GOES-R is scheduled to launch soon and put in geostationary orbit over North America for high bandwidth continuous monitoring of Earth, with only 120 minutes per year interruptions caused by stationkeeping. It will simultaneously monitor the sun with several instruments and of course it's solar panel. The GOES-R Website describes the satellite in detail throughout many pages and links, and two images are shown below.

I assume that over the course of each day, the shaft that supports the solar pannels and sun-pointing insturments rotates 360 degrees relative to the body of the spacecraft. How do all of the wires for power from the pannels and signal and control connections for the sun-pointing instruments not get twisted up and break after a few days of continuous rotation?

Watch the video below to get a perspecive of the size.

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above: screenshot from YouTube video.

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above x2: annotated illustrations of GOES-R spacecraft and its nadir-pointing and sun-pointing instruments.

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    $\begingroup$ Typically power and data are transmitted through rotating joints by the use of slip or roll rings. The biggest example of this I know of are the Alpha Gimbals on the ISS. diamondroll-ring.com/p.php?title=roll-rings_for_outer_space $\endgroup$ Commented Nov 18, 2016 at 18:09
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    $\begingroup$ @OrganicMarble Oh, I see: diamondroll-ring.com/roll-rings_internal_design.html they are literally rolling rings! That sounds much better than brushes, since there is almost no abrasion or friction. Nice!! $\endgroup$
    – uhoh
    Commented Nov 18, 2016 at 18:50
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    $\begingroup$ The alpha joints on the ISS rotate continuously. These joints break the ISS truss into three parts - the center part with all the modules mounted there, and the two outer parts with the solar arrays sprouting out of them. The beta gimbals allow the solar arrays to rotate on their long axes. topcoder.com/iss/files/2012/12/nasa-iss-longeron.jpg SARJs are the alpha gimbals, BGAs are the beta gimbals. $\endgroup$ Commented Nov 18, 2016 at 19:16
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    $\begingroup$ The gamma joints on the ISS are the thermal radiator rotary joints. They, unlike the alpha and beta joints, do not have the capability for continuous rotation, because they have fluid hoses passing through them, that have to get 'unwrapped'. They are also known as the Flex Hose Rotary Coupler and several spares were flown up in the last part of the shuttle program. $\endgroup$ Commented Nov 18, 2016 at 19:37
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    $\begingroup$ The Alpha rings will be the biggest slip rings in space. On Earth, they are used in larger applications, e.g. at the base of battleship gun turrets, in cranes etc. $\endgroup$
    – Hobbes
    Commented Nov 19, 2016 at 14:51

1 Answer 1


Goes-R uses a Slip Ring Assembly to transfer power and communications signals from the rotating solar wing to the stationary spacecraft body. The signals going through the slip ring use the SpaceWire network protocol to minimize the number of connections.

Slip rings come in several different shapes, using brushes, or sliding or rolling contacts to transfer electrical signals.

Rolling contacts are used e.g. for the Alpha joints on the ISS (which support the large solar panels).

Slip rings can contain a large number of contacts. This example has 6 contacts, but the same type is available with 70 contacts.

Diamond-ring rolling contact slipring

You can also get slip rings for hydraulics and radar signals (using waveguides), for example.

Slip rings suffer from electrical noise when rotating: it's very difficult to make perfect contact at all times. The circuits connected by the slip ring have to take this into account.

Slip rings have some advantages over a radio link:

  • a slip ring assy can transfer large amounts of power without polluting the local EM environment.
  • a slip ring is a passive component, far less complex than a transmitter/receiver combination.

The GOES-N data book is an extensive description of GOES-P's predecessor. It contains some information on the use of slip rings in that program. GOES-P uses a different design.

  • $\begingroup$ Wow, this is a really helpful review of slip-ring technology. Thank you for taking the time to write this up so nicely! $\endgroup$
    – uhoh
    Commented May 19, 2017 at 10:35
  • $\begingroup$ I've just asked the follow-up question Why does SpaceWire require nine pins? $\endgroup$
    – uhoh
    Commented May 19, 2017 at 10:54

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