The propulsion system designed to carry
MESSENGER through a six-year, nearly 4-billion mile trip to and
around Mercury is complete, marking a major step in the NASA Discovery
GenCorp Aerojet designed, built and installed
the propulsion system. Several members of the MESSENGER (MErcury
Surface, Space ENvironment, GEochemistry, and Ranging) management
and engineering teams visited Aerojet's Sacramento plant Jan. 28
for the system's official rollout, which included a salute to the
staffers who integrated the system with the spacecraft's composite
is one thing to view design drawings and computer-drawn renderings,
but it is another to see the realization of those designs,"
says MESSENGER Principal Investigator Sean C. Solomon, of the Carnegie
Institution of Washington (D.C.). "The MESSENGER science team
members are deeply grateful that the project and its industrial
partners have found the technical solutions - low-mass materials,
innovative integration of spacecraft and propulsion, and mission
design - that will enable the first mission to Mercury since 1975
and the first spacecraft ever to orbit that planet."
MESSENGER's lightweight, high-performance propulsion
system includes custom titanium tanks, a main bipropellant thruster,
and 16 small monopropellant thrusters positioned around the spacecraft.
Propellant will account for more than 55 percent of MESSENGER's
projected launch weight of 2,410 pounds (1,093 kilograms) - a lot
for a spacecraft that size, but necessary for the tricky task of
placing it into orbit around Mercury.
"It takes a lot of energy to slow
the spacecraft down once it reaches Mercury," says MESSENGER
Mission System Engineer Andrew G. Santo, of The Johns Hopkins University
Applied Physics Laboratory (APL) in Laurel, Md. "MESSENGER's
structure and propulsion system had to be very light to accommodate
a large amount of fuel, and the team has done a very nice job of
meeting those requirements."
MESSENGER will be loaded onto a truck today
for a three-day, cross-country trip to APL, which is building the
remainder of the spacecraft and manages the mission for NASA. After
vibration tests and a thermal "bake out" to clean the
structure at APL, the MESSENGER team will start integrating components
and science instruments on the craft in mid-February.
MESSENGER, part of NASA's Discovery Program
of low-cost, scientifically focused missions, is on track to launch
from Cape Canaveral Air Force Station in March 2004. For more information
on the project, visit http://messenger.jhuapl.edu.
For a closer look at MESSENGER's scientific goals, visit http://messenger.jhuapl.edu/science.html.