SpaceX will fire all nine engines of the Falcon 9 rocket currently on the pad at Cape Canaveral, Florida today as part of a full-on dress rehearsal for the second launch of its Dragon spacecraft. Dragon will attempt a rendezvous with the International Space Station after a series of maneuvers intended to prove the craft's orbital maneuvering and navigation system.

If the maneuvers and berthing all go as planned, astronauts will open up the spacecraft and unload the supplies, then reload it with items for Dragon to return to the Earth. Dragon is the first commercial spacecraft to attempt a rendezvous with the International Space Station, and the first cargo spacecraft to be reusable. The renewed availability of the ability to send cargo back down to Earth after the retirement of the shuttle will make a huge difference in Station operations.

If all goes well this afternoon, SpaceX has set a new date of May 7 for the launch. This carries an enormous political payload in an election year because of the Obama administration's attempt to jump-start a commercial orbital space launch industry in the face of heavy Republican opposition. This afternoon's webcast will begin at 2:30pm Eastern Time, with the actually test firing scheduled for 3:00pm. You can watch the webcast at the SpaceX website.