James Webb Space Telescope prepares for deep freeze
The James Webb Space Telescope (JWST) continued its long and meandering journey to space with a stop in Houston, Texas. The telescope has been moved to Johnson Space Center so it can undergo the last cryogenic test before the massive observatory is launched into space in 2018.
According to a NASA press release, the tests are designed to ensure the telescope can operate in the frigid temperatures of deep space. JWST will be placed inside Johnson Space Center’s Chamber A, the same cryogenic vacuum unit used by NASA to test Apollo mission hardware.
This will be the longest and final cryogenics test for the telescope. It is a critical end-to-end test verifying the performance of the entire vehicle. Once JWST is launched and deployed, it will be stationed nearly one million miles (1.5 million kilometers) from Earth at the Earth-Sun L2 (Lagrange) point – a distance that makes servicing missions nearly impossible to complete.
The telescope is currently inside a NASA clean room awaiting systems checks before it will be moved into Chamber A. Once in position inside the chamber, JWST will spend 100 days in near vacuum at, according to Spaceflight Now, temperatures colder than minus 370 degrees Fahrenheit (minus 190 degrees Celsius).
JWST is a joint project of NASA, the European Space Agency, and the Canadian Space Agency. It will be used to peer deep into the universe looking for the first stars that formed after the big bang or study the atmospheres of extra-solar planets.
The Webb telescope has been in development since 1996. The incredibly complex observatory is a scientific successor to the Hubble telescope but not a direct replacement. Unlike Hubble, JWST operates in infrared, looking at objects that are deeper in space than Hubble could achieve.
Moreover, JWST will have a much larger primary mirror surface area of just over 21 feet (6.5 meters), compared to Hubble’s eight feet (2.4 meters).
The telescope had previously been at Goddard Flight Center in Greenbelt, Maryland. It’s transportation required a combination of slow trucking and cargo flights while housed inside a protective cocoon-like enclosure.
The Webb team packaged the telescope for its highway migration to Joint Base Andrews, located just 23 miles south of Goddard. Once there, the entire truck and trailer were then loaded onto a U.S. Air Force C-5C Galaxy aircraft destined for Ellington Field in Houston. The telescope then traveled by truck to Johnson Space Center, arriving at Building 32.
Cryogenic testing is done to evaluate the ability of the large mirror array to withstand space temperatures without losing any mirror surface integrity. If any adjustment is required after launch, the mirror actuators behind each segment allow for the slightest adjustment to the focal plane. So precise are the actuators they can adjust the surface to within 1/10,000th of the width of a human hair.
The space-bound mirror surface area is what makes JWST unique, and the construction of the mirrors required a number of scientists and technicians at numerous facilities with various specialties and capabilities.
The total surface area specified by the designers required a unique honeycomb design allowing the telescope to conform to the dimensions of a rocket fairing. Additionally, the total weight of the telescope as cargo mass (about 15,000 pounds or 6,800 kilograms) demanded each mirror component only have a weight of about 90 pounds (40 kilograms).
To achieve this requirement, beryllium was used not only because of its light weight attribute but also its fantastic strength at space temperatures. This allows the mirrors to withstand the strain of launch as well as endure the temperature of space.
The mirrors are also coated in pure gold powder to allow for improved reflection of infrared light. The gold layer requires a very thin layer of glass to help protect its soft, vulnerable characteristics further complicating the mirror construction.
The previous test performed on JWST was the center of curvature test, an important optical measurement of Webb’s fully assembled primary mirror. The process of assembly and testing means the telescope components traveled around the country to states including Utah, Alabama, California, Colorado, Ohio, Maryland, New Jersey, and Texas.
Subsequently, the Webb telescope will then be sent along a 1,600-mile (2,600-kilometer) journey to Redondo Beach, California, where Northrop Grumman Aerospace Systems will prepare the telescope system for further testing once the package is married to the spacecraft bus and sunshield.
The telescope looks at infrared light and so sunshield deployment is essential in protecting the mirror array from any undesired heat, including the warm spacecraft bus.
ESA will be providing launch services on its Ariane 5 rocket which will launch out of ELA-3 near Kourou, French Guiana. Liftoff is scheduled for October 2018.
This article was written by Joe Latrell and Jerome Strach.
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