Author Topic: Flying around Mars  (Read 4091 times)

Offline anonymous

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Flying around Mars
« on: 07/14/2017 10:09 PM »
How would people fly around Mars? I've done quite a bit of reading about it as research for a science fiction story I'm trying to write, but I seem to be going round in circles, so I'd like to hear what other people think. I'm thinking about it in the context of Mars with scientific bases, rather like Antarctica today. Not one with railway lines, monorails or cable cars, no matter how much more efficient they might be.

The most obvious way is the ballistic rocket hopper, as proposed by Robert Zubrin. It avoids the difficulty of trying to fly in the Martian atmosphere, but it would use an enormous amount of fuel.

Then he proposed the winged supersonic rocket hopper, which is more efficient for flights of up to 2000 km because you can glide part of the way. It still uses an enormous amount of fuel.

Zubrin also proposed the winged supersonic nuclear hopper. There are so many problems in terms of flight weight, shielding, nuclear particles in the exhaust that I just can't take that option seriously.

Flying subsonically would use much less energy. There have been a number of proposals for subsonic planes that were based on terrestrial human-powered plane designs. Zubrin was very critical of this approach in the 1990s as leading to vehicles that were too large and fragile,

salotti.pagesperso-orange.fr/Zubrinvehicles.doc

but by 2008 he was much more positive about it,

https://books.google.co.uk/books?id=ss6bNgjwh6cC&pg=PA117

commending its greater efficiency and longer range, despite the size of the vehicles. He even suggested that they could be made VTOL with tiltrotors. The idea seems like a sort of cross between Perlan 2 and the V-22 Osprey. I found it rather attractive.

There was quite a bit of work done on the potential for manned rotor craft in the early 2000s by Larry Young and colleagues.

www.dtic.mil/get-tr-doc/pdf?AD=ADA532337

They found that the limits on the radius of rotors at 12-15 metres presented a limit on the carrying capability of rotor craft because the atmosphere is so thin. They were looking at the ability to carry one astronaut in a spacesuit as about the limit of what could be achieved, but they were limiting themselves to a tandem coaxial helicopter configuration. They did refer to the possibility of tiltrotors, but they didn't really explore their limits. It seems, though, that the tiltrotors would have to have wingspans of at least several tens of metres to have enough rotor lifting capability (the limit is 6N/m2) to be able to carry people in a pressurised cabin like Perlan 2 has.

VTOL is very appealing in Martian aircraft because of the limitations of requiring runways, the high speeds needed for take off and landing, and the way that the low atmospheric density seems to require arresting gear like on an aircraft carrier to stop planes in any reasonable distance. But that may be more realistic.

Supposing we accept a need for runways, how do we propel the planes? Airbus think that relying on propellers would be very difficult in the thin atmosphere and they suggested "a Mars aircraft would need to be a hybrid that used some means of thrust and soar dynamics to move above the red planetís surface."

https://www.sciencealert.com/this-new-airbus-glider-is-set-to-hit-the-stratosphere-as-the-highest-flying-winged-vehicle

How would it get off the ground in the first place? With rockets?

I suppose you could use rockets to get up and then glide a long way if you're in a subsonic glider with a high lift/drag ratio, so fuel consumption would be nothing like as horrific as in a supersonic winged hopper. But without some kind of VTOL you'd be very restricted in your ability to explore Mars, rather than just fly between bases.

There is a long-standing idea, dating back to the 1970s, of using underside rocket propulsion to take off and land a plane without a runway on Mars. It seems a rather dicey way of landing anything with a high lift/drag ratio, though.

There is also the possibility of using airships to fly round Mars. It would enable you to take off and land vertically, but you need truly enormous vehicles of greater than Hindenburg proportions to do it in the thin atmosphere, which seems impractical, much as I love the idea.

There doesn't seem to be an entirely satisfactory solution. Hoppers are smaller and neater, but they use so much fuel. I find tiltrotors appealing because they're so efficient and are still VTOL, but they would be very large and I'm not sure they're really workable. I suppose you could use rocket-launched or propeller-driven gliders to travel between bases, but landing seems rather hairy at such high speeds and I have a hard time picturing them landing and taking off with underside rockets away from bases. Am I just being too conservative? I suppose you could use them like planes on Earth and hoppers like helicopters. I really don't know. Can anyone give me some informed advice about the practicality and desirability of the different options?
« Last Edit: 07/14/2017 10:14 PM by anonymous »

Offline spacenut

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Re: Flying around Mars
« Reply #1 on: 07/14/2017 10:46 PM »
What about an airship using hydrogen left over from methane production.  Explosion or fire might be limited due to no oxygen in the Martian atmosphere.  One would only have to worry about high winds. 

Offline Jim

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Re: Flying around Mars
« Reply #2 on: 07/14/2017 10:59 PM »
What about an airship using hydrogen left over from methane production.  Explosion or fire might be limited due to no oxygen in the Martian atmosphere.  One would only have to worry about high winds.

Not enough atmosphere to work

Offline TomH

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Re: Flying around Mars
« Reply #3 on: 07/15/2017 02:16 AM »
What about an airship using hydrogen left over from methane production.  Explosion or fire might be limited due to no oxygen in the Martian atmosphere.  One would only have to worry about high winds.

The principle of buoyancy depends upon the buoyed object having a lower average density than an equal volume of the supporting medium (fluid). Pure hydrogen gas is usually molecular H2, not single atoms. Individual H2 molecules would float to the top of other Martin atmospheric gasses. Mars' average surface atmosphere is only 0.0059 the density of Earth's atmosphere at MSL. IOW, Mars' atmosphere is extremely low density. When you take the mass of the balloon and payload, add that to the mass of the hydrogen, divide and get the average density, you have something that has an extremely higher average density than an equal volume of Martian atmosphere. The denser a fluid (liquid or gas) the greater its ability to buoy a solid object. The lower the density of the fluid, the less its ability to buoy a solid. Thus Jupiter, with its immense gravity and dense atmosphere, has a tremendous capacity for buoyancy. (This ignores turbulence, radiation, static discharge, toxicity, etc.)
 
Density in relation to buoyancy is also a function of gravity or acceleration. (I am not discussing density in a pressurized closed system in zero G.) The fluid must also be under acceleration by gravitational pull or by increasing velocity. Mars' lower gravity causes its atmosphere to be less dense than it would be under 1G. Higher gravity or ΔV increases the buoyancy of a fluid. This is why the COPV flew to the top of the tank with such rapidity in the F9 CRS-7. Density is irrelevant in the absence of gravity or ΔV. An unsecured sphere filled with H or He sitting inside a tank of RP-1 in space will simply float around in the tank because lack of gravity and ΔV means there is no such thing as up or down.

Due to the combination of both low density of Mars' atmosphere (compounded by low gravity), getting this balloon to loft in the Martian atmosphere would be comparable to getting a 1m dia. uranium sphere with a 1cm dia. air filled core at 1 atmospheric pressure to float in water on Earth. It just isn't going to happen.
« Last Edit: 07/15/2017 03:10 AM by TomH »

Offline KelvinZero

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Re: Flying around Mars
« Reply #4 on: 07/15/2017 05:31 AM »
I found this link to an earlier forum thread about airships
Possible - sure! The atmospheric pressure of Mars corresponds to about 31-34 km in Earths atmosphere which is comfortably within the capabilities of high altitude balloons
..
it goes on to list some problems, but shortened for brevity.

Can anyone confirm that pressure? They also mentioned that CO2 might make things easier, since it is denser. Is that true? Can it be expressed as being comparable to a height lower than 31-34km?
Would it help significantly to use hot hydrogen? That might not be practical on earth.

I thought airships were being seriously considered for Mars, but I had assumed they were for scouting or something, not cargo. I couldn't find anything with a search, only an unlikely-sounding airship using actual vacuum for lift.

I found another link claiming pressure was like 30-60km on earth, with 30 being around Hellas Planitia.

Also, CO2 is about 60% denser than air. I guess that would improve the buoyancy of hydrogen by a similar factor, since hydrogen is way less dense than air, eg 14 times less dense.
https://en.wikipedia.org/wiki/Carbon_dioxide
https://en.wikipedia.org/wiki/Lifting_gas#Hydrogen
(These are earth temperature stats. No idea how mars temp affects them)

(I also vaguely recall speculating on using static charge instead of internal gas to stretch out a balloon. I think that was shot down fairly easily)

Helicopters were also seriously investigated. I remember seeing a youtube clip about that.

probably this one:

« Last Edit: 07/15/2017 06:01 AM by KelvinZero »

Offline TomH

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Re: Flying around Mars
« Reply #5 on: 07/15/2017 07:47 AM »
KelvinZero, eriblo is incorrect.

Wikipedia-Atmospheric Pressure Levels on Mars

The density of CO2 vs regular air on Earth is part of the overall equation, but pressure is what it comes down to. Even though CO2 molecules may be denser than the average gas mix in Earth's atmosphere, the CO2 in Mars' atmosphere is rarified. The molecules are farther apart because there is less upper atmosphere sitting atop the surface atmosphere, therefore the average density is lower, (and the gravity is lower as well) ergo the pressure is lower.

This calculator shows the pressure at 31km in Earth's atmosphere to be 1.20896 kPa, which is still twice the average pressure on the Martian surface of 0.6kPa. Keep in mind that is your starting pressure at the surface. You do not want a buoyancy based ship cruising around at surface altitude; you want to be at some altitude for safety. As soon as you begin ascending, that pressure begins to drop sharply, causing your lighter than air craft to begin losing buoyancy almost immediately.

Re. your comments: How would you keep that hydrogen hot? Also, those balloons that go to extreme altitudes on Earth are only able to carry payloads that are relatively low mass; on Mars you are going to be severely mass constrained. Further, what would you use for propulsion? (Consider the mass of the propulsion source and fuel.)

The bottom line is this. You might be able to use graphene for the balloon and H2 for the buoyancy gas and be able to loft micro-cameras and micro-radio relay devices that are at the whims of the winds.....maybe. But basic physics prevents the use of lighter than air buoyancy craft for cargo transport on Mars.

To the OP, the most efficient transport mode on Earth is cargo ship cruising at relatively slow speed. The second most efficient in terms of traction, resistance, fuel efficiency, etc. is rail. Obviously the first is not possible on Mars. Without debating ISRU production of steel, plastics, and concrete on Mars, my WAG is that in the long term (centuries or even millennia) some type rail system that can sweep dust off the track in front of the train is the most likely.
« Last Edit: 07/15/2017 09:32 AM by TomH »

Offline kkattula

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Re: Flying around Mars
« Reply #6 on: 07/15/2017 01:13 PM »
Hyperloop! With no need to produce a near vacuum, just a thin shell to keep the dust off the tracks.

For aircraft, how about rockets for VTOL and acceleration, with solar powered props and long, thin wings for cruise?

Offline ncb1397

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Re: Flying around Mars
« Reply #7 on: 07/15/2017 05:54 PM »
Using the specs of Felix Baumgartner's balloon:
mass: 1683 kg
volume: 850,000 m^3
http://www.redbullstratos.com/technology/high-altitude-balloon/

The Mars atmosphere weighs .02 kg/m^3 as measured by Viking 1, while hydrogen at the same pressure would weigh 2.01588/44.01(assuming a pure CO2 atmosphere for simplicity) as much or .0009 kg/m3. The martian atmosphere taking up the volume of the balloon would therefore weigh 17,000 kg while the balloon itself filled with H2 at equal pressure would weigh 2448 kg (it would be lighter than air with substantial margin for payload and altitude).
« Last Edit: 07/15/2017 05:58 PM by ncb1397 »

Offline anonymous

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Re: Flying around Mars
« Reply #8 on: 07/15/2017 08:27 PM »
For aircraft, how about rockets for VTOL and acceleration, with solar powered props and long, thin wings for cruise?

I think you're right. That hybrid approach does seem the best. Why didn't I think of it?


Offline Phil Stooke

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Re: Flying around Mars
« Reply #9 on: 07/15/2017 09:09 PM »
"a 1m dia. uranium sphere with a 1cm dia. air filled core "

Wow, quite the analogy!  I prefer my balloons a trifle lighter.  However, there is a large body of research suggesting ballooning on Mars is much more feasible than you suggest.  For instance:

https://trs.jpl.nasa.gov/bitstream/handle/2014/10475/02-2472.pdf?sequence=1&isAllowed=y

https://trs.jpl.nasa.gov/bitstream/handle/2014/39004/01-0803.pdf?sequence=1

https://trs.jpl.nasa.gov/bitstream/handle/2014/45259/09-0993_A1b.pdf?sequence=1

https://trs.jpl.nasa.gov/bitstream/handle/2014/38360/05-1506.pdf?sequence=1

So most likely the difficulties you suggest can be overcome.


Offline KelvinZero

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Re: Flying around Mars
« Reply #10 on: 07/16/2017 02:06 AM »
KelvinZero, eriblo is incorrect.
..
This calculator shows the pressure at 31km in Earth's atmosphere to be 1.20896 kPa, which is still twice the average pressure on the Martian surface of 0.6kPa.

Keep in mind that is your starting pressure at the surface. You do not want a buoyancy based ship cruising around at surface altitude; you want to be at some altitude for safety. As soon as you begin ascending, that pressure begins to drop sharply, causing your lighter than air craft to begin losing buoyancy almost immediately.

Re. your comments: How would you keep that hydrogen hot? Also, those balloons that go to extreme altitudes on Earth are only able to carry payloads that are relatively low mass; on Mars you are going to be severely mass constrained. Further, what would you use for propulsion? (Consider the mass of the propulsion source and fuel.)
Hi TomH,
The figures quoted were for https://en.wikipedia.org/wiki/Hellas_Planitia, not the average. So yeah, this thing would likely be restricted to just cruising around that one basin.

I think pressure changes much more slowly with height on Mars. Balloons can go higher than 30km on earth so I think we could come up with a decent safety margin.

I hadn't thought much about keeping the hydrogen hot. "Hot" is subjective of course, especially on Mars. Perhaps some alpha or beta radiation source? Also the balloon could be designed to act as a greenhouse. Its strength could be distributed into cells that increase its ability to retain heat theoretically without increasing weight. (As cells become smaller, their walls can become thinner and still retain the same pressure. The mass of the surface ends up being proportional to volume rather than surface area)

Offline KelvinZero

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Re: Flying around Mars
« Reply #11 on: 07/16/2017 02:28 AM »
Hey, random idea.

Would a very large wing be able to exploit some sort of ground effect that would be impractical on earth?

My argument is that although you would  have to fly very fast, very close to the ground, the almost-vacuum atmosphere on Mars might make this sort of flying more predictable than on earth, where you can be thrown around by stray gusts. You would never be surprised by a big rock either. The route would be extensively mapped.

Online Robotbeat

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Re: Flying around Mars
« Reply #12 on: 07/16/2017 02:57 AM »
Hey, random idea.

Would a very large wing be able to exploit some sort of ground effect that would be impractical on earth?

My argument is that although you would  have to fly very fast, very close to the ground, the almost-vacuum atmosphere on Mars might make this sort of flying more predictable than on earth, where you can be thrown around by stray gusts. You would never be surprised by a big rock either. The route would be extensively mapped.
Ive thought of a ground effect wing for Mars. But it's have to be huge to get the benefit because you'd have to fly high enough not to hit boulders. So not practical unless you could move all the boulders out of the way.
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Online Robotbeat

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Re: Flying around Mars
« Reply #13 on: 07/16/2017 03:02 AM »
With a Lithium-CO2 battery (or possibly a CO/O2 fuel cell) and an efficient airframe (think of a glider) you could get all the way to the other side of the planet on a single charge.

The main difficulty is landing. Landing speed would have to be very high due to the thin air. A cart on rails, a zip line, or perhaps a fast ground vehicle could be used to launch and recover the aircraft.

Otherwise you need to perfect vertical takeoff, vertical landing with either very high power motors and huge propellers or use rockets just for takeoff and landing. Since the rockets only need about 200m/s delta-V, you won't need much propellant per flight.

VTOL combined with high efficiency electric flight is my preferred method, but would be hard to develop.
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Online Gliderflyer

Re: Flying around Mars
« Reply #14 on: 07/16/2017 04:18 AM »
With a Lithium-CO2 battery (or possibly a CO/O2 fuel cell) and an efficient airframe (think of a glider) you could get all the way to the other side of the planet on a single charge.

The main difficulty is landing. Landing speed would have to be very high due to the thin air. A cart on rails, a zip line, or perhaps a fast ground vehicle could be used to launch and recover the aircraft.

Otherwise you need to perfect vertical takeoff, vertical landing with either very high power motors and huge propellers or use rockets just for takeoff and landing. Since the rockets only need about 200m/s delta-V, you won't need much propellant per flight.

VTOL combined with high efficiency electric flight is my preferred method, but would be hard to develop.

Zip line and ground vehicle landings have been done, but would be pretty terrifying with a 350-400 knot touchdown speed.



Another option is a skid landing, similar to older gliders. 400 knots is only ~twice the X-15 touchdown speed, and it *might* be possible to land at that speed assuming there was a prepared runway. If that isn't feasible, perhaps a hybrid VTOL/convention landing could be done. Use rockets to slow down and unload the wings until you get to a more normal landing speed. You still need a runway, but it would use less fuel than a pure VTOL.
I tried it at home

Offline KelvinZero

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Re: Flying around Mars
« Reply #15 on: 07/16/2017 05:38 AM »
This is interesting
https://en.wikipedia.org/wiki/Helios_Prototype

.. in that it was tantalisingly close to the highest pressure on mars with a maximum height of 29km, but I think it says this was not something it could sustain. It was aiming for a height record, not an endurance one.

What sort of saving are we looking at from gliding compared to simple ballistic flights? you have to be confident that you would do substantially better than the ITS that you probably already have, and already have all the supporting infrastructure for.

Would a modified ITS with some wings be more effective for this purpose?

How about the air-augmented NTR that some spaceX guy suggested? I don't fancy that for earth, but how about for  Mars? Im not really a terraforming proponent. Even if air pressure increases over many decades, I think people and especially children will live indoors, and outdoors will be fairly desolate and bombarded with radiation for the foreseeable future whatever we do. A few NTR crashes would probably be fairly tolerable.

Offline anonymous

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Re: Flying around Mars
« Reply #16 on: 07/16/2017 11:48 AM »
Maybe the limitations on rotorcraft aren't as severe as Young et al. concluded in 2005. They seem to have been working within the helicopter paradigm with only up to four rotors. The restriction on lift was because the stresses on rotor blades increase rapidly with a radius of more than 12-15 metres. Current thinking about terrestrial VTOL aviation is about electric motors allowing distributed lift, making it much more efficient. The limit on the speed of rotors is set by the speed of sound at the tip, so smaller rotors can do much more revolutions per minute, allowing a smaller total rotor area than with a helicopter.

There are designs like NASA's GL-10



and Joby Aviation's S2



Since a subsonic Mars plane of sufficient size to transport humans would need very long wings anyway, I wonder if it would be possible to generate enough lift that way to fly a reasonable payload.

Rockets for takeoff and landing would definitely work and maybe the fuel needs wouldn't be too great. You would need to carry at least enough for a takeoff, a landing, a takeoff and another landing. So perhaps 800 m/s in total.

Launch carts and zip lines strike me as accidents waiting to happen. Using the rockets in combination with a runway strikes me as a good idea. I'm wondering about infrastructure costs of the runways, though. You'd need a runway a few kilometres long to be constructed and maintained. I'm wondering if a cost-benefit analysis would show it paying for itself in terms of fuel savings.

Offline KelvinZero

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Re: Flying around Mars
« Reply #17 on: 07/16/2017 01:37 PM »
Ive thought of a ground effect wing for Mars. But it's have to be huge to get the benefit because you'd have to fly high enough not to hit boulders. So not practical unless you could move all the boulders out of the way.
Huge but flimsy. This just gave me an idea for a sort of flying jellyfish.

Start with something like that mars helicopter shown earlier. That can already fly with a small payload and no ground effect.

Have many of these (or fewer, larger ones) distributed over a very wide very light solar power sheet.

When they are running, the whole thing inflates into a dome.

The number of rotors necessary to maintain a ground effect will be proportional to the circumference, but the amount of solar power available will grow with the area, so at some scale the power collected will comfortably exceed the power required to hover.

Scale up even more and you can consider something more rigid. Perhaps it has hydrogen filled toruses, not to deliver positive buoyancy but to be rigid while still light. This would let it land anywhere on flimsy legs without collapsing into the dust.

I imagine the rotors somewhere near the rim rather than merely being proportional to the rim. The rotors themselves might be part of the mechanism to allow an intelligently adjusting skirt to conform to the landscape.

Offline MickQ

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Re: Flying around Mars
« Reply #18 on: 07/17/2017 09:57 AM »

Since a subsonic Mars plane of sufficient size to transport humans would need very long wings anyway, I wonder if it would be possible to generate enough lift that way to fly a reasonable payload.

Very long wings. OR. Multiple shorter wings ?

Offline anonymous

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Re: Flying around Mars
« Reply #19 on: 07/23/2017 11:39 AM »
The fuel required for even 800 m/s of delta-v from rocket propulsion is going to be a substantial proportion of take-off mass, so I did some more research about electric tiltrotors.

It seems the most efficient way to do an electric tiltrotor - or rather, a tiltrotor/SLT hybrid - is like this:



Click on the link below for an animation and a description of how it works.

http://electronflight.com/tiltrotorslt.php

The rotors and wings would have to be proportionately larger on Mars. I find it interesting that the shape of the airfoil is very much like those designed for proposed robotic Mars planes to operate in the thin Martian atmosphere. Longer, narrower wings make for a better lift/drag ratio, so the plane can manage a longer range, but shorter, wider wings would be more manageable in use.
« Last Edit: 07/23/2017 11:42 AM by anonymous »

Online 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 »

Online 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.
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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.

Online 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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