James Webb telescope: barely launched and already (a little) damaged

Not yet in active service and already damaged! Less than six months after its launch (December 25, 2021) and a perfect deployment – considered “the most complex of all space missions” – the James Webb Telescope (JWST) which is at Lagrange Point 2, approximately 1.5 kilometer from the Earth, was the victim of an impact of a micrometeorite, as NASA has just revealed on its blog. The incident took place between 23 and 25 May.

A priori, nothing dramatic, the impactor is classified in the category of meteoroids whose size is between interplanetary dust and an asteroid; but in this case, these are objects that do not exceed a size of more than 1 centimeter with a mass of less than 1 gram… In the current state of investigations, NASA has not assessed its exact dimensions but admits that it is a little bigger than she expected. “From the outset, the space telescope was designed to withstand bombardments from micrometeorites or, more precisely, its very high degree of performance must enable it to face any damage throughout its mission duration, which is set at least at five years. and a half”, explains Pierre-Olivier Lagage, astrophysicist at CEA Saclay, scientific manager of the MIRI instrument (Mid InfraRed Instrument).

One way to explain that statistically the JWST can withstand a certain number of impacts but that the one at the end of May comes a little early in the promising career of the instrument. NASA communicates openly on the evolution of its latest jewel which cost the modest sum of 10 billion dollars. Since its launch, it has already explained that it had experienced four other more modest impacts (the size of a grain of sand) and considers that “micrometeoroid strikes are an inevitable aspect of the operation of any what a spaceship”.

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You can change the shape of the mirror from Earth

The huge main mirror (25 square meters) consists of 18 hexagonal segments (petals) covered with gold in order, in particular, to observe in the infrared and, it is hoped, to detect the light of the first galaxies. It is exactly segment C3 that was hit by the impact. But again, without going into detail, the American space agency sought to be reassuring: “After the first evaluations, the team found that the telescope is still operating at a level that exceeds all mission requirements, despite a marginally detectable effect in the data”. Above all, for the past few days, engineers at the Goddard Space Flight Center (GSFC) have been modifying the position of the affected segment. “Behind each ‘petal’ are small motors to modify the direction and shape and minimize the consequences of a possible incident”, continues Pierre-Olivier Lagage. In short, this first hitch should be minimal and inconsequential.

And scientists even expect other events in the future and therefore seek to improve their predictions. The James Webb Telescope has to deal with ultraviolet radiation, various sources of cosmic rays or micrometeoroid rains. It can be maneuvered from Earth to make it change position in order to protect its instruments, or even place it in a safe position (turn it off) especially in the event of powerful solar storms so as not to damage its electronic components.

“A priori this incident will have no repercussions on the calendar” assures the CEA astrophysicist. The deployment of the James Webb is even in advance. For several reasons. First, perfectly placed in an optimal orbit on December 25, 2021 thanks to an Ariane-5 rocket, it has kept a substantial reserve of fuel (it has gone from ten to twenty years) which will be used precisely for maneuvering. Then, it took three months to deploy the 18 mirrors, which was achieved beyond expectations, with an alignment precision of 1 micron. Finally, each instrument is in the process of being tested. This is the case of the NIRCam camera (Near-InfraRed Camera), the main instrument for imaging in the near infrared, but also of the Canadian spectrograph NIRISS (Near Infrared Imager and Slitless spectropgraph) or the spectrometer NIRSpec (Near-InfraRed Spectrometer) developed by the European Space Agency (ESA).

A first historical image expected by scientists

“There remains the instrument, MIRI (Mid InfraRed Instrument), which my team is in charge of and which is a kind of “Swiss army knife” since it does classical imaging, spectroscopy and coronagraphy, adds Pierre- Olivier Lagage. We are making sure it works properly and should be finished around June 20.” Finally, the various scientific teams estimate that they are five to six days ahead of an initial deployment schedule that extends over six months! Something to absorb the misadventure of the micrometeorite.

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And after ? The official commissioning of the James Webb will be celebrated on July 12 with a first image released to the general public. Impossible today to know what shot it will be but the telescope is already shooting the distant universe. The choice will be made on the quality and the object observed. “We will not only have a good resolution, but thanks to infrared, we hope to see the galaxies born earlier, from the beginning of the universe”, concludes Pierre-Olivier Lagage. A first photo which will therefore be above all historic for astrophysicists. And the promise of groundbreaking discoveries.