A cold-gas thruster system, partially made from carbon nanotube material, was recently tested aboard a Black Brant IX suborbital sounding rocket, which was launched on May 16, 2017, at 5:45 a.m. EDT (09:45 GMT) from NASA’s Wallops Flight Facility in Virginia. Part of the thruster system was a Composite Overwrapped Pressure Vessel (COPV).
The COPV is an aluminum tank that is wrapped with a composite material to strengthen the tank’s ability to hold a fluid or gas under pressure. In the recent test, the overwrap material was a newly developed carbon nanotube yarn that has 200 times the strength and five times the elasticity of steel.
“We picked the COPV because the design properties require good tensile strength,” Michael Meador, Program Element Manager for Lightweight Materials and Manufacturing at NASA Glenn Research Center in Cleveland, Ohio, told SpaceFlight Insider. “But you could think about using these nanotube yarns in other structural components.”
Meador’s group did trade studies at NASA’s Langley Research Center that looked at incorporating nanotube materials with lower structural densities into a cryotank for a notional launch vehicle.
Meador said: “What we found out from those trade studies was that if you could reduce the density of the structural material by 25 percent or so, you could reduce the mass of the launch vehicle by 30 percent. So that is a real game-changer. We can’t think about any other single technology that would have that much of an impact.”
The nanotube fiber yarn used as the overwrap for the COPV in the test was manufactured by a company called Nanocomp Technologies, Inc., in Merrimack, New Hampshire. The company had developed it originally for use in lightweight data cables. Their initial emphasis was on the electrical properties of the yarn, so it was not very strong.
Since then, in collaboration with NASA, Nanocomp has modified their process for making this material. The yarn now has mechanical properties on a per weight basis that are comparable to or even a little bit better than carbon fiber.
Meador said: “Our idea in this project was to work with Nanocomp to increase the tensile properties of the fiber, and […] develop techniques to incorporate this into composites.”
Meador’s project is part of the Game-Changing New Developments program at NASA. Developing a nanotube fiber that can reliably perform its function within the systems of a launch vehicle, while reducing the weight of that launch vehicle by 30 percent, is indeed a game-changer.
“Game-changing program is all about maturing technologies and demonstrating them and their suitability for use in a NASA mission,” Meador said. “That usually involves making hardware, and it usually involves a flight test. We selected the COPV because the tensile properties of the fiber are particularly important for that component. And then we worked with Wallops to design an experiment where we could demonstrate the use of the COPV in a cold gas thruster system. We basically pressurized the COPV with argon and used it to make two maneuvers for the flight test. One was to wiggle the payload back and forth a little bit, and the second one was to spin the payload up prior to descent. They always do that to improve the aerodynamics.”
The COPV on the sounding rocket test performed exactly as was expected. The payload was recovered, but Meador and his group have not received the COPV back yet. They intend to do some post-test analysis on it to see if the structural integrity has changed as a result of the flight test.