission to Mars (interim solution).

As mentioned repeatedly: Everything you require for your expendable tanks are the same as the tanker. You need to launch on SH, you need to be able to do docking manoeuvres in space, you need to connect up propellant lines (and gas-return lines for tank pressurisation), you need to be able to transfer propellant from the tanks to the engines on the main vehicle.

In addition, because you seem to have (finally!) accepted that you can't launch a single expendable fully fuelled tank into orbit, you now invent another whole structure, the docking node that holds a bunch of tanks as a depot. The depot then has to transfer fuel to the main Mars vehicle... kind of like... you know... a tanker.

You have all the requirements of building tankers, plus you need a depot before it's usable. It's not an "interim" solution.

The only technology you are trying to skip is reusability, which only requires re-entry and landing. But if Starship can land on Mars, then the technology for reusable tankers has already been developed. If the technology to land tankers isn't ready, Starship can't go to Mars.

So again, there's no "interim" where the Mars Starship exists but the tankers don't. Either the landing technology is ready, making tankers viable, or you can't land on Mars.

5- Fuel depot could be sent to Mars orbit.

Having fuel in Mars orbit doesn't replace ISRU production for a manned Starship mission: Starship can't land while fully fuelled, hence can't launch back into Mars orbit without ISRU propellant on the ground. If they have that, then your proposal isn't needed. If they don't, then you can't send humans to Mars. Again, there's no "interim".

Just some remarques:

-Please don't get my phrases out of context like;
 
I dont think that a stainless steel tank coupled with six raptors engines will weigh that much

I dont think that a stainless steel tank coupled with six raptors engines will weigh that much in the overall balance of a $/per ton of payload (no heat shield, no legs/no extra fuel,.........etc.).


Quote
In addition, because you seem to have (finally!) accepted that you can't launch a single expendable fully fuelled tank into orbit, you now invent another whole structure, the docking node that holds a bunch of tanks as a depot. The depot then has to transfer fuel to the main Mars vehicle... kind of like... you know... a tanker.

I didn't accepted anything it was just to stay in Elon Musk philosophy of one versatile spacecraft namely SS, if I was to send fuel to orbit I will do it in a space shuttle manner I will put engines to the main tanker and two boosters (reusable).

Quote
As mentioned repeatedly: Everything you require for your expendable tanks are the same as the tanker. You need to launch on SH, you need to be able to do docking manoeuvres in space, you need to connect up propellant lines (and gas-return lines for tank pressurisation), you need to be able to transfer propellant from the tanks to the engines on the main vehicle.

The difference is that your tanker will require months of checks and refrubishments to be ready for the next mission, I don't think SS in orbit will be able await for that time, of course until SX reach a rapid reuse but this will require some time and considering EM time frame of Mars missions this won't be possible.



Quote
Having fuel in Mars orbit doesn't replace ISRU production for a manned Starship mission: Starship can't land while fully fuelled, hence can't launch back into Mars orbit without ISRU propellant on the ground. If they have that, then your proposal isn't needed. If they don't, then you can't send humans to Mars. Again, there's no "interim".

ISRU is also a long term reach goal, but still if we want getting the red planet relatively in short time it could still be possible with some SS modifications (interim solution or plan B).
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/24/2020 11:34 am
Quote
In addition, because you seem to have (finally!) accepted that you can't launch a single expendable fully fuelled tank into orbit, you now invent another whole structure, the docking node that holds a bunch of tanks as a depot. The depot then has to transfer fuel to the main Mars vehicle... kind of like... you know... a tanker.

I didn't accepted anything it was just to stay in Elon Musk philosophy of one versatile spacecraft namely SS, if I was to send fuel to orbit I will do it in a space shuttle manner I will put engines to the main tanker and two boosters (reusable).

Quote
As mentioned repeatedly: Everything you require for your expendable tanks are the same as the tanker. You need to launch on SH, you need to be able to do docking manoeuvres in space, you need to connect up propellant lines (and gas-return lines for tank pressurisation), you need to be able to transfer propellant from the tanks to the engines on the main vehicle.

The difference is that your tanker will require months of checks and refrubishments to be ready for the next mission, I don't think SS in orbit will be able await for that time, of course until SX reach a rapid reuse but this will require some time and considering EM time frame of Mars missions this won't be possible.

You dont seem to be making this connection. Shuttle took months of checks and refurbishments because it was built like the Shuttle- ie: by a committee in the 1970s.

Even oldspace tycoons like Tory Bruno believe a modern design can easilly reach fast turnaround times, though he was talking about the SSTO Venture Star.

https://twitter.com/torybruno/status/1296159004473937920?s=20

(discussion thread here, please read full tweetstorm before commenting: https://forum.nasaspaceflight.com/index.php?topic=51773.msg2122619#msg2122619)

Starship is being designed for fast turnaround, using lessons learned not just from the shuttle, but from SpaceX's own Falcon 9 program, which has surpassed the fastest ever shuttle turnaround in launch-to-launch. But not even the makers of the shuttle will touch a shuttle design anymore.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/24/2020 12:13 pm
Quote
In addition, because you seem to have (finally!) accepted that you can't launch a single expendable fully fuelled tank into orbit, you now invent another whole structure, the docking node that holds a bunch of tanks as a depot. The depot then has to transfer fuel to the main Mars vehicle... kind of like... you know... a tanker.

I didn't accepted anything it was just to stay in Elon Musk philosophy of one versatile spacecraft namely SS, if I was to send fuel to orbit I will do it in a space shuttle manner I will put engines to the main tanker and two boosters (reusable).

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As mentioned repeatedly: Everything you require for your expendable tanks are the same as the tanker. You need to launch on SH, you need to be able to do docking manoeuvres in space, you need to connect up propellant lines (and gas-return lines for tank pressurisation), you need to be able to transfer propellant from the tanks to the engines on the main vehicle.

The difference is that your tanker will require months of checks and refrubishments to be ready for the next mission, I don't think SS in orbit will be able await for that time, of course until SX reach a rapid reuse but this will require some time and considering EM time frame of Mars missions this won't be possible.

You dont seem to be making this connection. Shuttle took months of checks and refurbishments because it was built like the Shuttle- ie: by a committee in the 1970s.

Even oldspace tycoons like Tory Bruno believe a modern design can easilly reach fast turnaround times, though he was talking about the SSTO Venture Star.

https://twitter.com/torybruno/status/1296159004473937920?s=20

(discussion thread here, please read full tweetstorm before commenting: https://forum.nasaspaceflight.com/index.php?topic=51773.msg2122619#msg2122619)

Starship is being designed for fast turnaround, using lessons learned not just from the shuttle, but from SpaceX's own Falcon 9 program, which has surpassed the fastest ever shuttle turnaround in launch-to-launch. But not even the makers of the shuttle will touch a shuttle design anymore.

I meant shuttle external tank (+ engines) + the two boosters without the orbiters.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: rakaydos on 08/24/2020 12:24 pm
Quote
In addition, because you seem to have (finally!) accepted that you can't launch a single expendable fully fuelled tank into orbit, you now invent another whole structure, the docking node that holds a bunch of tanks as a depot. The depot then has to transfer fuel to the main Mars vehicle... kind of like... you know... a tanker.

I didn't accepted anything it was just to stay in Elon Musk philosophy of one versatile spacecraft namely SS, if I was to send fuel to orbit I will do it in a space shuttle manner I will put engines to the main tanker and two boosters (reusable).

Quote
As mentioned repeatedly: Everything you require for your expendable tanks are the same as the tanker. You need to launch on SH, you need to be able to do docking manoeuvres in space, you need to connect up propellant lines (and gas-return lines for tank pressurisation), you need to be able to transfer propellant from the tanks to the engines on the main vehicle.

The difference is that your tanker will require months of checks and refrubishments to be ready for the next mission, I don't think SS in orbit will be able await for that time, of course until SX reach a rapid reuse but this will require some time and considering EM time frame of Mars missions this won't be possible.

You dont seem to be making this connection. Shuttle took months of checks and refurbishments because it was built like the Shuttle- ie: by a committee in the 1970s.

Even oldspace tycoons like Tory Bruno believe a modern design can easilly reach fast turnaround times, though he was talking about the SSTO Venture Star.

https://twitter.com/torybruno/status/1296159004473937920?s=20

(discussion thread here, please read full tweetstorm before commenting: https://forum.nasaspaceflight.com/index.php?topic=51773.msg2122619#msg2122619)

Starship is being designed for fast turnaround, using lessons learned not just from the shuttle, but from SpaceX's own Falcon 9 program, which has surpassed the fastest ever shuttle turnaround in launch-to-launch. But not even the makers of the shuttle will touch a shuttle design anymore.

I meant shuttle external tank (+ engines) + the two boosters without the orbiters.
Exactly. Even oldspace thinks same day turnaround is possible if you get rid of that.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Slarty1080 on 08/24/2020 12:32 pm
About 30% using SEP and perhaps a Deimos tether (compare to about 3% for Earth's surface to LEO). But mass of propellant is less relevant than efficiency in this case. You could launch the propellant to LMO using CO/O2 rockets on Mars. The lower Isp is compensated nicely by the reduced energy cost per kg of propellant. Atmospheric ISRU on Mars may actually be easier than on Earth as direct air capture of CO2 is not cheap on Earth (but is easy on Mars).

Just the CH4 and O2 (or whatever propellant) would be needed to be delivered to LEO.

Also, you'd send it in large tanker variants of Starship fairly optimized for the trip. Not just regular versions of Starship. SpaceX already mentioned both tanker and depot variants of Starship. Most importantly: You wouldn't send the ship directly from mars to Earth but instead refuel a Starship tanker right at high Mars orbit, right before Earth injection burn. Dry mass-to-wet-mass would be reduced this way to around 0.1 instead of your 0.6 or so. (This makes an enormous difference.)

Secondly, you'd likely only put a small portion of the propellant in LEO. It makes sense to also refuel at HEO on the way to Mars, and if your propellant is coming from Mars anyway, might as well keep much of it in HEO to begin with as it gives you a greater benefit on the departure burn than the same amount of propellant in LEO. EDIT: Splitting the departure propellant between LEO and HEO like this almost halves the total amount of propellant needed for the same delta-v (say, 7.5km/s total starting in LEO), and the effect is significantly larger for faster transits than slower transit. I did NOT include that consideration below... If I did, the energy advantage for Mars over Earth would be about 15-20:1 instead of 10:1.

So again, I think you'd have roughly a 10:1 energy advantage (knocked down to, say, 4:1 by the lower sunlight intensity at Mars... which could be more-than-compensated-for, long-term, using areosynchronous orbital mirrors once you get to Terawatts of power... something you really shouldn't be doing at Earth... although this is all irrelevant if you use nuclear power which should be similar for Earth and Mars... tho the details get hairy).

Ok, for something quite a bit more technically complex, (than just refueling a Starship on Mars then launching it), this makes a bit more sense. 

I hadn't factored in the 'staging' like advantages of depots in High Mars/Earth Orbit at each end which do reduce the delta v of each leg, so increase the overall efficiency.  I already think Starship storage tankers (depots) are going to end up being used at High & Low, Earth & Mars Orbits.

On the solar PV efficiency question, it might make sense to ship the 'raw feed-stock' as far down the logistics pipe as you can, before converting it to usable propellant.  Solar PV is more efficient in HMO than on the surface, and HEO more so than HMO.  Also liquid CO2 and H2O should be easier to store than LCH4 & LOX, let alone LH2.
I had never considered shipping water and CO2 from Mars into Mars orbit. It's a really neat idea that does help solve some problems, although I'm not exactly sure how practical it would be. It would need two dedicated tanks in Mars orbit one for water and CO2 plus one for methane and oxygen. There might also be issues with the water freezing. I suppose that could be solved by an electrically powered heater, but I'm not qualified to comment on the practicalities or trades of that arrangement.

One thing that does appeal is the thought of putting half the solar power in orbit where it could receive nearly double the energy from the sun and avoid dust storms and still have the other half on the surface for base operations. Unfortunately there would still need to be ISRU producing methalox on the surface in order to re-tank the ships heading up to the orbital facility. So its doable but I suspect the issues will prevent it's use until a lot further in the future when they're optimising the logistics chain.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/24/2020 03:53 pm
1- I have calculated (online calculator) a 200 tons  payload to LEO with a second stage on top of SH

I bet you haven't, because...

I dont think that a stainless steel tank coupled with six raptors engines will weigh that much

...others have mentioned that the figures that estimate Starship's mass also estimate 40 tonnes for re-entry and landing. 25 tonnes for structure/heat-shield, and 15 tonnes for fuel.

Hence, if you're using a calculator that gives 100 tonnes payload (hence propellant) for the Starship tanker, then it will give 140 tonnes payload (prop) for the expendable version. If you got a higher figure, then you dropped the drymass to an unrealistic level.

3-The option of depot will mitigate the need for rapid  launch of tankers, SS bound for Mars will only be launched when all tanks are in place, this allowing time for further developement of rapid reuse of SH/SH while not delaying first mission to Mars (interim solution).

As mentioned repeatedly: Everything you require for your expendable tanks are the same as the tanker. You need to launch on SH, you need to be able to do docking manoeuvres in space, you need to connect up propellant lines (and gas-return lines for tank pressurisation), you need to be able to transfer propellant from the tanks to the engines on the main vehicle.

In addition, because you seem to have (finally!) accepted that you can't launch a single expendable fully fuelled tank into orbit, you now invent another whole structure, the docking node that holds a bunch of tanks as a depot. The depot then has to transfer fuel to the main Mars vehicle... kind of like... you know... a tanker.

You have all the requirements of building tankers, plus you need a depot before it's usable. It's not an "interim" solution.

The only technology you are trying to skip is reusability, which only requires re-entry and landing. But if Starship can land on Mars, then the technology for reusable tankers has already been developed. If the technology to land tankers isn't ready, Starship can't go to Mars.

So again, there's no "interim" where the Mars Starship exists but the tankers don't. Either the landing technology is ready, making tankers viable, or you can't land on Mars.

5- Fuel depot could be sent to Mars orbit.

Having fuel in Mars orbit doesn't replace ISRU production for a manned Starship mission: Starship can't land while fully fuelled, hence can't launch back into Mars orbit without ISRU propellant on the ground. If they have that, then your proposal isn't needed. If they don't, then you can't send humans to Mars. Again, there's no "interim".
I can't speak for Stardust but I've considered a stripped SS without tank mods as a short term solution and an assembly capable of refueling an entire mars fleet as a long term solution. I see everything else as an interim solution. That said, your criticisms of Stardust's idea are on point.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/24/2020 04:34 pm
This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.

It isn't just delta-v. Producing enough propellant to launch enough propellant as cargo to Earth, to fully fuel its own return plus one SS flight puts a burden on the ISRU production that puts disproportionate burdens on a Mars settlement that it doesn't on a few extra Earth launches.
Thus, the suggestion for shipping CO2 & water and processing into propellant on the way back.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/24/2020 05:24 pm
Microgravity can be used to assist the flow from one to the other.

For ullage, "milli" not "micro".

Not sure if it's enough to act as a steep enough hill to not need a dedicated pump. With 150 tonnes cargo-propellant plus 15% landing-propellant, the initial "pressure" is 3kN per milligee. (Assuming 3 milli-gee (typical ISS thruster burn), a half metre sump, and completely ignoring the fuel/ox ratio, you get around 19kPa / 2.8psi, dropping to 10kPa/1.5psi. Is that enough?)



This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.
[...] And gives a Mars settlement a legitimate revenue stream.

It's not a revenue stream. It's just paying for the cost of supporting a Mars settlement in a different way.
Any G will settle props. The higher the G the faster they get to the bottom of the tank. The lower the G the less slosh at the cost of time. Solution: low G for initial settling, higher G to damp out slosh and entrained bubbles, back to low G for transfer. Allow the receiving ship to replenish the depots high pressure gas reserves which are used in turn to pressurize  the depots tanks to facilitate transfer.


As for characterizing as a cash flow or an offset to expenses, that's an artifact of how the books are set up. It's a positive on one side or a negative on the other side. Impact is the same either way. "That which we call a rose..."
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/24/2020 08:26 pm
About 30% using SEP and perhaps a Deimos tether (compare to about 3% for Earth's surface to LEO). But mass of propellant is less relevant than efficiency in this case. You could launch the propellant to LMO using CO/O2 rockets on Mars. The lower Isp is compensated nicely by the reduced energy cost per kg of propellant. Atmospheric ISRU on Mars may actually be easier than on Earth as direct air capture of CO2 is not cheap on Earth (but is easy on Mars).

Just the CH4 and O2 (or whatever propellant) would be needed to be delivered to LEO.

Also, you'd send it in large tanker variants of Starship fairly optimized for the trip. Not just regular versions of Starship. SpaceX already mentioned both tanker and depot variants of Starship. Most importantly: You wouldn't send the ship directly from mars to Earth but instead refuel a Starship tanker right at high Mars orbit, right before Earth injection burn. Dry mass-to-wet-mass would be reduced this way to around 0.1 instead of your 0.6 or so. (This makes an enormous difference.)

Secondly, you'd likely only put a small portion of the propellant in LEO. It makes sense to also refuel at HEO on the way to Mars, and if your propellant is coming from Mars anyway, might as well keep much of it in HEO to begin with as it gives you a greater benefit on the departure burn than the same amount of propellant in LEO. EDIT: Splitting the departure propellant between LEO and HEO like this almost halves the total amount of propellant needed for the same delta-v (say, 7.5km/s total starting in LEO), and the effect is significantly larger for faster transits than slower transit. I did NOT include that consideration below... If I did, the energy advantage for Mars over Earth would be about 15-20:1 instead of 10:1.

So again, I think you'd have roughly a 10:1 energy advantage (knocked down to, say, 4:1 by the lower sunlight intensity at Mars... which could be more-than-compensated-for, long-term, using areosynchronous orbital mirrors once you get to Terawatts of power... something you really shouldn't be doing at Earth... although this is all irrelevant if you use nuclear power which should be similar for Earth and Mars... tho the details get hairy).

Ok, for something quite a bit more technically complex, (than just refueling a Starship on Mars then launching it), this makes a bit more sense. 

I hadn't factored in the 'staging' like advantages of depots in High Mars/Earth Orbit at each end which do reduce the delta v of each leg, so increase the overall efficiency.  I already think Starship storage tankers (depots) are going to end up being used at High & Low, Earth & Mars Orbits.

On the solar PV efficiency question, it might make sense to ship the 'raw feed-stock' as far down the logistics pipe as you can, before converting it to usable propellant.  Solar PV is more efficient in HMO than on the surface, and HEO more so than HMO.  Also liquid CO2 and H2O should be easier to store than LCH4 & LOX, let alone LH2.
Why wait to get close before starting feed stock conversion? It not like the PV is metered.


Every indication is that while transiting, freezing will be more of an issue than boiloff so storage shouldn't be a problem. Keeping the water liquid might be the hardest chore. Hmmm. Maybe this is a reason to not bother with conversion until further in.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/24/2020 09:48 pm
About 30% using SEP and perhaps a Deimos tether (compare to about 3% for Earth's surface to LEO). But mass of propellant is less relevant than efficiency in this case. You could launch the propellant to LMO using CO/O2 rockets on Mars. The lower Isp is compensated nicely by the reduced energy cost per kg of propellant. Atmospheric ISRU on Mars may actually be easier than on Earth as direct air capture of CO2 is not cheap on Earth (but is easy on Mars).

Just the CH4 and O2 (or whatever propellant) would be needed to be delivered to LEO.

Also, you'd send it in large tanker variants of Starship fairly optimized for the trip. Not just regular versions of Starship. SpaceX already mentioned both tanker and depot variants of Starship. Most importantly: You wouldn't send the ship directly from mars to Earth but instead refuel a Starship tanker right at high Mars orbit, right before Earth injection burn. Dry mass-to-wet-mass would be reduced this way to around 0.1 instead of your 0.6 or so. (This makes an enormous difference.)

Secondly, you'd likely only put a small portion of the propellant in LEO. It makes sense to also refuel at HEO on the way to Mars, and if your propellant is coming from Mars anyway, might as well keep much of it in HEO to begin with as it gives you a greater benefit on the departure burn than the same amount of propellant in LEO. EDIT: Splitting the departure propellant between LEO and HEO like this almost halves the total amount of propellant needed for the same delta-v (say, 7.5km/s total starting in LEO), and the effect is significantly larger for faster transits than slower transit. I did NOT include that consideration below... If I did, the energy advantage for Mars over Earth would be about 15-20:1 instead of 10:1.

So again, I think you'd have roughly a 10:1 energy advantage (knocked down to, say, 4:1 by the lower sunlight intensity at Mars... which could be more-than-compensated-for, long-term, using areosynchronous orbital mirrors once you get to Terawatts of power... something you really shouldn't be doing at Earth... although this is all irrelevant if you use nuclear power which should be similar for Earth and Mars... tho the details get hairy).

Ok, for something quite a bit more technically complex, (than just refueling a Starship on Mars then launching it), this makes a bit more sense. 

I hadn't factored in the 'staging' like advantages of depots in High Mars/Earth Orbit at each end which do reduce the delta v of each leg, so increase the overall efficiency.  I already think Starship storage tankers (depots) are going to end up being used at High & Low, Earth & Mars Orbits.

On the solar PV efficiency question, it might make sense to ship the 'raw feed-stock' as far down the logistics pipe as you can, before converting it to usable propellant.  Solar PV is more efficient in HMO than on the surface, and HEO more so than HMO.  Also liquid CO2 and H2O should be easier to store than LCH4 & LOX, let alone LH2.
I had never considered shipping water and CO2 from Mars into Mars orbit. It's a really neat idea that does help solve some problems, although I'm not exactly sure how practical it would be. It would need two dedicated tanks in Mars orbit one for water and CO2 plus one for methane and oxygen. There might also be issues with the water freezing. I suppose that could be solved by an electrically powered heater, but I'm not qualified to comment on the practicalities or trades of that arrangement.

One thing that does appeal is the thought of putting half the solar power in orbit where it could receive nearly double the energy from the sun and avoid dust storms and still have the other half on the surface for base operations. Unfortunately there would still need to be ISRU producing methalox on the surface in order to re-tank the ships heading up to the orbital facility. So its doable but I suspect the issues will prevent it's use until a lot further in the future when they're optimising the logistics chain.
I've been talking about sending raw feedstock back to earth and converting to props along the way but doing it LMO is attractive. It gives a natural growth path.


Sending props ISRU a synod before crew and depending on it to work is a high risk plan. A well discussed alternative is sending a depot from earth to LMO with return propellant and landing enough to get the crewed ships up to it. This takes the pressure off and gives a good opportunity for the crew to get ISRU working without depending on it.


Setting up an orbital propellant factory with feedstock supplied from Mars creates only an incremental logistics change, not a forklift. Coupled with lower capacity ISRU on the surface and at least one more synod of return propellant from earth creates a low risk operation with the terrible risk of, OMG, too much propellant on hand. What a problem!


Orbital ISRU seems to add another yet another layer of safety. If dust storms disrupt surface ISRU, a small reserve of propellant will enable an empty cargo ship to make orbit, tank up and return - as many times as necessary.


From there optimization for an HMO depot is yet again only an incremental change. Keep the systems overlapped until working smooth and the cost is having too much propellant. Follow this pattern and except for those dismal delivery numbers, Mars could deliver propellant to earth.


Which segues into another idea that has been beaten to death. Asteroid ISRU.


Let's not go too far back into the weeds but with a couple of depots in LMO and HMO, there is existing infrastructure if the asteroids pan out. /end weeds.


Freezing water. This problem is there whether making props in orbit or on the surface, so it pretty much cancels out. There will be handling issues in 0g but that shouldn't be a showstopper.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/24/2020 10:46 pm
Just for fun, I ran the numbers for percentage of Mars produced propellant reaching High Earth Orbit, using just standard methalox Starships as tankers, and depots in LMO and HMO:

I get 13% using propulsive capture into HEO, and 15% using aero-capture.

Eliminating legs, fins and heat-shield for the LMO-HMO & HMO-HEO legs makes negligible difference. (Except on the return leg).

Switching to hydrolox for LMO-HMO & HMO-HEO gives 15% (assuming same MR, which would be worse in reality, due to larger tanks)

Switching to hydrolox for every leg gives 19% (assuming same MR, which would be a lot worse in reality, due to EDL for larger tanks)


Everything else being equal, which it isn't, fully Hydrolox makes 50% more propellant available in HEO, which because you need less, enables 75% more payload than methalox.  More like 40% and 70% with propellant density factored in, and who know with ISRU production & storage factored in.


Using methalox for Mars to LMO, then SEP, I got 21% to 24% (1800 to 3000 Isp).

Using CO2/LOX, for Mars to LMO, then SEP, I got 14% to 15% (1800 to 3000 Isp).

Using CO2/LOX, for Mars to LMO, then hydrolox, I got 10%.

Using CO2/LOX, for Mars to LMO, then methalox , I got 8%. Might as well just send a Starship direct from the surface.


NOTE: All these trips are one-way. When you need to send an empty tanker back to HMO or LMO, it requires about 16% of the propellant just delivered for methalox, and 21% for hydrolox (lower density -> higher empty mass). Around 12% for SEP.

Edit: fix return %
This is really dismal. Especially since not going back for another load doesn't make sense.


What do the numbers look like comparing mars launch vs earth launch to deliver CO2 for CH4 production from lunar water? I thought about just delivering carbon but the handling difficulties just kept getting worse the more I thought about it.


With all the possible destinations in cislunar there are a lot of moving parts. If the numbers work Mars and Luna could conceivably become the go to for all cislunar refueling. If the numbers work.


To help the numbers it might work best as pure SEP and never touching the ground. Tankers bring CO2 up from Mars using whatever propellant works best. No raptors or legs. Fins and heatshield only if aerobraking. Return can be a low energy transfer to martian orbit. Slow, but it builds a pipeline over time and takes the load off of earth.


Not an overnight project.





Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: LMT on 08/24/2020 11:37 pm
Starship needs to be at least several days in orbit for refueling and has no protection against any debris larger than 1 mm. Potentially high risk of mission failure.

Altitude is a big factor.  ISS orbits at ~ 409 km.  Starship propellant loading could occur at ~ 250 km.  Debris flux is roughly an order of magnitude lower at the lower altitude (red vs. green line).
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: armchairfan on 08/25/2020 03:32 am
Do the math on the 100 Megatons-per-year tweet that Musk mentioned earlier.
If/when this becomes a thing, IMO we should seriously consider momentum exchange tethers at least for surface/LEO traffic and possibly interplanetary traffic too. The tether orbits would be carefully selected and maintained (mostly by nodal precession) to align with the synodic arrival and departure orbital planes. Just for scale, a 100km tether at 3 gees with starships attached tail-to-tail gives each ship a 2*sqrt(3*9.8*100000/2))/1000 = 2.4 km/s DV "for free". There are nuances but they're better discussed in a tethers thread.

Payload goes way up and propellant requirements go way down. Win/win!
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: spacenut on 08/25/2020 03:47 am
To me it is simple.  Launch several tankers in orbit.  Refuel the tankers.  Then when the Mars synod comes up, launch as many Starships as you have tankers in orbit.  Refuel Starships with one docking then go on to Mars.  Tanker/depots, can carry refrigeration, solar panels and shielding to avoid boil-offs while being filled for the Mars Starship synod.  Tanker/depots can either stay in orbit, or return after a Mars fueling run to be checked out and refurbished if needed, then returned to orbit be refilled.  No need for any other developments.  Starships are versatile and modular and can be used for cargo, tanker, passenger/crews, fuel depot, or any combination.  Just outfit them for whatever you need. 
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: cdebuhr on 08/25/2020 04:02 am
Here's a different idea I don;t think I've seen here yet ... if we get to the scale of Starship operations envisioned, we're going to need more launch complexes.  Lots more.  And they're probably going to need multiple pads.  Lots and lots of pads.  So build a complex with a dozen pads.  When you're ready to go somewhere, launch a salvo of all the tankers you're going to need more or less at the same time.  On orbit, the tankers do the tanker dance and transfer all the prop (except for landing fuel) to one tanker.  24ish hours later (or whenever the launch complex aligns properly with the staging orbit). The empty tankers come home, and the outbound Starship launches, rendezvouses with the full tanker, transfers a full load of prop, and executes its departure burn as soon as it is convenient to do so.


I've made no effort so far to qualify this idea to graduate beyond the Crazy Ideas Division.  I'm not sure where to start.  But I'm sure someone here can point out all the reasons this is a dreadfully, catastrophically bad idea.   Or not.  I eagerly await well reasoned feedback!
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/25/2020 04:47 am
Here's a different idea I don;t think I've seen here yet ... if we get to the scale of Starship operations envisioned, we're going to need more launch complexes.  Lots more.  And they're probably going to need multiple pads.  Lots and lots of pads.  So build a complex with a dozen pads.  When you're ready to go somewhere, launch a salvo of all the tankers you're going to need more or less at the same time.  On orbit, the tankers do the tanker dance and transfer all the prop (except for landing fuel) to one tanker.  24ish hours later (or whenever the launch complex aligns properly with the staging orbit). The empty tankers come home, and the outbound Starship launches, rendezvouses with the full tanker, transfers a full load of prop, and executes its departure burn as soon as it is convenient to do so.


I've made no effort so far to qualify this idea to graduate beyond the Crazy Ideas Division.  I'm not sure where to start.  But I'm sure someone here can point out all the reasons this is a dreadfully, catastrophically bad idea.   Or not.  I eagerly await well reasoned feedback!
To my eye the problem is massive over capacity of launch facilities and tankers. For a mars fleet of 10 ships, figure five tankers loading into the sixth for each Mars bound ship. That's 60 tankers, 60 SH and 60 pads that sit idle for most of a synod. There will be other refueling but this would be the big nut.


Operationally it's pretty intense. A large surge of personnel with little else to do when they're not launching. It wouldn't be 60 times what's needed for one launch but it would be up there. And think about that poor sucker that has to run from pad to pad lighting fuses. He's an interesting story. Got his start pulling the MGM lions tail.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/25/2020 05:01 am
When you're ready to go somewhere, launch a salvo of all the tankers you're going to need more or less at the same time.  On orbit, the tankers do the tanker dance and transfer all the prop (except for landing fuel) to one tanker.  24ish hours later (or whenever the launch complex aligns properly with the staging orbit). The empty tankers come home, and the outbound Starship launches, rendezvouses with the full tanker, transfers a full load of prop, and executes its departure burn as soon as it is convenient to do so.

Propellant boil-off isn't that bad. We're not using hydrogen. You can spread the fuelling of the accumulator-tanker out over a few months. At worst, you add one extra tanker mission a few days before the main Mars-SS launches.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/25/2020 05:02 am
This is why I wonder if, long-term, most of the propellant for trips to Mars might actually come *from* Mars.
It isn't just delta-v. Producing enough propellant to launch enough propellant as cargo to Earth, to fully fuel its own return plus one SS flight puts a burden on the ISRU production that puts disproportionate burdens on a Mars settlement that it doesn't on a few extra Earth launches.
Thus, the suggestion for shipping CO2 & water and processing into propellant on the way back.

You misunderstand, the "burden" isn't just producing the propellant that arrives in Earth orbit. It's the extra propellant needed to push that to Earth. Say SS has a return cargo mass of 50 tonnes and you need 600 tonnes for each SS you fuel in Earth orbit. (I haven't looked up the proper estimated numbers; for the purpose of this, it doesn't matter.) You need 12 returning ships for every one you can refuel in Earth orbit.

Alternatively, for each returning ship to supply enough fuel for itself to return, you'll have to launch the return ships to Mars orbit, then launch (via a tanker fleet on Mars) enough propellant to allow them to carry 600 tonnes of surplus propellant back to Earth. So even if you are only launching CO2+Water as cargo, you still have to produce a) the extra propellant needed to get those ships back to Earth with 600 tonnes of CO2+Water, and b) the extra propellant needed to launch the tankers to bring up that propellant into Mars orbit.

It's not just the cost of the cargo-propellant that ends up in Earth orbit. It's the propellant needed to fuel the ships that launch the propellant needed to fuel the ships that return the cargo-propellant to Earth. Earth surface to Earth orbit is usually a 5-7 times multiplier. (Ie, it takes 5-7kg of fuel to launch 1kg of payload.) I haven't worked out the ratio for Mars-surface to Earth-orbit, but it ain't zero.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/25/2020 05:06 am
Microgravity can be used to assist the flow from one to the other.
For ullage, "milli" not "micro".
Any G will settle props.

No it wont. Microgravity isn't enough to cause fluids to settle. Microgravity is what the ISS aims for in order to achieve high-quality science. Micro-g is functionally zero-g for the purposes of fluid flow.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 08/25/2020 05:12 am
Microgravity can be used to assist the flow from one to the other.
For ullage, "milli" not "micro".
Any G will settle props.

No it wont. Microgravity isn't enough to cause fluids to settle. Microgravity is what the ISS aims for in order to achieve high-quality science. Micro-g is functionally zero-g for the purposes of fluid flow.
Not true.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Star-Dust on 08/25/2020 08:31 am
1- I have calculated (online calculator) a 200 tons  payload to LEO with a second stage on top of SH

I bet you haven't, because...

I dont think that a stainless steel tank coupled with six raptors engines will weigh that much

...others have mentioned that the figures that estimate Starship's mass also estimate 40 tonnes for re-entry and landing. 25 tonnes for structure/heat-shield, and 15 tonnes for fuel.

Hence, if you're using a calculator that gives 100 tonnes payload (hence propellant) for the Starship tanker, then it will give 140 tonnes payload (prop) for the expendable version. If you got a higher figure, then you dropped the drymass to an unrealistic level.

3-The option of depot will mitigate the need for rapid  launch of tankers, SS bound for Mars will only be launched when all tanks are in place, this allowing time for further developement of rapid reuse of SH/SH while not delaying first mission to Mars (interim solution).

As mentioned repeatedly: Everything you require for your expendable tanks are the same as the tanker. You need to launch on SH, you need to be able to do docking manoeuvres in space, you need to connect up propellant lines (and gas-return lines for tank pressurisation), you need to be able to transfer propellant from the tanks to the engines on the main vehicle.

In addition, because you seem to have (finally!) accepted that you can't launch a single expendable fully fuelled tank into orbit, you now invent another whole structure, the docking node that holds a bunch of tanks as a depot. The depot then has to transfer fuel to the main Mars vehicle... kind of like... you know... a tanker.

You have all the requirements of building tankers, plus you need a depot before it's usable. It's not an "interim" solution.

The only technology you are trying to skip is reusability, which only requires re-entry and landing. But if Starship can land on Mars, then the technology for reusable tankers has already been developed. If the technology to land tankers isn't ready, Starship can't go to Mars.

So again, there's no "interim" where the Mars Starship exists but the tankers don't. Either the landing technology is ready, making tankers viable, or you can't land on Mars.

5- Fuel depot could be sent to Mars orbit.

Having fuel in Mars orbit doesn't replace ISRU production for a manned Starship mission: Starship can't land while fully fuelled, hence can't launch back into Mars orbit without ISRU propellant on the ground. If they have that, then your proposal isn't needed. If they don't, then you can't send humans to Mars. Again, there's no "interim".
I can't speak for Stardust but I've considered a stripped SS without tank mods as a short term solution and an assembly capable of refueling an entire mars fleet as a long term solution. I see everything else as an interim solution. That said, your criticisms of Stardust's idea are on point.

Don't be shy to swim against the tide, some time you should express what you think. ;D
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Slarty1080 on 08/25/2020 08:41 am
When you're ready to go somewhere, launch a salvo of all the tankers you're going to need more or less at the same time.  On orbit, the tankers do the tanker dance and transfer all the prop (except for landing fuel) to one tanker.  24ish hours later (or whenever the launch complex aligns properly with the staging orbit). The empty tankers come home, and the outbound Starship launches, rendezvouses with the full tanker, transfers a full load of prop, and executes its departure burn as soon as it is convenient to do so.

Propellant boil-off isn't that bad. We're not using hydrogen. You can spread the fuelling of the accumulator-tanker out over a few months. At worst, you add one extra tanker mission a few days before the main Mars-SS launches.
I would have thought that some form of large inflatable highly reflective screen could be used if there were problems. Does anyone have a handle on the scale of the boil off problem such as it is?
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: kkattula on 08/25/2020 09:15 am
Just for fun, I ran the numbers for percentage of Mars produced propellant reaching High Earth Orbit, using just standard methalox Starships as tankers, and depots in LMO and HMO:

I get 13% using propulsive capture into HEO, and 15% using aero-capture.

Eliminating legs, fins and heat-shield for the LMO-HMO & HMO-HEO legs makes negligible difference. (Except on the return leg).

Switching to hydrolox for LMO-HMO & HMO-HEO gives 15% (assuming same MR, which would be worse in reality, due to larger tanks)

Switching to hydrolox for every leg gives 19% (assuming same MR, which would be a lot worse in reality, due to EDL for larger tanks)


Everything else being equal, which it isn't, fully Hydrolox makes 50% more propellant available in HEO, which because you need less, enables 75% more payload than methalox.  More like 40% and 70% with propellant density factored in, and who know with ISRU production & storage factored in.


Using methalox for Mars to LMO, then SEP, I got 21% to 24% (1800 to 3000 Isp).

Using CO2/LOX, for Mars to LMO, then SEP, I got 14% to 15% (1800 to 3000 Isp).

Using CO2/LOX, for Mars to LMO, then hydrolox, I got 10%.

Using CO2/LOX, for Mars to LMO, then methalox , I got 8%. Might as well just send a Starship direct from the surface.


NOTE: All these trips are one-way. When you need to send an empty tanker back to HMO or LMO, it requires about 16% of the propellant just delivered for methalox, and 21% for hydrolox (lower density -> higher empty mass). Around 12% for SEP.

Edit: fix return %
This is really dismal. Especially since not going back for another load doesn't make sense.

What do the numbers look like comparing mars launch vs earth launch to deliver CO2 for CH4 production from lunar water? I thought about just delivering carbon but the handling difficulties just kept getting worse the more I thought about it.

With all the possible destinations in cislunar there are a lot of moving parts. If the numbers work Mars and Luna could conceivably become the go to for all cislunar refueling. If the numbers work.

To help the numbers it might work best as pure SEP and never touching the ground. Tankers bring CO2 up from Mars using whatever propellant works best. No raptors or legs. Fins and heatshield only if aerobraking. Return can be a low energy transfer to martian orbit. Slow, but it builds a pipeline over time and takes the load off of earth.

Not an overnight project.


The good news is that the slow, synod limited part of the tanker run, HMO to HEO, is fairly efficient both ways, so one full SS tanker, probably delivers enough methalox to HEO for 2 x outbound cargo SS, or 1 x fast transit crew SS, plus it's own return.  Although I guess it has to do it the previous synod. But that one trip needs 8 x Surface to LMO flights, and a couple of LMO to HMO, before the synod Mars departure window.*

I haven't done the numbers for water from the Moon, but given 80% by mass of SS propellant is LOX, it seems to me the best options is probably CH4 made on Mars or in Mars Orbit, shipped to Earth-Moon L2. Then make LOX on the Moon, ship it to L2 and return CH4.

Unless there is carbon freely available on the Moon.  If there's lots of CO or CO2 in the polar ice-traps, that might be better.


* These numbers are approximate, the exact numbers depend on so many assumptions and quanta of tanks capacities.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/25/2020 01:12 pm
Microgravity can be used to assist the flow from one to the other.
For ullage, "milli" not "micro".
Any G will settle props.

No it wont. Microgravity isn't enough to cause fluids to settle. Microgravity is what the ISS aims for in order to achieve high-quality science. Micro-g is functionally zero-g for the purposes of fluid flow.
If the tank contains an amorphous glob of frothy propellant and the tank starts accelerating around it at 1mm/hour/hour (example only) in a consistent direction eventually all the propellant will be settled at one end.


The ISS would prefer true 0g but with orientation changing 360deg every orbit, the PV changing orientation constantly and people moving around it's unachievable. The max allowable is probably buried down in the specs somewhere but microgravity, like micro brewery, is also a generic term.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: cdebuhr on 08/25/2020 01:34 pm
Here's a different idea I don;t think I've seen here yet ... if we get to the scale of Starship operations envisioned, we're going to need more launch complexes.  Lots more.  And they're probably going to need multiple pads.  Lots and lots of pads.  So build a complex with a dozen pads.  When you're ready to go somewhere, launch a salvo of all the tankers you're going to need more or less at the same time.  On orbit, the tankers do the tanker dance and transfer all the prop (except for landing fuel) to one tanker.  24ish hours later (or whenever the launch complex aligns properly with the staging orbit). The empty tankers come home, and the outbound Starship launches, rendezvouses with the full tanker, transfers a full load of prop, and executes its departure burn as soon as it is convenient to do so.


I've made no effort so far to qualify this idea to graduate beyond the Crazy Ideas Division.  I'm not sure where to start.  But I'm sure someone here can point out all the reasons this is a dreadfully, catastrophically bad idea.   Or not.  I eagerly await well reasoned feedback!
To my eye the problem is massive over capacity of launch facilities and tankers. For a mars fleet of 10 ships, figure five tankers loading into the sixth for each Mars bound ship. That's 60 tankers, 60 SH and 60 pads that sit idle for most of a synod. There will be other refueling but this would be the big nut.


Operationally it's pretty intense. A large surge of personnel with little else to do when they're not launching. It wouldn't be 60 times what's needed for one launch but it would be up there. And think about that poor sucker that has to run from pad to pad lighting fuses. He's an interesting story. Got his start pulling the MGM lions tail.
Obviously my lunatic idea is just that in the short to medium term, probably more trouble than its worth to launch a few, or even a couple dozen ships now and then.  Though it wouldn't have to be just for Mars.  It could also serve lunar missions.  Heck, even placing LARGE payloads direct to GEO might be able to use a complex like this.  As for Mars, if you just wanted to launch a few starships every synod, this might be overkill, but I'm thinking a bit further out ... Musk wast to send these things by the thousand, eventually.  Then again, by the time we're doing that, we may have other means at our disposal, and the whole discussion will be moot.

One other consideration.  I'm not thinking about mega-launch complexes like a giant KSC with dozens of 39As.  More like a launch complex is the style of Elon.  Maximum automation, "the best part is no part", etc.  Just what's needed for the specified mission and no more.  To slightly modify a recent thread title from this section "What is SS/SH launch complexes are unreasonably cheap?".
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Bob Shaw on 08/25/2020 01:38 pm
I wonder whether a cluster of 'parachutes' might work to both create a slight accelaration and to cool the Starship?

1. Set the Starship rotating once per orbit, pointing towards the Sun.

2. From the nose, eject one pilot parachute with subliming material inside strut balloons to form the shape, preferably going into nightside to avoid Solar thrust.

3. On the next orbit, eject six more as it passess into darkness to make the full umbrella.

4. The parachutes always point at the Sun, and suffer drag. The struts keep them stable. Over several orbits the Starship is protected from direct insolation and the fuel gradually sings to the bottom of the tank.

5. Some tanker LO is vented during docking and while the transfer continues.

Someone else can do the numbers - I'm trying to think of an almost passive way of doing all this!
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Bob Shaw on 08/25/2020 01:39 pm
I would have thought that some form of large inflatable highly reflective screen could be used if there were problems. Does anyone have a handle on the scale of the boil off problem such as it is?

See my post above for cooling and ullage!
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/25/2020 01:45 pm
When you're ready to go somewhere, launch a salvo of all the tankers you're going to need more or less at the same time.  On orbit, the tankers do the tanker dance and transfer all the prop (except for landing fuel) to one tanker.  24ish hours later (or whenever the launch complex aligns properly with the staging orbit). The empty tankers come home, and the outbound Starship launches, rendezvouses with the full tanker, transfers a full load of prop, and executes its departure burn as soon as it is convenient to do so.

Propellant boil-off isn't that bad. We're not using hydrogen. You can spread the fuelling of the accumulator-tanker out over a few months. At worst, you add one extra tanker mission a few days before the main Mars-SS launches.
To amplify on this a bit, The first mission standard build SS accumulators can follow Paul's last minute top off, maybe with some sunshade gizmos. The cargo ships can launch early and make a slower transit which would also ease the load on a tanker surge strategy.


A tank stretch depot with full shades and cryo cooler can be introduced one off at any time and mix n match with standard build accumulator SS's. If it works out, build more.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/25/2020 03:04 pm
When you're ready to go somewhere, launch a salvo of all the tankers you're going to need more or less at the same time.  On orbit, the tankers do the tanker dance and transfer all the prop (except for landing fuel) to one tanker.  24ish hours later (or whenever the launch complex aligns properly with the staging orbit). The empty tankers come home, and the outbound Starship launches, rendezvouses with the full tanker, transfers a full load of prop, and executes its departure burn as soon as it is convenient to do so.

Propellant boil-off isn't that bad. We're not using hydrogen. You can spread the fuelling of the accumulator-tanker out over a few months. At worst, you add one extra tanker mission a few days before the main Mars-SS launches.
I would have thought that some form of large inflatable highly reflective screen could be used if there were problems. Does anyone have a handle on the scale of the boil off problem such as it is?
In LEO the big thermal input is the sun. Keeping a ship oriented with one end pointed sunward minimizes the input and a shade can be not much wider than the ships diameter. Because we're talking about SS refueling, shading the nose keeps the aft end clear for operations.


Reflection from earth is a large secondary input. I'd WAG up to 25% of solar input at some points.   Happily, the point of greatest input, local high noon, has the ship very roughly oriented tail earthward. Not dead on, but in that direction. Shading this is more complicated than shading from the sun because of constantly changing orientation.


I wish I could put numbers on all of this and can't, so instead I offer arm waving and generalizations. One number I did find is the solar thermal input at earth is 1370W/m^2.


A standard SS sans shields could work as an accumulator if time between first tanker load and refueling is short. Maybe on the order of a 2-3 weeks. Adding minimum shielding extends this and full shielding yet more, but in the end it all will boil off.


That's why, IMO, anything short of good shading and a PV based Zero Boil Off (ZBO) system can only be a stop gap. I'm writing this dodging into shade as the morning sun sweeps across my deck to remind me of the magnitude of the problem.


Orbital refueling is great leverage for space operations and one element of making operations inexpensive is making them routine. Using standard build SS's as accumulators will probably work but the tanker surge needed to make it work, while itself may become routine, will be a special operation that by definition is not routine. Ergo, full fledged depots are necessary.


Now my curiosity is up and I'll probably spend some time pinning down some numbers and agonizing over some assumptions to guesstimate thermal input, thermal rejection of sunshields and PV requirements for a cryo cooler. Mass should not be an issue if I work with a 6 ring stretch to a stripped SS. If launched empty it would have plenty of mass margin to LEO.

Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: envy887 on 08/25/2020 03:27 pm
That's why, IMO, anything short of good shading and a PV based Zero Boil Off (ZBO) system can only be a stop gap. I'm writing this dodging into shade as the morning sun sweeps across my deck to remind me of the magnitude of the problem.

The "and" there isn't strictly required. Either good shading or a good active ZBO system will work without the other. The best solution is probably some combination of both, although I think it will lean heavily towards the shading.

In Earth orbit, if they point the nose constantly at the Sun, then the Earth will circle the vehicle once per orbit. In a sun-synchronous dawn-dusk polar orbit, the vehicle can shade one side, and roll once per orbit so that the nose is always pointed at the Sun and the shade is always pointed at Earth. That way the shade (or shades, if the nose is shaded as well), are both fixed relative to the vehicle.

For other more accessible orbits this also works, but the Earth shade needs to be able to rotate or slide fore-aft as the vehicle rolls once per orbit to stay pointed at the Earth. Or the shade could be fixed, but then it needs to fully cover one side of the vehicle and will occasionally be blocking the view of cold deep space.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/25/2020 03:34 pm
I wonder whether a cluster of 'parachutes' might work to both create a slight accelaration and to cool the Starship?

1. Set the Starship rotating once per orbit, pointing towards the Sun.

2. From the nose, eject one pilot parachute with subliming material inside strut balloons to form the shape, preferably going into nightside to avoid Solar thrust.

3. On the next orbit, eject six more as it passess into darkness to make the full umbrella.

4. The parachutes always point at the Sun, and suffer drag. The struts keep them stable. Over several orbits the Starship is protected from direct insolation and the fuel gradually sings to the bottom of the tank.

5. Some tanker LO is vented during docking and while the transfer continues.

Someone else can do the numbers - I'm trying to think of an almost passive way of doing all this!
The thrust would truly me micro (or less) but the there are downsides.


The slight impacts of another ship hooking up would overwhelm the chute G and just when the props need to be settled, they're not. Waiting for this system to resettle props will  be a long wait.


Second problem is that a depot receiving propellant and providing props need to settle in opposite directions. This can be overcome with plumbing but still an issue.


The consumables needed for settling is not great and arriving tankers will be in position to replenish the depot.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/25/2020 04:11 pm
That's why, IMO, anything short of good shading and a PV based Zero Boil Off (ZBO) system can only be a stop gap. I'm writing this dodging into shade as the morning sun sweeps across my deck to remind me of the magnitude of the problem.

The "and" there isn't strictly required. Either good shading or a good active ZBO system will work without the other. The best solution is probably some combination of both, although I think it will lean heavily towards the shading.

In Earth orbit, if they point the nose constantly at the Sun, then the Earth will circle the vehicle once per orbit. In a sun-synchronous dawn-dusk polar orbit, the vehicle can shade one side, and roll once per orbit so that the nose is always pointed at the Sun and the shade is always pointed at Earth. That way the shade (or shades, if the nose is shaded as well), are both fixed relative to the vehicle.

For other more accessible orbits this also works, but the Earth shade needs to be able to rotate or slide fore-aft as the vehicle rolls once per orbit to stay pointed at the Earth. Or the shade could be fixed, but then it needs to fully cover one side of the vehicle and will occasionally be blocking the view of cold deep space.
Yes, a sun synchronous orbit reduces shade dynamics but at the cost of an orbit with reduced utility. The gyrations an earth shield will need are why I mentioned it being a more complex problem.


AIUI, even a highly reflective shield still heats up and this thermal load is re emitted from both sides so half goes towards the ship. A second layer will mostly reflect this back to the first shield where it continues the reflection emission process.


Upshot is that more than one layer doesn't add much. But, since the deployment and tracking gear is the bulk of the mass and complexity, more layers doesn't add much to the cost.


The advantage of a cryo cooler is heavily dependent on reliability. Once it breaks down it's dead mass. A quick google yesterday showed me that since it's never been done in space, everything is theoretical. Fill and forget is a great ideal but with little engineering legacy, only an ideal.


You're probably right about depending on shades. Any cryo cooler flown will be an experiment.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/25/2020 04:15 pm
It's been pointed out that HEO is more mass effect than LEO for mars mission refueling. It also has the advantage of less earth thermal input.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: mmeijeri on 08/25/2020 05:47 pm
The advantage of a cryo cooler is heavily dependent on reliability. Once it breaks down it's dead mass. A quick google yesterday showed me that since it's never been done in space, everything is theoretical. Fill and forget is a great ideal but with little engineering legacy, only an ideal.

Cryocoolers have flown in space before (on telescopes?), and IIRC an experiment was done with one on the ISS. It ended after a few months when the cryocooler failed and the methane it was supposed to cool had to be vented. Not proven technology, but not entirely unproven either.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/25/2020 06:21 pm
The advantage of a cryo cooler is heavily dependent on reliability. Once it breaks down it's dead mass. A quick google yesterday showed me that since it's never been done in space, everything is theoretical. Fill and forget is a great ideal but with little engineering legacy, only an ideal.

Cryocoolers have flown in space before (on telescopes?), and IIRC an experiment was done with one on the ISS. It ended after a few months when the cryocooler failed and the methane it was supposed to cool had to be vented. Not proven technology, but not entirely unproven either.
I could be batting 0 on this but I think telescopes use cryo fluids to chill the sensor. The James Webb will use a cryo cooler.


Breaking down during an experiment on ISS doesn't have me whaling that cryo cooling on orbit can't be done. I believe it can be. But it does tell me that more work is needed to make it bullet proof.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: mmeijeri on 08/25/2020 06:24 pm
Breaking down during an experiment on ISS doesn't have me whaling that cryo cooling on orbit can't be done. I believe it can be. But it does tell me that more work is needed to make it bullet proof.

Absolutely, and fortunately it looks as if SpaceX's part in Artemis will help with that.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 08/25/2020 09:00 pm
Here's a different idea I don;t think I've seen here yet ... if we get to the scale of Starship operations envisioned, we're going to need more launch complexes.  Lots more.  And they're probably going to need multiple pads.  Lots and lots of pads.  So build a complex with a dozen pads.  When you're ready to go somewhere, launch a salvo of all the tankers you're going to need more or less at the same time.  On orbit, the tankers do the tanker dance and transfer all the prop (except for landing fuel) to one tanker.  24ish hours later (or whenever the launch complex aligns properly with the staging orbit). The empty tankers come home, and the outbound Starship launches, rendezvouses with the full tanker, transfers a full load of prop, and executes its departure burn as soon as it is convenient to do so.


I've made no effort so far to qualify this idea to graduate beyond the Crazy Ideas Division.  I'm not sure where to start.  But I'm sure someone here can point out all the reasons this is a dreadfully, catastrophically bad idea.   Or not.  I eagerly await well reasoned feedback!
To my eye the problem is massive over capacity of launch facilities and tankers. For a mars fleet of 10 ships, figure five tankers loading into the sixth for each Mars bound ship. That's 60 tankers, 60 SH and 60 pads that sit idle for most of a synod. There will be other refueling but this would be the big nut.

Except Elon isn't going for a fleet of 10 ships. He's going for a fleet of hundreds to thousands of ships.

https://twitter.com/elonmusk/status/1217990326867988480

Operationally it's pretty intense. A large surge of personnel with little else to do when they're not launching. It wouldn't be 60 times what's needed for one launch but it would be up there. And think about that poor sucker that has to run from pad to pad lighting fuses. He's an interesting story. Got his start pulling the MGM lions tail.

I don't think there will be as many personnel as you imagine. Quoting from a recent SpaceX job posting (https://www.jobilize.com/job/launch-engineer-control-flight-operations-starship-brownsville-spacex):

Quote
LAUNCH ENGINEER - LAUNCH CONTROL AND FLIGHT OPERATIONS (STARSHIP) RESPONSIBILITIES:
• Develop and execute launch, flight, on-orbit, and recovery operations streamlining future Starship launches
Drive development towards power on to launch in less than one hour with zero operators on console
• Help design automation back-end software (ControlCode, Stage0) to optimize how operators write and interact with automation
• Develop software and processes that automate how SpaceX tests and validates ground and vehicle software
• Support Falcon launch operations as needed

Obviously they won't climb that automation mountain in one day, but by the time they're launching hundreds of ships in one synod it should be a pretty well-oiled (and lightly staffed) machine.


When you're ready to go somewhere, launch a salvo of all the tankers you're going to need more or less at the same time.  On orbit, the tankers do the tanker dance and transfer all the prop (except for landing fuel) to one tanker.  24ish hours later (or whenever the launch complex aligns properly with the staging orbit). The empty tankers come home, and the outbound Starship launches, rendezvouses with the full tanker, transfers a full load of prop, and executes its departure burn as soon as it is convenient to do so.

Propellant boil-off isn't that bad. We're not using hydrogen. You can spread the fuelling of the accumulator-tanker out over a few months. At worst, you add one extra tanker mission a few days before the main Mars-SS launches.

The advantages aren't just propellant boil-off. It also reduces time spent rendevous-and-docking (increasing tanker utilization efficiency), it lets you combine airspace closure (NOTAM) windows, it lets you combine launch area personnel evacs and closures (streamlining operations vs. having a bunch of pads running on independent schedules), and it reduces closures of beaches and waterways. I would argue it also reduces the per-launch acoustic disruption to the local community, because by clustering the schedules it gives longer "quiet periods" between launch events.

Some may object that these costs aren't paid directly by SpaceX out-of-pocket, but they still incur political costs onto SpaceX. If you can't scale Starship (again, to thousands of launches per day) without completely disrupting modern air travel, then you can't scale Starship.

It also increases the density of launch pads per launch site. On the urbanized Earth, good candidate locations (and jurisdictions) for launch sites are relatively scarce, even after you add in the feasible off-shore launch sites. If you can fit 10x as many launch pads per launch site then that increases your maximum scale by 10x, while at the same time lowering your per-launch costs. Obviously the per-pad costs (eg fuel) don't go down, but the per-site costs (eg closures, security) do go down.

And your tanker use tempo increases rather dramatically.

And yeah, less boil-off.


I think cdebuhr's Crazy Idea is pretty brilliant, all things considered.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/25/2020 09:37 pm
If the tank contains an amorphous glob of frothy propellant and the tank starts accelerating around it at 1mm/hour/hour (example only) in a consistent direction eventually all the propellant will be settled at one end.

It won't overcome the "stickiness" of the froth, won't separate gas and fluid. Surface wetting and capillary effects dominate.

but microgravity, like micro brewery, is also a generic term.

As a technical term, microgravity means "millionths of a g". As a generic term, microgravity is a synonym for near-zero-g or orbital free-fall. Microgravity does not mean "anything lower than Earth gravity". It's weird to keep encountering the latter on a technical site. It's weirder that this is the only site where I've seen people do it.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/25/2020 09:53 pm
Re: launching in waves

It also reduces time spent rendevous-and-docking (increasing tanker utilization efficiency),

How?

If there's five ships, each spends as long doing rendezvous and docking. Launching them together doesn't make them dock quicker. If anything, clustering means they're more likely to get in each others way. (Eg, a tanker that's taking longer to dock than expected delays the others.)

it lets you combine airspace closure (NOTAM) windows, it lets you combine launch area personnel evacs and closures (streamlining operations vs. having a bunch of pads running on independent schedules), and it reduces closures of beaches and waterways.

OTOH, it reduces site efficiency, since it spends most of its time unused. It reduces manpower efficiency, since you need more ops people to handle the peak, who are unneeded during the lulls. It seems to go against the way SpaceX is costing their systems.

I would argue it also reduces the per-launch acoustic disruption to the local community, because by clustering the schedules it gives longer "quiet periods" between launch events.

OTOH, it puts vehicles in each others acoustic environments during critical pre-launch periods.

It also increases the density of launch pads per launch site.

Even denser is to use fewer pads more often. The best part is no part.

And your tanker use tempo increases rather dramatically.

Having fewer tankers used more often is a more efficient than many tankers used rarely.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: spacenut on 08/25/2020 10:35 pm
If you place a tanker in orbit to be a fuel depot.  It will take 5 tanker flights to fill it.  One tanker per week in 5 weeks you have a full tanker in orbit ready to fuel up a Mars bound Starship.  In 50 weeks you could have 10 full tankers for 10 Mars bound Starships.  18 months between synods and you can have 15 Starships going to Mars each synod.  You only have to produce 15 in orbit fuel depot tankers and 15 Mars bound Starships per synod along with say two reusable tankers to fill the depot tankers.  This is a total of 32 Starships.  All this could be done from one launch pad with one flight per week plus a little at the end for the Starships leaving earth. 

Musk said he will eventually be able to produce 100 Starships per year.  This would trippld the number of Starships going to Mars to 45. 

Now if you get 2-3 flights per week, just from one launchpad, a flotilla of at least 100 Starships could go to Mars every synod.  2-3 flights per week is not impossible from one pad.  Now they are going to build a Florida pad also.  So that gets two pads.  Musk may build another pad offshore of Boca Chica and offshore Florida also and still use the same onshore facilities.  That gives about 4 pads. 

There is no reason why a launchpad can't handle one launch per day if need be.  One or two a week from 3-4 pads can fuel in orbit tankers, and fly 100's of Starships per synod to Mars. 

This is just SpaceX, now if others want to join the Mars colonization, there will be others possibly filling the tanker Starship/Depots, to get a ride.  Blue Origin may build New Armstrong by then. 

I believe Starship will be the Model T or the Volkswagon of the space age.  Low cost to orbit.  Reusable, and lower maintenance.  Others will have to follow.  Then larger Starships. 
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Twark_Main on 08/25/2020 10:55 pm
Re: launching in waves

It also reduces time spent rendevous-and-docking (increasing tanker utilization efficiency),

How?

Because you eliminate phasing, and you eliminate the need to wait 12-24 hours for the launch site to rotate under the orbital plane. Every launch opportunity into the Mars departure parking orbit (1-2 per day) you can launch 10 tankers instead of 1.

If there's five ships, each spends as long doing rendezvous and docking.

Five ships seems a bit too small. You can't get a full tanker, for one.

Eight tankers would make good sense, because then you only need three rounds of rendezvous (comprising 7 rendezvous total) and you get a full tanker at the end (rather than ~half a tanker).

Launching them together doesn't make them dock quicker.

You're not waiting as long for phasing, and you don't have to wait for the launch site to line up again. That makes the rendezvous quicker. Naturally the propellant transfer takes the same amount of time, so that's no different either way.

If anything, clustering means they're more likely to get in each others way. (Eg, a tanker that's taking longer to dock than expected delays the others.)

That sounds like a "it hurts when I do this" problem. Solution: don't launch select parking orbits that are too close together. Work the problem like Goldilocks and choose a distance that's "just right:" not right on top of each-other, but it's not necessary to circle the Earth 16 times until your launch site is aligned either.

it lets you combine airspace closure (NOTAM) windows, it lets you combine launch area personnel evacs and closures (streamlining operations vs. having a bunch of pads running on independent schedules), and it reduces closures of beaches and waterways.

OTOH, it reduces site efficiency, since it spends most of its time unused.

You're conflating two separate issues: number of launch pads per site, and number of launch pads on Earth total. You're raising a problem that occurs if the latter number gets too high, but I'm advocating increasing the former number, not necessarily the latter (though the latter must increase anyway to reach SpaceX's goal of thousands of launches per day).

Due to the Mars synodic cycle, low utilization might be unavoidable. If so, pick your poison. Better to have unused pads than unused launch sites.

It reduces manpower efficiency, since you need more ops people to handle the peak, who are unneeded during the lulls. It seems to go against the way SpaceX is costing their systems.

Again, probably unavoidable. Take up your complaint with the laws of orbital mechanics. ;)

The more highly automated your launches are, the smaller this problem becomes. Hence SpaceX's desire to go "power on to launch in less than one hour with zero operators on console."

I would argue it also reduces the per-launch acoustic disruption to the local community, because by clustering the schedules it gives longer "quiet periods" between launch events.

OTOH, it puts vehicles in each others acoustic environments during critical pre-launch periods.

Fortunately that's no problem. Each launch pad would have to be far enough away to avoid fratricide in case of a RUD, so the nominal launch acoustics should be easily tolerated.

It also increases the density of launch pads per launch site.

Even denser is to use fewer pads more often. The best part is no part.

Again conflating. I'm not saying they need more pads, I'm saying they need leaner pads (ie the same number of pads at fewer unique launch sites).

Either way, SpaceX needs hundreds of launch pads globally. Would you rather they each have their own dedicated 30 km keep-out circle, or would it perhaps make sense to combine a few of them? That's the fundamental question.

https://twitter.com/elonmusk/status/1298019842356703232

And your tanker use tempo increases rather dramatically.

Having fewer tankers used more often is a more efficient than many tankers used rarely.

I'm not advocating increasing the tanker fleet size beyond the optimum (thus hurting utilization), I'm advocating using the tanker fleet efficiently.

That's why a system where tankers have a high flights-per-day utilization, as cdebuhr describes, makes sense.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: cdebuhr on 08/25/2020 11:50 pm
Re: launching in waves

It also reduces time spent rendevous-and-docking (increasing tanker utilization efficiency),

How?

Because you eliminate phasing, and you eliminate the need to wait 12-24 hours for the launch site to rotate under the orbital plane. Every launch opportunity into the Mars departure parking orbit (1-2 per day) you can launch 10 tankers instead of 1.

If there's five ships, each spends as long doing rendezvous and docking.

Five ships seems a bit too small. You can't get a full tanker, for one.

Eight tankers would make good sense, because then you only need three rounds of rendezvous (comprising 7 rendezvous total) and you get a full tanker at the end (rather than ~half a tanker).

Launching them together doesn't make them dock quicker.

You're not waiting as long for phasing, and you don't have to wait for the launch site to line up again. That makes the rendezvous quicker. Naturally the propellant transfer takes the same amount of time, so that's no different either way.

If anything, clustering means they're more likely to get in each others way. (Eg, a tanker that's taking longer to dock than expected delays the others.)

That sounds like a "it hurts when I do this" problem. Solution: don't launch select parking orbits that are too close together. Work the problem like Goldilocks and choose a distance that's "just right:" not right on top of each-other, but it's not necessary to circle the Earth 16 times until your launch site is aligned either.

it lets you combine airspace closure (NOTAM) windows, it lets you combine launch area personnel evacs and closures (streamlining operations vs. having a bunch of pads running on independent schedules), and it reduces closures of beaches and waterways.

OTOH, it reduces site efficiency, since it spends most of its time unused.

You're conflating two separate issues: number of launch pads per site, and number of launch pads on Earth total. You're raising a problem that occurs if the latter number gets too high, but I'm advocating increasing the former number, not necessarily the latter (though the latter must increase anyway to reach SpaceX's goal of thousands of launches per day).

Due to the Mars synodic cycle, low utilization might be unavoidable. If so, pick your poison. Better to have unused pads than unused launch sites.

It reduces manpower efficiency, since you need more ops people to handle the peak, who are unneeded during the lulls. It seems to go against the way SpaceX is costing their systems.

Again, probably unavoidable. Take up your complaint with the laws of orbital mechanics. ;)

The more highly automated your launches are, the smaller this problem becomes. Hence SpaceX's desire to go "power on to launch in less than one hour with zero operators on console."

I would argue it also reduces the per-launch acoustic disruption to the local community, because by clustering the schedules it gives longer "quiet periods" between launch events.

OTOH, it puts vehicles in each others acoustic environments during critical pre-launch periods.

Fortunately that's no problem. Each launch pad would have to be far enough away to avoid fratricide in case of a RUD, so the nominal launch acoustics should be easily tolerated.

It also increases the density of launch pads per launch site.

Even denser is to use fewer pads more often. The best part is no part.

Again conflating. I'm not saying they need more pads, I'm saying they need leaner pads (ie the same number of pads at fewer unique launch sites).

Either way, SpaceX needs hundreds of launch pads globally. Would you rather they each have their own dedicated 30 km keep-out circle, or would it perhaps make sense to combine a few of them? That's the fundamental question.

https://twitter.com/elonmusk/status/1298019842356703232

And your tanker use tempo increases rather dramatically.

Having fewer tankers used more often is a more efficient than many tankers used rarely.

I'm not advocating increasing the tanker fleet size beyond the optimum (thus hurting utilization), I'm advocating using the tanker fleet efficiently.

That's why a system where tankers have a high flights-per-day utilization, as cdebuhr describes, makes sense.
Well, I'm glad to see that my Crazy Idea has at least stimulated an interesting discussion!  For what its worth, I only see this idea as being even remotely viable if ground operations can be streamlined and automated to a degree that is almost unthinkable today, but which will be needed anyway (IMO anyway) to reach the scale of operations Musk envisions.  A few more points submitted for your collective consideration:

1) I know that on-orbit prop boil-off is not an insurmountable problem but ... "the best problem is no problem".  If you can get from first tanker launch to departure burn in 24-48 hours, the problem is very much reduced if not eliminated.

2) "The best part is no part" ... This is based solely on my gut feeling - counter arguments welcome: When trying to turn "parts" into "no parts", eliminating unique parts and subsystems is much more significant than just reducing the count of otherwise identical systems.  Getting rid of or reducing the need for cryocoolers/sunshades/prop storage heroics for the expense of needing a few extra tankers seems like a win to me.  Also relevant to this is the discussion in another thread: "What if Starship is unreasonably cheap".

3) One serious issue that seems to keep coming up whenever depots get discussed is the pesky problem of orbital mechanics - in short, plane changes suck.  I don't think I spelled it out in my original post, but the complete avoidance of this issue is one of the key benefits I see in tanker salvos.

4) I don't see this notion as applying solely to Mars.  Indeed, Mars may be one case where you've got so many craft going in one direction that large orbital depots may make more sense (eventually ... not anytime soon IMHO).   The advantage I see to a tanker salvo is that it allows you to put a Starship on just about any orbit or departure trajectory you wish quickly without having to worry too much about boil-off, excessive exposure to MMOD risk, etc.

Edit: I really need to proofread more carefully ...
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: yg1968 on 08/26/2020 03:06 am
Quote from: Tim Dodd
[Question:] How will lunar starship refuel? It needs to go back to Earth orbit, and then get refueled by multiple tankers to do that round trip each time right? Can’t make methane on the moon sans a large cow farm, right?

Quote from: Elon Musk
[Answer:] Starship propellant is ~78% oxygen, so an O2 plant on the moon would be enough. Otherwise, we could brute-force it with tankers to low Earth orbit. That’s probably faster.

https://twitter.com/elonmusk/status/1298426245991063554
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: OTV Booster on 08/26/2020 03:38 am
If the tank contains an amorphous glob of frothy propellant and the tank starts accelerating around it at 1mm/hour/hour (example only) in a consistent direction eventually all the propellant will be settled at one end.

It won't overcome the "stickiness" of the froth, won't separate gas and fluid. Surface wetting and capillary effects dominate.

but microgravity, like micro brewery, is also a generic term.

As a technical term, microgravity means "millionths of a g". As a generic term, microgravity is a synonym for near-zero-g or orbital free-fall. Microgravity does not mean "anything lower than Earth gravity". It's weird to keep encountering the latter on a technical site. It's weirder that this is the only site where I've seen people do it.
That 1mm/hour/hour was not an operational suggestion. It was meant to illustrate the props migrating to one end of the tank. Yes higher G would be needed. In an earlier post I suggested low G initially, higher G to get the props settled down, then back to a lower G while transferring. No exact definitions on what high and low G mean here, but not very much. Deci-G's would be overkill.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Paul451 on 08/26/2020 04:00 am
[edit: For those getting sick of this, I'll let it drop after this post.]

Re: launching in waves

It also reduces time spent rendevous-and-docking (increasing tanker utilization efficiency),
How?
Because you eliminate phasing, and you eliminate the need to wait 12-24 hours for the launch site to rotate under the orbital plane. Every launch opportunity into the Mars departure parking orbit (1-2 per day) you can launch 10 tankers instead of 1.

That's just rephrasing the original concept. It doesn't reduce time spent in rendezvous and docking manoeuvres.

Unless you are creating the strawman alternative that the launches in both scenarios have to be over the same period (within a day). In which case, no. That's a strawman. Don't do that.

One launch a day is fine. If the pads can operate more often than that, then they are still free for other customers. You squeeze the tanker flights in between paying jobs.

If there's five ships, each spends as long doing rendezvous and docking.
Five ships seems a bit too small. You can't get a full tanker, for one.

{Shrug} I just used the figure from Musk's presentation. It's "however many refuelling flights are required per Mars Starship."

If anything, clustering means they're more likely to get in each others way. (Eg, a tanker that's taking longer to dock than expected delays the others.)
Solution: don't launch select parking orbits that are too close together.

You misread what I wrote. If there is an issue with a tanker docking and transferring propellant, it holds up the whole fleet. It's less efficient to throw them all at the same target at the same time, rather than bring them in over a more natural pace.

You're conflating two separate issues: number of launch pads per site, and number of launch pads on Earth total. You're raising a problem that occurs if the latter number gets too high, but I'm advocating increasing the former number, not necessarily the latter (though the latter must increase anyway to reach SpaceX's goal of thousands of launches per day).

None of that has anything to do with anything I wrote.

Due to the Mars synodic cycle, low utilization might be unavoidable.

Making it foolish to try to jam as many launches into as short a period as possible if you don't have to.

And I don't believe you have to. Boil-off isn't that big an issue for an accumulation-tanker, so it makes more sense to spread the refuelling out as much as possible in order to operate fewer fixed resources more often.

It reduces manpower efficiency, since you need more ops people to handle the peak, who are unneeded during the lulls. It seems to go against the way SpaceX is costing their systems.
Again, probably unavoidable. Take up your complaint with the laws of orbital mechanics.

"This is an issue. I know, let's make it worse!"

It also increases the density of launch pads per launch site.
Even denser is to use fewer pads more often. The best part is no part.
Again conflating. I'm not saying they need more pads,

Then you misunderstood cdebuhr's proposal.

Either way, SpaceX needs hundreds of launch pads globally. Would you rather they each have their own dedicated 30 km keep-out circle, or would it perhaps make sense to combine a few of them? That's the fundamental question.

One that has nothing to do with the topic.

And your tanker use tempo increases rather dramatically.
Having fewer tankers used more often is a more efficient than many tankers used rarely.
I'm not advocating increasing the tanker fleet size beyond the optimum (thus hurting utilization), I'm advocating using the tanker fleet efficiently.
That's why a system where tankers have a high flights-per-day utilization, as cdebuhr describes, makes sense.

Again, I think you misunderstand cdebuhr's proposal.

He wants more tankers, more launch pads, with all the tankers launching at once to ensure the refuelling and departure process happens in one hit. That is the opposite of increasing the per-tanker flightrate.

Either that or I misunderstood him.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Robotbeat on 08/26/2020 05:26 am
Just for fun, I ran the numbers for percentage of Mars produced propellant reaching High Earth Orbit, using just standard methalox Starships as tankers, and depots in LMO and HMO:

I get 13% using propulsive capture into HEO, and 15% using aero-capture.

Eliminating legs, fins and heat-shield for the LMO-HMO & HMO-HEO legs makes negligible difference. (Except on the return leg).

Switching to hydrolox for LMO-HMO & HMO-HEO gives 15% (assuming same MR, which would be worse in reality, due to larger tanks)

Switching to hydrolox for every leg gives 19% (assuming same MR, which would be a lot worse in reality, due to EDL for larger tanks)


Everything else being equal, which it isn't, fully Hydrolox makes 50% more propellant available in HEO, which because you need less, enables 75% more payload than methalox.  More like 40% and 70% with propellant density factored in, and who know with ISRU production & storage factored in.


Using methalox for Mars to LMO, then SEP, I got 21% to 24% (1800 to 3000 Isp).

Using CO2/LOX, for Mars to LMO, then SEP, I got 14% to 15% (1800 to 3000 Isp).

Using CO2/LOX, for Mars to LMO, then hydrolox, I got 10%.

Using CO2/LOX, for Mars to LMO, then methalox , I got 8%. Might as well just send a Starship direct from the surface.


NOTE: All these trips are one-way. When you need to send an empty tanker back to HMO or LMO, it requires about 16% of the propellant just delivered for methalox, and 21% for hydrolox (lower density -> higher empty mass). Around 12% for SEP.

Edit: fix return %
This is really dismal....
Not at all! I think the numbers are pretty good, especially with SEP. (Or a Phobos tether, not listed.) We're about 10x that of Earth, particularly with the higher orbit taken into consideration.
Title: Re: Starship In-orbit refueling - Options and Discussion
Post by: Kansan52 on 08/26/2020 04:15 pm
So, once every Mars synod, 700 ships must launch so 100 ships can go to Mars. Seems like a good time for creation of several fuel depots so the tankers can launch before the synod reducing that laun