NASA Says a Tiny Space Rock Has Impacted The James Webb Space Telescope

The James Webb Space Telescope may not be as isolated as it appears in its new home far from Earth.

Because the telescope's pocket of space isn't completely vacuum, the inevitable has happened: a tiny piece of rock, a micrometeorite, has collided with one of Webb's mirror segments.

But there's no need to be concerned. The telescope's designers are well aware of the rigors of space, and Webb has been meticulously engineered to resist them.

"We always knew that Webb would have to weather the space environment, which includes harsh ultraviolet light and charged particles from the Sun, cosmic rays from exotic sources in the galaxy, and occasional strikes by micrometeoroids within our Solar System," says NASA's Goddard Space Flight Center engineer and technical deputy project manager Paul Geithner.

"We designed and built Webb with performance margin – optical, thermal, electrical, mechanical – to ensure it can perform its ambitious science mission even after many years in space." 

Webb's position in L2

Webb is located 1.5 million kilometers (slightly under one million miles) from Earth in the L2 area.

It's a Lagrange or Lagrangian point, where the gravitational interaction between two circling bodies (in this example, the Earth and the Sun) balances with the orbit's centripetal force to provide a stable pocket where low-mass objects may be "parked" to save fuel.

This is great for research, but these areas may also be used to collect other items.

Swarms of asteroids, for example, share Jupiter's orbit in two of the Lagrange points it shares with the Sun. Other planets, but with fewer asteroids than Jupiter, have asteroids in their Lagrange points.

It's unknown how much dust L2 has accumulated, but it would be naive to assume that the region has accumulated none at all.

As a result, Webb was designed to endure being bombarded by dust-sized particles flying at extraordinarily high velocities. Webb's design included not just models, but also test impacts on mirror samples to see what the effects of the space environment may be and how to reduce them.

Impacts can cause mirror segments to shift, but the telescope features sensors that can detect and alter mirror locations, allowing it to correct for any distortions that may occur.

Mission Control on Earth can also transmit changes to Webb to put the mirrors back in their proper places. Its optics can even be pre-programmed to avoid known meteor showers.

Webb was also developed with large error margins to ensure that the predicted physical deterioration does not bring the mission to a premature conclusion.

After a service mission, orbital debris impact damage to Hubble panels was discovered. (NASA)

It's certainly in a better position than Hubble, which has been subjected to not just micrometeorite strikes but also a steady bombardment of space junk while in low-Earth orbit.

Unlike Hubble, however, the distance to Webb prevents personnel from directly visiting and doing repairs. (Not that Hubble has lately been serviced; the last such mission was in 2009, and it will not be getting another.)

The micrometeoroid that collided with the telescope — somewhere between May 23 and 25 – was a completely random occurrence. However, the damage was more than predicted, presenting a chance to learn more about the L2 environment and develop ways to preserve the telescope in the future.

"With Webb's mirrors exposed to space, we expected that occasional micrometeoroid impacts would gracefully degrade telescope performance over time," says Webb optical telescope element manager Lee Feinberg of NASA Goddard.

"Since launch, we have had four smaller measurable micrometeoroid strikes that were consistent with expectations and this one more recently that is larger than our degradation predictions assumed."

"We will use this flight data to update our analysis of performance over time and also develop operational approaches to assure we maximize the imaging performance of Webb to the best extent possible for many years to come."