Messenger Peeks at Earth

LAUREL, Md., June 1 -- NASA's Mercury-bound Messenger spacecraft -- less than three months from an Earth flyby that will slingshot it toward the inner solar system -- successfully tested its main camera by snapping distant approach shots of Earth and the Moon. Messenger took a set of six pictures on May 11 with the narrow-angle camera in its Mercury dual-imaging system (MDIS).

This processed image is from the narrow-angle camera of the Mercury Dual Imaging System, or MDIS, on NASA's Messenger spacecraft. Earth was about 18.4 million miles (29.6 million kilometers) from Messenger at the time, but the main processed image clearly shows bands of clouds between North and South America on Earth's sunlit side. The Moon was 248,898 miles (400,563 kilometers) from Earth.

S. Edward Hawkins III, lead engineer for MDIS at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., said finding the Moon in the pictures was an unexpected bonus. "As we stretched the image, we saw this little object to the side, which turned out to be the Moon," he said. "That was exciting."

One of seven instruments in Messenger's science payload, the multispectral MDIS has wide- and narrow-angle imagers, both based on charge-coupled devices (CCDs) found in common digital cameras. MDIS has taken nearly 400 test shots since Messenger launched from Cape Canaveral Air Force Station last August, but all were of star fields, dark space or a calibration target on Messenger's lower deck.

The photo session was just part of the preparations for an August 2 Earth flyby, the first major adjustment to Messenger's flight path toward Mercury. While MDIS took its pictures, the Mercury laser altimeter team at NASA's Goddard Space Flight Center in Maryland checked its instrument's alignment by firing a high-powered laser at it from a ground-based Goddard telescope.

The mission operations and science teams are also finalizing plans to calibrate several instruments -- including the magnetometer, energetic particle and plasma spectrometer, and Mercury atmospheric and surface composition spectrometer -- during approach and departure observations of Earth and the Moon. During a 4.9-billion mile (7.9-billion kilometer) journey that includes 15 trips around the Sun, Messenger will fly past Earth once, Venus twice and Mercury three times before easing into orbit around its target planet.

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