The Mars-bound Curiosity rover will be begin steering toward the red planet during a lengthy thruster firing Wednesday, erasing the launch trajectory's deliberate aim away from the destination.

This is an artist's concept of NASA's Mars Science Laboratory spacecraft during its cruise. The spacecraft includes a disc-shaped cruise stage (on the left) attached to the aeroshell that contains the rover and descent stage. Credit: NASA/JPL-Caltech

Just like all planetary launches, the rocket actually fired the payload off-center from the target on a path to miss Mars by 38,000 miles to ensure the Centaur upper stage that is following the spacecraft won't hit the planet. The rocket motor wasn't subjected to the thorough cleaning to prevent Earth's microbes from contaminating Mars, thus the purposeful effort to prevent an impact.

The car-sized rover, packed inside the protective descent capsule, will use 8 thrusters located on the donut-shaped cruise ring atop the spacecraft to conduct the trajectory correction maneuver Wednesday starting at 6 p.m. EST (2300 GMT).

The first opportunity to perform the post-launch adjustment was available 15 days into the mission. But flight controllers opted to cancel that plan and wait six weeks before doing it now.

Seen as the largest maneuver the spacecraft will carry out during its 8.5-month trek from Earth to Mars, the thrusters are fired in a pre-programmed sequence over the span of 175 minutes to impart a velocity change of about 12.3 miles per hour.

"We are well into cruise operations, with a well-behaved spacecraft safely on its way to Mars," said Arthur Amador, Mars Science Lab's cruise mission manager at NASA's Jet Propulsion Laboratory in Pasadena. "After this trajectory correction maneuver, we expect to be very close to where we ultimately need to be for our entry point at the top of the Martian atmosphere."

The mission's trajectory -- as spelled out before launch -- included windows for 6 correction maneuvers. The last could occur as late as 9 hours before landing to fix any errors prior to atmospheric entry.

A burn in June will eye the precise corridor to the landing site where scientists want to send the rover within Gale Crater to determine if the area with its layered sedimentary landscape and apparent watery past was ever hospitable to life. The landing zone is a relatively small ellipse just 12.4 miles wide and 15.5 miles long -- a mere one-third the size of previous Mars rovers.

The $2.5 billion mission is headed for a late-night landing (California time) August 5 between 10 and 10:30 p.m. PDT (1 and 1:30 a.m. EDT Aug. 6) in Gale Crater.

As of Saturday, the spacecraft has traveled 73 million miles of its 352-million-mile trek to Mars, moving at 9,500 mph relative to Earth and at 69,500 mph relative to the Sun.

Mars Science Lab is spinning at 2.04 rotations per minute, communicating with Earth at a transmission rate of 2 kilobits per second and producing 780 watts of power from the cruise ring's solar arrays.

And the mission's Radiation Assessment Detector continues collecting data on the way to Mars.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

This special publication features the photography of British astro-imager Nik Szymanek and covers a range of photographic methods from basic to advanced. Beautiful pictures of the night sky can be obtained with a simple camera and tripod before tackling more difficult projects, such as guided astrophotography through the telescope and CCD imaging.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

Explore the Universe with these new versions of the award-winning Starry Night Software. Available now from the Astronomy Now Store.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

Astronomy Now is pleased to announce the publication of Exploring Mars. The very best images of Mars taken by orbiting spacecraft and NASA's Spirit and Opportunity rovers fill up the 98 glossy pages of this special edition!
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

This new poster features some of the best pictures from NASA's amazing Mars Exploration Rovers Spirit and Opportunity.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE