Author Topic: Mars "domestic" launcher  (Read 6915 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 »

Online 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.

Offline 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.

Online 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.


Online 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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Online 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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Online 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.
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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.

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