Near-perfect mirror ready to be mounted in NASA’s Roman Space Telescope

NASA has reached a milestone in the development of its newest telescope, Roman, set to launch in 2025, with the completion of its primary mirror.

The Roman Space Telescope, named after the space pioneer and “mother of Hubble,” Nancy Grace Roman, will investigate distant facets of the universe including seeking to understand dark energy and searching for exoplanets. It will also look for wandering rogue planets, which could be far more abundant in our galaxy than previously thought.

To look at into the depths of space, Roman needs a large primary mirror 2.4 meters across which will allow it to capture a field of view 100 times that of Hubble. That primary mirror has now been completed and polished so finely that the average of the bumps on its surface is just 1.2 nanometers tall.

The Roman Space Telescope’s primary mirror reflects an American flag. Its surface is figured to a level hundreds of times finer than a typical household mirror.
The Roman Space Telescope’s primary mirror reflects an American flag. Its surface is figured to a level hundreds of times finer than a typical household mirror. L3Harris Technologies

“Achieving this milestone is very exciting,” Scott Smith, Roman telescope manager at NASA’s Goddard Space Flight Center, said in a statement. “Success relies on a team with each person doing their part, and it’s especially true in our current challenging environment. Everyone plays a role in collecting that first image and answering inspiring questions.”

The mirror is a key part of a telescope as it directs light to science instruments such as Roman’s Wide Field Instrument, essentially a giant camera, and the Coronagraph Instrument, which can spot distant planets by blocking out the glare from nearby stars. To make sure the data is as accurate as possible, the mirror needs to have a near-perfect finish.

The mirror also needs to withstand the stresses of launch and the space environment, so it is made of special low-expansion glass which doesn’t expand and contract with temperature changes. By reducing the expansion and flex of the mirror, the telescope will be able to pick out more accurate details.

The mirror has been extensively tested alone, and the next step is for the mirror to be tested while mounted in its support structure.

“Roman’s primary mirror is complete, yet our work isn’t over,” said Smith. “We’re excited to see this mission through to launch and beyond, and eager to witness the wonders it will reveal.”

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