Industrial Engineering

Precise Motion Helps Rovers Gather Mars Samples, Photos

Precise Motion Helps Rovers Gather Mars Samples, Photos
Assembly Magazine August 2021
By Jim Camillo
https://www.assemblymag.com/articles/96539-precise-motion-helps-rovers-gather-mars-samples-photos

Many suppliers have equipment that has been used on one of the Mars rovers over the past 25 years. But, few companies have equipment on multiple rovers. Auburn, MA-based PI USA is one such company.

On the Curiosity Rover, 16 PICMA P-882–P-888 stack actuators precisely control feeder vibration in the rover’s sample handling system. This system consists of 32 sample chambers (including five that contain fixed references) arrayed around a sample wheel. The chambers are arranged in pairs with one actuator coupling each pair.

During sample collection, mineral powder is fed through a funnel into individual cells. The actuators ensure that the powder is shaken at variable amplitudes and frequencies in the range of 0.9 to 2.2 kilohertz to homogenize particle size or density segregation.

PICMA monolithic piezo actuators are ceramic insulated and have a low operating voltage, with sub-millisecond response time and sub-nanometer resolution. The actuators are fully compatible with ultra-high-vacuum machines. Common applications include nanopositioning, valves and semiconductor equipment.

NASA’s testing of the actuators validated their performance at more than 100 billion cycles, easily qualifying them for use on the Curiosity. Since the rover landed on the red planet in August 2012, all of the actuators have reliably performed under the harshest of conditions.

Another rover experiment, called ChemCam, involves interplanetary laser-induced breakdown spectrometry (LIBS). This noncontact technique uses a powerful, pulsed infrared laser to induce optical emission from surface samples. Each laser pulse produces a visible, sparking flash that is then evaluated by a fiber-coupled spectrometer.

The major advantage of LIBS is it allows for remote testing of a geologic sample. Such testing, however, requires precise focus control of the rover’s telescope.

PI’s miCos MT Series linear positioning stage ensures this precision. Powered by a stepper motor, the space-qualified stage axially positions the telescope’s secondary mirror to accurately collect an optical return from the sample, as well as place the sample within geologic context.

For the Perseverance Rover, which NASA developed several years later, PI provided a more-compact miCos MT Series stage. This one controls the focus of the telescope on the rover’s SuperCam.

Two algorithms help determine the optimum focus position. One algorithm uses a continuous wave laser to illuminate the target, while a photodiode at the back of the telescope records the fluctuating intensity of the positioning stage.

The other algorithm is based on photos taken by a Remote Micro-Imager. This device looks for the maximum contrast between adjacent pixels in a small field of view at the center of the image.

MT micro stages are especially suited for integration in limited space environments. They can be used for precision high-resolution positioning of small components such as fibers, optical components and laser diodes. The stages are equipped with zero-backlash ball bearings and a precision lead screw.

Perseverance’s SuperCam is placed on top of the rover’s Remote Sensing Mast to easily observe targets at far distances. It uses a color filter to provide color information of all photographed surfaces, and features a four-times-higher-resolution detector than the ChemCam.

SuperCam also uses additional algorithms and a more-dynamic complementary metal-oxide semiconductor chip to improve image quality.