2
$\begingroup$

The NASA Spaceflight article Arianespace press onward with dual-passenger Ariane 5 launch shows a photo of Intelsat 39 during testing. The dish reflectors are strangely shaped:

  1. rather than being round or square, their edges are irregular, like the coast line of an island
  2. the surface contours also appear bent and irregular, rather than having a pure parabolic shape.

and they are densely covered in little white dots, at least during this testing phase.

Question: Why the strange shape (especially the irregular edges), and what are all of those little white dots?


Intelsat 39 Intelsat 39

Intelsat 39 Intelsat 39

Image source and credit: Intelsat

Intelsat 39


Here's another example of "white dots", these kinds of images are common.

enter image description here

Source

$\endgroup$
  • $\begingroup$ Different but related question: How do commercial broadcast satellites in GEO produce such carefully shaped signal footprints? $\endgroup$ – uhoh Aug 6 at 22:37
  • 2
    $\begingroup$ I'm pretty sure the irregular shape is for beam shaping. They're contoured to specifically cover specific regions and not waste transmission power on empty patches like oceans. While also just a guess, the white dots are very reminiscent of a phased array system or they could be sensors to measure and tune the system after deployment. $\endgroup$ – Dragongeek Aug 7 at 0:34
  • $\begingroup$ @Dragongeek thanks! That's a lot of sensors to put on a passive reflector. I think there's a single feed horn that faces each one of these reflectors, no? What would be tuned in that case? $\endgroup$ – uhoh Aug 7 at 1:23
  • $\begingroup$ @uhoh - both of those satellites use Digital Beam Forming with Patch Antennas. Each patch is driven separately, and phase is used to steer and focus the beam. The antennas are flat, with thermal blankets, so I don't know why the dots (there are more dots than 'patches'). $\endgroup$ – amI Aug 8 at 10:14
  • 1
    $\begingroup$ @amI I'm pretty sure the large non-flat things are reflectors, illuminated by feed horns or antenna arrays at the "top" of the satellite (facing towards us and not so visible). Low res images here and here. It's possible they are using an electronic array instead of horns to illuminate the reflectors, but I don't think these big things are arrays. It would be handy to have a source one way or the other though. $\endgroup$ – uhoh Aug 8 at 11:37

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.