ONE GIANT LEAP

In the 2030s, a peculiar shadow slips across the reddish vista that is Mars.

The historic arrival of the first expeditionary crew from Earth to the Red Planet balances on an impulsive mix of rocket propulsion, determined will, and hard-earned luck. Outstretched landing legs of the craft near the planet. A powered and safe descent by humans onto Mars is a literal trial by fire.

Robotic spacecraft have been there before. Over the previous decades, Mars has been flown by, circled, crashed into, pinged by radar, camera profiled, listened to, parachuted onto, as well as bounced and rolled over, shoveled and drilled into, smelled, baked, tasted, and laser zapped.

But to date there remained one missing element in the exploration of Mars: actually stepping on the planet. In the 21st century, the sandy face of that faraway world is to be dotted by the first footprints of humans.

The roaring engines of the lander are reduced in power, and the vehicle comes to a full stop, ending a voyage from Earth of millions of miles and several hundred days.

The crew has endured the physical, psychological, and social stresses of long-duration space travel. But as the first crew members prepare to set boot on Mars, the human journey ahead, while momentous, is treacherous.

As sojourners from Earth representing multiple nations take those early first steps, the third and fourth planets of the solar system may well be everlastingly linked. Setting foot on Mars is one thing, however. Staying put on Mars is far more daunting.

Getting humans off planet Earth and transiting to planet Mars means tossing into space lots of throw weight made feasible by heavy-lifting rockets. There’s a lot of work involved in flinging humans and their accoutrements outward for the months-long journey: food, water, and exercise gear, not to mention radiation shielding and the essential supplies to haul to Mars.

Scientists and engineers have begun to chart the ideal location for establishing the first human outpost on the Red Planet. That “best” site would not be selected solely for safety’s sake. The place of choice must be of high scientific merit too, arguably, supplying the best conditions for finding the answer to whether Mars has spawned a “second Genesis” of life.

Mars is also being eyed for its resources to help prolong the stay time of expeditionary crews on the planet. A new lineup of spacecraft is now in blueprint stage to scour Mars for underground pockets of ice.

Powerful communication orbiters are also a must for messaging and video links between Earth and Mars.

The distance between the two worlds leads to delayed dialogue, even at the speed of light.

DOWN AND DIRTY

The first crew on Mars will benefit from all manner of robotic craft that preceded them into the orbit and onto the surface of the Red Planet. Now circling Mars, for instance, NASA’s Mars Odyssey, the Mars Reconnaissance Orbiter, and the Mars Atmosphere and Volatile Evolution Mission (MAVEN) are part of an international armada of spacecraft probing the Red Planet, a flotilla that includes Europe’s Mars Express and India’s Mars Orbiter Mission, or MOM.

Mechanical predecessors await on the planet’s surface as well. Getting automated machinery “down and dirty” on Mars has been a hit-and-miss tale of retro-rockets, parachutes, airbags, and a complicated contraption called a sky crane. A progression of triumphant U.S. robotic landers involves two Viking landers in 1976; the Pathfinder/Sojourner rover in 1997; rover twins — Spirit and Opportunity — in 2004; and the Phoenix lander in 2008. And in August 2012, the largest payload ever to reach Martian real estate was the NASA Mars Science Laboratory mission, successfully depositing the car-size Curiosity rover. In total, that Mars machinery had a mass of roughly 1,984 pounds.

VIDEO: CURIOSITY LANDING

Landing far larger payloads — crew-carrying spacecraft and life-sustaining habitats — safely on the planet demands use of still untried landing technologies. Here’s the catch: Placing equipment and crew on Mars is more difficult than rocketing onto Earth’s moon, Apollo style, due to the higher gravity of Mars and the presence of an atmosphere.

Yes, the Mars atmosphere is very thin, but it is still a force to reckon with, causing major heating on an entering spacecraft. It’s significant enough to threaten overheating but not thick enough to enable landing with only aerodynamic decelerators, especially for the larger masses needed to support human missions.

Studies indicate that the best tactic is to use aerodynamic decelerators until a Mars craft is heading for the planet at supersonic speeds. Then the aerodynamic system separates, and descent module rocket engines ignite so that the vehicle makes a powered descent above Mars, a final approach, and a relatively controlled landing.

Add in the human factor, and the challenge is even greater. For example, to parachute the first crew onto Mars — say, tucked inside a 40-ton lander — would require a parachute the size of the Rose Bowl. Huge inflatable aerodynamic decelerators and supersonic retropropulsion are now considered the technologies of choice to get people and paraphernalia on Mars.