<P> 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 . </P> <P> Longshot would have a mass of 396 metric tons (873,000 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 . </P> <P> A difference in the mission architecture between Longshot and the Daedalus study is that Longshot would go into orbit about the target star while the higher speed Daedalus would do a one shot fly - by lasting a comparatively short time . </P> <P> 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 . </P>

How long would it take to reach alpha centauri at the speed of light