Hubble’s Heir: James Webb Space Telescope’s Golden Mirror Unveiled –“The Largest Yet Sent into Space”




The JWST, the scientific successor to NASA’s Hubble Space Telescope, will be the most powerful space telescope ever built.
Scientists from around the world will use this unique observatory to capture images and spectra of not only the first galaxies to appear in the early universe over 13.5 billion years ago, but also the full range of astronomical sources such as star forming nebulae, exoplanets, and even moons and planets within our own Solar System. It’s targeted to launch from French Guiana aboard an Ariane 5 rocket in 2018. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

NASA engineers recently unveiled the giant golden mirror of NASA’s James Webb Space Telescope as part of the integration and testing of the infrared telescope. To ensure the mirror is both strong and light, the team made the mirrors out of beryllium.The 18 mirrors that make up the primary mirror were individually protected with a black covers when they were assembled on the telescope structure. Now, for the first time since the primary mirror was completed, the covers have been lifted.


Standing tall and glimmering gold inside NASA’s Goddard Space Flight Center’s clean room in Greenbelt, Maryland, the gold mirror will be the largest yet sent into space. Currently, engineers are busy assembling and testing the other pieces of the telescope.

Each mirror segment is about the size of a coffee table and weighs approximately 20 kilograms (46 pounds). A very fine film of vaporized gold coats each segment to improve the mirror’s reflection of infrared light. The fully assembled mirror is larger than any rocket so the two sides of it fold up. Behind each mirror are several motors so that the team can focus the telescope out in space.




This widely anticipated telescope will soon go through many rigorous tests to ensure it survives its launch into space. In the next few months, engineers will install other key elements, and take additional measurements to ensure the telescope is ready for space.

There are still a number of large milestones before the next generation telescope is launched in 2018. Recently, all of the 18 segments of the Webb telescope primary mirror segments were installed on the observatory’s backplane at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. But that’s just one component of the Webb.

Over the next two years, more components of the Webb will be integrated onto the spacecraft and it will visit three more locations before launch.

“From 2016 to 2018, there are installations and tests for the telescope and the telescope plus the instruments, followed by shipping to NASA’s Johnson Space Center in Houston, Texas where end-to-end optical testing in a simulated cryo-temperature and vacuum space environment will occur,” said Paul Geithner, Webb telescope manager – Technical, at NASA Goddard. “Then all the parts will be shipped to Northrop Grumman for final assembly and testing, then to French Guiana for launch.”

The two largest parts of the observatory are the primary mirror and the tennis-court-sized sunshield. Additionally, there are four scientific instruments—cameras and spectrographs with detectors able to record extremely faint signals—that will fly aboard Webb. All four flight science instruments were integrated into the Integrated Science Instrument Module (ISIM) in March 2014 and since have been undergoing multiple tests. However, the ISIM has not yet been added to the observatory.

Over the next year, teams at Goddard will work to complete the telescope by installing the other optics in addition to the primary mirror segments. The other optics include installing the aft-optics subsystem or AOS, secondary mirror and both fixed and deployed radiators. Once complete, engineers will connect the Telescope and instruments together when the ISIM is attached to the observatory.

Testing is a continuous part of the assembly process. “After the mating of the ISIM, to the Telescope there will be a room-temperature optical check before a simulated launch environment exposure,” Geithner said. That means the observatory will undergo vibration and acoustic testing to ensure it can endure the sound and shaking that occurs during launch. After those tests, there is yet another room-temperature optical check.

Once all of those milestones are accomplished, the observatory will then be prepared and flown to NASA’s Johnson Space Center, Houston, Texas.

Once at Johnson, the observatory will endure end-to-end optical testing in a simulated
cryo-temperature and vacuum space environment in Chamber-A. Chamber-A is NASA’s giant thermal vacuum chamber where the Webb telescope pathfinder or non-flight replica was tested in April 2015.

After NASA Johnson the Webb telescope will be then transported to Northrop Grumman in Redondo Beach, California where engineers will connect the telescope and instruments together with the spacecraft and sunshield to form the complete Observatory. Once every component is together, more testing is done. That testing is called “Observatory-level testing.” It’s the last exposure to a simulated launch environment before flight and deployment testing on the whole observatory.

What follows the flight and deployment testing is the shipping of the complete observatory to the launch site in South America where the Webb telescope is slated to launch in 2018.

NASA Goddard Space Flight Center

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