Project Daedalus
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Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society to design a plausible interstellar unmanned spacecraft. A dozen scientists and engineers led by Alan Bond worked on the project.
The design criteria were that the spacecraft had to use current or near-future technology and had to be able to reach its destination within a human lifetime (a flight time of 50 years was allocated). The target chosen was Barnard's Star, 5.9 light years away, which at the time was believed to possess at least one planet (the evidence on which this belief was based has since been discredited). The design was required to be flexible enough that it could be sent to any of a number of other target stars, however.
Daedalus would be constructed in Earth orbit and have an initial mass of 54,000 tons, including 50,000 tons of fuel and 500 tons of scientific payload. Daedalus was to be a two-stage spacecraft. The first stage would operate for two years, taking the spacecraft to 7.1% of light speed, and then after it was jettisoned the second stage would fire for 1.8 years, bringing the spacecraft up to about 12% of light speed before being shut down for a 46-year cruise period.
This velocity was well beyond the capabilities of chemical rockets, or even the type of nuclear pulse propulsion studied during Project Orion. Instead, Daedalus would be propelled by a fusion rocket using pellets of deuterium/helium-3 mix that would be ignited in the reaction chamber by inertial confinement using electron beams. 250 pellets would be detonated per second, and the resulting plasma would be directed by a magnetic nozzle.
The second stage would have two 5-meter optical telescopes and two 20-meter radio telescopes. About 25 years after launch these telescopes would begin examining the area around Barnard's Star to learn more about any accompanying planets. This information would be sent back to Earth, using the 40-meter diameter second stage engine bell as a communications dish, and targets of interest would be selected. Since the spacecraft would not decelerate upon reaching Barnard's Star, Daedalus would carry 18 autonomous sub-probes that would be launched between 7.2 and 1.8 years before the main craft entered the target system. These sub-probes would be propelled by nuclear-powered ion drives and carry cameras, spectrometers, and other sensory equipment. They would fly past their targets, still travelling at 12% of the speed of light, and transmit their findings back to the Daedalus second stage mothership.
The ship's payload bay containing its sub-probes, telescopes, and other equipment would be protected from the interstellar medium during transit by a 50-ton 7mm-thick beryllium disk. Larger obstacles that might be encountered while passing through the target system would be dispersed by an artificially generated cloud of particles some 200 km ahead of the vehicle. The spacecraft would carry a number of robot "wardens" capable of autonomously repairing damage or malfunctions.