MESSENGER Peeks at Earth

http://messenger.jhuapl.edu/news_roo...e_5_31_05.html

MESSENGER Peeks at Earth
May 31, 2005

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, or MDIS. 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 image is cropped from the
full
MDIS image size of 1024x1024 pixels, and the contrast has been adjusted
slightly to bring out the Moon in the same frame. The Moon was 248,898
miles (400,563 kilometers) from Earth.

Dr. 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 Aug. 3, but all were of star fields, dark space
or a calibration target on MESSENGER's lower deck. "The team is
elated,"
says Dr. Louise M. Prockter, MDIS instrument lead scientist at APL.
"These were our first 'real' images, and they're only going to get
better as MESSENGER moves closer to Earth."

The photo session was just part of the preparations for the Aug. 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. Closest
approach will bring MESSENGER 1,458 miles (2,347 kilometers) over
northern Asia; observers with small telescopes in Japan, Eurasia and
Africa will have the best chance to spot the spacecraft.

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. The upcoming Earth flyby and the Venus flybys, in October 2006
and June 2007, will use the pull of the planets' gravity to guide
MESSENGER toward Mercury's orbit. The Mercury flybys in January 2008,
October 2008 and September 2009 help MESSENGER match the planet's speed
and location for an orbit insertion maneuver in March 2011. The flybys
also allow the spacecraft to gather data critical to planning a
yearlong
orbit phase.

MESSENGER, short for MErcury Surface, Space ENvironment, GEochemistry,
and Ranging, is the seventh mission in NASA's Discovery Program of
lower
cost, scientifically focused exploration projects. Dr. Sean C. Solomon,
of the Carnegie Institution of Washington, leads the mission as
principal investigator. APL manages the mission for NASA, built
MESSENGER and operates the spacecraft.

Image

Taken May 11, 2005, this processed image comes 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 image clearly shows bands of clouds
between North and South America on Earth's sunlit side. The photo has
been cropped from the full MDIS image size of 1024 by 1024 pixels, and
the contrast adjusted to bring out the Moon in the same frame. (The
Moon
is actually much darker than the Earth - click here
images/earth_moon_relative.jpg for an image showing true, relative
brightness.)

The Moon was 248,898 miles (400,563 kilometers) from Earth at the time
of the image. The photo session was just part of the preparations for
MESSENGER's gravity assist flyby of Earth on Aug. 2 - the first major
adjustment to MESSENGER's flight path toward Mercury. MESSENGER was
launched on Aug. 3, 2004; after the Earth flyby, two flybys of Venus
and
three of Mercury, it will begin an unprecedented, yearlong science
orbit
around the innermost planet in March 2011.

Credit: NASA/Johns Hopkins University Applied Physics
Laboratory/Carnegie Institution of Washington.

Image

This computer-generated image simulates the view of Earth and the Moon
as MESSENGER's Mercury Dual Imaging System (MDIS) saw them while taking
test photos on May 11, 2005. Earth's orbit plane - known as the
ecliptic
- divides the top and bottom halves of the image.

The MESSENGER Mission Design Team created the image using the Satellite
Tool Kit software, developed by Analytical Graphics, Inc.

Credit: NASA/Johns Hopkins University Applied Physics
Laboratory/Carnegie Institution of Washington.