The craft's course on Tuesday gave scientists confidence to undertake a critical Christmas Day manoeuvre to fire it into orbit. It holds the key to Europe's first mission to explore whether life ever existed on the planet.
In preparation, mission control in the west German city of Darmstadt sent the first orbit-related commands to the craft on Tuesday. The mission's other component is a probe that is due to touch down on Mars early on 25 December.
Mars Express, which will relay data from the Beagle 2 probe and perform experiments of its own, was on track as it sped through space in the final hours of a nearly seven-month, 155 million km flight to Mars.
"It's perfectly on course," mission control spokesman Bernhard von Weyhe said in Berlin. The more precise the course, the lower the likelihood of problems when controllers fire the engine to send the craft into orbit, he added.
"The mood is concentrated but relaxed" at mission control, he said.
Once in orbit, the craft is meant to send back 3-D overhead pictures of the surface and scan for underground water with powerful radar.
"The mood is concentrated but relaxed"
Bernhard Von Weyhe,
spokesman, mission control
For its part, the 67-kg Beagle 2 is to parachute through the Martian atmosphere, bounce to a soft landing on inflatable bags, flip open, then start transmitting a signal that tells controllers it has safely touched down.
The first chance to pick up the signal will be when NASA's Mars Odyssey spacecraft passes overhead early on Christmas Day in Europe.
Also on 25 December, scientists at the Jodrell Bank Observatory in London will have a chance to train its radio telescope on Mars in an attempt to pick up the signal.
If both options fail, Odyssey will have a daily chance to pick up the signal on its orbit until Mars Express makes its planned first contact with the probe on 3 January.
Scientists believe that Mars, which still has frozen water in its ice caps, might have once had liquid water and suitable conditions for life, but lost those billions of years ago.
The European mission is the first search for signs of life on Mars since two US Viking landers probed the planet in 1976 but sent back inconclusive results.