Getting there is the easy part...
I read a fascinating article tonight on some of the challenges associated with a crewed Mars mission. I've read several books and articles on all of the standard problems that people think of when they think about sending humans to Mars: Launch weight restrictions, fuel restrictions, transit time, resource usage on-flight and on-mission, but it turns out that a lot of people have taken for granted one of the most obvious hurdles: actually landing on Mars.
Turns out that because the density of Mars' atmosphere is so low (1/100 that of Earth), landing large payloads, like you would need to land humans on the surface, is a very difficult proposition. Basically, the atmosphere is not dense enough to create enough drag on a large spacecraft to slow it sufficiently to use traditional landing techniques (parachutes, space shuttle-style lifting bodies) before you are a crater. Techniques that have been used to land on Mars previously, like deceleration thrusters (Viking) or airbags (Sojourner, MER) are either not powerful enough or expose the spacecraft to unacceptably high G-forces (10-20 G) that would kill human occupants. On the flip side, the Apollo-style lunar lander would also not be useful because in that case, Mars has too much atmosphere for a straight thruster-only descent - you would create very dangerous and unpredictable forces due to the interaction of the rocket plume with the atmosphere - something you didn't have on the airless moon.
So, there is this huge gap in knowledge that they are trying to figure out. How do you slow a 100 metric ton spacecraft from 7-10 km/s to under Mach 1 without killing everyone in the process? Turns out that might be the hardest thing about getting people on Mars.
Link to the article.
Turns out that because the density of Mars' atmosphere is so low (1/100 that of Earth), landing large payloads, like you would need to land humans on the surface, is a very difficult proposition. Basically, the atmosphere is not dense enough to create enough drag on a large spacecraft to slow it sufficiently to use traditional landing techniques (parachutes, space shuttle-style lifting bodies) before you are a crater. Techniques that have been used to land on Mars previously, like deceleration thrusters (Viking) or airbags (Sojourner, MER) are either not powerful enough or expose the spacecraft to unacceptably high G-forces (10-20 G) that would kill human occupants. On the flip side, the Apollo-style lunar lander would also not be useful because in that case, Mars has too much atmosphere for a straight thruster-only descent - you would create very dangerous and unpredictable forces due to the interaction of the rocket plume with the atmosphere - something you didn't have on the airless moon.
So, there is this huge gap in knowledge that they are trying to figure out. How do you slow a 100 metric ton spacecraft from 7-10 km/s to under Mach 1 without killing everyone in the process? Turns out that might be the hardest thing about getting people on Mars.
Link to the article.
posted by Professor B at 9:59 PM
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