Curt Godwin
November 27th, 2017
The James Webb Space Telescope underwent testing in space-like conditions at Johnson Space Center. Photo Credit: NASA
Personnel at NASA‘s Johnson Space Center have recently concluded the final round of cryogenic testing for the agency’s James Webb Space Telescope (JWST). This closing round of cryo-testing – taking nearly 100 days to complete – saw the observatory’s optical telescope and integrated science instrument module (OTIS) subjected to temperatures nearing -387 degrees Fahrenheit (-233 degrees Celsius / 40 kelvins) to ensure the operation of the JWST’s instruments in space-like conditions.
No repeat of Hubble
A key tenet of the frigid test regime was the validation of the alignment of the telescope’s 18 primary mirror segments. The mirrors, which had been assembled by engineers from Harris Space and Intelligence Systems, were previously tested under cryogenic conditions at NASA’s Goddard Space Flight Center.
Designed to act like a single reflective surface, the test at Johnson was the first time the telescope’s optics and instruments were tested together.
“The Harris team integrated Webb’s 18 mirror segments at Goddard and designed, built, and helped operate the advanced ground support and optical test equipment at Johnson,” stated Rob Mitrevski, vice president and general manager of intelligence, surveillance, and reconnaissance at Harris, in a release issued by NASA. “They were a key, enabling part of the successful Webb telescope testing team.”
Each of the 18 mirror segments on the JWST will have an array of actuators capable of moving the mirrors in increments of a fraction of a wavelength of light. Photo Credit: Chris Gunn / NASA
Ensuring the mirrors were properly aligned prior to launch is critical to the mission. With its location at a gravitationally stable orbit nearly 1 million miles (1.5 million kilometers) from Earth, mounting any sort of repair mission as had been done to correct the flawed primary mirror on the Hubble Space Telescope would not be practical (and impossible now that NASA’s fleet of shuttle orbiters are collecting dust in museums and tourist destinations).
Unlike Hubble, however, Webb has the ability to reshape each of its 18 mirror elements once in space. Each mirror is outfitted with small motors – also known as actuators – that are capable of adjusting each segment in very small amounts.
“They can move in steps that are a fraction of a wavelength of light, or about 1/10,000th the diameter of a human hair,” stated Lee Feinberg, optical telescope element manager for the Webb telescope at Goddard, in a release issued by the agency.
Nevertheless, engineers needed to know that the actuators would actually function as anticipated once subjected to conditions simulating the cold vacuum of space.
Mother Nature couldn’t derail testing
Prior to beginning the test program in earnest, the chamber in which the JWST was installed had to have its atmosphere removed. Engineers began evacuating the air from Johnson’s Chamber A on July 20, 2017 – a process that took approximately seven days – so that it could be chilled to space-like conditions.
The chill-down phase lowered the temperature of the chamber from ambient (room-temperature) levels to 40 kelvins over the following 30 days. However, near the end of the chill-down, Category 4 Hurricane Harvey barreled into the Texas coast.
Though the storm weakened to a tropical storm, it lingered over inland Texas, leaving some areas drenched in more than 50 inches (127 centimeters) of rainfall. Many of the personnel involved in testing Webb remained at Johnson throughout the storm to ensure the telescope’s testing was not interrupted.
Following 30 days at “cryo-stable” conditions, personnel began raising temperatures in the chamber before re-pressurizing it and opening the door.
“With an integrated team from all corners of the country, we were able to create deep space in our chamber and confirm that Webb can perform flawlessly as it observes the coldest corners of the universe,” noted Jonathan Homan, project manager for Webb’s cryogenic testing at Johnson, in a release from the agency.
Still more to be done before launch
Though Webb’s launch is scheduled for the first half of 2019, there is still much to be done to get the observatory ready for liftoff.
The combined optical elements and science instruments will next travel to Northrup Grumman Aerospace Systems in California where it will be integrated with the sunshield and spacecraft bus.
Once fully integrated, the telescope will undergo further tests to simulate the rigors of launch, before being shipped to Kourou, French Guiana, where it will launch atop an Ariane 5 rocket.
While those steps still lay ahead, the testing at Johnson was seen as a critical path forward.
“After 15 years of planning, chamber refurbishment, hundreds of hours of risk-reduction testing, the dedication of more than 100 individuals through more than 90 days of testing, and surviving Hurricane Harvey, the OTIS cryogenic test has been an outstanding success,” said Bill Ochs, project manager for the James Webb Space Telescope at Goddard, in a NASA release. “The completion of the test is one of the most significant steps in the march to launching Webb.”
If everything continues to go as NASA hopes, the JWST is scheduled to launch in 2019 atop an Arianespace Ariane 5 rocket from Kourou, French Guiana. However, the JWST has been repeatedly delayed and, as noted in a 2006 article appearing in Nature, the next generation telescope was estimated to cost somewhere around $4 billion.
The telescope has become known for its cost overruns and program mismanagement with Congress eyeing to scrap the project. However, in November of 2011, it was decided to complete the project – but to cap off its expenses at $8 billion. Space.com has noted that, as of this writing, the project is estimated at approaching a cost of some $9 billion.
Video courtesy of NASA Goddard
Curt Godwin
Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting – and safer – career field. He’s worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.
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