In its new home away from Earth, the James Webb Space Telescope may not be quite as lonely as it seems.
The pocket of space the telescope occupies isn’t a complete vacuum — and now the inevitable has happened, with a tiny piece of rock, a tiny meteor, hitting one of Webb’s mirror segments.
But don’t panic. The engineers who built the telescope are acutely aware of the harshness of space, and Webb has been carefully designed to withstand it.
“We always knew Webb would have to contend with the space environment, which includes harsh ultraviolet light and charged particles from the sun, cosmic rays from alien sources in the galaxy, and accidental strikes by tiny meteors within our solar system,” says engineer and technical deputy project manager Paul Geithner From NASA’s Goddard Space Flight Center
“We designed and built Webb with a margin of performance — optical, thermal, electrical, mechanical — to ensure it can perform its ambitious scientific mission even after many years in space.”
Webb occupies an area of 1.5 million kilometers (just under a million miles) of Earth called L2.
It’s what’s known as a Lagrange or Lagrangian point, where the gravitational interaction between two circular objects (in this case, the Earth and the Sun) balances the centripetal force of the orbit to create a fixed pocket where low-mass objects can be “off” to reduce fuel consumption.
This is very useful for science, but these areas can collect other things as well.
Jupiter, for example, has swarms of asteroids that share its orbit at two Lagrangian points that it shares with the Sun. Other planets also have asteroids at Lagrangian points, albeit less so than Jupiter.
It’s unclear exactly how much dust L2 collected, but it would be foolish to expect that the area didn’t collect any of it at all.
Therefore, Webb is specifically designed to withstand the bombardment of dust-sized particles traveling at extremely high speeds. Webb’s design not only included simulations, but the engineers performed effects test on mirror samples to understand what the effects of the space environment were, and to try to mitigate them.
Effects can move mirror segments, but the telescope has sensors to measure mirror positions, and the ability to adjust them, to help correct any distortions that may result.
Mission Control here on Earth can send mods to Webb as well to put the mirrors where they should be. Can even move away from well-known optics meteor showers advance.
And Webb was built with huge margins of error, such that expected physical deterioration over time would not end the job early.
It is probably in a better position than Hubble, which, in low Earth orbit, was subjected not only to the impacts of small meteors, but to the constant bombardment of space debris.
Unlike Hubble, the distance to Webb means technicians won’t be able to physically visit and make repairs. (Not that Hubble was recently serviced; The last such mission was in 2009and will not receive another.)
The micro-meteorites that hit the telescope – sometime between May 23-25 - were a random event. However, the impact was greater than expected, which means that it presents an opportunity to better understand the environment of L2 and to try to find strategies to protect the telescope in the future.
“With Webb’s mirror exposure to space, we predicted that the accidental micrometeorite collision would degrade the telescope’s performance over time.” Optical Telescope Element Director Webb Lee Feinberg says NASA Goddard.
“Since launch, we’ve had four small, measurable hits from micrometeorites that were in line with predictions, and these hits recently are larger than our decline predictions assumed.
“We will use this flight data to update our analysis of performance over time and also develop operational approaches to ensure that Webb’s imaging performance is maximized for many years to come.”
Webb’s first full-color spectroscopic images are still scheduled to arrive on schedule, at 12 July 2022. We can’t wait at all.
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