CAPE CANAVERAL, Fla. – The first step in any human expedition to Mars won’t be the longest, but it may well prove to be the hardest.

Mars Missions

The 90-Day Report Plan: The "Report of the 90-day Study on Human exploration of the Moon and Mars," commonly referred to as the "90-Day Report," began as an initiative from President George Bush in July 1989.

Mars Direct - Non-stop Flight to the Red Planet: Robert Zubrin's plan differs from the 90-Day Report plan in its simplicity, lower cost and useof available technology.

NASA: Putting Humans on Mars: The space agency’s most current plan to put a human on Mars discards most ideas from the 90-Day Report and resembles the Mars Direct plan with one major difference.

Simply stated, neither NASA nor any other space agency on Earth now has the rocket power needed to affordably get a Mars mission under way.

And the round trip itself – which could span a total of three years – exceeds anything humans have done in space to date.

"That’s a long time," said Ken Fernandez of the Advanced Space Transportation Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama. "That’s unprecedented as far as anything that NASA or anybody has done. It is a tremendous challenge."

That’s not to say, however, that NASA’s drawing board is blank.

In fact, engineers at Marshall have sketched out preliminary designs for a mammoth rocket that would be capable of launching three times as much cargo as NASA space shuttles.

Dubbed "Magnum," the rocket (see image below) would rival in size the 36-story Saturn 5 rockets that were used to launch astronauts on sojourns to the moon and back in the late 1960s and early 1970s.

Standing some 315 feet (96 meters) tall, the Magnum would use new strap-on, liquid-fueled boosters that would first be tested out on space shuttles.

Unlike the shuttle’s current solid-fueled boosters, the new boosters (see below) would sport jet engines that would enable them to fly back to a landing strip like an airplane rather than parachuting into the Atlantic Ocean.

The new Reusable First Stage boosters would be safer than current models because they could be turned off in flight, allowing astronauts to abort a mission during the first two minutes after liftoff. That option is not available to shuttle crews now because once a solid-fueled booster is ignited it burns until its fuel is exhausted.

Also known as "liquid-flyback" boosters, the new rockets would form the first stage of the Magnum, which would be capable of carrying 176,000 pounds (79,835 kilograms) of cargo into low Earth orbit.

That payload capability is critical to staging a human expedition to Mars.

The reason: Heavy equipment for the trip – such as astronaut transport vehicles and interplanetary space freighters -- first would be lofted into low Earth orbit before an expedition crew could embark on a journey to the Red Planet.

The early design work on the Magnum booster already is complete, but it’s unlikely the actual development of such a huge rocket will be undertaken anytime soon.

That’s because NASA for the next several years will have its hands full raising its infant International Space Station, a job that calls for the agency’s space shuttles to become frequent fliers over the first half of the decade.

"Right now, I think it’s fair to say the agency is focusing on current programs like the space shuttle – making sure the shuttle is safe – and also delivering on the International Space Station," Fernandez said.

"That’s probably going to occupy the main attention of the agency for four or five years down the road until the space station is fully operational. But beyond that, the agency will be open to new challenges."