A report discusses a new technique to prevent condensation on the cabin walls of manned spacecraft exposed to the cold environment of space, as such condensation could lead to free water in the cabin. This could facilitate the growth of mold and bacteria, and could lead to oxidation and weakening of the cabin wall.
This condensation control technique employs a passive method that uses spacecraft waste heat as the primary wallheating mechanism. A network of heat pipes is bonded to the crew cabin pressure vessel, as well as the pipes to each other, in order to provide for efficient heat transfer to the cabin walls and from one heat pipe to another. When properly sized, the heat-pipe network can maintain the crew cabin walls at a nearly uniform temperature. It can also accept and distribute spacecraft waste heat to maintain the pressure vessel above dew point.
The warmest portion of the spacecraft active thermal control system (ATCS) is connected to the heat-pipe network to allow the spacecraft waste heat to warm the pressure vessel walls. A backup electrical heater is attached to the ATCS loop/heat pipe interface to allow for heating in the event that the ATCS has insufficient energy to maintain the pressure- vessel walls above the dew point. A bypass control system sends ATCS fluid to the ATCS/heat pipe interface when there is sufficient energy for this purpose, and bypasses the heat-pipe network when there is not. This allows the backup electric heaters to efficiently heat the pressure vessel (without having to heat the flowing ATCS fluid). It also allows the flow to the ATCS/heat pipe interface to be modulated, thereby controlling the cabin wall temperature. The ATCS/heat pipe interface conductance is designed so that the energy input per unit length along the interface is roughly uniform. This allows the heat pipes to remain within their operational range.
A limited number of backup heaters provide a secondary source of energy to heat the cabin walls. This technique decreases control complexity, parts count, and heater power requirements. It also does not use long, massive lengths of coolant loop tubing to carry energy to the spacecraft walls.
This work was done by Laurie Y. Carrillo, Steven L. Rickman, and Eugene K. Ungar of Johnson Space Center. MSC-24526-1