Researchers to test alien soils for use in heat shield

Sep 17, 2012 by Steven Siceloff
A 2-inch by 4-inch brick is heated by a welding torch in a test of a concept for making heat shields from the soil of other worlds. Credit: NASA

(Phys.org)—An important test is coming up next week to see whether a heat shield made from the soil of the moon, Mars or an asteroid will stand up to the searing demands of a plunge through Earth's atmosphere.

At stake is the possibility that could leave Earth without carrying a heavy and instead make one on the surface of another world and ride it home safely. The weight savings opens new possibilities ranging from using smaller rockets to carrying many more supplies on an .

Michael Hogue, a researcher at 's in Florida, came up with the idea during a brainstorming session last year covering different ways to use extraterrestrial soils, known as regolith.

"Others were talking about how regolith can be used to make bricks or landing pads and I said, 'Well, if it's good for that, why can't it be used to make atmospheric entry heat shields?' " Hogue said.

NASA funded the concept research through its NASA Innovative Advanced Concepts, or NIAC, program.

Since then, a team of engineers has been trying out various and techniques to find out whether the idea has any potential. So far, the tests have been very successful, with small bricks of material standing up well to the intense heat of a blowtorch. A sensor placed behind the brick recorded temperatures of about 200 degrees F compared to the approximately 4000 degrees F the front side endured.

Researchers to test alien soils for use in heat shield
An artist's concept of a spacecraft using a heat shield made from the soil of another world, called regolith. Credit: NASA

"I expected some to fail," Hogue said. "There is an optimum range of density you need to hit for each material where it's light enough to have low enough , but also structurally strong enough to survive the forces of atmospheric entry. All of our formulations that we tested with a cutting torch at least passed that."

The dome-shaped bricks, each 2 inches thick and 4 inches in diameter and made of different combinations of material, will face their toughest test next week when they are placed inside the arc jet facility at NASA's Ames Research Center in California. There, they will be subjected to a scorching plasma stream that will put the through heating conditions similar to those seen during entry.

"That will ultimately determine whether this idea is feasible or not," Hogue said.

The concept, while promising, is far from becoming operational. At this point, Hogue puts the concept at a TRL, or technology readiness level, of 1 on a scale of 9, with 9 being an operational element. Working it up the TRL scale will take a series of evaluations, adaptations and inventions, including potentially trying out a sample disc on the bottom of a cargo spacecraft returning from the International Space Station.

Hogue said his attitude has gone "from guarded skepticism to hopeful enthusiasm" on the effort.

The potential weight-savings is too great to ignore, Hogue said.

Making the heat shield in space would likely be the work of a robotic device, or at least a heavily automated system to either mix the regolith with a rubbery substance in a mold or heat a large disc of regolith until the soil elements fuse together. The heat shield could then be cut and shaped as needed.

The primary advantage is that getting the finished heat shield off an asteroid or Martian moon would take very little force because the gravity is so low. The heat shield could be as big as anyone would want. It could be used to insulate a spacecraft whether it is going to the Martian surface or back to Earth.

The weight savings is critical to the plan because the regolith material is anything but light. A brick of regolith, actually made from Mars and moon simulant instead of actual extraterrestrial dirt, feels the same in the hand as a brick one builds a house from on Earth.

Also, the heat shield would not be reusable, but would be designed to have some layers fleck or burn off, a process called ablating. All heat shields except the space shuttles' were made of ablative material.

"You can make it massive and if it heats up and ablates off, all the better because the ablated mass takes heat with it," Hogue said. "After about five minutes you jettison the shield over water and you're done."

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SteveL
3 / 5 (2) Sep 17, 2012
Great idea. They will still need to take the glue with them. For the near term anyhow.

Getting the mass of the heat shield off the surface of a low gravity well such as the moon should be easily within reach of a solar powered EM rail system. But this would only be viable if there is a need for large quantities of heat shields, like in a mining operation.
JustChris
1 / 5 (1) Sep 17, 2012
The big question is what happens if the heat shield designed away from Earth is not developed and tested in time for the return launch window.
tscati
1 / 5 (2) Sep 17, 2012
Another wee problem - what if they have to abort the mission and return without landing? (Think Apollo 13 here)
alq131
1 / 5 (1) Sep 17, 2012
one benefit of space manufacturing is that you could just start an assembly line and pump out heatshields for delivery to parking orbits awaiting use. Lagrange points around the moon for example. if you were really good at orbital mechanics, you could build the heat shield on phobos, bump it to a slow earth return orbit, aerobrake (using itself as a shield) in earth's atmosphere then park it somewhere awaiting use. all with minimal thrusters (or ion engines on board).
Torbjorn_Larsson_OM
5 / 5 (2) Sep 17, 2012
@ SteveL:

They can sinter some mixtures as the article notes, and in the future they would likely have greenhouses for better bio-closure. Then you can grow plants, or genetically modified microbes, that contain rubbery compounds.

@ tscati:

You can't really abort these missions as of yet. (O.o)
Jeddy_Mctedder
1 / 5 (3) Sep 17, 2012
succesful exploration uses and scanvenges as much material as possible from the environment. bringing everything with you is a sure route to disaster when you find out you dont' have everything you need, or that it's too heavy to bring..
GSwift7
2.3 / 5 (3) Sep 18, 2012
The heat shield could be as big as anyone would want.


That's a really big advantage. In order to get a large spacecraft down to the surface of Mars, a much larger heat shield would be ideal. That would solve a lot of problems that currently stand in the way of a manned mission to Mars.

Don't forget that NASA is also testing inflatable heat shield designs right now. That might be an even better idea in the long run.
SteveL
1 / 5 (1) Sep 19, 2012
@ alq 131:
The main issue I have with using a Lagrange point for storing stuff from a far away production area is that some object that was moving at several thousands of MPH to get there in any reasonable amount of time has to come to a stop. I got the part about the aerobraking, but this still means some chemical propulsion in a location that is far from were it was produced.

That and as Lagrange points are natural locations for spaced based facilities you wouldn't want to clutter up the location or have something with significant mass heading at you at high velocity while you hope the braking rockets work before impact and you are vaporised.

Putting something into a defined and designated orbit should consume far less energy, and be easier to track.