SPACE EXPLORATION


A still image from video taken during the descent, in the moments before Perseverance touched down on 18 February g


but we [Cmosis] did have a heritage in providing imagers for space,’ Meynants added. His own history with designing CMOS


sensors for space exploration began in the 1990s while working for Imec as a researcher. He was involved in a number of projects for the European Space Agency (ESA), and some of those sensors ended up in space. Te imager onboard the Visual Monitoring Camera – nicknamed the Mars Webcam – on the Mars Express is a chip Meynants developed during his PhD at Imec, and it’s still operational. Te Mars Webcam – it has a resolution


similar to that of a standard 2003 computer webcam – was installed to confirm that the Beagle 2 lander had successfully separated from Mars Express back in 2003. After it had done its job it was switched off. Several years later, the camera was reactivated to gather images of Mars, both for public engagement activities and now for science, because although it has a low spatial resolution it has


a wide field of view, so it can track events happening in Mars’s atmosphere over time. Meynants said the Mars Webcam


sensor was initially made as a technology demonstrator, to show that CMOS sensors could be used in space – CMOS sensors are more tolerant to radiation exposure than CCDs, which tend to suffer from charge transfer degradation over time. Cmosis was also involved in projects


for ESA, for a docking camera to guide spacecraft docking with space stations or satellites, for instance. Te company had also worked on projects for JPL and Nasa in the past. Te cameras on Perseverance have three


main improvements over those that flew on Curiosity, say the JPL scientists in the paper. Firstly, the Cmosis CMV20000 sensors are colour chips, which gives better contextual imaging capabilities than the monochrome predecessors. Te second improvement is that the cameras have a wider field of view – 90° x 70° as opposed to 45° x 45° – which


12 IMAGING AND MACHINE VISION EUROPE APRIL/MAY 2021


means only five overlapping images are needed to create a 360° panoramic view (Curiosity needed 10 images to achieve the same effect). Te third improvement is that the 20-megapixel sensors can resolve greater detail than the older model. Meynants also made the point that


CMV20000 is a global shutter sensor. Te rover moves around the surface of Mars largely autonomously using six hazard avoidance cameras (controllers on Earth can’t make real-time decisions to drive the rover, because of the time delay in sending signals to and from Mars). All the data is acquired synchronously on a global shutter sensor, which ‘is a benefit for any kind of autonomous driving algorithm’, Meynants explained. ‘You don’t need to worry about rolling


shutter problems,’ he continued. ‘You can ensure all six cameras acquire images at the same time.’ With a rolling shutter sensor, exposure times can be synchronised but every row


@imveurope | www.imveurope.com


Nasa/JPL-Caltech


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