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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.'"
We don't really have to land the large vehicle. Getting within transporter range should be enough.
Oh, wait...
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Landing at mach one still sounds pretty fast -- better aim for water! Oh, wait ...
It is pitch black. You are likely to be eaten by a grue.
-dave
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Dunno about the rest of you, but the Hypercone immediately reminded me of a rolled-up condom.
I wonder when that idea...uh...arose?
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.
I did a project on this about a year and a half ago, and the solution we came to was in fact a parachute, but one capable of opening at Mach 2 or 3, similar to what Viking used. Unfortunately, since this has little use on Earth it is a very costly development process, and anything larger than Viking is significantly different, and a higher velocity opening speed would be nice. Following this a normal parachute, retro rockets, airbags or combinations thereof are still necessary.
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.
Overall, Mars is the hardest place to land in the inner solar system. the Moon and Mercury are small and have no atmosphere, so Apollo is an obvious and easy choice. Venus has an atmosphere so thick you can drop any funny shaped item in and it will drop to the surface at low speeds, assuming the static heat doesnt destroy it. Earth, obviously, you can do well enough if you're careful with the shape and throw up some parachutes at the end. Mars though has such a thin atmosphere it makes everthing hard.
This concept sure looks interesting though.
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 are an extension of humanity's collective intelligence, and they bring back to humanity at least as much data as a real, flesh and bone human. So why send humans at all? Of course, if we're talking about colonizing Mars for good, there's some terraforming to do, but heavy machinery isn't necessarily required for that either, and it's not going to start within our lifetime anyway, and the planet won't be ready for us in 200 years minimum anyway.
I say forget about hauling big stuff over to Mars. The only folks who care are prez Bush, for demagogic purposes, and people who think watching a Neil Armstrong type character utter some silly piece of wisdom when setting foot on a planet is the pinnacle of human space exploration. What we need is more research into nanotechnology, so probes get smaller and lighter, and educating people.
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
The current landing setup (the one used on the rovers) involves inflating airbags around the lander, then bouncing the lander into the surface at high speeds, then eventually coming to a stop after a few bounces. This is fine when your lander is filled with robotics, but would obviously be bad when the lander is filled with people.
The landing setup they're proposing is actually more like an air-braking system. It inflates around the lander while it's still at a high enough altitude, giving the lander a considerably larger volume. This would hopefully slow the lander as it continues its descent.
"In case of emergency, break glass. Scream. Bleed to death."
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.
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"
Bunch of NASA whiners must have replaced 'The Right Stuff' through worthless politically correct hiring practices - this new generation of 'engineers' and 'rocket scientists' have forgotten history and thus are being forced to re-invent the wheel. The logistics of these landings were worked out years ago - as you can plainly see in this simulation.
Glonoinha the MebiByte Slayer
Even if the atmosphere isn't as thick, it's still an atmosphere. Mach 4 is 1361.1 m/s. The escape velocity of Mars is 5.027 km/s. If you enter at Mach 4, you have nowhere to go but down. Deploy a large enough glider, and you will glide. Since the atmosphere isn't a vacuum, there will be drag. Fly around long enough, and you will slow down enough to glide safely in. I'd rather spend a few hours circling the runway than six seconds ramming into it.
UTF-8: There and Back Again
I thought it was going to be a story about my sex life.
"There is no real reason to send a manned flight to Mars. None."
wrong. More in a moment.
"You would need to send enormous amounts of gear, several hundred tons of water
and food and air enough for the journey, the time spent on the planet and
the trip back. "
and
"You would need a "mother ship" and at least two 'landers' with return
capability. In addition, a habitat for the humans. If you think you are a
treehugger, imagine the colossal amounts of resources needed to get there
and the environmental impact on Earth, just to start this type of endeavor."
Because it's hard is why it should be done.
"Think people. That grey matter is supposed to be used."
You first. I mean really.
Now back to the first part...Why?
1) The resulting spin off products will create new spin off companies.(The taxes returned from the companies that sold products created from the Apollo missions had gotten 13 time the return in taxes then the Apollo cost.)
2) New technologies and RnD help drive science.
3) This would almost certianly be a global project. Big Global Projects can help bring people together.
4) The environmental research and technology would help us develop a better understanding of enviromental controls on earth.
5) So we can stick out our just chest and say "Been there, where to next?" Not to consider the emotional impact on people is foolish.
6) More experience with space flight is another step towards off world mining and colonies.
Yes, there should be robotic exploration as well.
Personal, I would send drop ships to drop supplies before humans left for mars. Complete satellite arrays, rover to scout out select landing zones. Maybe even send the returning vessel ahead. Pack it with what they will need to return, and nudge it to mars. No rush, you can send it a couple of years ahead of time. You could also send some different landing tests.
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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.
The thermal heat capacity of space is also near 0. It's only "cold" in space because it's incapable of holding heat. If you put something in space, the only kind of cooling it can do is radiative. This is not nearly enough to counter the heating effect of solar radiation it absorbs.
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