[image-47] Steven Siceloff,
NASA's John F. Kennedy Space Center
Storing super-cold propellants is not easy on Earth, but it doesn't seem to be much easier to accomplish in space either. That's not stopping engineers from trying to perfect technologies, though.
"The longest we've kept liquid propellants in orbit is a matter of hours in the size of large propellant stages like Apollo and Centaur," engineer Adam Swanger told an audience during a Kennedy Engineering Academy session at NASA's Kennedy Space Center in Florida.
Some of NASA's far-reaching plans, most notably space-based fuel depots that would act as gas stations for interplanetary spacecraft, potentially would require the reliable storage of fuel and oxidizer for months at a time.
Before addressing these issues on a large scale, engineers are looking at promising techniques on a very small level as part of the academy's Accelerated Training Program, or ATP. One approach requires the International Space Station, while the other is a CubeSat design that would fly free in orbit to show that super cold materials can safely be stored in space without boiling off.
ATP is a six-month assignment with on-the-job training opportunities and diverse and targeted work assignments designed to establish the on-going work relationship, job maturity and technical expertise necessary to perform effectively within the organization. The program is based on internship, with direction from a mentor. At the end, participants are required to complete a written project plan and formally present the project results to a board.
Although space often is thought of as a cold place, satellites typically experience dramatic temperature swings of 500 degrees or more depending on whether they are in sunlight or not. Insulating liquid hydrogen, which at minus-423 degrees is one of the coldest materials known, poses a tremendous challenge to designers.
Swanger's experiment aims to liquefy and store the hydrogen and methane created by the life support system on the space station. Now, the excess chemicals are vented from the station regularly to disperse in space. If it works, it would be a first, since researchers have not tried to liquefy gases in space before, Swanger said.
"The idea is, if we somehow could capture these commodities, plumb them back into an experiment, we would then be able to liquefy them using a cryo-cooler and test zero boil-off and test microgravity liquefaction technologies," Swanger said.
The proposal calls for a device to be placed on the Japanese Experiment Module's exposed pallet, the platform on the Kibo scientific lab module that is open to space.
Swanger said the pallet location offers power and cooling feeds to the experiment, and also is close to the NASA-built Tranquility module where the excess chemicals are produced. Helium would be used in heat exchangers to cool the materials the same way a refrigerator uses water to cool air.
"We think with further refinement it will prove that it is feasible to liquefy the gaseous hydrogen and methane flow from the system on the International Space Station," Swanger said.
Jared Berg's focus was to create a tiny storage facility a bit smaller than a shoebox that could be launched as a secondary payload and operate on its own, keeping the chemicals inside cold.
The spacecraft, slated for launch in 2014, is called CryoCube-1 and uses the proven architecture of the experimental nanosatellites known as CubeSats. The cube would have fold-out sunshields and solar arrays on each end, along with doors that would open and close to either release heat from around the six-centimeter-diameter tank or shield it further from warm sunlight.
Instruments on the satellite will gauge how the liquid behaves in space.
"The ATP study was to prove that we could get temperatures low enough to condense oxygen on a satellite," Berg said. "We wanted to see how sensitive the (satellite) would be."
Kurt Smith's ATP effort centered on a concept for ground support equipment needed for NASA's Space Launch System, or SLS, a massive rocket comparable to the Saturn V. Smith worked on a design to retract a 1,500-pound plate that will hold umbilical lines to the rocket during processing and countdown, but safely pull away as the rocket lifts off.
"One of the things we try to do is keep the designs as simple as possible," Smith told the group.
Smith said he employed a childhood erector set to test his different thoughts, along with the numerous design tools available to engineers.
The ATP session took the design through a third of its development. Future work will refine the mechanism until it's complete and helping an SLS into space.