2 Martian applications is revealed by the appearance of the “Surface-sampler boom motor” in the list of  “Top Ten Problems” for the Viking development program between Feb 1973 and Sept 1974 (Ezell and Ezell 1984, p. 253).  After Viking there was a long pause until the Mars Pathfinder landed with the small Sojourner rover in 1997 which contained 11 maxon RE16 brushed motors. The Sojourner rover covered about 100 m before the lander communication link failed, thereby ending the mission after nearly 3 months. In covering the 100 m in just under 3 hours of driving time the drive motors rotated approximately 0.5 million times (with another 0.5 million during Earth based testing) with no indication of motor problems (Braun 1998).  Following the success of the Mars Pathfinder mission, two larger and much more capable rovers were flown on the Mars Exploration Rover (MER) missions that landed the rovers Spirit and Opportunity on Mars in 2003. Each rover contained 39 maxon motors for drive and steering functions, solar array deployment, camera mast actuators and the actuators for the science arm joints. Two different motor types were used, a modified RE25 as can be found in maxon’s standard program and a RE20 that was specially developed for the MER program. The success of these missions is well known and as of January 2012 Opportunity was still active and had driven nearly 35 km over the previous 8 years.  For the follow on MSL mission (launched in 2011), due to the increased distances the rover was expected to cover, brushless motors were selected. The development of these motors and associated gearboxes proved much more complex than expected and, as has been well documented in the press, ultimately led to a two year delay in the launch, emphasizing again the complexity involved in specialist motor design.   Selection of Motor Types for the ExoMars Application 

The ExoMars program (as originally conceived by ESA) envisaged many motors of numerous types being used for various different functions on the rover, a summary of which is shown in Table 1. For the purposes of the development program being reported on here, the requirements for the Drilling and Sampling mechanism, hereafter “Drill”, were considered. Where possible the RE20 and RE25 brushed motors that were used on the MER missions were used in the original design. However, three applications in the drill required new motor sizes or types. These were the Drill mandrel clamp which has to fit within the diameter of the drill bit (see Figure 1) and hence is limited to Ø13 mm, the main drill drive  Table 1: List of motor applications on the ExoMars rover  Function Motor type Quantity  on rover  Wheel Drive RE 20-25 6  Steering Drive RE 20-25 6  Deployment Drive RE 20-25 6  Camera Mast Pan Axis RE 20-25 1  Camera Mast Tilt Axis RE 20-25 1  Drill Positioner Translation RE 20-25 1  Drill Positioner Rotation RE 20-25 1  Drill Positioner Jettison RE 20-25 1  Drill Translation EC22long 1  Drill Rod Mag Rotation RE 20-25 1  Drill Rod Mag Clamp RE 20-25 1  Drill Rod Lower Clamp RE 20-25 1  Drill Mandrel (main drive) EC40 1  Drill Mandrel Clamp RE13 1  Drill Tool RE13 1 

SPDS=Sample Preparation & Distribution System   Function Motor type Quantity  on rover  SPDS CSTM RE 20-25 1  SPDS BSD RE 20-25 1  SPDS Jaw actuation EC22 1  SPDS De-block actuation RE 20-25 1  SPDS Position/Rotary  Motion RE 20-25 1  SPDS Dosing Mechanism RE 20-25 2  SPDS Carousel RE 20-25 1  Solar Array Deployment RE 20-25 1  Battery Isolation Switch RE13? 2  Life Marker Chip (LMC) Instrument Inlet Valve EC14fl 4  LMC Bellows pump EC8 4  LMC Rotary Valve RE13 4  Mars Organic Molecule Analysis (MOMA) Instrument RE10 2