Pet peeve: long term propellant storage is often implied as difficult, like violation of thermodynamics difficult. I think this is an absurd meme spawned because propellant depots are politically inconvenient for SLS, even though any long term BEO plans assume significant propellant storage.Even passive systems are meant to bring boiloff down to a few percent per year in a high orbit. Then you just add some active cooling. If you can't reliquify a very slow trickle of cold gas in an environment where oxygen lines freeze by accident then the notion of ISRU to aquire - then liquify and store - tons of hot gasses is absurd and the fact we have been doing this on earth for a century or so is absurd.
So Im thinking this MTH should also be this DSH. All these pieces won't emerge at once so it is just as interesting to think about what we do in the meantime. I think we can gain excellent confidence for a mars orbit mission just sitting in high lunar orbit, but without attention to our politicians we could end up with a lunar DSH that somehow proves irrelevant to Mars ambitions which would be a great pity.
At least SpaceX is shooting for completely reusable systems. SLS is not. It could have been.
I would prefer argon for SEP tugs vs xenon. Argon is in earths atmosphere and is far more abundant. It is also about 4-5% of Mars atmosphere. It could be extracted from Mars and launched up to fuel a SEP tug for it's trip back to earth, at least eventually. Xenon is very rare and with all the moving around between earth and Mars, to me it makes sense in the long run to use argon.
I don't think they are impossible...I do think we don't have them off-the-shelf, so putting them on the critical path makes programs around them much more expensive and easier to cancel. I absolutely support their development and I believe in the long run that they are necessary, that the mega-rocket cargo cult has to go away to make human expansion into space viable, even when there are lulls in government support.
My pet peeve is people counting their MCT's before they hatch. I believe mega rockets will return to being relevant when we're sending thousands of people to space every year...but we're not doing that for a long time and even multiples of current flight rates can be supported with systems that lift no more than 50 tons to LEO. I was personally amazed that those who slung mud at Ares/SLS for years completely changed tune with SpaceX saying about doing a rocket in that class, even though most of the arguments against the former system equally apply to any system SpaceX would field. I could be wrong about this and there are details to the MCT that make it a scalable system that has other commercial uses, but I've heard nothing of that nature yet. For expected near terms missions to Mars and the Moon, I overall think it makes more sense to do a single core reusable methane rocket that lifts about the same payload as Falcon Heavy, can support wider payloads; that can be later scaled up as demand increases. But hey, it's not my company!
Quote from: Darkseraph on 05/18/2015 02:43 amI don't think they are impossible...I do think we don't have them off-the-shelf, so putting them on the critical path makes programs around them much more expensive and easier to cancel. I absolutely support their development and I believe in the long run that they are necessary, that the mega-rocket cargo cult has to go away to make human expansion into space viable, even when there are lulls in government support.The problem is that argument is circular in that because they are not "off-the-shelf" (and if you refer to the ACES/Depot studies it nearly is) we should not put them on the "critical path" yet at the same time nothing that is NOT on the "critical path" is being funded so they will by default, never be "off-the-shelf" so they should never be on the critical path...This is exactly why we're here now. We choose a "goal" for which we develop a "critical path" but then specifically do not engage in any infrastructure or equipment development outside of that path but a lot of development within that path to achieve the goal. And pretty much ONLY the goal. This process has proved a failure at sustainment ever single time it has been followed, yet we continue to do the same thing over and over again and expect a different result. (This is the definition of crazy I will note)