The Beagle 2 Lander

LONDON, England (AP) -- Though space scientists have failed in two more attempts to confirm if Europe's first probe to Mars had safely reached the red planet, officials maintain they still haven't given up hope.

The efforts Friday by a NASA spacecraft and later by a British observatory were the third and fourth attempts to track the tiny Beagle 2 lander, since it was to have arrived on Mars shortly before 0300 GMT Thursday.

The probe -- designed to search for signs of life -- should have opened its solar panels and called home within a few hours. That didn't occur and scientists have trying ever since to locate it.

NASA's Mars Odyssey, which has been in orbit since 2001, had the first shot at communicating early on Thursday, but picked up nothing.

Jodrell Bank Radio Telescope

A powerful radio telescope at the Jodrell Bank Observatory in Cheshire, England, also failed to detect Beagle's call sign, despite scanning the Martian surface late Thursday.

On Friday, the NASA craft swept over the planned touch-down site on the Red Planet without picking up a signal. Friday evening, Jodrell scientists zeroed in on the planet again but with no luck.

The Stanford University radio telescope in California might be able to listen on Saturday, the agency said.

There was no immediate comment from the European Space Agency scientists Friday evening. But they had faced the first two failures with confidence and optimism, insisting it was too early to lose heart.

"We are not in any way giving up yet," Colin Pillinger, chief Beagle scientist, said at a news conference earlier in the day. "We will hang on testing and waiting and checking with Beagle 2 until Mars Express is able to look for us and that won't happen until Jan. 4."

The Beagle 2 on the Russian Soyuz rocket prior to launch

The Mars Express mother ship, which carried Beagle into space and set it loose a week ago, could offer the best chance to get a signal from Beagle.

The mother ship, which went into orbit around Mars on Thursday, is designed to beam back data gathered by Beagle. In the coming days, controllers must change its orbit from a high elliptical one around the equator to a lower polar orbit that will let it establish contact with Beagle.

Unlike Odyssey and the Jodrell telescope, its communications were specifically designed to hear the probe's transmissions, Pillinger said.

Pillinger said both the Mars Odyssey link and communications using Jodrell Bank were untested, but there were several more chances for Odyssey to pick up a Beagle signal. The next occurs at around 0700 GMT Saturday when Mars Odyssey passes over the landing site again.

After that the lander will go into an auto transmit mode, sending out a continuous on-off pulse throughout the Martian daylight hours to anyone able to receive it, the agency said.

Possible explanations for Beagle's failure to call home include an off-course landing in an area where communication with Mars Odyssey was difficult, if not impossible. Or transmission from the lander's antenna could be blocked from reaching Mars Odyssey or the ground-based telescopes, the agency said.

Despite the concerns, European Research Commissioner Philippe Busquin said the mission is a "fantastic achievement," whether scientists get any transmissions from the Beagle 2 craft or not. (Mars Express success)

"Even if not all parts of the mission have succeeded, we must still acknowledge its significance, and build upon the experience gained to ensure higher chances of success in the future," the European Union official said in Brussels.