Crossing the unknown

CuriosityOn Sol 376, August 27th 2013, Curiosity  achieved another mission milestone: the first use of the autonomous driving capabilities to fully drive itself through a potentially hazardous zone.

The autonomous navigation software – autonav – was uploaded to the rover following the April 2013 period of solar conjunction. It is designed to allow the rover to decide how best to handle driving safely on Mars, rather than constantly relying on command updates from Earth – something which can severely limit the rover’s daily progress if there are significant obstacles in the rover’s path or if the mission team want the rover to drive beyond the limits of what the  Navcams can see at the start of a day’s drive without routes having to be constantly re-plotted from Earth.

The drive of August 27th saw Curiosity successfully use autonomous navigation to cross ground that could not be confirmed safe before the start of the drive. While the drive team were able to establish a “bounding box” in which the rover was expected to keep during the day’s progress, a significant depression in the ground some 10 metres (33 feet) across could not be imaged in advance of the rover’s arrival, and so autonav was enabled in order for the rover to make its own way through the depression.

“We could see the area before the dip, and we told the rover where to drive on that part. We could see the ground on the other side, where we designated a point for the rover to end the drive, but Curiosity figured out for herself how to drive the uncharted part in between,” said JPL’s John Wright, a rover driver.

The road ahead: a mosaic panorama captured by Curiosity's Navcams after the Sol 376 traverse. The rise on the left of the image is part of "Mount Sharp"; the most distance highlands are the walls of Gale Crater

The road ahead: a mosaic panorama captured by Curiosity’s Navcams after the Sol 376 traverse. The rise on the left of the image is part of “Mount Sharp”; the more distance highlands to the right are the walls of Gale Crater (click to enlarge)

Crossing the depression required the rover to take several sets of stereo images of the terrain, compare them, determine potential routes to reach a the designated way-point, and then select the safest course to take.

While autonav has been used a number of times already in recent weeks, these have always been under controlled conditions and limited in scope. The Sol 376 traverse marks the first time Curiosity has been left entirely to its own devices to cross what has essentially been unknown ground for the mission team.  The drive means that the rover has now travelled about 1.39 kilometres (0.86 miles) since departing “Glenelg” and “Yellowknife Bay” early in July, and has a little over 7 kilometres (4.46 miles) to go before reaching the lower slopes of “Mount Sharp”.

Rapid Transit Route

To assist the rover’s progress, NASA have marked-out a “rapid transit route” using images from the High Resolution Imaging Science Experiment (HiRISE) camera aboard the orbiting Mars Reconnaissance Orbiter. This plots a rough course for the rover from “Glenelg” to the designated entry-point into the lower slopes of “Mount Sharp”, and which runs alongside a dune field which lays between the terrain the rover is on and the slopes of the mound itself.  Several potential waypoints have been identified along the route where the rover may stop for a few days at a time to allow further science work to be carried out.

The “Aeolis Mons expressway”: NASA’s “rapid transit” route Curiosity is following in order to reach the lower slopes of “Mount Sharp”, with potential science waypoints marked. The mound is towards the bottom of the image and the black diagonal band is a dune field which runs along the foot of the hill

The route itself, while plotted from space, will still be subject to daily drive planning sessions using ground-level images gathered by the rover. However, with autonav now fully tested, the hope is that Curiosity will be able to do far more navigation on its own, allowing it to travel up to around 100 metres per day, using a combination of an initial route uploaded from Earth, together with significant waypoints, and then using autonav to navigate zones beyond the limit of detailed Earth-side planning (around 40 or so metres out from the rover’s Navcams), or where the ground cannot be seen with any degree of clarity for planning purposes, as with the Sol 376 drive.

Science-to-Go

As noted last time around, it isn’t all drive. drive, drive, for Curiosity.  The rover is fully capable of conducting a range of science activities while “on the road” – as shown by the recent imaging of Phobos and Deimos. Additionally, the rover continues to monitor the Martian atmospheric environment using REMS, the Rover Environmental Monitoring System and to take readings on the radiation conditions close to the surface of Mars. When required, the rover can also use the Dynamic Albedo of Neutrons (DAN) instrument to measure sub-surface soil for evidence of trapped water molecules.

As well as this work, Curiosity is able to store samples of Martian rock and soil within the CHIMRA (Collection and Handling for In-situ Martian Rock Analysis), a system located within the rover’s robot arm turret, and primarily used for sifting and sorting recovered samples ready for onward passage to the on-board instruments. Recently, samples stored in this way from the second drill target in “Yellowknife Bay”, dubbed “Cumberland”, were delivered to the highly sensitive Sample Analysis at Mars (SAM) system so they can be analysed while en-route.

This set of three images shows views three seconds apart as the larger of Mars’ two moons, Phobos, passed directly in front of the sun as seen by Curiosity. The images were captured using the Mastcam telephoto lens on August 17, 2013, the 369th Martian day, or sol, of Curiosity’s work on Mars.

As well as recording the recent passage of Phobos passing Deimos in the night sky, Curiosity also observed Phobos as it travelled across the face of the sun in what is called an annular, or ring, eclipse. The event occurred on August 17th (Sol 369), when Phobos and the sun were directly over the rover, and the little moon was at its closest approach to the surface of Mars, thus making it look far bigger compared to the Sun than would otherwise be the case. Observations on the Martian moons by both Curiosity and Opportunity, still operating half-a-world away, help increase scientists’ understanding of Phobos’ orbit and how it may be interacting with Mars.

And What of Opportunity?

With all the focus on Curiosity, it is easy to forget that there is another rover operating on Mars – and has been doing so for almost a decade. Not bad for a mission originally cited as having a 90-day prime period, the belief being the solar-powered rovers of the mission would not survive much longer than that due to dust accumulation on their solar panel surfaces.

Launched in July 2003, Opportunity is much smaller and slower than Curiosity, but it is still going strong. One of a pair of rovers referred to as the MERs – Mars Exploration Rovers – Opportunity was for a time the only vehicle operating on the surface of Mars after its sibling, Spirit, ceased communicating with Earth in March 2010, after having been trapped in sand since mid-2009.

Curiosity's "little cousin" Opportunity, active on Mars since January 2004

Curiosity’s “little cousin” Opportunity, active on Mars since January 2004

Opportunity has travelled over 36 kilometres (22 miles) since arriving on Mars at the start of January 2004, and has recorded a long and distinguished list of science achievements during a drive which has seen it probe around a nuumber of craters, find possible evidence for free-flowing water on Mars and more.

Currently, the rover is exploring the rim of Endeavour crater, which at 22 kilometres  (14 miles) in diameter is far smaller than Gale Crater, but which nevertheless has a number of sites of geological interest to the science team managing Opportunity.

As a part of this work, Opportunity recently arrived at an area where two geological units, dubbed “Burns” and “Solander Point”, join one another. The plan is for the rover to study the nature of the contact point prior to proceeding onto Solandar Point, a rise on the crater rim, where it will work through the winter period in Mars’ southern hemisphere.

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All images and stills courtesy of NASA JPL.

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