Testing, testing, testing! Key to the success
of any spacecraft mission is thorough checkout and testing along
every step of assembly. This week the MESSENGER team installed
two temporary "engineering models" of the Power Distribution
Unit (PDU) and the Integrated Electronics Module (IEM). An engineering
unit is not the actual component that will be launched with the
spacecraft - rather, it is a test device that behaves as the "flight"
unit behaves, thus allowing engineers to check out the spacecraft
assembly. (Both units are obscured in this view by the Turnover
The PDU serves a function similar to that
of a circuit breaker box in a house. It routes power from the
solar panels and battery to the various subsystems and instruments
on the spacecraft. The IEM contains the main processor, fault
protection processor, the solid state recorder and interface circuits
to the rest of the spacecraft - in essence, MESSENGER's brain.
Installation of these test components indicates
that the spacecraft is getting ever closer to its March 2004 launch
date. After the spacecraft checks out, these test components will
be removed and the real flight units will be installed.
Last updated: May 20, 2003