Re: Armadillo April 11, 2004

At 09:54 AM 4/12/2004 -0700, you wrote:
>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