NASA Testing the Webb Telescope's MIRI Thermal Shield
The Mid-Infrared Instrument, known as MIRI, will fly aboard NASA's James Webb Space Telescope. The MIRI has a heat shield that is designed to protect the vital instrument from excess heat. At the time of the photo, the thermal shield was about to go through rigorous environmental testing to ensure it can perform properly in the extreme cold temperatures that it will encounter in space. This shot shows the Helium Shroud being lowered onto the shield for a test in one of NASA Goddard's vacuum chambers. The Helium Shroud is nicknamed the "Doghouse."
On the Webb telescope, the pioneering camera and spectrometer that comprise the MIRI instrument sit inside the Integrated Science Instrument Module flight structure, that holds Webb's four instruments and their electronic systems during launch and operations.
Webb is designed to obtain images and spectra in infrared light that is invisible to the human eye. As a consequence, the Webb telescope and ISIM must be cooled to a very low temperature (-383 F or -230 C) in order to avoid being blinded by their own infrared emission. The MIRI operates over longer infrared wavelengths than the other Webb instruments and, as a result, must be made approximately 35 degrees colder than the rest of the ISIM. The MIRI’s thermal shield is critical to achieving this lower temperature for the MIRI.
Surrounding the shield are tangles of cables that provide power to heaters and lead to temperature sensors that will help control and assess how the shield intercepts heat. Parts of the MIRI thermal shield are covered with aluminized thermal blanketing material to keep them cooler.
Inside the thermal vacuum chamber, all of this hardware was tested in an environment that mimics the strong vacuum and cold temperatures that Webb will experience in space. After things were set up in the test chamber, Goddard technicians sealed it up, evacuated all the air and lowered the temperature of the equipment to 18 to 23 kelvins (-427 F or -255 C).
The two black cylindrical parts at the front are protective pads covering two of six composite struts that will attach to ISIM; the pads will be removed before flight.
"These struts are designed to limit the conducted heat flow into the shield from ISIM," said Mark Voyton, MIRI instrument manager at NASA Goddard. "Underneath the shield is a black rectangular piece, part of the thermal shroud that mimics the MIRI shield's environment."
Engineers then used a Q-meter, a device designed to maintain temperature and measure the heat flow, to monitor the instrument. The test took three weeks to complete.
The James Webb Space Telescope is the successor to NASA's Hubble Space Telescope. It will be the most powerful space telescope ever built and will observe the most distant objects in the universe, provide images of the first galaxies formed, and see unexplored planets around distant stars. The Webb telescope is a joint project of NASA, the European Space Agency and the Canadian Space Agency.
Read more about the MIRI heat shield tests: www.nasa.gov/mission_pages/webb/news/miri-test.html
Text Credit: Laura Betz
Image Credit: NASA/Chris Gunn
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