The NASA Marshall Space Flight Center (MSFC) has begun simulated space environment testing on a key element of the James Webb Space Telescope (JWST), which has suffered its fair share of development problems.
The state of the art telescope is due to launch on an Ariane 5 in 2013, for an orbital destination nearly a million miles from Earth known as L2 – the second Lagrange orbital site.
While MSFC carry out work on the Backplane Structural Test Article, an ambiguous NASA memo from the Goddard Space Center noted: ‘JWST experienced a machining issue. A review team has been put together and processing of the engineering unit is continuing.’
The seriousness is as yet unknown, although that hasn’t halted MSFC’s testing of the anchor for the 18-segment mirror that will utilise its powerful infrared optics. The backplane test article, a lightweight composite material, was built by project subcontractor ATK Thiokol Propulsion.
According to August 31’s Marshall Star – the internal magazine for MSFC employees – the structure was loaded into the massive vacuum chamber inside Marshall’s X-ray Calibration Facility on August 8, for a four week long test at minus 420 degrees Fahrenheit, testing its flexibility and tolerance margins.
‘It’s about as cold as a machine can get and continue to function,’ said Kevin Russell, element lead for the James Webb project at Marshall.
‘At minus 459 degrees, or ‘absolute zero,’ the kinetic motion of subatomic particles simply ceases. That’s nearly the chill factor the James Webb will experience at its orbital destination – some 932,000 miles from Earth.
‘There, the deep cold of space can deform structural materials and warp ultra-sensitive optics. That’s why cryogenic testing on the ground is vital to the telescope’s optics and support structure.
‘These inverse-deformities are apparent at normal, sea-level temperatures. In the icy reaches of space, however, the planned cryogenic deformation shifts the elements back into perfect alignment.
‘Such meticulous analysis and precision fabrication is essential to mission success. When the James Webb reaches its planned orbit, it will be four times the distance from Earth to the moon. There will be no chance for a do-over later.’
MSFC’s 6,000 square foot X-ray Calibration Facility is over 30 years old, but was upgraded in 1989 to calibrate NASA’s Chandra X-ray Observatory, which was launched into space on one of the late Shuttle Columbia’s numerous flagship missions.
The largest optical test site in the world, the facility is NASA’s primary resource for horizontal vacuum testing of large-scale optics systems – housing to the 24-foot-diameter, 75-foot long stainless steel chamber, which can accommodate in-flight configurations of any payload to be launched from the space shuttle. The facility will begin receiving some of the 18 primary mirror segments for testing in 2007.
‘Each primary mirror segment will be tested twice over the next four years,’ noted Jeff Kegley, team lead for the X-ray Calibration Facility, ‘once to determine how much the mirror deforms at extremely cold temperatures and again to ensure improper deformations are corrected.’
The Northrop Grumman Corporation is the contractor for the telescope, which – it is hoped – will provide new insight into the origins of the universe, looking back more than 10 billion years at the so-called ‘cosmic dark zone,’ the period when the very first matter likely converged to form stars and galaxies.
From its orbital home at L2, one of five points identified by and named for 18th century mathematician Joseph-Louis Lagrange – where the gravitational pull of Earth and the sun balance one another – the telescope will have a clear sightline into our past.
Lagrange sites naturally deliver the centripetal force necessary to keep a satellite rotating in sync with Earth without excessive on board power requirements.
The L2 position enables JSWT to utilise its giant sun shield – half the size of a football pitch – to block out the Sun’s heat along with reflected light from Earth and the moon.
This shielding permits the telescope to focus accurately on faint astronomical signals from the depths of space, and ultimately deliver far more penetrating infrared studies of the ancient cosmos than ever before possible.
Article collated from L2 information and MSFC’s Marshall Star internal magazine (Rick Smith). Image: David Higginbotham/MSFC.