Valkyrie was Karigo's first interplanetary spacecraft, designed for the KSI Mars I mission. The vehicle was a Vertical Take off, Horizontal-Landing, Horizontal Takeoff, Horizontal Landing ship, or VTO/HL/HTO/HL (See: Mission Profile for details), and designed to be mostly reusable. It was also the first ship to employ the nuclear engine pioneered by Karigo.
The Valkyrie employs a double-delta, swept-wing design for maximum stability and lift. The bottom employs an active, liquid-gas fueled heat shield that allows it to withstand atmospheric entry at massive speed.
The engine is based on a nuclear saltwater rocket. In principle, water, containing dissolved salts of uranium fuel at a sub-critical mass. Freddie's design has the water flowing through a neutron bombardment phase before reaching the core of a small nuclear reactor at the ship's tail. The final stage coupled with the bombardment brings the uranium in the water to super-critcal. The resulting explosion is propelled through a magnetic nozel and pushes the ship forward. The engine has both high thrust and high specific impulse, coupled with remarkably high efficiency for a thermonuclear reaction.
While not strictly a "module" as compared to spacecraft assembled in orbit, various sections of Valkyrie are called Modules insofar as they are seperate pressure vessels. The Habitat Module includes a spinning section used to simulate gravity, storage for most of the expeditions food and medical supplies, as well as a large, zero-gravity experimental space and workshop.