On Wednesday, Nov. 17, NASA Headquarters held its final review for the mission prior to launch. A week later, on Nov. 24, a review committee approved Webb’s transition to the next stage in its preparations for launch. This week we’ve asked NASA’s Randy Kimble, Webb’s integration, test, and commissioning project scientist, to tell us how things are going at the launch site:
“The loading of propellants into the Webb observatory is complete at the Arianespace launch facilities in Kourou, French Guiana. This is an important step in the path toward launch.
“The vast majority of the launch energy required to send Webb to its operating orbit around the Sun-Earth Lagrange point L2 will be provided by the massive Ariane 5 rocket. Nevertheless, the observatory carries propellants of its own. After being released from the launcher, Webb will use its own system of small rocket thrusters to fine-tune its approach to its final halo orbit around the L2 point (illustrated below), where the telescope and instruments will cool in the shade of the enormous sunshield, protected from the heat of the Sun, Earth, and Moon. Mid-Course Correction maneuvers for refining the trajectory are planned (nominally) for 12.5 hours and 2.5 days after launch, with a third one month later, to ease Webb into its L2 orbit. Those same thrusters will be used periodically throughout the mission to maintain that orbit, with small maneuvers called ‘station keeping.’
“A second set of smaller thrusters on the observatory compensate for momentum buildup caused by the pressure of solar radiation onto the large area of the sunshield. Although Webb is designed to keep that pressure well balanced, angular momentum builds up as the telescope points at different targets, so occasional, small momentum-unloading maneuvers are required to keep the observatory’s reaction wheels within their proper operating ranges. Reaction wheels are flywheels in the Webb spacecraft that help keep the payload’s orientation stable.
“Propellant loading was the final major operation for the observatory itself, before it moves to the Final Assembly Building (BAF is the French acronym) for integration with the Ariane 5 launch vehicle.
“One special aspect of processing the Webb observatory at the launch site is the need to keep it clean. Unlike Hubble, whose telescope is enclosed in a protective tube, Webb can operate successfully with just the shade of the sunshield to protect it in space. While it is subject to the air on Earth, the environment around the telescope must be kept as clean as possible. This ensures that Webb’s mirrors and sunshield are not contaminated with small particulates or molecular films, both of which could reduce the observatory’s sensitivity. The 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. NASA’s Goddard Space Flight Center has also provided portable HEPA filter walls to augment the contamination control of the airflow near the payload. Goddard contamination engineers Eve Wooldridge and Alan Abeel have reported excellent results from the joint contamination control efforts for the roughly seven weeks Webb has been in Kourou so far. They note that continued vigilance is required for the remainder of the ground processing flow, as the most challenging facilities are still ahead.
“From Eve and Alan, ‘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.’ The launch site facilities that Webb has encountered so far have all performed well, thanks to these efforts. The next challenge is to transform the facilities in the BAF (which opens huge doors for the rockets and spacecraft), where Webb will be integrated with the rocket and then encapsulated. This can be done because of the excellent team Eve and Alan are so fortunate to work with. ‘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. They have cheerfully worked long days, six days a week, and have proven to be a strong morale-booster for the entire launch campaign team. While we all look forward to launching Webb and getting home to our families, we know we will miss each other and this amazing time in Kourou very much.’
“As Webb prepares to move to the final steps of ground integration, there are no more planned major ground tests of the payload – only minimal electrical checks. The Comprehensive Systems Test that was performed in late October to confirm the observatory’s health after arriving at the launch site represented the culmination of many years of testing. The successful completion of that major ground test put members of the Webb team who had traveled to Kourou in a reflective mood:
“Macarena Garcia Marin, ESA’s instrument and calibration scientist for Webb’s Mid-Infrared Instrument (MIRI), noted with pride the ‘can-do’ attitude and the wonderful feeling of camaraderie among the team that was required to get through years of often-grueling test campaigns. She was also thrilled by the opportunity to see a ‘sneak preview’ of the Webb launch, having viewed the most recent Ariane 5 launch (VA255, on October 23) from a distance of three miles away – ‘Breathtaking!’
“Scott Lambros, Webb instrument systems manager at Goddard, reported mixed feelings as ground testing of the observatory drew to a close: ‘Strangely enough, it’s sad to see the observatory going away – we’ve been working with it so long now, it’s like saying goodbye to a friend. It’s also sad that many of the wonderful people I’ve been working with in the last 19 years soon will be going in different directions. On the other hand, I am extremely excited to see Webb ready for launch and prepared to fulfill its scientific purpose out at L2.’
“As are we all.”
—Randy Kimble, Webb integration, test, and commissioning project scientist, Goddard
By Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center
And Alexandra Lockwood, project scientist for Webb science communications, Space Telescope Science Institute