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What’s left for the Webb telescope now: Waggling mirrors, turning on instruments ctm magazine


The James Webb Space Telescope as it will appear in orbit.

I met John Grunsfeld outside a coffee shop in Houston, across the street from Johnson Space Center, a little more than five years ago.

He had only recently retired from NASA after a long and storied career. Over the course of nearly two decades, Grunsfeld had flown into space five times, the latter three of which were missions to service the Hubble Space Telescope. A physicist by training, Grunsfeld had become affectionately known as a “Hubble Hugger” for his work on the venerable instrument in space.

He had then left the astronaut corps and gone on to lead NASA’s science missions as associate administrator of the agency’s science directorate. When we met late in the fall of 2016, Grunsfeld had just returned to private life. Now that he could speak more freely, I wanted to know what Grunsfeld really thought about the space agency’s science priorities. He was in Houston for his annual astronaut physical, and we enjoyed the pleasant late November sunshine as cars zipped by on NASA Road 1.

We discussed a number of topics, but what stood out to me during that conversation were the few minutes we touched on the James Webb Space Telescope. Grunsfeld explained his concerns about Webb and the hundreds of single-point failures it faced during the deployment process in space. So many things could go wrong, he said worryingly. He thought something probably would go sideways, and then where would NASA be the next time it went to Congress and asked for big money to fund an ambitious science project?

This conversation stuck with me, and as I spoke with other scientists and engineers over the years, each offered variations on this theme of concern. Over time, in my mind, it seemed probable that something very well could go wrong during Webb’s deployment or its transit to a Lagrange point 1.5 million kilometers from Earth. As delays mounted, I began to wonder whether the telescope would even launch. Perhaps none of Grunsfeld’s successors would want to assume the personal risk of Webb failing on his or her watch.

But then, something miraculous happened. On Christmas morning of 2021, the James Webb Space Telescope successfully launched from Earth. Thomas Zurbuchen, now NASA’s associate administrator for science, had made the call. If Webb was going to fail, he would take the blame.

Not only did Webb launch, its Ariane 5 rocket performed the flight with such precision that the spacecraft was able to save precious fuel for maneuvering, thereby extending its lifetime. Over the next two weeks, engineers and scientists executed hundreds of steps to unfold and fully extend the telescope and its massive sunshield. And then, finally, on Monday, the spacecraft performed one final major burn of its thrusters, falling into a halo orbit around the L2 point.

This means that the Webb space telescope has reached its final destination, a 180-day orbit around this L2 point, which keeps the telescope in line with the Earth as both the instrument and planet orbit around the Sun. Here, while using a minimum amount of fuel to hold its position, Webb can use its sunshield to keep the infrared telescope and its instruments cold.

The work is not done. The telescope has 18 primary mirror segments, which are moved by 132 actuators. These actuators have already been tested and shown to work. Now, over the next three months, telescope operators will fine-tune the alignment of these mirrors. During this process, scientists will use a Sun-like star named HD84406 to focus the mirrors. This star is located about 240 light years from Earth and can be found in Ursa Major near the bowl of the Big Dipper.

At the same time, in the wake of the sunshield, these mirrors and their scientific instruments will continue to cool in order to be able to detect the weak, ultra-distant signals of heat from the Universe’s oldest galaxies.

At times, it remains difficult to believe this is really happening. But all of the unprecedented stuff for this large space science project is complete, and now the commissioning of the instruments should be fairly routine. Webb won’t be ready for science operations until June, but the odds are very high that it will get there.

I have only been a very outside observer of this process over the last five years—knowing enough to be concerned about the fate of this $10 billion telescope but not facing any serious consequences should it fail. Even so, I have worried much, and more, about the fate of Webb. At times I have despaired about it ever making a science observation. And so I have felt elated over the last couple of weeks as everything has fallen neatly into place.

I can only imagine the utter delight of astronomers, physicists, and scientists who have worked directly on this project. Bravo to you all.



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