A NASA spacecraft hurtling toward Mars prepared to fire its thrusters Wednesday to put itself on course for an August landing.
Engineers closely tracked the one-ton rover nicknamed Curiosity, which has been cruising along since rocketing from Earth last November.
The engine firing is the most important task Curiosity will perform during its 352-million-mile flight to the red planet, but it's not unprecedented. Previous robotic explorers have had to adjust their paths several times en route to ensure a bull's-eye landing.
"Just because this is a well-traveled road to Mars given the number of trips we've made, I'm very careful to not let that experience cause us to be complacent," said Arthur Amador of the NASA Jet Propulsion Laboratory, which manages the $2.5 billion mission.
At the time of the course correction, Curiosity will have racked up 80 million miles and will be traveling at 10,200 mph relative to the Earth.
The day before, the team uploaded commands calling for the spacecraft to fire its eight thrusters for nearly three hours Wednesday afternoon, redirecting it closer to its target. Though it will execute the move without human interference, engineers will be on standby in the off chance that they have to abort.
"We should be very, very close to our desired aim point at the top of the Martian atmosphere" after the maneuver, Amador said.
If Curiosity did not tweak its position, it will miss Mars altogether. Engineers did this by design to prevent the rocket's upper stage that hoisted the spacecraft from hitting the red planet. Once Curiosity separated from the upper stage and was on its way, the team has several chances to fine-tune its trajectory before touchdown.
Curiosity, whose formal name is the Mars Science Laboratory, is aiming for a 96-mile-wide crater near the Martian equator that boasts a towering mountain in the center. The six-wheel, nuclear-powered rover planned to drive to the lower flanks and examine the layered deposits to determine whether the area once had conditions capable of supporting microbial life.
Armed with a suite of instruments including a laser to zap into bedrock and a jackhammer, Curiosity is more sophisticated than previous Mars surface spacecraft. Despite its capabilities, it won't be able to detect life. Instead, it will hunt for the chemical building blocks of life during its two-year mission.
Since Curiosity is too heavy to parachute to the surface, it will be lowered using a tether system similar to the sky cranes used to plop heavy equipment into remote sectors on Earth — a nail-biting move come August and a first for NASA.
Even before arrival, Curiosity has not sat idle. Several weeks after launch, Curiosity turned on its radiation detector to monitor high-energy particles streaming from the sun and exploding stars. Once at Mars, it will measure radiation levels on the surface.
Curiosity's voyage contrasts sharply with another space probe targeted at the Mars moon Phobos. Launched weeks earlier than Curiosity, Russia's Phobos-Ground probe got stranded in Earth's orbit and was expected to fall back to Earth this weekend.