SPHEREx put to the test in KASI thermal vacuum chamber

In this timelapse movie, scientists and engineers can be seen preparing NASA’s SPHEREx space telescope for tests inside a vacuum chamber at Caltech that simulates the environment of space. The process took more than two weeks and involved more than 20 people. The mission, which is planned to launch no later than 2025, will survey hundreds of millions of galaxies near and far. At the start of the movie, the telescope’s three so-called V-groove chillers can be seen as rings at the bottom of the structure. These chillers cool SPHEREx by radiating heat from the instrument to the cold of space (the telescope’s visible- and infrared-light detectors are very sensitive to temperature, so the telescope and detectors have to be kept very cold). Technicians can be seen wrapping gaps in the V-groove area of the telescope in a foil material so that light does not enter from the back during the tests. The telescope is then loaded into a special thermal vacuum chamber, which was built by team members at the Korean Astronomy and Space Science Institute (KASI). The chamber simulates the chilly temperature of space, allowing the team to test the telescope’s focus on the detectors. The V-grooves and telescope are cooled by active systems in the chamber for the tests. Near the end of the movie, a custom-made window is installed in the chamber that is made of sapphire and coated in gold. The window allows the team to project a simulated star into the chamber while reflecting heat from the laboratory. A series of measurements will test that the telescope is in focus and stays in focus through the shaking of launch. The highly reflective sapphire window also provided the team with an opportunity for a “selfie,” seen at the end of the movie.