Balloon Experimental Twin Telescope for Infrared Interferometry
WestStar Precision has been heavily involved with the fabrication of a complex, thin-walled, optical mounting structure for NASA’s BETTII (Balloon Experimental Twin Telescope for Infrared Interferometry) balloon-based telescope project. BETTII is based out of Goddard Space Flight Center in Maryland, and WestStar worked directly with NC State University’s Precision Engineering Center on BETTII’s critical, twin 4-optic telescopes. The telescopes will ascend 26 miles on a Helium balloon to improve viewing conditions and focus on individual stars within a star cluster or gas cloud—where new stars are ‘born’—to study infrared emissions as fusion begins within the star. The first launch is planned for October 2016.
NC State University’s Precision Engineering Center was contacted to propose a design and fabrication plan for the complex external optics for BETTII. During the design process, NCSU engaged WestStar Precision as a potential contractor to machine the mounting structure. WestStar’s extensive experience machining aluminum components for aerospace applications and their advice on design-for-fabrication was instrumental in designing the stiff, lightweight mounting structure such that it could be fabricated at a reasonable cost. NASA accepted the NCSU/WestStar design for the lightweight, all-aluminum mirrors and mounts, shown below.
NCSU was awarded the contracts to build the optics and WestStar was contracted to machine the telescope mounting structure. The finished mount is extremely stiff despite being nearly a meter long with thin, 1.5 millimeter walls and a total weight of only 12 pounds. The components machined by WestStar are shown below.
Museum Exhibit at North Carolina Museum of Natural Sciences’ Nature Research Center
In addition to the two copies of the mounting structure delivered to NASA, WestStar is donating a third copy for exhibition in the NRC. A complete telescope will be visible to the public along with a description of the mission, local contributions, and video footage captured by the museum’s documentary crew during machining at WestStar and NC State. This will give the public a rare glimpse of the advanced manufacturing capabilities in the triangle.
High-altitude balloon missions take several thousand pounds of equipment/instruments 26 miles up, where the atmosphere is calm, air pressure is 0.1% sea-level, and disturbances due to weather are far below. These missions last anywhere from 1 night (in the case of BETTII) to many months, and are used to prove a concept for a space-based mission, which may cost 10–50x as much.
A mission to the near-space environment imposes severe design restrictions. In the case of BETTII, the telescopes have to be made from 100% aluminum so all of the optical components will expand and contract at the same rate during the 250-degree thermal cycle during ascent. Also, the entire structure must be thin and lightweight so that the optics will heat and cool quickly and uniformly.
BETTII Science Objectives
The BETTII twin-telescopes will focus on individual stars within a cluster or gas cloud, where new stars are born. The wide aperture design gives exceptional spatial resolution, but makes fabrication a huge challenge. The infrared light beams collected from the ‘twin’ telescopes are compared in an interferometer. This gives scientists insight into the process of star birth, where the immense heat and gravitational forces of coalescing interstellar dust are sufficient to initiate fusion startup. The instrument can also be pointed at the Universe as it was 13 billion years ago to study the immediate aftermath of the big bang. The external optics were designed, assembled, and fabricated locally.
Special thanks to Dr. Stephen Furst for help in getting this written up. We’ll have more as this project moves forward. Don’t miss an update by signing up for the WestStar newsletter.
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JMD Manufacturing, Inc.
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Dr. Stephen Rinehart
Associate Lab Chief, Observational Cosmology Lab NASA/GSFC
Mail Code: 665
Greenbelt MD 20771
Dr. Thomas Dow
Director, NCSU Precision Engr. Center
Raleigh, NC 27695
Dr. Stephen Furst
Adj. Asst. Professor
NCSU Mechanical and Aerospace Engr.
Owner, Smart Material Solutions, LLC
4713 Altha St.
Raleigh, NC 27606