Two teams of researchers are hoping their tiny devices will mean big leaps for future Mars-bound humans, allowing them to carry powerful computers and generate life support materials from the planet’s atmosphere.
In one corner, NASA-funded scientists are tweaking microtechnology to produce compact systems that produce breathing oxygen or rocket propellant, vital components of any manned space mission.
"We’re looking at collecting the carbon dioxide from the Martian atmosphere and breaking it down for [crew needs]," said Batelle researcher Kriston Brooks, principal investigator of the study at Pacific Northwest National Lab (PNNL), where NASA has awarded a contract to develop the technology.
The goal, Brooks added, is to wrangle microtechnology into a usable system that would generate propellant for astronauts aboard a manned mission to Mars by 2030, a goal set by NASA’s space vision of renewing human space exploration outside Earth orbit.
"It’s all about helping to reduce the cost of missions for robotic sample returns and even human space missions," said NASA's Tom Simon, a systems engineer for in-situ resource utilization at Johnson Space Center. "We’re hoping that the work will be a great kick-start for using resources on Mars to enable us to meet our budget goals and constraints for exploration."
Meanwhile, two Purdue University researchers are adapting microchannel heat sinks — small copper plates lined with numerous grooves each three times the width of a human hair — with conventional refrigeration methods to build more efficient cooling systems.
"The microchannel heat sinks are absolutely ideal for those situations," said thermal engineer Issam Mudawar, the study’s leader and a Purdue mechanical engineering professor, in a telephone interview. "Though our immediate target is both computer chips and defense applications."
Setting up shop off-planet
NASA has set aside $13.7 million for Brooks’ four-year study, which engineers hope prove useful not just for Mars missions, but also lunar spaceflights and space station living as well.
Using local resources could reduce the cost of a moon or Mars mission by about 40 percent according to NASA studies, Simon told SPACE.com, adding that lunar resource-based technology is also under scrutiny.
"We’re hoping to be able to support by 2010 a small demo mission that not only produces just a couple of grams of oxygen, but will also be able to tell what water is on the moon," Simon said.
Currently carbon dioxide collected by the space station’s air scrubbers and hydrogen produced by the station’s Elektron oxygen generator are currently are dumped overboard, but Sabatier reactors, which generate methane from carbon dioxide, could help astronauts recover oxygen from what has to date been treated as waste gas, he added.
At the heart of Brooks and Mudawar's studies are advances with microchannels, which have allowed researchers to squeeze chemical and thermal processes into ever-smaller packages.
"What really got this started is microchip technology," Brooks told SPACE.com. "We thought, 'well, if we can make microchips so small, why can't we do the same thing chemically.'"
With multiple grooves separated by just 200 microns or so apart, microchannel plates offer improved heat and mass transfer rates. Since the spaces between groove walls are so small, the effects of gravity give way to other forces, similar to water’s capillary action, making the technology apt for space applications, the researchers said.
"You also have the advantage of redundancy," Brooks said, adding that the processes required to scale up from one microchannel to a 1,000-microchannel system are simpler than other processing methods.
For Mudawar, the differences in fluid flow between microchannels and the more conventional tubing used for heat sinks has allowed the development of even smaller cooling systems for electronics.
In order to produce oxygen or propellant for a spacecraft, Brooks is developing a closed-loop system of heat exchangers, condensers, phase separators and other tools into a working microchemical and thermal system (MicroCATS) device about one cubic foot in size.
Once the individual components are tested, they will be integrated into a bread board-sized system and tested in microgravity aboard NASA’s KC-135 aircraft, as well as inside atmospheric chambers to simulate the Mars atmosphere and temperature environment.
Brooks hopes the test will lead to a final setup, known as an In-Situ Propellant Production system (ISPP), that could sit outside a spacecraft on the Martian surface, absorbing carbon dioxide, then heating it up and passing it through a series of small reactors to separate the gas into methane and water, which is ultimately broken down into oxygen and hydrogen.
"Our goal is to be about one-third the weight of conventional systems," Brooks said. "Hopefully, we’d be able to catch a ride on a mission that’s going to Mars and people can test this out."
The oxygen and methane can be cryogenically stored in separate tanks – possibly even the same ones used to hold fuel for the trip to Mars – and later be used as propellant, Brooks said, adding that the system could also bolster life support as well.
"For example, on a space suit you could use it to collect carbon dioxide and regenerate it into oxygen," Brooks said. "What they do now aboard the space station is collect the carbon dioxide, absorb it then replace the (scrubbers)…we need to be able to close the look on life support."
Building a cooler system
At Purdue University, Mudawar and doctoral student Jaeson Lee have already demonstrated the potential of their microchannel heat sinks.
"We really have a working system now," said Mudawar, whose study is funded by the U.S. Office of Naval Research.
Two research papers based on the work appeared in a recent edition of the International Journal of Heat and Mass. Mudawar has also tested past heat sinks aboard NASA’s KC-135 aircraft in weightless experiments for a variety of space systems.
Mudawar and Lee were able to successfully use a one-inch square copper microchannel plate to serve the same evaporative cooling function as the one-meter long tubing used in a refrigerator. "The issue now is going to be packaging the cooling system around the device."
While Mudawar’s heat sink still requires a refrigerant to function – the researchers used R134a, which is found in household refrigerators and air conditioners – it offers much higher performance than conventional fans or dissipation metal fins. Future military weapons systems, such as advanced lasers, may require heat sinks capable of dissipating up to 10,000 watts per centimeter that current methods may not be able to handle efficiently.
"We were very satisfied with this technology," Mudawar said.
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