Japanese scientists will this month begin a last-ditch effort to save the Nozomi Mars probe, the country's first planetary mission.

The US$848-million Nozomi was designed by Japan's Institute of Space and Astronautical Science (ISAS) to investigate the red planet's atmosphere and its interaction with the solar wind (see Nature 423, 473; 2003).

But Nozomi ran into trouble soon after its July 1998 launch. A swing by Earth in December 1998 — intended to accelerate the probe using the planet's gravitational pull — failed to give it enough speed to reach Mars. Attempts to correct its course by firing its engines drained its fuel tanks. And during another Earth swing-by in April 2002, a solar flare damaged its power-supply system.

The flare seems to have damaged a circuit breaker that regulates the flow of electricity to some of the craft's essential systems, including its heater. The breaker now “works too much, turning off and on continuously”, says Yasunori Matogawa, ISAS scientist and director of Kagoshima Space Station from where Nozomi was launched.

Following a third, apparently successful, swing around Earth last week, the probe should finally reach Mars next January. But without the heater, the spacecraft cannot thaw the fuel it has left to manoeuvre itself into orbit around the red planet.

Later this month, ISAS scientists will try to fix the problem, sending successive commands to turn the power supply on. They hope that this will eventually burn out the circuit breaker, leaving the power switched on.

Matogawa says that they will probably know within the next couple of weeks whether the mission is likely to be saved. But even if initial efforts fail, they will keep trying until November. “I'd say there's a 50/50 chance,” Matogawa says.