Date: Tue, 13 Sep 1988 20:47-EDT From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #3 Contents: James R. Van Zandt rocket fuels Roger Arnold low inclination EML Andrew Bell Re: low inclination EML ------------------------------ To: space-tech@cs.cmu.edu Subject: rocket fuels Date: Tue, 13 Sep 88 13:08:43 EDT From: James R. Van Zandt Paul Dietz writes: > If the total delta-V required is 200 m/sec, and one is using a > monopropellant with Isp of 150 seconds, the fuel fraction is about 15% > (what's the Isp of hydrazine?). "Typical values of specific impulse are: hydrazine 230 s, solid propellants 290 s, and liquid hydrogen and oxygen 445 s." - Dr. Gary D. Gordon, "Spacecraft Technology", 1982. The exhaust velocity Ve is related to the specific impulse Is by: Ve = Is g, where g is the gravitational acceleration. The fuel fraction is calculated from initial_mass / final_mass = exp( delta_V / Ve ) or fuel_mass / initial_mass = 1 - exp( -delta_V / Ve ) (for small fuel fraction this is approximately delta_V/Ve ) If I've done the arithmetic correctly, we have these values: Is fuel fraction 150 12.5% 230 8.3% 290 6.7% 445 4.4% - Jim Van Zandt ------------------------------ From: telesoft!roger@ucsd.edu ( Date: Tue, 13 Sep 88 12:05:37 PDT To: space-tech@cs.cmu.edu Subject: low inclination EML Regarding electromagnetic launch through the atmosphere at low angles of inclination, here's a message that I think posted to the net a month or so ago. Don't recall seeing any responses, though, so maybe I blew it. Anyway, here it is: - Roger Arnold ucsd.ucsd.edu!telesoft!roger 8<------------------------(cut here)--------------------------------- Here's an idea for resolving the problem of electromagnetic launching through the atmosphere at low inclinations. It's one of those ideas that initially strike us as crazy, because it's so out of line with the kinds of systems we're used to. But when you start looking into the physics of it, maybe it's not so crazy... The idea is to fly the launch catapult to high altitude, avoiding 90% of the atmosphere. So the catapult needs to be several kilometers long? No problem! Build it into a verrry long flying wing. With an aspect ratio > 100:1, it would have a fantastic lift to drag ratio. A hundred small engines distributed along its length, independently throttled and thrust vectored for control, to keep all segments of the wing in alignment. A Burt Rutan or a Paul MacReady would have a field day designing the wing. I dibs the active control system. Building the catapult into a flying wing might even prove to be the cheapest way to build the catapult. Think about what it would take in the way of tunneling, excavation and trestle building to create a straight line track miles long up the side of a remote mountain. Then think about assembling a bunch of catapult/wing segments inside a hanger at Edwards, then rolling them out and linking them up on the dry lake bed. Bear in mind that nothing at all fancy is required for the wing structure itself. Since it will fly at high altitude, the wing loading will be low, and the load will be distributed along the length of the wing. Good old wood and canvas would do just fine. Anybody have a few tens of millions they'd like to invest? ------------------------------ Date: Tue, 13 Sep 88 16:30:28 From: Andrew Bell To: space-tech@cs.cmu.edu Subject: low inclination EML Problems with the flying wing: 1) Action/reaction is going to be a problem: the same force pushing the object into space will also be pushing the flying wing down. 2) Objects going at such high speeds near the muzzle are going to need a *straight* path. Canvas and wood just aren't going to be steady enough. 3) Your accuracy in placing things into space from a wind affected platform is going to suffer. I doubt you can place things precisely enough. I don't think digging a straight tunnel through rock is really such a big problem that you can't put the thing *inside* a mountain. This will save you from the elements and give a nice surface to build things on; the only thing you need is a place with little or no geologic activity. -Andrew Bell bell@cs.unc.edu ------------------------------ [ end ]