NASA
Approves MESSENGER Mission to Mercury
NASA approved
full-scale spacecraft development of MESSENGER, a science mission
to Mercury. The spacecraft will launch in March 2004,  and
beginning in April 2009 will orbit the planet for one Earth-year.
MESSENGER is short for MErcury Surface, Space ENvironment,
GEochemistry, and Ranging. The launch vehicle was not announced,
but the Delta 2 is the baseline vehicle for which the spacecraft
is designed.
The Principal
Investigator is Dr. Sean Solomon of the Carnegie Institution of
Washington. The Johns Hopkins University Applied Physics
Laboratory (JHU/APL), Laurel, Md, will design, build and operate
the spacecraft for NASA, in collaboration with industrial partners
GenCorp Aerojet (propulsion system) and Composite Optics, Inc
(integrated structure). Instruments and instrument subsystems in
the science payload are being supplied by JHU/APL, NASA/Goddard
Space Flight Center, the University of Colorado, and the
University of Michigan.
MESSENGER will
collect information on the composition and structure of Mercury's
crust, its geologic history, the nature of its thin atmosphere and
active magnetosphere, and the makeup of its core and polar
materials. MESSENGER will carry seven scientific instruments,
including a camera, laser altimeter, magnetometer and several
spectrometers. The spacecraft will globally image Mercury for the
first time.
MESSENGER's
five-year transit flight will include two flybys of Venus and two
flybys of Mercury, "gravity assists" that will help the
spacecraft refine its orbit to match Mercury's quick, elliptical
orbit around the Sun. MESSENGER’s orbit about Mercury will be
highly elliptical, 200 kilometers (108 nmi) above the surface at
its lowest point and more than 15,000 kilometers (8100 nmi) at its
highest. The plane of the orbit is inclined 80° to Mercury's
rotation axis, and the low point in the orbit is reached at
latitude of 60°N. The low northern hemisphere altitude will allow
for detailed measurements of Mercury's libration and the geology
and composition of the giant Caloris impact basin. MESSENGER's 12
months in orbit cover 2 Mercurean solar days. (The Mercurean solar
day, from sunrise to sunrise, is equal to 176 Earth days.) The
first solar day is focused on obtaining global map products from
the different instruments, and the second focuses on targeted
science investigations. Mariner 10, the only spacecraft to
previously visit Mercury, flew past it three times in 1974 and
1975, but gathered data on less than half the planet.
The
US$256 million MESSENGER mission is the seventh in NASA's
Discovery Program of lower-cost, scientifically focused space
flights and the third Discovery project managed by APL. The
mission cost figure does not include the launch vehicle and
mission operations.
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