Where on Earth (or Mars) are we?

Yesterday, our rover ‘landed’ and the Mission Operations Centre (MOC) in Harwell received a 360-degree colour panorama from the landing site. We now have time to do some preparations before we begin to command the rover to drive and acquire more data on Thursday.

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The first panorama of the ‘landing site’ in Utah. At the moment, the camera is mounted on a tripod. It will be mounted on the rover when we begin to drive.

When a landing on Mars is planned, it isn’t possible to specify an exact landing site. Instead, we have to plan for a landing anywhere within something called a ‘landing ellipse’ which for the ExoMars 2020 rover is 104 x 19 km. Luckily for us ours is only 2 x 2.5 km and we know that our rover is somewhere within this Utah-based landing ellipse. The question is where?

However, we have no communication with the field team, since real Mars rovers are not accompanied by humans who can give us inside information! Therefore yesterday the main challenge for the MOC team was to pinpoint the ‘landing site’ remotely from Harwell, almost 8000 km away! This task is called ‘localisation’.

The data available to the MOC team were the 360-degree panorama from the landing site, and images and 3D elevation data of the landing ellipse from Earth-orbiting satellites with similar resolution to the satellite data that is available for Mars.

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Comparing the 3D satellite data (left) with the panorama from the rover  (right) during localisation.

So, how did we perform localisation?

Through identification of features in the rover panorama and tying them to features in the satellite data, we gradually narrowed down the location of the rover to within a 300m radius. We then took measurements of these features to work out how far away they are from the rover’s camera. After a couple of hours, we had pinpointed the landing site to within a few metres.

So, where on Earth are we?

According to our localisation, the rover is approximately 100m north of a large ridge formed of red and white layered material. The rover is located near to five large boulders that for the purposes of geography and locating ourselves the MOC team have provisionally named ‘Monday’, ‘Tuesday’, ‘Wednesday’, ‘Thursday’ and ‘Friday’ (collectively, the ‘Weekday rocks’). By using the Weekday Rocks as points of reference, we can continue to improve the accuracy of our localisation each time we drive the rover to a new spot.

weekday-rocks

The ‘Weekday rocks’  with the large ridge complex in the background.

During localisation, ideas began to emerge about where we might like the rover to go and what science we could do once it gets there. All of our considerations were based on the over-arching mission aim: to find signs of life.

Now that we know where the rover is (or we think we do, at least), today’s task will be to plan the mission strategy in more detail. Tomorrow, we send commands to the rover and its journey begins!

-Frances Butcher

 

 

 

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