3/2/10

A Martian Airplane?


It wouldn't work.

But I spent a whole afternoon thinking about it, just to see if it would be feasible. It might be wasted effort, but just imagine how cool a space probe on Mars would be if it could fly through the atmosphere like here on Earth!

I had to look up a couple things. First of all, the gravity is lower, which is good. It's about 3.7 m/s2 as opposed to 9.8 m/s2 here on Earth. However, the Martian atmospheric density is only about 0.02 kg/m3, and here on Earth we're blessed with a thick 1.2 kg/m3 atmosphere. Atmospheric density is essential to lift (L=1/2CLrv2A), so if you have a density that is 1.7% of Earth's, you're going to get lift that is 1.7% of what it would be on Earth.

But I had fun brainstorming anyway. My initial idea was to have a solar powered plane similar to the NASA Pathfinder or Helios unmanned aerial vehicles. The Pathfinder weighs about 930 N on Mars, so you'd need at least that much force in lift, prefferably more because you have to lift off the ground. I played around with FoilSim, and the highest lift coeficient I can get is about 5. I then picked a realistic value for the velocity, just to see what ball park I'm in. On Earth the Pathfinder doesn't go much faster than 7-10 m/s, so I plugged 7 in. The result: 173 N. Definitely not going to cut it.

What really puts the nail in the solar-powered coffin is that the lower density means the propellers on such a craft would be completely useless, so you wouldn't be able to accelerate to 7 m/s to begin with. Oh, and another thing. The Sun is much further away, so the solar arrays won't get as much energy.

Where else can you get free propulsion on Mars?

I read somewhere that you could theoretically manufacture rocket fuel from the Martian atmosphere. Mars' atmosphere is 95% Carbon Dioxide, so you could make methane with the following reaction:

4H2 + CO2 --> CH4 + 2H2O

The problem with this is that you would only be able to fly but a few moments before the vehicle would have to land and wait a few more years to make more fuel.

Any other good ideas?

6 comments:

R2K said...

I am pretty sure it could work: Mars is similar to earth at 100,000 feet, and we have planes that could fly at these altitudes already. As you say there is less gravity, that more than compensates for the poor atmosphere. The helos solar plane would be a good model of something that could fly on mars.

DTH Rocket said...

Oh. So I'm not crazy.

The EGE said...

IIRC, there were plans once for a plane on Titan as well.

brianc said...

It's not only possible, but in the works!

http://marsairplane.larc.nasa.gov/platform.html

I'm going to make a model of this one someday.

DTH Rocket said...

Hey, thanks for the link. I've never heard about it until just now!

R2K said...

I think human powered flight would only be "enjoyable" on Titan (whereas here on earth it is possible but a real pain in the neck).

We could probably even fly on titan by flapping wings!

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