The search is back on for a spacecraft that disappeared during a landing attempt on Mars nearly six years ago, and there are hints that the location of the Mars Polar Lander might have been found.

Mars Polar Lander was headed for a touchdown near the south pole of Mars Dec. 3, 1999, but the spacecraft never reported home after it began its descent to the surface.

An investigation of the mishap concluded that the most probable cause of the failure was the generation of spurious signals when the spacecraft’s legs were deployed during descent.

Those bogus signals are thought to have given a false indication that the spacecraft had actually touched down. That, in turn, resulted in a premature shutdown of Mars Polar Lander’s descent engines, which would have resulted in the spacecraft crashing into the surface with devastating speed somewhere in the south pole region of Mars.

Mars Polar Lander was designed as one of the so-called “faster, better, cheaper” programs NASA put together in the 1990s with the goal of conducting highly focused missions for relatively small sums. During the Mars Polar Lander’s descent through the martian atmosphere, NASA received no telemetry data, so there was no way to know whether it reached its terminal descent propulsion phase. Even if it did , it is almost certain that early engine shutdown occurred, an investigative report concluded.

But nobody really knows what happened.

Alternative views

Following the loss of the Mars Polar Lander, NASA and the then National Imagery and Mapping Agency — now the National Geospatial-Intelligence Agency — combined forces to search for the missing spacecraft.

In their search for the lander or its wreckage during 2001, a study team pored over high-resolution imagery gathered by NASA’s Mars Global Surveyor (MGS) spacecraft, now in orbit around the red planet, in the hopes of spotting the lander and related gear, including a protective aeroshell, heat shield and parachute.

But doing so proved challenging, to say the least. One of the principal difficulties in finding the lander using images from the MGS is that the Mars Polar Lander is only somewhat larger — about six-and-a-half feet across — than the smallest objects the orbiter’s camera could see on the surface of Mars at that time.

Despite the problems, in an initial analysis, National Imagery and Mapping Agency researchers reviewed and assessed features seen in several images that they believe could indicate the presence of the lander and its protective aeroshell.

But an alternative view presented by NASA was that these features could be noise introduced by the camera system.

New observational tool

Fast forward to 2005. Enter, once again, the Mars Global Surveyor and its Mars Orbiter Camera , which is controlled from an operations center at Malin Space Science Systems in San Diego, Calif.

At the March meeting of the Lunar and Planetary Science Conference in League City, Texas, researchers described how the Mars Orbiter Camera is being used to obtain far-higher resolution imagery than it was originally designed to do .

The tactic is called “cPROTO”, short for compensated Pitch and Roll Targeted Observation, according to a paper that researchers Michael Malin and Ken Edgett, of Malin Space Science Systems, presented at the scientific meeting.

To acquire a cPROTO image, the entire MGS spacecraft is moved in pitch and roll directions, the team reported. “The ‘c’ in ‘cPROTO’ is for planetary motion compensation. While the Mars Global Surveyor is pitching and rolling as it orbits Mars, the planet also is rotating underneath it. The spacecraft’s pitch and roll are timed to account for the rotation of Mars, as well as the desired image resolution and target location,” according to their research paper.

Whereabouts of landers

Several tries are often needed to gather an image of a specific target because unexpected motions of the Mars Global Surveyor can cause specific targets to be missed by miles. Another problem is that only certain parts of Mars are accessible to cPROTO imaging at specific times during the year.

In addition, researchers have used a method called PROTO imaging, which uses no compensation for the rotation of Mars, to look for the lander. Both techniques have proven workable and produced images that not only were ideal for studying martian landforms and geologic materials, but also produced images of the locations of the Mars Exploration Rovers, Spirit and Opportunity.

Other PROTO and cPROTO efforts imaged the Viking and Mars Pathfinder landing sites.

Attempts also were made to image the British-built Beagle 2 landing locations. That spacecraft also failed to phone home in late 2003. A small impact crater was detected, “unusual for that part of Isidis Planitia,” a feature that also had a dark dune in it, Malin and Edgett said in their paper.

Additionally, the two researchers added that cPROTO images of candidate locations for the Mars Polar Lander are scheduled to be attempted this year.

Sources said the Malin Space Science Systems team is hot on the trail of the missing Mars Polar Lander and suggested that the Mars Global Surveyor in cPROTO mode would be trained on a suspected Mars spot this month.

While they expect those observations to be challenging, what really happened to Mars Polar Lander may soon, quite literally, be resolved.

Leonard David has been reporting on space activities for nearly 50 years. He is the 2010 winner of the prestigious National Space Club Press Award and recently co-authored with Apollo 11’s Buzz Aldrin the book “Mission to Mars — My Vision for Space...