Soon we will be witnessing the unfolding of another chapter in the Space Age. As the James Webb Space Telescope (JWST) prepares for launch, there is still much tension and uncertainty amongst the scientists and engineers involved and the space community at large. Every possible step has been taken to ensure the greatest chance of success, but there is a lot that has to go right for JWST to begin unveiling new parts of our universe to us. With a telescope of this scale, heading a million miles away, and the cost, time, and labor involved, mistakes cannot be afforded. Not only does the launch have to go just right, but that stage will perhaps be the easiest checkbox on its journey to becoming fully operational. Here are the major stages of deployment that have to be absolutely perfect for Webb to be successful.

James Webb Space Telescope and its launch vehicle, Ariane 5 rocket, at the launch pad in French Guiana. (NASA/Bill Ingalls)


First things first, the telescope has to get off the ground. It is set to launch from Arianespace's ELA-3 launch complex at the European Spaceport in French Guiana—a beneficial location as it is close to the equator where the Earth’s rotation can provide an additional boost. Already, JWST’s launch has been delayed a number of times for various reasons. The telescope has been on board the Ariane 5 launch vehicle awaiting the right moment. Of course, it’s not difficult to see why this would be the case, with just too much at stake to entertain the possibilities of contingencies in the plan for liftoff.

The Ariane 5 launch vehicle provides thrust for roughly 26 minutes after liftoff. Moments after the upper (second) stage engine will cut-off and JWST will be flying on its own. (NASA)

Separation and Solar Array

Once off the ground, the Ariane 5 rocket will have to separate from JWST after providing about a half hour of boost. From that point, Webb will be on its own in a stowed configuration. Soon after, it must deploy its solar array, which will power it the rest of the way, generating electricity from the Sun. Webb will only use about 1 kilowatt of power to function and use all of its scientific instruments, but the solar array is capable of providing almost double the power.

Webb's solar array will power it the rest after the booster is separated and begin generating electricity from the Sun. (Video courtesy of NASA)

Course Correction

To get to its final destination (a unique orbit around the Sun about one million miles from Earth), JWST will have to perform some important thrust correction maneuvers to set it on the right path, which will occur a few hours after separation from the launch vehicle and the solar array deployment. In total, the telescope will perform three mid-course correction (MCC) maneuvers throughout its journey. The second will occur approximately two days after launch and the third about 29 days into the journey.

Sunshield Deployment

About three days after liftoff, JWST will begin the deployment step with the first major maneuver in that phase—the unitized pallet structure deployment, which holds five sunshield membranes. This starts the telescope’s sunshield deployment phase. Covers that have been protecting the membranes to this point will be released on day five, and by day eight, all five sunshield membranes will be uncovered, fully extended and tensioning completed.

Demonstration of Webb's sunshield deployment phase. (Video courtesy of NASA)

Mirror Deployment

As it nears closer to its destination, Webb will need to start setting up its optical system. The telescope carries two sets of mirrors, the primary one, which is perhaps the most recognizable look of JWST with segmented hexagonal shapes, and a secondary mirror, which reflects light from the primary into the instruments onboard. The center portion of the primary mirror will already be out at this point in the journey (after sunshield deployment) and the secondary mirror will begin to maneuver and extend to it proper positioning on day 10. Approximately two days later, the left and right port of the primary mirror stage will begin. Once this is completed on about the 13th day, JSWT will finally be in its intended configuration.

The primary mirror of JWST will have to fold into place. (Video courtesy of NASA)

Orbiting the Sun

Finally, the telescope is fully deployed, but the journey is far from over. Between days 15 and 24, all 18 segments (hexagonal shapes) of the primary mirror will be tested. A few days after that testing is completed, JWST will perform its last MCC burn to set it off on the home stretch. Approximately one month in, Webb will enter a position in orbit known as the second Lagrange point (L2). Unlike the Hubble Space Telescope, JWST will not orbit around the Earth. Instead, it will be much farther away (approximately one million miles) orbiting the Sun. In short, the telescope will always be aligned with the Earth’s orbit around the Sun.

Unlike the Hubble Space Telescope, JWST will not orbit around the Earth. It will orbit the Sun. (Video courtesy of NASA)


The next couple of months will be spent testing the various instruments and functionality of JSWT to ensure that everything works as planned. This includes a long arduous process of aligning all the optics, including checking accuracy of individual mirror segments, matching images provided from each, and calibrating all of the scientific instruments. This will go on for quite some time, and after about six months into its journey, JWST will be ready for its first day at work to conduct scientific operations.

Getting it Right the First Time

When there was an issue with Hubble’s main mirror, multiple space shuttle missions visited the telescope in Earth orbit to make repairs (we even have in our collection flown Hubble instruments returned to Earth on the Hubble Servicing Missions!). This will not be the case with JWST. Because Webb’s final destination is a million miles away, it is quite unlikely that humans could ever visit it to correct any issues. For this reason, it is very important that the James Webb Telescope successfully completes each of these steps to become an operational space telescope.

In perhaps decades to come, JWST will remain the leading observatory and our best view of the universe. Guiding Webb to its final orbiting destination is an unprecedented endeavor and certainly a revolutionary moment in human history. It will survey parts of the universe never seen before and take us back to when the first stars and galaxies formed billions of years ago. What will it teach us? What theories will it challenge? What will it find? What angles of the universe will see for the first time? In six months’ time, after its long, nerve-wracking, and unprecedented journey, we may start to get those answers.

Related Topics Space Astronomy Telescopes Technology and Engineering
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