A hydrogen leak scrubbed today’s scheduled shuttle launch; the new plan is to launch the 100th mission since Challenger on Sunday (or the Ides of March), a schedule the oft-cited Phil Plait calls optimistic.

The Discovery crew members are set to fly the S6 truss segment and install the final set of power-generating solar arrays to the International Space Station. The S6 truss will complete the backbone of the station and provide one-fourth of the total power needed to support a crew of six.

As in war, NASA personnel are always fighting the last battle: we (think we) know what brought down Challenger and what destroyed Columbia, so we make sure to avoid those issues. It’s good to see that the hydrogen issue, which has not yet been a problem on a space flight (though as illustrated, hydrogen has doomed aeronautic activity), proactively taken care of.