The test chamber of NASA’s new cosmic mapper makes a grand entrance

This illustration shows a cross-section of NASA’s upcoming SPHERE mission, revealing the spacecraft’s telescope and detectors surrounded by three glowing photon shields that shield them from the sun. Credit: NASA/JPL-Caltech

After three years of design and construction, a month-long boat ride across the Pacific Ocean and a lift from a 30-ton crane, the custom test chamber for NASA’s next SPHEREx mission has finally reached its destination at Caltech’s Cahill Center for Astronomy and Astrophysics. Pasadena.

Scheduled to launch no earlier than June 2024, SPHEREx (short for Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) will create a unique map of the cosmos that will contain hundreds of millions of objects, including stars, galaxies, star-forming regions and other cosmic wonders. Unlike any previous map, it will provide images of individual objects, as well as a spectrum for each point in the sky. Spectra can hold a treasure trove of information about cosmic objects, including their chemical composition, age, and distance to distant galaxies.

With this dynamic graph, scientists will be able to answer questions about what happened shortly after the big bang, the prevalence of vital molecules like water ice in the planet-forming regions of our galaxy, and how galaxies originated and evolved over the life of the universe.

But for SPHEREx to make this possible, the telescope must not only be able to withstand the rigors of space, but also thrive in it. This is where the custom test chamber comes in. The size of a small SUV and made of stainless steel, the cylindrical chamber was built by the Korean Astronomy and Space Science Institute (KASI), a SPHEREx mission partner. It will be used to test SPHEREx’s detectors (essentially its cameras) and optics (the system that collects light from the cosmos).

cold light

Run by NASA’s Jet Propulsion Laboratory, SPHEREx will detect infrared light, which human eyes cannot detect. Sometimes called thermal radiation, it is emitted by hot objects, including stars and galaxies, as well as telescope instruments. The chamber is therefore designed to cool the detectors to about minus 350 degrees Fahrenheit (about minus 200 degrees Celsius) to ensure that their own heat will not overwhelm the light of the objects they are supposed to observe.

But first, the SPHEREx team must test whether the detectors are up to speed. This is determined by their distance from the optics, in the same way that moving a magnifying glass closer or further from your eye brings objects into focus or out of focus. The team will need to get the distance between the detectors and the correct optics to within 0.0003 inches (7.5 micrometers), or about one-tenth the width of a human hair. To do this, they will aim the optics and detectors at a projected source of infrared light located outside the chamber window, which is sapphire because the glass blocks infrared. The source will serve as a surrogate for the objects that SPHEREx will observe in space, and the resulting image will tell engineers if the spacing is correct.

Credit: NASA

“A number of factors can influence the focus position of our instrument when it reaches operating temperature,” said SPHEREx instrument scientist and Caltech researcher Phil Korngut. “It’s absolutely essential that we get this thing fine tuned before we fly, and the only way to do that is to do specific cryogenic optical testing in the environment provided by the KASI chamber.”

The chamber is also customized to calibrate the SPHEREx spectrometer, which will provide a spectrum of every point in the sky.

Long trip

In 2018, KASI launched a mission called NISS (Near-infrared Imaging Spectrometer for Star formation history), which has similarities to SPHEREx. Working on NISS gave the KASI team the right experience to build the custom chamber.

After traveling by ship from Korea to Long Beach, California, the chamber was transported north to Caltech. Too tall to fit through the main entrance of her new home, she had to move under the building: a 30-tonne crane lifted a removable section of an adjacent road, then lowered the test chamber, along with its components, in one height – a ceiling-mounted, windowless reception hall, informally known as “the Crypt”. The chamber was then transported to the SPHEREx test lab, where it will remain for approximately 18 months until hardware testing is complete.

“Not only the SPHEREx team at KASI, but the whole Korean astronomy community is very interested in SPHEREx data and its scientific purposes,” said Woong-Soeb Jeong, SPHEREx Principal Investigator for KASI. “Thus, KASI’s participation in the SPHEREx mission should have a great impact on research in our astronomy community. This legacy will be of great help in the development of our own medium or large class space telescope in the future. ”

NASA is finalizing plans for its next cosmic mapper

More information:
For more details on the SPHEREx mission, visit:

Provided by Jet Propulsion Laboratory

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