Deep space missions, like the ones going to outer planets and those that rely on solar photovoltaic power, need extremely large solar arrays to produce that power for their operations because the solar intensity is so low at those locations. Hence, there was a need for a thermal architecture and design that would not require such prohibitively large thermal power levels.
The solution relied on harvesting the preexisting waste heat from all the heat dissipation from electronics, instruments, etc., for their own functionality. For example, in the Saturn mission, the various electronics already dissipate about 200 W of heat that is simply “thrown away” to space from the spacecraft surfaces. The amount of thermal power that would be required for the safe thermal control of components within the spacecraft would be roughly of this magnitude in deep space for this class of spacecraft.
The proposed system utilizes a mechanically pumped single-phase fluid loop to pick up the waste heat from components attached to this loop’s tubing, and then direct it to a thermal flask that has tubing attached to it. The thermal flask is cylindrically shaped and contains essentially all systems and components in the spacecraft within it, with the exception of the solar array, antennas, thrusters, and various apertures of instruments to allow them an unobstructed view of space. Waste heat from the heat-dissipating components warms up the fluid, and is carried to the flask surface and deposited on it via the fluid loop’s flow. The entire flask is covered with multi-layered insulation (MLI) to minimize the heat loss from the flask to allow it to remain warm. The flask essentially creates a thermal environment within which the spacecraft components reside.
The flask (constructed of about 1/8- in. or 3-mm aluminum shell with local structural stiffeners) would essentially serve dual functions: (1) provide the structure to support various components within the flask, and (2) spread the heat coming out of the fluid loop tubing. The flask would then be almost uniform in temperature and create a very uniform environment for the components within the flask.
The only power required to operate this thermal control system is for running the fluid loop pump. For missions of this type, a typical input power for a pump would be ≈10 W. Additionally, all of the pump operational power is harvested as waste heat and contributes to the heat inserted into the thermal flask.
This is a novel concept because it almost eliminates the need for thermal control power for a large spacecraft designed for deep space. It is completely automatic, requiring no onboard or ground-directed control of its function. It also is simple in its implementation because all the spacecraft components are placed inside the shell.