Project Longshot

It would have been an uncrewed starship (about 400 tonnes), intended to fly to and enter orbit around Alpha Centauri B powered by nuclear pulse propulsion.

Similar to Project Daedalus, Longshot was designed with existing technology in mind, although some development would have been required; for example, the Project Longshot concept assumes "a three-order-of-magnitude leap over current propulsion technology".

[1] Unlike Daedalus, which used an open-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 active mission payload, which includes the fission reactor but not the discarded main propulsion section, would have a mass of around 30 tonnes.