NASA robotic arm precisely installing Webb Telescope mirrors

Space telescope’s 18 mirror segments require laser precision placement in prep for 2018 launch.

0 February 3, 2016
by Design Engineering staff

Artist's conception of NASA's James Webb Space Telescope (Credits: Northrop Grumman)

Artist’s conception of NASA’s James Webb Space Telescope
(Credits: Northrop Grumman)

Inside a massive clean room at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, Harris Corporation engineers are currently prepping the Hubble Telescope’s replacement, the James Webb Space Telescope (JWST), for its scheduled October 2018 launch date.

The largest and most powerful space telescope ever, the JWST will sport a 21.3-foot (6.5-meter) primary mirror, composed of 18 segments each measuring 4.2 feet (1.3 meters) across. Each hexagonal-shaped segment weighs about 88 pounds and is made with beryllium, due to its ability to withstand the extreme cold temperatures of space, and have a thin gold coating to reflect infrared light.

A robotic arm lifts and lowers each of Webb's 18 primary flight mirror segments to their locations on the telescope structure. (Photo Credit: NASA/Chris Gunn)

A robotic arm lifts and lowers each of Webb’s 18 primary flight mirror segments to their locations on the telescope structure. (Photo Credit: NASA/Chris Gunn)

However, simply dropping the segments in place isn’t an option, the Goddard team says, since they have to be precisely aligned to work in concert as a single mirror after it reaches orbit.

“In order for the combination of mirror segments to function as a single mirror they must be placed within a few millimeters of one another, to fraction-of-a-millimeter accuracy” said NASA’s James Webb Space Telescope Program Director, Eric Smith. A human operator cannot place the mirrors that accurately, so we developed a robotic system to do the assembly.”

Due to the expanded size of the mirror and its 18 primary flight mirror segments, the team needed to use a robotic arm called the Primary Mirror Alignment and Integration Fixture. Each piece is lifted and lowered onto the telescope structure and will function as one once the telescope is in orbit. The robotic arm can move in six directions to maneuver over the structure. While the robotic arm is placing the mirrors, a team of engineers simultaneously takes measurements with lasers to ensure accuracy.

The team is able to use reference points on the telescope structure called Spherically Mounted Retroreflectors. A laser tracker picks up the reference points and can determine where the mirror segments should be placed.

“Instead of using a measuring tape, a laser is used to measure distance very precisely,” said Matthews. “Based off of those measurements a coordinate system is used to place each of the primary mirror segments. The engineers can move the mirror into its precise location on the telescope structure to within the thickness of a piece of paper.”

Harris Corporation engineers are helping build the space telescope and are responsible for integrating components made by various members of the team to form the optical telescope element, which will collect light and provide sharp images of deep space. The Space Telescope is an international project led by NASA with its partners, the European Space Agency and the Canadian Space Agency.
www.nasa.gov


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