James Webb Space Telescope picture shows noticeable damage from micrometeoroid strike

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James Webb Space Telescope picture shows noticeable damage from
micrometeoroid strike
By Elizabeth Howell published about 3 hours ago

NASA is unsure how much of an effect space rocks will have on Webb's
lifetime after the event 'exceeded prelaunch expectations of damage.'


comparison shows bright spot from micrometeoroid impact
On the right, the state of the James Webb Space Telescope on June 21,
2022, after an unexpectedly large micrometeoroid strike and subsequent
responses, compared to the expected state on the left. (Image credit:
NASA/STScI)
A small space rock has proven to have a big effect on NASA's newly
operational deep-space telescope.

A micrometeoroid struck the James Webb Space Telescope between May 22
and 24, impacting one of the observatory's 18 hexagonal golden mirrors.
NASA had disclosed the micrometeoroid strike in June and noted that the
debris was more sizeable than pre-launch modeling had accounted for.
Now, scientists on the mission have shared an image that drives home the
severity of the blow in a report(opens in new tab) released July 12
describing what scientists on the mission learned about using the
observatory during its first six months in space.

Happily, in this case the overall effect on Webb was small. That said,
the report outlines the investigation and modeling that engineers are
undertaking to assess the long-term effects of micrometeroids on Webb.

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Based on fuel usage, the telescope should last 20 years in space. But
scientists aren't sure how much of an effect micrometeroid strikes will
have upon its operations, the report authors stated.

Micrometeroids are a known danger of space operations, and facing them
is by no means new to scientists; the International Space Station and
the Hubble Space Telescope are among long-running programs that are
still operational despite occasional space rock strikes. However, Webb's
orbit at Lagrange Point 2 about 1 million miles (1.5 million kilometers)
away from the Earth may change the risk profile considerably.

Webb engineers first detected deformations on the primary mirror during
the commissioning period during the alignment (or wavefront sensing)
phase, which put the 18 segments of the hexagonal mirror into the best
position to capture light.

These first six strikes met pre-launch expectations of rate as they came
in at a rate of once per month, the report stated. Moreover, some of the
resulting deformations are correctable through mirror realignments. But
it's the magnitude of one of these six strikes that caused more concern,
the paper noted, as it caused a significant blemish to a segment known
as C3. The strike in late May "caused significant uncorrectable change
in the overall figure of that segment," the report stated.

In this case, however, the overall impact to the mission is small
"because only a small portion of the telescope area was affected."
Seventeen mirror segments remain unblemished and engineers were able to
realign Webb's segments to account for most of the damage.

Jupiter and its moon Europa, left, are seen through the James Webb Space
Telescope’s NIRCam instrument 2.12 micron filter.

Jupiter and its moon Europa, left, are seen through the James Webb Space
Telescope’s NIRCam instrument 2.12 micron filter. (Image credit: NASA,
ESA, CSA, and B. Holler and J. Stansberry (STScI))
Engineers are still modeling how frequently such events will occur. "It
is not yet clear whether the May 2022 hit to segment C3 was a rare
event," the team wrote. By "rare," they said it is possible that they
happened to get a high-energy impact that should statistically happen
only once every few years.

Alternatively, it may be that Webb is "more susceptible to damage by
micrometeoroids than pre-launch modeling predicted," the team wrote.
Modeling is ongoing to estimate the hazardous population of
micrometeoroids and to figure out remedies, such as restricting pointing
direction.

One remedy could be minimizing the amount of time Webb points directly
into its orbital direction, "which statistically has higher
micrometeoroid rates and energies," the team wrote.

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Main mirror performance is assessed by how much it deforms starlight,
according to Astronomy magazine(opens in new tab), and measured using
what scientists call wavefront error root mean square. When Webb's
mission began, the affected C3 segment had a wavefront error of 56
nanometers rms (root mean square), which was in line with the 17 other
mirror portions.

Post-impact, however, the error increased to 258 nm rms, but
realignments to the mirror segments as a whole reduced the overall
impact to just 59 nm rms. For the time being, the team wrote Webb's
alignment is well within performance limits, as the realigned mirror
segments are "about 5-10 nm rms above the previous best wavefront error
rms values."

For now, engineers are keeping an eye on potential future
dust-generating events such as in 2023 and 2024, when Webb is expected
to fly through particles left behind by Halley's Comet, according to
Nature(opens in new tab).

NASA's meteoroid environment office at the Marshall Space Flight Center
in Huntsville, Alabama is modeling the impact risk to Webb associated
with Halley. NASA officials have also emphasized during recent media
briefings that the micrometeroid issue has their full attention, Nature
added.

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Elizabeth Howell
Elizabeth Howell