Students at Purdue University show promising breakthroughs on providing astronauts with fridges they can use in space.
It doesn’t sound remarkably groundbreaking, but astronauts need to eat while traveling through space. The dried or canned food that astronauts currently eat while in space has a shelf life of about three years. Vickie Kloeris, a food scientist who runs the International Space Station (ISS) Food System, said back in 2017 that astronauts returning from a mission to Mars will likely be faced with food somewhere between five to seven years old. With that time line, very few foods currently approved by NASA for spaceflight will not suffer nutritional degradation.
So, without completely adjusting the genetic makeup of the food we consume, is there a way to provide nutritious meals to astronauts who are making these perilous journeys?
A team of students from Purdue University, along with Air Squared Inc. and Whirlpool Corporation, is trying to find an answer through a conventional mode of keeping food fresh for longer—a refrigerator.
The project itself is funded by NASA’s Small Business Innovation Research program.
Fridge experiments have been sent to space before, but a lack of measured data and detailed documentation has made it difficult for new researchers to enter the field of refrigeration in space.
This team is aiming to design a fridge that can be sent into space ahead of the astronauts and which can operate as a freezer.
The Most Important Step in the Design Process is the First One—Research
A regular fridge makes use of vapor compression through a closed system that circulates liquid refrigerant through four stages: compression, condensation, expansion and evaporation.
Click here to watch a video on how the vapor-compression cycle works.
The vapor-compression refrigeration system.
Gravity normally helps move the liquid and vapor as it flows through the system, and it is also the basis for a fridge’s oil-lubrication system. The biggest hurdle is making this system not only efficient but also reliable in zero gravity.
Developing the Prototype or Three
The team knew that it had to design different prototypes to be able to test the fridge’s capabilities, and so it designed three different experiments:
- The real-size prototype is the size of a microwave that plugs into an electrical outlet and would be similar in size to one that would be used on the ISS. This one will be tested in flight.
- A larger version with sensors and other instruments to measure the effects of gravity on the vapor-compression cycle. Prior to in-flight testing, the team tested this version in the lab by rotating it, which gives a sense of how gravity currently affects the design.
- A final prototype to test the prototype’s vulnerability to liquid flooding and how that might damage the fridge.
The major problems of the oil-lubrication system not working in microgravity were circumvented by the Air Squared’s development of an oil-free compressor. The issue of oil leaving the compressor and being trapped within the system was no longer a problem.
The key hypothesis being tested was that pushing refrigerant liquid through the vapor-compression cycle at a higher velocity reduces the effects of gravity on the overall performance of the fridge.
It Works on Paper, but What About Real Life?
For the test scenario, students in the team tested various aspects of the fridge design while in flight. The flight consisted of 30 parabolas and included Martian, lunar, and micro gravities. During and just after the peak of each parabola, the team experienced an environment similar to microgravity, allowing them to test their equipment.
They made use of Zero Gravity Corporation’s weightless research lab.
The testing team was a formidable combination of students and teachers alike: Eckhard Groll, a professor and head of Purdue’s School of Mechanical Engineering; Leon Brendel, a Ph.D. student in mechanical engineering; and Paige Beck, a junior majoring in mechanical engineering.
Along with members of the team from Air Squared and Whirlpool Corporation, the team floated around with the experiments in the plane, waiting for the 20 seconds of microgravity at the peak of each parabola. During these intervals, the team tested the prototype, recorded data, and recorded actions into a microphone.
The testing process had a steep learning curve, as variables had to be adjusted while the plane was swinging through a parabola. “Sometimes I was too slow!” said Brendel, “But you learn as you go, and we successfully got the data we needed.”
The team is currently completing its data analysis.
Through a deeper analysis, the team can understand whether the constraints of high-flow velocity and the large pressure drop it creates can be eliminated, which would reduce the fridge’s energy needs.
What Have We Learned Thus Far, and What Comes Next?
Thus far, the data indicates two successes in the prototype.
First, the prototype can operate similarly in microgravity as it does on the ground.
Second, the team identified that the fridge was no more likely to flood in microgravity than on the ground, demonstrating reliability. Microgravity does not alter the cycle in ways that were not expected: it acted like a regular fridge would if it were rotated and inclined.
For now, more data must be analyzed to identify what needs to be adjusted for the next prototype. However, this experiment’s results were extremely promising. Hopefully, it’s sooner rather than later that we can provide our astronauts with nutritious and tasty meals as they explore the outer reaches of space.
