NASA science chief says it’s OK to be “worried” or “terrified” about Webb

NASA's science chief, Thomas Zurbuchen, has worked hard to bring the oft-delayed James Webb Space Telescope to the launch pad.
Enlarge / NASA’s science chief, Thomas Zurbuchen, has worked hard to bring the oft-delayed James Webb Space Telescope to the launch pad.


For scientists who spend a decade or more planning, designing, lobbying for, building, and testing exploratory spacecraft, the launch is always a pucker factor moment.

Years and years of work. Millions or even billions of dollars. It can all go up in a puff of smoke, in seconds, if something goes wrong with the rocket. Unlike with most human spacecraft, there are no emergency escape systems for scientific spacecraft. Some of these delicate payloads would be unlikely to survive the violent escape thruster firings, anyway.

“For most missions, launch contributes the majority of mission risk,” explained Thomas Zurbuchen, the associate administrator for science missions at NASA. “If the spacecraft is in space, most risk is behind us.”

However, there are exceptions to this rule, Zurbuchen explained in a new blog post for the space agency. For the Mars Perseverance mission launched last summer, for example, only about 10 to 20 percent of the mission’s risk was retired once the spacecraft reached orbit. The remainder lay ahead of the vehicle, particularly with its daring landing on Mars, and then performing a technically challenging sample acquisition and analysis.

The $10 billion James Webb Space Telescope, due to launch on a European Ariane 5 rocket late this year, offers an even more extreme example. In his blog post, Zurbuchen offers a frank and revealing analysis of Webb’s launch and assessment of the risks.

Once in space, Webb will need to travel about 1.5 million km from Earth to the L2 Lagrange Point beyond the Moon where it will be able to maintain a stable position without using much on-board propulsion. Along the way, and once there, some 50 deployments of the large, folded-up telescope will be necessary to prepare for scientific observations. This process will involve nearly 350 single-point failures, and if something goes wrong, it would scuttle the deployment without hope of repair. The number of single-point failures for Webb, by comparison, is a factor of three greater than the seven-minute landing of Perseverance on Mars.

It will take about three weeks to deploy Webb, and scientists will be on edge the entire time, Zurbuchen said.

“Those who are not worried or even terrified about this are not understanding what we are trying to do,” Zurbuchen wrote. “We have worked hard to build the team for this task and it has been a tough journey at times. This mission has a very troubled story with chapters that were disappointing, or even baffling. We are where we are because Webb has some of the best engineers and leaders I have ever met, and they have continued when others were ready to give up.”

Zurbuchen visited French Guiana last week to witness the launch of an Ariane 5 rocket. This rocket returned to service after a nearly year-long layoff due in part to the COVID-19 pandemic, but also because of an issue with its payload fairing. The launch of that rocket—which resulted in the successful deployment of two communications satellites—and one more Ariane 5 rocket must go well before the Webb mission flies.

During his trip, European launch officials told Zurbuchen that getting Webb safely into space was their highest priority. But for Zurbuchen, that will be little cause for relief. It will only be the first step of a journey during which Webb will be out of control of the scientists who worked so long to set it free.

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