Food is nearly all water, and water is heavy and bulky. Fresh food would also go bad within a few days. So great care has to be taken to make sure the food is lightweight, compact, stays fresh - and produces a balanced diet.

But there is more to worry about in space. There is no gravity to hold the food in place, so it will just float around. Anything that makes a powder, such as salt and pepper, are particularly difficult to deal with. But there are other foods that cause problems, too, such as bread, because it is crumbly, and as you eat it, the crumbs float away.

Condiments, such as ketchup, mustard and mayonnaise, are provided. Salt and pepper are available but only in a liquid form. This is because astronauts can't sprinkle salt and pepper on their food in space. The salt and pepper would simply float away. There is a danger they could clog air vents, contaminate equipment or get stuck in an astronaut's eyes, mouth or nose.

Many foods come in sealed pouches - similar to canned foods, but without the can.

All of the astronauts' food is canned, dehydrated, or otherwise packaged so it doesn't need refrigeration. So of course this means no fresh fruit, vegetables, etc.

The only utensil is a spoon. All of the food that requires a utensil to eat has some sort of sauce or at least some moisture to it, so it naturally sticks to the spoon. This allows astronauts to eat without having food drifting away. All the same, you have to move fairly slowly when eating, or the food will literally fly right off your spoon (and onto the wall).

Space food comes in packages that must be disposed of. Astronauts put their used food containers away in a trash compactor.

For a longer description of space food, read this connected article.