At 03:08 PM 1/7/2003 -0500, you wrote:
My vague plan for first orbital work post-X-Prize:On Tue, 7 Jan 2003, Ian Woollard wrote:> The optimised trajectory is interesting though- it goes subsonic, and > very nearly vertical up to about 30km and then separates and the second > stage burns briefly for a lob up to about 200km and then it restarts its > engines and does its orbital insertion burn. I figure the first stage > could land back at the takeoff site with hardly much fiddling- DC-X > style; so it looked about as good as a TSTO is ever going to be. Using > HTP for this might be good, because then the engines restart easily. Early plans for Kistler called for a TSTO using a dumb first stage to lob the second stage clear of the atmosphere (vertical trajectory, return to launch site for recovery). The second stage was a mass-optimized near-SSTO using LOX/H2. The virtue of this idea is that you don't need altitude compensation on the engines, and you don't need heavy landing gear, since the vehicle only supports its own weight while empty. In fact they also used tricks to get rid of the landing gear on landing, too (land on the heat sheild in a big net). ......Andrew
Take the X-Prize vehicle or a derivative, but instead of carrying 600 lb of passengers, carry an upper stage with an orienting launch cradle that can precisely point the stage and spin it before launch. When out of the sensible atmosphere, but well before apogee, the upper stage is aimed at a slight upwards angle above the horizon, spun up for stabilization, and launched.
If you still have vertical velocity from the booster, It is possible to chose a launch angle that will leave you in a circular orbit just as the last of the vertical velocity is bled away (without precise thrust termination, you are almost certain to be in a fairly eliptical orbit). You can reach circular altitudes higher than the booster would apogee, unlike the vangaurd style launches where the booster basically takes you to orbital altitude, and the upper stages insert. I wrote a sci.space.tech post about this a while ago, and nobody poked any holes in the idea.
The upper stage can be simple enough that I actually believe we can hit near-SSTO mass fractions with it for peroxide/kerosene. The tradeoffs between tank mass and nozzle mass will probably optimize to tank pressures around 100 psi or less, and there will only be a single axial engine probably directly wound in to the tankage. The engine would probably have to use an ignitor to avoid cat pack mass, and it would have burst disk valves. All the startup gear stays with the booster. The payload would just be a packet radio system stuck to the top of the tank with a bit of epoxy.
I think something like this could be flown a year after the X-Prize. Using disposable, flyweight upper stages should also ease regulatory concerns -- they will positively burn up when they hit the atmosphere. The step from there to a fully guided upper stage (let alone a reusable one) is larger than a lot of people give it credit, and I suspect it would demand more velocity from the booster, which will make development a lot more troublesome than just a straight up / straight down booster flight.
John Carmack
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