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The question Why is TESS' high gain antenna made of undulating BLACK fabric rather than metal? has had three bounties, and is probably the recipient of this sites longest answer.

My personal pet theory was that the undulations were a diffractive surface for the RF so that the receiver would be at an RF focus but not an optical focus, since TESS' attitude may unavoidably point the dish toward the Sun. However, now TESS is shown with a presumably RF-transparent cover over the antenna.

You can see lots of detailed photos of the construction of TESS and its individual components in the recent Spaceflight 101 page Photos: TESS Spacecraft Assembly & Testing

Here's a screen shot of a really excellent technical video of the mission Transiting Exoplanet Survey Satellite (TESS).

screen shot Transiting Exoplanet Survey Satellite

I just saw the Mashable article TESS is about to become your new favorite NASA mission which links to the new NASA video NASA’s New Planet Hunter: TESS and in this animation there is what looks like a fabric cover over the antenna, which is also shown in the photograph of TESS below, seemingly close to ready for launch.

Question: The appearance of TESS' dish seems to be evolving, what will be the final configuration? Will there be a fabric cover over the antenna once deployed? Will it still have that undulating black fabric on the dish under the white fabric cover? Was the cover over the dish added to the design recently?

screen shot NASA’s New Planet Hunter

below: TESS on Earth. From Mashable. Credit: NASA

NASA TESS spacecraft

below: from Solar Panels Opened on NASA’s TESS Satellite. Photo credit: NASA/Leif Heimbold

TESS solar arrays

below: from Spaceflight Now SpaceX poised to launch planet-hunter. "The Transiting Exoplanet Survey Satellite is prepared for encapsulation inside the Falcon 9 rocket’s nose shroud." Credit: NASA/Kim Shiflett

TESS on payload adapter

below: TESS' dish antenna, cropped from Spaceflight 101. Credit: TESS Project: NASA / MIT Lincoln Lab / Orbital ATK

enter image description here

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  • $\begingroup$ I don't think it's evolving, they just stuck some thermal insulation foil over the antenna. $\endgroup$ – Hobbes Apr 16 '18 at 15:52
  • $\begingroup$ @Hobbes my working theory is that the ripples are diffractive, allowing for RF to be focused while diffusing sunlight (a little bit, but not really like the pattern here), only because I have no other explanation). A second cover would moot that function, and so the roughly factor of two loss could be recovered, though perhaps it's not needed. $\endgroup$ – uhoh Apr 26 '18 at 7:12
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I'm afraid there is nothing terribly exciting about the "ripples". They are just artifacts of the manufacturing of the graphite composite fabric that is used for the shell of the dish. The shape is a plain vanilla reflector (axis displaced reflector, if you must know) with no important surface features. And as was mentioned, before launch the whole reflector was covered with an RF-transparent sun shade thermal blanket to help control its temperature.

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    $\begingroup$ Carlos, welcome to Space Exploration Stack Exchange! Thanks for contributing to the site. Does this answer come primarily from experience? If so, could you elaborate on how you came by this information? If you have a citable source, please include it in the answer. $\endgroup$ – called2voyage May 3 '18 at 18:49
  • $\begingroup$ I asked the engineer responsible for the antenna :) Unfortunately, I don't have a citable source beyond that. $\endgroup$ – Carlos N May 3 '18 at 19:23
  • $\begingroup$ That's good enough, folks around here are just curious. :) $\endgroup$ – called2voyage May 3 '18 at 19:51
  • $\begingroup$ @CarlosN you might consider also adding this (or a similar) answer to the question that it answers; Why is TESS' high gain antenna made of undulating BLACK fabric rather than metal?. There is one extremely long answer there that hasn't convinced me is actually an answer at all. Also, Why is graphite composite used instead of rigid metal? Since maintaining the specific shape is absolutely critical, it does not seem like an ideal candidate for trying to save weight by using materials that can't hold their shape! $\endgroup$ – uhoh May 4 '18 at 5:08
  • $\begingroup$ @CarlosN According to this answer the antenna is designed for about 26 GHz, which has a wavelength of only about 11.5 millimeters. These ripples are huge height excursions on that scale, particularly because they are in reflection. A 2 mm peak-to-peak ripple results in a 4mm peak-to-peak shift in path length, which about 0.35 λ and would present a sizable loss in efficiency and a seriously degraded and structured radiation pattern. It is extremely hard to believe that the spacecraft would be flown with these unintentional "artifacts". $\endgroup$ – uhoh May 4 '18 at 5:25

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