page_title: Timeline of Opportunity (rover)
section_title: Shoulder troubles
hierarchical_section_title: Timeline of Opportunity (rover) / Mission timeline / 2005 / Shoulder troubles
caption_attribution_description: English: Mars rover Opportunity examines en:Heat Shield Rock on Sol 349 of its mission, at approximately 13:27:37 Mars local solar time. Left Front Hazard Camera Non-linearized Downsampled EDR acquired on Sol 349 of Opportunity's mission to Meridiani Planum at approximately 13:27:37 Mars local solar time.
context_page_description: Opportunity is a robotic rover that was active on the planet Mars from 2004 to 2018. Launched on July 7, 2003, Opportunity landed on Mars' Meridiani Planum on January 25, 2004 at 05:05 Ground UTC, three weeks after its twin Spirit, also part of NASA's Mars Exploration Rover Mission, touched down on the other side of the planet. While Spirit became immobile in 2009 and ceased communications in 2010, Opportunity exceeded its planned 90 sol duration of activity by 16 years, 91 days. Opportunity continued to move, gather scientific observations, and report back to Earth until 2018. What follows is a summary of events during its continuing mission.
  Opportunity started in Eagle crater in 2004, literally landing inside on the crater basin, then it travelled outward making its way to Endurance crater. After this it went to Victoria crater, all the way making many panoramas, measurements, studying rocks and smaller craters, even what are thought to be meteorites. It then traveled to Endeavour crater, where it has been making its way south along the Western rim.
context_section_description: The "shoulder" joint of Opportunity's arm has had troubles since Sol 2 (January 25, 2004), the rover's second day on Mars. Engineers discovered that the heater on the shoulder azimuth joint, which controls side-to-side motion of the robotic arm, was stuck in the "on" position. Closer investigation revealed that the on-off switch had probably failed during assembly, test, and launch operations on Earth. Fortunately for Opportunity, the rover was equipped with a built-in safety mechanism called a "T-stat box" (thermostatic switch) that provided protection against overheating. When the shoulder azimuth joint, also known as Joint 1, got too hot, the T-stat switch automatically opened and temporarily disabled the heater. When the joint got cold again, the T-stat closed. As a result, the heater stayed on all night but not all day.
  The safety mechanism worked until Opportunity approached the first winter on Mars. As the Sun began to retreat lower in the sky and solar power levels dropped, it became clear that Opportunity would not be able to keep the batteries charged with a heater draining power all night long. On Sol 121 (May 28, 2004), rover operators began using a procedure known as "deep sleep," during which Opportunity disconnected the batteries at night. Deep sleep prevented the stuck heater (and everything else on the rover except the clock and the battery heaters) from drawing power. When the Sun came up the next morning and sunlight began hitting the solar arrays, the batteries automatically reconnected, the robotic arm became operational, the shoulder joint warmed up, and the thermostatic switch opened, disabling the heater. As a result, the shoulder joint was extremely hot during the day and extremely cold at night. Such huge temperature swings, which tend to make electric motors wear out faster, were taking place every sol.
  This strategy worked for Opportunity until Sol 654 (November 25, 2005), when the Joint-1 azimuth motor stalled because of increased electrical resistance. Rover operators responded by delivering higher-than-normal current to the motor. This approach also worked, though Joint 1 continued to stall periodically. Typically, the rover's handlers simply tried again the next sol and the joint worked. They determined that the Joint-1 motor stalls were most likely due to damage caused by the extreme temperature cycles the joint experienced during deep sleep. As a precaution, they started keeping the robotic arm out in front of the rover overnight, rather than stowing it underneath the rover deck, where it would be virtually unusable in the event of a Joint-1 motor failure. They stowed the arm only while driving and unstowed it immediately at the end of each drive.
caption: Opportunity extends its arm to analyze Heat Shield Rock on Sol 349 (early 2005).
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