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#476 Re: Interplanetary transportation » Organometallic Propellant » 2014-03-31 12:41:03
Dunno about Mars, but that has potential for launch to LEO or exit trajectory. High-Isp and dense at the same time is quite good. Non-cryo tankage is good.
I cannot speak as to the storage stability of the organometallic fuels, but 90+% strength hydrogen peroxide is storage-unstable beyond several days. It blows up. Quite stable but not usable as a rocket oxidizer at 50% strength and under. In between is, well, in-between.
Some call it "safe" up to 70%, I don't. Needs to be 90+% to be useful as a rocket oxidizer, some prefer even higher. The paper talks about 98+%.
GW
In this work ( http://hydrogen-peroxide.us/history-US- … roxide.pdf ) is said that H2O2 can be stored even for 15 years, in tanks of proper materials, with very minimal loss and if it is keep at 5°C, it can be stored fore even 17 years with no loss.
If H2O2 can be really stored for long times, H2O2-LiAlH6 may become the best propellant even for interplanetary travels.
#477 Interplanetary transportation » Organometallic Propellant » 2014-03-31 07:44:15
- Quaoar
- Replies: 24
I've found this interesting article about new organometallic non toxic hypergolic propellant: http://www.sps.aero/Key_ComSpace_Articl … ations.pdf
Some combinations like H2O2-lithium aluminium exahydride (LiAlH6) have a specific impulse of 469 s, even better than LOX-LH2, without all the problems of cryogenics. It may be interesting for a Mars mission?
#478 Re: Interplanetary transportation » VASIMR - Solar Powered? » 2014-03-30 10:17:58
My criterion for success in a vehicle hardware program where you intend to fly, is never to incorporate any new technology development as part of your program, use only off-the-shelf (mature) technology. The statistical history is that you never fly unless you avoid developing new technology in your program.
That being said, the electric propulsion that is flying right now is Hall effect, so use that as your baseline. Replace it with VASIMR or something similar, as soon as it is mature. If M2P2 matures in time, then use that. Design your system so that any of the 3 could be incorporated (a VERY important consideration too often ignored).
That way, you'll have a flyable vehicle soonest and cheapest, one that incorporates the best electric propulsion technology that has matured in time to make the trip.
GW
Here is a nested Hall effect thruster that can use xenon or krypton ( http://pepl.engin.umich.edu/pdf/IEPC-2011-246.pdf ).
Why not posting on your blog, a Mars mission with an hybrid chemical-electric spaceship?
#479 Re: Life support systems » Liquid CO2 for clothes washing » 2014-03-30 04:42:24
On Mars, it's not really necessary, water is almost everywhere. Certainly the lower latitudes are literally full of water. At times a cubic meter of soil is half water.
On the travel to Mars, this is an interesting argument, but you got to understand, clothes / dirtiness / smells / filth is minimized. You're not washing your clothes daily, as long as you don't have an accident you'll probably last weeks in the same pair of clothes before you or your shipmates are repulsed by the smell. You're not going to be super active, you're not going to smell any worse than the smells generated by the internal sewage systems (as far as I understand on the ISS, they aren't that great, and you get used to it).
This is, imo, especially true if you use a Mars-direct type system. You'll stink, but you'll get used to it. In summation, traveling there may be gross, but once you land, you're going to have water, natures solvent, to take care of things (water actually doesn't require detergents, you can wash without them, it just takes more effort / cycles to get the same result; detergents just make it easier and get rid of potential staining; if you don't care about that you don't need detergents).
But astronauts has to do a lot of sport to not hypotrophize muscle and hearth: during travels if they have a full gee spinning ship an intensive training can be avoided, but on Mars surface, with only 0.38 gee, I think 2 or 3 hours/day of gym will be necessary. So a water source is necessary.
Ice Lake is too north. Buried glaciers on mid latitude (25-35°) may be a good compromise, but are we certain that water are still present and we can find with a less than 50 meters drill?
#480 Re: Life support systems » Liquid CO2 for clothes washing » 2014-03-29 13:33:13
I still think it would be simplest to land where there's plenty of water ice. And your habitat will recycle wash water. Then we can simply wash in water, like we do on Earth.
It would be surely better, because we can also make ISPP without bringing hydrogen from Earth: at the moment the only site with known water ice is Ice Lake in Vastitas Borealis, but nobody likes it because it's 70° North.
#481 Re: Life support systems » Liquid CO2 for clothes washing » 2014-03-29 05:09:06
You still need some sort of dirt and grease solvent in your CO2, the analog to detergent in water. Liquid CO2 would be an analog to dry-cleaning. Not sure what that additive is, but I'd bet one already exists.
Liquid CO2 does require high pressure. Your washing machine would be pretty heavy, because it would have to be very stout.
GW
Please correct me if I'm wrong: CO2 is not a dipolar molecule like water, so grease can solve in it without need of a solvent.
The problem may be the mass of the washing machine, but assuming it's three times a conventional washing machine and that it can save 5 liters of water/day, in a 860 days travel we have speared more than four tons of water.
#482 Re: Interplanetary transportation » VASIMR - Solar Powered? » 2014-03-29 04:55:10
I'm not familiar with the M2P2 concept, myself. I had in mind either ion or plasma jet thrusters, combined with the lighter-weight solar power being discussed here. Although, this M2P2 thing is another candidate.
The biggest problem with any of the electric schemes is super-low vehicle acceleration. It takes "forever" to leave a parking orbit for a transfer orbit, and the gravity losses associated with the very long burn times are enormous.
So why not do the burn from parking orbit to transfer orbit impulsively with chemical rocket, and then shorten the transfer by using the electric to accelerate on the transfer to its midpoint? Then decelerate electrically the same way during the second half of the transfer.
There's still gravity losses with the electrics, but, at least the transit time is much shorter. Your vehicle will size out somewhere in between the big all-chemical system and the small all-electric system.
Reductions in both size and transit time. Is that not the win-win that we all want?
GW
A chemical-electric hybrid looks very promising, but wich kind of electric propulsion has to be choose?
1) VASIMR has the vantage of using cheep argon and the disadvantage to be too massive
2) Nested Hall effect thruster has the vantage of higher T/W ratio and the disadvantage of using very expensive xenon
3) M2p2 has the vantages of very high T/W ratio (almost 1 N/KW); to function with any kind of propellant from water to hydrazine; and to be used also as a cosmic ray shielding; and the disadvantage to be never tested.
#483 Re: Human missions » Yet another Mars architecture » 2014-03-29 04:42:30
This means a tank liner (bladder) during launch. Throw away the liner after the module is in space. That means any RP-1 contamination is thrown away with the liner. The issue with this is interior walls and furniture cannot be attached during launch.
Yes: astronauts have some kind of habitat assembly kit, and mount it after trow away the empty bladder.
#484 Re: Human missions » Whither the ISS? » 2014-03-27 05:09:09
Considering the price of a handful of Ba330 modules and the vastly enhanced capabilities, a logistics module or two, commercial crew transport and orbital resupply, and the Falcon Heavy launcher, why would we keep using the ISS?
The only question is whether to sink it before or after the Russians detach their modules.
ISS has an orbit too inclined to be useful. I think in a future we will need three bases, even smaller (just one or two BA330) but with manutencion and assembly capability: one in low equatorial orbit to support Moon missions, one in EML1 or EML2 for the Moon landers, and one in a LEO on the plane of ecliptic for interplanetary missions
#485 Re: Life support systems » Liquid CO2 for clothes washing » 2014-03-27 02:13:32
CO2 production is almost 1 kg/person/day: it can be liquefied and used for washing clothes, before be cracked and recycled.
Another option may be to use special clothes that don't need to be washed: I remember a Japanese astronaut on ISS experimented a special idrorepellant uderware, that can be used for more than a month without be washed, but I cannot find any data.
#486 Life support systems » Liquid CO2 for clothes washing » 2014-03-26 10:14:49
- Quaoar
- Replies: 14
I found this interesting paper by Tom Hill, who suggests to use liquid CO2 for clothe washing, saving a lot of precious water.
#487 Re: Human missions » Yet another Mars architecture » 2014-03-26 10:06:30
Another solution may be to use an enflatable tank inside an empty space: when the propellant is burned, astronauts throw away the tank and mount the forniture.
#488 Re: Interplanetary transportation » VASIMR - Solar Powered? » 2014-03-25 16:21:53
Bob:
What about combining solar-electric with conventional propulsion? Do the main burns conventional to leave orbit. Then apply solar-electric during the transfer, to vastly shorten travel time? Might that be the best way to avoid the slow spiral-out problem?
GW
Something like this?
#489 Re: Human missions » Yet another Mars architecture » 2014-03-25 15:04:49
Hi Quaoar:
Well, in the mission plan those illustrations came from, no empty tank was discarded, at the cost of bigger-than-minimum ships. Most would be left in orbit about Mars for future but unspecified use. Some would be in LEO upon the ship's return. Those could be either refueled or re-purposed. It's so expensive to launch stuff, I figured why throw stuff away?
I suppose that rearranging the internal structure of such a module might make it more appealing as habitat space, once vented. There would have to be included some sort of access door through which to load the interior equipment one might want. The propellant transfer piping would have to be designed for easy removal, as well.
And, to utilize the space inside both tanks, there would have to be some sort of connecting doorway designed-in. I'd guess that most of this could be designed-in with low (but non-zero) impact on the inert structure mass fraction of the module-as-a-propellant-tank in its initial mission.
GW
Thanks GW:
A space station in LMO may be very useful for for exploration and colonization.
A modular spaceship like your rigid baton can be done with thermal protection on the belly of every module to perform aerocapture or the thermal load will be to much for LH2? In this case, an umbrella like thermal shield like ADEPT on the head module can be used?
#490 Re: Human missions » Yet another Mars architecture » 2014-03-25 02:10:16
To GW:
Why not to redesign your modular spaceship, in a way that avery propellant module, after vented can be used as an habitat?
So every propellant module lived in low Mars orbit will became a space station, that will grow at every mission
#491 Re: Human missions » SLS and what asteriod will we go to » 2014-03-24 01:54:20
NASA's asteroid initiative includes two separate, but related activities: the asteroid redirect mission and the grand challenge. NASA is currently developing concepts for the redirect mission that will employ a robotic spacecraft, driven by an advanced solar electric propulsion system, to capture a small near-Earth asteroid or remove a boulder from the surface of a larger asteroid. The spacecraft then will attempt to redirect the object into a stable orbit around the moon.
Astronauts will travel aboard NASA's Orion spacecraft, launched on the Space Launch System rocket, to rendezvous in lunar orbit with the captured asteroid. Once there, they will collect samples to return to Earth for study.
I's a completely new technology to develop: if they really want to do that seriously (I belive not) they will employ more time and money than landing men on Moon and even on Mars.
Asteroid redirect capability may be usefull to avoid a deep impact, but i dont think it can be done completely unmanned. Astronauts has to go first to make geological prospection, study the best despin and moove strategy on the basis of asteroid structure (solid rock or granular aggregate), then fix the hardware. But to do such things, we have to built first a real reusable space ship with artificial gravity and flare protection, able to years long space cruise.
#492 Re: Human missions » Yet another Mars architecture » 2014-03-23 15:43:15
When the astronauts ran around the inside of those tanks, there was "artificial gravity", but only for so long as they continued to run. Use the astronaut's forward speed and the radius to those tanks, and you have the angular rate = forward speed divided by radius. The effective gravity is then radius x angular rate squared. You'll have to use consistent units, of course.
GW
With 3 m of radius astronauts can have almost one gee running at 20 km/h.
#493 Re: Life on Mars » Where Should we Send our Rovers to Mars to Look for Early Life? » 2014-03-23 07:56:02
For what ever site is selected One issue is how large is the rover and then what life detection intruments will be onboard. Then one must ask are we only looking for past life and whether we will even state any current exitance if it is found.
Searching for past life may be very difficoult for an unmanned rover, unless it has the luck of running in a fossil. Present life (if exist) can be easy to detect in ice samples.
#494 Re: Human missions » Yet another Mars architecture » 2014-03-23 07:46:53
The liquid hydrogen tank was living space, while the liquid oxygen tank was combination garbage dumpster and septic tank. That is, the toilet emptied into it, and the kitchen had a small airlock for kitchen scraps. This meant no door between tanks.
Thanks!
When the LOX tank become full, was the garbage flushed away in the space?
To do that today? Skylab was based on the S-IVB stage, so 6.6 metre diameter. Falcon 9 v1.1 is only 3.7 metres diameter. Delta IV has a 5 metre diameter core module, but the upper stage is pitiful. You could build a custom upper stage for a Delta IV Medium. Make it 5 metres diameter.
Can it be done 7-8 meters of diameter? I read that a payload can be 1.6 times larger than the lower stage.
Notice the Skylab workshop had windows in the multiple docking adapter and airlock, but not the workshop. However, Falcon 9 uses RP-1 and LOX, not liquid hydrogen. RP-1 is highly refined kerosene, storable at room temperature. It's chilled by the liquid oxygen tank, but not nearly as cold as LH2. Doing this with Falcon 9 would be a lot easier.
I fear RP1 may be difficoult to vent away: if it is almost like gasoline, will its smell remain in the rooms?
Probably LOX or LCH4 may be vented better.
#495 Re: Human missions » Yet another Mars architecture » 2014-03-22 15:21:23
The upper stage would be filled with cryogenic propellant during launch, but equipment bolted to the inside of the tank. Once in space, the module would be vented of propellant, warmed, and filled with air. ?
This is very interesting even for an ERV in a Mars Direct like mission: the LH2 tank for ISRU has a big volume that can be used for habitat douring the trip.
How can be avoided equipment damage by liquid hydrogen?
#496 Re: Life on Mars » Where Should we Send our Rovers to Mars to Look for Early Life? » 2014-03-22 12:07:50
For life sercing, the best sites are those with water: sending Exomars on a buried glacier may be very interesting (Elysium Planitia, Protonilus Mensae, Hellas Basin etc...): in one unmanned mission we can search life and make geological prospection, finding a water source for a future manned surface mission (I fear that a more than 500 days manned orbital mission will result in mental insanity for the astronauts even if they have a 100 ton habitat with a perfect artificial gravity and cosmic radiation shielding system).
#497 Re: Human missions » Yet another Mars architecture » 2014-03-22 09:02:41
I think part of their problem is they can't afford to develop the capture and retrieval system as long as they're developing SLS and Orion, each of which is costing something like 12 times as much as Falcon and Dragon combined!
The more logical think to do is to contract SpaceX to develop an heavy lift launcher for 1/4 of the money of SLS, or even less.
#498 Re: Human missions » Yet another Mars architecture » 2014-03-22 04:31:41
I think NASA would want to avoid rubble piles for their capture mission. How would they do that? Spectral analysis will help; with it you can determine whether the body is nickel-iron, stony, chondrite, carbonaceous chondrite, a mix, etc. But they might still have a rubble pile problem. They can also determine how fast the objects are spinning and would want to find a slow spinning object. There are some out there. So farm they have not identified any potential targets. Maybe they never will be able to, or maybe the search is still in preliminary phases.
Otherwise, I agree with you: NASA really doesn't need to do this mission.
If they really want to perform an asteroid capture mission, they have to start now in develping capture and retrial vehicle and hardware. But they are not seriously investing money in such mission plan.
Capture and retrial is a completly new technology and will take more than a decade to be operative. I also think it's better to go first on Mars: entry, descend, landing and ISRU are better known issues.
#499 Re: Human missions » Vastitas Borealis based mission » 2014-03-21 02:38:47
Having a certain source of water, even a sample return mission will be more simple. An ice sample may be a very good medium for detecting microbic life.
Wich is the precision range of a landing?
#500 Human missions » Vastitas Borealis based mission » 2014-03-20 09:34:38
- Quaoar
- Replies: 2
A well known water source has a big value for a Mars mission: ISPP can be done without bringing liquid hydrogen from Earth, and astronaut can bring only dry food, saving a lot of mass that can be used for scientific payload.
At the moment, exlcuding polar ice caps, the only known source of wather is the ice lake in Vastitas Borealis
(there are some known buried glaciers at mid latitudes, but we still don't know if the ice is too deep to be reached by the unmanned ERV hardware or not).
Ice Lake is about 70° N of latitude, so a mission will experience a cold winter. But the winter, in northen emisphere, is only four months, so I think may be a good trade to cope with four months of winter and having in exchange all the water we want (consider we have a 100 KW nuclear reactor to keep warm the habitat): rover can have fuel in abundance enhancing exploration range and with the mass saved, we can bring even two or three hoppers, that astronauts can use to go souther douring winter, exploring multiple sites in a single mission.
Even the safety will be enhenched: dry food is light, so the stocks may be enough even for 5 years, so if ERV fails to take off, astronauts can go home with the second ERV in the next launch window.