In its new home far from Earth, the James Webb Space Telescope may not be as alone as it seems.
The pocket of space occupied by the telescope isn’t a total vacuum – and now the inevitable has happened, with a tiny piece of rock, a micrometeorite, colliding with one of Webb’s mirror segments .
But there is no need to panic. The engineers who built the telescope are keenly aware of the rigors of space, and Webb was carefully designed to withstand them.
“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 exotic sources in the galaxy, and occasional micrometeoroid strikes in our solar system,” says Paul Geithner, Engineer and Technical Assistant Project Manager from NASA’s Goddard Space Flight Center
“We designed and built Webb with a margin of performance – optical, thermal, electrical, mechanical – to ensure that it can accomplish its ambitious scientific mission even after many years in space.”
Webb occupies a region 1.5 million kilometers (just under 1 million miles) from Earth called L2.
This is called a Lagrange or Lagrange point, where the gravitational interaction between two orbiting bodies (in this case the Earth and the Sun) balances with the centripetal force of the orbit to create a stable pocket where low mass objects can be “parked” to reduce fuel consumption.
This is very useful for science, but these regions can also collect other things.
Jupiter, for example, has swarms of asteroids sharing its orbit in two of the Lagrange points it shares with the Sun. Other planets also have asteroids in their Lagrange points, although rather less than Jupiter.
It’s unclear exactly how much L2 dust collected, but it would be foolish to expect the region to collect none at all.
Thus, Webb was specifically designed to withstand the bombardment of dust-sized particles moving at extremely high speeds. Not only did Webb’s design involve simulations, but engineers performed impact tests on sample mirrors to understand what the effects of the space environment might be and attempt to mitigate them.
Impacts can move mirror segments, but the telescope has sensors to gauge the position of its mirrors and the ability to adjust them to help correct any resulting distortions.
Mission control here on Earth can also send adjustments to Webb to put the mirrors back where they should be. Its optics can even be diverted from known meteor showers in advance.
And Webb was built with massive margins of error, so the expected physical degradation over time won’t end the mission prematurely.
It’s probably in a better position than Hubble, which in low Earth orbit has been subjected not just to micrometeor impacts, but to a constant bombardment of space junk.
Unlike Hubble, however, the distance to Webb means technicians won’t be able to physically visit and carry out repairs. (Not that Hubble has been fixed recently; the last mission of this type dates back to 2009and he will not receive another.)
The micrometeoroid that hit the telescope – between May 23 and 25 – was a random event. The impact, however, was greater than expected, which means it represents an opportunity to better understand the L2 environment and try to find strategies to protect the telescope in the future.
“With the Webb mirrors exposed to space, we expected that occasional micrometeoroid impacts would gracefully degrade the telescope’s performance over time,” says Lee Feinberg, Elements Manager for the Webb Optical Telescope from NASA Goddard.
“Since launch, we have had four smaller measurable micrometeoroid impacts which were in line with expectations and this one more recently which is larger than our assumed degradation predictions.
“We will use this flight data to update our performance analysis over time and also develop operational approaches to ensure that we best maximize Webb’s imaging performance for many years to come.”
Webb’s first color and spectroscopic images should always arrive on schedule, the July 12, 2022. We absolutely cannot wait.