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Small, cheap, reusable rocket launcher
The rocket launchers are not economical because they
are not reusable. When they reenter the atmosphere, their slender bodies soak up so much heat from the ambient atmosphere that they burn up. The Space Shuttle is somewhat reusable, but its slender body has to be protected with a thermal protection system that is expensive (because it covers large surface) and unreliable (because it has to be lightweight despite its large size). A rocket launcher shaped like a big conical reentry capsule would be more reusable than the Space Shuttle because its thermal protection system would be smaller (because it would cover only the bottom surface of the cone) and cheaper. The conventional rocket launchers are shaped like a pencil to minimize aerodynamic drag during the first minute of the flight. A cone-shaped rocket launcher would generate too much drag unless it was slowly lifted above the dense part of the atmosphere (to the altitude of about 30 kilometers) with a balloon or a helicopter. Hydrogen balloons are cheap, but not reusable. Helicopters are reusable, but they need special engines that can operate at the altitude of 30 kilometers. There are three such engines: 1. Hydrogen peroxide monopropellant turbine has simple design, but the monopropellant is rather expensive and its catalyst bed can be contaminated with commercial grade monopropellant. 2. Steamjet engine is described in U.S. patent 6,202,404. Its most practicable implementation, called mass injection precompressor cooling (MIPCC) is a turbojet cooled with copious amounts of water and liquid oxygen. The cooling enables the turbojet to generate thrust up to the altitude of about 30 km. More info: http://tinyurl.com/msqra 3. Electric motors are cheap and can operate at the altitude of 30 km. Their energy source can be either a battery or a generator standing on the ground. The motors and the batteries need a cooling system when they operate at high altitude. 3a.Magnesium hydride battery with Ni catalyst has the highest energy density (http://www.energyadvocate.com/batts.htm) but it is not yet mature technology. Li-ion batteries have energy density of only 534 kJ/kg, but they are very reliable and reusable. (They provide auxiliary power for my laptop computer.) The Li-ion batteries can be used as the power source if used up batteries are discarded during the flight. It takes about 300 watts of helicopter power to lift 1 kg of weight. At the beginning of the flight the total weight of the batteries is about one half of the launcher weight. During 15 minutes of vertical flight the helicopter reaches its maximum altitude of 30 km, drops off nearly all its batteries on parachutes, and finally drops off the launcher. When the helicopter descends, most of its propellers (rotors) are used as wind turbines which provide power for the remaining propellers. The last batteries are used up during landing. My laptop batteries cost $418/kg. Assuming payload fraction of 6 percent and total battery weight of one half the launcher weight, the batteries cost 418/0.06/2 = $3483 per kilogram of payload. The capital cost of the batteries may seem rather high, but the batteries are reusable and very easy to use. 3b.Aluminum wires linking the motors with a high voltage generator standing on the ground are expensive and difficult to use. High voltage generators are available from many sources, for example: http://www.kato-eng.com/hacgen.html They cost about $0.1/W. At the payload fraction of 6 percent, the generator cost is about 0.1*300/0.06 = $5556 per kilogram of payload. In the absence of the generator, the power is provided by the grid. The cost of connecting to the grid depends on the distance; electrical utilities charge between $10,000 and $50,000 per kilometer of transmission line. The wires must be reinforced with strong (Zylon) rope and suspended on balloons so that they do not touch the ground. The design of such helicopter is similar to the design of airborne wind turbine generator: http://www.skywindpower.com The helicopter is vulnerable to lightenings and strong winds, so it must fly near the equator (away from the jet streams): http://www.skywindpower.com/ww/page010.htm. Electric motors powered by batteries are the best choice because they are cheap, reliable, safe, and easy to use. If the helicopter lifts the rocket launcher above the dense part of the atmosphere, the launcher can transport payloads that have low density and large size, for example large space telescope or large greenhouse. THE LAUNCHER SCALES DOWN VERY WELL BECAUSE IT IS REUSABLE AND BECAUSE ITS ATMOSPHERIC DRAG IS NEGLIGABLE. ITS TRUNCATED CONICAL SHAPE LEAVES PLENTY OF ROOM FOR A VERY LARGE EXHAUST NOZZLE WHICH IMPROVES THE EXPANSION RATIO AND SPECIFIC IMPULSE. LAST, BUT NOT LEAST, THE SHAPE OF THE EXHAUST NOZZLE IS OPTIMIZED FOR FLIGHT IN THE VACUUM, BECAUSE IT IS NOT USED IN THE DENSE ATMOSPHERE. This means that a little guy can cobble together a little rocket launcher that has high specific impulse despite its primitive, low-pressure design, and that he can compete on launch cost with the giants of the industry (if he can afford the legal expenses). If the launcher has three stages, only the last stage has to be protected with the expensive composite called reinforced carbon-carbon. The second stage can be protected with a thick coating of silicone rubber. The first stage does not need any thermal protection. |
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