WASHINGTON, July 7 (UPI) -- At a NASA-sponsored briefing for journalists last December, scientists with the Mars Exploration Rover missions described the various hazards that could cut short the planned, twin 90 (Earth) day operations on the red planet and limit the amount of data shipped home by the robotic vehicles from their respective landing sites.
The biggest threat, the scientists said, was dust from the Martian surface, which would degrade the landers' solar arrays, eventually cutting electric power and causing the batteries to fail.
Of course, there was also the possibility that either, or both, of the rovers, named Spirit and Opportunity, would not even land successfully, suffering the same fate as the much smaller British lander, Beagle 2, which failed to establish communications with its controllers last Christmas Eve.
None of these bleak possibilities came to pass, despite several anxiety-causing episodes along the way. Instead, both rovers have performed much longer than mission planners had expected. Last Sunday, July 4, Spirit completed six months on the Martian surface, or double its planned operational lifetime. Opportunity stands to achieve the same milestone on July 25.
The challenge facing the mission engineers, at NASA's Jet Propulsion Laboratory in Pasadena, Calif., is to figure out how much longer the golf-cart-sized rovers can keep rolling along and to figure out how to fund the earthbound controllers, if necessary, for a while longer.
There is enough money to continue through September, or the end of the government's fiscal year. JPL officials are in touch with NASA headquarters in Washington about providing funds for a further mission extension, probably into 2005.
Extended funding or not, mission controllers are planning economy moves. July will be the last full month the rover team will be based in Pasadena. After that, they will use teleconferencing and shared data processing as long as necessary.
The first order of business over the next couple of weeks is to perform what controllers are deeming a "3,000 meter tune-up" on Spirit -- based on the distance it has traveled from its landing site, in an area named Gusev Crater -- before it embarks on an unprecedented climb up the hills called Columbia, in honor of the fateful space shuttle mission that ended in tragedy on Feb. 1, 2003.
Among other items, Spirit's tune-up will include:
-- Calibrating its front, hazard-avoidance camera. Mission engineers will pose the robotic arm in a series of positions and capture images to refine their ability to target objects. The team said it currently is experiencing about a one-inch error in predicting targets vs. their actual locations.
-- Giving Spirit its first "deep sleep," a mode that leaves the rover completely unpowered during the frigid Martian night. The idea is to save the energy that would be spent powering electronics and survival heaters that normally are turned on even when the rover is napping.
Spirit needs deep sleep to save energy in the coming days, controllers said. The main risk of the exercise is to the mini thermal emission spectrometer, which could be damaged by the cold if its heater is turned off. So, engineers are planning to complete two observations before they order the first deep sleep for Spirit. Opportunity has been using deep sleep for several weeks now, they said.
-- Re-lubricating one of the wheels. Spirit's right front wheel continues to draw roughly twice as much current as its other five. Controllers will order Spirit to drive to an area called Engineering Flats, a relatively hazard-free area about 20 feet from its current location. There, the rover will execute a series of diagnostic test drives and heating sequences over the course of four or five Martian days, called sols. The idea is to reflow lubricants to the wheel and correct the problem.
-- Testing visual odometry. The process uses navigation camera images taken during a drive to determine the rover's location. This feature has been improved over the course of the mission and engineers would like to use it on a regular basis to get Spirit where they want it to go more quickly. Sometimes the rover needs two or more sols to make a short approach when using the blind drive technique.
As Spirit prepares to head up the Columbia Hills, the Opportunity rover has been moving downward, further into the large crater called Endurance, located about a mile from its original landing site.
Opportunity is analyzing a hole it has ground into a rock called Tennessee, inside the Endurance crater, on an unusual surface nicknamed the Patio of the Gods, because it resembles paved stones. Controllers have moved the robot craft gingerly into the crater, conducting tests on a duplicate rover operating safely back in Pasadena, to make sure anytime Opportunity rolls down a slope it is capable of rolling back out.
Of the twin rovers, Opportunity has proven the most dependable, having operated almost without a hitch since its landing on Jan. 25. in an area along the equator called Meridiani Planum.
"I think it is entirely possible that we will make it through the Martian winter with at least one of these vehicles," said Steve Squyres, the chief scientist for the Mars rover mission. "If we can survive the deepest part of the winter ... and the situation starts to improve, conceivably we could go months beyond that. So it's not inconceivable that we could go into 2005."
Phil Berardelli is UPI's Science & Technology Editor. E-mail email@example.com