Newly developed Nanotube Technology could revolutionize spaceflight
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.
LEFT: A demonstration flight article is wound with carbon nanotube composites. RIGHT: COPV tank inside the sounding rocket. Photos Credit: NASA
This new carbon nanotube technology could potentially reduce the weight of a launch vehicle by 30 percent. But what, exactly, are carbon nanotubes?
First, one must understand that carbon nanotubes get their strength from the extremely strong bond between carbon atoms.
“When you get down to a scale of 1 to 100 nanometers, conventional physics breaks down, and that gives rise to new phenomena,” Meador explained. “With carbon nanotubes, the aspect ratio, the length divided by the width of the tube, is quite large, and that means it makes a great reinforcement for things like plastics and other materials.”
The nanotubes are made in a heated tube furnace by injecting a catalyst and a special mix of gases full of carbon atoms. What they generate is something that looks like black smoke. It is called a nanotube aerogel. That aerogel can be deposited onto a rotating drum to make a nonwoven fabric, or it can be grabbed and twisted and pulled onto a spindle to make a yarn out of it. The yarn is then further manipulated to make it into the material that was used to wrap around the pressure vessel in the recent test.
The nanotube yarn, then, is simply a million or so nanotubes with no binder between them. The yarn is all nanotube in the fiber. The only thing holding the fiber together are twists between the individual nanotubes interlocking between one another.
“We got interested in this technology initially in 2000,” Emilie Siochi, Research Materials Engineer at NASA’s Langley Research Center in Hampton, Virginia, told SpaceFlight Insider. “The reason is we thought there were data showing that the mechanical properties of carbon nanotubes far exceed those that are typically used for structural applications in aerospace. Especially for space exploration, we care about mass reduction. The initial analysis of how much mass we could save in large structures like launch vehicles [was] based on what we knew about the properties of carbon nanotubes at that time.”
LEFT: Shown here is a Composite Overwrapped Pressure Vessel, or COPV, in a test setup. The aluminum vessel was pressurized to test the overwrapped carbon nanotube yarn’s ability to strengthen or reinforce the vessel against the internal pressure forces. A number of these “burst-tests” were conducted to prepare the newly developed carbon nanotube yarn and the COPV for its launch test aboard a sounding rocket launched from NASA Wallops. Photo Credit: NASA Glenn Research Center. RIGHT: A spool of the newly developed carbon nanotube yarn developed in collaboration with NASA by Nanocomp Technologies, Inc. in Merrimack, New Hampshire. Photo Credit: Nanocomp Technologies, Inc.
Siochi and others at Langley did a series of analyses on how much the mechanical properties of the nanotubes would have to be improved in order to use them in spaceflight applications. The analysis told them the nanotube fibers would have to be doubled in strength.
“We spent many years trying to work with carbon nanotubes in the form that was available,” Siochi said. “This changed in 2004 when Nanocomp started making carbon nanotubes not in powder form but in large sheets. These sheets are now in a form that is very similar to what we can use for carbon fiber composites. We started working with them around 2010 because we were evaluating their material for our applications.”
The early versions of the carbon nanotube yarn, if looked at under a microscope, would show gaps between the individual nanotubes within the yarn.
“They (Nanocomp) have changed the process, and modified the chemicals they use to make the yarn,” Meador said. “They also did some post-processing techniques on them. To look at a cross section of the current yarn under a microscope, it looks more like a fiber. It is very consolidated and the gaps aren’t there anymore.”
Like any new technology, it takes time to gain acceptance of the technology as reliable for its designed tasks. Further development and testing on the carbon nanotube yarn will determine that acceptance.
“There are more improvements that can be made to get the strength up,” Meador said. “Nanocomp is working on that, and we are continuing to collaborate with them.”
Michael Cole is a life-long space flight enthusiast and author of some 36 educational books on space flight and astronomy for Enslow Publishers. He lives in Findlay, Ohio, not far from Neil Armstrong’s birthplace of Wapakoneta. His interest in space, and his background in journalism and public relations suit him for his focus on research and development activities at NASA Glenn Research Center, and its Plum Brook Station testing facility, both in northeastern Ohio. Cole reached out to SpaceFlight Insider and asked to join SFI as the first member of the organization’s “Team Glenn.”