NASA has successfully installed the primary mirror of the $10bn James Webb Space Telescope (JWST) – marking a significant step towards a fully functioning infrared observatory. Over the weekend of 8 and 9 January, engineers unfolded the 6.5 m primary mirror, which is made up of 18 hexagonal segments. Over the coming weeks, the telescope will carry out further orbital manoeuvres, with engineers carefully aligning each mirror segment as well preparing the scientific instruments to become operational.
More than two decades in the making, the JWST was launched on 25 December aboard an Ariane 5 rocket from the European Spaceport located near Kourou, French Guiana. It then began making its way to Lagrange point L2 – a point in space some 1.5 million kilometres away from the Earth in the exact opposite direction from the Sun.
The successful completion of all of the Webb Space Telescope’s deployments is historic
Gregory Robinson, NASA’s JWST programme director
For many space probes, launch is the most dangerous part of the mission. Yet for the JWST, it had to survive a series of hazardous deep-space unpacking manoeuvres, which involved unfolding its 6.5 m primary mirror as well as unfurling its tennis-court-sized sunshield. Any issue with the 344 “single-point” failures could hamper the observatory’s mission, or worse, make it unusable.
A day following launch, the JWST deployed its antenna assembly, which will be used to send some 29 Gbytes of data to Earth. The observatory then carried out several orbital corrections to fine-tune its trajectory to L2. Those steps, along with the precision of the launch, went better than expected with officials noting that the fuel saved from the burn should allow the observatory to operate for “significantly more than a 10-year science lifetime,” possibly for as long as two decades.
Coming out of its shell
The first unpacking of the telescope began on 28 December with the front and back sunshield pallets that hold the five layers of sunshield. Measuring 21 m × 14 m, the sunshield is crucial to protect the telescope’s scientific instruments and mirrors from the Sun, which need to operate at temperatures of around –233 °C.
Following the removal of the sunshield covers that protected the sunshield as it was folded for launch, on 1 January engineers began to deploy the two “mid-booms”, or arms, at either side of the telescope that pulls out the five sunshield layers.
After a pause to check the status of the JWST, tensioning those layers individually began on 3 January and was successfully completed a day later. At that point over 75% of the 344 single-point failures had been met.
“Unfolding Webb’s sunshield in space is an incredible milestone, crucial to the success of the mission,” noted Gregory Robinson, NASA’s JWST programme director in a statement. “Thousands of parts had to work with precision for this marvel of engineering to fully unfurl.”
With the sunshield in place, engineers then turned their attention to the telescope’s secondary and primary mirrors. Deployment of the tripod support structure for the secondary mirror was complete by 5 January. The secondary mirror is supported by three lightweight deployable struts that are each about 7.5 m long and had to unfold and then latch into position.
“[The JWST’s] secondary mirror had to deploy in microgravity, and in extremely cold temperatures, and it ultimately had to work the first time without error,” notes Lee Feinberg from NASA’s Goddard Space Flight Center, who is JWST’s optical telescope element manager. “It also had to deploy, position and lock itself into place to a tolerance of about one and a half millimetres, and then it has to stay extremely stable while the telescope points to different places in the sky.”
The [JWST] is an unprecedented mission that is on the precipice of seeing the light from the first galaxies and discovering the mysteries of our universe
NASA administrator Bill Nelson
Over the weekend, engineers then fixed into place the two “wings” of the JWST’s primary mirror. They were folded back to fit in the rocket and both wings – each consisting of three hexagonal segments – had to rotate into place and be latched onto the main mirror segment. Work on installing the left, or port, side began on 7 January then a day later the right side of the mirror was successfully latched into place.
“The successful completion of all of the Webb Space Telescope’s deployments is historic,” noted Robinson. “This is the first time a NASA-led mission has ever attempted to complete a complex sequence to unfold an observatory in space – a remarkable feat for our team.”
First light
NASA will now carry out a further orbital correction, warm some of the electronic systems and initialize the flight software. The ground team will command 126 actuators on the rear side of the segmented mirrors into position and flex each mirror – an alignment process that will take months to complete. Then the four main scientific instruments, which include spectrographs, imagers and infrared cameras, will be calibrated.
First images from the JWST are expected in June when it will begin its science mission and conduct routine operations. If all goes well during the final stages of alignment and instrument commissioning, then the JWST could revolutionize astronomy by peering back some 300 million years after the Big Bang when some of the first galaxies existed. It will also probe the atmospheres of the planets as they pass between the telescope and their parent stars. A new cosmic dawn: peering across the universe with NASA’s James Webb Space Telescope
“The [JWST] is an unprecedented mission that is on the precipice of seeing the light from the first galaxies and discovering the mysteries of our universe,” NASA administrator Bill Nelson noted. “Each feat already achieved and future accomplishment is a testament to the thousands of innovators who poured their life’s passion into this mission.”
“We are thrilled that the complex telescope unfolding worked successfully. Now we hold our breath for the optics alignment, the instrument commissioning, and finally the fascinating first science results,” says Günther Hasinger, director of science at European Space Agency, which along with the Canadian Space Agency has provided key components of the JWST.
