A kerosene-fueled X-33 as a single stage to orbit vehicle.
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From: Marvin the Martian on 4 Apr 2010 04:00 On Sat, 03 Apr 2010 23:45:52 -0800, Pat Flannery wrote: > On 4/3/2010 5:17 PM, Craig Bingman wrote: >> >> Hi Pat, >> >> I don't understand how deuterium would help at all. It weighs twice as >> much, it has no more enthalpy of combustion, and i would think that the >> increased mass of deuterium would hurt specific impulse by increasing >> the effective molecular weight of the exhaust. >> >> Can you or someone else give me a reality check on that one? > > Here's the article where that combo is mentioned, that came out well > before April 1st: > http://www.thespacereview.com/article/1591/1 The part before that > mentions the problems with fluorine: > http://www.thespacereview.com/article/1580/1 According to one poster to > this thread, the advantage liquid deuterium gives you is that it's a lot > more dense by volume than standard liquid hydrogen, so you can decrease > the size of your fuel tanks for the same amount of energy content. No, you have the same MASS, but only HALF the energy. Energy goes as the number of moles of H2/D2, not by the mass.
From: Alan Erskine on 4 Apr 2010 05:47 Sorry to interrupt, but I think you'll find I suggested this just before the X-33 program was cancelled. I said something along the lines that RP-1 takes up only 7% of the volume of Hydrogen and would solve that problem right there. Only problem is, the J-2 would have to be modified (yet again) to handle RP-1.
From: Pat Flannery on 4 Apr 2010 10:28 On 4/4/2010 1:47 AM, Alan Erskine wrote: > Sorry to interrupt, but I think you'll find I suggested this just before > the X-33 program was cancelled. I said something along the lines that > RP-1 takes up only 7% of the volume of Hydrogen and would solve that > problem right there. Only problem is, the J-2 would have to be modified > (yet again) to handle RP-1. In its operational VentureStar form, the large fuel tankage required for the LH2 was turned into an asset by making the fuselage very large in comparison to its weight during reentry and thereby reducing the reentry heat loads via the high drag and rapid deceleration on it to something that Lockheed thought could be dealt with by a lightweight metallic system rather than the Shuttle's troublesome and fragile porous silica tiles. Lockheed may have made a major slip here; although they never got specific about what their VentureStar TPS was to be made of, it was thought that it was titanium based. Examination of the debris of Columbia after it broke up during reentry revealed the surprising fact that in the presence of atomic oxygen at high altitude titanium burned at a lower temperature than aluminum did, so the VentureStar TPS may have been unworkable right from the beginning. Pat
From: J. Clarke on 4 Apr 2010 10:26 On 4/4/2010 10:28 AM, Pat Flannery wrote: > On 4/4/2010 1:47 AM, Alan Erskine wrote: >> Sorry to interrupt, but I think you'll find I suggested this just before >> the X-33 program was cancelled. I said something along the lines that >> RP-1 takes up only 7% of the volume of Hydrogen and would solve that >> problem right there. Only problem is, the J-2 would have to be modified >> (yet again) to handle RP-1. > > In its operational VentureStar form, the large fuel tankage required for > the LH2 was turned into an asset by making the fuselage very large in > comparison to its weight during reentry and thereby reducing the reentry > heat loads via the high drag and rapid deceleration on it to something > that Lockheed thought could be dealt with by a lightweight metallic > system rather than the Shuttle's troublesome and fragile porous silica > tiles. > Lockheed may have made a major slip here; although they never got > specific about what their VentureStar TPS was to be made of, it was > thought that it was titanium based. > Examination of the debris of Columbia after it broke up during reentry > revealed the surprising fact that in the presence of atomic oxygen at > high altitude titanium burned at a lower temperature than aluminum did, > so the VentureStar TPS may have been unworkable right from the beginning. I'd be surprised if they were going to use titanium--it's good enough for fast airplanes but it's far from the ultimate high temperature metal--nickel alloys in use in the '60s have usable strength well above titanium's melting point and a track record in such use.
From: Craig Bingman on 4 Apr 2010 13:04
In article <Of2dnetOKofmhCXWnZ2dnUVZ_gadnZ2d(a)posted.northdakotatelephone>, Pat Flannery <flanner(a)daktel.com> wrote: >On 4/3/2010 5:17 PM, Craig Bingman wrote: >> >> Hi Pat, >> >> I don't understand how deuterium would help at all. It weighs twice as much, >> it has no more enthalpy of combustion, and i would think that the increased >> mass of deuterium would hurt specific impulse by increasing the effective >> molecular weight of the exhaust. >> >> Can you or someone else give me a reality check on that one? > >Here's the article where that combo is mentioned, that came out well >before April 1st: >http://www.thespacereview.com/article/1591/1 >The part before that mentions the problems with fluorine: >http://www.thespacereview.com/article/1580/1 >According to one poster to this thread, the advantage liquid deuterium >gives you is that it's a lot more dense by volume than standard liquid >hydrogen, so you can decrease the size of your fuel tanks for the same >amount of energy content. The density of liquid deuterium is 162 kilograms per cubic meter The density of liquid hydrogen (H2) is 71 kilograms per cubic meter So it is slightly more dense per mole. However, dragging along more mass in the tank isn't the issue... If you filled the tank with hydrogen and some rocks, the tank would contain more mass, but no more energy. There is another small effect in favor of D2 (I can't believe I'm even saying this, given how much deuterium costs) and that is that its enthalpy of formation is slightly more energetic than H2. -246 vs -239 kJ/mol. Since hydrogen oxygen engines achieve their high specific impulse at least in part by running very fuel rich, and lowering the effective molecular weight of the exhaust with a lot of excess H2, one would think that there would be a big hit with deterium fueled engines. (Ve)2 is inversely proportional to the molecular weight of the exhaust. Seems like a big hit in Isp for a small increase in density. -- -- cbingman(a)panix.com |