Author Topic: Flying around Mars  (Read 4170 times)

Offline Robotbeat

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Re: Flying around Mars
« Reply #20 on: 07/23/2017 01:37 PM »
800m/s delta-V is way overkill. Half that or less.
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Offline anonymous

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Re: Flying around Mars
« Reply #21 on: 07/27/2017 07:04 PM »
It seems like the rotors for any craft capable of lifting people on Mars would have to be enormous, so I returned to the idea of using rockets for take-off and landing.

MAVRIC (link below) was a project by students at the University of Alabama looking at a rocket-powered Mars glider capable of carrying three astronauts. The wings were inflatable and the wingspan was 60 m. It would take off under methalox rocket power and accelerate to 100 m/s, then glide for about 150 km. (I would add a propeller to enable longer flights.) It was designed for a hard landing at 70 m/s, with 10 g forces and a stopping distance of 500 m! A round trip involved just 200 m/s of propulsive delta-v. The mass budget rose from 1500 kg to 6006 kg because the propulsion mass rose from 300 kg to 4827 kg because of the propulsion system needing to provide more thrust and longer burn times for the mission profile. I don't know why the mass of the propulsion system became so great.

http://rascal.nianet.org/wp-content/uploads/2015/07/2006-RASC-AL-UAL-TechPaper-Noteworthy.pdf

Why was the methalox rocket system so massive? It doesn't seem like it could have been the fuel itself. It should have only been several percent of the take off mass.

Would a simpler propulsion system, like Zubrin et al.'s gashopper, work out better even though the ISP is much lower? They showed a mass ratio of 1.3 to 1.5 for the CO2 propellant depending on temperature to give 400 m/s of delta-v to enable a round trip with soft landings.

EDIT: I see on page 27 of the report that its propulsion system (including fuel) also accounted for the vast majority of the mass.

http://studylib.net/doc/7303751/mars-gashopper---pioneer-astronautics
« Last Edit: 07/27/2017 08:24 PM by anonymous »

Offline Robotbeat

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Re: Flying around Mars
« Reply #22 on: 07/29/2017 02:57 AM »
Try CO/O2. 300s Isp if you pumpfeed it. Good density. Plentiful feedstock (CO2, not water or hydrogen needed). Efficient to electrolyze (doesn't have the inherent losses that Sabatier causes for methane), and a CO/O2 electrolysis capability is supposed to be flying on the 2020 rover.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline jsgirald

Re: Flying around Mars
« Reply #23 on: 07/29/2017 09:22 AM »
Try CO/O2. 300s Isp if you pumpfeed it. Good density. Plentiful feedstock (CO2, not water or hydrogen needed). Efficient to electrolyze (doesn't have the inherent losses that Sabatier causes for methane), and a CO/O2 electrolysis capability is supposed to be flying on the 2020 rover.

I didn't know electrolysis was even possible.
With a bit of searchiing I came across this Photoelectrochemical reduction of CO2 which is not electrolysis but looks ideal for Mars ISRU. Apparently a slow process but you're not going to have a high demand any time soon.

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Offline anonymous

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Re: Flying around Mars
« Reply #24 on: 07/29/2017 04:23 PM »
Frustrated with rotors and rockets, I wondered if a lift fan, like on the F-35B, would work on Mars. Its lift fan is much smaller than a rotor with equivalent lift capacity would be.

It turns out there have been a few proposals for robotic planes with lift fans. The earliest I know of is MASSIVA in 2004.

http://www.jbis.org.uk/paper.php?p=2004.57.306

The one I found most interesting is MIRAGE, from 2007, because it's much more massive than the usual robotic planes and much more comparable to one able to transport people. Its lift fan could do VTOL with a take-off mass of 433 kg. The lift fan would be just 0.9 m in diameter! A lift fan seems clearly the solution to the vertical lift problem on Mars.

MIRAGE would use a blended wing body with a Co-Flow Jet (CFJ) airfoil, which considerably increases lift per surface area compared to a conventional airfoil and consequently reduces drag and vehicle weight. It would have a wingspan of 4.8 m and a wing area of 6 m2. It would have a propeller with a diameter of 1.4 m at the front. Powered by hydrogen fuel cells, it could fly for up to 5 hours at Mach 0.45 and have a range of 1778 km.

http://www6.miami.edu/acfdlab/publications/AIAA-2007-244-577.pdf

I can imagine scaling the plane up by an order of magnitude in mass and a few times in dimensions to create something reasonably compact that could fly a few people in a pressurised cabin.

I don't know about hydrogen fuel cells, although they offer the best performance and range with 15.8 MJ/kg. Lithium-oxygen batteries would be the lowest-maintenance option and they could theoretically offer 18.7 MJ/kg, but you have to still carry the battery around, so it's only equivalent to 9.3 MJ/kg. The best you can actually get may be about 10 MJ/kg, equivalent to 5 MJ/kg. A carbon monoxide-oxygen fuel cell would offer 6.4 MJ/kg, which may be better than you can ever actually get out of lithium-oxygen batteries.

http://selenianboondocks.com/2016/09/energy-needed-to-get-to-orbit-using-various-fuels-from-various-planets/

http://large.stanford.edu/courses/2011/ph240/zhong2/

Offline anonymous

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Re: Flying around Mars
« Reply #25 on: 07/29/2017 04:40 PM »
A methane-oxygen fuel cell offers 11.1 MJ/kg and a methanol-oxygen one 8.5 MJ/kg. They would be much more practical than hydrogen-oxygen, but still need water extraction for refueling. I prefer the idea of just being able to refuel a plane with electricity, rather than needing all the infrastructure for rocket fuel production to refuel it. The penalty seems to be less range.

Offline Robotbeat

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Re: Flying around Mars
« Reply #26 on: 07/30/2017 01:43 AM »
I like the CO-O2 fuel cell.

By the way, lithium-oxygen fuel cell wouldn't work on Mars unless you brought along oxygen. HOWEVER, there's also such a thing as a lithium-CO2 battery, and it could get nearly the same performance.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline anonymous

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Re: Flying around Mars
« Reply #27 on: 07/30/2017 11:34 AM »
They seem to be turning from lithium-air to sealed lithium-oxygen batteries on Earth because of difficulties using air and I was assuming they'd use the same technology on Mars. A lithium-carbon dioxide battery would be cool, but it might take a lot of development.

Offline MickQ

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Re: Flying around Mars
« Reply #28 on: 08/07/2017 09:44 AM »
Throw 'Zapata Racing flyboard' into your favourite search engine.  This is. COOOOOOOOL.
Gaseous CO/O2 ?

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