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Kbd512:
Can't answer your questions because I'm not a turbine expert. The textbooks make no mention of supersonics on the compressor side. Turbine side is different: always has been low supersonic coming out of the turbine nozzles. Shapes on that side are not suited to be propellers or fans, though.
Spacenut:
I quite agree that spin artificial gravity needs investigation. Instead of taking 6 months to poke around inside a BEAM attached to ISS, the way to do that is to buy 4 or 5 B-330's from Bigelow, launch them individually on the Atlas-5's they fit to ISS, and dock them together adjacent to the station. These will need a bit of refit by deleting some of the solar panels, and adding fold-out decks to the module cores, nothing particularly hard about that. Then just spin the damned thing up to around 4 rpm and see how habitable it could be. If you can get a conventional toilet to flush, you've solved the very hardest human-factors item for life support (ha! ha!).
All:
I think the inflatable and foldable heat shields should receive a bit of acceleration in their funding and schedule. But, NASA should be paying very close attention to Spacex's Red Dragon landings. Those start in 2018, if Spacex can get its act back together and start flying again. Those no-chute high-ballistic-coefficient retropropulsive landings, if successful, will be light years ahead of anything NASA knows how to do. If NASA were smart, it would ramp up its participation in, and support for, that effort.
By the way, my figures, bogus though they are, show a 6 metric ton capsule at touchdown, carrying 2 tons of dead-head payload inside. The propellant load to execute the landing is only 1.8 tons. What comes out of hypersonics for ignition is only 7.8 tons. So I don't think the propellant load for a retropropulsive landing is excessive, even in air that thin.
The hard part is the extremely precise shallow entry "window" you must hit, and the precision entry trajectory you must fly in spite of unpredictable density variations from "nominal" by around a factor of 2.
Eventually, I see the inflatable or foldable heat shield technologies added to the retropropulsive landing technology, to decrease the stringent requirements either faces alone. This would make precision landings far more reliable. But you don't have to wait for that combination in order to go.
All:
I'm not so sure that extremely-efficient life support is a make-or-break for going to Mars. We already know we could do it entirely by packed expendable supplies, but that takes a huge vehicle, because the weights and volumes are so large. We have some technologies from the various stations that already help reduce that penalty.
So, I suggest we base the ship design on what we have working right now, knowing it will be a bit larger and heavier than some might like. If we get the life support improved, fine, take advantage of it by sending more people and payload. If not, we still get to go with what we have. So what is wrong with that as a mission design management philosophy?
All:
The electric propulsion we have working right now is Hall thrusters using xenon, I believe. I'm no expert about any of that. We also have solar power panels, and we have nuclear power supplies, that could run these things. The only real trouble is size: where are the big ones? Fix that, and we have another piece we can use to go to Mars. If a better thruster comes along by the time we go, fine. But start with what you got. Just scale it up, build it, and test it, so at least that will be ready.
The application for this is the stuff we send ahead unmanned to the site at Mars, be it surface or orbit. Cargo doesn't care about trip time. Spiralling out and spiralling in is not a problem for cargo. It is for men. I think nearly all the different plans require stuff be sent ahead. So, we already know we need this item to send it. So, where is the electric thruster / power supply scale-up program?
Address these, and you pretty much have the long poles in the tent addressed.
GW
Last edited by GW Johnson (2016-12-31 10:41:19)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Since we show little sign of proving technologies to sustain human life on Mars, we do have to ship all the needful for the first two or three missions, and they will have to spend considerable efforts establishing greenhouse technology, soil treatment, fuel and oxidiser manufacture and water extraction (for examples), after they have found a good location.
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The bigelow Beam like all of the others have just 1 drawback in that they only come with 1 attachment hatch which means 1 and done unless we send up a node unit to make them mate to in order to make them have a large axis to spin them on.
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If you can get a conventional toilet to flush, you've solved the very hardest human-factors item for life support
Can't we figure out the minimum gravity required for this to work, just using the Vomit Comet? They can do partial-g with that thing. 30 seconds at Lunar gravity should be enough to tell you how plumbing would behave, right?
Use what is abundant and build to last
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Most of the ones we use down here require 10-40 seconds for a complete cycle, depending on whether they are a pressure valve or gravity tank design. That includes at least some tank-filling. A lot of those tanks take 1-2 minutes to fill completely.
At lower gee, I would expect a slower gravity tank emptying process, a slower bowl flush (also partly gravity-driven), slower splash processes, and higher splash levels. There comes a point where it splashes out of the bowl, and may splash out of the tank (those joints not generally sealed, just a lid).
I'm not at all sure that constant partial-gee can practically be flown in the Vomit Comet, or that transients exceeding 30 sec can be observed there. And yet long up-close observations at reliable gee are what we need to modify the existing designs, and they will need modification. Not that it couldn't be done in the plane, but it might be more effective if done in a partial-gee spin habitat in orbit.
GW
Last edited by GW Johnson (2017-01-01 16:43:03)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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A zero-G parabola lasts 20 to 25 seconds. Lunar G lasts longer, and Martian G lasts longest of all. Having trouble googling those times now.
Of course you realize there are alternatives Terry Kok argued for a composting toilet instead of grey water sewage processing. That means no flush at all.
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We got off into this toilet discussion because I made a joke about life support. The "ha! ha!" didn't make it into the quote. I don't know anything about incorporating the little emoticon symbols I've seen others use.
Composting toilets do risk an odor problem. They need to be in a sealed-off compartment. Otherwise, you consign the crew to living inside a sewer, as far as their noses are concerned.
The same is true of water-based sewage treatment: it needs to be elsewhere because of the odors. But it usually is elsewhere, anyway.
I'm not at all certain you want to fully treat 100% of your sewage materials all the time. Such raw sewage is a part of how you turn rock dust into real soil. It's not the only part, but it is an important part.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Just use a good cieling fan to suck up the fumes or spray the scent of roses often.....
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