CCD CAMERAS: CCD scrutinizes Martian happy face

Images of Crater Galle on Mars, named after a German astronomer and informally known as the “happy face” crater, were taken in April using CCD detector technology by e2v (Essex, England) in the high-resolution stereo camera (HRSC) on board the European Space Agency (ESA) Mars Express spacecraft (see figure). The HRSC obtained images of the Martian surface with a ground resolution ranging between 10 to 20 m/pixel. The images of this 230 km diameter impact crater are mosaics created from five individual strips, each tens of kilometers wide.

The HRSC mission includes imaging the entire planet in 3-D for topography in full color at a surface resolution on the order of 10 m. Selected areas will be imaged at a resolution of 2 m to provide tight pointing accuracy by combining images at the two different resolutions. “As the 2 m resolution image is nested in a 10 m resolution swath, we will know precisely where we are looking,” said Gerhard Neukum, HRSC principal investigator from Freie Universität Berlin (Berlin, Germany). “The 2 m resolution channel will allow us to pick out great detail on the surface.”

For space applications, CCDs are generally large-area devices housed in radiation-tolerant structures, according to Joanne Bugg of e2v. A back-illumination process thins the active CCD to less than 10% of the thickness of a human hair to provide high quantum efficiency, low readout noise, and stable device performance (particularly useful for low-light scientific applications). Front illumination is used for the company’s “startracker” devices, however, because of the need to image at high light levels.

A startracking camera on the ESA’s Venus Express, which began orbiting Venus in April, scanned the stars as the craft approached the planet, helping to guide the craft to Venus. The imaging device in the startracker will help to pinpoint targets to support the study of the chemistry and composition of Venus’ hot, high-pressure atmosphere. Data collected over approximately 500 Earth days will provide detail on the planet’s surface and history and should help scientists to understand more about climate change on Earth.

MRO images

In other Mars-related news, the CCD sensors in NASA’s HiRISE (High Resolution Imaging Science Experiment) telescopic camera on the Mars Reconnaissance Orbiter (MRO) captured their first test images of Mars on March 24-two weeks after the spacecraft entered its orbit around the Red Planet. The first color images were captured on April 6. Of 25 CCD image sensors on the NASA Mars probe, 14 are time-delay integrated devices arranged in a long imager format to generate the required very wide image.

The MRO is currently orbiting Mars and will gradually reduce its orbit over the next six months. Once it has reached its optimum location, it will begin scientific investigations, relying on the CCD image sensors to help determine the Red Planet’s water and ice history. The detailed reconnaissance will also allow NASA to identify suitable landing zones for future planned robotic explorers and to establish whether the planet would support future human outposts.