NASA's Mars program riding on a rover heading for touch down

In less than eight hours, the world will witness either the greatest feat yet in the history of solar-system exploration or another humbling reminder that, yes, it is hard to land spacecraft on Mars.

If all goes well, mission managers anticipate touchdown of NASA's one-ton rover Curiosity at around 1:31 a.m. Eastern Daylight Time Monday, or around 3 p.m. local Mars time.

The goal of the $2.5 billion mission is to explore Gale Crater and its central peak, informally known as Mt. Sharp, for evidence that the area may once have been capable of supporting life.

One measure of the mood at NASA's Jet Propulsion Laboratory in Pasadena, Calif., comes from Adam Steltzner, the lead mechanical engineer for the Mars Science Laboratory's unique descent and landing system.

"We're rationally confident, emotionally terrified, and we're ready" for entry, descent, and landing of Curiosity, he says.

Indeed, the traditional touches that indicate entry is imminent have cropped up among members of the flight team, notes Brian Portock, the Mars Science Laboratory (MSL) mission manager. Mission control is loaded for bear with the requisite supply of peanuts for the flight team. One engineer overseeing communications links has grown his version of a play-off beard. And a flight director known for unique hair styles during missions is sporting a stars-and-stripes theme, on majority vote of his colleagues: a mohawk tinted with red and blue on top and with the hair remaining on the sides of his head cut into stars, Mr. Portock said during the final pre-entry status briefing on Sunday.

Much rides on the outcome of this mission in an age of looming, deep budget cuts, and not just for the scientists and engineers associated with the mission, notes Scott Hubbard, former head of NASA's Mars Exploration program and the architect of the methodical approach the agency has taken since the late 1990s to exploring the red planet.

"The stakes for NASA and the science community are quite high," says Dr. Hubbard, who also served as head of NASA's Ames Research Center at Moffett Field, Calif., and is now a consulting professor at Stanford University in Palo Alto, Calif.

Twice before, he says, the agency's Mars effort suffered major mission failures that led to a restructured Mars program – once after the loss of the Mars Observer orbiter in 1993 and again in 1999 with the losses of the Mars Climate Orbiter and the Mars Polar Lander. Each time, he says, the agency analyzed the failures, then bounced back to loft five consecutive successes since 1999.

This time, Curiosity's trip is taking place against a unique backdrop of a proposed budget for Mars exploration that represents a 40 percent cut over its predecessors, he says.

"There's nothing in the pipeline after MAVEN next year," he says, referring to the launch of an orbiter slated to help unravel the history of Mars' atmosphere and the planet's transition from a warm, wet orb early in its history to the dry conditions researchers observe today. The proposed cuts puts the Mars program into "pretty much a going-out-of-business mode."

A success, however, would make a strong case for keeping the program alive and healthy, especially if in the next three to six months Curiosity uncovers organic material in the rocks and minerals that could represent the dog-eared calling cards of ancient, simple forms of life. Finding  such markers would make a strong case for continuing along a path that ultimately leads to a Mars sample-return mission – a consistent, high priority in the once-a-decade agenda astronomers draw up for space missions and other key research priorities.

From a technology perspective, Mars Science Laboratory represents the maiden voyage of a system NASA hopes will serve as the foundation for future Mars missions, says Doug McCuistion, current head of NASA's Mars Exploration Program.

Through all of the past agenda setting, as well as in conversations with scientists now about how to move forward at Mars on a budget so tight it may not even be able to squeak, no one envisions missions that will require placing anything heavier than one ton on the Martian surface, according to Mr. McCuistion.

Curiosity and its curious landing system represent "the workhorse for the future," he says.

Given all the tests engineers have performed on Curiosity and its landing system, if the landing fails, it will more likely be the planet's fault rather than NASA's, Hubbard suggests – a gust of wind hitting the craft at the wrong time during its descent, or the rover coming to wheels-extended rest on an oddly shaped rock, causing it to tumble turtle-like into a position from which it can't right itself.

"Then the question is: Whither the budget for NASA?" he says, adding that if the US backs off from its strong Mars exploration program, other spacefaring nations will continue to move ahead. Indeed, last week India's prime minister reportedly gave his OK for the country's first mission to Mars, an orbiter that could be launched in November 2013.

Even in the face of a failure – for which there would be reams of data to pour over for learning its hard lessons – walking away from Mars exploration "would be foolish in my mind," Hubbard says.

Over the past 15 years – from a rover the size of a small microwave oven to MSL – the effort also is leading to the technology for a sample-return mission as well as eventual human exploration.

Curiosity's heavily instrumented heat shield and the radiation measurements taken during its cruise phase to the autonomously-guided maneuvers the descent stage will perform to place Curiosity in the smallest landing zone yet identified, typify the progressive steps in technology that have been built into the current program form the beginning.

Even if Curiosity ends up as a bent tangle of wheels, arm, and mast, "what we lose is incredible if we don't do it again," McCuistion says.

Given the enormous talent the nation has amassed to conduct these kinds of missions, "I think that last thing the nation can afford is to have the kind of gap between Viking and Pathfinder that we had" between 1980, when the Viking missions ended, and 1996, when Pathfinder launched.

At Mars, "the science is on the surface," he says. Losing the "core competency" the US has in Mars exploration "would be hard to rebuild."