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Modern communications satellite in GEO are big, majestic beasts. They are quite large and voluminous. They can sport quite an array of antennas and handle huge bandwidths and multiple communications functions.

I've often wondered what they at least roughly look like inside.

I like to think of them as the big black box in space that Agent Dale Cooper experienced in the episode Part 3 (Twin Peaks), that they have a door and you can go inside and work on stuff if needed.

Intellectually I assume that's no the case; they are not built to be boarded, don't have doors or airlocks and probably very little wasted space.

But is the non-bus area of these spacecraft a sealed volume with commercial racks which are full of modules with blinking LEDs and switches, or is just a bunch of sealed boxes, each filled with custom circuit boards.

Question: What do large, modern communications satellites in GEO look like inside? I'm sure construction details are sensitive and proprietary, but is there anything that's been shared publicly about at least roughly some kind of layout? Do they have doors? Do they have pressurized spaces inside, or compartments?


cropped & brightened from Twin Peaks What's Up with the Beginning of Part 3? Season 3 Episode 3; Mauve Zone

cropped & brightened from Twin Peaks What's Up with the Beginning of Part 3? Season 3 Episode 3; Mauve Zone

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    $\begingroup$ I’ll continue looking for larger satellite examples. But in the meantime here are the designs of a micro satellite: directory.eoportal.org/web/eoportal/satellite-missions/… $\endgroup$
    – und3niable
    May 19 at 2:17
  • $\begingroup$ @und3niable cool, thanks! It is possible that some old Spaceflight 101 article might have something but it would take some time to search through it, and it's currently under a substantial reconstruction phase. $\endgroup$
    – uhoh
    May 19 at 2:19
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    $\begingroup$ Is something like this what you are looking for? youtu.be/ksVNIRY-_nY $\endgroup$
    – und3niable
    May 19 at 2:20
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    $\begingroup$ Sounds good, I’ll do some more research and formulate a full answer soon enough $\endgroup$
    – und3niable
    May 19 at 2:24
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    $\begingroup$ I'm hoping the answer is a creamy nougat center. $\endgroup$
    – DrSheldon
    May 19 at 23:24
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The basic visible design is usually

  • two Y walls, North and South that carry the baulk of the heat generating equipment, payload or platform, though the latter is usually concentrated at the -Z end.
  • at least two floors, one near the -Z end one near the +Z (Earth pointing) end. There could be additional floors at the +Z end for payload equipment that needs a proximity to the Earth face. The platform equipment is grouped around the -Z floor.
  • the +-X (East/West) sides are less uniform and could be panels or left with no structural element.
  • regardless of the structural elements the +-Z and +-X sides would be blanketed except for where equipment protrudes

Internally the basic load bearing structure is usually a combination of a central thrust cylinder and shear panels. The central cylinder connects the floors. There is probably an example somewhere that doesn't have a central cylinder but it is typical that there is one. The shear panels are interior vertical panels that connect the central cylinder, floors and Y walls.

Propellant tanks are usually arrange either:

  1. stacked inside the central cylinder
  2. four, with one in each quadrant around a small central cylinder
  3. a combination of the above

Interior structure is usually painted black, as are the bulk of internally mounted equipments. Propellant tanks are usually blanketed.

Doing a search for "satellite name" + "AIT" or "clean room" might show up some other part assembled photos. The first image is a screenshot from about 51 seconds into one of the videos on this link of Thor 7. The outside of a Y wall is visible at the left of the image with antenna feed horns visible protruding from under blankets at the top (+Z) end. On of the -+X walls is open on the right of the image and one can vaguely see that its all black in side but the central cylinder and Y walls can be seen at least.

The grey items protruding from the edges of the Y walls are radiation cooled TWTAs and it is probable the business-end of these devices that can be seen in rows on the inside of the far Y wall. enter image description here

The image below is the first drawing I could find. The sharper eyed amongst you will notice that its not a geostationary communications satellite but regardless it does serve to illustrate the concepts above.

  1. The floors, central cylinder and shear walls are all visible.
  2. The solar panels are shown folded flat against the Y walls and aren't that easy to distinguish and this design has panels on the +-X walls (which would be East West on a geostationary satellite).
  3. Note in this case the apogee kick motor is shown as a solid motor, this is universally not the case these days and would either be a bipropellant engine in the same place or some external arrangement of electric thrusters.

GPS satellite exploded view

Finally, to answer the sub-questions:

I think "doors" are rare. It is more likely that there would be access gaps in panels that are covered in blankets for flight.

There would be next to no pressurised items except perhaps for reaction/momentum wheels, unless you are talking about one of the older Russian designs where the whole interior compartment is pressurised.

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    $\begingroup$ You forgot to indicate where the door is :-) Thanks for a profoundly thorough answer! $\endgroup$
    – uhoh
    May 19 at 23:37
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    $\begingroup$ Specific to a communications satellite, I recall seeing a photo of one under construction a long time ago, and there were heat pipes and waveguides everywhere. Like, crammed full of waveguides. No idea how old the picture was or if it's reflective of how they're built today though, what with phased array antennas becoming more of a thing. $\endgroup$
    – Tristan
    May 20 at 1:25
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    $\begingroup$ @Tristan I don't know if all of Inmarsat 5 F4's separate feed horns have individual waveguides or coax, but it certainly must look pretty cool inside. $\endgroup$
    – uhoh
    May 20 at 22:21

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