Holding a telescope perfectly still in space is harder than it sounds. This week, NASA’s Nancy Grace Roman Space Telescope showed it can do just that, and then its Coronagraph Instrument opened its eyes to cosmic light for the very first time.

A steady hand for deep exposures

From September 15 to 21, the mission team put Roman’s fine-guidance system through a series of tests, and it passed. This system is what lets the observatory lock onto its targets and stay there. A small portion of each of the 18 detectors in Roman’s main instrument, the Wide Field Instrument, is assigned to rapidly watch a separate guide star, a star whose position is precisely known. Roman’s attitude control system points the spacecraft in the right direction, and the guidance data then helps hold it steady so it doesn’t drift. Without it, Roman’s images would not be as crisp.

This matters because a single deep exposure can last anywhere from minutes to hours. The fine-guidance system reports guide star positions about four times every second, allowing the attitude control system to make tiny corrections. The tests confirmed that Roman can stay stable to better than 1/100,000 of a degree, for half an hour at a time during Wide Field Instrument observations, and for eight hours at a time during the longer Coronagraph observations.

To picture that precision, it is roughly like keeping a laser beam focused on a U.S. dime from about 150 miles (240 kilometers) away. The team plans to fine-tune the system to stretch that analogy to about 230 miles (370 kilometers).

A new way of guiding

Roman also has something new up its sleeve. Unlike other space telescopes, it has no separate guider instrument. Instead, it will guide on spectra, the detailed patterns of wavelengths in a star’s light, rather than just tracking a star’s point-like appearance. Since Roman is already built to measure spectra for science, the same information can be used to position the telescope precisely. The team expects to validate this spectral guiding mode in the coming weeks.

The coronagraph’s first glimmer

On September 22 and 27, the team tested the fine-guidance system together with the Coronagraph Instrument. This instrument is a technology demonstration designed to block the glare of a star so that faint planets and dusty disks around nearby stars can be seen. It is demanding work: even tiny vibrations or pointing errors can let starlight leak through and wash out a planet that may be a very small fraction as bright as its star. Fortunately, the coronagraph has its own internal stability process, making it steadier still than the Wide Field Instrument.

The instrument woke up on September 1 and went through electronic and mechanical checkouts in the middle of the month. For its first observation, the team adjusted the focus and pointed at a faint star in the Large Magellanic Cloud, a neighboring galaxy. The image contained extra “noise” because the detectors were deliberately kept warmer than their final operating temperature, which helps make sure no contamination sticks to them.

The second observation, on Sunday, September 27, confirmed the pointing. This time the detectors were cooled for better sensitivity, and the team aimed at a new patch of the Large Magellanic Cloud where many stars were expected in a single frame. That is exactly what they saw.

We were kicking the tires, making sure light goes through the system.

Vanessa Bailey, Roman Coronagraph Instrument scientist, NASA JPL

What comes next

These were deliberately limited tests. They confirm that the coronagraph can produce a focused image, and they begin a step-by-step process of increasingly complex tasks that will prepare the instrument for its future observations of planets and dusty disks around nearby stars. Roman is still in commissioning, so more checkouts, including the spectral guiding validation, are still to come.

Sources