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Due to the dynamics of launch, the kinetic energy of rotation must be several orders of magnitude greater than the kinetic energy of launch. For the 25 km proof of concept system, atmospheric heating limits the ribbon length to around 2 km. Therefore, to meet the kinetic energy requirement, the mass of the counterweight (CW) should be approximately 25 ton. The large mass results in a large tension in the ribbon which, in turn, results in a small displacement of the ribbon during launch. Also, the large mass keeps the ribbon from dropping into a higher density atmosphere which may result in a higher surface temperature of the ribbon.
Altering the angle of attack of the ribbon can increase lift and drag as well as increase atmospheric heating or it can reduce atmospheric heating by decreasing lift and drag. As such, the CW for the proof of concept system will be designed as a fuselage with a tail boom and elevator. Also, the CW will be designed to reel itself in and out during down time and for maintenance and repair. Finally, the CW will be designed to withstand the high g loading resulting form rotation, absorb the shock due to launch, and dampen the vibrations of the ribbon. Therefore, the CW contains within its structure the necessary batteries, flywheels, motor generators, spindles, gears, electronics, and extra ribbon required to perform the task. An illustration of the CW is shown here.
For a second generation system, there are approximately 160 CWs (80 on each side). Each CW has a final mass after ribbon deployment of 2.5 tons. The CW is designed to deploy a thin layer of ribbon approximately 400 km long. During deployment, the motor produces approximately 60 kW of power which is dissipated through nichrome wires at the base of the CW. At launch, the CWs absorb the shock of launch and dampen any oscillations in the ribbon. On occasion the ribbon will need to be replaced. Power is delivered to the CWs by ground based high powered solid state lasers. Solar panels made of Aluminum Gallium Arsenide photovoltaic cells receive the energy from the lasers. The energy is condition and delivered to the motors. For 160 CWs, it takes approximately 35 days to reel up the ribbons and another 35 days to redeploy. Total down time is approximately 70 days.
Space Track Launch System
A more detailed review of the counterweight for the proof of concept system can be found in the
Proof of Concept paper. A review of the counterweight for the second generation system can be found in the STLS Counterweight paper.
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Updated Aug 2012