Silence From Mars Lander Prolongs a Tense Vigil

Scientists continued to hope that a U.S. spacecraft on Mars, lost in radio silence near the Martian south pole for nearly two days, would revive itself today to finally heed Earth’s insistent commands.

For two hours Saturday night, beleaguered flight operations managers listened vainly for any signal from the Mars Polar Lander. They expected to resume their uneasy vigil today.

As they waited for the lander to reveal its presence, space flight engineers at the Jet Propulsion Laboratory faced their sternest test: The engineering trial now in progress on an alien world 158 million miles away is not just a matter of mechanical design and manufacturing skill. It also is a test of engineering imagination, of how cleverly engineers anticipated the unknown and incorporated its mysteries into the lander’s circuits and computer code.

Indeed, as flight operations managers failed repeatedly to contact the spacecraft over the last two days, they greeted each new setback with what has become the mission’s mantra:

“This was not unexpected,” said Polar Lander manager Richard Cook after three long communications periods ended Friday without an electronic flutter from the $165-million lander.

“This was not unexpected,” echoed Deep Space 2 project manager Sarah Gavit after five chances to contact the $29.2-million Deep Space 2 probes jettisoned from the spacecraft failed to yield a signal.

Each time, the mission engineers quickly turned to yet another contingency plan--to try again for the winning move in an earnest game of expectations and assumptions. All the while, a gilded robot with blue outstretched solar wings is perched like a mechanical butterfly on the frigid slopes of the Martian south polar terrain. Or so NASA still hopes.

A planned communications blackout began just before the lander’s hypersonic descent into the Martian atmosphere Friday and, consequently, mission managers do not know for sure if the spacecraft even separated from its protective shell or if its 12 descent engines fired properly.

There are at least 100 so-called fault paths already mapped out, each a veritable maze of problems and possible solutions.

At several points this weekend, prearranged contingency plans could allow JPL flight operations engineers to establish contact with the spacecraft, either by relying on its on-board computer to react, by using a different antenna, by employing a backup radio or by using the orbiting Mars Global Surveyor as a relay station.

Late Saturday, JPL flight controllers transmitted a stream of commands to Mars in the hope that the instructions could motivate the lander to move its antenna in an elaborate search pattern to locate Earth.

Although they got no response Saturday night, JPL engineers still hoped that the three-legged lander could awaken itself from a self-induced protective mode and radio Earth this morning to begin a 90-day exploration of the Martian polar climate and geology. The protective mode is but one possibility, however.

The craft also may have landed awkwardly on a slope, or perhaps horizontally, causing its antennas to point in an unexpected direction.

The lander carries a robot arm to sample the soil of the Martian south pole, an advanced weather station, a brace of cameras and a microphone to relay the sounds of another planet for the first time.

If the spacecraft fails to signal Earth today, it could do so perhaps Thursday, depending on which of many potential glitches is at fault and a thicket of pre-programmed possibilities.

The uncertainty, however, does not appear to have outwardly shaken any official’s confidence in the Polar Lander mission.

“The spacecraft is on Mars; we are confident of that,” said Polar Lander project scientist Richard Zurek at midday Saturday. “For us the next 24 hours are going to be very important. By noon Sunday, we will be in a whole different ball game.”

But with each new opportunity to contact the spacecraft--with the rising expectations and the falling hopes--JPL engineers and scientists have found themselves on an emotional roller coaster.

“We are getting a little bit seasick from the adrenaline waves back and forth,” said Suzanne Smrekar, the Deep Space 2 project scientist.

On Saturday, failing batteries on Mars were sapping hopes at JPL in Pasadena that contact could be established with the two small Deep Space 2 microprobes released by the Polar Lander as it entered the Martian atmosphere Friday. New images of the suspected landing site released late Saturday raised the possibility that the probes hit a huge crater in terrain rugged enough to perhaps damage them.

The microprobes, designed to slam into the planet’s soil, have tiny batteries that are not rechargeable. In scientists’ second contingency plan, the two probes were expected to start transmitting automatically late Saturday, in the hope they might be heard by the Surveyor orbiting overhead. If the probes did call attention to themselves, project engineers won’t know until today at the earliest, when the Surveyor will start relaying its recorded data to Malin Space Science Systems in San Diego.

If they went into that mode, they could exhaust their batteries in five to 16 hours. But, depending on the probes’ physical condition, they might be capable of transmitting intermittently for a few days.

The lander, in turn, is expected today to attempt to take advantage of the Surveyor--which entered Mars orbit two years ago--on the assumption that the probes will have exhausted their resources.

If that happens, the lander will transmit to the Surveyor between 10:50 and 11 a.m. The Surveyor would transmit the data to Earth immediately because the fate of the lander has the highest priority.

If nothing works by Monday morning, there is another fallback plan to allow contact to be established with the solar-powered lander as late as Thursday.

Then the contingencies start getting really complicated. If it has not heard from Earth at that point, the craft is preset to start rearranging its computer programs and switching telecommunications states.

“We will have to move deeper into our strategy,” said Mars program manager Chris Jones. “It’s gotten very complex, but the strategy can be made to deal with it.”

Said Cook, “We are sprouting new ideas as we go along. . . . As time goes by, we are less confident. But the team is still upbeat.”

The ability to draw on such engineering precautions became especially important after the loss of the $125-million Mars Climate Orbiter in September. An arithmetical error put that spacecraft in the wrong orbit around Mars.

Even though JPL navigators detected the error at the last minute, they could not order a course correction that could have saved the craft because no one had worked out the engineering details in advance.

When the Polar Lander arrived at the same decision point, the navigators had an array of 12 pre-calculated course corrections to choose from.

“We are engineers and scientists and we are trying to do what we can do,” Zurek said. “We can’t back [the lander] up and land it again, so let’s do the things we can do.

“The spacecraft should be on the ground, protecting itself,” he said. “In fact, it may be getting more sleep than we are.”

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Mars Landing on the Web

Web sites offering information on Mars and the Polar Lander mission:

* JPL’s main Mars site will post the latest pictures and updates throughout the 90-day mission: https://marslander.jpl.nasa.gov or https://mars.jpl.nasa.gov/msp98

* JPL’s home page has links to the latest Mars projects as well as probes sent to other planets over the last 20 years: https://www.jpl.nasa.gov

* JPL’s Mars Education site includes activities for children and teachers. In one section, pages can be printed, folded and glued to create a model of the Mars Polar Lander: https://mars.jpl.nasa.gov/education/

* UCLA, where the primary science team is based, offers a site focusing on experiments involving the Mars Volatiles and Climate Surveyor payload: https://www.marspolarlander.com

* The Planetary Society will mirror JPL’s site and offer its own content in conjunction with its PlanetFest ’99 gathering at the Pasadena Convention Center: https://planetary.org

* The Mars Society, which advocates human exploration of the Red Planet, will mirror JPL and offer its own content: https://www.marssociety.org

Source: Associated Press