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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.'"
Jet engines require oxygen, of which there is very little in the Martian atmosphere.
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.
the current airbags wrap around the vehicle and it bounces off the ground, producing 10-20G of force, which isn't very human friendly. The hypercone airbag is used to slow the vehicle down before opening parachutes.
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."
This is how JPL intends to land the next rover, Mars Science Laboratory: http://video.google.com/videoplay?docid=1404791803 599052711.
The 'airbag' approach means BOUNCING.
...'tracts of land'... it will probably never be safe for humans because we don't handle extremely high G impulses well.
Humans don't bounce too well, and neither does anything with too much mass (inertia). It was okay for the landers because they are much smaller than a manned spacecraft was.
(analogous to the oft-quoted maxim that you can drop a mouse from any height and it will survive, but a cat will not)
As the craft gets heavier, the size of the airbags that would be required to safely land it would I think increase geometrically.
Even with huge
I think the GP was probably referring to the scarcity of water on Mars rather than its hardness, but could be wrong...
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
It has been mentioned before in both SF and Scientific Literature. It is easier because you have Olympus Mons which takes you WAAAAY up so that you avoid most/all of the little atmosphere that is there. The gravity is obviously less which helps a lot. The problem of the moon getting close to the tether was avoided by sending elevators up and down at calculated intervals to set up a resonance motion therefore making the cable undulate like a string, therefore avoiding the moon altogether.
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.
Random and weird software I've written.
He's talking about deploying a space elevator from Mars-stationary orbit to Mars, not from Earth to Mars. Jesus christ.
Read Zubrin's _The Case for Mars_, which goes into quite a lot of detail. It covers cancer risks, etc. It *doesn't* cover the landing issue, beyond assuming aerobraking.
The basic scheme is to send an atmosphere converter ahead of the manned mission to create a stock of methane and oxygen propellants for the return, as most of the mass you'll need is still fuel. Mars has a surface gravity around 1/3 of Earth's, so quantities required are much lower than for the trip out. In a way, you're right about using nuclear power to lessen the weight somehow. The fuel factory uses a nuclear reactor.
You might be still be right about it never happening, though. Ten years ago, Zubrin thought it could be done for 55 billion. He might well have been conservative, there's been ten years of inflation, and of course we're broke. I wonder how many of these we could have flown for what we've spent in Iraq?
http://en.wikipedia.org/wiki/Mars_Direct
What you do with a computer does not constitute the whole of computing.
Try jumping into a pool with no water in it...
Just as the air in your pool is considerably less dense than the water that would normally do the job of stopping you from hitting the bottom, the atmosphere on Mars in considerably less dense than the atmosphere on Earth. A parachute that would bring you to nice easy landing on Earth would bring you to a nice messy landing on Mars. Gliding and flight are trickier for pretty much the same reasons.