Europe's Mars Express orbiter, the "mothership" to Beagle 2, has carried out a major engine burn to sweep it into a polar orbit of the Red Planet.
Mars Express will be in position to "speak" to Beagle
The spacecraft has been heading away from Mars, preparing for the manoeuvre - a crucial first step to bring it into a lower orbit around Mars.
The orbit change will put Mars Express in prime position to talk to Beagle 2.
European space agency controllers changed the orbit by firing the engine for four minutes at 0800 GMT.
Mike McKay, flight operations director at Esa's European Space Operations Centre (Esoc) in Darmstadt, Germany said ground controllers were "delighted".
"To date, [Mars Express] has been a fantastic success. It's a first for Europe," Mr McKay told BBC News Online.
In its current polar orbit, the craft will carry out more frequent overflights of the Beagle 2 landing site, making the chances of it picking up a signal from the British lander more likely.
No signal has been heard from Beagle since it was due to touch down on 25 December. Efforts to contact it using Mars Express will begin in earnest on 7 January, when the orbiter makes a pass of Beagle's landing site.
Scientists on the Beagle project regard this opportunity as their best chance of receiving a signal from the silent lander.
Mr McKay said he was confident that - if Beagle was able to communicate - Mars Express would pick up the lander's signal.
"With Beagle 2 we are extremely optimistic. We overfly on 7 January at an altitude of 315 km. We will fly directly overhead Beagle."
"If Beagle is in the right state to transmit, we will see it, because the Mars Express radio and the Beagle 2 radio are the only ones that have been designed to work together," he explained.
Beagle 2 scientists had said they were planning to send "blind commands" to their probe via the US space agency's Mars Odyssey craft, in the hope of prompting a response from the silent lander.
But Mr McKay said there was a chance this reconfiguration of Beagle could delay the opportunity for Mars Express to get in touch with its "baby" on 7 January. He added it was his understanding that the team were still deciding whether to send these commands.
Mars Express' orbit change will also ensure the beginning of its science mission to study the Red Planet's geology and to search for water beneath the surface.
Tuesday's manoeuvre shifts Mars Express from an elliptical orbit about 188,000 kilometres (117,000 miles) above Mars' equator to an orbit roughly the same height but over the planet's poles.
At this distance from Mars, the orbiter was using up less fuel as it made the 90-degree correction of its orbit.
Water may remain beneath the surface of Mars
The craft will be progressively lowered over the next week. On 4 January at 1300 GMT the craft will slow down to reduce its distance from the surface to 40,000 km (25,000 miles).
Later in the day, controllers will curb the probe's speed still further so it orbits at up to 12,000 km (7,456 miles) from Mars - though the craft may at times swoop as low as 200 km (125 miles) from the surface.
Mars Express will then take about six to seven hours to make a complete orbit of the planet.
This is the final, or operational, orbit, in which Mars Express will turn on its instrumentation to try to contact Beagle and to carry out its scientific analysis of Mars.
Scientific instruments carried aboard Mars Express include a high-resolution stereo camera which will provide accurate pictures of the planet's terrain and spectrometers to determine the composition of Mars's rocks and atmosphere.
In April, the orbiter's radar altimeter will map the underground structure of Mars, scanning 5 km (3 miles) beneath the surface for signs of water and geological activity.
"It will be looking for glaciers, lakes, permafrost and also looking for whether there are tectonic plates under Mars," Mr McKay added.
"What is the structure below Mars? How was it created? What is the history of Mars? All those questions that are unclear."
The craft had completed its Mars Orbit Insertion (MOI) manoeuvre at 0247 GMT on 25 December. This brought the orbiter as close as 400 km (249 miles) from the Martian surface.
Afterwards, the probe was moved into a highly elliptical orbit around the planet's equatorial region in preparation for today's manoeuvre.