The future of human and robotic exploration will mean trips to deep space destinations like the moon, Mars, or asteroids. But getting there and returning home on one tank of gas while carrying a sizable payload is almost impossible. The solution? In-space refueling technology, which enables spacecrafts to tank up in low Earth orbit.

Last year, the Augustine Commission, a blue-ribbon panel charged with reviewing America's human spaceflight program, emphasized the need for NASA to purse this technology in their final report to the White House. Now NASA has put out a call for a $200 million mission to show how to store and transfer rocket propellants in space.

In-space refueling technology would allow smaller and cheaper rockets to be used for missions that would otherwise be outside their weight class. It will also considerably enhance the capabilities of larger rockets. "Instead of sending the rockets fully fueled to asteroids or to Mars we would launch them partially fueled to get more payload into orbit," Chris Moore, deputy director of advanced capabilities for NASA told Foxnews.com. "Then we'd top off the propellant by docking with depots in lower Earth orbit."

NASA wants to focus on liquid oxygen and liquid hydrogen, the fuels that power the main engines of the space shuttles and commercial rockets. The challenge is finding ways to store and maintain the propellant, which requires extremely cold temperatures. Heat from solar flares or a rocket engine's exhaust could evaporate the fuel or cause the tanks to expand and even explode. So any demonstration must also successfully transfer the fuel to a docked spacecraft in a zero-gravity environment.

The technology could also provide a boost to the commercial space industry. NASA could purchase fuel in orbit from commercial companies which would operate refueling tankers or possibly even permanent depots. "We could create a small space economy in propellants and refueling," Moore said.

A time-lapse photo of a rocket launch powered by new aluminum-ice propellant. Credit: Purdue University

Last week researchers from Purdue and Penn State University launched a rocket that uses an unconventional propellant: aluminum-ice. The fuel mix, dubbed ALICE, is made of nano-aluminum powder and frozen water, and gets its thrust from the chemical reaction between the ingredients. The propellant is environmentally friendly, and it could perhaps allow spacecraft to refuel at locations like the moon, where water has been discovered.

Using aluminum for fuel is not completely new--the space shuttle's solid rocket boosters use a small amount of the metal, as will NASA's Ares rocket. But the new work involves making aluminum one of the key ingredients by using nanoscale particles. These tiny particles, when ignited, combust more rapidly than larger particles, forcing more exhaust gases out of the metal and giving the rocket the necessary kick.

The oxygen and hydrogen in water molecules enhance the combustion of the aluminum. Freezing the propellant keeps it intact, avoiding any premature reactions.

The propellant was able to lift a rocket 396 meters during an August flight test, which was funded by NASA and the Air Force Office of Scientific Research. Now, for even better performance, the researchers are working on adjusting the ratios of different ingredients and possibly mixing the nano-aluminum with larger aluminum particles.

A water-based propellant might one day mean that spacecraft could carry less fuel when traveling to distant locations like the moon or even mars. But it would also be nice to have a "greener" fuel for rocket launches back on Earth.