Satgen316 Get ing into Orbit Pt 2 by GM4IHJ 15 April 95 Iniold fashioned science fiction movies , the giant rocket rises up from the earth on a great fiery column, which continues to thrust it upwards until all its fuel is exhausted. That is fiction. Rockets are not efficient when used this way. Keeping all the massive fuel tanks and primary engines onboard for the gull thrust period , is not good practice. It takes the greater part of the fuel load to lift the rocket for the first 20 kilometres , whilst earth gravity resistance is fiercest. At which point, more than 75% of the fuel has been used. So it is good engineering to discard the heavy first stage fuel tank and primary engines , and start up a smaller secondary engine to carry aloft the remaintng smaller fuel load and payload. Higher still , this secondary engine and fuel tank can be discarded, and, a very small third stage engine and fuel tank can be used to take the payload up to orbit. There are many possible variations on this theme. Some 3 stage rockets are given supplementary boosters strapped to the first stage, and fired with that stage, in order to increase the size of the payload being carried aloft. Both the main rocket stages and the boos ers can use solid fuel, burning like a firework, but in cases where heavy lift is required, liquid fueled main stages are preferred. This last year a new kind of launcher has appeared, made up from redundant ICBM Inter continental ballistic missile stages, with the nuclear warhead removed, and a satellite carrier mounted in its place. A perfect example of turning "Swords into Ploughshares". Both the recent launch of RS15 into space, and , the less fortunate aborted launch of Techsat and Unamsat, used ex military ICBMs adapted to civilian usage. Given the vast numbers of these otherwise useless launchers reoeased from the super poier armouries, this is clearly a good way to dispose of them. So we could perhaps soon see more ex ICBMs taking Amsats aloft, rather more cheaply than is presently the case with launches by civilian designed and built rockets. Perhaps there is a greater element of risk, in this use of old redundant military material, but Radio Amateurs are not rich, and launch costs are one of the biggest obstacles for Amsat builders. This month should also see ( or have seen ), the launch of commercial digisats OrbCom 1 and 2 via a quite different type of launcher utilizing the winged rocket Pegasus XL. Pegasus and its payload are carried aloft on a big Lockheed jet transporter, before release at high altitude , out over the Pacific Ocean, to start the rocket propelled part of their flight. Perhaps this type of launch could be a future route to space for Amateur satellites, dispensing as it does, with some expensive launch site costs and, the problem of launch trajectories passing over or near to sensitive population centres.