Ready for Mars: ExoMars has just a single chance to get captured by Mars’ gravity

The ExoMars Trace Gas Orbiter is on a multiyear mission to understand the methane and other gases in Mars' atmosphere at low levels and could be evidence for possible biological or geological activity.

The 3.7 tonne mothership is carrying the 577 kg Schiaparelli lander that will test key technologies in preparation for ESA's 2020 rover mission.

The pair have almost completed their 496 million km journey, and are now speeding towards a critical stage: releasing the lander on Sunday and the lander's descent and touchdown next Wednesday, at the same time as the main craft begins circling the planet.

"They are now on a high-speed collision course with Mars, which is fine for the lander -- it will stay on this path to make its controlled landing," says flight director Michel Denis at mission control in Darmstadt, Germany.

"However, to get the mothership into orbit, we must make a small but vital adjustment on 17 October to ensure it avoids the planet. And on 19 October it must fire its engine at a precise time for 139 minutes to brake into orbit.

"We get just a single chance."

Following months of intensive simulations, the team is now changing to 'real-time/full-time' shifts, and will work in the main control room from tomorrow.

The team will oversee separation, set for 14:42 GMT on Sunday, the adjustment 12 hours later to avoid hitting Mars and, finally, the main engine burn starting at 13:05 GMT on Wednesday.

A last pre-arrival correction was made this morning at 08:45 GMT to ensure the craft is perfectly lined up for separation and arrival. The thruster burn delivered a tiny kick of 1.4 cm/s -- all that was needed after an earlier series of extremely precise adjustments in July and September.

"This week, we uploaded the commands to fully charge the lander's batteries and prepare the orbiter's data-handling system as well as power- and thruster system for separation and the subsequent trajectory tweak," says spacecraft operations manager Peter Schmitz.

"Next week, before the big burn, we will place it into a special 'failop' mode to minimise any risk that an onboard glitch could interfere with the firing of the engine, which absolutely must happen at the planned time for us to get into orbit."