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3 Jun 2004
(Source: Johns Hopkins University Applied Physics Laboratory)

MESSENGER Mission News
June 3, 2004

? Awaiting the Big Push

With MESSENGER in the late testing stages, final launch preparations will soon begin. A few days before MESSENGER is mated to the upper stage of the Delta II launch vehicle, the team will fill the spacecraft's propellant and pressurant tanks.

Like many NASA deep-space missions requiring a lot of maneuvering capability, the MESSENGER spacecraft sports a bipropellant main engine, which, like an automobile engine, needs fuel and an oxidizer to run. Automobiles use gasoline (or diesel) as fuel; the oxidizer is simply oxygen from the atmosphere. Since MESSENGER will be working in the vacuum of space, it needs to carry its own oxidizer (in this case, nitrogen tetroxide) to combine with its hydrazine fuel. Hydrazine is a clear liquid that smells like ammonia and ignites when it meets the right oxidizer, making for a rather simple motor design. Once the fuel and oxidizer are sprayed into the engine nozzle in proper proportions - you have ignition! No spark plugs or other devices are needed to keep the engine running.

Hydrazine is also the lone propellant for the 16 smaller thrusters that help steady the spacecraft. No oxidizer is used in the thrusters so there is no combustion; the fuel sprays out over a heated material (a "catalyst") that causes it to break apart into nitrogen and hydrogen gas, moving the spacecraft in the direction opposite to where the thruster is pointed.(This is a practical application of Sir Isaac Newton's Third Law of Motion: "For every action there is an equal and opposite reaction.") To simplify the spacecraft design the MESSENGER team taps off the main hydrazine tanks to run the small thrusters, thus avoiding the need for yet another tank for yet another fuel.

MESSENGER carries 595 kilograms (more than half a ton) of propellant; this includes 97 kilograms (214 pounds) of hydrazine for control and 269 kilograms (593 pounds) to burn with the 229 kilograms (505 pounds) of nitrogen tetroxide in the high- performance "biprop" mode. Helium (2.25 kilograms, or 5 pounds) is used to maintain pressure in the fuel and oxidizer lines. The hydrazine is stored in two large, custom-designed titanium tanks and the oxidizer in a third, similar tank. A smaller tank holds the helium, and an extra supply of hydrazine is carried in a small auxiliary tank.

Expendable Launch Vehicle Status Report June 3, 2004

George Diller
Kennedy Space Center
(321) 867-2468

LAUNCH PAD: SLC-17B, Cape Canaveral Air Force Station
LAUNCH DATE:? July 30, 2004=20
LAUNCH WINDOW: 2:17:44 a.m. - 2:17:56 a.m. (EDT)

MESSENGER is undergoing prelaunch testing at the Astrotech Space Operations facilities near KSC. Autonomy testing of the spacecraft continues. This verifies MESSENGER's ability to operate on its own when not in direct contact with Earth. Installation of thermal blankets has been completed as required by the schedule up to this time. In upcoming work, the flight battery is scheduled for installation June 8 and the solar arrays will be installed June 21. Spacecraft fueling is planned for the end of this month.

The review to assess readiness to begin stacking the Boeing Delta II rocket on Pad 17-B was successfully completed May 19. Vehicle stacking is currently scheduled to begin on June 21, after the Global Positioning System (GPS) II-R12 launch, tentatively scheduled to launch on June 9. The launch period for MESSENGER extends through Aug. 13.

MESSENGER was built for NASA by the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

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Last Updated: 3 Jun 2004