SSTO ( Single Stage to Orbit) is something of a dream for Earthbound space travelers, but it has already been achieved from the moon. If it hadn't, the Apollo missions could not have been a success.
But a problem still remained in that you still needed a descent stage combined with an ascent stage. There were no facilities for refueling on the moon, which required that all fuel for both descent and ascent had to be carried in one package. This had some significant disadvantages. One of them is the mass penalty. The more mass you have to carry, the more penalty you have to pay in additional mass for propellant. This can be quite expensive, since it is so costly to get that stuff to the moon in the first place.
What if that mass penalty can be minimized? That's what in-situ resourcing proposes to address. If you can get your propellant from the moon itself, then you won't have to carry it with you. This can make a big difference in terms of cost and complexity in getting from lunar orbit and back.
The earlier post today describes a technology that could do just that. By harvesting lunar oxygen, it will do away with that mass penalty and by doing so, will create opportunities to do some interesting things on the moon.
Here's some spreadsheet calcs that I've been fooling around with. I took this from some 'what if' calculations that I did last fall- for a type of SSTO which used beamed energy instead of burning the propellant. The ISP numbers and such may not be 100% accurate, since I haven't updated it completely. But the idea is basically the same as what I tried to calculate back then. I was tryijng to figure out how to beat the mass penalty. It appears that this has already been done with ISRU technology mentioned in the previous post.
Well done.
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| The circled numbers are the masses needed for liquid hydrogen. Note the additional margin for cargo and crew |
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