"The CGI will test an innovative camera design that enables direct imaging and spectroscopy of exoplanets in close orbits around distant stars." This design holds the potential for the first direct detection of an Earth-like planet.

The Nancy Grace Roman Space Telescope, formerly known as WFIRST, has been in development for nearly a decade under NASA's leadership. Its primary mirror, identical to the Hubble Space Telescope's main mirror, measures 2.4 meters in diameter. The MPIA in Heidelberg, Germany, has built essential opto-mechanical components for the CGI, one of the telescope's two scientific instruments. This instrument will test a novel measurement technique for detecting exoplanets through direct imaging.

"If it reliably images gas planets similar to Jupiter close to their parent stars in the form of a point of light, as expected, the technique could be used to detect and study rocky planets like Earth with future space telescopes."

MPIA's Contribution to the CGI
MPIA has designed and manufactured six flight models and six engineering models of Precision Alignment Mechanisms (PAM). These mechanisms adjust and stabilize optical components, such as mirrors and filters of the CGI during observations. They were meticulously crafted and tested at MPIA's facilities, with support from the company von Hoerner and Sulger in Schwetzingen.

Since spring 2022, Oliver Krause, head of the Infrared Space Astronomy research group, and his team have been delivering these CGI core elements to JPL at the California Institute of Technology (CalTech) in Pasadena, USA. JPL, part of NASA, is involved in the technical development of space probes.

MPIA is a direct partner of NASA and JPL in the CGI project. NASA and JPL were particularly impressed by MPIA's outstanding work on the mechanisms for NIRSpec and MIRI, the central instruments of the James Webb Space Telescope, which have been providing spectacular images and data since mid-2022.

The PAM flight models have been installed in the CGI and extensively tested for space flight. Identical engineering models are used to verify specifications on the ground, including a lifetime model that has performed over 27,000 movements, roughly double the expected load during ground tests and the mission. The CGI was delivered to NASA's Goddard Space Flight Center on May 19, 2024, where it will be integrated into the telescope and undergo further functional and stress tests.

A Camera Design for the Search for a Second Earth
The CGI uniquely combines coronagraphy and adaptive optics for space use. Coronagraphs block out bright objects to make fainter ones visible, a method previously used for detecting exoplanets through direct imaging. However, these masks often cause significant image artifacts, limiting the detection of exoplanets to those at relatively large distances from their parent stars.

To find smaller planets with narrower orbits, the CGI is also equipped with an adaptive optics system, which enhances brightness contrast between the star and the planet. This technology typically reduces disturbances in ground-based telescope images caused by Earth's atmosphere. For the CGI, it mitigates the telescope's optical system distortions.

This capability allows scientists to detect exoplanets closer to their bright parent stars than ever before, visible as bright points of light. The CGI aims to identify planets around stars a billion times brighter, similar to the contrast between Jupiter and the Sun, an improvement by up to a factor of a thousand compared to current capabilities. A built-in spectrograph will facilitate studying the atmospheres of these planets.

Precision Technology
To achieve these goals, the PAMs from MPIA must ensure extreme accuracy and stability in positioning optical elements like filters, coronagraphs, and mirrors over several hours. During operation, the PAMs must not tilt more than 40 milliarcseconds (with 3.6 million milliarcseconds in one degree) over eight hours. This precision allows for detecting a person's height from Los Angeles to Heidelberg.

These stringent requirements and the CGI's complexity make it the most elaborate and expensive scientific instrument to be stationed in space. If initial space tests are successful, the CGI will be available for astronomers to study exoplanets. Success with the CGI could lead to its optimization for future space telescopes, such as the Habitable Worlds Observatory, bringing the direct imaging of a second Earth within reach.

Related Links
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