The main mirror of the Nancy Grace Roman Space Telescope, which collects and focuses light from near and far cosmic objects, has been completed. With this mirror, Roman captures breathtaking space views with a field of view 100 times larger than Hubble images.
“It is very exciting to reach this milestone,” said Scott Smith, Roman Telescope Manager at NASAGoddard Space Flight Center in Greenbelt, Maryland. “Success depends on a team in which each person does their part. This applies in particular to our currently challenging environment. Everyone has a role to play in collecting that first picture and answering inspirational questions. “
Roman will look through dust and across long stretches of space and time to examine the universe with infrared light that human eyes cannot see. The level of detail these observations reveal is directly related to the size of the telescope mirror, as a larger surface area collects more light and measures finer features.
Roman’s main mirror is 2.4 meters in diameter. While it’s the same size as that Hubble Space TelescopeThe primary mirror is less than a quarter of the weight. Thanks to significant technological improvements, Roman’s mirror weighs just 186 kilograms.
The primary mirror, along with other optics, will send light to Roman’s two scientific instruments – the wide-field instrument and the coronagraph instrument. The first is essentially a huge 300-megapixel camera that offers the same sharp resolution as Hubble over nearly 100 times the field of view. With this instrument, scientists can map the structure and distribution of invisible dark matter, study planetary systems around other stars, and study how the universe evolved to its present state.
The coronagraph demonstrates a technology that blocks the glare from stars and enables astronomers to directly image planets in their orbit. If coronagraph technology works as expected, planets nearly a billion times weaker than their host star will be seen, allowing detailed studies of giant planets around other suns.
Roman will observe from a vantage point about 1.5 million kilometers from Earth in the opposite direction to the sun. Roman’s barrel shape helps block unwanted light from the sun, earth, and moon, and the spacecraft’s remote location helps keep the instruments cool and ensure weak infrared signals can be detected.
Since the primary mirror will be exposed to different temperatures between production and testing on Earth and operations in space, it is made of a special ultra-low-expanding special glass. Most materials expand and contract when temperatures change. However, if the shape of the primary mirror changes, the telescope will distort the images. Roman’s mirror and its support structure are designed to reduce bending, thus maintaining the quality of the observations.
The development of the mirror is much more advanced than it was at this stage as the mission uses a mirror that has been transferred to NASA by the National Reconnaissance Office. The team modified the shape and surface of the mirror to achieve Roman’s scientific goals.
The newly surfaced mirror has a layer of silver less than 400 nanometers thick – about 200 times thinner than a human hair. The silver coating was specially chosen for Roman because it reflects near infrared light. In contrast, the Hubble mirror is coated with layers of aluminum and magnesium fluoride to optimize the reflectivity for visible and ultraviolet light. Likewise the James Webb Space TelescopeThe mirrors are gold-coated in order to do justice to longer-wave infrared observations.
Roman’s mirror is so finely polished that the average bump on its surface is only 1.2 nanometers high – more than twice as smooth as the mission requires. If the mirror were scaled to the size of the earth, these bumps would be only a quarter of an inch high.
“The mirror was made exactly to the optical recipe of the Roman Space Telescope,” said Bonnie Patterson, program manager at L3Harris Technologies in Rochester, New York. “Because it is so much more fluid than required, it offers even greater scientific benefit than originally planned.”
Next, the mirror will be mounted at L3Harris for additional tests. It has already been extensively tested in cold and ambient temperatures. The new tests are carried out with the mirror attached to the support structure.
“Roman’s primary mirror is done, but our work isn’t over yet,” said Smith. “We are excited to be with this mission through to launch and beyond, and look forward to the wonders it will reveal.”
The Nancy Grace Roman Space Telescope is administered in Goddard, which includes NASA’s Jet Propulsion Laboratory and Caltech / IPAC in Pasadena, California, the Space Telescope Science Institute in Baltimore, and a science team of scientists from research institutions in the United States.