Status: Study 2004.

Solaris X was a design of Roderick and Randa Milliron of Interorbital Systems (IOS) of Mojave, California. The concept used a rocket powered vertical takeoff from water in the territorial waters of Tonga, followed by a parachute descent to a splashdown at sea. IOS had been founded in 1996, with the ultimate objective of development of its Neptune-Solaris Orbital Spaceliner, a two-stage manned orbital launch vehicle. The orbiter stage in this configuration, the Solaris X rocket plane, was the company's X Prize entry. Wally Funk, one of the 'Mercury 13' female astronauts, was announced as the pilot of the Solaris X.