Primary data relay electronics unit on ISS truss fails

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ISS managers are meeting to make a plan to deal with the failure on Saturday of the #1 data relay electronics box on the S0 truss of the station.

The unit, called an MDM, has an identical backup in place so no station operations have so far been effected. However, that backup had failed back in 2014 and required a spacewalk to replace it, so it is not clear to me as yet whether the station has any additional spares available to replace the newly failed unit. If so, it will still require a spacewalk to make the switch.

If there is no spare, they will likely have to ship one up on the next cargo flight, as the MDM is essential for operating the solar panels and radiators as well as the robot arms.



  • Dick Eagleson

    Looks like the CRS-11 trunk is going to get an extra piece of payload. Hope the Dragon isn’t too near it’s mass or volume limit to overly complicate a sudden addition to its manifest, but if anything has to get bumped, that’s life.

    Convenient that this failure happens just before a scheduled resupply mission and not just afterwards.

  • Gealon

    Mmmm, I seem to remember commenting about the startling lack of spare parts back when the 2014 failure occurred. Seems nothing’s changed.

  • Gealon: It appears you did not notice the more recent post on BtB, noting that they have the spare part and are doing a spacewalk today to install it.

  • Gealon

    It would appear you are correct good sir, I had not refreshed the page since the day before I believe. Though I think my original comment still stands, they only have the one spare aboard yes? If this were the true interplanetary spacecraft testbed it’s supposed to be, the station should have a more generalized construction where, as it was stated in the later topic, boards can just be swapped out. At the very least have more then a single spare part if it’s so critical. Perhaps, as it was mentioned in the other topic, having a chip fab aboard would assist in the replacement of malfunctioning hardware. As I recall there is a 3D printer aboard the station but that is for strictly mechanical parts, and ones made out of plastic at that.

  • Edward

    Spare parts is an interesting topic. There is not a lot of space to store spare parts, and they are expensive to deliver, taking up, on the resupply ships, space and weight that could be used for productive items. So a question is: what parts are important enough, urgent enough, and subject to failure enough so that one or more spares are needed on board?

    ISS logistics must be quite an interesting job to have.

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