For NASAs 2001 and 2003 shots, the agency has already announced plans to send first an orbiter to map the planets surface composition and then, two years later, a pair of rovers that will act like robotic field geologists during their 90-day missions.

Here are thumbnail sketches of the spacecraft NASA has or hopes to have in the stable of vehicles that it and its international partners will use to explore Mars beginning in 2005.

• The Mars Reconnaissance Orbiter will follow the modern water on Mars, using its eagle-eyed camera to image spots where the wet stuff may have flowed in the planets recent past. The camera will be capable of resolving features as small as 8 inches (20 centimeters) across better than commercially available satellite images of our own Earth. A visible to near-infrared spectrometer will map the surfaces mineral composition at finer resolutions than a similar instrument will do aboard the 2001 orbiter. All data acquired by the satellite will give scientists a better idea of what areas to target with later landed missions.

• A long-range, long-lived rover possibly powered by a radioactive fuel source will represent a step-up in size from the 2003 rovers. NASA hopes the mammoth rover could schlep upward of 660 pounds (300 kilograms) of scientific instruments on a trek across a wide swath of Mars, possibly covering the equivalent of the 135 miles (220 kilometers) that separate Washington, D.C. and Philadelphia. The mission would last as long as two years. Experiments would examine risks in the Martian atmosphere and environment to future human missions, as well as a search for organic chemistry in the planets soil. The rover could carry a weather station and perhaps a drill to dig up to 6 feet (1.8 meters) below the surface. The lander itself would arrive DOA at Mars, as will be the case in 2003. However, before expiring, it will demonstrate two important capabilities required for future missions: pinpoint landing and hazard avoidance.
• The first NASA "Scout" mission may make it to Mars during this launch opportunity. The standalone mission would be outside the standard orbiter and/or lander Mars track. Indeed, the mission could involve a balloon or airplane, or perhaps even multiple small landers similar to the British Beagle 2 lander. The goal is to promote out-of-the-box thinking and competition within the Mars community.
• The French space agency hopes to launch a science orbiter in this time frame, perhaps with NASA-contributed instruments aboard. The orbiter will represent the first time "aerocapture" is used at Mars, where the satellite takes a steep plunge into the Martian atmosphere to slow down and circularize its orbit around the planet, saving fuel in the process. The orbiter will also drop off four small probes, called NetLanders, on Mars. Three of the tiny probes will land on one side of the planet and the fourth on the far side, allowing the on-board seismometers to measure "marsquakes" and map the inner structure of Mars.
• The Italian space agency may also pony up their own orbiter in 2007, which would act as a relay for smaller missions such as the Scouts and boost the rate at which data can be beamed from Mars to Earth. The satellite will be based on a commercial, Earth-orbiting satellite the Italians are developing.

• Things begin to grow vague after 2007, although NASA hopes to team up again with the Italians, this time on a joint science orbiter. One proposal calls for it to follow up on the 2003 Mars Express orbiter that the European Space Agency hopes will use ground-penetrating radar to reveal the presence of subsurface water on Mars.

• This date represents the absolute earliest NASA and the French would aim to collect a sample of Martian soil and rock for return to Earth. The mission would involve a U.S. lander and rover collecting the samples perhaps a few pounds (kilograms) at most that would be blasted into Mars orbit by a small rocket. There a French orbiter would snag the samples and return them to Earth, or Earth orbit, for pick up by a space shuttle. The cost of such a mission could push $1 billion, which has forced NASA to leave it on the fuzzy edge of its current roadmap for exploring Mars. Indeed, NASA officials already concede it could slip to 2014.

2013:

• The French would launch a science orbiter during this opportunity.

2016:

• NASA would continue to collect and return samples to Earth from Mars surface.