PASADENA, Calif. NASA may send a modified version of its wildly successful Pathfinder spacecraft on a repeat journey to Mars in 2003, relying on that missions tried-and-true cushioned landing technique to ensure the probes survival.

The Mars Mobile Lander option, complete with a large-scale rover, is one of two being considered for the upcoming launch opportunity, NASA officials announced on Friday.

The second would be to launch the Mars Surveyor Orbiter, a scientific satellite similar to the Mars Global Surveyor currently circling the planet.

(SPACE.com reported earlier Friday that NASA was eyeing the two missions for the 2003 opportunity, based on interviews with several NASA scientists.)

A Mars mission in 2003 could rely on the Pathfinder's entry, descent and landing approach -- including the parachute slow-down and airbag bounce-down.

Scott Hubbard, NASAs Mars program director, said Friday that the agency culled the orbiter and lander from 100 different proposals.

"Weve narrowed what we are going to do down to these two options if one is ready to go," Hubbard said in a telephone interview.

Over the next two months, Lockheed Martin Astronautics will lead a study on the orbiters risk, cost and readiness for the 2003 shot; NASAs Jet Propulsion Laboratory will do the same for the lander.

Ed Weiler, NASAs associate administrator for space science, will then make a final decision in early July, a scant three years before any potential launch date, (although both could be scrapped if found unready for launch).

"Our budget will support only one of these two outstanding missions for the 2003 launch opportunity, and it will be a very tough decision to make," Weiler said in a prepared statement. Either mission would cost NASA in the $300 million range.

Hubbard stressed there was no clear favorite at this time.

"Its like saying, 'do you like fish or steak?': they both have their good points and both have some risks associated with them," Hubbard said. "But quite frankly, either one of these would advance the state of our knowledge about Mars."

NASA had originally planned to send a lander-orbiter spacecraft pair to Mars every two years for the next decade. NASA has since scaled back that effort in wake of the back-to-back losses of the $125 million Mars Climate Orbiter and the $165 million Polar Lander spacecraft late last year.

If given the nod, engineers would design the Pathfinder-like Mars Mobile Lander to literally bounce down on the Red Planet swaddled in air bags just as the original mission did on July 4, 1997 to great fanfare.

Mars Pathfinder made history during its landing in the Ares Vallis region of the planet. Unlike any mission before or since Pathfinder relied on a unique combination of a heat shield, rockets, parachute and a 17-foot (5-meter) diameter cluster of airbags to make a cushioned landing on Mars.

A Mars mission in 2003 could rely on hardware similar to that used during the successful 1997 Pathfinder mission.

The tenacious Vectran fabric airbags allowed mission planners to discount any fears of sharp rocks jeopardizing the spacecraft during landing: it simply bounced off them before coming to a stop.

"The Mars Pathfinder landing system has a degree of robustness to it that is very appealing," Hubbard said.

Unlike the original Pathfinder mission, however, the 2003 version of the lander would be literally dead on arrival, serving only to safely deliver a rover to Mars' surface. The wheeled robot would dwarf Pathfinders Sojourner in size and capability.

The Mars Mobile Rover, as the more than 286-pound (130-kilogram) rover would be known, would then roam the martian terrain independently, acting as a robotic field geologist. It could travel up to 100 yards (meters) a day for up to a month, measuring the mineralogy and geochemistry of its surrounding soil and rocks. It would beam its scientific findings either directly to Earth, or via a relay satellite in martian orbit.

(FIDO, a prototype of the rover, is currently undergoing a two-week field test in an undisclosed location in the American West.)

The Mars Surveyor Orbiter would recover the science lost with the destruction of the Climate Orbiter in September 1999, as well as break new ground in the search for water.

The satellite would carry a complex suite of instruments, including a high-resolution camera, atmospheric infrared sounder, spectrometers, magnetometer and laser altimeter.

The probe would help scientists seek traces of carbonates on the martian surface. The minerals, which so far have avoided detection, would point to a past on the planet where standing water, whether in the form of lakes, ponds, rivers or streams, was commonplace.

NASA would design the orbiter to ensure it could last a full decade in orbit. That would allow it to serve as a telecommunications relay for future martian missions.

If the orbiter comes out on top in July, it would mean a wait until 2006 at the earliest for the next NASA spacecraft to actually land on Mars nearly a full decade after Pathfinder.

NASA plans to send at least one spacecraft to Mars every 26 months over the next decade, whenever the alignment of the Red Planet and Earth is suitable for launches.

Since the twin losses last year, NASA has gone back to the drawing board to reconfigure the architecture of its ambitious Mars exploration program. Weiler said NASA would unveil more complete program plans later this year, including the makeup of missions slated for 2005, 07 and beyond.

It has already canceled plans to send a lander to Mars in 2001, opting to launch only an orbiter. The 2001 lander, which has already been completed and was in contention for the 2003 slot, will now likely never leave Earth, Hubbard said.

Over the last six months NASA has toyed with everything from launching a Polar Lander repeat in 2002 to sending an entirely new class of spacecraft called "Scouts" to Mars.

"I dont view this as a scaling back of the plans for Mars as much as a standing back to take a deep breath," Hubbard said of the ongoing efforts.