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Spacecraft that must operate in cold environments at reduced heat load are at risk of radiator freezing. For a vehicle that lands at the Lunar South Pole, the design thermal environment is 215 K, but the radiator working fluid must also be kept from freezing during the 0 K sink of transit. A radiator bypass flow setpoint control design such as those used on the Space Shuttle Orbiter and ISS would require more than 30% of the design heat load to avoid radiator freezing during transit - even with a very low freezing point working fluid. By changing the traditional active thermal control system (ATCS) architecture to include a regenerating heat exchanger inboard of the radiator and using a regenerator bypass flow control valve to maintain system setpoint, the required minimum system heat load can be reduced by more than half. This gives the spacecraft much more flexibility in design and operation. The present work describes the regenerator bypass ATCS setpoint control methodology.

Biological water processors are currently being developed for application in microgravity environments. Work has been performed to develop a single-phase, gravity independent anoxic denitrification reactor for organic carbon removal [1]. As a follow on to this work it was necessary to develop a gravity independent nitrification reactor in order to provide sufficient nitrite and nitrate to the organic carbon oxidation reactor for the complete removal of organic carbon. One approach for providing the significant amounts of dissolved oxygen required for nitrification is to require the biological reactor design to process two-phase gas and liquid in micro-gravity. This paper addresses the design and test results overview for development of a tubular, two-phase, gravity independent nitrification biological water processor.

As part of NASA’s TransHab inflatable habitat program, a Radiation Shield Water Tank (RSWT) is being developed to provide a safe haven from peak solar particle events. The RSWT will provide an 11 ft. (3.35 m) diameter by 7 ft. (2.13 m) tall “safe haven” with a 2.26 in. (0.0574 m) thick wall of water for astronaut residence during peak solar events. The RSWT also functions as a water processing storage tank and must be capable of being filled and drained at will. Because of the unique shape of the RSWT, standard bellows and bladder designs cannot be used for inventory control. Therefore NASA has developed a bladderless tank where capillary forces govern the positioning of the liquid inventory. A combination of hydrophobic and hydrophilic membranes and wetting surfaces allows the tank to be filled and emptied as desired. In the present work, background on space-borne radiation is presented, the bladderless RSWT concept is described, and its theory of operation is discussed.

Thermal qualification of space equipment is performed in a thermal/vacuum (T/V) chamber. Here the chamber pressure is maintained near 10−6torr, imitating the vacuum of space and ensuring that all heat transfer occurs by conduction and radiation. In addition, the chamber walls are flooded with liquid nitrogen to simulate the background radiation from space. When performing tests in T/V conditions, an equivalent sink temperature for the test article is normally specified. However, the quartz infrared lamps that are currently used in T/V testing cannot be used to provide a uniform sink temperature over surfaces with varying optical properties. The present work defines an innovative method of applying the sink temperature that yields uniform results despite variations in the surface optical properties.

The US Space Shuttle on-orbit waste heat rejection is currently accomplished through a combination of radiators and a Flash Evaporator System (FES). Three of the FES units have been rebuilt to date owing to corrosion problems. In addition, the FES has experienced freeze-ups on-orbit. As part of NASA's Orbiter Upgrade Program, a Water Membrane Evaporator (WME) is being developed as a replacement for the FES. The WME will be installed on the Space Shuttle starting in the fall of 2001. It will use hydrophobic micropore membrane technology to passively control a water liquid/vapor interface. Waste heat that will be acquired from the Orbiter Freon-21 coolant loops will evaporate water at the interface. The water vapor will pass through the membrane and be vented to space. The WME program takes advantage of the recent advances in hydrophobic micropore membrane technology to provide a simpler and more robust heat rejection device than the current FES.

The temporal variation of Earth emitted infrared radiation (IR) and albedo are examined for the case of a spacecraft operating in a Space Station Freedom (SSF)-like orbit with a period of 94 minutes and an inclination 28.75°. Seventy three randomly selected days of daily average Earth IR and albedo measurements from the Earth Radiation Budget Experiment were used to calculate the effective IR and albedo constants for the Earth during representative orbits. The time average effective IR and albedo extreme values, including a correction for diurnal effects, are presented for multiple periods of up to 4 hours. The statistical variation of IR and albedo over various time intervals is also presented, as are the results of a study of the correlation between IR and albedo. The results of the present study are used to recommend the design environments that should be used for future spacecraft in orbits with inclination and altitude similar to SSF.

The Space Shuttle humidity separator prefilter was developed to remove debris from the air/water stream that flows from the cabin condensing heat exchanger to the humidity separator. Debris in this flow stream has caused humidity separator pitot tube clogging and subsequent water carryover on several Shuttle flights. The first design concept of the prefilter was flown on STS-40 in June, 1991. The prefilter was installed on-orbit. Video footage of its operation revealed that the prefilter did not pass water at a constant rate, resulting in a tendency to slug the humidity separator. The results from this flight test have resulted in a complete redesign of the prefilter. In this paper the first prefilter design is described, the flight results from STS-40 are examined, and the on-orbit performance of the prefilter is explained. The redesigned prefilter is described with emphasis on the features that should allow successful reduced gravity operation.