Date: May 14, 2010
Title: Next Generation Space Materials
Podcaster: Bob Hirshon
Organization: American Association for the Advancement of Science (AAAS) http://www.aaas.org
Description: Carbon composite materials are light, strong and heat resistant, which is why they are used to make protective cockpits in high performance race cars. But even though they were developed by the aerospace industry, they haven’t yet been used to make space capsules. In this podcast, Bob Hirshon speaks with a NASA engineer about the materials and a new project testing their usefulness in next generation space vehicles.
Bio: Bob Hirshon is Senior Project Director at the American Association for the Advancement of Science (AAAS) and host of the daily radio show and podcast Science Update. Now in its 23rd year, Science Update is heard on over 300 commercial stations nationwide. Hirshon also heads up Kinetic City, including the Peabody Award winning children’s radio drama, McGraw-Hill book series and Codie Award winning website and education program. He oversees the Science NetLinks project for K-12 science teachers, part of the Verizon Foundation Thinkfinity partnership. Hirshon is a Computerworld/Smithsonian Hero for a New Millenium laureate.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by the Education and Outreach team for the MESSENGER mission to planet Mercury. Follow the mission as the spacecraft helps to unlock the secrets of the inner solar system at www.messenger-education.org.
Welcome to 365 Days of Astronomy podcast. I’m Bob Hirshon, host of the AAAS Radio show and podcast, Science Update. For today’s show, I spoke with NASA mechanical engineer Dan Polis, who is part of a team at the Goddard Space Flight Center that is just completing a three-year project to design a next generation crew capsule, designed of carbon composite materials. These are the super-strong, lightweight materials made of carbon fibers in a plastic resin matrix. They’re used in tennis rackets, golf clubs, bikes and high performance race-cars. Polis says the properties that make composites so useful in sporting goods also make them useful for aerospace.
When you swing a tennis racket, you want it to be stiff, to return the energy to the ball, and you want it to be light so you don’t get fatigue.
In the case of aerospace applications, light weight means less fuel. He also says that composites can be customized for different uses.
One of the unique things about composites is that you can tailor the properties, similar to wood when they make plywood. They take the fibers and they put them in all different directions to get uniform properties. We can take advantage by putting fibers in one direction, if we’re doing a metering structure that we want to be stiff like a tube, stiff in one direction and not others. And that makes it extremely efficient as opposed to metals. They’re essentially isotropic, and they’re uniform in all directions. And there’s not much tailoring you can do there.
Along with being strong, lightweight, and easy to customize, carbon composites are stable at a wide range of temperatures, unlike metals, that expand and contract. That’s especially important for instruments that must be finely calibrated, like the James Webb Space Telescope.
And it operates at 35 Kelvin. And the whole metering structure that holds all the instruments and optics is made of composites that we’ve custom designed basically to have no expansion all the way down to 35 Kelvin. And that will hold all the instruments relative to one another stable.
Even more extreme are the conditions faced by the MESSENGER spacecraft, which is headed toward orbit around the planet Mercury next March. MESSENGER is the first spacecraft made entirely of composites, because it has to withstand temperatures of 800 degrees Fahrenheit—not only keeping its instruments from frying, but keeping them stable enough to make precise measurements of the planet’s surface, atmosphere and magnetosphere. For MESSENGER, the thermal stability of composite materials was absolutely essential.
Polis says that now that composites have proven themselves on uncrewed spacecraft, crew capsules are the next frontier.
And so now one of NASA’s big thrusts is to use composites in those applications. And there are certain unique challenges. One of which for a capsule is leakage. So you have astronauts in there; composites are more permeable than metals. If you hit them, structurally they’re still, they could still be fine, but they could have small, what we call micro-cracks that will allow gas to leak in. And since you’re only bringing a certain amount of gas for survival up there, that costs weight, or there needs to be other solutions. So to solve that there are potential membranes to use to get around that problem.
Polis said that another design challenge is that that composite capsule has to sit atop a metal rocket.
We were given certain constraints on our design and one of those was we’re going to interface with a rocket at six points. So that was a metallic design, that the rocket would push up at six points and about 100,000 pounds at each of those six points. It’s what I call a significant point load. If you were designing an all-composite solution from the capsule all the way down to the rocket, you would pick it up in a ring. So you would distribute that load instead of at six points, around the whole capsule. So that is where a composite design inserted into a metallic system takes a penalty. We had a design solution for that, but it’s not optimal. So that’s one of the places where you typically have to cross over from a metallic world to a composite world and there’s some difficult design solutions there.
Polis says private industry is also doing a lot of innovating in composites—especially Boeing, which is introducing the Boeing 787 Dreamliner, the first passenger plane made mostly of composite materials.
Now they offer extreme advantages in that industry because they don’t have the issue of fatigue. So metals if you bend them back and forth, you know if you bend a paper clip back and forth at low stresses it can break. That’s a fatigue phenomenon. Or just very low stresses for many cycles can cause cracks to propagate. And so in the aircraft industry, that’s important, and Boeing’s gone to an all-composite aircraft.
As to the future, he says composite’s next big splash could be in commercial space applications. In fact, they’ve already made a splash. In 2004, the SpaceShipOne aircraft was made of carbon composite material and it won the $10 million Ansari X prize by being the first aircraft to make a sub-orbital space flight twice in two weeks. Last year, the Space Composites company and Virgin Galactic introduced SpaceShipTwo, the next generation sub-orbital aircraft, about twice the size of SpaceShipOne. The new aircraft is scheduled to take paying passengers into sub-orbital space in 2011.
Polis points out that these aircraft don’t have nearly as many technical hurdles to jump as capsules that travel to the moon or Mars. But the manufacturing techniques used to build the craft could help inform NASA efforts in the future. For the 365 Days of Astronomy podcast, I’m Bob Hirshon.
End of podcast:
365 Days of Astronomy
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