Concerned NASA scientists reestablished communications Friday with the troubled Mars rover Spirit as a second US spacecraft, Opportunity, neared the Red Planet ahead of its planned arrival on the surface this weekend.
Spirit suffered a "very serious anomaly" and stopped normal transmissions on Wednesday but a signal was received overnight, reviving hopes of working out the communications problems with the spacecraft, flight controllers with the National Aeronautics and Space Administration said.
"The flight team for NASA's Spirit received data from the rover in a communication session that began at 1326 Universal Time and lasted 20 minutes at a data rate of 120 bits per second," the US space agency said, revising previous figures on the length and speed of the transmission.
Data sent by the solar-powered rover, which arrived on Mars on January 3, was captured by one of the giant antennas of the international Deep Space Network near Madrid, Spain, NASA said.
The transmission speed of 120 bits a second was well below the normal speed of 11,000 bits a second but even the weak signal was welcomed at NASA's Jet Propulsion Laboratory here after two days of worrying silence punctuated by an occasional meaningless "beep."
"The spacecraft sent limited data in a proper response to a ground command, and we're planning for commanding further communication sessions later today," Mars Exploration Rover Project Manager Pete Theisinger told reporters.
NASA engineers plan to ask Spirit to provide further information about its condition in an effort to work out why the rover fell silent on Wednesday, its 19th day on the Red Planet.
NASA usually sends daily instructions to the rover and Spirit sends back information several times a day using two US satellites orbitting Mars. Two attempts earlier Friday to communicate with Spirit using the Mars Global Surveyor and Mars Odyssey satellites had failed, however.
Announcing the breakdown in communications on Wednesday, a somber Theisinger said NASA was "very concerned" by problems that may be due to glitches in the robot's software or hardware troubles in the onboard computer.
The breakdown came just as the rover was to begin searching the surface of the planet.
The six-wheeled Mars Exploration Rovers are 1.6 meters (5.2 feet) long and have a 1.5-meter high (4.9-feet high) camera mast. Each rover is packed with sensitive equipment to search for signs that there may have been water on Mars in the past that could have sustained life.
While engineers seek to resolve the communications problems with Spirit, its twin, Opportunity, is on a perfect trajectory for an arrival on the surface at 9:05 pm Saturday (0505 GMT Sunday).
Spirit is in the Gusev Crater, a rock-strewn, dusty terrain that NASA experts believe might have once been a lake. Opportunity is to land on the Meridiani Planum, described by NASA as one of the "smoothest, flattest places on Mars."
The 820-million-dollar Spirit and Opportunity project is the most ambitious ever to the Red Planet and follows a number of failed voyages to Mars including a European mission. Its demise was acknowledged on Friday.
The European Space Agency (ESA) said final efforts to coax a call from Europe's lost Martian lander Beagle 2 would take place this weekend but the chances of success are negligible. The British-built mini-lab was due to have landed on December 25 but has failed to radio home.
Theories that the Red Planet was once awash with water received dramatic backing meanwhile from data relayed to Earth from Europe's unmanned spacecraft Mars Express.
First results from Mars Express sketched the vision of a planet whose surface was once sculpted by seas and glaciers and confirms indications its South Pole is capped by frozen water, ESA said.
Spirit Beeps It's Alive And "Commandable": NASA
(official status report follows below)
The command was tailored to the assumption that the rover's onboard computer is currently in a "fault mode", and the beep confirms that it has detected a serious fault, either in the hardware or the software.
The fact that the rover responded at all, however, is encouraging.
It suggests that the most serious potential cause of the malfunction -- a power failure -- has not occurred, although on the basis of what this reporter knows up to now it is still possible that the rover has suffered a partial power failure and is currently in a power-saving mode.
The timing of the problem suggests that it may have been caused by a software error triggered by the rover's incomplete reception of the set of commands transmitted to it yesterday morning to set its planned sequence of actions for the day. A serious thunderstorm over the Canberra tracking station in Australia during the uplink prevented the full set of commands from being received by the rover.
At this morning's press conference, JPL spokesmen stated their belief that the rover's computer was adequately programmed to recognize such an incomplete command set, and would deal with it by simply rejecting the entire set of new radioed orders and instead following a simpler set of preprogrammed instructions for the day. But on the basis of what we know at this point, it is probably not coincidence that Spirit's silence is due to a separate problem totally unrelated to that flawed command sequence.
If so, the problem now facing JPL's engineers is to try to unsnarl the precise nature of whatever errors may have been produced in the rover's software by such an incomplete command set -- or by some other cause, such as a possible physical "upset" produced in one part of the computer's memory by a cosmic ray or solar radiation.
This could be an extremely involved process, and it will certainly require extreme caution on the part of JPL's engineers, and extensive ground testing to confirm the appropriateness of every corrective command before it is actually radioed to Spirit.
The Venus radar-mapping orbiter Magellan was almost destroyed twice during the first few days in which it orbited Venus -- thanks to an incredibly subtle software error which was only triggered by a set of circumstances which occurred about one one-millionth of the time, and which took four months to be tracked down and corrected.
One additional hopeful fact, however, is that -- while spacecraft have frequently been lost before as a result of software errors -- in almost every case this has been because the software error caused the spacecraft to lose its attitude lock on the Sun, so that its solar arrays could no longer recharge its batteries and it ran out of power. Since Spirit is simply sitting on the surface of Mars with a set of rigid solar arrays fastened to its back, there is at least no danger of that happening in this case.
The next regularly scheduled press conference regarding Spirit's status is not set until 10:00 AM Pacific time Friday morning. It is possible, however, that if new important developments occur, JPL will hold an unscheduled press briefing later today to report them -- something which has occurred many times in the past.
JPL Status Report
However, the team is still trying to diagnose the cause of earlier communications difficulties that have prevented any data being returned from Spirit since early Wednesday.
"We have a very serious situation," said Pete Theisinger of NASA's Jet Propulsion Laboratory, project manager for Spirit and its twin, Opportunity.
Spirit did send a radio signal via NASA's Mars Global Surveyor orbiter Wednesday evening, but the transmission did not carry any data. Spirit did not make radio contact with NASA's Mars Odyssey during a scheduled session two hours later or during another one Thursday morning.
It also did not respond to the first two attempts Thursday to elicit an acknowledgment signal with direct communications between Earth and the rover, and it did not send a signal at a time pre-set for doing so when its computer recognizes certain communication problems. The successful attempt to get a response signal came shortly before 9 a.m. Pacific Standard Time.
No single explanation considered so far fits all of the events observed, Theisinger said. When the team tried to replicate the situation in its testing facility at JPL, the testbed rover did not have any trouble communicating. Two of the possibilities under consideration are a corruption of flight software or corruption of computer memory, either of which could leave Spirit's power supply healthy and allow adequate time for recovering control of the rover.
Engineers will continue efforts to understand the situation in preparation for scheduled communication relay sessions using Mars Global Surveyor at 7:10 p.m. PST and Mars Odyssey at 10:35 PST. Efforts to resume direct communications between Spirit and antennas of NASA's Deep Space Network will resume after the rover's expected wake-up at about 3 a.m. PST Friday.
Meanwhile, mission leaders decided to skip an optional trajectory correction maneuver today for Opportunity, the other Mars Exploration Rover. Opportunity is on course to land halfway around Mars from Spirit, in a region called Meridiani Planum, on Jan. 25 (Universal Time and EST; Jan. 24 at 9:05 p.m. PST).
"We have a very serious anomaly on the vehicle," said Pete Theisinger, project manager for the Mars Exploration Rover mission.
The emergency came as the National Aeronautics and Space Administration prepared for the arrival on Mars this weekend of the second exploration rover, Opportunity.
NASA said Wednesday that thunder and lightning storms over Australia had prevented scientists from sending Spirit its daily instructions.
But experts now think a more serious problem caused the blackout.
Theisinger said NASA experts had sent a command to Spirit on Thursday but are not sure if they got an acknowledgement.
"I'm told that they think they got it, that would mean that the spacecraft thinks it is on the fault side of the tree for some reason, that would mean we've got positive power, some elements of the software are working. So that would be good news, but again, we need to confirm that."
And Theisinger admitted that NASA was "very concerned".
Spirit arrived on Mars January 3 and started searching for signs of past life on the red planet last week.
Its twin rover, Opportunity, is due to touch down this weekend. The 820 million dollar mission expects each solar powered robot to keep working for about three months.
NASA stopped receiving data from Spirit at about 1440 GMT on Wednesday, Theisinger said.
Engineers first noticed the problem when they tried to send instructions to Spirit on Wednesday. They had attributed the lack of response to storms around the Deep Space Network antenna in Australia.
Spirit is in the Gusev Crater, a rock-strewn, dusty terrain that NASA experts believe might have once been a lake and so could have supported life if there was water.
NASA usually sends daily instructions to the rover and Spirit sends back information several times a day using two US satellites orbitting Mars.
After troubles with the Mars Pathfinder mission in 1997 NASA had warned before Spirit left Earth in June that the latest attempt to find signs of life on Mars would be risky.
The six-wheeled Mars Exploration Rovers are 1.6 metres (5.2 feet) long and have a 1.5 metres (4.9 feet) high camera mast. Each rover is packed with sensitive equipment to search for signs that their may have been water on Mars in the past that could have sustained life.
Since it landed on Mars, Spirit's 360-degree camera has sent back spectacular colour and infra-red panoramic images of the surface.
But problems with the airbags that cushioned the January 3 landing held up the start of the exploration on the surface.
The second, Opportunity, is due to land on another part of the planet at about 0500 GMT Sunday. Each rover was intended to work for at least 90 martian days, which would have taken the Spirit mission until late April.
The expeditions were intended to overcome the disappointment of the Orbiter, which left Earth in December 1998 but disappeared on arrival, as well as the Polar Lander rocket, which crashed into the planet in 1999 when its landing system broke down.
A US Pathfinder rocket was the first vehicle to land on Mars in 1997. A small robot was put on the surface to gather information.
President George W. Bush last week announced a new space initiative aiming to set up a manned base on the moon from about 2015 and which would eventually send human missions to Mars and beyond.
AFP wire reports were partly used to file this report
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Martian Science Season Gets Off To A Rocky Start
Pasadena - Jan 20, 2004
NASA's Spirit rover has successfully driven to its first target on Mars, a football-sized rock that scientists have dubbed Adirondack. The Mars Exploration Rover flight team at NASA's Jet Propulsion Laboratory, Pasadena, Calif., plans to send commands to Spirit early Tuesday to examine Adirondack with a microscope and two instruments that reveal the composition of rocks, said JPL's Dr. Mark Adler, Spirit mission manager. The instruments are the Mössbauer spectrometer and the alpha particle X-ray spectrometer.
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