Lunar Rocket-sled to Orbit

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• Using a lunar rocket-sled to orbit (LRSTO) provides the chance to recapture nearly all rocket exhaust and recycle the precious hydrogen while providing man ratable transportation to lunar escape velocity (about 2400 meters per second). Since a rocket-sled moves nearly horizontally, it is possible to encase the track on which the vehicle rides in a long pressure vessel set upon the lunar surface for that portion of the track the rocket uses while burning. Open doors at the ends of the pressure vessel allow the rocket to enter and escape. A short section of track is moved out of the way and a door is closed after the rocket passes as it enters and as it exits the pressure vessel. This traps the exhaust gasses.

• The rocket sled concept was demonstrated on Earth to more than lunar escape velocity. On the 30th of April, 2003 the United States Air Force set the absolute land speed record with a rocket sled traveling at over 2880 meters per second. Various changes would be necessary to adapt this concept to lunar conditions and the requirement to carry passengers.

• The lunar version rocket-sled would ride on a magnetic levitating track. In an example configuration an electric tractor would push the sled up to 850 meters per second in 18 seconds with a maximum acceleration of 50 meters per second squared using about 7.7kilometers (4.8 miles) of track. The sled would coast for 1.2 seconds and enter the pressure vessel while the tractor would be diverted on its separate track going outside the pressure vessel. The electric tractor would be on a narrower gage track so the tractor and its track could drop beneath the rocket sled track. The remaining 1550 meters per second to escape velocity would be provided by a liquid hydrogen-liquid oxygen rocket with an exhaust velocity of 4300 meters per second. So 70% of the mass of the vehicle at rocket ignition would reach escape velocity. Rocket acceleration would start at 34.9 meters per second squared and reach a maximum of 50 meters per second squared before burnout. The trip through the long pressure vessel would last about 37 seconds and cover about 61 kilometers (38 miles). If the track starts level and levitates the rocket-sled until circular orbit velocity is reached and then merely provides a means of correcting the position of the rocket-sled, keeping it in the center of the long pressure vessel, then the pressure vessel would follow the shape of the orbital path and end up near 300 meters higher than the starting elevation. If the track starts a downhill slope somewhat before circular orbit velocity is reached, the track exits the pressure vessel closer to the starting level with a slightly upward slant.

• While Earth bound tests did not use a pressure vessel, they did run a rocket sled through an 11,000 foot long 184 inch diameter tube full of helium. The pressure vessel on Luna could be constructed from local materials using Sintered Brick Construction methods. The electrical portion of the acceleration helps avoid damage to the pressure vessel because the rocked sled is already moving when the rocket engine starts. So the otherwise erosive effects of rocket exhaust are dispersed.

• An LRSTO would be used for personnel transportation for a well developed lunar base. It might also be easier to build than an all electric cargo launching system. If so, it could serve for cargo launch until an all electric system is built.