Separately, NASA officials declined to estimate the odds for a successful landing next month.

Just before the attempt to land the Mars Science Laboratory carrying Curiosity on Aug. 6, mission managers said Earth will be positioned below the Martian horizon as the spacecraft descends toward its landing site near Gale Crater. While the spacecraft can send limited data as it approaches the thin Martian atmosphere, the repositioned Odyssey spacecraft that has been orbiting Mars since 2001 is now in a better position to relay confirmation of a landing back to NASA controllers at the Jet Propulsion Laboratory (JPL, Pasadena, Calif.).

Without the repositioning maneuver on Tuesday (July 24), NASA officials said Odyssey would have arrived over Curiositys landing site about two minutes after a sky crane tries to lower it to the surface. A six second thruster burn moved Odyssey about six minutes ahead to align its orbital pass with the planned landing site.

Mission managers previously reported that Odyssey had unexpectedly entered a safe mode on July 11, raising concerns about how long it would take to receive confirmation of a landing. The issue has since been resolved, and NASA said Odyssey is now operating normally.

Confirmation of Curiositys scheduled landing on Mars is expected to reach Earth at 1:31 a.m. eastern time on Aug. 6. Two other spacecraft NASAs Mars Reconnaissance Orbiter and the European Space Agencys Mars Express will record radio transmission for later playback. Only Odyssey will be in a position to relay information in near real time, NASA said.

In preparation for the risky landing attempt that marks the first time a sky crane will be used to lower the SUV-sized rover to the surface, mission managers also said they had completed a week-long process of rebooting and configuring the spacecrafts two redundant main computers. The uplink included spacecraft configuration parameters for entering the Martian atmosphere, descent, landing and surface operations.

Earlier this week, engineers began configuring Curiositys navigation system in advance of the landing attempt. That step involved configuration of two inertial measurement units on the spacecrafts descent stage.

Given the unprecedented size and weight of the Curiosity rover, NASA engineers were forced to come up with a risky sky crane technique to land on Mars. Onboard computers will be required to automatically execute a series of complex commands during the approximately seven minutes it will take for the spacecraft carrying Curiosity to descend through the atmosphere to the Martian surface.

Ask if mission planners had calculated the chances for success, JPL spokesman Guy Webster replied: No. Important risks are the unknowns, which resist calculating. Related story:

Video: '7 minutes of terror' for next Mars probe

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NASA preps spacecraft for risky Mars landing attempt