Capacitors are used to resonate with the drive coils and provide intermediate energy storage in the mass driver. Capacitors (high energy density) have a much lower energy density than that of inductors or flywheels (factor of 30 to 60 times worse) and power factor correction capacitors can be even another factor of 20-50 times worse. Part of the problem is overcome by the sector capacitor being used many times (100-500) per launch. But still, capacitor mass and lifetime are serious problems because of the high throughput rate forced upon mass drivers by SCR's. Some SCR switched lunar mass drivers require to half cycle oscillations in a sector capacitor over a design lifetime of 10 years. In addition the SCR's are required to operate with about 4x10 half cycle oscillations in this same period. Previous work has been done researching the energy density and lifetime of capacitors (Appendix A ref. 11). For the large number of cycles required, only power factor correction capacitors are adequate. They have an energy density of 2-4 J/Kg and have a 100% voltage reversal capability. Generally, high energy density capacitors with energy densities of 40-150 J/Kg have relatively low lifetimes shots and only a 25-50% voltage reversal rating. These two factors make them unacceptable in SCR switched mass drivers. Other comments to make are that sector capacitors should be comprised of a bank of about ten individual capacitors individually fused. This is so that failure of a capacitor, if it shorts, does not short the rest of the sector capacitor rendering it useless. A slight increase in ringing frequency would result but would be acceptable. Buckets used in mass drivers were originally considered to contain superconducting coils based on experience from the M.I.T. Magneplane project. During the course of research on Mass Driver Two it was found
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