In New Year’s Eve, the NASA engineers succeeded in one of the most critical phases in the unfolding of the James Webb Space Telescope – albeit not entirely without problems. At $ 9.7 billion, the most expensive unmanned vehicle in space travel history is so huge that it only folded up to fit into the European Ariane 5 heavy-lift rocket, which was launched on Christmas Day. Now “Webb” has to be unfolded in space and, in particular, the tennis court-sized sun shield has to be pulled apart by two telescopic rods on both sides of the spacecraft to a distance of 14.3 meters. According to NASA, the successful pulling up of the port side of the shield ended at 10:49 p.m. Central European Time. At 4:13 hrs, the starboard side had also been fully pulled up.
For those responsible at NASA, the European space organization ESA and the Canadian CSA, who jointly operate Webb, a step has been taken that was looked forward to with great nervousness. Because while aerospace engineers have decades of experience with the remote-controlled deployment of rigid components on satellites and space probes – such as antennas and solar panels – the shield is a stack of a total of five wafer-thin aluminum-coated plastic films.
Shielded from the warmth of the sun
Their behavior when extending the telescopic rods cannot be completely controlled. It’s like pulling a rope that is loosely compressed on a table – the change in shape cannot be predicted in detail, Mike Menzel from NASA’s Goddard Space Flight Center told the specialist portal “Spaceflight Now”. In addition, the packed film for the rocket launch was fixed with 107 actuators, all of which had to be properly detached last night. If even one of them hadn’t responded to the signals from the ground control at the Space Telescope Science Institute in Baltimore, this could have meant the failure of the entire company, which had been prepared for about three decades.
Because without the huge sun shield, the telescope optics made of gold-plated beryllium could not be shielded from the heat of the sun and cooled to its operating temperature of less than 50 degrees above absolute zero. The instrument would then itself glow in the infrared thermal radiation that it is intended to observe in order to explore the earliest stars and galaxies, young solar systems veiled by cosmic clouds, or the atmospheres of planets around other stars.
Nevertheless, not everything went as smoothly as the picture book start on Christmas Day, the two orbit correction maneuvers after separating the upper level and opening the support structure along the longitudinal axis of the sun shield. Instead, an anomaly occurred when a protective film was peeled off. “Circuits that should indicate that the protective cover has rolled up, did not trigger,” it said in a blog post published by NASA that night. “However, secondary and tertiary information sources showed that this was the case”. The two telescopic poles were therefore extended several hours late.
But with that the unfolding of the space telescope, which consists of a total of 344 individual steps and in which, among other things, 400 pulleys and 90 pull ropes with a total length of more than 400 meters are involved, is not over yet. The engineers should look forward to the next step, the tensioning and spacing of the five layers of film, with particular apprehension, because the film had already torn during the test on the floor. This procedure should take place today during New Year’s Day.
Later in January, the secondary mirror will be folded out and the flanks of the 6.5 meter primary mirror swiveled out. At the end of January, the James Webb telescope, hopefully fully unfolded, will reach a solar orbit 1.5 million kilometers from Earth, where it is expected to begin its observation program in the summer after cooling down sufficiently, adjusting its optics and testing its four infrared cameras .