Mars Rover Curiosity: motion control from PI and PI miCos

Endless tests and qualifications had to be passed before the precision positioning equipment was sent on its long journey to Mars. Failure was not an option, but cost definitely was an issue and budgets are tighter now than in the early days of space exploration. Manufacturers with the best commercial off-the-shelf products (COTS), proven quality systems and the ability to make the necessary modifications for the tough space requirements are high on the list when it comes to providing the ingredients for a 21st century space mission.

CheMin Instrument: piezo stack actuators for sample feed and preparation

PI Physik Instrumente's contribution to the Mars mission, the PI Ceramic monolithic piezo actuators (PICMA) were put to use in the Chemistry and Mineralogy instrument (CheMin). CheMin is an X-ray diffraction-capable mineralogy instrument whose purpose is to determine if water was present in the formation of Martian rocks and soil.

A sample-handling system is required to feed mineral powder samples through a funnel into the individual sample cells. The powder in the tunable sample cells must be shaken at variable amplitudes and frequencies in the range of 0.9-2.2kHz to homogenise particle size or density segregations. The precisely controlled vibrations are generated by PICMA multilayer piezo actuators from PI Ceramic. These ceramic-encapsulated actuators emerged after rigorous tests by NASA's JPL as the highest reliability piezo stacks commercially available. Multiple samples passed 100 Billion cycles of life testing with no failures, maintaining greater than 96 per cent of their performance at the end of the test.

ChemCam and the MT-40 Autofocus Positioning Stage by PI miCos

The instrument equipped with the PI miCos precision motorised positioning stage is called ChemCam (Chemistry and Camera instrument), consisting of a laser-induced breakdown spectrometer and a high-resolution imaging camera. ChemCam determines, through laser-based remote pretesting, which rocks in the vicinity of the rover (distances up to 9m) warrant a closer examination with in-situ instruments. The high-power laser beam evaporates the rock and the light emitted from the plasma is analysed with the spectrometer (follow this link for further information).

A specially modified and space-qualified MT-40 linear positioning stage from PI miCos focuses the analysing system at the desired distance by translating the secondary mirror of the telescope. Due to violent shocks and vibration during launch and landing, every component in the stage, from the stepper motor to the crossed roller bearings and limit switches, had to be closely examined and optimised to eliminate the possibility of failure or performance loss. For fast and precise focusing, high resolution and linearity are required and backlash has to be controlled tightly - not an easy task given the very wide operating temperature range of the instrument. Modelling and thermal compensation were used, as well as special vacuum-compatible lubricants for all moving parts. In the end the modified stage passed all the tests, and the decision to go with a COTS part for cost control reasons proved right.

Shortly before Curiosity left the Earth in November 2011, miCos joined the PI family of companies. Together they are now ready to take on any precision positioning challenge, in air, under high vacuum conditions on Earth and in locations as remote as Mars. For further details, go to www.pi-usa.us.