The Thermal Design Evolution of the Phoenix Robotic Arm

Phoenix, NASA's first Mars Scouts mission, will be launched in 2007 and will soft-land inside the Martian Arctic Circle, between north 65° and 72° North latitude, in 2008 to study the water history and to search for habitable zones. Similar to the IDD (Instrument Deployment Device) on the Mars Exploration Rovers (MER), Phoenix has a Robotic Arm (RA) which is equipped with a scoop to dig into the icy soil and to deliver the soil samples to instruments for scientific observations and measurements. As with MER, the actuators and the bearings of the Phoenix RA in a non-operating condition can survive the cold Martian night without any electrical power or any thermal insulation. The RA actuators have a minimum operating allowable flight temperature (AFT) limit of -55°C, so, warm-up heaters are required to bring the temperatures of all the RA actuators above the operating AFT limit prior to early morning operation. The complications of sizing the warm-up heaters of RA actuators, especially the wrist actuator, include the wide range of thermal environments experienced by the arm, the available heater locations that are constrained by the mechanical design, and the warm-up duration requirements. In spite of these challenges, a feasible RA warm-up heater design was achieved which satisfied all the requirements with minimal operational complexity. This paper presents the evolution of the warm-up heater design and the design implementation.