The primary mirror of the Nancy Grace Roman Space Telescope, which will gather and focus light from near and far cosmic objects, has been completed. Roman can capture stunning views of space using this mirror with a field of view 100 times greater than Hubble images.
The primary mirror, measuring 2,4 meters across, sends light to the two science instruments of Roman - the Coronagraph Instrument and the Wide Field Instrument.
Roman will gaze through the dust and across wide swaths of space and time to observe the universe using infrared light, which is not visible to human eyes. The amount of detail these observations will uncover is directly related to the size of the mirror of the telescope since a bigger surface picks up more light and finer features are measured.
From a vantage point, Roman will observe about 1.5 million km away from Earth in the opposite direction to the Sun. The barrel-like shape of Roman will help block unnecessary light from the Sun, Earth, and Moon and the distant location of the spacecraft will help to keep the instruments cool, making sure it can detect barely perceptible infrared signals.
Since it will undergo a variety of temperatures during production and testing on Earth and space operations, the primary mirror is made of an ultralow-expansion glass Most materials change shape as temperatures change but if the primary mirror changes shape, the images from the telescope will be blurred. The mirror of Roman and its system of support are built to minimize flexing that will maintain the accuracy of its observations.
The mirror progress is much further advanced than it would normally be at this point as the project leverages a mirror that has been moved from the National Reconnaissance Office to NASA. The team changed the form and surface of the mirror to meet the missions of the Roman telescope.
The freshly resurfaced mirror sports less than 400-nanometer silver coating - about 200 times thinner than a human hair. For Roman, the silver coating was chosen explicitly because of how well it reflects near-infrared light. In comparison, Hubble's mirror is coated with aluminum and magnesium fluoride layers to maximize the visible and ultraviolet reflectivity of light. Likewise, the mirrors of the James Webb Space Telescope have a gold coating appropriate for their longer wavelength infrared observations.
The mirror of Roman is so finely polished that the average bump on its surface is only 1.2 nanometers tall - more than twice the smoothness expected by the expedition. If the mirror were sized to be the size of the Planet, those bumps would only be a quarter of an inch wide.
"Roman's primary mirror is complete, yet our work isn't over," said Scott Smith, Roman telescope manager at NASA's Goddard Space Flight Center. "We're excited to see this mission through to launch and beyond, and eager to witness the wonders it will reveal."
