NASA's newest space telescope is hard at work despite an ongoing instrument glitch and continuing small micrometeoroid strikes.
The James Webb Space Telescope (JWST or Webb for short) has been in space for nearly 10 months and has been gathering science observations since July. Even this early in the observatory's tenure, it is already offering scientists a new view of the universe and performing better than expected. And that work is continuing apace despite a finicky wheel and a drizzle of impacts from tiny space rocks.
"We knew we were going to be getting micrometeoroid hits throughout the mission," Eric Smith, NASA project scientist for JWST, said Monday (Oct. 17) during a presentation to NASA's Astrophysics Advisory Committee. "We expected this, we're seeing it and we're still in good shape."
Webb is unusually vulnerable to such impacts, Smith noted. Unlike the Hubble Space Telescope, for example, JWST's primary mirror isn't housed in a protected tube. Instead, it's exposed to space and stretches across 21 feet (6.5 meters), which Smith compared to a catcher's mitt against more protected observatories.
At this point, JWST has experienced a total of 33 micrometeoroid events, according to Smith's slides. But the most damaging one came before JWST began science observations; in late May, a particularly large micrometeoroid struck the observatory's mirror, leaving its mark on one golden hexagon. The team estimates that a strike of that size should occur about once a year, Smith said.
"So we got that at month five," he said. "We haven't seen another one yet, so it's still consistent with the statistics that we expected."
Smith noted that, at the current impact rate, Webb will still be meeting its five-year performance requirement 10 years into the mission. Scientists estimate that the observatory has enough fuel to operate for 20 years.
Although the team isn't too worried about the impacts, scientists are considering coordinating observations so that the mirror isn't facing straight into the direction the observatory is traveling to reduce micrometeoroid impacts, like turning away from a particularly heavy gust of wind. However, this measure would complicate the already-intricate process of piecing together JWST's observing schedule.
"It doesn't change, really, whether a target is visible; it just changes when it's visible," Smith said.
Meanwhile, the team is also addressing a glitch in the observatory's Mid-Infrared Instrument (MIRI). The instrument contains a grating wheel to focus on specific wavelengths of light when conducting medium-resolution spectroscopy, one of MIRI's four observing modes. JWST team members noted friction in the wheel in late August and paused medium-resolution spectroscopy to investigate the issue.
The team is now working to understand the cause of the issue, then will develop a response plan to be approved by an anomaly review board NASA convened for the incident.
"Once they're confident they understand why they measured this increased friction, they'll work out what to do next," Smith said. "They do anticipate recovering this, though."