Freeze-dried ice cream, popularly marketed as "Astronaut Ice Cream," is a type of snack first developed by the National Aeronautics and Space Administration (NASA) for astronauts to eat in space. Freeze-dried ice cream is completely dehydrated, so it is nearly light as air and dry to the touch, cannot melt, and does not require refrigeration or preparation. It's easy to eat by hand and won't make a mess. Freeze-dried ice cream was first used by astronauts on the Apollo missions of the 1960s and 70s, and it is still used on space flights today. It is also available in many science museum gift stores and similar novelty shops. Freeze-dried ice cream is usually Neapolitan, with a stripe each of chocolate, vanilla, and strawberry flavors. It is made out of real ice cream, so it tastes like ice cream and contains all the original nutrients, but has a dry, crunchy texture. Freeze-dried ice cream sandwiches can also be found, along with other snacks like pizza and peaches. Freeze-dried ice cream and other "Astronaut" food is ideal for hiking trips or other occasions in which one wants to bring food but travel light. Freeze-dried ice cream is made through a process called lyophilization. The ice cream is frozen to -40° Fahrenheit (-40° Celsius) and placed in a vacuum chamber. Air is removed from the vacuum chamber, and then the chamber is heated, allowing the ice to vaporize, dehydrating the ice cream. Through this process, the intermediary liquid state (water) between solid (ice) and gas (vapor) that would exist in natural conditions is bypassed. This change of state from a solid directly to a gas is known as sublimation in physics.