When President Bush announces an ambitious plan on Wednesday to send astronauts back to the moon as a stepping stone to a manned Mars flyby, many may wonder why not aim for the Red Planet directly.
One big reason is practice. Many scientists believe that before astronauts attempt to reach Mars, a so-called "camp site" on the moon is needed to test out transportation and survival capabilities.
The moon is an average 250,000 miles from Earth — a stone's throw compared to the average 48 million miles that separate our planet and Mars. There are many critical questions about surviving on a hostile surface that still need to be addressed, such as radiation exposure, microgravity concerns and keeping up supplies of air, food, water and energy. Most believe it's best to figure out these issues from a place that's closer to home.
As a 1992 NASA report states, "the relatively accessible moon affords valuable experience in living on a hostile planetary surface while still maintaining the option to return quickly to Earth in an emergency."
Getting to Mars, even in a fly-by mission, is a grand goal that's "surpassingly fascinating and desirable," says Harley Thronson, director of technology in the Office of Space Science at NASA headquarters in Washington. But, he adds, "It's virtually certain we would need an intermediate step like the moon to get there."
Here are some key factors scientists need to address to establish a lunar base camp and a subsequent manned trip to Mars.
According to a May 1992 NASA report, nuclear energy could offer powerful propulsion for the heavy-lifting that will be required to carry the significant supplies for setting up camp on the lunar surface. It will also be critical in cutting the traveling time to Mars and reducing travelers' exposure to dangerous radiation.
The Radiation Problem
Among the most critical worries facing lunar inhabitants and Mars explorers is exposure to cancer-causing doses of radiation. Radiation from solar flares or cosmic ray "storms" can last for days and astronauts could be exposed to massive doses since they will be spending record time in space.
To protect humans in space, scientists will need to improve their ability to predict space weather and solar storms, as well as develop safe, shielded vessels. Once warned, explorers could take refuge in shielded capsules in spacecraft or in underground bunkers on the moon or Mars.
Air to Breathe
Any spacecraft or habitat must have adequate air suitable for human breathing. One important aspect of maintaining breathable air is establishing recycling systems that remove carbon dioxide and contaminants.
On lunar and Mars surface camps, explorers could possibly establish a steady oxygen supply by mining minerals from soil and extracting elements needed to create oxygen.
For a moon outpost or a Mars journey to be feasible, explorers will need to grow most of their food supplies. This could involve building greenhouses for growing vegetables, and possibly even developing meat products in laboratory nutrient solutions.
In order to manage human waste and other waste, extreme recycling will be required. Astronauts on the space station already use systems to recapture water from their urine and perspiration. Solid human waste could be treated and used to fertilize greenhouse products. It will also be important to recycle any supplies that have served their initial purpose.
Unlike the robotic rover now probing Mars' surface, human explorers will require a steady drinking water supply. On the moon, water could be gleaned from polar permafrost detected by a space probe in 1998. A fuel cell system used to power space ships and machinery could create water as a byproduct. Whatever water is generated can't be wasted so a purifying system that would recycle urine and other liquid products would also be critical.
Keeping in Touch
Instant messaging, cell phones and gadgets such as Blackberries have revolutionalized how quickly people can reach one another on Earth. On Mars, instant communication will be much more difficult, if not impossible, since a radio signal between Earth and Mars can take up to 20 minutes. As a result, astronauts will need to be self-reliant in the event of an emergency.
Living in Microgravity
Astronauts living for long periods on space stations have experienced substantial muscle loss, as well as bone weakening. This will become even more significant for lunar base camp inhabitants and Mars explorers who will live for much longer periods in space.
Physiologists and engineers have been working on ways to combat this problem by developing exercise systems that work in space. These systems are not only needed to keep up muscle tone but also to provide some kind of pressure to the human skeleton to prevent bone loss. Centrifugal systems are one way of providing force on the skeletal system.
Protecting Against Temperature Extremes
Temperatures on the moon range from -233 F to 212 F, with an average surface temperature of -9 F. Temperatures on Mars range from -170 F to 17 F, with an average surface temperature of -76 F. To provide a habitat with consistent, warm temperatures, it may make sense to go underground where temperatures would remain fairly consistent with average surface temperature. These underground habitats would then need powered heating systems to keep it warm.
Lunar inhabitants and future Mars explorers will need unlimited supplies of energy. This could be derived from photovoltaic solar panels on the surface, although solar-blocking dust is a concern on both surfaces. Nuclear power is also considered a vital resource, according to a 1992 NASA report: "Nuclear surface power systems are capable of providing Mars base power to a megawatt level with reliable, long lifetimes."
Some believe that unexpected energy solutions may be discovered in exploration. Astronauts could find combustible materials on the moon or Mars that they could burn for heat.