Curiosity Mastcam Filter Wheel
The Mast Camera, or Mastcam, aboard NASA's Curiosity Mars rover is built with two cameras – the left has a 34 mm focal length; the right, a 100 mm focal length. Behind each lens is a rotating wheel (circled in pink) arranged with filters. In addition to providing color images of the rover's surroundings, the cameras and their filters help scientists determine from afar the composition of rocks by the wavelengths of light, or spectra, they reflect in different colors.
Figure A is an illustration of the color filter wheel. The rectangle between the clear and green filters at top indicates where the wheel became stuck; the red arrow shows the direction the mission was trying to nudge the wheel to return it to the clear filter, which is its standard setting. The mission has also attempted to rotate the filter wheel in the opposite direction, as indicated by the yellow line, in order to see if it's obstructed in that direction as well.
The filter wheel is part of a spur-and-pinion mechanism, with the spur teeth around the filter wheel. The actuation uses a small motor that drives the pinion gear both forward and backward. Despite having been commanded at more than twice its normal torque, this motor has been unable to move in the counterclockwise direction.
If unable to nudge the wheel back to the clear filter, the mission would rely on the higher resolution 100 mm right camera as the primary color-imaging system. The camera needs to take nine times more images than the left to cover the same area, which could affect how the team scouts for science targets and rover routes. The ability to observe detailed color spectra of rocks from afar would also be degraded.
Curiosity was built by NASA's Jet Propulsion Laboratory, which is managed by Caltech in Pasadena, California. JPL leads the mission on behalf of NASA's Science Mission Directorate in Washington. Malin Space Science Systems in San Diego built and operates Mastcam.