That on/off/on-again NASA Dawn mission to asteroids Ceres and Vesta is now on schedule for sendoff – with the launch period for the spacecraft opening on June 20, 2007.

According to Dawn team member, Marc Rayman of the Jet Propulsion Laboratory, hardware and software subsystems already on the spacecraft were recently exercised to help uncover problems ranging from incomplete solder connections on a microchip or a broken wire, to software bugs, to unexpected interactions between subsystems that must work together.

In a Dawn Journal of July 29, Rayman reported that the Dawn probe is undergoing comprehensive performance tests. The spacecraft’s ion propulsion subsystem and the instruments for collecting scientific data are awaiting their respective shakeouts slated for this month, he said.

Receiving “extra testing” before being mated to the spacecraft, Rayman said, were power processing units that help run Dawn’s trio of ion engines.

So far….so good…but miles to go before Dawn reaches its asteroid targets.