I was watching the livestream of the SpaceIL team when they were attempting to land Beresheet on the Moon. As near as I can remember, at around an altitude of 15km above the surface, the SpaceIL control team suddenly lost contact with both the spacecraft and NASA in the US. Communications with the lander picked up when the lander was about 2km above the surface and then lost again when they were unable to stop the descent. I don't remember them reestablishing contact with NASA.

Do we know what caused these communication outages? Was it a problem on the Beresheet side or Earth side? (Or am I totally misremembering what happened?)


2 Answers 2


Earlier in the stream they mentioned a glitch or unusual behavior with the IMU, but contact remained.

Later in the burn the engine shutdown unexpectedly and they immediately reset the spacecraft to restore regular operation. This made the telemetry uplink drop out for a moment, before returning. It's not clear to me from the stream if the engine ever started again, and presumably the next signal loss is impact.

  • 1
    $\begingroup$ What's the IMU? $\endgroup$
    – Mithical
    Apr 15, 2019 at 5:27
  • 2
    $\begingroup$ @Mithrandir Inertial measurement unit, a tool used to get the approximate position of the spacecraft. $\endgroup$
    – Antzi
    Apr 15, 2019 at 8:44

A recent update blames it on what I'd call a "command error"; apparently the full ramifications of the command that was sent weren't understood.

Six days after SpaceIL's Beresheet spacecraft crash-landed on the lunar surface, we now have an explanation for what went wrong: A software command uploaded to fix a sensor problem started a chain reaction that shut down the main engines, dooming the lander.

it was the first time SpaceIL flight controllers had experienced an IMU failure during the mission, and they sent an "activation command" to restart the unit. Landsman said an IMU failure on its own would not have caused Beresheet to crash, as the spacecraft has redundant units.

The Post report, as well as a SpaceIL press release from today, said the command kicked off a chain reaction in the spacecraft that ultimately caused an engine shutdown as Beresheet sped towards the lunar surface. Landsman confirmed to me that the command was sent in response to the IMU failure.

Would like more details though. Source.


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