Refrigeration in space: now it’s possible
Working in space is certainly a fascinating prospect, but when it comes to the food served inside zero gravity space vehicles, astronauts often complain about the taste. This is due to the fact that meals have to be freeze-dried in order to minimise their size and weight and to ensure a longer shelf-life.
The use of traditional refrigeration systems like those on earth is impossible, as most terrestrial refrigerators need gravity to function. Although the components requiring lubrication with liquid oil are proving the biggest brainteaser for engineers, some interesting projects are now underway which are set to revolutionise this aspect.
ISS space refrigerators
The International Space Station, which is in continuous orbit around the earth, is a great setting for the study of new refrigerant solutions. Currently, NASA is using eight refrigeration units without rotating components, created specifically for use at zero gravity.
This system is known as Freezer Refrigerator Incubator Device for Galley and Experimentation (aka FRIDGE) and is the result of careful planning and scrupulous attention to detail. Considering that inside, it contains no rotating parts or fans at all, there is no need to use liquid oil for lubrication.
Among the various problems that need to be resolved during the construction of this space refrigerator, is the issue of heat dispersal. Starting from the assumption that, without gravity, warm air will not rise, engineers have had to connect the equipment, which is the size of a microwave oven, to the existing water-based cooling system on-board the ISS.
There are currently six operational refrigeration units on the ISS and they are mainly used for experimental research. In any case, a further two units for the conservation of fresh food sent from earth or grown in on-board hydroponic greenhouses are planned.
The future of space refrigeration
Scientific research never stands still and this is also true in the case of refrigerators designed to be used in space. The above-mentioned solutions face considerable issues connected with the extremely high energy consumption required for food storage.
NASA has therefore commissioned several research teams to develop a high energy efficiency refrigeration unit which can store fresh food for astronauts and which will be installed on future spaceships for interplanetary voyages.
One of the most promising projects is the result of collaboration between Purdue University, Air Squared INC and the Whirlpool Corporation. It aims to build a refrigerator which runs on compressed steam, designed to provide the appropriate temperatures for food storage while reducing energy consumption.
The device is based on technology recently patented by Air Squared Inc, involving the use of a compressor scroll and an inbuilt expander. These two components operate on a common tree and can therefore be protected by a single semi-hermetic shell.
Another advantage of using a compressor scroll is that it does not require lubrication oil: this makes this sophisticated refrigerator a perfect solution for use at zero gravity. The prototype is now ready for microgravity testing which, if as successful as the developers hope, will open the doors to largescale production and a new approach to refrigeration in space.
Translated by Joanne Beckwith
