ESC keynoter addresses Curiosity and Mars Science Laboratory

The Curiosity rover and Mars Science Laboratory program were the focus of an Embedded Systems Conference keynote address titled “Anatomy of Mars: Challenges in Time and Space for Spacecraft,” presented Wednesday by Luke Dubord, Avionics Subsystem Engineering, Flight Electronics and Software Systems, Autonomous Systems Division, NASA JPL.

“Any embedded system starts with the environment, wherever you are,” Dubord said. He presented an illustrated map of Mars from the 1600s showing a lush planet with plenty of water carried by canals. From a more modern perspective, Mariner 4 returned pictures showing a Martian surface not so exciting. The Viking program provided pictures from the surface.

In addition to lacking canals and lush vegetation, Dubord said, Mars is really cold, with a mean temperature of -63°C with lows of -143°C and highs of 35°C. And atmospheric pressure is low—about one hundredth of Earth’s. Those conditions can be mimicked on Earth. But the gravity on Mars is one-third of Earth’s, and while we can create temperature and pressure extremes in Earth-bound laboratories, “we can’t fake gravity,” he said. JPL can test bit and pieces, but the project executes for the first time in the real environment. “There is no chance of repairing your system, except to upload new software, which is a powerful thing,” he said, but the hardware must work.

Further, launch windows present a deadline that can’t be missed. You can’t afford to miss the two-week window that occurs every two years, a limit set by the universe that can’t be rescheduled to accommodate delays, Dubord said. Further challenges are presented by planetary protection requirements, he said. We don’t take bacteria to Mars. And bringing samples back at some point will present the opposite problem.

And finally, Mars, he said, is really far away—250 million km at the time of landing, with light taking 14 minutes to traverse the distance. “You cannot joystick the thing down,” he said. “Ground commands take 14 minutes to execute. Rovers have to take care of themselves” as autonomous systems, able to safely land at zero altitude with zero velocity. The challenges are such that only 50% of attempted landings have been successful.

Curiosity successfully landed in Gale Crater, which may have once contained water and which contains a mountain called Mount Sharp. The rover will investigate biological potential and the role of water, geology, chemistry, and surface radiation, Dubord said.

Curiosity includes a variety of instruments, including SAM (Sample Analysis at Mars), CheMin (short for Chemistry and Mineralogy), MARDI (Mars Descent Imager), RAD (Radiation Assessment Detector), and DAN (Dynamic Albedo of Neutrons), a Russian instrument designed to detect subsurface water.

The Spirit and Opportunity rovers landed using airbag system. Curiosity was judged too heavy for this approach, Dubord said, and consequently employed a Skycrane, a rocket-powered descent stage that lowered the rover to the surface via tethers and then flew off to a crash landing. “People thought we were nuts,” Dubord said, but testing, testing, and more testing (including EMI/EMC testing to assure compatibility between subsystems with no interference) ensured that the approach worked. The tests involved an Earth-bound “scarecrow”—a rover without a brain.

Dubord described the project as a system of embedded systems. “Two compute elements [on the rover] run the whole show,” he said, although the descent stage needed enough smarts of its own to safely fly off when the landing tether was cut after depositing the rover on the surface. The BOM might look like that of any embedded system, with a complement of processors, memory, and FPGAs. A software-defined radio handles communications.

Dubord concluded his presentation by describing upcoming missions, including InSight and Mars 2020.