Roman’s coronagraph took its first images, holding aim steadier than a dime at 150 miles

Engineers at NASA’s Goddard Space Flight Center say the Nancy Grace Roman Space Telescope can now hold its pointing to better than 1/100,000 of a degree, a precision the agency describes as “roughly comparable to focusing a laser beam on a U.S. dime from about 150 miles (about 240 kilometers) away.” The day after those guidance tests wrapped up, the telescope’s coronagraph took its first observation.

Begoña Vila, Roman’s guiding instrument systems lead at Goddard, put the stakes plainly: every observation depends on staying pointed at the right patch of sky long enough to collect an image, and that can mean minutes or hours.

Fine-guidance tests from September 15 to 21

NASA’s September 30 mission blog post lays out the sequence. The team ran the fine-guidance system from September 15 through 21 and measured stability better than 1/100,000 of a degree. Roman has two instruments with different needs, so the blog gives two durations: half an hour at a time for Wide Field Instrument observations, and eight hours at a time for Coronagraph Instrument observations.

The dime is NASA’s comparison, and the blog words it as comparable, not as a record that beats it. The same post says the team intends to keep tuning the system until the equivalent distance stretches from about 150 miles to roughly 230 miles (370 kilometers), a sign that the current figure is a starting point.

Vila’s description of the job explains the number. The coronagraph works by positioning a mask so that a star’s glare is blocked while a much dimmer planet or dust disk stays visible nearby, which is why its observations are the ones NASA rates for the full eight hours of steadiness. NASA’s coronagraph page adds that the instrument’s electronics process 1,000 images per second to compensate for spacecraft jitter.

For scale, 1/100,000 of a degree is 0.036 arcseconds, a sliver of sky far finer than anything a person could pick out by eye. NASA’s own comparison translates that sliver into a coin-sized target at a distance of 240 kilometers.

Light on a Large Magellanic Cloud star, September 22

The coronagraph’s first image followed on September 22. JPL’s account of the test image says the instrument, which the Jet Propulsion Laboratory in Southern California designed and built, activated its cameras in space for the first time after powering on September 1 and finishing system checks in the middle of the month.

Vanessa Bailey, a coronagraph scientist at JPL, said the result “confirms that the instrument can produce a focused image,” and called it “a very limited test that kicks off a methodical process of increasingly complex tasks.” The target was a faint star in the Large Magellanic Cloud, a small neighbor galaxy of the Milky Way, and the detectors were deliberately kept warmer than their operating temperature to avoid contamination. A second observation on September 27, after the detectors were cooled for better sensitivity, showed multiple stars.

Deformable mirrors and a photon-counting detector

The Roman Coronagraph Instrument is a technology demonstration that JPL describes as the first active coronagraph to fly in space, meaning deformable mirrors adjust to correct optical imperfections as it works. NASA’s coronagraph systems page says those mirrors are about 2 inches across, each carrying more than 1,600 independent actuators, and can be shaped to accuracies smaller than the diameter of a helium atom. Its electron-multiplying detector runs at about minus 130 degrees Fahrenheit and can pick out individual photons.

The instrument sits behind the same 2.4-meter primary mirror as the rest of the observatory, which NASA’s observatory overview says will operate at the Sun-Earth L2 point. Roman is still in the commissioning phase that NASA’s commissioning page describes as turning on, adjusting and calibrating systems on the way there, and the page cautions that the schedule is subject to change.

Those supporting systems explain why the first image was treated as a test, not a science result. The coronagraph page lists wavefront sensing that measures optical irregularities and directs corrections, masks that must be positioned exactly, and thermal control that holds components stable to within millikelvins. Bailey’s description of the September 22 image as a limited first step in a methodical sequence matches that list: each of those pieces has to be exercised in space before the instrument attempts the faint targets it was built for, and JPL’s page puts the start of its observations in early 2027.

The next job named in the September 30 blog is spectral guiding, a technique that steers by wavelength patterns rather than by a point-like star image. NASA says the team plans to validate it in the coming weeks, which would add a second way of holding the coronagraph on target besides the star-tracking method used so far.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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