Out in the rocky mountains, you feel closer to space. The veil of air is thin; the stars and planets seem nearer. So it’s fitting that the capital of the movement to send humans to Mars is at the University of Colorado in Boulder.

In the interests of journalistic full disclosure, I must note here that it’s a movement I’m proud to be part of. Since 1981, I’ve gone to Boulder for occasional conferences of Mars flight enthusiasts; the most recent was last August. I still remember the very first “Case for Mars” conference, organized by a band of graduate students who had no idea what sort of reception their proposed convocation would receive. After all, the last government official to endorse manned flight to Mars had been Richard Nixon’s soon-to-be-disgraced vice president, Spiro Agnew-an unfortunate patron saint.

In the early years of the Space Age, American citizens and aerospace engineers alike assumed that the moon landing was only the first step in an uninterrupted sequence of manned flights that would lead to Mars within 10 to 15 years. But in the ’70s, post-Apollo retrenchment eliminated Mars from even the most optimistic NASA timetable; with the political perception that we had won the space race, NASA’s budget was cut by two-thirds. The agency’s remaining energies were concentrated on the space shuttle program, and manned flight to Mars vanished from official consideration.

Yet people came to Boulder in ‘81. They gathered hesitantly, almost shyly, with no official backing from any agencies or corporations. Many had kept the faith during a decade when talk of manned interplanetary flight was almost taboo. Each seemed astonished to see so many others stepping out of intellectual closets to proclaim that they, too, thought a human mission to Mars was feasible and desirable, and that they, too, had a new idea or suggestion to bring it closer.

But last summer, the conference brimmed with boldness. This time, more than 700 people gathered not only to exchange ideas, but also to form a new “Mars Society” and sign a “Mars Declaration” stating their belief that human flight to Mars had at last become feasible and was more desirable than ever. (That declaration has since been posted on their website at www.marssociety.org, and copies have been sent to Washington.) At the main podium, a parade of speakers delivered wildly imaginative presentations with the stated purpose of making all others look too moderate. The conferees were astonishingly eclectic: NASA scientists and astronauts; university researchers and graduate students; even ordinary citizens, some of whom brought their children. Vendors offered Mars T-shirts and Mars calendars.

Since the conference’s planners, led by private-sector space engineer Bob Zubrin, founder of Pioneer Astronautics in Lakewood, Colo. (see “Mars on a Shoestring,” TR November/December 1996), were aggressively inclusive, the quality of the presentations varied enormously. Ideas were thrown around, thrown out and vigorously recycled. Specialized sessions dealt with everything from the engineering and medical challenges of a Mars mission to the legal and philosophical issues raised by human exploration of the planet.

Mooning Over Mars

if humans are to make it to mars, however, it will take much more than excitement. The successful flights of astronauts to the moon and back during the Apollo program of 1968 to 1972 rank as some of the greatest historical achievements of human technology; engineers overcame challenges in dozens of fields, including propulsion, thermal protection, communications and navigation, in a coordinated fashion. But the technological challenge of a manned mission to Mars represents a different order of magnitude.

Consider the basic numbers. One three-man Apollo mission used a single Saturn-V booster that placed about 120,000 kilograms of spacecraft and propellant in a low “parking orbit” just beyond the edge of Earth’s atmosphere. After another rocket firing and a three-day voyage, two of the crew landed on the moon and spent several days venturing out onto the surface to collect specimens, take photographs and deploy instruments. Total mission duration for one of the Apollo flights was 10 to 12 days.

For Mars, many of these figures would go up dramatically. Most mission strategies require assembling a vehicle in parking orbit out of several components launched separately, adding up to 400,000 to 500,000 kilograms. The outbound voyage would last six to 10 months, followed by a sojourn on the martian surface lasting more than a year; during that time, crew members would make hundreds of trips outside rather than the three or four that Apollo spacesuits, tortured by rough usage and abrasive lunar dust, barely completed. The full mission would take close to three years and the astronauts’ exposure to medical hazards such as long-term weightlessness and cosmic rays would be 100 times higher than it was for the lunar missions.

So at first glance, a Mars mission seems as though it would be many times more difficult than the lunar landings, and consequently many times more expensive (in current dollars, Apollo cost about $80 billion). But in the view of experienced space planners and economists, space technology has already reached levels that would enable Mars missions at costs equal to or even less than those of the Apollo program (see “Cheap Seats?,” right).

On a Wing and Thin Air

while mars enthusiasts may not yet know enough about the martian soil, they already know one important thing about the martian air: It is very thin. And though the martian atmosphere has less than 1 percent of the pressure of Earth’s atmosphere at sea level, a few aerospace engineers are drawing up blueprints for small unmanned airplanes capable of flying across vast expanses of the martian terrain. Such a plane’s instruments could survey complex geological regions, including many that look too rough for surface rovers.

Larry Lemke, a robotics expert from NASA’s Ames Research Center in California, told a plenary session about one winged mission. A 150-kilogram vehicle with a 10-meter wingspan, on the scale of a powered hang glider here on Earth, would be launched from Earth folded inside a probe. After the probe entered the martian atmosphere, it would drop its heat shield and pop open a small stabilizing parachute. The airplane would unfold itself during the descent, and detach from the parachute for its free flight. The winged robot could carry 20 kilograms of instruments, including an infrared pointed spectrometer to map mineral and ice deposits, and a suite of geophysical field instruments to spot traces of the planet’s geological history. Lemke’s team has already charted a 2,000-kilometer, three-hour course down Mars’ Vallis Marineris canyon (which is longer than the United States is wide).

The thin martian air, Lemke insisted, would not be an issue. At the planet’s surface, he pointed out, Mars’ air pressure is about the same as Earth’s at 24,000 meters’ elevation. Since NASA’s unmanned solar-powered “Pathfinder” aircraft routinely cruises at this altitude on Earth, it provides the proof of concept that a more specialized vehicle could also fly on Mars. “Aerodynamics is not a problem,” Lemke told the meeting.

Nor is technology a problem, Lemke said. “The Mars airplane has benefited from a lot of technological advances over the last 20 years from areas with no connection to astronautics. There has been work in radio-controlled aircraft, in lightweight structures, in electric propulsive motors, and in military deployment systems.”

The concept is so viable, Lemke believes, that he is calling for a launch in the year 2003, to celebrate the centennial of the Wright brothers’ first heavier-than-air flights. “We should mark the 100th anniversary of the first airplane flight on Earth with the first airplane flight on Mars,” he said.

Powering Up

whether robot airplanes fly on mars or not, for human voyages a key consideration will be the power plant that gets the explorers there. One possibility that was considered at the Mars meeting was nuclear power. The nuclear-powered rocket has been a mainstay of science fiction for generations, and in the 1960s the Atomic Energy Commission actually designed and tested several uranium-235-powered prototypes to serve as upper stages in space. By ejecting superheated hydrogen gas, they provided thrust as strong as chemical engines of similar size, but could get that same thrust while expending only half as much fuel mass. This efficiency would have been a tremendous advantage for the heavy manned Mars vehicles then under consideration.

Indeed, space nuclear power was the theme of several of the breakout sessions at the conference. The session I attended met in a windowless classroom in the basement, and was led off by Roger Lenard, an engineering manager from the Department of Defense’s Sandia Labs in Albuquerque, N.M. Lenard has advocated the use of nuclear power in space since his stint as director of the Timberwind project, a nuclear-powered anti-missile system designed as part of the “Star Wars” defense system. But Timberwind collapsed a decade ago under bad publicity over potential environmental impacts-firing it in combat threatened to contaminate large areas of the Pacific Ocean, including New Zealand.

Despite such concerns, nuclear power has remained popular in the imaginations of a core group of specialized engineers, and enthusiasm for extraterrestrial use of nuclear energy reached critical mass at the conference. Space nuclear advocates such as Lenard have been waiting for decades to get a mission approved, and they believe Mars is their best chance. By targeting a planet too far away to be considered anybody’s backyard, they hope to sidestep the “not in my backyard” attitude of anti-nuclear activism.

Lenard criticized what he saw as NASA’s tendency to avoid the subject of nuclear power because of its controversy. And even within NASA Mars mission studies that include nuclear power, he found what he considered to be unrealistic design constraints. In 1989, Lenard worked with NASA as a nuclear power specialist on a Mars design reference mission. That project included a single bimodal nuclear reactor, which first provided propulsion for beginning the Earth-to-Mars leg, and then provided electric power during the trip and on the surface. But bimodality is a bad idea, Lenard argued. “The design demands of a good propulsion system are antithetical to the design demands of a good power system,” he said.

Propulsion systems require a temperature as high as possible-3000 K-and operate for only a few hours at a time. “And you don’t worry a great deal about retaining all fission products,” he added, since they fade safely into the already-radioactive background of space. In contrast, providing electrical power (both in flight and on the surface) requires only modest temperatures and modest efficiency, but the system must operate over long periods.

In Lenard’s analysis, other Mars enthusiasts haven’t thought these issues through. “They presume that one development program for a reactor that does two or three things is automatically cheaper than two or three separate programs,” he told the packed room. “But we reject that. When the requirements are so mutually exclusive, this becomes a program with enormous risk, with long lead times and high cost.”

Still, excepting the wild card of political acceptability, nuclear technology is the top contender to power a Mars mission. Without nuclear propulsion, early manned missions to Mars would have to rely on chemical engines, making the vehicles larger and perhaps doubling the freight bill for getting a ship into orbit. More exotic non-nuclear systems capitalizing upon such concepts as “inertialess propulsion” and anti-gravity remain wildly imaginary and decades in the future at best.

Life on Mars

although power is clearly a challenge for a mars mission, as I moved from session to session and seminar to seminar, I began to see that there is another area that represents the core of the challenge-and it’s not really a technological problem. When the Apollo missions went for the moon, it was hardware that was most crucial-the rockets, the navigation, the crew control systems and even the rocks that were the mission’s goals. But with Mars as a destination, the focus kept falling on life.

For a successful manned mission to Mars, many different aspects of the meeting suggested, we must consider life on many scales. Microscopic nano-fossils may indicate past life on Mars, and will be a prime objective for exploration. At the level of medicine, we must determine how to preserve human health under flight conditions. In sociological terms, we will need to understand the proper mix of crew skills, and the proper crew organization for multiyear missions beyond the range of radio conversations.

Radio signal round trip time ranges from eight to 30 minutes, depending on how far apart Mars and Earth are at any given time, so today’s earthside frustration with playing voicemail tag will become the norm for Mars travelers. In a simple demonstration of a communications delay using banks of video recorders and periodically swapped cassettes, I organized an exercise in which attendees at a 1997 medical conference in Houston faced a simulated medical emergency on Mars. As actor-astronauts followed a checklist of responses to the crisis, the earthside medical team had to learn to anticipate the martian team’s needs and progress.

Amazingly, both the terrestrial and extraterrestrial teams adapted within an hour to the interplanetary rhythm, providing adequate questions and answers in a surprisingly efficient fashion. But the exercise only used a four-minute delay, and the scripted medical scenario was well defined. Future experiments will have to address more realistic delays and more unpredictable scenarios, as space planners prepare for the temporal challenge of Mars.

The communication challenges of the Mars mission also apply to the folks left behind on Earth. In the realm of politics and diplomacy, we must muster the national perseverance and international cooperation needed for such a long-term project. On the interplanetary scale, we should consider quarantine standards to protect Earth from any extraterrestrial life forms that might hitch a ride home from Mars. Finally, on perhaps the universal scale, I saw impassioned argumentation about the desirability of and the strategies for someday modifying the climate of Mars to make it more earthlike-in other words, to “terraform” it. Only a few of these issues were at all significant during the 1960s moon landings, but many of them would become critical to a successful human mission to Mars.

And that may be the key to securing government commitment to such a project, for such questions of life resonate on Earth, as well as in space. It seemed to me that a human Mars program-not just a one-time “flags and footprints” dash but a sustained sequence of expanding expeditions-could result in the same sort of broad-based technological invigoration that the Apollo challenges fueled 30 years ago. If designed properly, this bold project could accelerate innovative research also applicable to terrestrial problems, both known and as yet unknown.

But that was an argument for the politicians and the bean counters at the federal budget office. At the conference I was surrounded by people already persuaded, as I am, that the project is desirable, even urgent. And although Mars was not visible to the eye that week-it was just emerging from the sun’s glare in the pre-dawn skies-its image burned brightly in my mind. To me, in an inversion of everyday traffic rules, the red light in the sky signified “Go!”