How exactly do you drive the one-ton Mars rover Curiosity, when the driver is, on average, 150 million miles away? With a one-way time delay of around 13 minutes, it certainly isn’t a matter of sitting down in front of a monitor and waggling a joystick.
While we’ve tackled just about every aspect of NASA’s Curiosity rover, from the radiation-hardened on-board computers through to its nuclear-powered laser, we’ve never really discussed navigation — a rather important aspect, as most of Curiosity’s two-year prime mission will be spent driving the few miles to Mount Sharp.
In short, there are two ways that Curiosity can navigate the surface of Mars: NASA can transmit a series of specific commands, which the rover then dutifully carries out — or NASA can give Curiosity a target, and then trust the rover to autonomously find its own way there. In both cases, the commands are transmitted to Curiosity via NASA’s Deep Space Network — the worldwide network of big-dish antennae that NASA uses to communicate with spacecraft, and carry out some radio astronomy on the side.
To decide which navigation method to use, NASA uses the Rover Sequencing and Visualization Program (RSVP), which is basically a Mars simulator. RSVP shows Curiosity’s current position on Mars, along with surface topology, obstacles (rocks), and so on. RSVP can then be used to plot a move (go forward 10 meters, turn 30 degrees right, go forward 3 meters) — or to pick an end point, which Curiosity will dutifully, autonomously navigate to. To safely navigate Mars, Curiosity uses its Hazcams (hazard avoidance cameras) to build a stereoscopic map of its environment, identifies which objects are too large to drive over, and then plots out a course to the end point.
When Curiosity finishes its drive, it transmits a bunch of thumbnail images from its on-board cameras to NASA, which are then used to work out Curiosity’s exact location on Mars. This data is fed into RSVP, the next day’s movements are plotted, and so on and on.
In other news, Curiosity is now deep within Yellowknife Bay, a shallow depression on the surface of Mars where NASA will hopefully find an interesting rock that will become the first victim of Curiosity’s percussive hammer. Yellowknife Bay is pictured above, along with the step (about 2ft high) that Curiosity had to cross to descend into the bay. Curiosity will spend the next few days in Yellowknife Bay, while the NASA/JPL engineers enjoy a long-overdue break, and then begin the long trek to Mount Sharp, which will probably take up most of 2013.
Finally, a beautiful bonus image — think of it as a Christmas gift from ExtremeTech. What you see above is Saturn, all of its rings, and its moons Enceladus and Tethys (bottom left). This unique image, which is a mosaic of hundreds of images, was captured by the NASA/ESA/ASI Cassini orbiter as it passed through Saturn’s shadow, roughly 500,000 miles (800,000km) from the planet. With Saturn between the Sun and Cassini, and the dramatic viewing angle, this is probably the best view of Saturn’s rings that you will ever see.
Cassini has only taken an image from the shadow of Saturn once before, in 2006 — and that time, Earth was visible (10 o’clock, at the edge of the rings).
