Friday am update: The Falcon 9 rocket lifted off on schedule Friday morning from Florida, and put its Dragon spacecraft into a good orbit. After this primary mission, the second stage of the Falcon 9 rocket is now undergoing an extended, four-orbit mission before it returns to Earth. This experimental flight should help demonstrate the upper stage's ability to perform direct insertion into geostationary orbit.

SpaceX's next launch should come about three weeks from now.

Original post: When SpaceX launches its 15th resupply mission to the International Space Station, possibly as early as Friday morning at 5:42am ET (09:42 UTC), the company plans to fly the Block 4 version of its Falcon 9 rocket for the final time.

The company's next two launches in July were already known to be flying on the latest and presumably final revision to the Falcon 9 rocket—the Block 5 variant. But during a news conference Thursday, the company's manager for the Dragon spacecraft program, Jessica Jensen, confirmed that there will be no more Block 4 flights after the impending space station launch.

The Block 5 version of the rocket, which has been optimized for reusability, has flown one time when it made a successful flight in May. Since then, SpaceX has been working through its inventory of previously flown rockets. The booster scheduled to fly Friday first launched just a little more than two months ago, on April 18, sending NASA's planet-hunting TESS spacecraft into a lunar resonant orbit. This 10-week turnaround was remarkably fast for a Block 4 booster, but SpaceX says its Block 5 should be able to fly much more rapidly.

Indeed, SpaceX intends to fly each Block 5 first stage it builds a minimum of 10 times, which would be hugely significant, as SpaceX has thus far only ever reused each of its Falcon 9 rockets a single time. Additionally, the company hopes to reduce the turnaround time between launches of a Falcon 9 booster, now several months, to a matter of weeks, or less.

Because SpaceX has no plans to fly Friday's booster again, it will be expended into the ocean. However, the rocket's second stage will make a much longer "coast" in space before de-orbiting after four revolutions around Earth. This is likely another test of the second-stage engine's ability to fire after a longer period of dormancy in space.

During Thursday's news conference, Jensen said SpaceX was still working an issue with a thermal panel on the Dragon spacecraft. This could delay the launch, but she said employees were proceeding for now as if the launch will go ahead on Friday morning.