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NASA?s full Artemis plan revealed: 37 launches and a lunar outpost
Jeff Findley wrote on Thu, 30 May 2019
07:33:03 -0400: In article , says... We know what is in the Martian atmosphere. We know how to extract fuel from it. Well, no, we don't, in any effective way, unless your plan is to use up over half your cargo capacity hauling LH2 to Mars. Yes, that's the initial plan, at least for SpaceX. They plan on sending a couple of Starships, uncrewed, to Mars to work on propellant production ahead of sending a crew. Those initial Starships would be carrying all the LH2 they need to produce the return propellant needed for later crewed Starships. This plan doesn't work very well when you look at the details. It's also not the SpaceX plan that I've seen. https://www.inverse.com/article/5129...rting-a-colony According to this, the missions look like this: 2022 (two cargo ships): "The ships would place power, mining and life support infrastructure for future flights. They would also confirm water resources and identify hazards." 2024 (two cargo ships plus two manned ships): "They will be tasked with setting up a propellant production plant, combining Martian water, ice, and carbon dioxide to create methane and liquid oxygen to fuel the ships and come back home. The humans would be tasked with collecting one tonne of ice every day to fuel the plant." Note that use of Martian ice collected by humans to fuel the propellant plant? And you're going to need water for your people. You don't have to send everything on one ship. On the first mission, you send to uncrewed Starships to make propellant for the return trip. Yes, something on the order of half their cargo is LH2. The rest is processing equipment, power generation, power storage, and etc. Pretty much everything on those first two ships exists just to make propellant. Over 60% of their cargo must be LH2 if you're going to make enough methane to fuel two Starships for the return trip. And note that your plan is not the SpaceX plan. Your plan presumably leaves four Starships sitting on Mars while two of the six make the return trip to Earth using the fuel that the first two ships made. The SpaceX plan says you bring lots of other stuff beside 'fuel production' on those first two ships, including vehicles, life support, ****loads of solar panels, etc. The SpaceX plan says those first two ships bring rovers to locate water. Fuel production doesn't start until humans are on site with the start of the second mission. 'Stay time' of that mission will be on the order of 14-18 months. That says that SpaceX expects some 420-544 tonnes of Martian ice will be made into fuel during the manned stay. That nominal 500 tonnes of ice gets you around 55-60 tonnes of LH2, or enough to refuel a single Starship. So the SpaceX plan doesn't seem to work, either, unless you leave five Starships behind. Obviously, bringing your own LH2 doesn't work (it reduces your cargo too much for you to do much other than very long 'flags and footprints' sorts of missions) and requiring people to be on scene to move Martian ice at a tonne a day doesn't work (you can't move enough ice at that rate to get all the ships refueled). So, equally obviously, you either need the manual workers to move a lot more ice than that (unlikely) or else you need to somehow automate the ice collection. On the second mission, you send two crewed Starships. Those would have the water necessary for the crewed missions. How big are your crews? You're going to need a tonne and a half of water for each person. Plus they, too, are going to have to carry that 60+ tonnes of LH2. Plus food. Plus vehicles (which your plan doesn't send on the first ships). Plus everything else needed to establish some sort of base, if you're doing more than 'flags and footprints'. If you're going to do more than 'flags and footprints' (and you are, because you can't make fuel for the return trip fast enough), you need two years or so of water per person you send. That's around a tonne and a half of water per person. That hundred tonnes of cargo per ship is going fast... Again, water comes on the crewed Starships. Also, with some water recycling, you don't need the full two years or so of water per person. How much water you need depends on how efficient the recycling is. We have a lot of experience with this on ISS, so it's "simply" a matter of running the numbers and doing the engineering trades. There's a trade off here between what the recycling equipment weighs vs what the water weighs. And if your plan is to use in situ water (and pretty much every plan includes that as a requirement) you're going to have to build that water extraction plant that you can't know how to build until you go and analyze the hell out of everything (according to Jeff) but you can't go do THAT until you can build a water plant. That wouldn't come until later. Until a Mars base can bootstrap in-situ water production, you're stuck sending more LH2 and processing equipment on uncrewed Starships and sending more water with crewed Starships. But yes, once that in-situ water production gets going, you can replace the LH2 and some of the water on future Starships with other cargo and/or more people. Musk's ambition is to set up a Mars colony. As such, he's already planning on sending a crap ton of Starships to Mars. His ambition is the opposite of flags and footprints. And Musk doesn't appear to be planning to haul hundreds of tonnes of LH2 to Mars. Musk appears to be planning on relying on in situ water from the get go. And that's not practical, either, unless they can move a hell of a lot more than a tonne a day of water. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
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