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The 100/10/1 Rule.
I've been simulating single stage to orbit (SSTO) launch to low earth
orbit (LEO) in orbiter space flight simulator for a little while now. Consider your basic space shuttle main engine (SSME) powered single stage to orbit (SSTO) rocket. Hydrogen is the most powerful chemical rocket fuel known (excluding exotics). To reach low earth orbit with a cryogenic fuel of this nature, a mass ratio of 10 to 1 is required (the 10/1 rule). That is 10 parts of fuel and oxidizer to one part rocket. After accelerating to a stable orbit roughly 1% of the fuel is remaining (more or less, depending upon the ascent trajectory profile, the launch latitude, and final orbit inclination and altitude). That's roughly 100 parts gross liftoff weight to 1 part residual fuel (the 100/1 rule) or 10 parts empty weight to 1 part residual fuel (yet another 10/1 rule). Thus the usable payload delivered to an orbital station or spaceport is roughly 1% of the gross liftoff weight, and 10% of vehicle empty weight. In this case this is fuel which can be immediately converted into energy and water (via a fuel cell), and water that can then be reconverted back (using solar energy) into propellant and oxygen. This isn't very much. However that's the reality of climbing the gravity well of Planet Earth. In order to increase this payload, the obvious solution is converting the rocket itself into payload. In this scheme the engine is removed from the vehicle (roughly 20 percent of empty weight) and returned to Earth in a cleverly designed nose cone engine carrier, and the tankage, the oxygen, hydrogen, pressurization, residual fuel tanks and the RCS - reaction control system, is then immediately pressed into service as payload for infrastructure in constructing the space station or orbital spaceport itself. Thus, the usable payload fraction is then increased by a factor of seven (7) or so, dependent upon the amount of equipment or infrastructure necessary to successfully reenter and recover a seven thousand pound space shuttle main engine (SSME) from low earth orbit. For a reasonably designed single space shuttle main engine powered single stage to orbit launch vehicle, this represents 3500 pounds of residual fuel and 25,000 pounds of infrastructure. This is not trivial. Plus, you get the engine back. Adding some GEM-60s improves the numbers. -- Get A Free Orbiter Space Flight Simulator : http://orbit.medphys.ucl.ac.uk/orbit.html |
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The 100/10/1 Rule.
Brian Gaff wrote:
Does this take into account the efficiency changes during ascent, and I wonder who would reuse an engine probably dumped in the Atlantic? I mean solids are one thing, but... It's already been demonstrated by Boeing. It's not a problem. I'm aiming for the Bahama plateau, the Great Bahama Bank. The engine won't even get wet, and the slashdown should be very soft. Plus the nozzle is facing upwards, surrounded by airbags and flotation devices. Not sure about using the bits of the vehicle as payload, Surely you would eventually have enough spare rcs etc, in orbit to start a space spares shop! There is never enough redundancy in space. We're talking about very large structures, which would eventually be parted out as numerous very small craft. You want to colonize space, right? The limiting factor is water for fuel, but water that is recycled never really goes away, so eventually enough water will be accumulated to allow missions to Ceres. -- Get A Free Orbiter Space Flight Simulator : http://orbit.medphys.ucl.ac.uk/orbit.html |
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The 100/10/1 Rule.
On Mar 1, 7:30 pm, kT wrote:
I've been simulating single stage to orbit (SSTO) launch to low earth orbit (LEO) in orbiter space flight simulator for a little while now. Consider your basic space shuttle main engine (SSME) powered single stage to orbit (SSTO) rocket. Hydrogen is the most powerful chemical rocket fuel known (excluding exotics). To reach low earth orbit with a cryogenic fuel of this nature, a mass ratio of 10 to 1 is required (the 10/1 rule). That is 10 parts of fuel and oxidizer to one part rocket. After accelerating to a stable orbit roughly 1% of the fuel is remaining (more or less, depending upon the ascent trajectory profile, the launch latitude, and final orbit inclination and altitude). That's roughly 100 parts gross liftoff weight to 1 part residual fuel (the 100/1 rule) or 10 parts empty weight to 1 part residual fuel (yet another 10/1 rule). Thus the usable payload delivered to an orbital station or spaceport is roughly 1% of the gross liftoff weight, and 10% of vehicle empty weight. In this case this is fuel which can be immediately converted into energy and water (via a fuel cell), and water that can then be reconverted back (using solar energy) into propellant and oxygen. This isn't very much. However that's the reality of climbing the gravity well of Planet Earth. In order to increase this payload, the obvious solution is converting the rocket itself into payload. In this scheme the engine is removed from the vehicle (roughly 20 percent of empty weight) and returned to Earth in a cleverly designed nose cone engine carrier, and the tankage, the oxygen, hydrogen, pressurization, residual fuel tanks and the RCS - reaction control system, is then immediately pressed into service as payload for infrastructure in constructing the space station or orbital spaceport itself. Thus, the usable payload fraction is then increased by a factor of seven (7) or so, dependent upon the amount of equipment or infrastructure necessary to successfully reenter and recover a seven thousand pound space shuttle main engine (SSME) from low earth orbit. For a reasonably designed single space shuttle main engine powered single stage to orbit launch vehicle, this represents 3500 pounds of residual fuel and 25,000 pounds of infrastructure. This is not trivial. Plus, you get the engine back. Adding some GEM-60s improves the numbers. -- Get A Free Orbiter Space Flight Simulator :http://orbit.medphys.ucl.ac.uk/orbit.html Using big parts of the vehicle as payload would seem to be a big win. Proposals to use the Shuttle's external tanks to build a big, rotating space station go way back. But you have to design the whole program around such a goal. And they didn't. Back when the Shuttle was being designed, they probably waved away a lot of possibilities by saying "It'll launch things so cheaply we don't have to worry about that. And besides, a bare shell of a tank still has to be furnished, so there'll be several shuttle loads for each tank just to make it useful." Etc., etc. Vehicle-as-payload might make a lot of sense in a scenario of more ambitious commitments, but ... well, that takes us right back to some other major discussions recently, doesn't it? -michael turner |
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