NASA

An artist's conception dating back to the 1990s shows a space vehicle powered by an electric propulsion drive approaching Mars. Electric propulsion is still the preferred technology for getting to the Red Planet.

Now that the International Space Station is complete, NASA is touting it as a test bed for future voyages to Mars. But when will those voyages start? Would you believe Oct. 9, 2033?

That's one of the best dates available for launching a Mars mission, according to Ben Donahue, space exploration engineer at Boeing Advanced Systems. At this week's International Space Station and Mars Conference, presented in Washington by Explore Mars, Donahue explained that the alignments of Earth and Mars make 2033 an "easy year" for interplanetary navigation. And after all, President Barack Obama did call for a mission to the environs of the Red Planet by the mid-2030s.

But in reality, the prospects for a Mars mission depend less on the celestial almanac and more on national priorities. If getting humans to Mars somehow became a national imperative, as getting humans to the moon did a half-century ago, the job could be done "before the end of the decade," said Larry Williams, vice president of strategic relations for SpaceX.

SpaceX is one of the fastest-rising stars in the aerospace industry, but even Williams acknowledges that any effort to send astronauts beyond Earth orbit would probably have to be government-led, not industry-led.

Williams compared beyond-orbit exploration to the creation of ARPANET, the federal government's forerunner to the Internet. "I would say there's probably a good return on investment" for government-led projects, in the form of economic competitiveness and prestige, he said. He wouldn't go so far as to predict that spaceflight would be the next big thing, "but I can't think of anything that's going to be more of that 'next thing,'" he said.

What's to be gained? The space race of the 1960s led to a revolution in satellite technology, opening the way to benefits ranging from global telecom and data networks to GPS navigation. The Internet's rise in the 1990s transformed the world economy again. Travel beyond Earth orbit may well lead the way to new resources, markets and frontiers in the 2020s and 2030s. And some folks, such as SpaceX founder Elon Musk, believe it's imperative for us Earthlings to spread out through the solar system in order to guard against a planet-killing catastrophe like the one that killed off the dinosaurs.

But the "why" question is a huge tale unto itself. For now, let's concentrate on the "how." Here's how the experts at the ISS-Mars Conference sized up the road between the space station and the Red Planet:

Simulating scenarios: Six volunteers are more than halfway through their simulation of a 500-day mission to Mars and back, conducted inside an isolation chamber at a Russian institute. NASA is considering a different kind of simulation next year, which would involve transmitting voice communications to and from the station with a 10-minute delay. Several experts at the conference, including Apollo 11 moonwalker Buzz Aldrin, suggested that a prototype Mars transit module should be attached to the station for a series of on-orbit simulations leading up to a full-length mock Mars trip. One of the potential prototypes is an inflatable module built by Bigelow Aerospace.

However things work out, NASA and the space station's other international partners should have a lot more time to draw up their tests. The current plan is to extend operations on the space station to at least 2020, and NASA Administrator Charles Bolden said the partners are already talking about a further extension to 2028.

Testing technologies: One of the big problems for interplanetary travelers is the heightened exposure to space radiation. To address that issue, NASA is looking at active-shielding systems that could set up a protective magnetic field around a spacecraft. Another strategy calls for packing the food, water and supplies stored up for the astronauts (as well as the waste material they produce) in such a way as to shield them during the trip to Mars.

Other potential technologies include measures to counter the health effects of spending long periods in zero-G, as well as next-generation propulsion systems. The International Space Station could serve as a test bed for all these technologies. NASA already has agreed to test an experimental VASIMR plasma engine at the space station. The consensus at the conference was that solar electric or nuclear electric propulsion systems were the way to get to Mars, perhaps boosted initially by chemical rockets.

Doing dry runs: The current vision for space exploration doesn't call for going straight from the space station to Mars. Rather, NASA plans to take a series of incremental steps along the "flexible path" through deep space. Obama has called for a trip to a near-Earth asteroid by 2025, for example. That would serve as a "dry run" for deep-space transportation systems, said Bret Drake, exploration architect at NASA's Johnson Space Center.

Even though the White House nixed the Constellation Project's back-to-the-moon goal, a limited number of lunar trips could serve as dry runs for surface operations on Mars. A trip to Mars orbit and back, without touching down on the Red Planet, would represent another step along the way. The early missions may actually send astronauts to a deep crater on one of the Red Planet's moons, Phobos, from which they can manage a remote-controlled army of robots on the Martian surface itself.

Relying on robots: If and when humans go to Mars, robots will have already blazed the trail. One such robot, the Curiosity rover, is being prepared for launch this November. NASA and its international partners are deep into negotiations over a series of robotic missions leading up to the transport of fresh soil and rock samples from Mars to Earth for study.

Eventually, robotic production facilities will be sent to Mars to manufacture the fuel and oxygen that will be required for the astronauts who follow. When the complete scenario for a human mission is worked out, Donahue says robots should be sent out first to conduct a full dress rehearsal.

The long road vs. the short road: How long would a human mission last? It depends. One type of trip, known as an "opposition-class" mission, would get the astronauts to Mars in 217 days, give them a 30-day stay, and bring them back in 403 days. In contrast to that 650-day trip, the "conjunction-class" mission would last 916 days: 210 days to get there, 496 days at Mars, and 210 days on the return trip.

The 210-day transit time is "nearly identical" to the length of a typical tour of duty on the International Space Station, said former astronaut John Grunsfeld, who is now deputy director of the Space Telescope Science Institute. So taking a trip to Mars, or coming back, may not be all that much different from what space station astronauts are experiencing now. The big difference is that when their stint in space is done, returnees from the space station get to rest or recuperate. That won't be the case when astronauts finish a 210-day trip to Mars.

NASA

This graphic compares the trajectories for an opposition-class mission to Mars (left) with a conjunction-class mission (right). Both missions are launched in 2037, but the shorter mission returns to Earth in 2039 while the longer mission doesn't end until 2040.

"I think it's still an open question in terms of what it will take ... when crews do land on Mars so they can get to work," Grunsfeld said.

That's not the only open question. I've intentionally glossed over the biggest one: Is this trip really necessary? In the past, we've talked about the prospects of finding evidence of past or present Martian life, or creating a second home for Earth's species ... but I'd love to hear what you think. Tell me why we should go to Mars, or why not, in your comments below.

More about NASA's future course:

• Scientific shortfalls limit NASA's spaceflight ambitions
• Gallery: Seven out-of-this-world destinations
• Which way for NASA? A step-by-step path
• NASA lines up jobs for Robonaut

Join the Cosmic Log community by clicking the "like" button on our Facebook page or by following msnbc.com science editor Alan Boyle as b0yle on Twitter. To learn more about my book on Pluto and the search for planets, check out the website for "The Case for Pluto." 

The space android called Robonaut 2 was just unpacked from its box last month, but NASA is already thinking up jobs for the darn thing to do, such as replacing parts on the International Space Station and wielding a fire extinguisher. The robotic exercises are among five sets of tests that mission planners have drawn up for next year, aimed at addressing future challenges in spaceflight.

Experts on space station utilization as well as future exploration have been discussing the proposed tests for some time now, said Pete Hasbrook, increment manager for the ISS Program Office at NASA's Johnson Space Center. A go-ahead for Robonaut's chores and the other space station tasks is likely to come later this month, he said today in Washington at Explore Mars' first International Space Station and Mars Conference.

Robonaut 2 is a 300-pound robotic torso equipped with a camera-equipped head as well as a pair of arms with five-fingered hands. It's designed to take on simple tasks that might otherwise be done by an astronaut, inside or outside the space station. The contraption, developed in partnership with GM, was delivered to the station aboard the shuttle Discovery in February and is due to begin checkouts in May.

Hasbrook and his fellow planners are looking farther ahead, to the station's experimental program between March and September of 2012. During that time frame, they'd like Robonaut 2 to simulate a spacewalking routine that requires the use of a grabber tool and a pistol-grip drill to work on a type of electronics box known as an orbit replaceable unit, or ORU. The robot could also be commanded to pick up a fire extinguisher and spray its contents onto a simulated experiment rack ... as if there were a fire in space.

Those are the kinds of jobs that Robonaut might be asked to do, under human supervision, during an actual spacewalk or a real emergency.

Testing technology ... and psychology
Now that the space station's construction phase is complete, Hasbrook and others are thinking about ways to use the orbital outpost as a test bed for the technologies that will be needed for future space missions. Here are three other experiments that Hasbrook said were under consideration:

• Taking an extra look at data from the Alpha Magnetic Spectrometer, a physics experiment due to go up during the next space shuttle mission, to gain further insights into the radiation environment in outer space.
• Conducting trials of equipment that could provide "active" radiation shielding for spacecraft, perhaps by setting up an electromagnetic field to repel the charged particles thrown off by the sun.
• Installing cameras on remote-controlled, thruster-equipped gizmos that float around in space like high-tech beachballs. The devices, known as SPHERES, could conceivably be used to inspect out-of-the-way corners of the space station or look over the shoulders of spacewalkers.

The fifth test has more to do with psychology than technology, and it could be at least as interesting as Robonaut's workouts: For seven days, audio and video transmissions between the space station and Mission Control would be delayed by 10 minutes. That arrangement is aimed at simulating the signal gaps that would be encountered during missions to Mars or other far-out destinations.

The 10-minute delay would even apply to the phone calls and video chats that space station astronauts conducted with their loved ones on Earth, Hasbrook told me. That might be frustrating for the astronauts, but the folks at Johnson Space Center are intrigued by the idea, said Trey Brouwer, ISS integration manager in flight operations for the United Space Alliance.

As a safety measure, data transmissions from the space station would not be delayed. Brouwer said the mission planning team still has to develop the detailed flight rules for the experiment. For example, what's the protocol in case a real emergency comes up during the simulation?

More autonomy for humans in space
Brouwer said the experiment would help NASA plan for scenarios in which ground controllers couldn't interact with astronauts in real time due to the immense distances involved. During a mission to Mars, the communications gap would vary depending on the changing distance between Earth and Mars. Theoretically, it could take as little as 3 minutes or as long as 22 minutes for a signal to get from one planet to the other.

Under those conditions, the home-planet headquarters would serve less as "Mission Control" and more as "Mission Support." Astronauts would have to have far more autonomy during a mission. At least that's what researchers have reported in previous studies on Mars mission architecture.

Next year's simulation is likely to be an eye-opener, for the space station astronauts as well as ground controllers.

"It's going to be an interesting exercise because we are so used to 'baby-sitting,'" Brouwer said. "The crews have really relied on us, and we're going to have to step away from that."

Join the Cosmic Log community by clicking the "like" button on our Facebook page or by following msnbc.com science editor Alan Boyle as b0yle on Twitter. To learn more about my book on Pluto and the search for planets, check out the website for "The Case for Pluto."

Sierra Nevada Corp.

An artist's conception shows Sierra Nevada Corp.'s Dream Chaser approaching the International Space Station. The Dream Chaser is one of the projects under consideration for NASA support.

Last updated 11 a.m. ET April 7:

NASA Administrator Charles Bolden says that commercial spaceships are an essential part of the space agency’s future, but that the next step in space commercialization depends on Congress.

Bolden touched upon the financial realities facing his agency today during an appearance at the International Space Station and Mars Conference in Washington. The two-day conference is aimed at looking at the long-term prospects for America's space effort, including missions to the Red Planet, but Bolden also touched upon shorter-term issues. For example, what will the space agency do about human spaceflight after this year's retirement of the space shuttle fleet?

For the really short term, NASA will have to rely on the Russians for transporting astronauts back and forth, but Bolden is hoping that commercial U.S. spaceship companies will step in to fill the gap. Not just hoping. He's counting on it.

"NASA cannot do both provisioning to low Earth orbit and exploration," Bolden said. The idea is that commercial companies will take care of the resupply of the space station, while NASA turns to the longer, more difficult job of developing the spaceflight systems for trips beyond Earth orbit. The way Bolden sees it, his agency can't afford to create a fleet of space taxis at the same time it's developing the more capable craft required for the next space frontier.

"There is no magic money," he said.

That's why NASA wants to rent rather than build those space station transports. Two companies, Orbital Sciences and SpaceX, are already receiving millions of dollars to build and test spaceships for ferrying cargo into orbit. Now NASA is on the verge of awarding as much as $280 million more for spacecraft capable of launching astronauts, in the second phase of a program known as Commercial Crew Development, or CCDev2.

Last month, industry analysts at FBR Capital listed their favorites for CCDev2 money: Orbital Sciences, Boeing, SpaceX and Sierra Nevada Corp., with AlliantTechsystems (ATK), Blue Origin, Excalibur Almaz and United Launch Alliance also on the short list.  

Some observers suggested that the awards would be announced as early as Wednesday, but Bolden kept mum. He suggested that the payout depended on whether Congress approved a spending plan that provided $312 million for the program, which would cover the awards as well as administrative costs.

"If it's less than $312 million, then we've got to go back and look at where we are with CCDev2," Bolden told reporters.

So the CCDev2 contractors may have to wait a bit longer for the final word, particularly if the fiscal stalemate in Congress results in a government shutdown. Bolden issued a preliminary advisory this week, telling agency employees to stand by for further word on which folks would be furloughed.

Although there's been no official word, a prolonged shutdown could complicate preparations for the shuttle Endeavour's upcoming trip to the space station. Space station operations, however, would be little affected, because keeping the multibillion-dollar orbital facility and its residents safe is seen as an essential function.

Update for 11:50 p.m. ET: Space News' Brian Berger reported in a Twitter update that CCDev2 contractors have been "told to be on standby Thurs. afternoon for word from NASA. But don't hold your breath."

Meanwhile, the shutdown showdown continues, but Bill Gerstenmaier, NASA's associate administrator for space operations, told me tonight that a shutdown wouldn't have any immediate impact on the preparations for Endeavour's flight. "Think about it," he said. Gerstenmaier pointed out that the launch was postponed from April 19 to April 29, due to a Russian scheduling conflict. That means there are roughly 10 days of wiggle room in the pre-launch routine. Of course, it all depends on how long the shutdown lasts ... if it happens at all. 

Update for 11 a.m. ET April 7: The CCDev2 announcement has been delayed indefinitely, apparently because of the continuing back-and-forth over the federal budget, according to John Elbon, vice president and program manager for commercial crew programs at the Boeing Co.

Join the Cosmic Log community by clicking the "like" button on our Facebook page or by following msnbc.com science editor Alan Boyle as b0yle on Twitter. To learn more about my book on Pluto and the search for planets, check out the website for "The Case for Pluto."