Webb Telescope Component Completes Critical Tests as Mirror Installations Continue

Less than three years from its launch, the James Webb Space Telescope (JWST), an international collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA), continues to take shape. As 2015 rolled into 2016, engineers working on the JWST have been busy testing one of its essential science components. On Wednesday, Jan. 6, NASA announced that it had completed electromagnetic interference testing on JWST’s Integrated Science Instrument Module (ISIM), critical for knowing how the “eyes and ears” of the space telescope will react to these kinds of emissions in deep space. In addition, over half of JWST’s mirror segments have been installed, with the 13th mirror segment currently being put into place.

ISIM Electromagnetic Interference Tests Completed, More Cryo Tests Coming Up

The ISIM, described as the “brain” of JWST, underwent a series of tests where it not only was exposed to electromagnetic emissions, but also emitted these signals in a bid to gauge how these forces will affect the rest of the spacecraft. While 10 days were allotted for these tests, which occurred in an “anechoic” (“no echo”) chamber, engineers were able to complete the tests in 8.5 days, ahead of schedule. These tests are critical because the ISIM contains the Webb’s essential scientific instruments, which include its Near-Infrared Camera (NIRCam), Near-Infrared Spectrograph (NIRSpec), Mid-Infrared Instrument (MIRI), and Fine Guidance Sensor/Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS).

The ISIM recently completed these tests inside NASA’s Electromagnetic Interference (EMI) laboratory at its Goddard Space Flight Center, located in Greenbelt, Md. This unique white room was described as having conical structures jutting out of its walls, which NASA stated are meant to “absorb the electromagnetic energy in order to minimize reflections.” The room is engineered to not reflect or radiate possible interference.

NASA Goddard’s Chief Electromagnetic Compatibility Engineer John McCloskey explained: “The anechoic material minimizes reflections in order to give maximum control of the test. A metal wall is like a mirror for electromagnetic waves. These walls are designed to absorb the radiated energy and minimize reflections so that we know what we are actually measuring. We need to know that what we are measuring is actually coming directly from ISIM and not from multiple reflected paths in the room.” The ISIM was reported as having passed the tests with “flying colors.”

McCloskey added: “Despite a few setbacks, our team finished the test ahead of schedule and beat the deadline. This test is important because when the James Webb Space Telescope is operating in space and identifying distant galaxies and other astronomical objects, we will have confidence that these are indeed real objects and not blips caused by electromagnetic interference.”

Next up, the ISIM will undergo its third and final cryogenic test; it is currently inside NASA Goddard’s thermal vacuum chamber. This test will ensure the module is ready for the frigid temperatures of deep space, as the JWST will operate at the second Lagrangian point, L2, 1 million miles (1.5 kilometers) away from Earth. Temperatures here will be a bone-shatteringly cold -387 degrees Fahrenheit (-232 degrees Celsius, or 40 K). These temperatures are approximately 260 degrees colder than any place observed on Earth.

The elephant-sized ISIM has survived two previous rounds of cryogenic testing. A previous AmericaSpace article underscored why these deep-freeze tests are also vital, with JWST’s Deputy Project Manager Paul Geithner emphasizing why they must take place: “We complete these tests to make sure that when this telescope cools down, the four parts of the heart are still positioned meticulously so that when light enters the telescope we capture it the right way. The biggest stress for this telescope will be when it cools down. When the telescope structure goes from room temperature to its super cold operating temperature, it will see more stress from shrinkage than it will from violent vibration during launch.”

In addition, it is critical these instruments function in space properly, as JWST will not be able to be serviced on-orbit unlike its predecessor, the Hubble Space Telescope, which operates in low-Earth orbit.

Mirror Segment Installation More Than Halfway Completed

While the ISIM continues to undergo testing, at present time a dozen mirror segments have been installed during JWST’s primary mirror assembly; the 13th mirror is poised on a robotic arm, ready for installation. NASA announced the 12th mirror segment was installed Jan. 2 in the large clean room at NASA Goddard. Mirror installation commenced in December, and by all accounts has been rolling along well. At present time, only the mirrors on the “wings” are left to be installed. When completed, the telescope’s backplane assembly will boast 18 mirror segments.

Lee Feinberg, NASA’s Optical Telescope Element Manager at NASA Goddard, enthused: “This milestone signifies that all of the hexagonal shaped mirrors on the fixed central section of the telescope structure are installed and only the three mirrors on each wing are left for installation. The incredibly skilled and dedicated team assembling the telescope continues to find ways to do things faster and more efficiently.”

NASA stated that while the JWST is shaping up, over the next two years prior to launch its components will continue to go environmental and optical testing. In December, it was announced that ESA, one of the partners in JWST’s mission, had signed a contract with Arianespace securing an Ariane 5 launch vehicle for an early morning launch in October 2018. Shortly thereafter, space watchers will see JWST spread its “wings” for the first time, as the telescope will be a true “time machine,” looking back at every phase in our Universe.

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