NASA-LLIS-2736

Abstract

<strong>Abstract:</strong> <br>The Space Shuttle Orbiter rejects heat from onboard electrical equipment, crew members, and other sources to an independent ground refrigerant loop through an onboard heat exchanger. Ground-provided umbilicals that separate from the spacecraft at launch provide primary loop single-phase coolant to the onboard heat exchanger from the circulation unit located at the base of the launch pad. The collected heat is in turn rejected from this primary coolant loop to a secondary two-phase refrigerant system. This method of heat rejection proved to be unreliable and difficult to control for the ground cooling system operator because the spacecraft heat loads varied. A much more stable, reliable system was put in place when a third intermediate loop was implemented into the ground cooling system with a heating element that allowed the refrigerant loop to operate at a constant set point.