The development of a conformal nanotube process is enabling for many applications in solar physics and space astrophysics (e.g., direct detection and imaging of exoplanets). Coronagraphs are key heliophysics instruments because they image coronal mass ejections (CMEs), which are the most energetic phenomena on the Sun. CMEs have wide-ranging impact on the heliosphere, from interplanetary spacecraft to Earth-orbiting satellites, communications, and astronaut safety; in short, they are major drivers of space weather. In a typical space-based coronagraph, an external occulter blocks light from the disk of the Sun so that the corona (about a million times dimmer) can be imaged. The occulter must suppress both diffracted light and stray light.

Significant progress has been made in developing carbon nanotubes for many space applications, especially extreme stray light suppression. Coronagraphy is among the most challenging applications, and the most challenging (but necessary) form is a three-dimensional coronagraphic baffle. A solar baffle will be built, and difficult technical barriers will be addressed such as catalyst deposition and uniform growth on a complex tube used for a novel compact coronagraph.

While the primary objective will be to deliver the solar coronographic baffle, optimization of multiple aspects of carbon nanotubes will continue for spaceflight use to make the technology more broadly applicable to NASA missions. Atomic layer deposition (ALD) will be used on a larger, more intricate part, and CVD will be performed with modified gas flow. This means it is quite likely that parameters such as adhesion and short wavelength performance will need to be monitored, and adjustments will be required to the process. The primary approach to catalyst deposition for the baffle is ALD.

One of the most challenging aspects of growing nanotubes on the solar baffle is its geometry. The baffle is a tapered, threaded, thick-walled tube that has many sharp angles that can divert flow. Currently, silicon or alumina is the best choice of materials. Alumina foam is also frequently used in nanotube furnaces as an insulator material to prevent tube end heating. It will be determined if this material is amenable to reforming to the required shape.

Carbon nanotube formulations primarily geared towards enhanced stray light control on a variety of instruments have been developed. The technology is being further developed to make it 10 to 100 times blacker than alternate surface treatments from the near UV to far infrared, and a large variety of substrates suitable for spaceflight instrumentation.

This work was done by John G. Hagopian, Manuel A. Quijada, Gregory B. Hidrobo, Karrie D. Houston, Qian Gong, Douglas M. Rabin, and Vivek H. Dwivedi of Goddard Space Flight Center; and Peter Chen of the Catholic University of America. GSC-16956-1

Photonics Tech Briefs Magazine

This article first appeared in the November, 2015 issue of Photonics Tech Briefs Magazine.

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