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Robert Zubrin's Mars Gashopper Airplane
Fraser Cain writes "Universe Today has a story about Robert Zubrin's (Mars Society President) Martian Gashopper Aircraft proposal to NASA. It uses solar power to liquefy carbon dioxide and then use it as a propellant to take off, fly hundreds of km above the surface of Mars like an airplane, and then land vertically again."
The Carbon dioxide is much more concentrated on Mars than on Earth. It would take a lot longer to get enough for fuel, and you would need more propellant to overcome Earth's larger gravity.
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They've done test flights here on Earth, so I'm assuming it works here.
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CO2 sublimates, doesn't it?
It does under Earth's amospheric conditions. You can liquefy CO2 by putting it under high pressure (5+ atmospheres, IIRC). When they release the liquid CO2 it'll probably produce gas and small crystals that will sublimate away, like what happens when you discharge a CO2 fire extiguisher on Earth.
It would be neat to watch a rocket powered aircraft that trails dry ice snow instead of smoke and flames...
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It also gives mission control a better idea of what they might want to look at next: during a hop, take a few photos and send them back for review and planning. That and the photos can be stereoscoped to give a better idea of terrain features. No more landing in a crater they can't get out of :-/
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RTG's don't release any chemical compounds, they are only used as heat sources (in this case heating banks of thermocouples to generate electricity) - the fuel pellets are usually bound in plastic to make handling safer.
I don't think CO2 is essential to the system... it just happens to be the most handy gas available on mars. Its really like a VTOL aircraft with jet engines except that the gas is heated electrically rather than by burning fuel. An earth-based gashopper would just use air.
CO2 has a relatively warm freezing point, -78C, compared with -196 for nitrogen, and -182 for oxygen. So, it's convenient for that reason too. I'm sure you could make a similar system for our atmosphere, though liquid nitrogen is trickier to deal with than CO2.
Only so long as the bottom of the chasm has quite a bit of open and reasonably flat terrain, and as long as the chasm is several times wider than the wingspan of the Gashopper. (And the winds are low.)
All this become possible once we develop terrain avoidance software considerably more sophisticated than the current generation, and a computer considerably more powerful, yet lighter and less watt hungry than the current generation...
In short, this is a typical Zubrin proposal. Long on wildly handwaving the advantages (while throwing darts at NASA), and very short on a realistic assesment of the problems and challenges that lay between here and there.
A really big one might help with moon mining as proposed here. Of course it would literally have to hop as wings are useless on the moon.
The plan is to use stored, compressed atmospheric gasses as propellant for a winged aircraft.
Sit back, and think about this for a second.
Now, tell me again about how this would work on the moon except for the wings.
You can't take the sky from me...
> The same 50 kg would weigh about 41 lbs on Mars.
Do martians use the imperial system now?
For the imperial impaired (like me) 41 lbs == 18,6 kg
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Take off and landing are difficult... for HTOL aircraft. This is designed to use VTOL (vertical thrusters) to gain altitude, which won't rely on wings for lift; instead, the thin atmosphere and low gravity are beneficial, as both drag forces and gravity forces are reduced. During takeoff, this thing is basically a rocket, for which thin atmosphere and low gravity are benefits.
Once it hits altitude, it begins to fly; it's going to need a huge wingspan to do that, true, but it can get most of the speed from
Similarly, the landing is vertical, which means that all it needs to do is cancel horizontal speed and then use the vertical thruster as a brake to make a soft landing, roughly the same way the Apollo modules landed on the moon. Stability is the only issue with these, and its a surmountable obstacle.
Bottom line: there's no real reason to believe the takeoff/landing of this is unworkable - Apollo worked the same way. Flight is the only question mark, and we're pretty good at understanding how to make things fly; if they can make it fly in a low-density vacuum chamber on Earth, using helium to simulate the low-gravity condition, it seems likely they can make it fly on Mars.
Disclaimer: I am not a aerospace engineer, though I did take a few aero courses in college.
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The other side of the coin is that an Earth vehicle can save energy by using lift to take off horizontally, because the atmosphere is thicker. A martian one will probably need to take off vertically, and won't experience lift until it reaches a much higher cruising speed. Once at that speed, it can fly a long way without as much drag, but once you want to land you have to worry about slowing down, so the device had better measure its fuel carefully or have a large wingspan that is retracted just before landing, once again vertically.
Although it sounds less practical than using the same energy for rovers, it might be OK as a proof-of-concept (or proof-of-bad-idea) for a future mission that uses the CO2 to leave orbit on a return trip.
Last Friday (Nov. 19) was a big milestone for many small companies like Robter Zubrin's. This is when NASA announced its 2004 SBIR Phase I awards. And yes, this Gashopper is one of them.
a rds/2004topic.html There's really some innovative stuff going on. Also, to the future rocket scientists out there: if you want to work in aerospace, this is an excellent site to find small companies doing NASA subcontracting.
Check them all out at: http://sbir.gsfc.nasa.gov/SBIR/sbir2004/phase1/aw
IWARS.
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