March 5, 2014
Creating Gas Stations In Space: MIT
Lee Rannals for redOrbit.com - Your Universe Online
MIT scientists have come up with a concept to create gas stations in space in order to help fuel future lunar missions.Current missions require spacecraft to carry fuel in case of emergency, but this extra fuel means there is less room for space agencies to launch heavier payloads. The team at MIT has come up with two cost-efficient fuel station designs in space that take advantage of the “contingency propellant” that spacecraft carry.
The team is proposing the idea of using contingency propellant from past missions to fuel up future spacecraft. As a mission heads back to Earth, it could stop by one of these galactic gas stations and drop off a tank of contingency propellant for the next mission to pick up on its way to the moon as its own emergency supply. If this next mission ends up not needing the propellant, then it would drop it off at the depot again.
The researchers say a gas depot may end up accumulating contingency propellant from multiple missions, which they are calling “stockpiling.” If this scenario plays out, future missions wouldn’t need to launch with so much fuel because spacecraft could stop off by the depot to grab the fuel before heading off to the moon.
“Whatever rockets you use, you’d like to take full advantage of your lifting capacity,” Jeffrey Hoffman, a professor of the practice in MIT’s Department of Aeronautics and Astronautics, said in a statement. “Most of what we launch from the Earth is propellant. So whatever you can save, there’s that much more payload you can take with you.”
During Apollo missions, spacecraft took a route close to the moon’s equator in order to save fuel. However, with gas depots future lunar missions would enable space agencies to explore farther reaches of the moon, such as the polar caps.
The researchers created two depot designs to improve the efficiency of a basic scenario in which missions would explore the surface of the moon for seven to 14 days. In these designs, gas depots would be stationed at regions in space between the Earth, moon and sun that maintain gravitational equilibrium. Objects at these points remain in place, keeping the same relative position with respect to the Earth and moon.
Hoffman said transferring fuel between the depot and a spacecraft would simply involve astronauts using a robotic arm to pick up a tank. The alternative is to siphon fuel from tank to tank like a car at a gas station. This scenario would be trickier because of how liquid behaves in a gravity-free environment.
“In building the International Space Station, every time a new module is added, we’ve had to hook up new fluid connections,” Hoffman says. “It’s not a trivial design problem, but it can be done.”
The MIT team said the main drawbacks for both depot designs are maintenance, keeping depots within the Lagrange point, and preventing “boil-off,” which is when fuel not kept at cold-enough temperatures boils away. If the team can find solutions for these challenges then gas depots could help change future lunar missions.
“One of the problems with large space programs is, you invest a huge amount in building up the infrastructure, and then a program gets canceled,” Hoffman says. “With depot architectures, you’re creating value which is robust against political uncertainty.”
Hoffman and his students — Koki Ho, Katherine Gerhard, Austin Nicholas, and Alexander Buck — outline their depot architecture in the journal Acta Astronautica.