By Todd Halvorson, USA TODAY
Getting a six-wheeled car-size rover safely onto the surface of the red planet? Daunting, sure. But NASA did it with Curiosity.
Sending humans on a mission to Mars? That requires overcoming even more outlandish obstacles.
Here's a look at five of the top challenges to safely getting astronauts to Mars, as well as potential solutions.
Are we there yet?
Problem: Trip time.
A round-trip human expedition to Mars, using current technology, could take two to three years. The slower you go, the more supplies you are forced to take and the higher the odds of a catastrophic collision with a meteoroid. Astronauts would lose more muscle and bone mass as a result of the longer stay in microgravity. And they would be exposed to larger doses of cosmic rays and solar energetic particles, increasing the probability of cancer.
"The main concern is clearly the radiation exposure to the human crew during such long journeys in deep space," said former astronaut Franklin Chang-Diaz, who shares the world record for most space flights - seven - with Jerry Ross.
"The long voyages in weightlessness are bound to substantially debilitate the crew," he added. "At Mars arrival, they must have a way to rehabilitate themselves before going to work, a tall order for the first mission in a very hostile environment."
Solution: Speed up the trip.
"All of these issues are greatly ameliorated with significant reductions in interplanetary transit time, which could be possible with advanced propulsion systems, potentially far more capable than the chemical and nuclear thermal rockets being considered," said Chang-Diaz, an MIT-trained physicist.
Chang-Diaz is developing an advanced plasma propulsion system that would cut the round-trip time on Mars missions to five months. The Variable Specific Impulse Magnetoplasma Rocket uses magnetic fields to guide superhot plasma out of an engine nozzle, producing an immense amount of thrust. A one-year trip to Mars could be cut to just 39 days.
Chang-Diaz said advanced high-power electric propulsion and nuclear electric power systems "could revolutionize in-space transportation by greatly reducing the interplanetary transit time."
The Big C
Astronauts traveling to Mars, or working on its surface, will be exposed to potentially high doses of galactic cosmic rays and what scientists call "solar particle events" - solar flares that spew highly energetic particles into interplanetary space. Galactic cosmic rays and solar flares create radiation that would increase the chance of an astronaut getting cancer. Genetic defects in offspring, and even death, also are possibilities.
Spacecraft propelling astronauts to Mars - and habitats on its surface - must be equipped with shielding sufficient to block space radiation.
Conventional aluminum shielding would have to be thick and, consequently, too heavy, thus, impractical. A better choice might be water, which absorbs radiation.
"One concept would be to have the walls be where you store your water - your water storage tanks," said Don Hassler of Southwest Research Institute in Boulder, Colo.
A regenerative water recovery system, like the one on the International Space Station, would be required to replenish tanks. Liquid hydrogen fuel also provides good shielding.
On the Martian surface: Soil, dust, rocks and pulverized rocks around the landing site would be dug up and used to sheath aluminum or inflatable habitats. Spacesuits worn during sorties outside habitats might require modification to provide radiation protection. Solid water jackets might be worn beneath spacesuits, and a thin layer of polyethylene could be used in suits. Helmet visors would be coated to reduce the chance of cataracts.
Sex in the solar system
Problem: Human nature.
Sex in space is a subject that has fascinated people ever since men and women started flying together in low-Earth orbit. Cramped quarters in Russian Soyuz spacecraft and U.S. space shuttle orbiters, relatively short flights and the extreme level of professionalism among astronauts and cosmonauts make it unlikely. But the International Space Station is as big as a five-bedroom house. Four- to six-month flights now are the norm, and round-trip missions to Mars could be much, much longer.
Solution: Can we talk?
Sex in space might seem like a frivolous subject, but it's actually a big deal. It's human nature. Let's face it. So says none-other-than the National Academy of Sciences, an independent group of distinguished scholars that advises the U.S. government on matters of scientific research, engineering and technology.
"Ignoring the potential consequences of human sexuality is not appropriate when considering extended-duration missions," an academy committee said in a 2008 report.
The committee reviewed NASA's Bioastronautics Roadmap - a document that examines crew health and performance issues for missions beyond Earth orbit - and determined that human sexuality was given no consideration.
"This oversight should be corrected," the committee said. "Areas of concern for the 30-month Mars mission include the potential psychological and physiological consequences of sexual activity, consequences that could endanger life, crew cohesion, performance and mission success."
Problem: Zero G.
The lack of gravity in transit - and reduced gravitational forces on the surface of Mars - could be cosmic kryptonite to even the most invulnerable of astronauts.
Long stays in a microgravity environment, or a reduced gravitational environment, could severely weaken explorers on Martian expeditions.
Bone and muscle mass will be lost at alarming rates. The cardiovascular, pulmonary and immune systems will weaken. Vision could be impaired. The vestibular system will be all out of whack, and balance could be off as a result.
Solution: Flying gymnasiums, pharmaceuticals, spinning spaceships.
Exercise, and a lot of it, is one of the best ways to combat the medical maladies caused by lengthy stints in microgravity.
On board the International Space Station, astronauts spend two hours a day walking and running on a treadmill, riding an exercise bike, working out with a resistive exercise machine, trying to ward off the ill effects of living and working in weightlessness.
Station crews also adhere to strict diets that are analyzed by nutritionists. Flight surgeons prescribe medicines to counteract bone loss. Nutritional supplements are added to diets when needed.
Medical research on the station will help scientists find ways to fix the problems.
"We call them countermeasures to treat the crew members or help the crew members overcome those challenges so that they can be healthy when they arrive, ready to do a mission at a new planet," said NASA Space Station Program scientist Julie Robinson.
A rotating spacecraft would create artificial gravity that would keep astronauts in tip-top shape. But that idea still remains the fictional stuff of books and movies.
You can't take it (all) with you
Problem: Provisioning an expedition.
Escaping Earth's gravity well remains a feat that nearly exceeds the capability of human engineers. Launching supplies into Earth orbit also costs millions and millions of dollars per mission. For instance: Rocketing four McDonald's Quarter Pounders With Cheese would cost roughly $10,000. On average, that's about the cost of launching a pound of payload into orbit.
So limiting the amount of supplies hauled along on a trip to Mars is important to making such a mission affordable.
Solution: Live off the Martian land.
Use the planet's natural resources, and its thin atmosphere, to significantly reduce the amount of fuel and supplies that must be shipped from Earth, at great expense, to sustain an expedition.
Give an astronaut a salad, and he will eat for a day. Teach them to grow lettuce, peas and radishes hydroponically, and a space garden could help feed astronauts on a Martian expedition.
Power a spacecraft with chemical propellants, and astronauts can fly back to Earth from Mars. Teach them to turn carbon dioxide in the Martian atmosphere into liquid methane, and they can manufacture some of the rocket propellant needed to fly home.
Haul water across interplanetary space, and astronauts have a chance to survive in a hostile environment. Teach them to turn ice at the Martian poles into water, and you cut mission costs significantly, making expeditions more affordable.
Todd Halvorson also writes for Florida Today.