Spirit, the first of the probes launched, made its third flight path correction this week, in a manoeuvre that involved igniting its engines for some two minutes, according to the Jet Propulsion Laboratory (JPL) in Pasadena, California.
Another three flight path corrections are necessary ahead of Spirit's Mars landing, said Louis D'Amario, head of probe navigation at the JPL, AFP reported.
A Rover robot on Spirit will be sent out to explore the planet for three months.
The second probe, Opportunity, is also carrying an identical robot, though is set to touch down on the opposite side of Mars to Spirit some three weeks later.
The two probes started up their onboard computer in the past two weeks, to prevent any corruption of the information files that might have been provoked by unusual levels of radiation during solar storms in late October and early November.
“We had no evidence of memory problems, but we considered it prudent to reboot both spacecraft to assure memory integrity, using the sleep-wake cycle that we plan to do each night after the rovers are on the surface of Mars,” said Peter Theisinger, project manager for the Mars Exploration Rover Project at the JPL.
On Wednesday, Spirit was 91.5 million kilometres from Mars. The probe had travelled about 397 million kilometres (246 million miles) since its 10 June launch.