19/12/2022
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A voice counted 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 it would work because we had actually had 15 years of preparation, but the pressure was still high after a long launch campaign with a number of technical problems that we should have solved,” says Daniel de Chambure, head of the 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 short of an “Apollo moment” for astronomy, an extraordinarily complex and ambitious mission. Humanity was looking forward to the next “big eye in the sky,” a quantum leap in technological capabilities that would extend our field of vision to the origins of galaxies and stars.
The hope of a new generation of astronomers was in the nose cone of the ESA-supplied Ariane 5 rocket that had just disappeared behind the clouds over Europe’s launch site in Kourou, French Guiana.
The takeoff itself was expected to take about 30 minutes. Kourou’s job would be over once they received confirmation that Webb had automatically deployed the solar array, generated its own energy, and contacted the team at the Space Telescope Science Institute (STScI) in Baltimore, Maryland, USA.
Rehearsals 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 rehearsed over and over what to do with Webb once in space. These rehearsals were fully computer simulated, making 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 who programmed the simulations began introducing anonymous problems for the flight team to detect and correct.
“The scariest 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.
Impression of Webb’s journey into space
During this simulation, Massimo’s team tried everything. They sent manual commands to accomplish the unfolding. When that didn’t work, they started doing “some dance moves” where they shook the spacecraft in hopes of dislodging the panel. When time was running out and the team had really pulled out all the tricks, the simulation finally cooperated and the panel was unfolded.
“That was very exciting, and something we wouldn’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 4:00 AM that Christmas morning and headed to work where he determined that everything was still fine with the launcher on the platform. An hour and a half before launch, he entered the main control room and saw to it that final pre-launch tasks were completed. Standard procedure requires all these final preparations to be completed 40 minutes before launch. After that, 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 stage was automatic. The flight operations team focused entirely on monitoring the launcher’s status, ready to abort if anything went wrong. During the last seconds the 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 that the launcher sent back, looking for even the slightest deviation from the predictions.
The team followed the takeoff and the different phases. First the boosters were disconnected, then the shell opened in two halves so that Webb emerged at an altitude of 110 km, then the first stage separated, the second stage was ignited and later knocked out. 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 deployed 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 go that way.
Webb’s separation from Ariane 5
It was assumed that during the few minutes it took Webb to calculate and perform the orbiting maneuver, the spacecraft would move out of view of the rocket’s camera and the unfolding 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 precise that the position correction maneuver was superfluous. Webb’s onboard software realized that, so skipped this and moved on to the next task, which was to deploy the solar array 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 disconnect was a result of a few extra things the Kourou team had done. First, it was decided to calibrate the launcher’s Inertial Management Units (IMUs) as close to launch as possible. These devices provide information about the missile’s movements that is used for the onboard calculations that drive the guidance systems. Because these were calibrated so carefully, Ariane 5 knew exactly where it was and where it was going.
Second, the team carefully tuned the linkage 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 trajectory track, the team made another special adjustment, this time to protect Webb himself. NASA was extremely concerned that any residual atmosphere in the nose cone would cause air bubbles trapped in the folded sunshield to expand and tear away the delicate sunshield layers from the telescope. So ESA has developed a system that forces the last air molecules out of the nosecone 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 when the sunshield was deployed and found to be undamaged, the early unfolding of the solar array was immediately apparent to the team. Yet the true value of the launcher’s extreme injection accuracy was not known until that evening, when the Baltimore team ordered the spacecraft to perform another maneuver.
Massimo was on duty while they prepared for mid lane correction 1a. This was the essential extra push to ensure that Webb successfully reached the final position at 1.5 million km from Earth. To calculate the necessary ignition time, Webb was tracked for nearly 12 hours, after which the flight dynamics team at NASA’s Goddard Space Flight Center pored over the numbers. It was then that the magnitude of Ariane’s achievement really became apparent.
The trajectory injection was so precise that the ignition would not last as long as expected. “We knew then that we would have extra fuel,” says Massimo.
After the maneuver, they started tracking and calculating again. It turned out that the fuel saved could now be used to keep Webb in operational orbit and thus extend the life of the mission.
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Twice as much science, twice as many discoveries
When the calculations were complete, NASA announced that thanks to ESA and its contributing partners, Arianespace, ArianeGroup and the CNES, Webb’s lifespan 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.
At that time, however, the revelry was rather subdued. On that Christmas Day 2021, most people were eager to go home to their families. But the memories of what they accomplished that day are still vivid.
“You can see on the base that people are very proud to have launched Webb. You can still see them wearing their Webb polo shirt,” says Daniel. And in the humble world of space operations there is no clearer display of 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 purchase 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 (the MIRI European Consortium) in collaboration with NASA’s Jet Propulsion Laboratory (JPL) and the University of Arizona. The Webb is an international partnership of NASA, ESA and the Canadian Space Agency.