The US space agency's robotic rover Spirit is approaching the summit of a hill it has been climbing on Mars since the end of last year.
Spirit should have a spectacular view from the summit
It now has less than 70m to drive in order to reach the peak of "Husband Hill" on the Red Planet and should complete the climb this week.
When the rover gets there, it will take photos of what should be a spectacular view and scout for sites of interest.
The twin robots Spirit and Opportunity have been on Mars since January 2004.
Husband Hill has two local summits, dubbed one and two.
Spirit is now about six vertical metres below summit one, the higher of the two, rising about 80m above the floor of Gusev Crater.
"The path from here to there does not seem to present any impassable barriers," Steve Squyres, rover lead scientist, wrote in an update on the Cornell University website.
From the summit, scientists hope to observe layered rocks which may lie in a basin to the south.
Layered rocks are an important scientific target on the Red Planet, because they can form through the action of water.
Both Spirit and Opportunity have uncovered evidence for the past presence of water at their landing sites.
The rovers are working after more than one-and-a-half years on Mars
Spirit has driven nearly 5,000m (3 miles) since it touched down on the three billion-year-old volcanic plains of Gusev Crater.
It has just finished a thorough investigation of a rock called Assemblee, which has an unusual composition and the highest levels of the metal chromium ever discovered in a rock on Mars.
On the opposite side of the planet, Opportunity has been continuing observations of the geology of Meridiani Planum. It is driving to a region which has been dubbed "Erebus".
Here, mission scientists hope to examine more of the bedrock that underlies Meridiani's dark red dunes.