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Why is cryogenic propellant transfer any more difficult than other difficult things SpaceX have already done (eg landing a rocket, and building a full flow stag
by geertj 2y ago
Why is cryogenic propellant transfer any more difficult than other difficult things SpaceX have already done (eg landing a rocket, and building a full flow staged combustion engine)? They do this on earth every time they fuel the rocket. I understand it will be more difficult in space, but I don’t see why specifically this problem is the real engineering target over say, reuse.
- preisschild 2y agoLanding/reusing a rocket isn't new and has been done before.
- K0balt 2y agoI wouldn’t go so far as to say it is the “real” engineering target, but it is a foundational capability that underpins the ability for humans to explore beyond the earth-moon system, and it is fraught with difficulty and uncertainty. Fuel transfer and storage in orbit is problematic in many respects.
- geertj 2y agoVery hard and foundational capability need not be correlated though. I think the more likely explanation that orbital refueling hasn't been done yet is not that's it's exceptionally hard, but that there hasn't been a need for it. Orbital refueling needs rapid reuse, and that has only been possible recently (with Falcon 9, and soon Starship).
- K0balt 2y agoGood point?
- GuB-42 2y agoFrom the article: > Like a lot of space technology, orbital refueling sounds simple, has never been attempted, and can’t be adequately simulated on Earth.[18] The crux of the problem is that liquid and gas phases in microgravity jumble up into a three-dimensional mess, so that even measuring the quantity of propellant in a tank becomes difficult. And for cryogenic propellents specifically: > Getting this plan to work requires solving a second engineering problem, how to keep cryogenic propellants cold in space. Low earth orbit is a toasty place, and without special measures, the cryogenic propellants Starship uses will quickly vent off into space.
- objclxt 2y ago> They do this on earth every time they fuel the rocket. I understand it will be more difficult in space, but I don’t see why specifically this problem is the real engineering target over say, reuse. The article goes into this in some detail. In particular: * You have to get the propellant into space. This is going to take a large number of flights (~15) at a pace that has not been done before for a vehicle of that size (a launch every six days) * You need to launch at pace because otherwise the propellant will boil off, which is another issue - you need to shade or insulate the propellant for a much longer period of time in much harsher conditions * There is no gravity: whereas on earth the propellant separates relatively cleanly into liquid and gas this isn't the case in space
- exe34 2y ago> There is no gravity: whereas on earth the propellant separates relatively cleanly into liquid and gas this isn't the case in space can you use a plunger, instead of a pump? more like a syringe?
- imglorp 2y agoYeah, a 9 meter diameter one, which adds mass and volume and complexity and detracts from the payload. Instead what they do is use thrust to accelerate the whole vehicle a little, which presses all the liquid into one end of its tank where it can be pumped out. Instead of carrying special settling thrusters, they originally planned to use ullage gas for this but it's not clear that can work. deeper discussion with math: https://forum.nasaspaceflight.com/index.php?topic=60124.60 https://forum.nasaspaceflight.com/index.php?topic=60124.60
- exe34 2y agoplastic balloon?
- pantalaimon 2y agoWhat plastic is elastic at those temperatures? (-182 °C)
- foreverobama 2y ago[dead]