Landing on Mars

GW Johnson · 2013-09-04 09:05:24

You guys weigh in, tell me which propellant combinations might actually prove practical to manufacture on Mars. I simply don't understand propellant manufacture well enough to pick the winner. The range of lander masses that I got was 34 tons for LOX-LH2 all the way up to 90 tons for NTO-UDMH (see the "exrocketman" posting I cited above in #399). I got 68 tons with LOX-CH4 and 78 tons with LOX-RP1. All were sized for a fixed payload mass of 3.2 tons. Metric of course.

It makes quite a difference, to both the mission transit design, and to what has to be maintained as a reusable vehicle. Whatever we use on that first manned visit to Mars should stay there, and continue to be used with locally-manufactured propellants. The landers can even be used suborbitally for very long-range transport of critical items, between sites very far apart.

GW

SpaceNut · 2013-09-08 09:57:20

It might be easy to change a LOX-LH2 landing engine to use LOX-CH4 but NTO-UDMH or LOX-RP1 seems to be a problem when you look at ignition or temperatures of the fuels/oydizer combinaions....

GW Johnson · 2013-09-09 11:34:47

I really don't think kerosene is something we could practically manufacture on Mars, but it might be somewhat representative of a hydrocarbon heavier than methane, that we might dream up a process for. It is a very well-known technology. But, I'd bet we can find a way to ignite or keep-unfrozen any of these choices, though.

I really don't think NTO or any of the hydrazines might actually be practically manufactured on Mars, without a source of fixed nitrogen. That's a huge obstacle there, as far as I know. But, we already know those propellants can be easily stored, and we have had engines that re-light multiple times in vacuum with them, for decades now. That's pretty much the technology of the shuttle OMS maneuver engine pods.

I suspect LOX-LH2 would actually be the "easiest" to manufacture on Mars, using mined ice and electrolysis as the basis. LOX is not too much trouble to liquefy and store; LH2 is much trickier to do, with the ortho vs para form problem perhaps now the easiest problem of several to resolve.

On Mars, the truly fundamental problem is "where is the ice deposit big enough to be worth mining?" We now know for sure that Mars has lots of water still (in the scientific sense), the trouble is that it's just not "everywhere". The kind of ice lenses Phoenix found near the pole is not the kind of deposit that supports practical mining and manufacture. What we need is a buried glacier 10+ meters thick and many, many km in lateral extent.

BTW, it'll be subliming as we dig it out. Every mine hole has to be regolith-buried when not in use. There will be one whale of a lot of regolith-moving operations involved in this activity. The machines will look like heavy mining and road-building equipment. That takes a big lander, even if shipped in small pieces and assembled on site. These things will not be carried by a series of Apollo-like dinky-little landing modules. No way. We need real "landing boats" of very significant size.

They're not gonna fit existing payload shrouds for launch to LEO for this mission. Something else to think about.

We have orbital observations of where some such buried glaciers might be (emphasis on "might"), but we have absolutely no ground truth about it. I have never seen a robot probe design capable of determining that kind of ground truth, either. So, if we are going to plan on making LOX-LH2 to return, where do we land?

Tough question. We have to be close enough to walk to the ice, or it ain't gonna work. We're talking front end loaders, bulldozers, and large pressure-vessel process machinery here, with maybe even some pick-and-shovel work by more than 2 men. Long range transport is simply out of the question, that first time up with propellant manufacture.

As for making methane out of water, and the CO2 in the "air", the low inlet densities make all your machinery (whatever it is) look very large and heavy and energy-intensive, compared to what we are used to here at home, by about a factor of 14. My guess is you can make 1's, not 100's, of kg per day. You'll not accumulate enough to return a crew (tens of tons), not even in a year's stay, even if it doesn't break down or encounter unexpected problems.

And you will encounter unexpected problems (lots of emphasis on "will"). Done robotically before the men arrive offers a potential way out, except that robots-as-we-know-them-today are simply inept at solving unexpected problems. Put the men there to solve those problems, and you are right back to the inability to accumulate tons of propellants in time. Plus, with LOX-CH4 you still have to solve basically the same water problem as LOX-LH2, to get the oxygen and the hydrogen.

So I dunno which one to try. And I don't yet see much of a path to resolving this in time for a mission in the 2030's, much less the 2020's we'd all like to see. NASA has no plans to send the right kind of probes that could locate the propellant-making resources. I don't see anybody else sending the right kind of probes, either.

That puts me back to the costly-but-sure-thing concept: first mission relies on propellants-sent-from-Earth. Which means it is an LMO-based mission, sending down multiple ferries to multiple interesting sites, and emplacing the machinery to experiment with propellant manufacture at the most promising ones after the men return home. Leave the ferries in a higher Mars orbit, with whatever propellant is left over, for the next mission to use. What's the point of going all that way with men, and only making one landing? That's really dumb!

Meanwhile, we have to guess which propellants might actually be made on Mars most practically, and build the first-mission ferries to use that. That way subsequent missions (including planted bases) can refuel and re-use the same ferries. Right now, I'd guess LOX-LH2 from ice. But with an engine compartment big enough to accommodate being refitted with different engines. And with compartmentalized tankage to accommodate being re-plumbed for different propellants. That's heavier, and so is structural robustness necessary for long-term reusability. My assumptions of inert structural weight 20% are quite likely too low.

Any other ideas? Opinions?

GW

Rxke · 2013-09-10 00:26:49

GW, first let me re-iterate my gratitude for the fact you go to the trouble to actually write out your musings in a clear, structured way. It is always a huge pleasure to read your posts. Even at 6 AM, heh.

Your costly but sure thing concept sounds very reasonable. But... Expensive (needs to be said) which will always lead to people screaming bloody murder.

Only way around this is to semi sell of or fund or sponsor... the different pieces to different parties. McLarenMitshubishi sponsoring lander #1, Arianespace funding tanker #3 etc etc.

Hugely complex re: politics and legals implications. We're not ready for that, I'm even not sure this is what we would want....

Or SpaceX and Orbital Sciences et al come up with a plan to do the ferrying really cheap and standardized, while NASA and other Governmental agencies (JAXA, Arianespace Roskomov etc) come up with other non-built-in-series parts....

Sigh, I dunno. 2030's all of a sudden seems unrealistic.

Last edited by Rxke (2013-09-10 00:27:14)

JoshNH4H · 2013-09-10 12:11:18

Hey Rik, long time no speak; Good to see you back!

GW, I agree for sure on kerosene. While it's not impossible to manufacture heavier hydrocarbons on Mars (Think polymerization) it's not easy. Even polymerization requires ethene, which is nontrivial to manufacture from methane or other simpler compounds.

With regards to mining water, there is supposedly a buried sea, discovered by Mars Express in 2005. It is huge and supposedly pretty deep, which is exactly what you're talking about.

However I think for industrial operations on that scale we want to look at first establishing a smaller industrial capacity, and then building the big machines from there. It may also be worth noting that the water ice could be contained by, in part, building a shadow shield, which should slow sublimation.

Rxke · 2013-09-10 12:48:03

(Hi Josh,

yes, I all but fully regressed to a lurking state... )

JoshNH4H · 2013-09-10 13:33:57

Come back to the Land of the Living and post with us!

JoshNH4H · 2013-09-10 21:10:57

On Mars? Why?

GW Johnson · 2013-09-15 16:14:25

Regarding the expensive assembly in LEO: most of this is propellant. If it were water, the very-strong form we call ice could be launched into LEO by light gas gun for something approximating $100-300 per kg.

Water could be turned into LH2 and LOX on-orbit. If we had a water NERVA, we could just use it as water, which is even easier and cheaper. Maybe my expensive do-it-the-hard-way "baseline" is not quite as expensive as it seems at first glance.

All of this should have been thought out and tested decades ago, starting in the 1970's. We could have flown such a mission anytime after about 1995, and expected the crew to come back alive and reasonably healthy. The light gas gun thing is new, this decade.

GW

Quaoar · 2013-12-19 15:41:12

Hi to all,

I've found some interesting article on landing on Mars: supersonic retropropulsion may be good if the rockets fire not straight but inclined at 30° from the thrust axis, just like the Dragon Rider escape rockets, that may be perfect suited to land on Mars. In supersonic retropropultion the angled rockets slow the air flow around the shield moltiplicating the drag and acting like an air augmented rocket.

http://adl.stanford.edu/papers/JSR_Bakhtian.pdf

Another simulation based study shows that, for spacehip up to 40 mT and 10 m diameter heat shield, it is possible to land on Mars with direct entry and supersonic retropropulsion. Heavier spaceships has to do first an aerocapture and after an orbital entry.

http://www.ssdl.gatech.edu/papers/confe … 9-6684.pdf

Last edited by Quaoar (2013-12-19 15:42:39)

JoshNH4H · 2013-12-19 16:05:15

That's really interesting. Do you have any idea what the multiplicative effect is?

GW Johnson · 2013-12-19 18:47:51

In my ancient Hoerner drag "bible", there is NASA-generated data for a single centerline jet in Mach 2 retro-propulsion on a Mercury capsule shape. It acted to reduce drag by a factor between 1 and 2, dependent upon the massflow magnitude of the jet. This test ignored retro-plume flip-flopping instability.

If you put multiple jets around the periphery, I dunno what happens to the drag. Increase, decrease, who knows? The Super Draco thrusters on Dragon are fitted like that. They are canted at roughly 45 degrees, so that their nozzles point through the aftershell, not the heat shield itself. Cant angle ought to put the kibosh on plume instability.

How much cant is needed for stability? No one knows, I suspect. My intuition and wind tunnel experience suggests that 10-15 degrees would work. But I dunno for sure. Without repeatable data, I doubt anybody knows. Yet. But at least some folks are looking at it.

GW

JoshNH4H · 2013-12-20 01:01:00

Well, I could see there being an effect whereby the force that pushes the plume away from the centerline of the heatshield generates an increased pressure on its face. I can't say for certain, of course. Especially because of the supersonic flow conditions. I don't know whether that would be considered a good thing or a bad thing, either.

What do you think of the idea of canting the engines inward instead of outward, to increase the pressure on the heatshield?

GW Johnson · 2013-12-20 11:16:59

I kinda like outward for what I guess would be better flip-flop stability. The vehicle sort-of "looks like" a concavity to the oncoming flow. This would also act to increase the "effective" diameter by extending the region disturbed by the jets.

Those effects acting together would seem to me to increase the drag. But all of that requires some wind tunnel testing to confirm. For blunt objects, you only need to exceed Mach 3 to get into "hypersonics", where the shock envelope size and shape is pretty much independent of the actual Mach number.

When I was a student there long ago, UT Austin had a Mach 5 wind tunnel with a 5-inch by 7-inch test section. It was fairly cheap to use. The answers we all seek on this issue could be resolved reasonably quickly with a clever model in that wind tunnel, and for likely well under $1M.

GW

JoshNH4H · 2013-12-20 13:39:44

Ah, if only there were a Newmars directorate at NASA

Quaoar · 2013-12-21 02:58:57

JoshNH4H wrote:

Well, I could see there being an effect whereby the force that pushes the plume away from the centerline of the heatshield generates an increased pressure on its face. I can't say for certain, of course. Especially because of the supersonic flow conditions. I don't know whether that would be considered a good thing or a bad thing, either.
What do you think of the idea of canting the engines inward instead of outward, to increase the pressure on the heatshield?

According to the work quoted above, canting the rocket inward will cause the plume to act like an aerospike, reducing the drag: good for a take-off, not for a landing.

GW Johnson · 2013-12-21 10:50:49

That aerospike effect is what the retro-plume stability thing is about. Doing an aerospike in reverse, the plume has to reverse somewhere, but to which side does it bend? That bend induces side loads the attitude controls must be able to handle. If that plume bending flip-flops around from one side to another, unsteadily, you can tumble the vehicle. It drives you to a much more powerful, authoritative attitude control.

The idea behind cant outward is to start that retro-plume reverse bend in a particular direction. That way it doesn't flip-flop around, and your attitude control is an easier design. The only real question is how much cant is enough to stabilize the idiot thing?

A few easy cold-gas jet tests in a cheap hypersonic wind tunnel could answer that well enough to permit a successful design. That design could be flight-proven in suborbital entry tests here, then verified for the final probe or two we send to Mars, before we use it to land men there.

But, we'd better get on with it. If the landing is about 20 years from now, there's not much time left to get all that done. Tougher yet if we accelerate to a landing only 10 years from now, but still doable. 5 years? Hard to get a good job done (test on 1 probe, if any).

GW

SpaceNut · 2017-01-15 10:02:20

Adept, HIAD and Ballutes all are still being worked as the means to raise the low limit of landing mass to Mars to the 20mt and upwards....

"Large Supersonic Ballutes: Testing and Applications"

RobS · 2017-01-15 12:14:53

I gather the fact that the Falcon 9 first stage flies into its own plume at 3000+mph in its retrorocket burn has convinced people that supersonic retropropulsion works, even without a cant. So that has diminished NASA's interest in these other technologies (though they are still being worked on).

SpaceNut · 2017-01-15 14:56:00

The engines are surounded with heat shield materials to keep the burn up from entry from happening as the plume will force the heat away for the rest of the trip down....

SpaceNut · 2020-06-28 18:13:12

many comparisons are made for the ntr versus pebble reactors as well in several topics.

Mars_B4_Moon · 2024-06-06 05:21:30

Robots not humans

Intuitive Machines wants to help NASA return samples from Mars
https://techcrunch.com/2024/05/14/intui … from-mars/

The next big mission will the NASA's Mars Sample Return

Icebreaker Life is or was a Mars lander mission concept proposed to NASA's Discovery Program, it involves a stationary lander that would be a near copy of the successful 2008 Phoenix and InSight spacecraft, but search for life and would carry an astrobiology science platform.

SpaceX Red Dragon was a 2011–2017 concept for using an uncrewed modified SpaceX Dragon 2 for low-cost Mars lander missions

the Biological Oxidant and Life Detection (BOLD) is a concept mission to Mars focused on searching for evidence or biosignatures of microscopic life on Mars.

India, Japan and Europe have plans for Mars, sanctions have been put on Russia since the invasion of Ukraine

there might be a Chinese mission and China has stated it wants to beat NASA / JPL the joint NASA ESA mission or Space-X to Mars.

Last edited by Mars_B4_Moon (2024-06-06 05:21:49)

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