At a movie theater near you, NASA has made it to Mars. “The Martian” stars Matt Damon as an astronaut stranded on the red planet, almost surely doomed, but surviving on his ingenuity, STEM education and goofy sense of humor.

For America's civilian space agency, humans-to-Mars is an aspiration bordering on an obsession. “#JourneytoMars” is the agency’s ubiquitous Twitter hashtag. Trying to fight its way out of a period of strategic uncertainty and chaos, NASA has aggressively branded its programs as being part of "an unprecedented human journey to Mars," as NASA administrator Charles Bolden put it in a speech in June.

The bold talk glosses over technical and political realities. NASA's flat budget won't pay for a Mars mission. At the moment NASA can't even get an astronaut to the International Space Station without buying a seat on a Russian rocket. A new NASA space capsule that was conceived in 2005 likely won't be ready until 2023, according to NASA's latest estimate, and it's built for 21-day missions, not for trips to Mars.

The agency is working on numerous projects – a jumbo rocket, new methods of propulsion, research on long-duration spaceflight, etc. -- that may play key roles in a human mission to Mars. It is improving its capabilities, and figuring out what it would take to keep astronauts alive on a distant world. But even if all goes swimmingly, NASA is looking at a Mars mission in the 2030s at the very earliest.

“We’re setting expectations for something that is decades away. The public has a short attention span,” said Lori Garver, the former deputy administrator of NASA under President Obama.

Doug Cooke, a former NASA associate administrator for exploration, thinks NASA needs to spell out intermediate steps to Mars. There's one obvious stopping point between the third and fourth rocks from the sun: The moon. Cooke says it could be a proving ground for off-world living.

"There needs to be more of a plan for actually getting there," Cooke said. “You can’t have a flat-line budget indefinitely and think you’re going to put all of this together by 2030.”

John Grunsfeld, NASA’s top official for science and an astronaut himself – he fixed the Hubble Space Telescope several times in orbit -- doesn’t see a problem with the Mars-centric media relations.

“Sure, ‘JourneytoMars’ is a slogan. There’s no question about that. But it does capture the excitement of the various activities that we’re doing. Each individual piece does have traceability to future missions to Mars," Grunsfeld said.

He added, “One of the reasons I wanted to be an astronaut was to go to Mars. So I’m very impatient.”

Mars is far away, inhospitable, and due to the orbital dynamics of Earth and Mars, any mission to the red planet's surface would take at least two years round-trip (a fly-by, without landing, theoretically could be done in about 500 days). The technical challenges are significant, but NASA's engineering prowess is legendary, and this may be a case where the impossible simply takes longer.  The most serious challenge may be budgetary.

When President George H. W. Bush proposed a human mission to Mars in 1989 as part of a massive new push in outer space, sticker shock sank the plan. Estimates put the cost in the range of $400 billion.

The consensus among space policy analysts is that a NASA mission to Mars with astronauts would require a political mandate that currently does not exist. This is not the 1960s, when the agency’s budget spiked in a race to beat the Soviet Union to the surface of the moon. Today there is limited geopolitical competition in human spaceflight.

“We don’t have a mandate by Congress or the president to go to Mars in any time frame and budget that is anything like Apollo,” Garver said.

In recent years, the agency has had to build its strategies around flat budgets. "Budget is mission-critical" is a catch phrase at headquarters. NASA retired the space shuttle program in 2011 not because the hardware was old or dysfunctional, but to free up several billion dollars a year to build new rockets and capsules that could go beyond Low Earth Orbit.

The agency has been tugged in different directions in recent years, with dizzying results. President George W. Bush put forth a plan in 2004 to return to the moon with astronauts. The resulting program, Constellation, envisioned an array of new hardware, from big rockets to a lunar lander. But Obama killed Constellation, saying in 2010, "I understand that some believe that we should attempt a return to the surface of the Moon first, as previously planned. But I just have to say pretty bluntly here: We’ve been there before."

Members of Congress, keen on keeping lucrative contracts in their districts, preserved some of its elements, notably the Orion spacecraft, which may not be ready for its first test flight with astronauts aboard for another eight years. Where can Orion go? It's overbuilt for missions to the space station. Right now, NASA plans to send it to lunar orbit as part of the Asteroid Redirect Mission.

Obama backed a mission to an asteroid as an interim step to Mars. The proposal was understood to mean an asteroid in its natural orbit around the sun. NASA realized that such a mission would take hundreds of days and require expensive new hardware to house astronauts for such a long journey. The agency went to a backup plan, saying it would snag an asteroid with a robotic spacecraft and haul it back to a lunar orbit, where it could be visited by spacewalking astronauts delivered there by Orion.

Astronauts from the International Space Station answer questions from the cast and crew of "The Martian." (NASA)

NASA struggled to find a suitably sized, catchable asteroid, and reworked the plan again. The current goal is to send the robotic vehicle to a large asteroid, break off a boulder, and bring the boulder back to the lunar orbit for inspection by astronauts.

Meanwhile, NASA is building the Space Launch System, a heavy-lift rocket that could be used to send Orion to the vicinity of the moon. The SLS would have to be upgraded significantly to be used in Mars-mission architecture.

Any return to the moon would require a lander. An international partner could potentially step in and provide that critical piece of hardware, said John Logsdon, professor emeritus of the George Washington University Space Policy Institute.

“The line that’s being followed carefully is that we would be happy to go back to the moon with somebody else. But we’re not going to build the lander,” Logsdon said.

Going to Mars raises a suite of technical challenges. NASA engineers need to figure out how to land heavy payloads on Mars. They also have to devise systems to protect astronauts from radiation in outer space.

NASA can point to progress in understanding how to keep astronauts alive on Mars by letting them live off the land. Jim Green, NASA’s director of planetary science, said the next Mars rover, scheduled for launch in 2020, will have instruments that can extract oxygen from the Martian atmosphere. Already, the Curiosity rover has found nitrates in the soil that would be handy for an astronaut needing fertilizer in a greenhouse.

And then there’s the water: Mars, Green said, has more moisture in the soil than previously believed, and more humidity in the air. It’s possible the ephemeral, salty water suggested by a much-hyped study announced Monday comes from fresh-water ice or aquifers below the surface, he said.

Green, a consultant on the movie “The Martian,” said Matt Damon’s character could have taken advantage of that water.

Grunsfeld, the science official, thinks the next big step for NASA might involve an effort to detect Martian life. This is a more delicate matter than most people realize: If there is life there -- and that's a huge if -- it could be contaminated by microbes aboard NASA’s non-sterilized spacecraft and rovers. An experiment might inadvertently discover stowaway Earth-life rather than genuine Martian life.

Grunsfeld has an idea: Drive a rover to the edge of a crater that features the kind of intriguing, dark-streaked gullies suggestive of periodic flows of liquid water. "Carry along a little rocket launcher that has a sterilized bucket that you shoot on a wire. Drag the bucket up, collect this wet soil, and analyze it from a distance with a chemical laser," he said.

“I’m just brainstorming,” Grunsfeld added.

It’s not clear that the U.S. government will ever decide that a human mission to Mars is worth the cost, and Mars may wind up visited first by private-sector dreamers. SpaceX founder Elon Musk talks often of colonizing Mars, and near his desk in his SpaceX headquarters in California is a painting of Mars terraformed into a blue planet.

Musk's standard line is that he'd like to die on Mars, just not on impact.

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