NuSTAR: Slumped by Design

The above image shows some of the “slumped” glass segments created at the mirror development lab at NASA’s Goddard Space Flight Center. Image Credit: NASA/JPL-Caltech/GSFC

The glass optics for NuSTAR were shaped at NASA's Goddard Space Flight Center (GSFC) mirror development lab. The mirror team was led by Will Zhang. They worked over a decade to perfect their new technique to rapidly produce high-quality X-ray mirror optics. They began with readily-available, commercial glass, similar to what is used for laptop computer screens. The glass was then carefully placed atop a properly figured and polished quartz cylindrical “mandrel” inside a high temperature oven. As the oven heated to about 600 C (1100 F), the glass softened and sagged under its own weight, wrapping itself around the mandrel. When the glass was removed, the resulting segment was a near perfect replication of the mandrel’s surface. To build up the concentric layers of the final NuSTAR optics, the team used over 70 quartz mandrels of increasing radius.

After this process, which was called “slumping,” the glass segments were shipped to Denmark where they were coated with a multilayer surface optimized to enhance the reflectivity of the mirrors over the entire NuSTAR energy range. The coated glass was then shipped to Columbia University where they were assembled into the final flight optics units. In total, NuSTAR has two optics units, each comprised of 133 shells and each shell comprised of up to 24 individual mirrors. The slumping, coating, and assemblage of the nearly 5000 glass pieces which make up the NuSTAR optics commenced in the Spring of 2009 and took just over one year to complete.

By September 2009 NASA had refined its 2011 launch estimate. NuSTAR was scheduled to launch in August.

To be continued.

NuSTAR is a Small Explorer mission led by the California Institute of Technology in Pasadena and managed by NASA's Jet Propulsion Laboratory, also in Pasadena, for NASA's Science Mission Directorate in Washington. The spacecraft was built by Orbital Sciences Corporation, Dulles, Virginia. Its instrument was built by a consortium including Caltech; JPL; the University of California, Berkeley (UC Berkley); Columbia University, New York; NASA's Goddard Space Flight Center, Greenbelt, Maryland; the Danish Technical University in Denmark; Lawrence Livermore National Laboratory, Livermore, California; and ATK Aerospace Systems, Goleta, California. NuSTAR will be operated by UC Berkeley, with the Italian Space Agency providing its equatorial ground station located at Malindi, Kenya. The mission's outreach program is based at Sonoma State University, Rohnert Park, California. NASA's Explorer Program is managed by Goddard. JPL is managed by Caltech for NASA. For more information on the NuSTAR mission, visit www.nasa.gov/nustar and www.nustar.caltech.edu .

-