Refueling In Space | Out Of This World Weekly
Refueling on Earth is something that we all have to deal with. Pull up to the gas station, insert pump, and fuel up the car until you get a full tank. Spacecraft on Earth refuel in a very similar way, when they are on the launch pad, liquid hydrogen and liquid oxygen are commonly pumped into rocket fuel tanks just before takeoff. These super cold gases are loaded just before takeoff because they will turn from a liquid to a gas. As they naturally warm up and simply boil off the surface of the liquid, they are vented so that pressure in the tanks doesn’t become so great that they burst. Most of this propellant is used up on launch because it is very hard to keep these freezing cold liquids at low temperature in outer space for long periods of time. This ability to keep liquified gases cold would greatly enhance our ability to reach the outer solar system as well as decrease the amount of time needed to reach closer objectives.
Space is thought of as a very cold place and it can be, reaching temperatures of just a few degrees above absolute zero. Unfortunately, this is the temperature that is reached in the deepest, darkest space with absolutely nothing around. In Earth orbit, temperatures can vary by 500 degrees depending on whether direct sunlight is shining on an object. This means that temperatures ranging from –250 degrees F to 250 degrees F can occur within a short time. This doesn’t help super cooled liquids stay cold for long, with large tanks only being able to stay cooled for hours at a time before evaporating. If we are ever going to refuel spacecraft with liquid coolants, we need to find ways to keep those super cooled liquids cold for long periods of time.
NASA knows this and is working on a program using micro experiments. One of these experiments would use a small CubeSat in Low Earth Orbit, while another would use equipment mounted on the outside of the space station. The space station experiment would attempt to capture excess Hydrogen and Methane that is regularly vented into space and liquefy it using liquid Helium so that tests can be run on the liquified gases. Turning excess gas back into liquid may be necessary to keep large reserves of liquid available in space. The other experiment involves a small cube satellite sent into orbit with liquified gases held in a six centimeter diameter tank. The satellite would use a series of shields that could be deployed to protect the cargo from direct sunlight and enable the tank to release heat when the temperature is low enough to cool the liquified gas as much as possible. Combinations of these techniques and others, like possibly keeping a refueling station in the L2 Lagrange point where it would be shielded from the Sun from the shadow of either the Earth or the Moon to help keep it cool, should eventually allow for refueling of spacecraft and this will allow much further exploration of our Solar System.