In Space with a Little HOBO
Astronauts working in spacesuits to build the Space Station may get even colder than the suit designers imagined. Measuring the effects of extremely low temperatures on astronauts was the first step in making a better space suit.
Space suits must provide complete life support, safety, comfort, and mobility when astronaut leave the ship for up to 8.5 hours.Space suits therefore must provide compartments for the storage of food, water, oxygen, and waste, as well as protection from temperature extremes, vacuum, and micrometeoroids.
The suit, including gloves, boots, and helmet, contains many subsystems, each with a variety of sensors, transducers, and control elements. One area that needs improvement is the temperature inside the gloves.
The figure below shows the suit’s complexity.
- First inner and outer liners of swimsuit fabric for comfort.
- Next transport tubes for cooling and ventilation.
- Third the pressure garment and its cover restraint.
- Next layers of Mylar insulation, and a ripstop liner.
- Outermost is the thermal micrometeoroid garment (TMG).
The general principle behind the space suit is that the astronaut’s body makes heat that is controlled by the life support system. If it gets to hot in the suit, either because the astronaut is working hard or in direct sunlight, the water cooling removes the heat. The reverse problem is when the astronaut can’t put enough heat into the space suit to stay warm.The lack of heat is felt first at the body’s extremities, notably the fingers tips. Boots can be heavily insulated to keep toes warm, but glove insulation is limited by the need for manual dexterity. Space walk efficiency can be adversely affected when astronauts’ hands become uncomfortably cold.To study the problem and improve glove design, NASA outfitted space suit gloves with tiny, battery-powered temperature loggers. The instrumented gloves were worn by astronauts Bernard Harris and Michael Foale during NASA’s STS63 mission flown by space shuttle Discovery.
To monitor the temperature of the astronauts’ fingers, the gloves of the space suits were equipped with HOBO Littler temperature loggers. The units were secured between the outermost and insulation layers on the glove backs, out of the 100% oxygen environment of the glove interiors.
Four of the data loggers were connected via a cable 8-10 inches long to small thermistors sewn into the finger tips. A fifth HOBO measured the temperature on the back of the glove where the devices were placed.The data indicated that because the suits were being subjected to environments colder than their design limits, they were unable to keep the astronauts comfortable during the EVA if there were lulls in the astronauts’ metabolic rate. Rather than trying to further insulate the gloves, NASA engineers have decided to move to internal heaters for the finger tip areas.