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#451 Re: Interplanetary transportation » Landing a flying saucer on Mars » 2014-04-20 10:22:13
Kendall Brown, an EDL expert in the Exploration and Mission Systems Office at Marshall Space Flight Center, said a cross-agency study using then-current design reference missions (DRMs) took parachutes entirely out of the landing sequence for a human expedition. Instead, either a rigid or inflatable aerodynamic decelerator would slow the entry vehicles from hypersonic speeds to supersonic speed in the Mach 2.5-3 range. At that point, the EDL system would shift to rocket propulsion for the remainder of the landing. It will not be easy to ignite a set of downward-facing rocket engines as they fly through the Martian atmosphere at three times the speed of sound.
I think SpaceX solution of putting Super Draco rocket pods backward and canted outward at 45° will work: if rockets are inside the Mach cone, they will not be hited by supersonic stream, and if they are hypergolic, like they are, ignition will be quite easy.
Super Draco pods will be perfect for a hab that has to remain on Mars surface, but not for a MAV, because 45° canted out rockets lost too much delta-V to be useful for orbital ascend. This problem can be fixed munting another ascend rocket in the middle of the thermal shield or using basculant rocket pods that fire at 45° outward douring descend and straight during ascend.
Happy Easter to all!
#452 Human missions » Cheep simulation of low gee environment » 2014-04-16 03:52:27
- Quaoar
- Replies: 14
We know a lot of body modification in microgravity, and almost nothing in law gee environment like a Mars 0.38 gee. To save mass for a space mission, it can be very useful to know how much gee fraction astronauts need to avoid negative effects of microgravity, and if periodic centrifugation in a short arm centrifuge can be enough or not (it's easier and cheeper fitting a 2.5 - 3 meters radius centrifugue in a Falcon H/Delta IV launched module that building a spinning ship).
I propose a way to study the issue on Earth with low cost stuff.
1) Instead of 6° head down bed rest, microgravity can be better simulated with head-up bathing in a swimming pool: differential hydrostatic pressure give a very good body fluid shift, and floating in the water, subjects can moove almost like astronaut do in microgravity.
2) low gee environment can be either simulated on Earth in this way: subjects have to be suspended orizontally to the roof with some kind of climbing harness, keeping the feet on a horizontal centrifuge: we can choose from a 2.5-3 meters radius that can be fitted in a Falcon H/Delta IV module or a 15-20 meters that can give a better simulation of Mars surface.
#453 Human missions » LOX/CO2-Diborane rocket for reusable landing boats » 2014-04-14 05:32:18
- Quaoar
- Replies: 8
I found this interesting article of Zubrin about CO2-Diborane rocket for MAV, that has an exaust velocity of almost 3 km/s with an O/F ratio of 2.5.
Zubrin's idea is to bring diborane from Earth, get atmospheric CO2 from Mars, and use it as oxidizer for orbital ascending.
http://www.google.it/url?sa=t&rct=j&q=& … 2518,d.Yms
On wikipedia, I also fond that diborane, with LOX as oxidizer and an O/F ratio of 1.96 has an exaust velocity of almost 4 km/s, second only to LOX-LH2 rockets.
http://en.wikipedia.org/wiki/Liquid_rocket_propellants
So we can imagine a resuable landing boat like GW's design, with single fuel-dual oxidizer rockets, that use LOX-diborane for the descend, get CO2 from Mars atmosphere, and use it for ascend, saving a lot of mass, but without complication and energy needs of chemical processing: only a compressor to get CO2 and to store it as a liquid.
#454 Re: Interplanetary transportation » Landing a flying saucer on Mars » 2014-04-12 06:11:59
Sounds like a great technology, I'm excited to see the results!
It may be interesting to confront pros and cons of LDSD v.s ADEPT
#455 Re: Human missions » Absorbed Surface Radiation » 2014-04-11 02:42:48
By the way, I have access to the Curiosity paper through my university and I'd be glad to email it to you if you're interested. I believe you have my email?
One interesting table discussed the radiation under the surface. According to the paper, under 2 m of regolith the annual GCR dose will be 15 mSv, 1.5 Rem. While not trivial, this is well within acceptable limits. Although their models are more complex than this, I found the halving distance to be about .45 m for every meter past the peak radiation level at .1 m below the surface. Overall, for depths greater than 10 cm, a good approximation is:
R(D)=R_0*1.5*.5^(D/.45)
Where R(D) is the radiation that would be experienced by a person under D meters of shielding and R_0 is the radiation that they would experience with no shielding. Using the density estimate from the Curiosity paper (2800 kg/m^3), and assuming a habitat pressure of 500 mb, the depth of shielding would have to be 4.8 m. At this depth, the annual radiation dose for a person who remained inside would probably be about .2 mSv, or .02 Rem. Compared to .3 Rem per year on Earth, this is negligible.
However, this calculation is meaningless if the regolith used for shielding is itself radioactive.
I live in Rome, one of the most radioactive cities in the world: we have almost 0.2 REM/year, but the frequencies of neoplasies are almost the same of other less radioactive cities. I suppose that 1.5 REM/yr for 500 days are less than 0.5 REM/yr. for 80-90 years.
#456 Re: Human missions » Yet another Mars architecture » 2014-04-10 01:51:45
Nope. The lander will land on Mars surface, and it won't lift off again. The Mars Assent Vehicle will lift off, carrying crew to Mars orbit. In my design, the MAV will have extra large propellant tanks because it will be the TMI stage. So the MAV is used for trans Earth injection.
Interesting: have you posted your design?
#457 Re: Life support systems » Crops » 2014-04-09 15:09:13
It was flight tested successfully as a one-meter long model propelled by pulses of high-explosive (dynamite or something similar) back about 1959, so we have known for half a century it will work.
GW
It was tested in atmosphere, where the plate is cooled convectively. In space the plate will be cooled radiatively so pulse frequency has to be lower and the plate (probably some alloy of tungsten) has to function as a radiation shield, as a shock adsorber and as a heat radiator. The ship will need also very powerful RCS rockets to mantain attitude douring pulse.
And first of all, the first nuclear pulse has to be fired in high Earth orbit.
#458 Re: Human missions » Yet another Mars architecture » 2014-04-09 14:44:19
And I was concerned with my design. That is an Interplanetary Transit Vehicle, Dragon as escape pod, and Mars lander, all docked together. The assembly has to be balanced on a tether while rotating for artificial gravity, and has to be safely tucked behind an ADEPT aeroshell during aerocapture. Counter weight for artificial gravity would be the spent TMI stage, so the tether could be cut and the counter weight released on approach to Mars. But the ITV has to be balanced for artificial gravity, and balanced behind the aeroshell for Earth aerocapture, with Dragon but without the Mars lander. To achieve that ballance, that implies the Mars lander should be coaxial with the rest. In other words, should be on the "roof", between the ITV and tether. But the assembly would de-spin after releasing the counter weight, so zero-G as it aerocaptures. Then remain in zero-G in Mars orbit. So un-docking the Mars lander would be easy.
To avoid the tether whipping back, the tether would be released with the counterweight. That is, cut at the ITV/Lander. This requires a new tether on the MAV, so it can be used as counter weight during transit back to Earth.
Will the rockets of the lander be used also for trans Earth injection?
#459 Re: Interplanetary transportation » Nuclear combustion » 2014-04-09 14:37:46
To reduce power consumption, we really want something to reduce radiant heat loss from the plasma. I suspect the 20,000 watts per inch diameter are due to radiant heat loss. Can we create a layer of something that reflects specific electromagnetic frequencies emitted by hot plasma? Such as a gas? Laminar layers of gas to prevent radiative and convective heat loss?
I suspect plasma can be tuned to become reflective at some frequencies using Langmuir waves: a possibility may be a plasma sandwich with an hot positive core between two cold negative layer tuned to be reflective at the frequencies emitted by hot layer.
But, instead of using plasma windows as the walls of the chamber that contain the reaction, why not using the plasma window as a reaction support?
I imagine a stack of windows of uranium exafluoride plasma, mantained at 14000° K by nuclear reactions, with hydrogen or water steam propellant that flows between the windows, gaining an exaust velocity of 27 km/s for hydrogen or 11 km/s for water.
#460 Re: Human missions » Yet another Mars architecture » 2014-04-08 15:30:17
I may be wrong, but there is a shape issue with aerocapture, entry, even just plain hypersonic flight. You cannot have one module's shock wave impinging upon an adjacent module. That causes extreme shock-impingement heating, and is what nearly cut the tail off one of the X-15's on its Mach 6.7 flight decades ago. That bird was carrying an experimental scramjet nacelle on its ventral fin stub, instead of a nice "clean" fin. The compression spike shock angled right up through the tail section in a beautiful Mach 6 conical shock pattern. Cut away Inconel-X superalloy structure, it did.
To do aerocapture (or entry, or hypersonic flight) you want one single very clean shape exposed to the hypersonic wind blast, such that none of the shock waves it inevitably sheds can directly impinge upon adjacent surfaces. For small space probes, this is easy to do as a single heat shield panel of some kind, behind which you can hide pretty much whatever you want. For a big cluster, I have doubts this can be done. At least in any practical way.
GW
We can have a one piece 40-50 tons triconic habitat with thermal protected belly that detatchs from the "Johnson Express" and aerocaptures in low Earth orbit. The rockets and lightweight almost empty tanks insert propulsively, rendez-vous and dock again with the hab, ready to be refueled and reused.
On Mars orbit we can choose to do an all propulsively inserction or a split and redocking arrive, with the full loaded habitat that aerocaptures, the rest of the ship that inserts propulsively and the lander that performs an aerocapture followed by an atmospheric entry.
An alternative may be to have a 20 meters diameter ADEPT like deployable aeroshell with all the modules that dock concentrically around the habitat, forming a compact cluster inside the heat shield. After aerocapture, the modules can detatch and redock in line forming a long baton for artificial gravity.
#461 Re: Interplanetary transportation » Pit stop in L2? » 2014-04-08 09:48:57
I found this work ( http://pdf.aiaa.org/preview/CDReadyMJPC … 8_4520.pdf ) about a direct evaporation bismuth Hall thruster.
Bismuth is cheep and has a lower ionization energy than xenon.
#462 Re: Human missions » Yet another Mars architecture » 2014-04-08 07:26:28
I would think every module should have its own thruster system to maintain attitude until a vehicle can dock with it and put it where it needs to go. The trouble is spin, can't let that happen. But, it's a minimal thruster rig that can be turned off, or even removed and repurposed.
GW
Why not to add a thermal protection on the belly to perform aerocapture?
Mars atmosphere has a variable density and may be dangerous to aerocapture with LOX and LH2 in the tanks: so your modular spaceship can do Mars arrive propulsively and use aerocapture only for Earth for return, when the tanks are almost empty and the ship is lighter, saving hunderds tons of propellant mass.
#463 Re: Interplanetary transportation » A proposed rocket fuel proton-antineutron deuterium » 2014-04-08 06:44:19
According with this guy, it's impossible
#464 Re: Interplanetary transportation » VASIMR - Solar Powered? » 2014-04-08 06:14:46
On second thought, GW's idea, of storing water and electrolyze it, seems fantastic: LOX-LH2 rockets, working with a perfect stoichiometric O/F ratio of 8:1 have slightly lower exaust velocity (almost 4.4 km/s instead of 4.6) but I think its very convenient to trade 0.2 km/s for the semplicity of water storage.
Another option may be to use a tripropellant rocket with a more classical LOX/LH2 ratio of 6 and and some RP1 to be bourned with the oxigen in excess (almost 0.8 tons every 9 tons of water for a good LOX/RP-1 ratio of 2.5)
I imagine this kind of ship with a concentric shells water tank sourrounding the habitat, to protect astronauts from GCR and SPE.
The ship will have solar panels for life support and a SAFE-400 100 KW nuclear reactor, completely dedicated to electrolisys, cooling and liquefaction, that can produce almost 500 kg/day of LOX-LH2.
Nuke weight almost 500 kg: I don't know how much weight electrolisys and cooling equipment, but I think it's in the range of 2-4 tons.
To have also electric propulsion, just add another 100 KW SAFE-400.
In this way, we may have a ship that can go and refuel everywhere, just like a water NERVA, but that can be built now with very minimal R&D.
#465 Re: Life support systems » Crops » 2014-04-08 06:05:04
Real colonization needs bigger ships than we usually contemplate.
We have known since the late 1950's how to build one version of such a thing: nuclear pulse (explosion) propulsion. Those ships are quite large (must be immense to have good Isp), something like 10,000+ tons at launch.
Think 20,000+ tons, Isp 12,000+ sec, vehicle acceleration 2 to 4 gees during burns. Made out of 1 or 2 inch steel plate, like a marine ship, so there's a lot of shielding effect there. Big enough to spin about any axis you want, for artificial gravity. With modern nuke device technologies, performance should be even better, and the nuke "side effects" less.
In ships like that, you can ship any crops and farm animals you could possibly imagine, along with hundreds to thousands of colonists. But, NOBODY is working on this idea. Not since 1965.
GW
Sorry GW, but I've some doubt if Orion propulsion would really work as figured: can the tail plate survive many nuclear explosions without breaking or melting?
Will nuclear exolpsions be perfectly simmetrical, to accelerate the ship without putting her in an uncontrollable tumbling?
Will the ship mantain her attitude douring pulses, avoiding dangerous offset that will expose the habitat outside the shadow sield?
A gas core NTR will be more manageable.
#466 Re: Interplanetary transportation » VASIMR - Solar Powered? » 2014-04-07 14:45:19
How about splitting the water at 9:1 oxygen:hydrogen, then diverting some of the oxygen to life support. That plus a little kerosene would get better propellant ratios, perhaps, for a tripropellant engine.
GW
It may be better, but water electrolisys will produce 5.4 Kg/Kw per day of oxygen and hydrogen, so a spaceship with 20-30 KW of solar panels will produce 19.4-29.4 tons of propellant in 180 days, that may not be enough for a 4-4.5 km/s delta-V of Earth orbital inserction if the ship is quite massive like your projects. Propellant production can be done in Mars orbit but it will take almost the woole lenght of the surface Mission, so it may be better to store LOX and LH2 with a good active cooling system. Even in this case, a LOX-RP1-LH2 tripropellant rocket may be a good option because it has a good exaust velocity and LH2 is only 6% of the whoole propellant mass, resulting less tankage and cooling power.
Another option may be to mount very big solar arrays or one or two 100 KW SAFE-400 nuclear reactor: in this case we can store water and produce 45-90 tons of propellant in almost 100 days.
#467 Re: Life support systems » Crops » 2014-04-07 12:44:04
Aquaculture requires a lot of water. And some people here have argued to clean clothes without liquid CO2, as an extreme measure to conserve water. NASA's current water processing equipment on ISS is rated to recycle wash water, yet people think it's necessary to avoid water. Do you realize how much water that takes?
Liquid CO2 washing was proposed for a first mission where is not known if there is water or not in the landing site. But a colony is supposed to be found on a reliable water source like a buried glacier: no water no colony. If we are talking about early missions were astronauts farm crops in enflatable greenhouse I agree with you that fishs are premature.
The trouble with only vegetarian diets is that vegetable proteins usually laks in some essential amminoacids, and to fix it is necessary to eat many kind of variety. So astronauts have to farm many kind of crops in a little greenhouse and this can be very difficoult. An alternative to have a balanced diet may be to add some dry food from Earth.
A cereal with a well balanced amminoacid composition is farro ( http://en.wikipedia.org/wiki/Farro ), that was anciently used to feed Roman soldiers: I never found it in US, but in Italy is still used as a base for very good soups and special breads. It may be interesting for a Mars settlement.
It will be also possible to develop special GM crops for Mars, with high harvest gain (thiny stalk for a 0.38 g environment), low water need, balanced amminoacid and starch composition, radiation resistence and vitamin enriched, so animal proteins will be not necessary.
And seeds are reasier to transport. Remember, 6 months in space, and at least some if not all of that in zero-G. I have argued that a far future, advanced Mars settlement could transport cattle using hybernation. You would transport young calves, just weened from milk. But it's so expensive to feed and house cattle on Mars, that it will be a very long time before that happens.
Besides, I already find "vegan Mars" attracts some people.
Animals will arrive only when the colony will be well developed and spaceships will be bigger, with artificial gravity and cosmic ray shielding (mini-magnetosphere or something like it). Only some female puppies and frozen male sperm to start. The bulk reproduction will be done in situ.
#468 Re: Life support systems » Crops » 2014-04-07 08:15:40
I find it interesting how molecular structures are so similar. The same structures repeated again and again. Chlorophyl is the same as hemoglobin, just chlorophyl has a single atom of magnesium in the centre instead of iron, an chlorphyl has a hydrocarbon tail. That tail acts as an antenna, but the whole molecule is tuned. Chlorophyl A and Chlorophyl B are only different by one small group on the body of the molecule, not the antenna tail, 'A' has CH3 while 'B' has CHO. Vitamin B12 is very similar again, but has a single atom of cobalt in the centre instead of iron or magnesium. However, B12 is a bit deformed. Hemoglobin and chlorophyl have neat symetrical bodies, with 4 nitrogen atoms bonded to the central metal atom, and 4 hexagonal carbon rings with 3 of the carbon atoms replaced by the metal and two of the nitrogen atoms. So these hex rings share atoms. Between the hex rings, are penta rings, where 2 of the carbon atoms share an atom with the hex rings, and one carbon is again that same nitrogen. Vitamin B12 is the same, but one of the hex rings is only a penta ring, that's why I call it deformed. B12 has a hydrocarbon tail just like chlorophyl, and bonded at the same place, but the end of that tail has an amino acid, and that tail is folded in so the amino is bonded to the central metal (cobalt) atom. Interesting.
http://upload.wikimedia.org/wikipedia/c … _b.svg.png http://www2.estrellamountain.edu/facult … chlphl.gif http://upload.wikimedia.org/wikipedia/c … alamin.png
Evolution uses the same sinthesys path with some variation to build different molecoules for many purpose.
#469 Re: Life support systems » Crops » 2014-04-07 08:13:16
A full vegan diet is not so healthy as many thinks
http://austriantimes.at/news/General_Ne … esearchers
but, on a Mars colony, may be very easy and cheep to couple greenhouses with aquaculture, farming herbivor fishs feeded with cereals wastes: giant gourami and catfish are very easy to grow and can be a very reliable sources of animal proteins. Later we can introduce "low cost" animals like chikens and after porks. So the colonist have meet and need only to import from Earth milk powder for children.
Only when colony has grown enough, milk cows for children can be imported.
#470 Re: Interplanetary transportation » VASIMR - Solar Powered? » 2014-04-06 11:16:54
Quaoar:
I'm not sure that "cryocoolers" suitable for use in space on cryogenic propellant tanks are a "mature" technology or not. Bob Clark or RobertDyck may know more about that. But, I'm pretty sure such a thing could be made ready in a small handful of years; it's not far-future, blue-sky stuff.
I am very intrigued with the notion of accelerating/decelerating along the transfer to cut transit time, using electric propulsion. This would be a dual/hybrid propulsion set-up, like we discussed above, with conventional propulsion doing the impulsive burns at Hohmann transfer delta-vees, at each end of the transfer.
I don't have a good way to estimate how much transit time reduction might be achieved this way. Does anyone have a method of calculating this?
Here's another notion for stable LH2/LOX propellant storage long-term: why not store it as water, even as ice? Just electrolyze what you need for the next burn, with solar electrolysis along the way? Does that sound like a feasible thing to do?
Producing LOX-LH2 from water will result an O/F ratio of 9 that is a bit higher, but if you use a tripropellant rocket like RD-701 (LOX-RP1-LH2) it may be work vewry well: we can store only water and kerosene, with the tanks that surround the habitat, resulting a very good cosmic ray shielding: with 50 g/m2 of water and kerosene around the habitat, astronauts will take only 35 REM/year at solar minimum and near 13 REM at solar maximum ( http://www.cs.odu.edu/~mln/ltrs-pdfs/NASA-97-tp3682.pdf - kerosene and water have almost the same shielding power of polyethylene).
An RD-701 like rocket has a very high thrust with an exaust velocity of 4 km/s that is still very good.
RD-171 was projected to work with 79% LOX; 15% kerosene; 6% LH2: to be optimized for using LOX and LH2 from water the newer version will be function with an higher percent of LH2 (something like 77.6% LOX; 13.8 % RP-1 and 8.6% LH2) resulting an higher exaust velocity (4.2 km/s?).
#471 Re: Human missions » Yet another Mars architecture » 2014-04-06 11:00:59
This might be off-the-wall, but it seems to me that converting a propellant tank to habitable space involves a lot of effort and maybe significant hardware weight that could be avoided by using a different approach.
Why not just build the habitable spaces as dedicated modules, and then dock propellant tanks and propulsion items to it, in space. All of these may then be "optimized" for their roles, especially if you want to re-use this vehicle for multiple missions. The only things needing replacement are the life support consumables and the propellants, and periodically for maintenance, the engines. GW
To perform docking, has every module an indipendent RCS?
#473 Re: Interplanetary transportation » VASIMR - Solar Powered? » 2014-04-02 05:28:22
I'm thinking about it. Too many loose ends still not yet tied up with the Mars Mission 2013 posting.
For example, LOX-LH2 active cooling for your orbital ship and for your landing boat on Mars surface can be considered a mature technology or we have still to do some R&D?
But employing more than one kind of propulsion is starting to make a great deal of good "gut-feel" common sense.
GW
It may be very interesting.
#474 Re: Human missions » What if te next major planet out was a brown dwarf? » 2014-04-01 01:52:04
When travel times with current technology are measured in years, it seems a bit silly to talk about sending manned missions to the Oort cloud. We would need some real breakthroughs in propulsion.
Back of the envelope for a really large (20,000+ ton) nuclear pulse propulsion ship: Isp 20,000 s and vehicle acceleration 2 gees "typical". Distance to target: assumed to be 10 billion km. Delta Vee one way from here to there: assumed to be 30 km/s. Carry enough nukes for 60 km/s two-way trip, as a single stage vehicle. I may be wrong, but I got a mass ratio of 1.358, for 23% nuke propulsion charges of the total departure mass. It accelerates in about 0.2 hr to 15 km/s, and takes around 21 years to get there, coasting at 15 km/s.
Clearly, even a nuke pulse propulsion ship like that would have to fly much, much faster to make such a voyage practical.
Go to 65% propellant, mass ratio 2.857. Total delta vee 206 km/s. 103 for the 1-way trip. coast velocity near 51.5 km/s. 1-way travel time now near 6 years.
Now make it a 1-way mission, so the coast velocity is 103 km/s. Still near 3 years.
Guys, we really need "warp drive" for these sorts of missions.
GW
There is even the nuclear salt water rocket by Zubrin: http://en.wikipedia.org/wiki/Nuclear_salt-water_rocket
#475 Re: Interplanetary transportation » Organometallic Propellant » 2014-04-01 00:59:11
Lithium is a no-go as a content of any rocket fuel being considered for Earth launch because it's rather rare abd has demonstrated effects on mood even in small concentrations.
Lithium was used for bipolar disturb therapy: if astronauts go mad it can be benefic 
.
So, if we want an orbital ship for a Mars mission we have to continue using hypergolics. These new R-4D derived Aerojet rockets have 335 s of Isp with NTO-Hydrazine and 330 with NTO-MMH ( http://ntrs.nasa.gov/archive/nasa/casi. … 001339.pdf ): very impressive!