Project Longshot was a conceptual design for an interstellar spacecraft, an unmanned probe intended to fly to and enter orbit around Alpha Centauri B, it would be powered there by nuclear pulse propulsion. Developed by the US Naval Academy and NASA from 1987 to 1988, Longshot was designed to be built at Space Station Freedom, the precursor to the existing International Space Station. Unlike the somewhat similar Project Daedalus, Longshot was designed solely using existing technology, although some development would have been required.
Unlike Daedalus' closed-cycle fusion engine, Longshot would use a long-lived nuclear fission reactor for power. Initially generating 300 kilowatts, the reactor would power a number of lasers in the engine that would be used to ignite inertial confinement fusion similar to that in Daedalus. The main design difference is that Daedalus would rely on the fusion reaction being able to power the ship as well, whereas in Longshot the internal reactor would provide this power.
The reactor would also be used to power a laser for communications back to Earth, with a maximum power of 250 kilowatts. For most of the journey this would be used at a much lower power for sending data about the interstellar medium, but during the flyby the main engine section would be discarded and the entire power capacity dedicated to communications at about 1 kilobit per second.
Longshot would have a mass of 396 metric tons (870,000 lb) at the start of the mission, including 264 tonnes of Helium-3/Deuterium pellet fuel/propellant. The active mission payload, which includes the fission reactor but not the discarded main propulsion section, would have a mass of around 30 tonnes.
A difference in the mission architecture between Longshot and the Daedalus study is that Longshot would go into orbit about the target star while Daedalus would do a one shot fly-by lasting a comparatively short time.
The journey to Alpha Centauri B orbit would take about 100 years, at an average velocity of approximately 13411 km/s, about 4.5% the speed of light, and another 4.39 years would be necessary for the data to reach Earth.
See also 
- Interstellar travel
- Project Orion (nuclear propulsion)
- Project Daedalus
- Project Icarus
- Spacecraft propulsion
- Alpha Centauri Bb
Beals, K. A., M. Beaulieu, F. J. Dembia, J. Kerstiens, D. L. Kramer, J. R. West and J. A. Zito. Project Longshot: An Unmanned Probe To Alpha Centauri. U S Naval Academy. NASA-CR-184718. 1988.
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The full text of Project Longshot: An Unmanned Probe To Alpha Centauri at Wikisource (Please note that the article cited here refers to an Alpha and Beta Centauri as the orbital target of the mission, but the correct nomenclature for these two components of the Alpha Centauri binary star system is Alpha Centauri A and B. Beta Centauri is an entirely different, unassociated star.)
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