From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.tech Subject: Re: Reentry without ablation or ceramics? References: <9186edb5.0305121517.3f7bfc4f@posting.google.com> <9186edb5.0305152010.d27c97@posting.google.com> NNTP-Posting-Host: 209.88.68.230 Message-ID: <9186edb5.0305192235.3607d942@posting.google.com> Henry Spencer: >"Easily" is a relative thing. :-) Water is so effective a coolant >that the problem (according to people who've looked at transpiration >cooling) is not supplying *enough* water, but reliably supplying >a very slow and very evenly distributed trickle of it with >lightweight plumbing. (Tiny orifices for flow control can plug >up very easily.) Transpiration cooling does seem very interesting for an RLV. To try to get an idea of how much water it takes, I have made some more graphs. See: http://www.spacetethers.com/transpiration.html I don't take into account how having this layer of relatively cool steam will reduce the amount of heat getting to the vehicle. Also, I only use the heat of vaporization. In reality there will be more heat going into the steam after it boils. For both of these reasons, water mass amounts should be lower than what I have. Some interesting points in this less than perfect data: 1) If you are cooling the whole vehicle (not just the nose) it takes more water the more wing area you have. 2) If you are just cooling the nose, then the more wing area the less water it takes. 3) Cooling just the nose of a suborbital rocket coming back from a tether rendezvous takes very little water! Even cooling the whole vehicle is not too bad, like 1.6% of mass. Ya!!!! No need for big wings. And as Henry said, aluminum could work fine. 4) Cooling a whole vehicle from orbital speed could take 25% of the reentry mass. A more accurate simulation would reduce this, and maybe by a lot. If anyone knows how to calculate something more accurate for transpiration cooling please let me know. Actually, any pointers to good info on transpiration cooling would be appreciated. I found and ordered: http://www.stormingmedia.us/cgi-bin/80/8039/A803973-108-1t.php But don't know how good it is yet. -- Vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Vincent Cate Space Tether Enthusiast vince@offshore.ai http://spacetethers.com/ Anguilla, East Caribbean http://offshore.ai/vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You have to take life as it happens, but you should try to make it happen the way you want to take it. - German Proverb