A year ago, a perfect launch of the James Webb Space Telescope took place

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19/12/2022
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A voice spoke backwards in French from ten to one and then announced “décollage”, lift-off! The 15-year collaboration between NASA, ESA and the Canadian Space Agency had just reached its most critical point: the launch itself. Whether the James Webb Space Telescope would actually make it to space depended on what happened next.

Webb’s launch campaign highlights

“On the day of the launch, the pressure was extremely high. We were convinced that we could succeed, because we had actually already had 15 years of preparation, but the pressure was still high after a long launch campaign with a number of technical problems that we had to solve,” says Daniel de Chambure, head of ESA- office in Kourou in French Guiana and former Ariane 5 project manager for Webb.

It is no exaggeration to say that the whole world was watching. Years of development and promising prospects made Webb the long-awaited successor to the NASA/ESA Hubble Space Telescope. So Webb was nothing less than an “Apollo moment” for astronomy, an extraordinarily complex and ambitious mission. Humanity looked forward to the next “big eye in the sky”, a quantum leap in technological possibilities that would expand our field of vision to the origins of galaxies and stars.

The hope of a new generation of astronomers lay in the nose cone of the ESA-supplied Ariane 5 rocket, which had just disappeared behind the clouds above Europe’s launch site in Kourou, French Guiana.

The actual launch was expected to take about 30 minutes. Kourou’s job would be over when they received confirmation that Webb had automatically installed the solar array, generated its own energy, and contacted the team at the Space Telescope Science Institute (STScI) in Baltimore, Maryland, USA.

Exercises and simulations

Massimo Stiavelli, who heads the Webb mission office in Baltimore, knew the stakes were high: no solar panel, no mission. In the years leading up to this moment, Massimo and the STScI flight operations team had practiced over and over what to do with Webb once in space. These tests were completely computer simulated, which made them feel very real. In the beginning everything would be ‘nominal’. This means that the spacecraft would behave as expected. Then the small team of engineers programming the simulations began introducing anonymous problems for the flight crew to detect and fix.

“The most frightening experience was during a simulation where the solar panel did not open. So we ran on batteries, and then you know that at some point you will run out of energy,’ says Massimo.

Impressions of Webb’s journey into space

During this simulation, Massimo’s team tried everything. They sent manual commands to perform the deployment. When that didn’t work, they started doing “some dance moves” shaking the spacecraft in hopes of dislodging the panel. With time running out and the team really pulling out all the tricks, the simulation finally cooperated and the panel unfolded.

“It was very exciting and something we didn’t want to try in real life,” says Massimo.

But before the flight operators could take over, Daniel and his team had to fulfill their promise to get Webb safely into orbit.

The extreme precision of the launch

The day started early. Daniel got up at 4 a.m. that Christmas morning and went to work, where he found that everything was still fine with the launcher on the platform. An hour and a half before launch, he went into the main control room and made sure the final pre-launch tasks were completed. Standard procedure calls for all these final preparations to be completed 40 minutes before launch. Then it’s time to wait for the team.

“You get a little nervous because you have to wait,” he says. To ease the tension, he met with the media to answer their questions. Seven minutes before launch he returned to the control room and the countdown began.

Everything at this point was automatic. The flight operations team focused solely on monitoring the launcher’s status, ready to abort if anything went wrong. During the last seconds, ignition took place: first the main engine, seven seconds later the boosters.

The rocket took off from the platform. The operators constantly monitored the telemetry data sent back by the launch vehicle, looking for even the slightest deviation from predictions.

The team followed the start and the different phases. First the boosters were disconnected, then the shell opened in two halves, so Webb emerged at an altitude of 110 km, then the first stage separated, the second stage was ignited and later ejected. Finally, at an altitude of 1,400 km, Ariane released Webb. The camera on the rocket watched as the space telescope drifted away, adjusting its trajectory along the way. A few minutes later, when it was right on track, Webb automatically installed the solar panel and began sending signals to Massimo’s team in Baltimore. Daniel and his team had completed their task.

But it didn’t quite work out that way.

Webb’s separation from Ariane 5

It was assumed that during the few minutes it took Webb to calculate and execute the orbiting maneuver, the spacecraft would move out of sight of the rocket’s camera and the deployment of the solar array would not be visible. But 70 seconds after unplugging, the solar panel unfolded.

In Kourou, it was clear why. Ariane’s launch had been so accurate that the position correction maneuver was redundant. Webb’s onboard software realized that, so it skipped this and moved on to the next task, which was to install the solar panel and make contact with Baltimore. It was impressive to see how accurate the launch was.

“I still remember the reactions of the ESA and NASA colleagues around me when it happened. Everyone was very excited,” says Daniel.

Special adjustments

Webb and Ariane 5: a perfect fit

The extreme accuracy of the track injection on the break was a result of a few extra things the Kourou team had done. First, it was decided to calibrate the launch vehicle’s Inertial Management Units (IMUs) as close to launch as possible. These devices provide information about the missile’s movements, which is used for the onboard calculations that drive the guidance systems. Because these were so carefully calibrated, Ariane 5 knew exactly where it was and where it was going.

Second, the team carefully tuned the coupling and alignment of the upper stage accelerators so that there was no jitter after the ignition of the upper stage and the trajectory was undisturbed.

In addition to the track, the team made another special adjustment, this time to protect Webb himself. NASA was extremely concerned that any remaining atmosphere in the nose cone would cause air bubbles trapped in the folded sun shield to expand and tear the delicate sun shield layers away from the telescope. So ESA has developed a system that forces the last air molecules out of the nose cone before the envelope opens and Webb is exposed to the vacuum of space. “We also thought it was a huge achievement that the residual pressure was well below the norm after several demonstrations on previous Ariane 5 flights,” says Daniel.

Although it was not confirmed until later that this system had worked, as the sun shield was deployed and found to be undamaged, the early deployment of the solar panel was immediately apparent to the team. Still, the true value of the launcher’s extreme injection accuracy was not known until the night the Baltimore team ordered the spacecraft to perform another maneuver.

Massimo was on duty as they prepared for midfield correction 1a. This was the essential extra push to ensure Webb successfully reached the final position 1.5 million km from Earth. To calculate the required ignition time, Webb was tracked for nearly 12 hours, after which the flight dynamics team at NASA’s Goddard Space Flight Center crunched the numbers. It was at that point that the extent of Ariane’s achievement really became apparent.

The track injection was so accurate that the ignition would not last as long as expected. “We knew then that we wanted extra fuel,” says Massimo.

After the maneuver they started tracking and raining again. It turned out that the saved fuel could now be used to keep Webb in operational orbit, thus extending the life of the mission.

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Twice the science, twice the discoveries

When the calculations were complete, NASA announced that, thanks to ESA and its contributing partners, Arianespace, ArianeGroup and CNES, Webb’s lifetime had now doubled. Instead of a 10-year mission, Webb now had enough fuel on board to remain operational for 20 years. Twice the observations, twice the science, twice the discoveries.

By turning a routine launch into Ariane 5’s finest moment, the European team had doubled down on humanity’s next great leap toward a better understanding of its origins.

“This was a wonderful moment and a reward for all of us, especially after all the thanks from the NASA Webb project team,” said Daniel.

Back then, however, the party was quite subdued. On Christmas Day 2021, most people were eager to go home to their families. But the memories of what they achieved that day are still vivid.

“You can tell on base that people are very proud to have launched Webb. You can still see them wearing their Webb polo shirts,” says Daniel. And in the humble world of space operations, there’s no more obvious pride than that.

More information
Webb is the largest and most powerful telescope ever launched into space. Under an international cooperation agreement, ESA has launched the telescope using the Ariane 5 launch vehicle. During the collaboration with the partners, ESA was responsible for the development and qualification of the modifications to Ariane 5 for the Webb mission and for the procurement of the launch service by Arianespace. ESA also provided the powerful NIRSpec spectrograph and 50% of the MIRI medium-infrared instrument, which was designed and built by a consortium of nationally funded European institutes (MIRI European Consortium) in collaboration with NASA’s Jet Propulsion Laboratory (JPL) and the University of Arizona. Webb is an international partnership between NASA, ESA and the Canadian Space Agency.

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