The achievement marks an important milestone for Roman’s mission to investigate dark matter, dark energy and other cosmic mysteries. Even small improvements in optical precision could help the space telescope capture clearer images while surveying vast regions of the universe.

“All of Roman’s extensive survey will rely on the wide-field instrument,” said Dave Hickey, wide-field instrument systems engineer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Many of the main objectives of this mission, such as the study of dark matter and dark energy, would not have been possible without it, so it’s both exciting and extremely relieving to see it working so well.”

NASA tests Roman’s Wide Field Instrument

Following the observatory’s launch, engineers began a comprehensive testing campaign to confirm that every component worked properly both independently and as part of the complete system.

The team first examined the instrument’s 18 detectors, each roughly the size of a post-it note, along with the electronics that operate them. Engineers then evaluated the element wheel, a rotating mechanism that holds filters and other optical components.

These filters allow selected wavelengths of light to reach the detector, separating incoming light into individual colors. This capability will be essential as Roman studies enormous areas of the sky and gathers data about distant cosmic structures.

Engineers next tested the instrument’s internal calibration systems by activating light-emitting diodes, or LEDs. The LEDs act as tunable light sources that can produce different colors and brightness levels in response to commands from Earth.

By measuring how the detectors respond to these controlled signals, scientists can identify differences in sensitivity and make corrections that ensure accurate observations.

The team also tested the instrument’s positioning mechanism. It was moved from a deliberately unfocused position used during launch to a position expected to produce the clearest images. Engineers also examined the thermal control system, which maintains the temperatures required for the equipment to function correctly.

“Calibrating an instrument is like tuning a piano or guitar before a concert,” said Maxim Rizzo, wide-field instrument systems engineer at NASA Goddard. “Tweak everything until it’s exactly how you want it, and then leave the settings alone for consistent performance during use.”

Roman’s optical system was already close to perfect

While one team prepared the Wide Field Instrument, another worked to improve the optical alignment of the entire telescope.

The results were encouraging from the beginning. Roman’s mirrors and other optical components were already positioned with extraordinary precision, so engineers needed to make only minor adjustments.

“Thanks to the extraordinary preparation work done on the ground before launch, the telescope was performing well even before we started adjusting all the mirrors and other optics,” said Matthew Volcker, Roman’s optical systems director at NASA Goddard. “All the testing and modeling work done by Goddard and contractors L3Harris and BAE Space and Mission Systems left only minor modifications needed to align everything to near perfection.”

Reaching this level of precision is especially challenging for a spacecraft. The forces of launch can cause tiny shifts in sensitive equipment, while the conditions in orbit differ significantly from those on Earth. Roman launched on August 30 with an optical system that had been thoroughly tested before leaving the ground.

“Our ground-based experiments could not accurately reproduce the environment Roman would experience in space, including the absence of gravity,” Bolkar said. “There are also slight differences in temperature changes and moisture content. Despite these challenges, recent evaluations showed that ground tests were excellent, with both instruments matching or exceeding predicted performance.”

Engineers moved a mirror by less than the width of a hair

Roman uses a complex arrangement of mirrors and optical components to collect light from distant objects and direct it to two scientific instruments. The light must follow an extremely precise path to produce sharp images.

Even microscopic misalignment can affect how accurately the telescope focuses light. Fortunately, Roman’s optical system had been tuned so precisely that only minuscule movements were required to improve its performance.

“We moved the secondary mirror about one-sixteenth the diameter of a human hair,” said Alden Jarling, a senior optical engineer at NASA Goddard who worked on Roman’s research. “This adjustment fine-tuned the height of the secondary mirror above the primary mirror. If you scale that height to the height of the Empire State Building, the change in height is slightly smaller than if you stacked pennies on top of the tower.”

Although such a movement is nearly impossible to assess on a human scale, adjustments of this size can make a major difference when a telescope is designed to study objects across vast cosmic distances.

The team initially focused on Roman’s coronagraph, which was producing images that were slightly out of focus. The problem was less severe than engineers had expected, making it relatively easy to correct.

The coronagraph now meets the team’s demanding performance expectations. Engineers will continue refining its camera settings and determining the optimal configuration for its deformable mirror, which can change shape to precisely correct incoming light.

In the coming weeks, the research team plans to test the coronagraph’s ability to block unwanted light. This function is essential for observing faint objects located near much brighter sources.

After optimizing the coronagraph’s focus, engineers returned to the Wide Field Instrument to make additional adjustments.

Roman’s image quality beats expectations by nearly 30%

Final measurements produced especially impressive results. Roman’s Wide Field Instrument achieved optical performance nearly 30% better than the team’s predictions.

Before launch, engineers set an image quality requirement of approximately 90 nanometers RMS, or root mean square. This measurement represents the amount of optical error in the system, indicating how far incoming light deviates from an ideal, perfectly focused wavefront.

To put the scale in perspective, 90 nanometers is approximately 1,000 times thinner than a human hair. At such tiny dimensions, even seemingly insignificant defects can reduce the sharpness of an astronomical image.

After the latest modifications, however, engineers measured an optical error of just 63 nanometers RMS—significantly better than the original requirement.

This improvement means Roman can produce sharper images than its designers originally anticipated. The enhanced performance should strengthen the telescope’s ability to conduct detailed observations across vast areas of the sky.

“All the images we get from the Roman space survey will be even clearer than we expected,” Jarling said. “This is a remarkable result of years of careful modeling, precision measurements and testing.”

With both scientific instruments meeting or exceeding expectations, Roman has cleared another important milestone on the path toward routine observations. The results demonstrate the extraordinary precision of the telescope’s design and offer promising prospects for future investigations into the hidden structure and evolution of the universe.