Thermal Strategy for the Phoenix Robotic Arm Deployment

The Mars Scout Phoenix Lander successfully landed in the Martian northern latitude on May 25, 2008. The Robotic Arm, which was designed to dig and to transfer soil samples to other Lander instruments, contained a number of actuators that had specific operational windows on the Martian surface due to the bearing lubricant. The deployment of the Robotic Arm was planned for Sol 2 (Mars days are referred to “Sols”). A few weeks before Mars landing, the Robotic Arm operations team learned that a strict flight rule had been imposed. It specified that the deployment shall be accomplished when the actuators were at or above −25°C since the deployment activity was qualified with the actuators at −40°C. Furthermore, the deployment plan identified a window of opportunity between 13:00 Local Solar Time (LST, equivalent to dividing the Sol into 24 equal Martian hours) and 15:30 LST. Previous analytical work was focused on sizing electrical heaters to warm-up the actuators for early morning operation (8:00 LST) in the worst-cold thermal environment. The actuator minimum operating temperature for surface operations was −55°C. For mission planning purposes, an assessment of the need or lack thereof for thermal conditioning of the Robotic Arm actuators was

necessary. This paper will first present the strategy for determining whether conditioning was necessary including the use of initial flight temperature data. The paper will, then, include the results of the thermal conditioning analysis using extreme and expected surface thermal environments and how the deployment was conducted from a thermal design perspective.