Have you ever tried designing a packaged food system for a mission in to outer space? It's no picnic.
The functions of food packaging manufactured and unwrapped on earth are fairly standard - it must protect, preserve and be transportable.
But, try to develop a package system for use in zero-gravity conditions and these functions become almost impossible to achieve, particularly when space centres worldwide are racing to get to Mars - an expedition which would require a food shelf-life of five years.
Michele Perchonok, advanced food technology project scientist at Nasa's Johnson Space Center in Houston, Texas, talks Packaging Gateway though the process of modifying commercial materials and sealing them, in order to enable the consumption of safe and nutritious foods in space.
Sarah Blackman: How is packaging modified to preserve food during space missions?
Michele Perchonok: We use all commercial materials currently and we vacuum package our rehydratable foods - the ones that are dry - and we vacuum package our beverages.
Our wet foods are thermostabalised and we remove as much head-space from their packages as we can, but we don't vacuum package wet food because it is too difficult to do.
There are commercial products we are looking for - higher barrier poly-based materials. Our only high barrier materials right now are the foil-layered materials, and we are trying to get away from these.
SB: Why are foil-layered materials unsuitable for space packaging?
MP: There are a few reasons. For one, they are a little bit denser and the second reason is that right now our rehydratables are contained in a polymaterial and, to maintain the shelf life that's required, we need to overwrap them with a foil laminate which means extra mass and extra volume. Also, we are looking at emerging technologies, such as microwave sterilisation and high pressure processing, and quad-laminate foil packaging just doesn't work with those processes.
SB: A mission to Mars could take up to three years. How far away are you from developing a packaged food system which could work over this period?
MP: We are proposing that by 2020 we will have a packaged food system that will work. We are not very close to that right now because we don't have foods that have the required five-year shelf life.
So, we are looking at packaging materials, processes that we can preserve the food with, formulations and the environmental changes we can make that help maintain or extend shelf lives.
SB: How can fruits and vegetables be packaged to make sure the crew gets a nutritious diet?
MP: Well, they're not going to. With the current technologies, I don't think it's going to get much better. We might be able to extend the shelf life of fresh fruits and vegetables to maybe a month, depending on the fruit and vegetable, but it won't make much of a difference.
So, we are actually proposing that once they get to the Mars surface, and that would be after a six month transit mission to Mars, they grow fresh fruits and vegetables on the surface, in environmental chambers, hydroponically.
SB: How are packages initially sealed and then resealed once opened in space?
MP: They are not resealed so right now all packaging is made for individual serving sizes. The crew cut open the package, eat the food and throw it away. So, a few of their special preference items that they request could be in zip-lock bags, but it gets very difficult to keep food around. It's ok for cookies and candy and such, but not for anything that is sensitive to oxygen and moisture. Once some of the wet food is opened, they have to be eaten within four hours, otherwise the crew may get sick.
SB: Does this pose challenges when attempting to keep the weight of the food supply to a minimum?
MP: Yes, but in weightlessness or microgravity it is very difficult to transfer food around.
If you think about the fact that you have a bulk pack of grilled chicken, for example, then you would need to have plates or something to put the food on once it comes out of the big package.
Those plates would either become more trash or they would have to be cleaned, which means cleaning materials and more water usage. So, right now in microgravity, it just makes a lot of sense to package individual serving sizes.
One of the preservation technologies that we use is our thermostabiliser process for canned food, but instead of using cans we use pouches because cans are heavier and you can't stow them efficiently.
SB: How do astronauts rehydrate their food in space?
MP: We have a water dispenser with a needle and the needle pierces a one-way valve septum and introduces the water. When the needle is pulled out, the septum is closed up again. The crew will then wait for the food to finish hydrating - a beverage might take five minutes and a food item might take 15 minutes - before they open the package.
SB: How has space packaging developed over the years?
MP: Well, things have certainly changed. For our Mercury and Gemini days we were using tubes and cubes, which contained pureed foods and small foods that were compressed. In our Apollo days we actually had a harder, non-flexible package that was used for our rehydratables. We realised that this was taking up too much trash volume because you couldn't crumble it. Now everything is flexible so that they [the crew] can crush the trash bag and get everything in there without having too much void space.
SB: What can the packaging industry learn from space science and technology?
MP: If we were able to find what we call our holy grail - a non aluminium-based barrier polymaterial that is clear - then, even though the packaging and food industry is not looking for a five-year shelf life, the quality of the food is certainly going to be even higher after six months or a year.
So, it's going to affect all of us, as well as the fact that poly-material is that much better for the environment because foil material doesn't degrade.
Also, once we get on to the Mars surface, one of the potential ways to get rid of the trash is by incineration, and if you incinerate the foil it's not going to work.