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Six Minutes of Terror - Landing Humans on Mars
OriginalArlen writes "Universe Today has a fascinating article discussing the difficulty of executing EDL (entry, descent, landing) on Mars for vehicles bigger than MER, Viking and Pathfinder, and the challenges for manned craft in particular. Airbags can't be used for obvious reasons, but the atmosphere is too thin to be used for parachutes or aerobraking by large heavy vehicles. The stronger gravity (compared to the moon) makes an Apollo-style powered descent impossible. The best current idea is a huge inflatable torus called a hypercone: 'Imagine a huge donut with a skin across its surface that girdles the vehicle and inflates very quickly with gas rockets (like air bags) to create a conical shape. This would inflate about 10 kilometers above the ground while the vehicle is traveling at Mach 4 or 5, after peak heating. The Hypercone would act as an aerodynamic anchor to slow the vehicle to Mach 1.'"
Would a space elevator be more feasible on Mars with the reduced gravity and atmosphere? Admittedly, you have to find a way to get a counterweight and cable all the way there, but it may be worth the tradeoff of the high speed landing with airbags, parachutes, rockets, and everything else we lug there to make it a slow crash. And surely rockets would be more useful than they say, otherwise, there's no way to get back off the planet.
If the problem is that you can't land the whole crew at once because of weight... why don't you land each member separately, in tiny containers and then a big load with the unmanned portion of the mission? Another advantage of something like this is that if one of the landings fails and you lose a team member your mission is still safe.
The main problem with landing is that you pick up quite a bit of speed from falling towards the planet. On Earth we take advantage of the air resistance in a relatively thick atmosphere to slow down the space shuttle as it returns. Mars has a MUCH thinner atmosphere so for large objects this won't work. You either end up going in at such a flat angle that you just bounce straight off the atmsophere like a skipping stone, or you go in too steep so that you are unable to lose enough speed before hitting the surface. It is possible to land on objects with no atmosphere ( like the moon ) using retro-rockets to slow down your descent, but because mars has a much stronger gravity this becomes impractical.
Perhaps I am inclined to think things like this because everybody around me has an infection for which the only antidote is "robots", but... Robots!
We should send a massive fleet of robots down and they can build a runway of some sort. Once they've finished that, they can also build a little village complete with a bar. That way when people go to mars, they have a place to land, and then they can get a drink and maybe some munchies.
A space elevator would actually not be such a bad idea. You can deploy it from orbit, and since Mars has a lower mass than earth it would significantly reduce the requirements of the cable. Getting the damned thing there might be a bit difficult thou.
Nuclear.
I suspect mach 1 on Mars is not the same as mach 1 on Earth (due to different speeds of sound in the planet's respective atmospheres). Which are they actually refering to in this case?
What about a huge blimp? You carry frozen helium all the way to mars, then heat it before entry to fill a huge blimp.
There should be a "-1:Groupthink"
You know, that would work but for the trick with slowing down once touched-down. Here, we use some parachutes to slow the shuttle down, and that is a HUUUGE runway... and that runway was a single concrete pour that lasted several years. And the air here is much denser, making those parachutes much more efficient than they would be on Mars.
The logistics alone in making that runway are impossible without getting people there first... and then what about the materials?
For large sets, this will be our guide even unto death, for the LORD will work for each type of data it is applied to...
We should focus on establishing a presence in space first. Let's get space working for lots of people, not just a select three at a time (plus celebrity). Think asteroid mining. Collecting hydrogen from the solar wind. Solar power arrays beaming clean energy back to Earth. Once we have refueling and industrial capacity in orbit or on platforms around the solar system, conquering the gravity wells of the other planets will merely be costly.
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Do we really need to land heavy stuff on Mars? "Something heavy" here means some spacecraft with human creature comfort (you know, a hull, life support systems, etc... in order to keep wetware inside alive). However, there is no need for manned flight to other planets anymore: probes do a much better job more easily, at a fraction of the cost, and a probe's survivability is much less of an issue.
Probes don't do a better job of colonizing other planets. Terraforming Mars is only a step in its colonization. The first and most important step is having people live on Mars. Second, there are all sorts of unpleasant things that can happen to people on Earth. In addition to the small chances of extinction, I think there's a good chance that we reset civilization in the next century or two. Aggressive space colonization can get us a foothold in space before nuclear war, a biological weapon, or other human-made disaster can set back Earth-side civilization to the early industrial age or earlier. Alternately, we could face centuries or millenia of stagnation in a "water empire" style government. In other words, colonizing space, particular the Moon, Mars, and other select bodies is a great way to diversify the habitat of human life.
We could wait for the next big technology advance like nanotech, or we could get started with the capabilities we currently have rather than count on the uncertain future to do our work for us.
Another point is that we can expand our economy into space. Sure you can expand it profitably into deep ocean, Antartica, etc. No reason not too unless you're an environmental type in which case you should like the absence of an environment to harm in space. But space has the benefit that there's a lot more of it with a lot of energy and mass available, dwarfing anything available on Earth. Economic expansion past a certain point will require a presence in space.
I had two solutions after reading the article. Both of which require rethinking the design of the CEV a bit.
The real challenge is that no matter what you do, you are moving *fast* at the beginning of the entry to the Martian atmosphere.
1) Very Large Heat Shields. The primary challenge to this is that it is next to impossible to launch them from earth. So don't launch them from earth-- assemble in earth orbit instead. This would require switching to more established systems after reaching mach 1.
2) Very large, lighter-than-air lifting body. Essentially imagine somethng like a large delta-shaped zepplin which could be assembled in low mars orbit and land on its own control surfaces after bleeding off enough of the helium gas to make it slightly heavier than air. K would be bled off through a combination of boyancy, drag, and lift. This is a tough design to get right and would also require pre-assembly in low earth orbit (and then final assembly in low Mars orbit). I am not quite sure how to make something strong enough to survive the atmospheric forces at that speed, however.
It seems like very large heat shields seem like a winner in this case.
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You're going to have a lot harder time landing on a body with no surface (or at least it's so deep we don't know where it becomes solid).
I'm a little bothered that the article dismisses as useless components that in actuality will probably be used for landing on Mars and are unrelated to the problem addressed in the article, and it tends to treat each idea as a complete solution, rather than pieces of a multistate solution.
The problem is not touching down on the surface. It's that first bit of decelleration during which you cover most of the distance to the ground. You've got to bleed off a lot of speed really fast, and Mars atmosphere isn't very conducive to accomplishing that. The article does cover this part well.
Previous landers, especially the Mars Exploration Rovers, have used multiple stages. The first is the heat shield. Because of their small size, the MER's have a high surface area/mass ratio. The heat shield slowed them down to mach 2 and a supersonic parachute deploys. Then retrorockets fired, slowing it to a complete stop a little ways above the ground, and lastly, the cable cut, dropping it relatively gingerly onto the airbags.
So just for the little MER's, there were actually 4 stages involved: heat shield, parachute, retro-rockets, and airbags. Although the article on focus on the airbags in its discussion of the MER, those were really only to allow a margin of error for the retrorockets (although a needed one), and were unrelated to the supersonic transition part.
The hypercone is basically a specially-shaped parachute, but it still won't slow a lander sufficiently to survive hitting the ground. I'm expecting the final solution if we ever commit to it will include heat shield, hypersonic chute, possible a middle stage chute, main chute, retrorockets, and airbags.
Also, you mention lighting a rocket in a supersonic airstream is hard (I'm not sure about that...the combustion chamber is static), and the article claims it would be better if Mars had no atmosphere. Regardless, if you're committing to rockets for anything more than what a modestly sized parachute leaves you travelling, then it doesn't much matter if you use the rockets down near the ground, or as part of a longer de-orbit burn. Either way you're getting rid of KE.
Overall, Mars is the hardest place to land in the inner solar system.
Hard I suppose is relative, but as I understand it Mercury, Venus, and the Moon all require more delta V to get there once you take into account the advantages of atmospheric braking. More delta V means "harder" for me.
Also, the problem with a retro rocket the whole way isnt just that its heavier gravity (just means more fuel,) but also the process of igniting a rocket with an incident airflow of mach 3 or higher is not a trivial problem.
Cover the exhaust outlet. Then there's no incident airflow of mach 3 until you pop the cover off. Or start the retro before you enter real atmosphere. Probably other ways as well. It's a solved problem so it doesn't matter how "hard" it is to do.The flight simulator X-Plane has dynamics for Mars (or did have, years ago), and there were a few planes that would fly in a Mars atmosphere. They had to fly quite fast and had fairly (but not obscenely) large wings.
I don't think the Shuttle would cut it, however.
I've always thought that floating cities on Venus would be pretty cool. You wouldn't need to break that much, because at 50km up the atmosphere is already as dense as it is on Earth at sea level.
You bring up an interesting idea.
This is where design validation comes in. For those not familiar with this term in the context of system engineering (and, in particular, system engineering of complex aerospace/defense systems), design validation generally refers to the activity whose purpose is to show that a design actually meets the customer's needs (i.e., that it is a 'valid' design). The effort takes design requirements into consideration, of course, but should also make use of system modelling based on the design, among other inputs.
Assuming the statement of work includes support for design validation, and the team doing the validation is competent, a lot of the risk of incomplete requirements can be mitigated, at least in theory. However, the engineering of complex, never-been-done-before systems always has associated 'escape' risks. A lot will depend on how the development effort is phased, and whether or not sufficient system engineering is performed up front, with sufficient lead time to modify/add to the design without severely negatively affecting the overall development in terms of cost or schedule.
In the end, of course, dealing with a competent and ethical development group is key. In my opinion, the contracts folks shouldn't "get in the way" of doing the right thing if problems surface. But in today's world, with today's financial sensitivities--and today's ethics--there are risks.
Actually it is. You can get either effect you want.
On the side facing the sun, you have the most reflective colors possible, either reflective (polished metal) or white. On the side that is in the shadow of your own craft, you use the darkest shade of black you can find.
The Space Shuttle already does something similar. The cargo doors are black on the inside, and they are opened as needed to release the excess heat (mostly generated from the trip into orbit).
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Now, that's an interesting idea -- a lighter-than-air lander. But is it even possible in an atmosphere as thin as Mars?
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