Author Topic: Mars "domestic" launcher  (Read 7083 times)

Offline RoboGoofers

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Mars "domestic" launcher
« on: 01/16/2018 05:00 PM »
I have been thinking about BFS and whether it would make sense for a future colony to have a smaller domestic launcher for satellites or even P2P transport. What would a rocket designed to be used exclusively in Mars SOI look like?

Here are some of my assumptions:
Short and wide.
reusable and likely overbuilt
SSTO
Would a heat shield be needed? what would reentry be like from LMO?

Maybe it'd look like BO's Goddard. Or maybe the LEM (I don't know how much aerodynamic protection it would need)

It is not specifically spaceX, topically, but spaceX adjacent. It's fine to say, "BFS will be able to do all the potential missions. So what if it's overkill; it's reusable," but were I a colonist, i would view a BFS as a lifeboat and shelter of last resort and not want to risk it unduly.

could a launcher be stuffed into a cargo BFS or two, largely assembled? I figure a Raptor would be too large on a smaller craft if you still want redundancy. SpaceX has said it's scalable so maybe it could be scaled down as needed.
« Last Edit: 01/16/2018 06:09 PM by RoboGoofers »

Offline envy887

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Re: Mars "domestic" launcher
« Reply #1 on: 01/16/2018 06:21 PM »
Entry from LMO will be around Mach 10, so roughly twice as energetic as the hottest F9 entry to date, and more like what the XS-1 booster will see on entry. Dedicated TPS will be required, but it could be Inconel or titanium and potentially require zero service between flights for a more or less indefinite service life.

I wonder if titanium balloon tanks would work, or if metal shingles over CFRP structure makes more sense.

Offline acsawdey

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Re: Mars "domestic" launcher
« Reply #2 on: 01/16/2018 06:35 PM »
Entry from LMO will be around Mach 10, so roughly twice as energetic as the hottest F9 entry to date, and more like what the XS-1 booster will see on entry. Dedicated TPS will be required, but it could be Inconel or titanium and potentially require zero service between flights for a more or less indefinite service life.

I wonder if titanium balloon tanks would work, or if metal shingles over CFRP structure makes more sense.

A titanium balloon tank for LOX seems like a bad idea (isn't Ti incompatible with LOX?). Also given that a Mars SSTO would not have to be a bleeding-edge vehicle, I think you'd want it to be somewhat resiliant and serviceable, which sounds more like inconel shingles over CFRP.

How about a vehicle with multiple small engines with electric turbopumps for engine-out capability. Steering by differential throttling (precise control of pump rpm). Don't need super high chamber pressure to use large expansion ratio given low atmospheric pressure.

Online rakaydos

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Re: Mars "domestic" launcher
« Reply #3 on: 01/16/2018 08:10 PM »
What about a Carbon Monoxide ISRU hopper probe? something that could put small payloads into orbit, or do infinite point to point hops.

Offline RoboGoofers

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Re: Mars "domestic" launcher
« Reply #4 on: 01/17/2018 12:41 AM »
What about a Carbon Monoxide ISRU hopper probe? something that could put small payloads into orbit, or do infinite point to point hops.

I'm not familiar with that type of engine, but I'm sure it has it's niche. I was thinking of something F9 scale (scaled to Mars), but sure, they'll need small sat launchers too.

Don't go too far afield from SpaceX, though, to keep the mods happy. I would think SpaceX would be more likely to leverage their methalox work and adapt it to a smaller engine than start anew on another propellant.
« Last Edit: 01/17/2018 12:48 AM by RoboGoofers »

Offline TripD

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Re: Mars "domestic" launcher
« Reply #5 on: 01/17/2018 01:12 AM »
What about a Carbon Monoxide ISRU hopper probe? something that could put small payloads into orbit, or do infinite point to point hops.

What things are you planning to put into orbit from Mars?

Offline RonM

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Re: Mars "domestic" launcher
« Reply #6 on: 01/17/2018 02:22 AM »
If the settlement had "domestic" spacecraft, it might be easier to ship satellites to Mars as cargo on a BFS and then orbit them via the smaller spacecraft.

Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #7 on: 01/17/2018 02:52 AM »
I'd say make it run on CO/O2 and have a more reusable heatshield. Requires zero water, only needs to suck in atmosphere, and it should be pretty energy efficient. This would be good for point-to-point transport, too, as the launch site wouldn't need to mine any water.

Or, a smaller BFR/BFS two stager might be more efficient for launch to orbit if you have water handy, with the first stage CO/O2 and the second stage hydrolox. That should reduce the required energy for ISRU by a lot and minimize the amount of water needed. Should be capable of a very large payload with a relatively small vehicle, too.

Methane is great in the early days and because it's practically free on Earth, but on Mars it might make sense to eventually switch to CO/O2 and hydrolox. Using hydrolox on a first stage would be inefficient.

Making methane requires the Sabatier reaction, which has losses in the form of heat, which limits its efficiency compared to CO/O2 or hydrolox. However, it's possible you could store the hydrogen and CO2 and only run the Sabatier Reaction when you actually need heat (i.e. in the winter), thus acting as a kind of thermal storage. That would reduce the drawback of using methane.
« Last Edit: 01/17/2018 02:57 AM by Robotbeat »
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Offline RoboGoofers

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Re: Mars "domestic" launcher
« Reply #8 on: 01/17/2018 02:59 AM »
I can't find any videos on YouTube of a CO/O2 rocket firing, which is my baseline for feasibility. Has one been built?
« Last Edit: 01/17/2018 03:01 AM by RoboGoofers »

Offline speedevil

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Re: Mars "domestic" launcher
« Reply #9 on: 01/17/2018 04:27 AM »
I can't find any videos on YouTube of a CO/O2 rocket firing, which is my baseline for feasibility. Has one been built?

Nobody really bothers with CO/O2 as CO is really quite toxic, is cryogenic, and the performance is pretty crap, so nobodies tried.

In principle, you can add some CO into LNG, and reduce the embodied water use of a methane/oxygen rocket.


Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #10 on: 01/17/2018 12:14 PM »
I can't find any videos on YouTube of a CO/O2 rocket firing, which is my baseline for feasibility. Has one been built?

Nobody really bothers with CO/O2 as CO is really quite toxic, is cryogenic, and the performance is pretty crap, so nobodies tried.

In principle, you can add some CO into LNG, and reduce the embodied water use of a methane/oxygen rocket.
wrong, it has been tried. Hypergols are toxic, too. But who cares? You're not going to fire the rockets inside, and outside is a toxic, near-vacuum CO2 atmosphere anyway and anyone outside would be wearing protective spacesuits or would be dead from vacuum. You can get 300s ISP at Mars sea level, which is just fine and better than many propellants at Earth sea level.

And the flip side of lower Isp is that it takes less energy to produce the propellant. ISRU is likely to be either energy or water constrained, so this is an advantage.

I also hate when people say "performance" when they mean Isp. You don't always want high Isp as higher Isp requires more energy.
« Last Edit: 01/17/2018 12:29 PM by Robotbeat »
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Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #11 on: 01/17/2018 12:16 PM »
I can't find any videos on YouTube of a CO/O2 rocket firing, which is my baseline for feasibility. Has one been built?
Yes, one was built like in the 1980s.

There's no use for such a rocket except on Mars and Venus, so there's very little incentive for people to make one on Earth.

But it's perfect for a Mars domestic rocket.
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Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #12 on: 01/17/2018 12:32 PM »
It's important to note that the solid oxide electrolysis cell flying to Mars aboard the 2020 rover will be producing not just O2 but also CO. CO/O2 will be the FIRST ISRU technology actually demonstrated on any planetary body. That's a bigger deal for making a domestic rocket than whether it's easy to find YouTube videos of a rocket firing.
« Last Edit: 01/17/2018 12:33 PM by Robotbeat »
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Offline Norm38

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Re: Mars "domestic" launcher
« Reply #13 on: 01/17/2018 03:38 PM »
^^^ I wasn't aware the MOXIE experiment is a 2020 rover payload. 
I think it's important to note that per the Mars Direct architectures I've seen, after the Hydrogen brought from Earth is fully reacted with C02, there is still more O2 needed, so the MOXIE ISRU will be running on Mars basically from day one.
Maybe the first use of CO/O2 fuel will be short range, low altitude hoppers for local area exploration?

Offline RoboGoofers

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Re: Mars "domestic" launcher
« Reply #14 on: 01/17/2018 06:40 PM »
If we're talking a BFR supplied colony, they'll already have to have methane ISRU up and running, so it seems the simplest solution would be to use existing infrastructure and methalox. but if we want to assume CO/O2, that's fine.

What about the shape? I assume the landing will define the shape more than the launch. Reusability is key so no deployable 'shutes or HIAD.

considering surface altitude varies drastically between Olympus Mons and Hellas Planitia, if creating a single launcher for all P2P locations, would it be simpler to just be a full propulsive deorbit, roughly as you would do on a body with no atmosphere?
« Last Edit: 01/17/2018 10:00 PM by RoboGoofers »

Offline moreno7798

Re: Mars "domestic" launcher
« Reply #15 on: 01/17/2018 11:43 PM »
If the settlement had "domestic" spacecraft, it might be easier to ship satellites to Mars as cargo on a BFS and then orbit them via the smaller spacecraft.

Sounds redundant to me. Just drop them in orbit when you get there.

Offline RonM

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Re: Mars "domestic" launcher
« Reply #16 on: 01/18/2018 12:11 AM »
If the settlement had "domestic" spacecraft, it might be easier to ship satellites to Mars as cargo on a BFS and then orbit them via the smaller spacecraft.

Sounds redundant to me. Just drop them in orbit when you get there.

BFS doesn't go into Mars orbit, it lands directly. It can't just drop satellites off. To deploy satellites an incoming BFS will require a deployment mechanism, adding mass and complexity. Each satellite will need its own engine to slow down and enter orbit. With a smaller local spacecraft a satellite can be taken to the appropriate orbit and dropped off. That is an extra flight, but using locally produced propellant and a local multipurpose vehicle. Depends on which is cheaper, hauling extra mass from Earth for deployment or using the local spacecraft.

Offline speedevil

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Re: Mars "domestic" launcher
« Reply #17 on: 01/18/2018 01:00 AM »
BFS doesn't go into Mars orbit, it lands directly. It can't just drop satellites off. To deploy satellites an incoming BFS will require a deployment mechanism, adding mass and complexity.

Wondering if this is true.

BFS enters as normal for the first part of the trajectory and then aerodynamically shapes the trajectory till it's on a closed trajectory with a moderate apoapsis*50km or so, waits till the peak and then circularises.

This will use less propellant than actually landing.
You can then throw satellites out into LMO with no delta-v needed.

Also, you can at uncircularised apoapsis throw satellites out the airlock, and they only need to circularise while BFR does not, and comes in for a landing as normal at a lower initial entry speed.

The normal entry: ( http://forum.nasaspaceflight.com/index.php?topic=43920.msg1765634#msg1765634 ) Nominal ignition only occurs at 570m/s, in some parts of the trajectory it is actually shaping the trajectory down so that it can stay in the atmosphere. It can 'just' not do this, and pass through ending up at an orbit with a moderate apoapsis and periapsis in the atmosphere.
Normally until 570m/s it uses no propellant for entry, the aerodynamic portion of the flight is entirely propellant-free.

I think this might actually save propellant, in either case.
If the sats are required to circularise, this is obvious as you reduce landing mass.

In the case that BFR  circularises following aeroshaping of the orbit, reducing the mass by (say) 20 tons of satellites would save far more propellant than landing that 20 tons.

Landing takes of the order of 700m/s of fuel. Circularisation far less.
« Last Edit: 01/18/2018 01:03 AM by speedevil »

Offline QuantumG

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Re: Mars "domestic" launcher
« Reply #18 on: 01/18/2018 01:07 AM »
Aerobraking to change a satellite's orbit has been done, but aerocapture into a planetary orbit has never been attempted - as far as I'm aware.

In an case, why would you bother? Just refuel on Mars and do whatever missions you want to do there. It's a fully reusable vehicle. Use it as many times as you need.
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline speedevil

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Re: Mars "domestic" launcher
« Reply #19 on: 01/18/2018 01:18 AM »
Aerobraking to change a satellite's orbit has been done, but aerocapture into a planetary orbit has never been attempted - as far as I'm aware.

In an case, why would you bother? Just refuel on Mars and do whatever missions you want to do there. It's a fully reusable vehicle. Use it as many times as you need.

If you have ISRU already and lots of propellant.
I could see it being useful for a deployment of 'Marslink'.

As a technical point, BFS aerobraking into mars involves a point at which it's in a circular orbit. It just happens that this is 'deep' in the atmosphere.

It does require more knowledge of the atmospheric conditions. This could be a second BFS coming along six hours after the first though.

Offline dwheeler

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Re: Mars "domestic" launcher
« Reply #20 on: 01/18/2018 01:48 AM »
I can't find any videos on YouTube of a CO/O2 rocket firing, which is my baseline for feasibility. Has one been built?
Yes, one was built like in the 1980s.


Not sure if this is what you were thinking of:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19910014990.pdf

Quote
The results of the theoretical analysis indicate that a specific impulse in the range of 260 to 280 sec is realistic for the assumption of a low pressure engine. Specific impulses of 290 to 300 sec should be used, however, for the assumption of a higher pressure, pump-fed engine.

This was a 1991 study into using CO/O2 to fuel the return leg from Mars back to Earth.

Offline RoboGoofers

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Re: Mars "domestic" launcher
« Reply #21 on: 01/18/2018 03:39 AM »
Aerobraking to change a satellite's orbit has been done, but aerocapture into a planetary orbit has never been attempted - as far as I'm aware.

In an case, why would you bother? Just refuel on Mars and do whatever missions you want to do there. It's a fully reusable vehicle. Use it as many times as you need.

If you have ISRU already and lots of propellant.
I could see it being useful for a deployment of 'Marslink'.

As a technical point, BFS aerobraking into mars involves a point at which it's in a circular orbit. It just happens that this is 'deep' in the atmosphere.

It does require more knowledge of the atmospheric conditions. This could be a second BFS coming along six hours after the first though.
A issue with dropping them off after aerocapture is that they're in whatever orbit is convenient for BFS to land at it's destination. They would need large plane changes to get to useful inclinations. They also need to be sent fully fueled for this, reducing payload to surface.

Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #22 on: 01/18/2018 03:44 AM »
I can't find any videos on YouTube of a CO/O2 rocket firing, which is my baseline for feasibility. Has one been built?
Yes, one was built like in the 1980s.


Not sure if this is what you were thinking of:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19910014990.pdf

Quote
The results of the theoretical analysis indicate that a specific impulse in the range of 260 to 280 sec is realistic for the assumption of a low pressure engine. Specific impulses of 290 to 300 sec should be used, however, for the assumption of a higher pressure, pump-fed engine.

This was a 1991 study into using CO/O2 to fuel the return leg from Mars back to Earth.
Precisely. An actual (very low performance) engine was built and tested.
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Re: Mars "domestic" launcher
« Reply #23 on: 01/18/2018 04:00 AM »
Many feel that some mesh of satellites for navigation and comms will be needed quite early, perhaps as soon as the second or even first landing. If these could be dropped off with a (very early) BFS on the way in, even if not in optimal orbits, is that helpful? A domestic launcher could well go get them later and reposition to better orbits.
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Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #24 on: 01/18/2018 04:21 AM »
If we're talking a BFR supplied colony, they'll already have to have methane ISRU up and running, so it seems the simplest solution would be to use existing infrastructure and methalox....
...simplest solution is to just use BFR. But BFR and any methalox launcher would be difficult to support in remote bases and wouldn't be as efficient.

Energy efficiency is a pretty big constraint. I calculate a full ITS tanker would take about 1 Megawatt for a two Earth years to fill up. And over a thousand tons of water. So any place on the planet you plan on traveling to either requires you to bring at least some of your return propellant with you (super inefficient energy-wise) or set up a significant mining operation. CO/O2 means you just need a big solar array (or nuclear reactor) and a big MOXIE with some liquifiers and tanks. Super easy to set up in any location you like.
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Offline speedevil

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Re: Mars "domestic" launcher
« Reply #25 on: 01/18/2018 05:56 AM »
I could see it being useful for a deployment of 'Marslink'.

As a technical point, BFS aerobraking into mars involves a point at which it's in a circular orbit. It just happens that this is 'deep' in the atmosphere.

It does require more knowledge of the atmospheric conditions. This could be a second BFS coming along six hours after the first though.
A issue with dropping them off after aerocapture is that they're in whatever orbit is convenient for BFS to land at it's destination. They would need large plane changes to get to useful inclinations. They also need to be sent fully fueled for this, reducing payload to surface.

It only reduces payload to surface if it either overloads the heatshield/aerosufaces and requires delta-v to keep it on a bearable trajectory, or the payload is volume constrained (in the case where you don't circularise the BFS after aerobrake).

If you are circularising after the initial aerobraking, then yes it will reduce payload to the surface, by the amount of the circularisation burn.

The circularisation burn is on the order of 70m/s, not 700m/s for landing, so it's perhaps 5-10 tons.

And if you were contemplating increasing the size of your ISRU before you'd have liked to, just to get up a minimal constellation, this may pay off immediately.

In principle, two BFRs can deploy a medium altitude constellation in two planes. Electric plane change isn't quite as terrible on earth, as LMO is 3.2km/s, not 7.8.

« Last Edit: 01/18/2018 06:01 AM by speedevil »

Offline RoboGoofers

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Re: Mars "domestic" launcher
« Reply #26 on: 01/18/2018 02:37 PM »
If we're talking a BFR supplied colony, they'll already have to have methane ISRU up and running, so it seems the simplest solution would be to use existing infrastructure and methalox....
Energy efficiency is a pretty big constraint. I calculate a full ITS tanker would take about 1 Megawatt for a two Earth years to fill up. And over a thousand tons of water. So any place on the planet you plan on traveling to either requires you to bring at least some of your return propellant with you (super inefficient energy-wise) or set up a significant mining operation. CO/O2 means you just need a big solar array (or nuclear reactor) and a big MOXIE with some liquifiers and tanks. Super easy to set up in any location you like.

So how long would it take to fill a F9-class mars rocket (15-20,000 kg to LMO) with CO and O2 at a remote site, and how much power would it require? How large would the tanks be, and what is the reentry profile.

we should not discuss the merits of different propellants and ISRU methods divorced from it's effect on the design of a rocket. You created another topic for CO/O2 already for that, which i'm reading through now.
https://forum.nasaspaceflight.com/index.php?topic=21544.0

If you want to build a rocket around CO/O2, that's great. Maybe someone prefers a CO2/Magnesium powder hybrid rocket. Hell, you can bring Kerosene if you want (i mean, please don't suggest this), but how does that decision effect the design of the rocket?
« Last Edit: 01/18/2018 02:54 PM by RoboGoofers »

Offline acsawdey

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Re: Mars "domestic" launcher
« Reply #27 on: 01/18/2018 04:25 PM »
So, poking around at a simple CO/O2 engine model in RPA lite. How does this sound for a little mars hopper/orbiter:

1 MPa chamber pressure (145 psi)
200:1 nozzle
0.52 O/F mixture ratio
270 isp at "optimum expansion" of 0.005 atm (~ mars surface?)
283 vac isp

With a super low chamber pressure, you could do this with electric pumps and very light weight tanks that just have enough pressure for the pumps to be happy.

If you crank the same thing to 10 MPa you'll get about 290-294 isp.

Offline Norm38

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Re: Mars "domestic" launcher
« Reply #28 on: 01/18/2018 04:57 PM »
Which uses less fuel, to allow a BFS to place cargo in Mars orbit?

1)  BFS makes a direct atmospheric entry, lands.  Then refuels and boosts back up into Mars orbit.

2)  A Mars supplied tanker lifts fuel to an orbital depot.  The BFS brakes into orbit, drops its cargo.  Refuels for landing, lands.

Offline RoboGoofers

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Re: Mars "domestic" launcher
« Reply #29 on: 01/18/2018 05:24 PM »
Is it logical to use this analogy: Using BFS on Mars for orbital launches is like using a BFR/S scaled 3 times larger to launch BFS payloads into LEO?

Offline Zed_Noir

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Re: Mars "domestic" launcher
« Reply #30 on: 01/18/2018 10:54 PM »
Is it logical to use this analogy: Using BFS on Mars for orbital launches is like using a BFR/S scaled 3 times larger to launch BFS payloads into LEO?

Yes. But you don't need to spend resources to developed and build another series of vehicles. That can only be used to and from the Martian surface with few other applications.

Of course if you have a few dozen spare billion dollars laying around, you might planned differently.

Offline speedevil

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Re: Mars "domestic" launcher
« Reply #31 on: 01/18/2018 11:04 PM »
Which uses less fuel, to allow a BFS to place cargo in Mars orbit?

1)  BFS makes a direct atmospheric entry, lands.  Then refuels and boosts back up into Mars orbit.

2)  A Mars supplied tanker lifts fuel to an orbital depot.  The BFS brakes into orbit, drops its cargo.  Refuels for landing, lands.

3) BFS aerobrakes into orbit, circularises, drops all its cargo, and lands.

Once you drop ~20 tons of cargo into orbit, you use enough less propellant on landing that you paid for the circularisation burn.
If you drop it all in orbit, you have quite a lot of propellant left over.
If you aerobrake into orbit, circularise, and refuel there, you can carry considerably more than 150 tons into orbit.

Circularisation takes of the order of 10 tons of fuel, landing 100, for the same initial heat loading on reentry, you can carry 250 tons of cargo to Mars (with 100t less propellant).

(edit: I wonder if I will ever stop typing fuel when I mean propellant)

« Last Edit: 01/18/2018 11:06 PM by speedevil »

Offline QuantumG

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Re: Mars "domestic" launcher
« Reply #32 on: 01/18/2018 11:09 PM »
3) BFS aerobrakes into orbit, circularises, drops all its cargo, and lands.

Aerocaptures into orbit. i.e., a manoeuvre that's never been done before by any spacecraft.

Why risk that when you can just land and refuel?
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline speedevil

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Re: Mars "domestic" launcher
« Reply #33 on: 01/18/2018 11:18 PM »
3) BFS aerobrakes into orbit, circularises, drops all its cargo, and lands.

Aerocaptures into orbit. i.e., a manoeuvre that's never been done before by any spacecraft.

Why risk that when you can just land and refuel?

The risk for the first BFS with no atmospheric survey is probably too large.
However, if you can simulate landing, you can, with knowledge of the atmospheric density profile from a few minutes before (a small survey probe) simulate aerocapture - it is just a failed landing which does not curve hard enough into the atmosphere to remain in the deep part.

The question was what's the most efficient way - aerocapture is significantly more efficient to get payloads into orbit than launching them later in any way, and may be 'free'. (modulo uncertainty in trajectories due to poor knowledge of the atmosphere).

Hypersonic lifting reentry of a complex body  to vertical landing has never been done either.
The problems are basically the same as aerocapture.

Offline QuantumG

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Re: Mars "domestic" launcher
« Reply #34 on: 01/18/2018 11:30 PM »
Direct entry is vastly different to aerocapture. The degenerate case is getting to within 10 km of landing and then boosting again. It's completely unnecessary when you have a reusable vehicle and propellant sitting on the ground.

I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline speedevil

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Re: Mars "domestic" launcher
« Reply #35 on: 01/19/2018 12:27 AM »
Direct entry is vastly different to aerocapture. The degenerate case is getting to within 10 km of landing and then boosting again. It's completely unnecessary when you have a reusable vehicle and propellant sitting on the ground.
In what specific ways is it vastly different to aerocapture.
- from 35:53 in the IAC talk.

All the way down to 3km/s or so, BFS is positioned so that aerodynamic forces try to keep it in the atmosphere.
It does this precisely so that it does not skip off the atmosphere - it is actively forcing its trajectory down to keep it in the atmosphere at a downwards accelleration of about three times mars G at points.

As a first approximation, flip the lift vector from down round slowly to up at around 5km/s, and you end up in an elliptical orbit with an periapsis of some 35km, at a little more than LMO speed.
Precisely which elliptical orbit you end up in depends on the detailed trajectory design.
The heating is of a similar magnitude in the initial entry, and perhaps slightly less in the latter part to landing.

If you already have ISRU fuel on the ground, and have not well characterised the atmosphere, that is clearly the way to go.
« Last Edit: 01/19/2018 12:39 AM by speedevil »

Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #36 on: 01/19/2018 12:29 AM »
Yeah, I don't think aerocapture would be wildly difficult for BFS.
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Offline QuantumG

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Re: Mars "domestic" launcher
« Reply #37 on: 01/19/2018 12:42 AM »
Hypersonic manoeuvring is already a dicey proposition - but yeah, eventually anything is possible. So what?
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Online Lar

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Re: Mars "domestic" launcher
« Reply #38 on: 01/19/2018 12:50 AM »
Hypersonic manoeuvring is already a dicey proposition - but yeah, eventually anything is possible. So what?

(mod) No need to get so dicey, people are exploring the trade space, you already made your point that you think it's a bad idea.
« Last Edit: 01/19/2018 03:42 PM by Lar »
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Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #39 on: 01/19/2018 01:12 AM »
Hypersonic manoeuvring is already a dicey proposition - but yeah, eventually anything is possible. So what?
Did you watch the animation of BFS hyperbolic entry on Mars? It's doing exactly that: precision hypersonic maneuvering: http://www.spacex.com/sites/spacex/files/mars-entry.mp4
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Offline RonM

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Re: Mars "domestic" launcher
« Reply #40 on: 01/19/2018 04:05 PM »
So, with all this discussion about aerocapture, are you guys saying there is no need for a Mars "domestic" launcher. That's what the thread is about.

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Re: Mars "domestic" launcher
« Reply #41 on: 01/19/2018 04:24 PM »
So, with all this discussion about aerocapture, are you guys saying there is no need for a Mars "domestic" launcher. That's what the thread is about.

My take? There isn't a need for one immediately. BFS can do it all. But in the long run, one size fits all isn't the optimal cost. intially? when you have limited development resources? absolutely it is.

But as Mars and the rest of our system see a robust industrial and transport infrastructure develop? Yes of course there will be specialty vehicles. Including this one. Because that's the lowest cost approach. The American West was settled initially with a lot of Conestogas but eventually there were lots and lots of specialty vehicles.

That's my take. The question is not if, but when.. .when is it time to do this? I'd say when transport is cash flow positive at the earliest, and there's enough traffic that specialization  will have significant use.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
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Offline speedevil

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Re: Mars "domestic" launcher
« Reply #42 on: 01/20/2018 12:34 AM »
So, with all this discussion about aerocapture, are you guys saying there is no need for a Mars "domestic" launcher. That's what the thread is about.

CO/O2 may be very much better geared for Mars orbit - if it is substantially easier to produce.
It requires no water, though the efficiency I'm unsure of - I've never found decent estimates for CH4/O2 in large plants.

kWh/kg to LMO might be considerably better.

Might it be better enough than CH4/O2 to make things like lifting propellant for topping off BFS in orbit is worth it?
Or better enough so you can get BFS to mars with 250 tons of cargo and no landing propellant and add that on orbit, or even ferry stuff down?

If it costs half (kWh/kg) what BFS costs to launch a kilo to orbit, you might be able to top up BFS in orbit after a minimal fuel launch to more than the normal fill, and get 150, not 50 tons back to earth.

I guess for further computation, you'd need some figure on the relative costs of CH4/CO production. If it's cheap enough, it can be an enabler.
If it's not substantially cheaper, losing the commonality of methane all around isn't worth it.

I guess an aside might be if Raptor can run on CO, or a CO/CH4 mix.

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Re: Mars "domestic" launcher
« Reply #43 on: 01/20/2018 12:47 AM »
So, with all this discussion about aerocapture, are you guys saying there is no need for a Mars "domestic" launcher. That's what the thread is about.


CO/O2 may be very much better geared for Mars orbit - if it is substantially easier to produce.
It requires no water, though the efficiency I'm unsure of - I've never found decent estimates for CH4/O2 in large plants.

kWh/kg to LMO might be considerably better.

Might it be better enough than CH4/O2 to make things like lifting propellant for topping off BFS in orbit is worth it?
Or better enough so you can get BFS to mars with 250 tons of cargo and no landing propellant and add that on orbit, or even ferry stuff down?

If it costs half (kWh/kg) what BFS costs to launch a kilo to orbit, you might be able to top up BFS in orbit after a minimal fuel launch to more than the normal fill, and get 150, not 50 tons back to earth.

I guess for further computation, you'd need some figure on the relative costs of CH4/CO production. If it's cheap enough, it can be an enabler.
If it's not substantially cheaper, losing the commonality of methane all around isn't worth it.

I guess an aside might be if Raptor can run on CO, or a CO/CH4 mix.


If there was access to water, could h2o2/co also work?

Offline speedevil

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Re: Mars "domestic" launcher
« Reply #44 on: 01/20/2018 01:14 AM »
If there was access to water, could h2o2/co also work?
There are lots of potential propellants on Mars from H2O2/CO, H2O2 monopropellant, Mg/O2, CH4/O2, H2/O2, Fe/O2, Al/O2, ...

All of them have their own issues, but I think it's safe to say of all of them that there is no nicely published efficiency of (at specific sites on Mars surface) for kWh/kg to LMO (for example), or more relevant metrics like (kg/year to LMO)/kg-landed.

Storage power varies - for example, CH4 is going to take a lot less power to keep cold than H2 but you can just stick H2O2 in an uninsulated tank. Sites access to resources (solar, water, minerals, secure flat spots) varies. ISP varies.

It's a huge pile of complicated trades.

An approach at such a table, or best guess at whole system efficiencies of fuel generation would be great.

« Last Edit: 01/20/2018 01:16 AM by speedevil »

Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #45 on: 01/20/2018 02:49 AM »
If there was access to water, could h2o2/co also work?
There are lots of potential propellants on Mars from H2O2/CO, H2O2 monopropellant, Mg/O2, CH4/O2, H2/O2, Fe/O2, Al/O2, ...

All of them have their own issues, but I think it's safe to say of all of them that there is no nicely published efficiency of (at specific sites on Mars surface) for kWh/kg to LMO (for example), or more relevant metrics like (kg/year to LMO)/kg-landed.

Storage power varies - for example, CH4 is going to take a lot less power to keep cold than H2 but you can just stick H2O2 in an uninsulated tank. Sites access to resources (solar, water, minerals, secure flat spots) varies. ISP varies.

It's a huge pile of complicated trades.

An approach at such a table, or best guess at whole system efficiencies of fuel generation would be great.
Not that hard to back out how much energy needed to reach LMO for various propellants as long as you keep it simple. I've done it several times already in this discussion to back up my intuition.
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Offline speedevil

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Re: Mars "domestic" launcher
« Reply #46 on: 01/20/2018 03:25 AM »
Not that hard to back out how much energy needed to reach LMO for various propellants as long as you keep it simple. I've done it several times already in this discussion to back up my intuition.

That is the almost trivial part.

How does the total landed mass trade with the total mass you can orbit, counting everything from trucks scraping up propellant, to the on/off cycling penalty of the ISRU due to solar for each days effort is where it gets hard, to storage losses differing, to ...

It is very unclear that the simple metric of kg of propellant used per kg of payload is useful other than as a first cut to eliminate  options like H2O2 monopropellant for SSTO to LMO.
« Last Edit: 01/20/2018 03:27 AM by speedevil »

Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #47 on: 01/20/2018 07:25 PM »
Energy scales much of the surface infrastructure needs. I didn't say propellant mass, I said energy.
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Re: Mars "domestic" launcher
« Reply #48 on: 01/20/2018 10:18 PM »
In addition to type of propellant, another important design consideration is where does the spacecraft come from?

I see three basic options:

1) Bought in parts on BFS and assembled on Mars (could be an issue if depending on how big the parts can be)
2) Complete smaller vehicle launched from Earth (something like the Lockheed Martin reusable lander design)
3) Built on Mars (requires extensive industrial capacity).

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