The Mashable.com article TESS is about to become your new favorite NASA mission shows a beautiful photo of the TESS spacecraft in a state that looks like it is nearly ready to launch.

There is a panel with array of what looks like mirrors on one side. What are they for? How do they work? Are they related to or the same as the large panels shown in the question What are these very large, square panels on Inmarsat 5's? or something completely different?

below: TESS on Earth. Cropped from Mashable.com. Credit: NASA

detail of the NASA TESS spacecraft

below: "A look at TESS inside the PHSF at NASA's Kennedy Space Center in Florida." Cropped from Space.com's NASA's TESS Exoplanet-Hunting Mission in Pictures. Credit: Kim Shiflett/NASA

another detail of the NASA TESS spacecraft

below left: TESS on Earth. Mashable.com. Credit: NASA. right: Screenshot of YouTube video NASA’s New Planet Hunter: TESS Click for full size.

NASA TESS spacecraft NASA’s New Planet Hunter TESS

  • $\begingroup$ From the video of tess, it looks like place for antenna... Wasnt able to spot this is the video $\endgroup$
    – zephyr0110
    Apr 10, 2018 at 4:51
  • $\begingroup$ @Prakhar the dish antenna is the large circular thing facing the camera, but it is covered and so you may have missed it. See The appearance of TESS' dish seems to be evolving, what will be the final configuration? for more about that. The panel I am asking about is to the right of the dish, as seen in the image. $\endgroup$
    – uhoh
    Apr 10, 2018 at 7:00
  • $\begingroup$ Ah, right. Interesting. Any guesses from your side? $\endgroup$
    – zephyr0110
    Apr 10, 2018 at 11:10
  • 1
    $\begingroup$ I guess that is not a very sexy part of the spacecraft bus. Every paper I can find just ignores it. I saw a reference in one to "heatpipes and radiators" but not tied back to a diagram. My throwdown answer is radiator but I can't confirm it yet. $\endgroup$ Apr 10, 2018 at 21:26
  • 1
    $\begingroup$ @OrganicMarble I find the use of glass' unique optical properties extremely sexy, but that's just me. $\endgroup$
    – uhoh
    Apr 11, 2018 at 1:58

1 Answer 1


The silvery/mirror like surface on the spacecraft are Optical Solar Reflectors. They are very effective radiators to dissipate the internal heat from the spacecraft. The mirror effect reduces absorption (i.e. reflects visible light where the Sun's intensity is strongest) while the quartz material itself radiates very effectively in the infrared (i.e. radiates heat).

Your guess that these are effectively the same as those on Inmarsat 5 is correct. However Inmarsat, being a geocomm satellite, has significant higher heat dissipation, and therefore needs much larger radiator area - hence the deployable radiator.

Here's an image of a recent GOES satellite with an engineer "admiring themselves in the mirror" to illustrate the widespread use of these devices, be they deployable or not.

enter image description here

  • $\begingroup$ Thanks for your answer and for finding the Wikipedia article! With such an ambiguous name, no wonder nobody found it until now. $\endgroup$
    – uhoh
    Apr 30, 2018 at 2:51

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