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Mass drivers can be used to propel spacecraft in two different ways: A large, ground-based mass driver can be used to launch spacecraft away from the Earth or another planet, or a spacecraft could have a mass driver on board, flinging large pieces of material into space to propel itself. A hybrid design is also possible.
Prototype mass drivers have existed since 1975. Most were constructed by the Space Studies Institute in order to prove their properties and practicality.
A ground-based mass driver would be a large installation for launching vehicles. It would consist of some electrical power station and a long linear motor. Vehicles would be placed on the launcher and accelerated. They could be released at escape velocity for interplanetary voyages, or they could be launched at near orbital velocity and use a short rocket burn to circularize their orbit. The Earth's strong gravity and thick atmosphere make such an installation difficult, so many proposals have been put forward to place such an installation on the Moon.
The coils can be constructed of aluminum to save mass, and to permit them to be constructed from lunar materials. The best known performance occurs with an aluminum coil as the payload. The coils of the mass-driver induce eddy-currents ( paramagnetism) in the payload's coil, and then act on the resulting magnetic field. There are two sections of a mass-driver. The maximum accelerationIn physics, acceleration (symbol: a is defined as the rate of change (or time derivative) of velocity. It is thus a vector quantity with dimension length/ time˛. In SI units, this is metre/second˛. To accelerate an object is to change its velocity over a part spaces the coils at constant distances, and synchronize the coil currents to the bucket. In this section, the acceleration increases as the velocity increases, up to the maximum that the bucket can take. After that, the constant acceleration region begins. This region spaces the coils at increasing distances to give a fixed amount of velocity increase per unit of time.
In the prototypes, the payload would be held in a bucket and then released, so that the bucket can be decelerated and reused.
In this mode, the major proposal for use of mass-drivers was to throw lunar dirt at space habitats so that they could process it using solar energy. The Space Studies Institute showed that this application was reasonably practical.
A second possibility is to build a mass driver on Earth that can launch radioactive wasteRadioactive waste is waste material containing radioactive chemical elements which does not have a practical purpose. It is often the product of a nuclear process, such as nuclear fission. Waste can also be generated from the processing of fuel for nuclea into space (or into the Sun, which is already extremely radioactive). One design ([1]) for such a launcher that could be constructed using current technology requires the launcher to be about 2 km long and accelerate the cargo at 10,000 g (100 km/s˛). Each launch would require about 300 GJ. If this were driven by a nuclear power plant, only about 10% of the power generated by the plant would be required to dispose of its waste safely and permanently.
A third possibility for building a mass driver is a compromise system: a mass driver accelerates a payload up to some high speed which is not high enough for launch. It then releases the payload, which completes the launch under its own power. This would drastically reduce the amount of thrust that would be required for a launch, while allowing the mass driver design to use well-tested maglevMaglev can refer to General Magnetic levitation Magnetic levitation trains. components.
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