HOUSTON -- Nearing the end of its first week at Mercury, NASA's MESSENGER spacecraft is in good health, in the right orbit and almost ready to snap its first pictures of the solar system's innermost planet since it slipped into orbit last Thursday.

Artist's concept of the MESSENGER spacecraft at Mercury. Credit: NASA
 
The first picture from MESSENGER will show territory on the dense, scorched world never before seen during the probe's three fleeting flybys in 2008 and 2009 or by the Mariner 10 spacecraft in 1974 and 1975.

The Mercury Dual Imaging System, MESSENGER's stereo, color and black-and-white camera, will take its first picture since orbit insertion March 17 as the spacecraft flies high over Mercury's south pole. The image time is scheduled for 0740 GMT (3:40 a.m. EDT) next Tuesday.

More than 350 images will be gathered by the MESSENGER camera over about six hours, then the data will be downlinked to Earth.

Eric Finnegan, MESSENGER's mission systems engineer, said the MDIS camera will be moved from the stowed position to an operational orientation for the picture-taking campaign. Officials plan to release images on a nearly daily basis as the pictures are radioed back to Earth.

The $446 million Mercury Surface, Space Environment, Geochemistry and Ranging mission is funded by NASA and managed by the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

MESSENGER is the first spacecraft to ever orbit and conduct long-term observations at Mercury. It is scheduled to spend at least one Earth year studying Mercury. That is equivalent to four revolutions of Mercury around the sun.

The probe fired its main engine Thursday for about 15 minutes to bend its trajectory enough for Mercury's gravity to capture MESSENGER in a looping egg-shaped orbit angled over the planet's poles.

"The team is relieved that things have gone so well, but they remain busy as they continue to configure the spacecraft for orbital operations and monitor its health and safety in the new environment," said Peter Bedini, MESSENGER's project manager at JHUAPL.

This image of a crescent Mercury was captured during a MESSENGER flyby in October 2008. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
Finnegan told Spaceflight Now the spacecraft is in an orbit with a closest approach 128.5 miles above Mercury's surface and a high point of 9,482.7 miles. The orbit is inclined 82.5 degrees to Mercury's equator and it takes MESSENGER more than 12 hours to complete one circuit of the planet, according to Doppler tracking data.

Those numbers are consistent with MESSENGER's targeted orbit before the insertion burn last week.

Controllers plan to fire MESSENGER's main engine every few months to adjust the low point of the probe's orbit back to an altitude of about 125 miles because the sun's gravity gradually tugs the satellite's altitude higher. The first such correction maneuver is planned for mid-June, Finnegan said.

Engineers switched on six of MESSENGER's seven science instruments Wednesday to start commissioning and calibrations, according to Finnegan.

MESSENGER carries the Energetic Particle and Plasma Spectrometer, a Magnetometer, the Mercury Atmospheric and Surface Composition Spectrometer, the Mercury Laser Altimeter, a Neutron Spectrometer, an X-Ray Spectrometer and the Mercury Dual Imaging System.

All but the imaging system were turned on for testing beginning Wednesday. The dual camera will be powered up for image collections next week.

Beyond the more than 350 pictures on tap for March 29, the MDIS camera will acquire 1,549 images over the entire six-day commissioning period. The imager will gather more than 75,000 pictures during MESSENGER's observation phase.

The yellow box shows the field of view for the first planned image from MESSENGER since it entered orbit. Black regions show areas of Mercury's surface unseen in previous spacecraft visits. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
MESSENGER's operational mission is slated to begin April 4.

The spacecraft will help scientists compose a global map of Mercury, yield data on the planet's chemical and mineral make-up, explore its magnetic field and tenuous atmosphere and probe its interior, including an immense iron core than by be surrounded by molten material.

With a diameter of about 3,000 miles, Mercury is about one-third the size of Earth and only slightly later than the moon. Surface temperatures on the pockmarked planet range from -300 degrees Fahrenheit to 800 degrees Fahrenheit.

MESSENGER is equipped with a ceramic fabric sunshade and heat radiators to fend off the powerful rays of sunlight at Mercury. The 8-by-6 foot sunshade keeps the probe's sensitive electronics cool without having an expensive thermal system.

The Nextel cloth sunshade, similar to blankets used on the space shuttle, keeps the spacecraft operating at room temperature while absorbing temperatures as high as 700 degrees Fahrenheit.

Since its launch in August 2004, MESSENGER flew past Earth once, Venus twice and Mercury three times, taking a scenic and fuel-efficient 4.9-billion-mile route to orbit around the solar system's innermost planet.