NASA engineers have moved the secondary mirror of the Nancy Grace Roman Space Telescope by about one-sixteenth of the width of a human hair. The optics of its main camera are now sharper than the team expected.
The telescope launched on 30 August 2026 on a Falcon Heavy rocket. It is heading for a point called L2, about a million miles (1.6m km) from Earth, and will circle that point rather than sit still. The first checks and adjustments are part of about 90 days of preparation before the main work begins.
The gap between two mirrors
Focus is the position where light from a star gathers into a point instead of a blur. On Earth, a camera lens is focused by turning a ring. On Roman, the focus changes with the distance between two mirrors: the secondary mirror moves slightly up from the main one or down towards it.
NASA says that if the telescope were as tall as the Empire State Building, the change would be a little less than the thickness of a US one-cent coin.
Before launch, the team left the alignment mechanism out of focus on purpose so it could withstand the shaking at liftoff. After the camera was switched on, they moved it to the planned best position. The main camera has 18 detectors, each about the size of a sticky note, and all have now been checked.
An optical error of 63 nanometres
The camera was required to have an optical error of about 90 nanometres. The measured error is 63 nanometres. That is about a third less, and NASA calls it "almost 30% better than required". The reports compare the result with the requirement and do not say what the models predicted. A nanometre is a millionth of a millimetre, so the allowed error is about a thousand times thinner than a hair.
The optics worked very well even before the adjustment, said Matthew Bolcar, who is in charge of Roman's optical systems. He linked this to ground tests and models at Goddard and at contractors L3Harris and BAE Systems. Bolcar also noted that conditions in space, such as weightlessness, cannot be fully recreated on Earth.
"All the pictures from Roman's space surveys will be even sharper than we expected," said senior optical engineer Alden Jurling.
Pointing check and first coronagraph images
The pointing system passed its check between 15 and 21 September. Each of the 18 detectors sets aside a small part for its own guide star. The stars' positions are reported about four times a second, so the computer can correct small drifts. The telescope holds steady to better than one hundredth of a thousandth of a degree, for about half an hour during observations with the main camera and up to eight hours with the coronagraph. NASA compares this with aiming a laser at a dime from 240km (150 miles) away.
The coronagraph is the telescope's second instrument. It blocks the light of a star so that planets and dust discs around it can be seen. On 22 September it made its first observation of light from space, a faint star in the Large Magellanic Cloud. The image has a lot of noise because the detectors were kept warmer than their working temperature, to stop contamination from sticking to them. The team cooled them on 27 September, and the instrument imaged a new field with many stars. Scientist Vanessa Bailey called it a "very limited test" that begins a series of increasingly complex steps.
The first coronagraph images were slightly out of focus, but less than the team expected, and the fix was fairly simple. The instrument now meets expectations, but it has not yet imaged a planet.
The team will fine-tune the coronagraph's cameras and its deformable mirrors. It will show the instrument's ability to block light "in the coming weeks". The team will also test a new way of pointing that uses the spectrum of stars instead of a separate instrument.
NASA expects the first Roman pictures by early 2027. Science work begins when preparation ends, and no exact date has been announced.