A sped-up view of ESA-CNES rover ‘egress’ testing that took place in one of Europe’s largest mock-Mars landscapes.

Every journey begins with a single step – or in this case a downward trundle.

The egress of Europe’s ExoMars 2018 rover off its lander will be the second most stressful moment of the mission after Mars landing.

So to build up experience in the problem, a half-scale rover on a mock-up lander was placed in the outdoor 80 x 50 m ‘Mars Yard’ of French space agency CNES for a two-day test campaign on 28-29 October.

It was controlled remotely by a team based at ESA’s ESTEC technical centre, a thousand kilometres away in the Netherlands.

They were given no idea where in the sprawling Mars Yard the rover was located for each test scenario – the only information they could access came from cameras and sensors in the rover and lander.

Adding to the difficulty, real-time remote control of the rover was out – the sheer distance to Mars will make it impractical reality. Instead they could receive telemetry at regular intervals then send back a to-do list of telecommands.

For the purposes of testing these communication passes came once every hour – in reality they would occur once or twice a day.

The team on the ESTEC side came from ESA’s Automation and Robotics section and ExoMars project as well as from industrial partners Trasys Space Belgium, Thales Alenia Space Italy and Altec Italy. In addition the testing was also tracked from ESA’s ESOC control centre in Darmstadt, Germany.

For each egress they worked to build up a detailed virtual model of the rover’s surroundings, as well as stitching together a panorama from the various camera views.

The lander has two sets of ramps down to the surface, so the team had to decide which way down was safer. This video shows a rapid time-lapse version of the whole process – in reality the rover took more than two minutes to egress off the lander each time.

A total of five egress tests were performed: four ended in success and one in failure – the rover descended down at too steep an angle and began to topple off. In real life the mission would have ended there, but in this case it was safely caught by helping hands.

The incident demonstrated the importance of such simulations, which also allowed the practical testing of various software tools developed over years of research.

The testing was organised by ESA’s Planetary Robotics Laboratory in cooperation with CNES and ESOC. The results will be used will be valuable inputs in the design of the actual ExoMars mission.