Astronauts have been going to space since 1961, but they still don’t have a refrigerator to use for keeping food cold on long missions to the moon or Mars.
Through experiments conducted in microgravity, a team of engineers from Purdue University, Air Squared Inc., and Whirlpool Corp. has shown that a prototype they developed could potentially overcome the challenges of getting a traditional fridge to work in space just as well as it does on Earth.
The canned and dried food that astronauts currently eat during missions has a shelf life of only about three years. The team’s project, funded by NASA’s Small Business Innovation Research (SBIR) program, aims to give astronauts a supply of food that could last five to six years.
The team recently ran three experiments to test various aspects of the fridge design onboard a specially designed plane that flew in microgravity 30 times – for 20-second intervals – during each of four flights. The plane, Zero Gravity Corporation’s (ZERO-G) unique weightless research lab, is the only testing space of its kind in the United States. (See a video of the in-flight experiments.)
Data analyzed so far from the experiments on the flights, supported by NASA’s Flight Opportunities program, indicate two big successes of the team’s prototype. First, the prototype can operate just as well in microgravity as it does on the ground. Second, the team determined that the prototype was no more likely to flood in microgravity than in normal gravity. Liquid flooding could damage a fridge.
Even though fridge experiments have been conducted in space before, they either didn’t work very well or eventually broke down. In practice, the fridge design would cool food through a vapor-compression cycle, similar to the process that a typical fridge uses on Earth, but without the need for oil. Having an oil-free vapor-compression cycle removes concerns about oil not flowing where it should in zero gravity.
The team’s prototype is about the size of a microwave, ideal for potentially fitting into the International Space Station’s rack systems, EXPRESS Racks, that store research experiment payloads. Air Squared built the prototype and the oil-free compressor inside, which acts as the heart of the fridge.
The team’s experiments aimed to test a common hypothesis that pushing refrigerant liquid through a vapor-compression cycle at a higher velocity would reduce the effects of gravity on the fridge’s performance. A detailed analysis of the data will show whether the constraint of these high-flow velocities and the large pressure drop they create can be removed, which could improve the fridge’s performance by saving energy.
Visit the Purdue website for more information.