Carbon nanotubes: blacker than black

The NASA Goddard Space Flight Center has a team of scientists testing micro- and nanotechnology to use on spacecraft. The goal is to reduce the reflection off the surface of the instruments so that data do not get polluted by the scattered light. The carbon nanotubes that the team grows have proven to be 10 times better than the NASA Z306 paint, currently used on spacecraft instruments. The nanotubes are also very robust and can be grown on different materials. The team is really close to getting the carbon nanotubes approved for spaceflight.

Video source: NASA Goddard / YouTube.

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STEPHANIE GETTY, NASA GSFC ADVANCED INSTRUMENTATION DEVELOPER: My name is Stephanie Getty. I use micro- and nanotechnology to make better scientific instruments for spaceflight.

JOHN HAGOPIAN, NASA GSFC OPTICAL PHYSICIST: My name is John Hagopian, I’m an optical physicist at the NASA Goddard Space Flight Center. The exciting part about this work is it’s kind of pushing new boundaries on what we do with nanotechnology in terms of optics.

What is a carbon nanotube?

STEPHANIE: It is a hollow tube that’s made entirely out of carbon and the diameter is a nanometre. [HOLDING MODEL] If this was the size of an actual nanotube and you were to scale me up proportionately, then I would be tall enough to reach the moon. Because the nanotubes are so small, we can only use a scanning electron microscope to be able to see them.

How are nanotubes grown?

STEPHANIE: The method that we use is called catalyst assisted chemical vapour deposition. And that grows carbon nanotubes on a substrate.

Substrate: silicon, titanium, or other +
Catalyst: iron +
Gas: ethylene +
= carbon nanotubes.

JOHN: You put the substrate in this tube. You heat the tube up to about 750°C and you flow a gas and the gas has carbon in it. Because of the catalyst layer you start to assemble these tubes. Carbon takes a very specific form as it grows.

Why blacker than black?

STEPHANIE: So one example where carbon nanotubes can enhance the performance of a scientific instrument in space is through their ability to absorb light. 

JOHN: The Z306 paint is the blackest thing that we put on instruments right now. The fact that we are blacker than that I guess makes us blacker than black in terms of peformance. When light from the Earth or a star hits an instrument or structures inside of the instrument it gets scattered over all angles. A lot of the data gets contaminated. So it turns out up to 40 per cent of the data could be unusable. 

STEPHANIE: So the current telescopes use black paint to reduce the reflection. But the black paint isn’t perfect—it still shows a reflection.

JOHN: Over the course of our work, we were able to optimise the carbon nanotubes to make them 10 times darker than the paint. You could get a better observational efficiency; you are not throwing away 40 per cent of your data.

Orientation matters

JOHN: The Goddard samples were grown multi-walled so they’re not just single walled nanotubes and they’re also oriented straight up and down. The reason that the oriented samples are darker is because their low density light can go in, it gets rattled around in there and it gets absorbed. 

VOICEOVER LAUNCH COUNTDOWN: 4, 3, 2, 1, and lift off …

Testing for spaceflight

STEPHANIE: So when we prepare a new technology for spaceflight we need to consider the different environments that that technology is going to experience.

JOHN: If we’re going to fly something in space, we can’t have the nanotubes falling off and contaminating mirrors, so we had to make sure that they were very robust. Over a long period of time after all of these experiments, we discovered that aluminium is really the trick to getting the nanotubes to stick. So now they’re … you have to scratch them off. They’re very robust.

STEPHANIE: So we’re interested in vibration testing for these carbon nanotubes to determine how well they adhere to the substrate and whether they will be liberated during launch. The other thing that we do test is thermal conditions. When your spacecraft is flying through space, it gets very cold and actually it gets exposed to radiation. And so those are two of the other tests that we expose our technology to before we fly them. 

JOHN: So the first instrument that we are using them on right now is actually ORCA. That’s an Earth science instrument. Another thing that we’ve looked at is using them on LISA, which is a gravity wave experiment.

Did you know …

STEPHANIE: One area where carbon nanotubes have made it into the market place is in sporting goods, to make stronger, more robust, lighter weight bicycle frames, tennis rackets. Those are some examples of where you can go out and buy carbon nanotube composites.

Almost there!

JOHN: At this point we feel like we have nanotubes that are robust, we can grow them on different materials. They’re very dark, so we’re very close now to getting them to a point where we can qualify these for spaceflight use.

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