Neil Cheatwood is principal investigator of the Inflatable Reentry Vehicle Experiment (IRVE-3). In July, the IRVE-3 team tested an inflatable heat shield that protects spacecraft from extreme temperatures and hypersonic speeds when entering a planet's atmosphere or returning to Earth.
NASA Tech Briefs: How does IRVE-3 differ from traditional heat shields?
Dr. Neil Cheatwood: Whenever we go to another planet that has an atmosphere, we try to make use of the atmosphere to help us either slow down to go into orbit, or slow down enough to actually land. Otherwise, we need to carry propellant. We typically use an aeroshell. That structure serves as a cocoon to protect a payload, and we need to make it an aerodynamic shape so that it performs properly in the atmosphere.
IRVE-3 is an example of what we call a HIAD, a hypersonic inflatable aerodynamic decelerator. It is a deployable decelerator that is inflated to take its shape. By hypersonic, I mean it needs to survive the heat pulse, so we typically deploy it outside the atmosphere.
On a traditional approach, we're limited by the size of the launch vehicle shroud, and we put in a rigid structure, just like you would build the structure of your house. What we've replaced that with is an inflatable deployable structure, something that can be much larger than that launch vehicle shroud and that provides us our stiffness. Then we drape over that a flexible thermal protection system that is not intended to carry any significant amount of the aerodynamic load.
NTB: What does IRVE-3 look like?
Dr. Cheatwood: Our construction was an inflatable structure that looked like a stack of differing size donuts, forming kind of an innertube pyramid. And we have pressure measurements in each of those. Our outermost material was a Nextel ceramic cloth: two layers of that. That's the part that had to withstand the highest temperatures. Behind that, we had a couple layers of insulation, which is known as pyrogel. Those two layers serve to knock down that temperature from the outer layers down to something we could handle on our inflatable structure. Within that stack, we had thermocouples at different layers, so we could then compare our temperature histories with what we predicted pre-flight, both in the design of the system and actual pre-flight.
NTB: How will we see this technology in practice in the future?
Dr. Cheatwood: Our ultimate goal or hope would be to fly one of these from the International Space Station. The recently demonstrated Dragon [from SpaceX] is really our only way to bring [cargo] down from the Station right now, at least within the US. The other commercial provider, Orbital [Sciences], has an upmass capability in their Cygnus module that we could mate with.
You could forego some of the upmass and have a stowed HIAD instead. After they bring up the [gear] to station, the astronauts could take it and get rid of what they call "garbage" right now. They could load it up with as much stuff as they put in -- the more mass the better, because we're looking for ballast -- and then we could come back in. That would give us an entry at 7.5 kilometers a second. This would be a HIAD 8 to 10 meters in diameter, and it would give us heating rates on the order of 30 watts per cm 2, which is twice what we saw on IRVE-3. That particular flight test would be a very good demonstration test for something that you could almost immediately turn around and use for Mars.
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