What happens after the James Webb telescope is launched? A six-month roadmap

The long awaited space telescope is just days from launch, but it's dozens of steps, and millions of miles, away from doing science.

Originally Published: 
The James Webb Space Telescope's primary mirror at NASA Goddard

It’s finally here. Most likely. Assuming no further delays, the long-awaited James Webb Space Telescope will launch atop an Ariane 5 rocket from French Guiana on Christmas Day.

The multi-billion-dollar space telescope that has been more than 20 years in the making will be on its way to its perch 1 million miles away from Earth.

But the reality is, despite decades of work and billions of dollars, a successful launch — assuming it goes off as planned — is still just the beginning of the final stretch for the James Webb Space Telescope. It’s not headed for Earth orbit like the venerable Hubble Space Telescope, but will fly directly to Lagrangian point 2 (L2), a spot 1 million miles away where Earth and the Sun’s gravity cancel out, allowing the Webb to orbit the Sun with our planet permanently at its back.

Along the way, dozens of tiny things still have to go just right before NASA can officially begin science observations, and they all must take place far away from any human help in the cold dark recesses of deep space.

The first hours of Webb— So you’ve successfully launched your rocket and it didn’t blow up. Congratulations! It’s only additional perils from here on out, beginning with the rocket placing the Webb telescope into space, are:

  • T+27 minutes: If all goes well, this is when Webb will separate from the upper stage of the Ariane 5 launch vehicle, which only provides thrust for about 26 minutes after liftoff in French Guiana.
  • T+33 minutes: Webb will deploy its solar panels and begin generating power. It’s an automated action crucial to the telescope’s success — it doesn’t carry a nuclear power source like the Voyager deep-space probes. Without solar power, it will quickly deplete its batteries.
  • T+12.5 hours: Webb conducts the first of three mid-course correction engine burns to ensure it’s pointed the right way toward L2.
  • T+24 hours: Webb’s high gain antenna, held in the Gimbaled Antenna Assembly, automatically positions itself to point back to Earth. It’s the last automatic deployment of the mission, with all other commands coming from human operators on Earth. The mission won’t necessarily fail if the antenna deployment goes awry, but it will significantly reduce the amount of data the mission can return at once.

What the first 30 days look like for Webb.


The first week of Webb—

  • T+2 Days: Webb initiates the second of three mid-course correction burns.
  • T+3 Days: Webb begins the multi-step process of deploying its five-layered sunshield by unfolding its forward sunshield pallet, part of the Unitized Pallet Structure holding the shield. Parts are whirring and warming and preparing for the next steps in deployment. If all goes well, the aft sunshield pallet will deploy the same day. The two pallets fold outward and down, forming with the Webb spacecraft bus — the main skeletal or space frame — a plane perpendicular to the column formed by the still folded mirror segments.
  • T+4 Days: Webb’s mirrors and other components are lifted two meters relative to the plane of the sunshield pallets on the Deployable Tower Assembly. This gives the sunshield room to deploy fully and will later help further thermally isolate the telescope mirrors and instruments from solar energy.
  • T+5 days: The Webb deploys its after-momentum flap. This is a reflective control surface designed to counteract the force of sunlight on the tennis court-sized sunshield. The reflective sunshield will naturally act as a solar sail, and lead to unwanted torque and other accelerations, but the momentum flap will dampen these effects to help keep Webb’s view on the universe stable.
  • T+5 Days: Protective covers in place over the sunshield since before launch now roll up in preparation for the shield’s deployment.
  • T+6 Days: The sunshield booms extend on either side of the Webb bus, creating the diamond-like configuration for the sunshield as the shield membranes unroll.
  • T+7 Days: The Webb begins a tensioning process to pull taut each of the five layers of the sunshield, completing the process by day eight.

The second week of Webb—

  • T+10 Days: Webb’s secondary mirror swings from behind the Deployable Tower Assembly to its operational position in front of the primary mirror. It’s one of the most crucial moments of the telescope’s deployment — where a bad antenna could slow the rate data could be sent home, and a solar panel failure could reduce the scale of operations, failure of the secondary mirror would mean no images from Webb at all.
  • T+11 Days: The aft instrument radiator, essential to keeping the telescope’s sensitive infrared instruments cool enough to see, deploys.
  • T+12 Days: The left wing of the primary mirror folds out and locks into place. Webb’s primary mirror comprises 18 beryllium segments, but those segments are divided into a central portion and two side wings, folded tight to the central column for launch. Each wing contains three mirror segments.
  • T+13 Days: The right wing of the primary mirror folds out and into place, completing the full 21-foot diameter mirror and marking the full deployment of the James Webb Space Telescope.

But that’s not all she wrote — weeks of travel and calibration remain before the Webb can begin doing any science.

The third week of Webb—

  • T+15-24 Days: Each primary mirror segment and Webb’s secondary mirror are adjustable via six actuators, and ground operators will spend days carefully aligning each segment to form a cohesive mirror system.

A road map of all the little adjustments Webb has to make on its way to L2.

NASA and M. Clampin, GSFC.

The fourth week of Webb—

  • T+29 Days: The third, final, and most crucial course correction burn takes place, inserting the Webb into orbit at the L2 point. A failure here and the Webb sails onward into deep space.
  • T+29.5 Days: Once successfully in orbit at L2, the telescope’s primary job for the next three weeks will be to just chill — the scientific instruments need time to literally cool down. The telescope’s instrument suite must reach minus 388 degrees Fahrenheit To retain the necessary sensitivity to the infrared spectrum.

The next five months of Webb— Once Webb is safely in orbit at L2, all its components will have fully deployed, and its instruments are cold as hell. Can we do science yet?

Nope. The telescope’s mirror segments must be further aligned to ensure it can take sharp images by focusing on a distant star, which will take about two weeks.

Then the mirror segments must be further adjusted, this time taking into account each of the four scientific instruments on the telescope, another weeks’ worth of careful effort by operators on the ground.

Then, once the optics are finally aligned, months of instrument checks remain, ensuring that the instruments can receive and process the images focused by the mirrors.

It’s summer: Finally, we can science!— Finally! All has gone well, everything checks out, and a 20+ year journey is finally at its end: Scientists can start using their time on the Webb to image the faintest galaxies in the Universe, stare at exoplanets and even produce stunning images of planets in our Solar System.

It’s no sooner than mid-summer 2022.

This article was originally published on

Related Tags