A metal-making process known to the ancient Romans could be pressed into service to bring Mars into the Iron Age - and start opening the solar system to human habitation.
"If you look at the soil composition of Mars, the one thing that really strikes you is that it's 5 to 14 percent iron oxide," said Dr. Peter Curreri, a materials scientist at NASA's Marshall Space Flight Center. "It's almost ore-grade material."
Using Mars ore, Curreri says, early explorers could build receivers to generate electricity from radio waves beamed from a mother ship in Mars orbit. While NASA does not have a program to put humans on Mars, it is developing technologies and mission concepts for such a possibility.
A gleam in the eye
"What really put the gleam in my eye," said Curreri, "when I got into space 20
years ago as a graduate student, was the concept that if you can process
materials in space for use in space, you can really open up the frontier.
Putting a manufacturing device on the Moon or Mars can provide products that
weigh 20 times or more the weight of the propellants to deliver it. That becomes
a very powerful lever."
Curreri's NASA career has focused on learning how to process materials in the microgravity environment of Earth orbit. Now he is looking to the planets where processes would take place in gravity fields less than that of Earth.
In a recent study, Curreri and Dr. David Criswell of the University of Houston borrowed from several concepts to provide a new twist on making Mars habitable. They presented the results, "Potential for In Situ Rectenna Production on Mars," at a recent space development conference in Albuquerque, N.M.
Curreri's study has several drivers, including the high price of the manned Mars mission proposed in 1989 and a requirement to develop a non-nuclear Mars mission option.
The high price tag spurred Mars supporters to look at the possibility of using local materials to make propellants for the return trip. The non-nuclear option led to the Solar Clipper. This combines an ion drive with large solar cell arrays proposed in new NASA studies of solar power satellites, another 1970s idea. The unmanned Solar Clipper would boost itself to a high Earth orbit over the period of a year. After the crew arrives on a small, faster craft, the Solar Clipper would use a chemical rocket to make the final boost to Mars.
In several schemes under study, the manned crew would be preceded to Mars by an unmanned propellant factory. This craft would refine the Martian carbon dioxide atmosphere and mixed it with hydrogen (brought along or electrolzyed from water ice in the polar caps) to make liquid oxygen and methane to power the crew's return to Mars orbit.
Unleaded or regular?
"Say we had to make a trip to California by car," Curreri explained. "We could
build a tractor-trailer rig and haul a huge tank of gas to get us out there and
back. It's like that now with rockets because we have to take the propellant for
the return trip all the way out there. Or, we could build a smaller car and
refill when we get there."
The idea for making Mars propellant originated in the early 1970s with the late Dr. Gerard O'Neill of Princeton University. It has been promoted vigorously by Dr. Robert Zubrin, an aerospace engineer who felt that "living off the land" would make the journey cheaper than a mission that attempted to take everything with it.
Refining your own propellants becomes a challenge if you restrict yourself to solar power systems on the surface, Curreri says. To satisfy the mission's needs, astronauts would have to deploy the equivalent of six football fields of solar arrays and then keep them dusted off, and use fuel cells or batteries for power during the night - after the expense of landing them.
Curreri thought that the Solar Clipper could be pressed into double duty once it arrives at Mars. The Clipper's solar cells would provide more than enough power to run the Mars outpost. The trick is getting the electricity to the ground.
Red means iron
That can be done by beaming it as microwaves that a special rectifying antenna -
the rectenna - turns into direct current electricity. Engineers at NASA's
Johnson Space Center had considered that possibility but found themselves boxed
in at two ends of the radio spectrum. At the long wavelengths that are easily
broadcast now, the outpost would need a 20 km-wide field covered with rectennas.
A small field is possible, but that requires broadcasting at much shorter
wavelengths that engineers do not expect will be practical in the near future.
Curreri and Criswell took a different approach. Mars is rich in iron.
"That's why it's the Red Planet," Curreri explained. "It's covered with rust."
Iron has little use in aerospace vehicles because it is heavy and corrodes readily. In Mars' gravity field, only 0.38 that of Earth, iron and everything else weighs less. Iron will not corrode readily because Mars' thin atmosphere has virtually no free oxygen.
And, most of a rectenna's mass is in the metal for the dipole antennas.
"What if you were to make that metal on Mars?" Curreri asked. "You could make refining the ore a part of the propellant refining process."
Using water to convert carbon dioxide to methane also yields carbon monoxide, a reducing agent that reacts with rust to produce carbon dioxide and free iron.
"It's a process that's been used since the time of the Romans to refine iron ore," Curreri said.
A chemical reactor could process Mars' air and soil into rocket propellant and into rectenna parts. The iron would be rolled up as strips to make dipoles and wire to form a mesh reflector behind the dipoles. the waste, or slag, would formed into insulator strips going between the dipoles.
A powerful place to be
"If we put the Solar Clipper 17,023 km up, it would be in aerosynchronous orbit,
meaning its orbital period matches the rotation of Mars, then we would have
continuous power," Curreri said. This is is like the geosynchronous orbit used
by communications satellites around Earth so an antenna is always pointed at the
satellite.
The initial Mars lander would carry enough materials to make a 1.5 km-wide rectenna that would provide 150 kilowatts of electricity to power the refinery. As it cranked out rocket propellant, iron, and slag, automated equipment would expand the rectenna to 20 km in diameter. That would boost the power output to more than 7 megawatts, enough to run a large exploration base. Continued expansion would only require the shipment from Earth of rectifier circuits which are small and lightweight.
Unlike solar arrays that would have to be dusted off periodically, the rectenna would require little maintenance since the dust particles are too small to interact with the radio waves. And the rectenna would work year-round, night and day, with the exception of short eclipses during the spring and autumnal equinoxes.
"Eventually you end up with a power-rich environment on Mars," Curreri said. "Then Mars becomes the second safest place in the solar system for humans. It's an attractive haven instead of aborting a mission and trying to come home."
Curreri says this would be the start of an interplanetary economy.
"We should begin marrying the concepts for the exploration of space with the utilization of space," he said. "The key is to build. Rather than just going to Mars to say we did it, you want to go there and build an infrastructure so people could stay and live."