John Carmack wrote:
http://www.armadilloaerospace.com/n.x/Armadillo/Home/News?news_id=253
An off-the-wall thought on your hover tests and nitrogen capacity: if your propellant tank has a manhole cover, maybe you can put some stainless steel floats inside the tank to fill up some of the ullage volume? They're available cheap from McMaster-Carr, plain 304 or 316 stainless spheres with no mounting spuds.
http://tinyurl.com/2vver
This might let you do a partial propellant load without needing god's own GN2 supply.
I had thought about putting something inside the tank to take up volume, and we had considered floats in the past for slosh control, so that sounds like a pretty good idea.
Running the numbers for 20 cubic feet of floats:
308 x 6" = $23,562 129 x 8" = $15,205 38 x 12" = $15,382
Rather expensive. If we just wanted to cover the surface for slosh control, we would only need about 80 x 6".
Interestingly, the full-up X-Prize propellant load in the bigger tank uses the same amount of nitrogen, because it starts with a higher pressure in a smaller amount of ullage. It is actually 100 lb of nitrogen, which is a strong incentive to use helium when you are aiming for max performance.
John Carmack
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