Europe's first Mars space craft is suffering from a power glitch.
However, controllers believe it will make no difference to the mission itself.
Beagle 2 should land on Christmas Day
Engineers carrying out routine checks on Mars Express as it speeds though space have found it is down to 70% power.
A faulty connection between the craft's solar wings and a unit that distributes the electricity generated by the arrays is to blame.
The power shortage is expected to have no impact on the state of the space craft or the mission objectives.
The European Space Agency (Esa) said in its latest mission statement: "This anomaly has no effect on the state of the space craft and has no impact on the mission during the whole trip to Mars, including the orbit insertion phase once at destination."
Jocelyne Landeau of Esa's operations centre in Darmstadt, Germany, told BBC News Online it was too early to say what the full implications of the power shortage would be.
She said the situation would be assessed in the coming weeks in collaboration with scientists and Esa officials.
Overall, the spacecraft is in good shape
The problem should have no impact on the space craft's journey to Mars or the life time of the mission.
However, it may mean changes to how the various instruments on Mars Express are deployed once it arrives at the planet.
"For the moment the general spirit is that we can carry out the mission, there is no doubt about it," Ms Landau said.
The testing phase is part of a series of standard "health checks" that are carried out on all space craft on the way to their destination. The Beagle 2 lander is scheduled to be checked this weekend.
Esa officials are confident about the mission. "In fact," says Rudolf Schmidt, Mars Express Project Manager, "overall, the spacecraft is in good shape. We are simply getting to know its personality."
Mars Express is now 10 million kilometres from the Earth. It should arrive at the Red Planet on 25 December 2003.
The European probe is currently at the head of a fleet of three space craft heading to the fourth planet from the Sun.
Just behind it is the US space agency's Spirit rover; and behind that is Nozomi, a Japanese satellite that will go into orbit around Mars.
The Americans have a second rover, Opportunity, which they hope to launch on Saturday. All the space craft are timed to arrive within days of each other.
They are taking advantage of a close alignment between Mars and Earth which makes it a particularly favourable time to be heading to the Red Planet.