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#1 Human missions » Mars One » 2012-06-05 16:55:08
- MatthewRRobinson
- Replies: 93
The Introductory Video:
http://www.youtube.com/watch?v=6QoEEGyS … re=related
And the Website:
http://mars-one.com/en/
Interesting, looks like it could work, but I think the psychological effects of them knowing they'll die on Mars is too much.
Not to mention, it's pretty much a guaranteed that someone will die on Mars very publicly. A 2-year mission carries a tremendous amount of risk in terms of getting everything to keep working...
But an indefinite stay? It's pretty much by definition a "pull to break" test, that can only end one way, and not a way that will help space exploration's publicity.
Not to mention, they'll need repair capabilities for everything, either that or constant resupply shipments.
I think a much better idea would be a station. That's how it's always been done, and with ISRU coming back isn't that much harder than going there.
Stage the missions so that with each successive mission, more crew arrives than departs, so the colony grows, while some astronauts can stay longer than others.
It's especially good for such an isolated mission - I can recall at least one example of an astronaut that got depressed and had to be returned to Earth from LEO.
That capability simply won't exist with this mission. And they'll be staying a lot longer than 6 months.
#2 Re: Human missions » Sustainable Access to Mars: Interplanetary Transportation Architecture » 2012-05-23 20:26:43
MatthewRRobinson wrote:The point I'm interested in returning to is ERV vs. MAV+MTV. I haven't seen a reply to that yet, so I'm guessing we're agreed on ERV?
Most have trouble following the acronyms from one mission to the next as the function while being simular are way different in duration and or size....
[....]
ERV: Earth Return Vehicle,
An unmanned ERV is sent to Mars. At the next launch window, a manned ERV is sent to Mars. The ERV lands, and the crew ride either one back home at the next return window.
It's essentially Zubrin's ERV from Mars Direct, except I would personally prefer something reusable (and thus single-staged) and that can perform an aerobrake in Earth's upper atmosphere so it can be reused.
MAV+MTV refers specifically to the architecture used in MRDM 5.
MTV: Mars Transfer Vehicle
Large, trans-habbed equipped spacecraft that cannot enter an atmosphere, to serve as a habitat for transit in-between Earth and Mars orbit.
MAV: Mars Ascent Vehicle
Small spacecraft that only goes from martian surface to Mars' orbit, and possibly back again.
There's a lot of boxes to think outside of, in addition to the ones implied by the mission designs in the previous post. Two of my favorites are inappropriate holdovers from Apollo: one launch/one mission, and one mission/one landing. Those two are still part of many of the concepts in the previous posting, to one extent or another.
What you want to do is collect a list of tried-and-proven concepts, and then rearrange them outside the constraints of these boxes. You don't want to use anything not yet well-proven by the time you actually go. Significant ISRU ought to be tested thoroughly on the first manned mission to Mars (after very extensive unmanned testing both here and on Mars).
I'd be afraid to bet lives on it until after that final test, though. Just my humble opinion, being a suspenders-and-belt-and-armored-codpiece sort of guy, yet still unafraid to think outside some largely-unrecognized boxes, at the same time.
GW
As has been stated a few times, most mission architectures, those discussed here and those that NASA's seriously considered, involve sending any ISRU assets to Mars a full launch window before sending any astronauts. By the time the astronauts arrive, it'll all be fully fueled up. If it fails to fuel up, then mission designers and engineers will have to scramble to assemble a different launch scheme to send the assets to Mars fully fueled, and fix the ISRU technology.
The compression ratio is important because of product density (largely its pressure). Material strength need be only what is necessary to contain the product you require. Most of this chemistry stuff takes place at 1 to several atm. If 1 atm is good enough, the compression ratio from 7 mbar to 1013 mbar is about 140, which is doable in any of several ways.
Since I last corresponded on this thread, I found out about an absortion (adsorption?) compressor rig. You absorb CO2 at 7 mbar, confine the "sponge", heat it to drive the CO2 out, which is near 1 atm. It's an analog to the confined dry ice vaporization I suggested, except it works straight off atmospheric CO2. Works anywhere on Mars. The product comes out near 1 atm pressure, which is apparently chemically useful for synthesizing methane from CO2 and water. No super-high pressures there.
That'll work, we just gotta try it enough to work all the bugs out, before risking depending on it. Some of that can be done here, the final check being maybe an unmanned trial on Mars.
Purity is an issue to be evaluated. I'm not sure, but I think this absorption compression thing is the same basic technology that's in the oxygen system in the F-22. It seems to be having troubles, and I'd hazard a guess that's a purity-of-product issue. Mars's atmosphere is not just pure CO2, so the same risk applies.
GW
Well, once we've got it at 1 atm or more, then shouldn't purifying it be a somewhat simple process? Given that we have something on the order of more than a year to do it, it shouldn't require a very massive system to purify it by whatever method is deemed best.
#3 Re: Human missions » Land Crew in large pressurized Rover » 2012-05-23 20:20:20
Much like the other thread that MatthewRRobinson has ask with regards to and on the benefits of ERV, MAV and MTV the elements surface Habitats, ect.... These are all parts but until you link them together with the right words is just an alphabet soup.... even the athlete is just another piece to use in another manner for a set of mission words.
[...]
Well, it's really two different mission architectures, that specifically focus on how the crew gets to and from Mars, irrelevant of how the hab and other cargos get there:
ERV: Earth Return Vehicle,
Unmanned ERV sent to Mars. At the next launch window, a manned ERV is sent to Mars. The ERV lands, and the crew ride either one back home at the next return window.
It's essentially Zubrin's ERV from Mars Direct, except I would personally prefer something reusable (and thus single-staged) and that can perform an aerobrake in Earth's upper atmosphere so it can be reused.
MAV+MTV refers specifically to the architecture used in MRDM 5.
MTV: Mars Transfer Vehicle
Large, trans-habbed equipped spacecraft that cannot enter an atmosphere, to serve as a habitat for transit in-between Earth and Mars orbit.
MAV: Mars Ascent Vehicle
Small spacecraft that only goes from martian surface to Mars' orbit, and possibly back again.
Actually returning to the same spot is a bad idea in my opinion, I know many scenario's do that but your just going to be re-examining the same ground and to get good scientific data your going to want to explore several places far apart with each mission. This is how they did it in Apollo and it's the logical approach if your looking for knowledge. I think many scenario's involve repeated landings in one spot is because they are in a 'colony' building mind-set and want to accumulate hardware towards some kind of permanent base. This is false, the first missions will be scouting parties not the toe-holds of future colonies, their job is to learn as much as possible about Mars and scout for more attractive places to explore and resources that can be useful. Making camp on the first land you see is always a mistake, that's how the Pilgrims off the Mayflower ended up in freezing cold Massachusetts rather then their intended destination Virgina.
Btw with regard to Rovers, if our mass budget allows perhaps 2 rovers each massing 10-15 mt each could be brought in on one lander, that would make them each the size of a large Unimog but you would be looking at a fairly large payload fairing maybe 7 m to accommodate 2 side by side 5 m rovers.
Rovers are theoretically movable from one landing sight to another by topping off the fuel tank and sending them autonomously to the next landing sight if its within the vehicles maximum one-way range. You probably wouldn't want to count on it though, high likelihood of getting stuck in difficult terrain. A bit of Solar power that allows them to move at a slow but steady pace but with nearly unlimited range might be desirable if the future landing sights are known years in advance.
I think the best shot would be to save all those extra launches and rovers by just launching one, and maybe a second as backup, and put all the landing sites within one-way range of eachother, giving a good margin of error so the rover doesn't have to go to the very edge of it's range.
There's really no greater chance of it getting stuck on the Martian terrain transiting from one hab to another than there is a chance of it getting stuck in any other situation.
Unlike the MER's, we really can just send a guy with a shovel and/or jack out there if it does get stuck. But, once again, all issues faced transiting from one hab site to another are no different than any other excursion.
One interesting idea might be to have the wheels run on motors - the internal combustion engine is used to generate electrical power to charge the batteries. Effectively, the liquid fuel serves as an energy reserve to charge the batteries with. But you only burn CH4/O2 enough so that the batteries are always just slightly below a full charge.
That way, even if you don't run out of liquid fuel, the solar array will boost your range by providing some drive power even when the internal combustion engine is running, and it would make using the solar array as a backup much easier, since the solar arrays partially power the drive system all the time anyways. Not to mention, motors aside, an electrical drive system should be easier to repair and maintain than one that involves shafts and large moving parts. Mainly I say that because the area that has the best chance of getting scraped up badly is the chassis/undercarriage. A direct drive system from the internal combustion engine with large shafts and such would be extremely difficult to repair. But if all that's on the undercarriage is cables, then field repairs should be relatively easy.
That's something different designers of a Mars mission must face than the Apollo missions - the stuff doesn't just have to work and work well, but also should be easy to repair, even if worse comes to worse, because unlike Apollo the crews will be there for more than a year.
#4 Re: Human missions » Land Crew in large pressurized Rover » 2012-05-21 11:59:13
I notice that most mission architecture land the crew in an immobile Habitat type structure and then if mass budgeting allows a pressurized rover is inserted somewhere else in an um-manned cargo lander, it seems the rover is the first thing to get cut when mass needs to be shaved. As the pressurized Rover is critical to making long distance excursions and field studies any performance reduction their has a big impact on the science potential of the mission. I propose that instead the Rover be scaled up until it is a FULL EDL payload (~20 mt depending on the EDL architecture) and the crew be delivered to the Martian surface IN said rover ready to 'hit the ground rolling'.
Scenario:
The Mars Rover Lander (MRL) is pre-positioned in Mars orbit in a slow cargo flight. The Habitat the crew has used for the Interplanetary Transit (ITH) would brake into Mars orbit and then dock with the MRL for crew transfer and then the ITH remains in orbit and acts as the Habitat for the Earth return portion of the trip docking with a Earth Return booster stage with a long duration consumables module (ERS) in-order to make the return. In event of failure to dock with the MRL or a determination that it is unfit the surface landing can be scrubbed and the docking made with the ERS instead with a wait in Mars orbit for the return window to open.
On successful landing of the MRL the crew is inside a functional vehicle charged with 2-4 weeks of consumables and the main stock of scientific equipment. The Rover brings the crew to the immobile Habitat lander and Assent Vehicle and can house the full crew on long duration excursions and then return to the Habitat and ISRU and/or Power sources for recharge/restocking.
...
The thing that I don't like is that this is extremely unsustainable. It's that lack of valuing reusability that led to Apollo dying so quickly, as opposed to the Space Shuttles, which despite being extremely expensive, kept going for 30 years. Not only would you need to design a large, lightweight spacecraft that can survive EDL, but it also has to do it and then start driving around afterwards? It's not too much of a leap, unless you plan for the thing to take off again. But that's exactly the problem; it can't take off again.
I would say, I like the proposal... Conditionally. If, it is only used for one or two missions, and the rest use a different architecture. The MRL would be a great asset on the ground, there's no argument there, but as a lander I consider it a serious failure because it can't take off again. Just imagine if in Apollo we had to launch two Satun V's for every mission, one to land a LEM, and another to land a big rover. Now hopefully you see where my objections are coming from.
Also, consider that you're lobbing around a lot of extra weight carrying the MPS used for landing on the rover. It's not a problem on the HAB, but on the rover you need an engine to move the whole thing, so that extra weight is really going to hurt your range, which will have a huge impact on what science can be done.
Alternatively, I would propose giving the rover standardized "racks" and slots where different scientific packages can be carried. Instead of taking all the scientific equipment with you wherever you go, just take some of it. If you're driving off to do scientific mission X, there's no reason to carry the big scientific package to do scientific mission Y, that's a waste of rover range. Especially when it comes to equipment like drills. No reason to carry that big rig along when you're doing an unrelated mission; you can just leave that at the immobile hab and give yourself more range with the weight savings.
And I's also suggest some way of getting rid of the MPS and other such weight. It could probably be very easily done in a way it's been done before; put all the MPS and such lander, non-rover mass on a pad that the rover sits on, like like what's been done here. Or, alternatively, you might even use a sky crane system like MSL, or maybe even a combination of the two. But however you do it, I highly recommend somehow getting rid of lander MPS mass.
Advantages:
Interplanetary transit Hab dose not need to be designed for Martian EDL and can be re-used for Earth Return. Likewise no 'throw-away' minimalist landing capsule.
Personally, I'd favor an architecture where you don't have to throw-away anything. Though, like I said, I can't argue that such a rover would be an enormous asset.
The Scientific equipment can be stowed on and integrated with the rover allowing significantly bulkier, power-hungry equipment (drill-rigs?) while also elimination surface logistical work of moving equipment to-and-from another lander or a laboratory inside the immobile habitat. The Rover takes all equipment with in ware-ever it goes.
I already replied to this one, and I do agree, except that the rover should take some equipment, depending on how much mass savings it can turn up. If most the packages are pretty light, then I'd go ahead and let them stay on the rover. But heavy rigs like a drill rig, should be detachable to allow for longer-ranged missions.
A larger 'maxed' Rover's power-train and structural frame should allow for higher speed/safety (sliding scale, pick your preferred point) during excursions.
That's an advantage? It sounds like extra weight. Extra weight that's worth what it brings (a mobile lab almost), but I wouldn't list that as an advantage.
Full Crew in Rover avoids splitting up the crew during long excursions allowing all critical skill sets (science, engineering, medical) to be present at all times for crew mutual-support (like Lunar Rovers buddy system). Also avoids difficulty of maintaining communications between Rover and distant Hab.
Rover is sufficiently robust in Life-support (weeks without recharge) that it functions as a life-boat in case of main Hab failure. Repeated Repair attempt EVA's can be made from the Rover to attempt to restore primary Habitat. With access to ISRU plant and outside power life-support could be maintained even longer, albeit at a level so cramping that it would be deleterious to the research objectives.
Definitely agree there. If used in combination with the ERV architecture, that means there'd be three entirely separate redundant life support systems. NASA's rule of three. They'd be happy with that, as would anyone else in the aerospace industry.
Accuracy of landing ellipses necessary for mission successes vastly reduced to levels at or below current capabilities. Only a failure of landing accuracy AND rover mobility strands the crew unable to reach the Habitat before consumables are exhausted. Adjustment to Martian gravity can also occur without haste if the crew is coming from a 0g or less then Martian g condition during transit.
If you use an ERV with a powered descent phase, then that problem is handled. You could even package a very small unpressurized moon-rover like "buggy" with the ERV in case somehow you land a few too many km's away to walk.
No comments on the other 4 advantages, other than a nod.
Also, this whole time you've seen me keep mentioning an ERV. I agree with the idea of landing a rover, or even landing the crew in a large rover, but I think doing away with an ERV is a big mistake. IMO it's just outright nonsensical to use ISRU and make it a mission-critical aspect in the sense that the MAV requires it, but not use it to produce the propellant used for TEI. It's even a little comical. It's like MRDM managed to get the disadvantages of both without getting the advantages of either.
ISRU/ERV
+ Much lower mission mass
- New Technology becomes mission critical
All-up Propellant
+ Safer
- Much more mission mass
ISRU MAV + All-up ITH
- Compromised mission mass (Because aerocapture is impossible, the compromise is far towards the "heavier" side)
- New technology becomes mission critical
If you're going to bring along the ISRU equipment, you'd might as well use it for everything; it's not going to make any difference in safety, and it's going to save an absolutely tremendous amount of mission mass. Not to mention, it means your ITH (which is now an ERV) is already equipped with a heat shield to allow for aerocapture into Mars orbit. And, to add another point, as opposed to a MAV, the ERV would be another backup life support system on the surface that could be not only used for an emergency, but used for months, during which time the crew could continually attempt repairs on the HAB and Rover.
Impaler:
I quite agree with you. Leave the transfer habitat in orbit for return. That provided a huge payoff in Apollo. Why sacrifice the benefits of "lunar orbit rendezvous" at Mars?
Because in Apollo we didn't have ISRU to save mission mass.
The lander could be itself the habitat, as in Apollo. Or, maybe not, if its engines are solid core nuclear, as in NERVA. Who yet knows? Depends upon what we might get operational in the next 5 years or so.
It would be handy to have at least a small shirtsleeve environment on the surface in which to eat, sleep, and do whatever lab work supports "exploration". That last item is far more important than it might sound, and is something we did NOT do on Apollo. That surface habitat could be nothing more than the inflatable version of a Quonset hut. That engineering problem is not all that hard to solve.
As for rovers, it's design depends mostly on the size, mass, and endurance of the astronaut's spacesuit, because that is the "payload" for every astronaut being carried. Why not consider a mechanical counterpressure suit? They are 2-4 times lighter, and unbelievably more supple than the "traditional" gas balloon suits we currently use.
If we were to back off from the arbitrary NASA requirement of 1/3 atm equivalent body compression, to about 1/5 to 1/4 of an atm, we could build one today in the lab that worked (we already did, way, way back in 1969), and we could "develop" it to a usable form in about 5 years, given the "right" contractors.
A lightweight astronaut/suit requires FAR LESS of a rover, maybe even one that is unpressurized (just carry an inflatable Quonset hut with you). Such a thing might even be able to "fly" on rocket engines to very long ranges, compared to what we are used to thinking about (surface battery cars). Liquid propellants really do store more energy per unit mass than any battery ever imagined, so far.
Flying rovers; an idea worth looking into, maybe, but that's a lot of extra mass for MPS. And just look at the range of a car 2-ton SUV with a 20 gallon gasoline tank, and try to get that same range with a 2-ton rocket with a 20 gallon gasoline tank. No reason that the rover needs to be battery-powered. You're right in that liquid propellants store more energy, so the rover can just use an internal combustion engine designed for CH4/O2. Liquid-fueled internal combustion engines are something we have plenty of experience with 
The only disadvantage, is that you can charge a batter with solar panels or nuclear powerplants that provide semi-continuous and continuous power, respectively. But internal combustion is a different story. For that, I'd imagine the same ISRU plant that produced our ERV's propellant could also fill some large storage tanks with propellant for our rover.
Alternatively, or maybe even in addition, you could put solar panels or an RTG on the rover and give it unlimited range. Albiet, once you run out of liquid propellant, you'd be moving a lot more slowly, though it does mean in the event of an emergency you'd eventually get back to the hab, MAV, or ERV.
Gotta think way outside the "traditional boxes" to really solve these problems. There are a few of us (very few) who did that professionally. From 1976 until 1994, I did exactly that, for aerospace/defense applications. And I was very good at it. Space travel stuff is really no different.
That's why I come up with these wild-seeming ideas. If you look closely, they might actually work. Maybe, they are not really so wild after all.
GW
At the very least they're thought-provoking 
#5 Re: Human missions » Sustainable Access to Mars: Interplanetary Transportation Architecture » 2012-05-21 11:00:21
On the compression thing: I cannot claim to be familiar with everything that has been proposed. I am familiar with recip and turbine. And basic thermodynamics. Yes, we have compressors on submarines that charge air banks from 1 atm to 500 atm. They are gigantic, heavy things, carried by a sub weighing 4-7000 tons. That kind of thing does not miniaturize well. And, we're talking about a compression ratio final/input of 500.
Most of the aircraft compression machinery we have is under-30 for compression ratio, most of them under 15 or so. What goes on in a shop air compressor and what goes on inside a piston engine are comparable at compression ratios in the 6-11 range. All of these devices are light enough to fly, and all of them miniaturize well. It is the lower compression ratio that allows them to be miniaturizable and be flightweight.
Mars's atmosphere is 7 mbar, except up on the highlands and mountains where it's nearer 2 mbar. But let's go with 7 mbar. Picking a challenging miniaturizable/flightweight compression ratio like 30, that's a bottled gas pressure of 210 mbar, or about 20% of 1 atm. Most of the chemistry processes I know of take place at 1-30 atm. Well, it seems like that might be a serious problem. Although, exploring low-pressure chemistry is something we can do, right here. But dollars to doughnuts, I'll bet you it ain't ready yet to go to Mars.
On the other hand, lets look at the submarine high-pressure air bank compression ratio of 500, and use that at 7 mbar. 3500 mbar, about 3.5 atm, that's usable with chemistry processes we already use industrially. The only problem is the huge tonnage of machinery for a throughput that scales down directly with inlet density (about 0.6% of that here). Heavy, inefficient. I see not much promise down that path.
Take some dry ice frost, pack it tightly into a steel can with a valve and an outlet pipe, and seal it up. Heat it with low-grade energy (solar thermal would work, albeit slowly). The CO2 vaporizes, but cannot expand, so the pressure rises by the specific volume ratio at a constant process temperature. That's a factor in the hundreds to around a thousand (don't have a thermodynamic properties table for CO2 handy).
There's a compression ratio comparable to the sub's high-pressure air bank, done with steel cans, high-pressure tubing, ordinary gas bottle plumbing, and a solar-thermal panel. Admittedly, it's a batch process, not so amenable to robotic operation. But it could be done. All you need is a source of dry ice.
That's the numbers for the kind of problem we are talking about here. If you want to make methane and oxygen out of CO2 and H20, on Mars, the poles are the place to do it. Unfortunately, that's not where the first landing(s) will take place.
That's also a part of my point: every site on Mars is different. There is no one "average Mars" we can put in a simulation chamber here on Earth.
GW
Okay, as someone far less knowledgable, I have a lot of respect, but something about this greatly bothers me.
Pressure is a force exerted over an area. Material strengths retain a set amount of force. So I don't think you can use compression ratios to determine the type of mass requirement that a system will have. Not to mention a submarine's air charge system needs to work in minutes, not years like an ISRU unit, and they have no need to be lightweight, and as such are built with very heavy materials. Isn't that all a bit like saying we can't build a Moon rover because jeeps are so heavy?
Back to my earlier point of pressure, I really don't actually know, but I think material strength means that a material can take a certain amount of force loading before breaking, right?
If so, then you can't use compression ratios at all.
Let me compare a compression ratio of 500 from a submarine's air charge systems to a Mars ISRU unit, working with one square meter of material, and how much material strength it needs (directly proportional to the net force on the material).
First, the submarine. Pressure from outside (because we're working with one square meter, I'm replacing pascals with newtons) is 1 atm, which on one square meter is 101,325 newtons.
Force on the inside, 500 atm, is 50,662,500 newtons per square meter.
So, simple vectors say to subtract, not to divide. So the force that the material will need to withstand is 50,662,500 N - 101,325 N = 50,561,175 N
Now, the Mars ISRU.
0.7 mbar = 709.275 N/m^2
3.5 bar = 354,637.5 N/m^2
At one square meter;
354,637.5 N - 709.275 N = ~353,928 N
Which is compared to
50,561,175 N
Which means a submarine's air compression systems must be built to withstand 143 times greater force per exposed surface area than an ISRU unit.
I'm not arguing compressor design, I know next to nothing about that aside from pistons, what I'm saying is that all the parts exposed to the charged air in a submarine must withstand a much greater force of pressure than the parts in an ISRU compressor.
And as for ISRU as a whole, the thread is really about mission architecture, so if you don't want to bet human lives on it with the first landing, then the three leading architectures (at least as I see it) and the only ones NASA's seriously considered, MRDM 5, Mars Semi-Direct and Mars Direct, all are designed so that we don't bet human lives on ISRU working. As RobS said, there'll be a fully fueled Earth Return System (be it an ERV or MAV+MTV) waiting on Mars when the crew arrives.
The point I'm interested in returning to is ERV vs. MAV+MTV. I haven't seen a reply to that yet, so I'm guessing we're agreed on ERV?
The the mission architecture is starting to look a lot like Mars Direct, albiet using reusable vehicles instead. Differences: A single-stage ERV that can perform aerocapture for EOI, dock with a booster or a few in LEO, and get launched on TMI by boosters that will either free return around Mars back to Earth and EDL, or just EDL from a highly elliptical orbit. Thereby making every vehicle reusable, except of course for the ones that are staying on the Martian surface.
Aerocapture EOI is perhaps the weakest point. On the first pass, we only need to capture into a highly elliptical orbit, though, no need to burn 2 km/s lowering the apoapsis if we can come back and do that later, and thus make the burn a lot less intense. All that's needed is to drop below escape velocity, into an elliptical orbit to perform another aerobraking maneuver at periapsis to drop into LEO.
So, then, what kind of Delta-Vee is needed? Since we're leaving Earth with 4.2 km/s, I think it's safe to assume our return velocity will be in a similar range, about 4.2 km/s above LEO velocity, for a total of about 12 km/s. A velocity of 10 km/s at about 70 km altitude gives an aposapsis of only 27,000 km, far below geostationary orbit. Or, alternatively, you could save .8 km/s of atomspheric burn and initially enter an orbit with an aposapsis halfway to the moon (120,000 km). So the arrival aerocapture scrape only needs to burn off 1.2 km/s, starting at 12 km/s. Surely the small delta-vee makes this doable, despite the high initial velocity?
#6 Re: Human missions » Sustainable Access to Mars: Interplanetary Transportation Architecture » 2012-04-26 00:04:29
"But, working off the assumption of 4.3 km/s for a free-return, and an ERV amassing 32-34 tons (with LH2 for ISRU), the ERV could be sent to Mars with 3 F9H launches, two boosters and the ERV itself, though an MTV would mean an additional launch for a total of four, or even more, depending on how the packaging can or can't be arranged."
Can you expand on that? 4.3Km/s for free return? Have to know exactly what you're getting at
Sorry if I glossed over things a bit too quickly - the 4.3 km/s figures just comes from earlier in the thread, I really don't know much on free return trajectory calculation, but the page you linked stated 4.2 km/s for less than 180 days to Mars, and I know the trajectory for an Aldrin Cycler takes about 4.45 km/s, so I think it's fairly safe for now to work off of the 4.3 km/s figure stated earlier in the thread, though sometime - maybe this weekend, I'd like to check it's validity and get more info on free returns.
What I meant was, in an ERV-type mission, you could send an ERV on TMI with 3 Falcon Heavy Launches. Two of the launches would carry a booster each, and the third launch would carry the ERV itself, for a total of two boosters and the ERV.
Meanwhile, the total mass required for a propellant-filled MTV, according to some estimates I ran, would require four full launches, and maybe more if the packaging can't be arranged in four launches.
Thanks for asking, it's much better than posting a reply without fully understanding, lol 
#7 Re: Human missions » Sustainable Access to Mars: Interplanetary Transportation Architecture » 2012-04-22 16:18:27
Ok, let me add some more random speculation here..
I've started with figures from this:
http://smartech.gatech.edu/jspui/bitstr … tories.pdf
What they say is, 4.2Km/s from LEO will get you to Mars in under 180 days.
Likewise, 3Km/s from LMO will get you to Earth in under 180 days.[...]
Back tracking and you now need again a mass ratio of 1.6 so you've started in high Earth orbit with 65 tonnes. That's as opposed to 81 tonnes where you take your fuel all the way, but only to orbit.
Of course I've left out the issue of getting the capsule fueled. But then I've also left out on the flip side the issue of the extra mass the vehicle now needs to land, and by virtue of this extra structural strength to cope with actual landing.
On the basis of this crude calculation, would you save much mass? Probably. Enough to make a difference? Probably not. Its only a crude comparison and the devil is in the detail but my take on it is you can make it to Mars, safely and elegantly, with conventional propellants - and personally I'd prefer to have the safety in having something in Mars orbit at all times.
Cheers
Brilliant work with the elliptical orbits! That's actually a bit of a game-changer the mass savings are so drastic.
But, working off the assumption of 4.3 km/s for a free-return, and an ERV amassing 32-34 tons (with LH2 for ISRU), the ERV could be sent to Mars with 3 F9H launches, two boosters and the ERV itself, though an MTV would mean an additional launch for a total of four, or even more, depending on how the packaging can or can't be arranged.
The difference is only 75% the launch mass, and personally I don't really see the benefit of having a spacecraft in orbit, maybe a GEO satellite or even use the MRO that's already there for communications, but a manned habitable spacecraft sitting unused in orbit for about two years just seems like a bit of a waste of mass.
Essentially, an ERV is a MAV and an MTV already docked together - albiet a bit less luxurious, more along 15-25 m^3 per person instead of the ~50 of an MTV (The Shuttle had ~8.6, IIRC that it had 60 m^3). What this means, is that you have the safety of having something in orbit at all times, except instead of having to launch a MAV and go dock with it - it's already sitting right there.
#8 Re: Human missions » Sustainable Access to Mars: Interplanetary Transportation Architecture » 2012-04-17 20:53:11
Well, it goes like this. If you have a place of safety both on Mars and in orbit, you're in a very good position when things go wrong. That would be my ideal.
That thought crossed my mind, but then again, it's not like you can take it home unless it's during a return-launch window, so it's still not that much different from a vehicle that's only there during the window. Though there is an argument to having an extra life-support system nearby, but even to that, can an orbiting vehicle support the entire crew for additional months than the months already needed for Mars transit? At some point you're going to have to accept some risk, and I think having so many backup life-support systems is past that point. We already have a rover, a HAB, and at least a MAV on the surface, assuming there's not an extra MAV filling it's tanks with ISRU for next mission. That's 4x the options Apollo had, granted it's a much longer stay, and I don't think 5 life support systems has so much advantage over 4 as to warrant two additional very costly delta-vee maneuvers (MOI, TEI), 5/4 is long past the point of diminishing returns. The safety standard has been 3 systems, so I'd think 3 life support systems is optimal.
Connecting up with something that is already on a free return trajectory means accelerating to Mars escape velocity. And it probably also means having little remaining fuel. So you've committed yourself to deep space.
Now, I've got very little problem with the task of actually docking. Or put it this way, provided something else doesn't go wrong, I trust the navigation system more than anything else.
But what can go wrong? Well, propulsion failure of one sort or another. Mostly this will put you into a high orbit. And maybe you can recover from that. But there is a small window into which you can put yourself into Mars escape but then fail to dock. Then you're on a free return trajectory that most likely will come somewhere near Earth but someone will have to go send a rocket and some duct tape for you to manage to recover.
Unfortunately, I don't think it's really possible or practical to have a backup for a failure in-between escape velocity and TEI, or when the mission first launches, escape velocity and TMI. If you're on a course that will keep you from docking, then you're probably on a course that won't take you near Earth - that problem is just as present with or without free return, though. And really there's no possible "safety net" for a total MPS failure in that velocity window. Instead, we just make the MPS more trustworthy by doing things like using more than one engine (MRDM uses 3, a bit overkill IMO). One idea I like might be to have your RCS use the same propellant as your MPS - if the MPS fails, you can use RCS thrusters to finish the burn, granted it'll take much longer.
Or, like Dragon, just use your RCS in the first place. Using dozens of thrusters built with great endurance should be very safe.
There are of course worse failures.
I don't mean to argue too much here.. I'd like to see a free return idea work but for me to feel comfortable with it, you'd have to show me a rocket that's simple, has been tested on Mars itself, and is obviously reliable. Probably meaning you've taken some compromises in performance too.
Oh, and the other thing about free returns is the kind of failure where nothing goes wrong - its just that you've failed to launch into a tight window. That to me is more likely.
With a target that's orbiting, you get a second chance.
That, I think, is by far the best argument against free return, and the only one that has me really doubting it. I wonder what it takes to design the rocket to launch in a dust storm? How fine is the dust? Will the vehicle need extra shielding for it? When it comes to starting the engines, I'm sure you'd want to purge them first. But one very serious threat might be dust gathering in the combustion chambers of the RCS. Maybe you could cover them after the initial landing, then run a check and make sure they're clear before launch? Or maybe even make an RCS purge system...
That eliminates a dust storms keeping you from launching, but since those can last months, you may want that ability even if you're not doing a free return docking. The real issue, is a system on the MAV/ERV failing and the vehicle being unusable until the window closes. Most architectures I've seen have two such vehicles, though, so you could simply use the backup. And on top of that, any failure will probably mean that vehicle is out of commission, anyways. It's a small window where the failure is major enough that you can't launch with it, but minor enough so that it can be repaired.
And, worst to worst, you could just make the MAV/ERV capable of sustaining life for the entire trip back, just on low rations and small space.
To be fair, though, at that point there's really not much of a reason to make it dock with anything.
And also, to be fair, I admit it is possible a system could fail that could warrant a shut-down and restart which would make you miss the launch window, that would be very possible.
Oh btw.. Perhaps if you're looking for a suitable compromise its putting a vehicle into high orbit - even a week long one if you wish. Deimos transfer orbit might be worth looking at - that saves you half your DeltaV over low Mars orbit. I actually had that in the back of my head earlier.
Also, you can have hybrids where at some stage you capture into low orbit for convenience of refueling, but then use electric thrust to get you to a high orbit. Like I said, one thing we do have is time.
Rather than a hybrid (which would add a huge amount of complexity and cost to the vehicle), If I was going for MOI, then I'd just refuel it in orbit. As for your MAV ferry, I'd consider making it like the ERV - give it a much higher mass ratio than necessary, and use propellant from the main tanks to fill the MTV. Granted, though, that that re-fuelling in orbit incorporates a lot more risk into the mission.
~
On the topic of MAV+MTV v. ERV in general, one of the worst decisions I've seen was MRDM v5. Keeping the MTV in orbit saves mass on having to take the Mars Transit life support and cabin and having to land it and take off again. So I can see the point in that. But then, they decided that refuelling it in orbit would be unsafe, so they brought along the propellant from Earth, so overall that drastically increased the mission mass. That's just insane, to me.
You did have a fair point on capturing a free-return MTV; if a vehicle system fails before/during launch, then you miss the capture.
But if you keep the MTV in orbit, then you either
1) accept the fact the risk is greater, because of the many launches to refuel it in orbit
(The launches may not have to make a tight window, but we're talking about a spacecraft that can launch multiple times from the ground (not a pad), with absolutely no ground support; so it's impossible to inspect, refurbish, or service the vehicle to any significant extant, and there's no ground infrastructure to handle it, and if it fails once, then the entire mission is doomed without any possible abort/contingency.)
2) accept a drastically higher mission mass because it brought the propellant from Earth.
In either case, it seems facing this situation, the very best solution is just a big ERV that sits on the surface.
-You don't have to make any tight launch window, like with a free-return MTV
-You don't have to bring the propellant from Earth
-You don't have to take many risky launches to refuel it in orbit
So it either saves a lot of mass, or it makes the mission drastically safer.
I realize I started this post advocating a free-return MTV, but by now, upon looking at it in detail, I think the above points very strongly make an all-out surface ERV the very best case.
*An orbiting MTV with propellant from Earth drastically increases mission mass.
*An orbiting MTV refueled in orbit drastically increases mission risk.
-You could make the MAV capable of TEI, but then there's not much reason to have the MTV aside from showers and comfort; at that point, your MAV is almost as massive as a full-up ERV, anyways. Overall mission mass could probably be reduced at this point by dropping the MTV and making the MAV an ERV.
*A free-return MTV is also a lot more risky.
Overall, I just don't see anything better than an all-out ERV. It's either a little heavier but much safer, or much lighter and just as safe.
#9 Re: Human missions » Sustainable Access to Mars: Interplanetary Transportation Architecture » 2012-04-16 21:16:32
"I don't see where the mass saving is in doing that, though. The propellant for TEI is still gained via ISRU on Mars, in both cases. Merely the architecture means you don't need ISRU propellant to lift the mass of the Mars Transit Vehicle from Mars surface to MO. But the propellant for doing that in any case is provided via ISRU, and it would probably cost a lot more total mass, actually, because you have to lift the ferry from the surface to MO, land it, and repeat, probably quiet a number of times."
Its not really intended to save Mars-derived propellant. In fact it probably requires somewhat more. What it does save is on development costs and time and emphasises safety. You'v got numerous abort options and one thing I really like is designing for the situation where what you're trying to do isn't in the manual.
As for the comments about boosters and the final line.. Can you explain more?
I'm happy to answer more specific questions too.
I, too, like the idea of using components common to multiple vehicles. But one thing, is, though, that the only major difference in-between a larger craft and a smaller craft would be tankage and structural components. You could use the same type of engines, for example, just use more of them. Avionics, ECLSS, powerplants, etc. could all still be common to both. The vehicles have enough differences already so that they can't be the same type of vehicle, like Endeavor and Discovery, don't they? What differences do they have?
As for the boosters, it's really the simple architecture RobS mentioned in the reply to the OP, and I built on it. A Falcon 9 RLV lifts 60% the payload of a non-RLV Falcon 9. Applying a very similar number to the Falcon 9 Heavy (F9H), and we assume the F9H RLV can lift 32 tons to LEO.
Make multiple boosters, all identical. They're very similar in design to the upper stage of a Falcon 9 RLV, Pica-X heatshield, can return and land on Earth, and they have a dry weight ~4 tons or less. They don't need significant thrust, and they have docking rings that can connect them to eachother and can quickly separate.
You launch 2-3 boosters, depending on how much umph you want (low energy, high energy, small payload, larger payload) using F9H RLV's, then you launch the payload to be launched TMI, and the whole thing docks together as an assembly.
The boosters perform TMI in a staged manner, separating upon burnout. All of the boosters, except the final one, will be in a highly elliptical orbit around Earth. With a small delta-vee at apogee, either immediately or after a few orbits, they can re-enter Earth's atmosphere and land just like the F9 RLV's second stage.
For the final booster on TMI; you have two options. If Mars needs a booster, then you have it land on Mars with the payload. If not, then it performs a Free-Return and re-enters and lands back at Earth.
That's how to launch stuff to Mars.
Now, for what "stuff" you launch at Mars, I need to do a little more research on that.
When doing ISRU, what fraction of the final propellant produced on Mars do you need to carry in LH2 from Earth?
(Ex, 6 tons from Earth: 30 tons on Mars. What's the real ratio?)
I toyed with the idea of making elements free-return and every time I thought about it I didn't like it when it came to human safety.
What's wrong with human safety on free-returns?
#10 Re: Human missions » Control cost or go home » 2012-04-15 19:20:25
Louis, why are you talking about building rockets on Mars? I could see it several decades after human arrival, but sooner? The Falcon system is designed to be reusable. The Falcon second stage masses about 53 tonnes, fueled, and is being designed to return to the Earth's surface from low Earth orbit. A Falcon Heavy could put an entire second stage into Earth orbit and after it burns its fuel to send cargo on its way to Mars, the second stage could actually land itself on Mars, where it could be refueled and used as a rocket. It looks to me that Musk has the problem of supplying Mars with rockets solved already.
Besides, 100 people would build a pretty primitive rocket; the Falcon system requires a thousand or two. Why should 100 people build a primitive rocket when they can get a sophisticated one that has been tested many times?
Only issue is, you'd want to use a reusable Falcon Heavy. The Falcon 9 RLV would reduce launch payload by 40%. Apply the same to the Falcon Heavy, and that's 31.8 tons into LEO, not 53.
So you'd need a new vehicle, but the technologies of the F9 RLV upper stage will both produce and prove those needed technologies. Essentially you could launch a smaller F9 RLV upper stage, that weighs 31.8 tons instead of 53.
Amazing subtlety, though. 53 ton payload, 53 ton upper stage! So maybe they'll launch a "booster" (RLV upper stage) with a non-reusable heavy, but a payload with a reusable one? Anyone know the mass ratio of a F9 second stage?
RobS wrote:Louis, why are you talking about building rockets on Mars? I could see it several decades after human arrival, but sooner? The Falcon system is designed to be reusable. The Falcon second stage masses about 53 tonnes, fueled, and is being designed to return to the Earth's surface from low Earth orbit. A Falcon Heavy could put an entire second stage into Earth orbit and after it burns its fuel to send cargo on its way to Mars, the second stage could actually land itself on Mars, where it could be refueled and used as a rocket. It looks to me that Musk has the problem of supplying Mars with rockets solved already.
Besides, 100 people would build a pretty primitive rocket; the Falcon system requires a thousand or two. Why should 100 people build a primitive rocket when they can get a sophisticated one that has been tested many times?
You may be right. It's difficult to keep up with Musk. He is a game changer and one day he will be recognised as such.
It could be that he makes transit costs so low that my concerns our now irrelevant.
My concern is with the economics more than anything else. Far flung colonies often effectively subsidise imports. I was thinking this is a good way for the Mars colony to subsidise imports which will help it grow and prosper. If the Mars colony doesn't make Mars-Earth transit cheap then it will be obliged to pay hugely inflated prices for imports.
I think this approach may still be relevant. A Mars colony can set the transit costs at $0 if it wishes i.e. it can supply all the rockets and fuel for nothing. That will make communication between Earth and Mars cheaper than between the USA and China. Obviously it cannot do that in an unlimited sense, but by doing that it creates all sorts of economic opportunities that will generate revenue and expand the colony. Space X, even with all its resources, might find it difficult to offer such huge subsidies.
However, I am certainly not dogmatic on this point. If Musk and Space X can offer cheap reusable rockets then I am more than happy with that. I don't think the Mars colony should build rockets unless it is important to do so. There are other high priorities e.g. energy generation and agriculture.
Really quiet amazing, if you consider this;
The reason you could make it on Mars for $0, is that Mars would operate under a "command" economy, there would be no such thing as money, so long as it's a mission and not a state or colony. In other words, you're just assuming you can plop down the systems to build a rocket, and demand people build it for no pay. Of course, if these are people who have a strong work ethic, love their work, or share Musk and Zubrin's vision, then they would. But you can't gaurantee that once the population becomes a real population, rather than astronauts in a station.
The astronauts in the ISS do what ground control says, because that's kind of their job. They're being paid for it back on Earth, and they love it.
But it's different when they're actually permanently, living there. Paying them in Earth money, to spend on goods on Earth, won't work.
Of course, saying "do it or you won't get vital shipments" might work, but that's outright hostility.
Personally, to keep this issue from coming up, I'd keep it to the basics. Everyone there, or at least 99% of them, will agree that the colony needs to be self-sufficient. Once it becomes self-sufficient, they will be true Martians, independent of Earth. What they do from there will be their own choice.
As you said, however, it would be in their best interest to attract more Martians, to expand their economy, add redundancy, etc. But how do you incite people to work? In the Soviet Union, "people will starve if you don't farm harder" simply didn't work. Enforcing work by law would be a tyranny. You have to pay them. But what good is money when there's nothing to spend it on? You'd need a Martian market so money has value (Selling/buying food, parts to keep systems running, machine shop and 3d printer services, etc.).
A business might also offer tickets to Mars for free, if they enter a service for a few years. Their service for a few years, and a small salary to keep them going, pays for their ticket to Mars.
(You have to remember money is nothing more than a measure of "Work * Time", the work that they put into making rockets would need to be greater than the work it takes for the rockets to fly back and forth, thus earning the business profit.)
More interesting than any the issues addressed, though, is that we're having to address issues of this kind at all. You have to remember, once you get to colony, you're dealing with establishing a new World, quiet literally, not just a mission to the moon where they're professional astronauts that stick to a plan, a colony is making a society.
#11 Re: Human missions » Sustainable Access to Mars: Interplanetary Transportation Architecture » 2012-04-15 18:40:40
I think if this "getting to mars and back safely" problem can be solved in a way that everyone can see is optimal, then we've got to start putting on the table exactly what principles we are working with, use every physical trick we have at our disposal, and exhaustively (and methodically) work through the space of all options.
And indeed a lot of the tricks (or tools) being used are about saving fuel. Which in and of itself is a reasonable goal.
It has to be said though, that as launch costs go down, it gets harder to justify doing some things that may save some fuel. Or put another way it gets harder not to use fuel where it would either add to safety or save money in avoiding complexity or development costs.
Presently we're talking about potential near term costs in the order of $2,500 per Kg into LEO. That figure might go down to $1,000 if Musk has anything to do with it.
This crew are promising $500, specifically for fuel
Even if you work with the more conservative figure then 100 tonnes of fuel costs $100M. Yes, ok, I'd love that for pocket money, but it starts to become a second order problem relative to all the development costs and hardware involved. Yes in the decades to come we're going to have to get better at it still (and options like fusion propulsion come to mind) but if we're talking about exploration and about the near term (next 15 years) then I personally wouldn't worry too much about fuel. I'd simply not want to waste it.
A very interesting concept. It'll be interesting to see what becomes of it. But, I'm somewhat cynical. Wiki says some guns have gotten up to 11 km/s, and that's pretty surprising. But aerodynamic drag goes by the velocity squared, and currently rockets that leave the ground with zero speed and accelerate from 2-4 g's in the atmosphere, suffer something on the range of 2 km/s losses from aerodynamic drag. That's while traveling below 1 km/s.
IIRC, some early rockets (The Mercury-Atlas?) experienced a max Q around 10,000 pounds per square foot, at 6 G's liftoff.
So, the pressures they'll be working with for max Q, with the velocity they'll need to overcome aerodynamic drag, will both be extremely extravagant. Granted, an ice cone with a SRB on the back might be able to take a lot.
It'll be interesting to see how this technology goes... While I think there's a fair chance it'll work, I wouldn't be depending on it.
Now about the architecture. Obviously, every bit of mass you don't have to re-accelerate is a bonus. More importantly though is this. Every bit of mass you don't have to get back off Mars is even better. Hence my allergy to huge earth return vehicles with engines sized to get all that fuel off the planet all in one go.
As regards to the starting post on this thread, we save on energy by having the "bus" not capture into Mars orbit and thus enjoying a free return. Fair enough. But remember the energy saved is only on the mass of the (nearly) empty bus itself - which I take has been built fairly lightly to start with.
The point, actually, isn't to save the mass of the dry bus, but to save the expensive hardware that makes up the bus.
We then lose in terms of the safety issues from "missing the bus". Yes, it can be done if you have to. But you are adding risk and then begging the question "can it be done better?"
Like I said, the ERV would have enough supplies to return on low rations, having been refilled from the surface habitat. Upon arriving to Earth, the dragon capsule portion could separate and re-enter. Loss of ERV, but crew, capsule, and Bus all still survive.
Another issue is that yes, you can save fuel by having a low mass space habitat. But there is a lower limit - because mass equals shielding. Now, I've also thought about arranging tankage to provide extra shielding - and that in itself is a good idea. But the problem there is you can only rely upon the shielding of the relatively thin walls of the tankage. The fuel itself would provide good shielding, but the problem is, you use the fuel up as you go. So again, I think that sets a fundamental minimum to the mass of the space hab.
That isn't to say though that you can't engineer a lighter space hab with the same level of radiation protection simply by making it smaller. Its just that it gets rather cosy as you do..
I think the need for radiation protection is rather over-rated. IIRC, the exposure for even a 6-month journey would be something that would increase your chance of cancer by a small percentage in the later years of life. In fact, I was even thinking of doing away with the whole Bus' design and just using a single propellant tank. Because the real threat is CME's, and other such solar storms. Those can release enough radiation to kill. So, use a single propellant tank slightly wider than the habitat, and point it, and the engine assembly, at the sun. Free enormous radiation shield. Of course, inside the habitat you also use the supplies (food, water, etc) to make a sort of radiation shelter to further increase protection.
We still have unresolved issues to do with EDL. And I'd be worried about reclaiming parachutes. You'd have to retract it in a relatively short time whilst still in the air, and maintain your vertical descent enough to avoid it folding on top of you. Not a big problem. But again, if you apply the principle of total reusability you can get yourself tied in knots - reminds me of the folks trying to design the Plastiki.
I think I'll drop that idea altogether...
Ok, now for a concrete proposal of my own. Feel free to be be mean.
My architecture revolves around two basic vehicles. Each has two slightly different forms. The first of these is the key to the whole system.
Its a vehicle designed for ascending from the surface of Mars into orbit, taking with it a cargo. There are two versions of this vehicle. One manned. One purely carries fuel. But there is a large degree of commonality to design and interoperability. The manned version is your Mars landing/ascent capsule. Its also your Earth landing capsule The unmanned version is a fuel ferry. You'll need at least two of these for the sake of redundancy.
The main feature of the fuel ferry is that its able to transport processed methane/lox to Mars orbit a few tonnes at a time. So refueling the following vehicles typically requires multiple trips. One thing we do have on our side, is time.
The second vehicle again has two basic forms but its basically a methane/lox rocket. The common elements are the engine, tankage and heat shield. One version carries the space hab. This version also docks with the manned landing/ascent capsule. The other version is simply a tractor for ferrying unmanned items. Again we have commonality of design and interoperability. We also have only that mass of tankage and engine that is sufficient to the task.
As the manned version of this vehicle approaches Mars, the crew enter the landing/ascent capsule, undock and land. The vehicle/space hab pair aerocapture into orbit. Then the vehicle refuels. On approach to Earth the same procedure applies. So this vehicle is fully reused.
The unmanned vehicle basically follows the same process, cycling between the two planets and picking up fuel in Mars orbit. This vehicle also has the job of transporting the hydrogen tank (for fuel processing) and when this happens, the hydrogen tank remains attached to the vehicle and shares the aerocapture process. This means you can recycle the hydrogen tank - if it makes sense to do so.
Depending on how you design the Mars habitat and optimise, you may need 2 or 3 tractors to establish your presence on Mars. When you're finished you have all the expected gear on the surface, including habitat, power supplies, rovers, and finally the 2 fuel ferries and possibly a spare landing/ascent capsule (yes I love redundancy).
One of those tractors carries the initial fully fueled hydrogen tank. There is also an unmanned flight of the space hab. All of these vehicles are refueled in orbit. So at most you need 5, but possible 4 of these vehicles. And they're all essentially the same platform.
Before the first manned mission everything is checked out, fueled and functional. There is a spare, fully fueled space hab/return vehicle in Mars orbit. There are two fully functional fuel ferries. There is even a spare landing/ascent capsule waiting on Mars. Yes, all of this probably means having to spend 4 years from the word go to the first manned flight - due to the rate at which you can produce fuel.
The first manned mission proceeds as you would expect, on a fast trajectory, transferring to a capsule and then landing. The space hab they traveled in now becomes a spare in orbit.
When the crew ascend into Mars orbit they claim the original space hab. That then makes its journey to Earth. The second space hab is now the spare and it gets refueled.
And so the cycle repeats..
As you can see, what I have proposed is nearly fully recyclable.. to the limits of endurance of the hardware involved.
It is possible to leave a large enough reserve of Hydrogen in orbit around Mars that it will serve ongoing missions. A larger tank is also more efficient in terms of volume to area ratio. So you also have a buffer against unexpected losses and less leakage/evaporation. By making this tank large you also make it possible for the tank to serve several missions - potentially half a dozen. If it fails, then you have the reassurance that at any given time there is always another fully fueled space hab vehicle also in Mars orbit.
The humans enjoy the fact that the only thing that flies with the humans is the space hab, the capsule, the minimum mass of tankage and engine, and only enough fuel to do TMI.
That's about as optimal as it gets.
Indeed, you can further optimise, by giving the space hab a fairly high orbit around Mars. This means you've got a lower energy trans Earth injection. So you can actually engineer a faster flight home if you wish.
It leaves you with abort options at every stage. The possibilities for repair and improvisation are many.
Now if you're a fan of electric propulsion you've got the option of using that for the unmanned transport. Likewise for nuclear. The point is that by optimising the manned part of the flight (which is what the original poster does) you're taking away a lot of the motivation for high Isp engines. Its down to the cost of fuel and I don't think 100 tonnes or so is too much to pay for safety and simplicity in that part of the mission. I personally don't mind nuclear, but I'd sooner trust my life to a bog standard chemical rocket than to a fairly new nuclear design (and its not radiation - its reliability)
I leave others to do the math, but I think that's fairly optimal - and elegant - and safe. And I'm sure it can be improved. Have fun!
And yes, I've skated over some EDL issues. Bite me
Interesting... Kind of like Mars Direct and the OP architecture's ERV's. Except, instead of refueling on the surface, you're using spacecraft in orbit, that take the role of the ERV's.
I don't see where the mass saving is in doing that, though. The propellant for TEI is still gained via ISRU on Mars, in both cases. Merely the architecture means you don't need ISRU propellant to lift the mass of the Mars Transit Vehicle from Mars surface to MO. But the propellant for doing that in any case is provided via ISRU, and it would probably cost a lot more total mass, actually, because you have to lift the ferry from the surface to MO, land it, and repeat, probably quiet a number of times.
My own OP, I think, needs some heavy revision. For one thing, the idea of using boosters akin to a F9 RLV upper stage - with a Falcon Heavy payload of 36 tons - is just genius. Only upon completion of the the final booster's TMI burn is the assembly on an escape trajectory from Earth, so all earlier separated boosters are in a highly elliptical orbit. They aerocapture and return, just like the F9 RLV upper stage. The final booster essentially becomes my original "bus", except instead of propulsive EOI after free return, it can do an aerocapture. And instead of Timberwind NTR's, it can use LOX/LH2.
Want a higher energy trajectory? Just launch an extra booster. It may require that the next-to-last booster not separate, though (so essentially the final booster is just a propellant tank).
What I love is the sheer simplicity of it. It's almost as simple as Mars Direct, except all the hardware is reusable. It's the best of both worlds.
#12 Re: Human missions » Landing on Mars » 2012-04-15 18:08:13
Standard military weapons-release speed is 485 knots indicated. At sea level, that's about 0.85 Mach. Definitely subsonic at all low altitudes of any interest. Condensation clouds can exist in the intake of a jet parked static on a carrier deck.
I tried ballutes as a stabilizing drogue back in the mid 80's. Ribbon chutes worked better, and were good to 2.5 Mach, if you bagged it properly for control of opening shock. Different application, same decelerators.
These were ram-air inflated devices, though. In space, you are really talking about low to medium-pressure forced inflation of a shaped balloon. Not quite the same thing. It was the ram air inflation I found unreliable, unlike a ribbon chute.
GW
Okay, that's great input, I had a feeling transonic wasn't required to cause condensation.
As you said, though, we're not working with ram-inflated devices.
I decided to check the source wiki used for saying "It is a parachute braking device that is optimized for use at high altitudes and high supersonic velocities." That sentence had cited this: http://ntrs.nasa.gov/archive/nasa/casi. … 017080.pdf
The page itself details some tests of ram-air inflated ballutes, simulating conditions of a Martian re-entry, according to the summary.
The actual tests occurred at mach 3.15 with a dynamic pressure of 1843.4 N/m^2, and the ballute broke (one of the inlets were torn from the body).
More interestingly, though, the paper references earlier tests that had been done on smaller ballutes;
"Usry, J . W.: Performance of a Towed, 48-Inch-Diameter (121.92-cm) Ballute
Decelerator Tested in Free Flight at Mach Numbers From 4.2 to 0.4. NASA
TN D-4943, 1969."
Starting at mach 4.2.
Here's the actual paper;
http://ntrs.nasa.gov/archive/nasa/casi. … 008066.pdf
And that paper references another one, some goodyear tests, where ballutes and ribbon chutes were wind-tunnel tested at even higher mach numbers, up to mach 10.
http://ntrs.nasa.gov/archive/nasa/casi. … 027566.pdf
To be honest, I've only skimmed through it, and one thing that stands out to me is the part on page 67 that notes that ribbon chutes were experiencing "breathing" and coning at mach 2.5 +, while the ballutes faired better at the very high mach numbers.
NASA's decision to use Ribbon chutes makes sense, since they work in the mach range of the systems they're used for; the Shuttle's SRB's, or the smaller space probes that can decelerate to those lower mach numbers.
Now, quoting the OP:
Have you all seen this?
http://www.universetoday.com/7024/the-m … ed-planet/
It basically says that you can't land a large manned vehicle on Mars with the standard heat shield-parachute-thruster combination because the heat shield can't be large enough to slow the vehicle down to Mach 2 (when you can deploy parachutes) before you hit the ground. The atmosphere is too thin. But it's too thick to fire thrusters straight ahead of you at Mach 2+ because the exhaust plume is too dynamic and the resulting shaking could shake your vehicle apart. It advocates a "hypercone," a big inflatable structure, at Mach 5, to slow down the ship. I suppose a super-large heat shield, assembled in Earth orbit, would do it as well; that possibility is hinted at.
If ballutes can work at much higher mach numbers, then you've entirely circumvented the issue stated in the OP, and the issue the last pages have been dealing with (new heat shield tech.) ; you don't have to slow the vehicle to mach 2 at all, you just have to slow it to something like Mach 4.
Even better if we could re-create those wind tunnel tests from the goodyear paper, but scaled up and in atmosphere for mach 6+.
#13 Re: Human missions » Sustainable Access to Mars: Interplanetary Transportation Architecture » 2012-04-13 22:03:24
Are people having a timeout problem? I just wrote a post and lost it!
Anyway, Musk seems to want to create sustainable access to Mars, just as you propose. His system starts with reusable Falcons and Falcon Heavies that return to the launch site. He said somewhere a reusable system puts 40% less in orbit, but that's still about 36 tonnes for a Falcon Heavy. If you put that much in orbit for hundreds of dollars per pound (i.e., less than $36 million for 36 tonnes) you don't need Timberwinds or ballutes; you go to Mars with RP1 and LOx, because it would be so cheap. RP1/LOx gives an exhaust velocity of 3.4 km/sec; you need a mass ratio of 3.6 to achieve 4.3 km/sec (the velocity to go to Mars on a free return trajectory, 6 months outbound). So you need to launch a 36-tonne payload and 3 36-tonne propulsion stages. Each would come with a docking collar attached to it with explosive bolts. They'd simply dock together, and when a particular stage burned up its fuel you'd fire the explosive bolts and separate. The first two propulsion stages would gradually aerobrake to low Earth orbit and return to the launch site; the third would go to Mars and possibly land there, where eventually you could refuel it with methane/LOX (which is very similar to RP1). Refueled, with 33 tonnes of methane and LOX (with a 3-tonne structure and heat shield) it could launch 13 tonnes into Mars orbit, or maybe 10 with enough fuel to return to the surface. If you built it into the lander/ERV the ERV would already be on top.
Wow, that is really dumbfoundingly straight-forward. Entirely reusable, and very direct. For here and now, that is probably the best architecture there is.
As for the third stage, since it's on a free return trajectory, if it's not needed on Mars, it can simply loop around and come back to Earth and aerocapture, granted a little extra propellant for more course corrections and orbital adjustments (which could probably be reduced to very little: simply make it aerocapture into a highly elliptical orbit and perform the orbital adjustments at apogee.)
But still, that involves 4 heavy launches for every 36 tons launched at Mars. It would surely require some extra analysis, but it would be interesting to see how the costs of a Timberwind engine would compare with the reduced launch costs. You only pay for a development program once, so then the question is; how many times can you reuse the Timberwind-bus MTV (can you even turn a profit?), and how long would it take for it to pay itself off? All assuming, of course, the NTR program is allowed in the first place (I wasn't around then, but I haven't heard anything about protestors at the NERVA program.)
It would be possible, using NTR, to cut those launches in half, and using a design like the Falcon 9 RLV upper stage, it could aerocapture back at Earth instead of even needing any propellant (Though, with a mass ratio of 1.55 giving the needed propulsion, it's also very easy to carry enough propellant for propulsive EOI).
Furthermore, you could either use the extra velocity (5.76 km/s at mass ratio of 1.8) for a shorter transit time, or add in more payload with the second launch for more tonnage to Mars.
(Booster: 30t total, 4t dry, 42 tons of payload to TMI, 100 m/s spare (4.4 km/s). In total, that's 2 heavy launches for 42 tons of payload TMI.)
~
Timberwind aside, using LOX/LH2, you could still get 4.75 km/s even if each booster had 6.5 tons dry mass. But at 4 tons (I think 3 is a bit optimistic, including landing gear, RCS and heat shield), 5.26 km/s, for a shorter transit time, or, launch 2 regular boosters and a smaller booster (8t lighter than the others) packaged with 8 tons of extra payload, with 200 m/s to spare for course correction (for a total of 44 tons TMI, enough for a 20t ERV, 16t HAB, and 8t rover/ISRU/supply package.).
If I assume the 3-ton figure for dry mass on each propulsion stage, it can be done with only 2 boosters at 451 ISP. With the 4-ton figure, 2 boosters can launch a payload of 31 tons to TMI (with 200 m/s to spare).
~
The LOX/LH2 looks most promising, I don't think Timberwind would be worth 2 launches instead of 3, but in truth only numbers will tell accurately enough to make a decision on (but only experience will tell for sure), examining the costs of Timberwind development, political struggle, and engine cost/reusability of MTV v.s. savings from less launches.
Btw; I used a spreadsheet to get this, checking the 340 ISP RP-1/LOX, 36 ton wet mass, 3 ton dry mass, I had to drop the payload to 33 tons to get 4.3 km/s out of it, and that's with no extra Dv for contingency or course corrections.
#14 Re: Human missions » Landing on Mars » 2012-04-11 20:04:38
No one has tested a ballute yet, so I don't know how much is known about their properties or what will work. Does anyone have references to them?
wikipedia is always a great place to turn
http://en.wikipedia.org/wiki/Ballute
Of course, I say that because you can confirm and look at the sources themselves.
wiki:
"It was used as part of the escape equipment for the Gemini spacecraft.[3]"
3. http://www.hq.nasa.gov/office/pao/Histo … /ch8-4.htm
According to the article, they've been used on bombs, too.
The clouds would seem to show they're being used at trans-sonic or super-sonic speed, correct?
The ballutes in my proposal are used in-tandem with the heat shield, so plasma formation is still okay.
Either
1) The ballute deploys after significant heating has stopped
or
2) The ballute is well-protected from the hypersonic airflow by the spacecraft.
1., only if 2. is impossible or impractical.
Also, I imagine the ballute, unlike the bombs in the picture above, is on the end of a hose/cable that is at least a few meters or tens of meters out from the ERV; so as to catch the maximum amount of undisturbed air, to get the most drag. So most likely 1. is the case.
Then again, a third option might be possible: Deploy the ballute, but hold it close to the spacecraft; it gives the lifting force of the balloon to have some very small effect on the descent rate, and once significant heating is over, extend it. This shouldn't be too hard, since I envision the hose/cable is already retractable by motor. In this case, it's just making it extendable and retractable, instead of just retractable.
(The reason for the retractable ballute is that the ERV is supposed to be reusable. Think it's hard recovering ejected parachutes on Earth? It's bound to be a much harder, and even exceptionally dangerous thing to do on Mars, and it would entail a significant amount of work to be done on the ERV by EVA. The ballute is mounted on the "dragon" portion, so they'd be doing this work high off the ground, too. Overall it's much safer and probably even saves weight to make it retractable, as opposed to all it would take to make these OPS possible.)
#15 Re: Human missions » Landing on Mars » 2012-04-11 18:10:27
I'm sorry if it's a little off-topic, but I can see my thread here might get focused on this one particular issue, seeing how much concern there is on it right now. So that all the discussion on that thread doesn't get centered on that one issue, I want to ask it here.
What the plan calls for is aerocapture of a surface habitat (~20 ton mass range), and separately, an ERV (~20-30 ton range).
The re-entry and landing method of the habitat isn't important, and it lands on a low-energy trajectory.
However, the ERV must be fully reusable and land on a slightly higher-energy trajectory. Would PICA-X, a ballute (down to at least mach 2.5), and powered descent be sufficient?
For the PICA-X part, I want to cite that it can potentially survive hundreds of Earth-orbit re-entries (*source, 2), perhaps making it possible for a PICA-X heatshield to survive a few, or even ten or more Trans-Mars EDL's?
#16 Human missions » Sustainable Access to Mars: Interplanetary Transportation Architecture » 2012-04-11 17:48:25
- MatthewRRobinson
- Replies: 80
Much of the space community, and perhaps much of the world, is looking forward to the first manned mission to Mars. But, in all the proposals and designs I've seen, MRDM is the biggest perpetrator, the program is terribly unsustainable, even less sustainable than Apollo. Apollo launched with ~200 tons of hardware, and returned only 6. Unlike the ISS, which was constructed by, although it was more expensive than other LEO vehicles, a reusable vehicle, access to the moon required a vehicle that was 50% heavier, and entirely non-reusable.
If Elon Musk's goal of creating a colony on Mars that costs half a million to go to is to ever become a reality, a mission architecture that throws away billions of dollars of hardware with every flight is absolutely unacceptable. A popular thought is, "we'll get there eventually, but it's not time now", that's the exact same thought that's stagnated our space program for the last half-century, and will doubtlessly ground our species until our death if it continues. The imaginary future where prices are lower and spaceflight is easy will never come unless we build it - and that is exactly what this mission architecture is for. Even if reusability doesn't bring costs down to $500,000 per ticket round-trip, which it very well may, lack of reusability will ensure each mission costs tens of billions, and hundreds of millions if not billions per ticket, at least.
Sustainable Access to Mars is key for any long-term endeavor on Mars, be it a single station, or multiple outposts across the martian surface, or even a colony, Sustainable Access to Mars (SAM) is a must. SAM isn't the entire Mars Mission, but is the architecture by which cargo and personalle are delivered to and from Mars, so discussion on a single site, multiple sites, crew size, whether to have a ground vehicle or not, etc. are not directly relevant to SAM. I.e, SAM is about getting to and back from Mars, not what happens on the surface.
Here's what I propose:
First, a fleet of 3 unique vehicles is used (not including the surface hab, or possible ground vehicles, which are not unique to SAM, and the specific details of which are not relevant to SAM) ;
1- The Earth Return Vehicle (ERV)
The Earth Return Vehicle consists of two modules mounted together, similar to Apollo's Command Module and Service Module. They do not separate under any ordinary circumstances, but can separate for emergency aborts.
The vehicle's side is coated with sufficient PICA-X heatshield to allow for tens or hundreds of interplanetary-velocity (~10.5 km/s) Martian aerocaptures and re-entries. (PICA-X can be used to create a heat shield capable of hundreds of Earth re-entries *source, 2)
The "Command Module" portion is a modified Red Dragon, modified to include an opening Pica-X coated nosecone (fitted over the docking port) and a ballute. The nosecone opens for docking, but otherwise remains closed. The Dragon retains enough of it's own heatshield (apart from the ERV's heat shield) for a single interplanetary Earth re-entry (~12 km/s) without the "Service Module" in case of failure of Earth Orbit Capture. It also retains enough landing thrust to land on Mars without the Service Module portion in case of ERV Main Propulsion System failure during vertical powered descent over Mars.
The "Service Module" portion uses CH4/LOX engines and propellant tanks sufficient to give the ERV vehicle enough Delta-Vee for Mars ascent and Trans-Earth Injection (combined, roughly 6.4 km/s minimum).
2- The Supplementary Transit Habitat Module (Suphab)
The Suphab is an extremely small, lightweight module. It, along with the ERV, provide the habitat space and supplies for Earth-Mars and Mars-Earth transit.
3- The Trans-Mars Bus (Bus)
The Trans-Mars Bus is the "tractor" that delivers the surface habitat and/or cargo to Mars, and delivers the ERV's and Suphab to and from Mars.
The Bus consists of five propellant tanks, a communications array, an avionics bus, a low-power powerplant, a Timberwind NTR Main Propulsion System, and a robotic arm (which can be fitted with a robonaut for EVA, esp. for EVA on the NTR MPS if that should become a necessity).
Four propellant tanks, from a head-on view, are arranged in an "X" configuration, at each point of the X. The fifth propellant tank is, from a head-on view, at the center of the "X", but offset behind the other four propellant tanks, leaving the actual center of the "X" empty. The engine assembly is mounted on the rear of the fifth propellant tank. The first four propellant tanks act as a radiation shield from interplanetary radiation, and the fifth acts as both a radiation shield from interplanetary radiation and a radiation shield from the NTR engines.
(The center of the "X" will have enough room for the nose of the ERV (The dragon "CM") docked with the Suphab which docks to the Bus, but does not have enough room to encompass a surface habitat.)
First:
The Bus is launched into LEO, along with an unmanned ERV and surface habitat. The entire assembly docks in orbit, then the Bus uses it's NTR to perform TMI for a low-energy transfer to Mars.
On arrival to Mars, the Bus, Surface Hab and ERV all undock, and the Surface Hab and ERV each aerocapture separately, then enter Mars' atmosphere for reentry.
After they have undocked, the Bus, now free of payload mass, performs a final course correction burn for a free-return around Mars back to Earth.
The habitat uses a heat shield, parachutes and a very small amount of thrust to land. The ERV, on the other hand, uses it's re-usable (although ablative PICA-X) heat shield, then a non-detaching ballute to descend. Once at low altitude and near terminal velocity, an engine ignites and uses a very modest amount of Delta-Vee in a powered vertical descent. Once landed, the ballute (which has a hose connected to the vehicle) is vented by opening a valve on the ERV and is retracted and stored, making it re-usable.
The ERV then begins ISRU.
The Bus, on the other hand, now free from any cargo mass, performs a free-return back to Earth, and captures back into Earth orbit using a very small amount of remaining propellant.
Second:
This time, the bus is docked with the Suphab and a manned ERV. The Suphab being significantly lighter than the Mars surface hab, the assembly is able to perform a much higher-energy TMI, meaning a shorter transit time for this manned flight.
On arrival to Mars, the ERV undocks and re-enters; the Suphab remains docked to the Bus for the duration of the mission, making it, too, reusable.
One of the key arguments against total ISRU is the lack of abort ability during re-entry and landing, however, the manned ERV is composed of a service module and a dragon command module that can separate and use it's own heat shield, ballute (the same that is normally used), and thrust to land, making abort possible during reentry. Although the service module would be lost, the ERV that landed on Mars earlier would be used to return to Earth, anyways.
Should the ERV fail to aerocapture completely, let us assume the velocity we failed to lose in aerocapture is less than the delta-vee carried for the powered descent phase: The ERV can then use it's powered descent propellant to perform a propulsive MOI, then perform a very small Delta-Vee burn at apoapsis to drop the periapsis into Mars' atmosphere. In this emergency landing, the dragon CM can separate and land under it's own power.
Once again, with the free return complete, the Bus+Suphab perform EOI.
Return To Earth:
For the Return, the Bus performs a low-energy TMI transfer from Earth with Suphab docked. The ERV launches from Mars and performs it's own TEI. The two rendezvous and dock, allowing the crew to access the Suphab, and the Bus to use it's NTR to capture into Earth orbit with the ERV and Suphab docked, meaning no hardware is lost whatsoever.
However, should the rendezvous with the Bus fail, the ERV, having been restocked with supplies from the surface hab (possibly produced on Mars), has sufficient supplies for the crew to survive the duration of the TEI transit on small rations. Upon arriving to Earth, the dragon portion of the vehicle can separate and survive Earth re-entry, enabling the crew, but not the entire ERV, to return intact.
Additional Surface Habs
By launching only a surface hab without an ERV, and docking with the Bus to make a surface hab+Bus assembly, it is possible for the Bus to conduct a higher-energy TMI transfer, decreasing transit time significantly, perhaps making it possible to launch a manned hab to Mars without an ERV attached.
An additional surface Hab does not necessitate an additional ERV: if part of the "surface hab" package is a surface vehicle, then an additional ERV does not need to be launched if the new surface hab is within driving distance of an already existing ERV. The effect, however, is that the average on-Mars stay time for the crew would increase, but only if the additional surface hab is manned, adding crew but not an additional ERV.
~
The mission is very low mass, and most importantly, no hardware needs to be replaced with each mission, meaning only 1-2 super heavy launches per additional mission for NTR LH-2 propellant and minor mass such as perishables for the Earth-Mars flight (on-surface and return provisions could be produced on Mars), which is 1-2 super heavy launches depending on the precise mission mass. At the cost of an additional launch, an additional HAB+cargo can be added to the surface station to expand an existing one, or for a new one to be created, but that is the only instance where new hardware is specifically needed; when you want new hardware to stay on Mars.
Using SpaceX low-cost re-usable launch vehicles, the cost for continuing service to Mars could be comparable to that of the Space Shuttle's continuing service to the ISS, and possibly even cheaper (more sustainable and/or more open to expansion), when considering each return mission happens less often than once a year during launch windows.
This is, opposed to MRDM v5, which calls for 7 super heavy (Ares V/SLS) launches per mission! *source, p.30
~
The key is the lower costs, making it possible to sell tickets to Mars for lower prices than would otherwise be possible. With this setup, and the possibility of a profit, human sustained presence on Mars is assured. However, with a throw-away hardware architecture, that even Mars Direct is guilty of, you're limited by the price of the hardware.
Let's say it's somehow possible to make an interplanetary Mars-transfer spacecraft that can crew 100 passengers, and costs less than a space shuttle, 2 billion dollars. Ignoring the costs of launching the crew and passengers into LEO, making a profit, costs of launching propellant into orbit, launching the spacecraft itself into orbit, and all other costs, that is still $20/million per person, even using those insane numbers like 2/billion for a 100-passenger to Mars spaceship. Now, that is why reusable hardware is a must for sustained access to Mars.
~EDIT:
Given the political sensitivities of NTR, it would be interesting to look at this proposal with the "Bus" using chemical propulsion instead. Two alternatives I can imagine are;
1. LOX/LH2 propulsion.
or
2. LOX/CH4 propulsion.
In the LOX/CH4 propulsion method, the mission is altered somewhat. Instead of going on a free return, and performing a ~4,500 m/s EOI, the bus would perform a propulsive MOI after separating from it's cargo. The ERV would carry significantly greater tankage, as well, and there would be a much higher rate of CH4/LOX production by ISRU. Over the course of the mission, the ERV would launch, dock, and refuel the Bus from it's own propellant tank, one launch at a time. This would involve new technology; on-orbit refueling, and involve the ERV launching into Mars orbit and reentering a number of times, but would save a tremendous amount of mission mass. The new technology isn't particularly difficult, but the multiple ERV launches and returns might make the mission somewhat risky.
But neither of those things should be exaggerated. The new technology (in-flight refueling) is something jet aircraft do all the time. Doing it in space just means forming a seal; something we've done countless times with on-orbit docking. When you consider on-orbit refueling as a combination of hard-docking and mid-air refueling, the technology really isn't new at all.
As for the multiple launches and reentries, not only did the Space Shuttle fly 134 reentries with only 1 re-entry failure (due to foam breaking off from the ET), but soon we'll have real-world data from SpaceX on the exact same thing as the ERV with the reusable Falcon 9. (Note, this year, SpaceX will begin scale testing of this with the "Grasshopper", source, source2)
As for the Timberwind NTR, I don't think it's quiet as far-fetched as a lot of people may think. We've been using RTG's for a long time, and recently, with Curiosity, it's been publicized as a "nuclear-powered Mars rover" a number of times. It may be an RTG, but in the public's eye, it's a nuclear powerplant, and seeing as it draws electrical power from radioactive decay of radioactive material, it's not really an incorrect understanding. It seems like a huge step towards nuclear power in space. (Which, btw, actually has flown before, source) it's not quiet as far-fetched as many think it is.
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