The MESSENGER spacecraft has 16 small thrusters
(arrows "1" and "5") in addition to the main
engine (arrow marked "M"). Thrusters marked "1"
indicate 1 pound of thrust, while those marked "5" develop
5 pounds of thrust. At launch the spacecraft at launch will carry
about 611 kilograms (1,347 pounds) of fuel, about 90% of which
will be used during main engine burns.
However, the small thrusters play several important roles. The
5-pound thrusters help hold the spacecraft steady during main
engine burns and are also used alone for small course corrections.
The smaller, 1-pound thrusters are used in conjunction with the
gyroscopes to maintain the spacecraft's orientation during normal
cruise and orbital operations. In this image, the small thrusters
are temporarily covered (red caps) for protection during assembly
- though the main engine bell is visible through its temporary
four-pronged protective structure.
Last updated: April 22,