Bright light from sources such as the Earth or bright stars is scattered on surfaces of scientific instruments and creates noise in scientific observations. All scientific instruments have baffles, stops, and other components that are used to reduce the amount of stray light that decreases signal to noise. The use of an improved material on these components can decrease the number of control measures to simplify design. For Earth-viewing instruments, a significant fraction of the data collected is unusable due to contamination of imagery because of scattering of light from high-contrast regions to dim regions such as ice/water or cloud/water scene boundaries. Lastly, viewing dim companions to bright stars requires extraordinary reduction in scattered light to allow imaging.
Researchers at the NASA Goddard Space Flight Center (GSFC), led by John Hagopian, have been engineering low-reflectance materials that utilize carbon nanotubes to decrease the total amount of light that is reflected by a factor of 8; that is, the total integrated scatter or hemispherical reflectance is eight times lower than in surface treatments currently used by NASA. This is about 0.5% total integrated scatter versus nearly 4% for Z306 paint at 1-micron wavelength. NASA GSFC is also growing nanotubes on alternate substrates more suitable for structural applications. Performance characteristics can be seen in the graph.
Currently, carbon nanotube surface treatments are limited to components that can fit within a nanotube furnace. These typically accommodate samples up to 4" in diameter. Scaling the system up to accommodate larger components would be of great benefit. The process for growing carbon nanotubes also requires that the substrate be exposed to a 750 ° C environment. Therefore, an alternative process that results in comparably dark carbon nanotubes would also be beneficial and allow more widespread use of this technology.
Control of stray light by engineering low-reflectance surface treatments has numerous benefits, including:
- Simplification of instrument stray light controls to achieve equivalent performance,
- Increasing observational efficiencies by recovering currently unusable scenes in high-contrast regions, and
- Enabling low-noise observations that are beyond current capabilities.