When NASA's 2006-launched Far Horizons spacecraft reaches the distant planet Pluto in 2015, all the major world of the classical solar system will have been explored by robot probes.
Beyond Pluto and the Kuiper Belt is an immense gulf-4.24 light years in distance-to the nearest star.
While the notion of sending an automated spacecraft to Alpha Centauri C, the Sun's nearest stellar object, seems like science fiction today, a serious, successful study about such a space probe was completed 23 years ago this week.
With the exception of a fully operational thermonuclear fusion power source, there's no reason why NASA (or an international space consortium) couldn't send a sophisticated probe to the Alpha Centauri star system-within the next 10 to 25 years.
Known as Project Longshot, the first practical interstellar mission study was spearheaded by an unlikely duo, NASA and the U.S. Naval Academy between 1987 and 1988.
Longshot didn't receive much media attention back then, but it now stands as a seminal, conceptual interstellar mission effort.
Designed to be constructed in Earth orbit at a space station, Longshot uses both 1980s-era technology and futuristic fusion power technology. But just like the 1980s, the development of sustained inertial confinement fusion (or ICF) remains just beyond the reach of engineers in the 2010s. However, there have been significant advances in ICF experiments in recent years; it remains the most likely power source to get to the stars during the 21st century.
The Longshot interstellar mission was conceived as an unmanned probe that would fly, one way, to the Alpha Centauri system. Its speedy star trek would get a nice kick courtesy of a nuclear ICF pulse engine.
Compared to today's ponderous gravity assisted space probes, Longshot's 100-year-long trip to Alpha Centauri-at 4.5 percent the speed of light-would be like comparing its Roadrunner status to the 1970s NASA Voyagers' Wily Coyote.
The heart of Longshot's quickened space pace is a nuclear fission power reactor that would generate 300 kw of juice.
The reactor would power a 250 kw laser for communicating with home; the remaining juice would then fire a battery of lasers in the engine that would-in turn-ignite inertial confinement fusion.
Onboard lasers would target frozen hybrid helium-3/deuterium pellet fuels to create a sustained pulse of thermonuclear micro explosions. But Longshot would need to hold 264 tons of the pellet propellant for the long, lonely interstellar voyage.
Longshot's mission payload would mass around 30 tons which leaves enough room for nifty navigation, communications and science instrumentation.
For most of its long commuting phase, Longshot would operate on low power while sending a data stream about the interstellar medium back to Earth.
During the century that will pass before Longshot reaches the nearest star, several generations of mission team members will come and go. Perhaps entire families of technical specialists-from grandfathers to their great granddaughters-will be involved with the Longshot mission effort on Earth. They will live and die before the spacecraft ever reaches its distant goal.
Longshot is truly a long-term commitment. Unfortunately, thanks to the vagaries of U.S. politics, long-term commitment and space projects never seem to mix well. But there's always hope that an international effort would be better insulated.
According to Longshot's team of creators, K.A. Beals, M. Beaulieu, and others, the journey to Alpha Centauri would take about 100 years at an velocity of 13,411 km/s. It would take four years for telemetry to reach Earth.
Lou Varricchio, M.Sc., is a former science writer at the NASA Ames Research Center in Mountain View, Calif. He is a current NASA-JPL Solar System Ambassador program member and received the U.S. Civil Air Patrol's Gen. Charles "Chuck" Yeager Aerospace Education Achievement Award in 2009.