James Webb Telescope: How to keep a $10 billion instrument 100 percent clean

Any small particulates or molecular films could drastically reduce Webb's sensitivity.
Brad Bergan
An artist's depiction of Webb (left), and the real telescope in Europe's clean room (right).1, 2

The more sensitive the instrument, the harder it is to keep clean. 

Essentially, this was the case for the James Webb Space Telescope while it awaited launch late last year, after it arrived at Arianespace center, in Kourou, at the end of a long journey from California. But as long as it stayed on Earth, it was in danger: The air, temperature, and pressure surrounding the telescope and its 21.6-foot primary mirror could drastically reduce the platform's sensitivity.

Until Webb was launched on December 25, 2021, an around-the-clock contamination control protocol was in place. Several space agencies collaborated to keep the telescope and its equipment in pristine condition.

Maintaining the James Webb Telescope called for daunting cleaning procedures

"One special aspect of processing the Webb observatory at the launch site is the need to keep it clean," says NASA's Randy Kimble, a scientist assigned to Webb's integration, test, and commissioning project in a NASA blog post. "Unlike Hubble, whose telescope is enclosed in a protective tube, Webb can operate successfully with just the shade of the sun shield to protect it in space."

As we know from more than two years of a global pandemic, Earth's atmosphere is filled with particulates, living creatures, and more dirty microscopic objects that leave their mark on everything from windows to the human immune system. While a telescope as sophisticated (and expensive — at $10 billion) as Webb "is subject to the air on Earth, the environment around the telescope must be kept as clean as possible."

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"This ensures that Webb's mirrors and sun shield are not contaminated with small particulates or molecular films, which could reduce the observatory's sensitivity," says Kimble in the NASA blog.

To ensure the highest levels of cleanliness, all space agencies involved in developing the James Webb Space Telescope collaborated to create a system capable of pulling it off.

NASA Chris Gunn
The enormous James Webb Telescope, in Europe's mega-spaceport. Source: NASA / Chris Gunn
Every surface of the James Webb Telescope was cleaned daily

"NASA, ESA (European Space Agency), Arianespace, and French space agency (Centre National d'Etudes Spatiales) teams have cooperated very closely to custom-clean the launch facilities to Webb's demanding requirements," Kimble explains. "NASA's Goddard Space Flight Center has also provided portable HEPA filter walls to augment the contamination control of the airflow near the payload."

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Two contamination engineers associated with Goddard, Alan Abeel and Eve Woolridge, saw significant success implementing contamination control for seven weeks straight during Webb's stay in Kourou, pre-launch. But utmost vigilance was required to keep the colossal successor to Hubble in perfect condition for its historic launch.

"Our NASA contamination control engineers and technicians have transformed facilities that are not designed for scientific spacecraft into well-controlled clean rooms not just with HEPA filters, but by covering, cleaning, removing, bagging, and sealing over items incompatible with Webb's stringent cleanliness requirements, and then cleaning every surface daily," Woolridge and Abeel say of the challenge of keeping Webb clean.

Integrating Webb with the rocket that would loft it to space

Before Webb could be lofted into space, the facilities in the BAF (the section of Arianespace with enormous doors to allow rockets to pass through) needed to be prepared for the next challenge: integrating Webb — already a giant object — into the rocket that would send it on its way. But Woolridge and Abeel's engineering team were up for the task.

"We maintain that this is not just the largest contamination control team in the world doing this type of work; it is the best and most hard-working," say Abeel and Woolridge. Indeed, long hours and unforgiving work weeks called for the strongest morale possible. The team "cheerfully worked long days, six days a week, and has proven to be a strong morale boost for the entire launch campaign team."

Keeping Webb in perfect shape — In the final weeks before Webb's launch, all major ground tests came to a close, with only non-invasive electrical tests carrying forth. If significant measures were not taken to keep the James Webb Telescope clean from contaminants, dust, and other particulates, these might have been picked up by some test failures. But major failures were supported in the weeks and months preceding the launch.

With Webb already sending its first test image of a distant star — along with millions of ancient galaxies — from its position in Lagrange point 2, it seems Woolridge and Abeel's work, along with the rest of the engineering team, completed the critical task of keeping Webb, a $10 billion instrument — in top shape.

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