LCROSS Anomaly

From: Derek C Breit (
Date: Tue Aug 25 2009 - 19:56:48 UTC

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    Spacecraft Anomaly
    Mon, 24 Aug 2009 09:58:30 PM MDT
    Upon starting an early morning communications pass on Aug. 22, 2009, the
    Lunar Crater Observation and Sensing Satellite (LCROSS) mission operations
    team discovered the spacecraft had experienced an anomaly.
    According to spacecraft data, the LCROSS Internal Reference Unit (IRU)
    experienced a fault. The IRU is a sensor used by the spacecraft's attitude
    control system (ACS) to measure the orientation and trajectory of the
    spacecraft. The anomaly caused the spacecraft ACS to switch to the Star
    Tracker Assembly for spacecraft positional information and caused the
    spacecraft's thruster to fire excessively, consuming a substantial amount of
    fuel. Initial estimates indicate that the spacecraft still contains
    sufficient fuel to complete the full mission.
    LCROSS mission operations declared a 'spacecraft emergency' and were
    allocated additional communications time on the Deep Space Network. The team
    conducted procedures to mitigate the problem and were able to restart the
    IRU and reduce fuel consumption to a nominal level. Automatic operations
    procedures also were implemented to minimize the possibility of another IRU
    anomaly from occurring while the spacecraft is out of contact with the
    ground. Since the re-start, the IRU has not experienced any additional
    The team continues to actively assess and mitigate the situation and is in
    contact with the manufacturers of the IRU and star tracker to investigate
    the root cause of the problems. Mission managers remain optimistic the
    LCROSS mission can reach its successful conclusion with projected impact at
    the lunar south pole currently set for 4:30 a.m. PDT on Oct. 9, 2009.
    LCROSS is a low-cost, highly risk-tolerant, fast-tracked mission of
    opportunity that was co-manifest with the Lunar Reconnaissance Orbiter. Both
    spacecraft launched from Cape Canaveral, Fla., on June 18, 2009. The main
    LCROSS mission objective is to confirm the presence of water ice in a
    permanently shadowed region near a lunar pole.
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