Off-Earth modification, repair and assembly of Starships

[LMT]

Where round-trip forces are modest, an inflatable tanker system could boost tanker infrastructure efficiency, yes:  e.g., cycling between a LEO LOX trawler depot and a lunar base. 

Some custom lunar spaceport infrastructure would be needed to manage that notional flight configuration.  Still, using inflatables, such a system could plausibly offer a full order-of-magnitude improvement over SpaceX baseline propellant-to-payload ratio.

If it cycles between LEO and LLO, the custom lunar spaceport infrastructure goes away.

The extra infrastructure could be as simple as an elevated landing ring.  Not a significant factor.

...or it could require something more complicated. It's unknown at the present time.

Construction of a single landing structure is not a significant factor in a system for order-of-magnitude improvement in propellant-to-payload ratio. 

More problematic still, it would require the depot to have A) high-thrust engines sufficient for landing, and B) sufficient structural stength to resist not only internal pressure, but also significant deformation due to the high-thrust engines (limiting maximum size and minimum mass). This is, indeed, becoming a "significant factor."

A Starship configured for this purpose, with a full complement of 3 sea-level Raptors + 6 vacuum Raptors, would have thrust to land the 9,300 t cargo at a lunar base. 

Your depot deformation reasoning is off.  Thrust isn't the issue, but the actual acceleration of the structure, which is modest in this ultra-heavy LEO-lunar run.  F=ma.

[magnemoe]

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.

[docmordrid]

An inflatable tanker would be fine for hypergolic propellants, but how does that work with cryogenic propellants? Any flexible material at room temp would be brittle at cryogenic temps.
>

Thin Red Line has worked with Bigelow on their habitats, and NASA. Wonder how it scales?

!ink...

Lightweight Inflatable Cryogenic Tank

NASA Kennedy Space Center

Teamed with Technology Applications Inc., Thin Red Line’s inflatable UHPV technology is investigated as powerful alternative to cryogenic COPV’s. UHPV’s extreme simplicity permits incorporation of a much broader spectrum of corrosive content (LOX, LH2, LCH4, etc.) compatible liner materials. For propellant depots UHPV can be packaged for launch, filled in-situ, and repeatedly depleted to almost zero residual

[Twark_Main]

An inflatable tanker would be fine for hypergolic propellants, but how does that work with cryogenic propellants? Any flexible material at room temp would be brittle at cryogenic temps.

Kevlar works great at cryogenic temperatures.

If you need a tanker to quickly refuel SS, then send up a tanker SS, refuel it with multiple tanker SS flights, and do a single refuel transfer to the outgoing SS. No need for a permanent fuel depot until propellant is produced on the Moon, asteroids, etc.

Don't forget, if successful, SS is going to be ridiculously cheap. SpaceX is optimizing for cost, not performance. Any orbital construction or repair would have to be cheaper to be useful. If a landed SS on Mars needs repair, as long as there's a spare for the crew to use to return to Earth, it would make more sense to scrap the ship and use the materials at the Mars base.

I happen to agree with you actually, but others insisted on the (hand-waved imo) "requirement" that the tanker be huge and lightweight, backwards-justifying on-orbit welding. My point is that there are better alternatives even in that (contrived) case.

[Twark_Main]

Where round-trip forces are modest, an inflatable tanker system could boost tanker infrastructure efficiency, yes:  e.g., cycling between a LEO LOX trawler depot and a lunar base. 

Some custom lunar spaceport infrastructure would be needed to manage that notional flight configuration.  Still, using inflatables, such a system could plausibly offer a full order-of-magnitude improvement over SpaceX baseline propellant-to-payload ratio.

If it cycles between LEO and LLO, the custom lunar spaceport infrastructure goes away.

The extra infrastructure could be as simple as an elevated landing ring.  Not a significant factor.

...or it could require something more complicated. It's unknown at the present time.

Construction of a single landing structure is not a significant factor in a system for order-of-magnitude improvement in propellant-to-payload ratio.

Again, "because mass ratio" isn't a real engineering justification, whether or not it's been seasoned with the phrase "order-of-magnitude improvement."

What is the resultant cost savings that justifies this landing structure (and the above-mentioned constraints on TWR and rigidity)? Because I can't find any.

More problematic still, it would require the depot to have A) high-thrust engines sufficient for landing, and B) sufficient structural stength to resist not only internal pressure, but also significant deformation due to the high-thrust engines (limiting maximum size and minimum mass). This is, indeed, becoming a "significant factor."

A Starship configured for this purpose, with a full complement of 3 sea-level Raptors + 6 vacuum Raptors, would have thrust to land the 9,300 t cargo at a lunar base.

But the Starship would need to hold the bag, so the bag still needs to withstand >1/6 g, which is unnecessary otherwise.

Your depot deformation reasoning is off.  Thrust isn't the issue, but the actual acceleration of the structure, which is modest in this ultra-heavy LEO-lunar run.  F=ma.

I'm not sure what mathematical imprecision you think I'm guilty of here, but I assure you I have a good grasp of basic high school physics (linear/rotational kinematics, etc). With that in mind, let's skip the pedantry.

[LMT]

An fuel depot who can be one tanker or an dedicated tanker with an sort of sun shade

And in LEO, it must also be an "Earth shade" [Kutter et al. 2008], due to Earth's IR flux, which is max in LEO.  The cartoon of the LEO LOX depot exposes tanks upward for this reason, with sunshade film + solar panels below.  Here it would make sense to store LCH4 in the more exposed tanks, due to its higher boiling point.  Beyond that, some additional sunshade film could be envisioned across the exposed tanks, just as needed.

Refs.

Kutter, B., Oneil, G., Pitchford, B., & Zegler, F. (2008, September). A practical, affordable cryogenic propellant depot based on ULA's flight experience. In AIAA Space 2008 Conference & Exposition (p. 7644).

[LMT]

Where round-trip forces are modest, an inflatable tanker system could boost tanker infrastructure efficiency, yes:  e.g., cycling between a LEO LOX trawler depot and a lunar base. 

Some custom lunar spaceport infrastructure would be needed to manage that notional flight configuration.  Still, using inflatables, such a system could plausibly offer a full order-of-magnitude improvement over SpaceX baseline propellant-to-payload ratio.

If it cycles between LEO and LLO, the custom lunar spaceport infrastructure goes away.

The extra infrastructure could be as simple as an elevated landing ring.  Not a significant factor.

...or it could require something more complicated. It's unknown at the present time.

Construction of a single landing structure is not a significant factor in a system for order-of-magnitude improvement in propellant-to-payload ratio.

Again, "because mass ratio" isn't a real engineering justification, whether or not it's been seasoned with the phrase "order-of-magnitude improvement."

What is the resultant cost savings that justifies this landing structure (and the above-mentioned constraints on TWR and rigidity)? Because I can't find any.

More problematic still, it would require the depot to have A) high-thrust engines sufficient for landing, and B) sufficient structural stength to resist not only internal pressure, but also significant deformation due to the high-thrust engines (limiting maximum size and minimum mass). This is, indeed, becoming a "significant factor."

A Starship configured for this purpose, with a full complement of 3 sea-level Raptors + 6 vacuum Raptors, would have thrust to land the 9,300 t cargo at a lunar base.

But the Starship would need to hold the bag, so the bag still needs to withstand >1/6 g, which is unnecessary otherwise.

Your depot deformation reasoning is off.  Thrust isn't the issue, but the actual acceleration of the structure, which is modest in this ultra-heavy LEO-lunar run.  F=ma.

I'm not sure what mathematical imprecision you think I'm guilty of here, but I assure you I have a good grasp of basic high school physics (linear/rotational kinematics, etc). With that in mind, let's skip the pedantry.

Another confused post.

re "cost savings":  Order-of-magnitude improvement in propellant-to-payload ratio gives order-of-magnitude reduction in Starship tanker fleet, including the SSH fleet - with corresponding and obvious cost savings.  It's a justification of the "inflatable tanker" concept, which you liked yesterday.

re "the bag still needs to withstand >1/6 g":  No, inflatables would be drained during lunar approach, because Starship return needs no inflatable propellant.  If you disagree, run the rocket equation.

re "pedantry":  You conflated high thrust with high acceleration, forgetting the F=ma.  Basic mistake; basic correction.

[LMT]

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.

With ISEP, LEO depot loading and unloading could be accomplished without expenditure of propellant.  Ullage acceleration from Lorentz force:  it's one potential advantage of a strong geomagnetic field.

[Twark_Main]

Where round-trip forces are modest, an inflatable tanker system could boost tanker infrastructure efficiency, yes:  e.g., cycling between a LEO LOX trawler depot and a lunar base. 

Some custom lunar spaceport infrastructure would be needed to manage that notional flight configuration.  Still, using inflatables, such a system could plausibly offer a full order-of-magnitude improvement over SpaceX baseline propellant-to-payload ratio.

If it cycles between LEO and LLO, the custom lunar spaceport infrastructure goes away.

The extra infrastructure could be as simple as an elevated landing ring.  Not a significant factor.

...or it could require something more complicated. It's unknown at the present time.

Construction of a single landing structure is not a significant factor in a system for order-of-magnitude improvement in propellant-to-payload ratio.

Again, "because mass ratio" isn't a real engineering justification, whether or not it's been seasoned with the phrase "order-of-magnitude improvement."

What is the resultant cost savings that justifies this landing structure (and the above-mentioned constraints on TWR and rigidity)? Because I can't find any.

More problematic still, it would require the depot to have A) high-thrust engines sufficient for landing, and B) sufficient structural stength to resist not only internal pressure, but also significant deformation due to the high-thrust engines (limiting maximum size and minimum mass). This is, indeed, becoming a "significant factor."

A Starship configured for this purpose, with a full complement of 3 sea-level Raptors + 6 vacuum Raptors, would have thrust to land the 9,300 t cargo at a lunar base.

But the Starship would need to hold the bag, so the bag still needs to withstand >1/6 g, which is unnecessary otherwise.

Your depot deformation reasoning is off.  Thrust isn't the issue, but the actual acceleration of the structure, which is modest in this ultra-heavy LEO-lunar run.  F=ma.

I'm not sure what mathematical imprecision you think I'm guilty of here, but I assure you I have a good grasp of basic high school physics (linear/rotational kinematics, etc). With that in mind, let's skip the pedantry.

Another confused post.

Nope, but again thanks for your sincere and genuine concern about my mental state.

re "cost savings":  Order-of-magnitude improvement in propellant-to-payload ratio gives order-of-magnitude reduction in Starship tanker fleet, including the SSH fleet - with corresponding and obvious cost savings.

Incorrect, because the vast majority of the upmass is propellant (and tanker dry mass to LEO), not the depot. Do the math.

It's a justification of the "inflatable tanker" concept, which you liked yesterday.

"Liked" is a gross oversimplification of my opinion on the proposal (I blame social media for the collapse of discourse into a "Like/Dislike" dichotomy). See this post for a little more subtlety about my position: https://forum.nasaspaceflight.com/index.php?topic=49327.msg2046557#msg2046557

re "the bag still needs to withstand >1/6 g":  No, inflatables would be drained during lunar approach, because Starship return needs no inflatable propellant.  If you disagree, run the rocket equation.

So what's the point of bringing the inflatables to the Moon again?

It's (obviously) impossible to "run the rocket equation" without you saying what your mission architecture looks like.

re "pedantry":  You conflated high thrust with high acceleration, forgetting the F=ma.  Basic mistake; basic correction.

Again, I did not. There's no confusion in my mind (only in your own imagined version of my mind) and no correction needed. Thanks for being so generous and persistent with your Physics 101 tutoring offer, however I must politely decline.

[LMT]

re "cost savings":  Order-of-magnitude improvement in propellant-to-payload ratio gives order-of-magnitude reduction in Starship tanker fleet, including the SSH fleet - with corresponding and obvious cost savings.

Incorrect, because the vast majority of the upmass is propellant (and tanker dry mass to LEO), not the depot. Do the math.

It's a justification of the "inflatable tanker" concept, which you liked yesterday.

"Liked" is a gross oversimplification of my opinion on the proposal (I blame social media for the collapse of discourse into a "Like/Dislike" dichotomy). See this post for a little more subtlety about my position: https://forum.nasaspaceflight.com/index.php?topic=49327.msg2046557#msg2046557

re "the bag still needs to withstand >1/6 g":  No, inflatables would be drained during lunar approach, because Starship return needs no inflatable propellant.  If you disagree, run the rocket equation.

So what's the point of bringing the inflatables to the Moon again?

It's (obviously) impossible to "run the rocket equation" without you saying what your mission architecture looks like.

re "pedantry":  You conflated high thrust with high acceleration, forgetting the F=ma.  Basic mistake; basic correction.

Again, I did not. There's no confusion in my mind (only in your own imagined version of my mind) and no correction needed. Thanks for being so generous and persistent with your Physics 101 tutoring offer, however I must politely decline.

No, all confused.  Start with the actual post, read it, and explore the topic.  You're just making up a story now.

[Nevyn72]

I think things are getting to the point where we probably really need a separate thread just for in-orbit refueling systems.

A thread headlined for off Earth modifications, repairs and assembly is a whole other subject matter.....

If I'm not being too forward here's one I've just put together.

https://forum.nasaspaceflight.com/index.php?topic=50157.0

[Paul451]

I think things are getting to the point where we probably really need a separate thread just for in-orbit refueling systems.
A thread headlined for off Earth modifications, repairs and assembly is a whole other subject matter.....

We're only 5 pages in. Losing a few pages to a side-topic isn't unusual, nor especially bad. It's not like this is a tight-topic, like the mission threads.

The biggest issue seems to be that LMT is acting as if everyone is talking about his own pet concept, when in reality no-one is.

The side-topic spun off from edzieba discussing building significantly enlarged tankers in LEO, fuelled from Earth, to extend the capacity of BEO missions.

[That said: No objection to the spin-off thread. It'll take or it'll die.]

[Twark_Main]

...

No, all confused.  Start with the actual post, read it, and explore the topic.  You're just making up a story now.

Sadly the linked post doesn't address any of my points, so I guess you and me are done here.

[oldAtlas_Eguy]

This topic is heavily related to a business case. To show that a particular business case is valid requires one or more of the following:

1) That the service or product is ultimately cheaper to the customer than existing alternative providers.

2) That the service or product does not exist from existing providers and can be purchased at reasonable cost for its value to the customer.

3) That the service or product gives value added vs existing alternate providers. ( Such as more reliability, faster, customization to better meet customer needs, etc.)

[LMT]

Start with the actual post, read it, and explore the topic.  You're just making up a story now.

Sadly the linked post doesn't address any of my points, so I guess you and me are done here.

The biggest issue seems to be that LMT is acting as if everyone is talking about his own pet concept, when in reality no-one is.

My opinion on that in the new thread.

[Oersted]

Pls stop the tit for tat, it is ruining the thread.

[edzieba]

To save miles of nested quotes:

RE: "why not balloon tanks (or other inflateables)"
- Balloon tanks preferable in every way, but cost to develop a whole new vehicle with balloon tanks.

RE: "why depot?"
- Fewer Starships tied up floating in orbit full of propellant waiting for crewed ships to launch = less inventory doing nothing.

If you want to depart a fleet of 10 Starships for a Mars transit, and it takes a day to cycle a pad between tanker launches (total time from launch to next tanker and booster being recovered, checked, moved back to the pad, restacked, and re-filled), and you need 4 tankers per launch, you need 40 days to get your fleet of 10 full tankers ready, with 10 Starships tied up for 40 days on top of those doing the ferrying. With a 10x capacity dedicated depot, you tie up no Starships for that same period. With sufficient boiloff resilience, you could space out your tanker flights over a much longer period (taking advantage of natural gaps in launch cadence) to stock the depot, whereas doing the same means you could tie up 10 Starships for a year or more generating no revenue. That makes an economic case for a depot needing to cost less than the lost economic output (with extra cost over lack of flexibility from a smaller ready fleet) of the number of full tankers needed to provide the same in-orbit propellant load over the period of time over which they will be loaded.

[Twark_Main]

To save miles of nested quotes:

RE: "why not balloon tanks (or other inflateables)"
- Balloon tanks preferable in every way, but cost to develop a whole new vehicle with balloon tanks.

Except you are developing a new vehicle. You're just doing it the really-really-hard way (assembly in orbit) rather than the easy way (assembly on the ground).

RE: "why depot?"
- Fewer Starships tied up floating in orbit full of propellant waiting for crewed ships to launch = less inventory doing nothing.

If you want to depart a fleet of 10 Starships for a Mars transit, and it takes a day to cycle a pad between tanker launches (total time from launch to next tanker and booster being recovered, checked, moved back to the pad, restacked, and re-filled), and you need 4 tankers per launch, you need 40 days to get your fleet of 10 full tankers ready,

This assumes only one launch pad, which by the time they're sending 10 Starships per synod won't be very likely.

with 10 Starships tied up for 40 days on top of those doing the ferrying.

Nope. Only the first Tanker is tied up for 40 days. The second Tanker is tied up for 36 days, the next for 32 days, etc. So on average, in the limit, it's half the number of Tanker-days.

More likely imo is that the transit Starships will be left in orbit, but uncrewed. Then transfer passengers at the last minute via a 1000-ish passenger E2E vehicle (using the "cargo door docking port" I've mentioned before, so swapping out the docking port is relatively easy).

With a 10x capacity dedicated depot, you tie up no Starships for that same period. With sufficient boiloff resilience, you could space out your tanker flights over a much longer period (taking advantage of natural gaps in launch cadence) to stock the depot, whereas doing the same means you could tie up 10 Starships for a year or more generating no revenue. That makes an economic case for a depot needing to cost less than the lost economic output (with extra cost over lack of flexibility from a smaller ready fleet) of the number of full tankers needed to provide the same in-orbit propellant load over the period of time over which they will be loaded.

This argument boils down to, "the depot has no opportunity cost, because it's otherwise pretty useless, unlike Starships." But this is an economic argument against depots. The tankers can pay for themselves with other work, but the depot cannot.

And again, if you're developing a new vehicle anyway (which you are), just make it an inflatable and get all the same advantages (more actually, since the depot can be much larger) without hassle of on-orbit assembly and the risk that your zero-g/vacuum welds won't proof-test successfully.

[Eka]

To save miles of nested quotes:

RE: "why not balloon tanks (or other inflateables)"
- Balloon tanks preferable in every way, but cost to develop a whole new vehicle with balloon tanks.

Except you are developing a new vehicle. You're just doing it the really-really-hard way (assembly in orbit) rather than the easy way (assembly on the ground).

RE: "why depot?"
- Fewer Starships tied up floating in orbit full of propellant waiting for crewed ships to launch = less inventory doing nothing.

If you want to depart a fleet of 10 Starships for a Mars transit, and it takes a day to cycle a pad between tanker launches (total time from launch to next tanker and booster being recovered, checked, moved back to the pad, restacked, and re-filled), and you need 4 tankers per launch, you need 40 days to get your fleet of 10 full tankers ready,

This assumes only one launch pad, which by the time they're sending 10 Starships per synod won't be very likely.

with 10 Starships tied up for 40 days on top of those doing the ferrying.

Nope. Only the first Tanker is tied up for 40 days. The second Tanker is tied up for 36 days, the next for 32 days, etc. So on average, in the limit, it's half the number of Tanker-days.

Nope. Conservatively it is possible to launch 4 SS/SH per day per pad. launch initial receiving tankers #1, #2, #3, and #4 on first day. Next few days, launch the refueling tankers, and on the final days launch the SS to go to Mars. The SS will leave for Mars 6 hours apart, but that isn't a problem.

If you have two launch pads, you can halve the number of days by doing simultaneous launches. In this case two tankers go up at once, and one transfers to the other, then that one transfers to the one already in orbit or receives from the one in orbit.

BTW: The tankers in orbit are cheap. When filled they aren't doing nothing. They are propellant storage tanks. I expect SpaceX will stage many cargo ships in orbit, and fuel them up over the many months before the synod transfer window. Then when it is close to time they will top them off, and off they will go in wave after wave. Some of these cargo ships will have been stored in orbit for over a year. The human carrying ones will be interspersed, but they will meet up with full tankers that have been in orbit for a long time. EM wants to eventually build up to 1000+ ships sent per synod. It will take lots of time to get them all into orbit and fueled up.

[Twark_Main]

[snip]

Nope. Conservatively it is possible to launch 4 SS/SH per day per pad.

Yes, thank you. I meant to say that but I forgot. So edzieba's numbers are even more unrealistic.

launch initial receiving tankers #1, #2, #3, and #4 on first day. Next few days, launch the refueling tankers,

Why launch the tankers before the refueling flights? That would seem to tie up the on-orbit tankers for longer than necessary.

What I can see is staging tankers in orbital planes with different RAAN, so you have additional tanker launch opportunities per launch site per day. Is that what you mean?

If you have two launch pads, you can halve the number of days by doing simultaneous launches. In this case two tankers go up at once, and one transfers to the other, then that one transfers to the one already in orbit or receives from the one in orbit.

Not sure how the orbital mechanics works out on "simultaneous" launches from multiple launch sites rendezvousing. Seems easier imo to have multiple planes of tankers, and have each launch site just refill tankers in different planes as the schedule allows.

BTW: The tankers in orbit are cheap. When filled they aren't doing nothing. They are propellant storage tanks.

Right, but that still has an opportunity cost. It's not a large cost, but it's still worth minimizing when possible.

I expect SpaceX will stage many cargo ships in orbit, and fuel them up over the many months before the synod transfer window. Then when it is close to time they will top them off, and off they will go in wave after wave. Some of these cargo ships will have been stored in orbit for over a year. The human carrying ones will be interspersed, but they will meet up with full tankers that have been in orbit for a long time. EM wants to eventually build up to 1000+ ships sent per synod. It will take lots of time to get them all into orbit and fueled up.

Bingo. The only thing I would (possibly) change is to directly refill the human carrying Starships (skipping the on-orbit tanker) when empty of passengers, and late-load the passengers in. Fewer tankers used, and you skip refilling with passengers onboard, but you add a passenger transfer step. Which conops you choose depends on how you weigh those costs/risks. Six of one, half dozen of the other.