The Hubble Space Telescope Orbiting Systems Test (HOST) platform is carrying experiments to validate components planned for installation during the third Hubble Space Telescope servicing mission and to evaluate new technologies in an earth orbiting environment. There are four experiments on the HOST platform. The NICMOS Cooling System will allow zero-g verification of a Reverse Turbo Brayton Cycle Cooler which should allow longer life operation than the current dewar system. (2) The HST 486 Computer will allow the identification of any radiation susceptible parts in the DF-224 replacement and demonstrate hardware and software responses to Single Event Upsets (SEU's). (3) Solid State Recorder will compare on-orbit operation of the flight spare solid state recorder with the current HST unit. (4) Fiber Optic Line Test will use the same 4 kbps data stream that is sent to the orbiter's Payload Data Interrogator (PDI) and will be routed to a laptop computer for post-flight comparison.