4:40pm ET Sunday update: The Falcon 9 rocket took off amid a dense canopy of fog on Sunday, but nevertheless it successfully delivered a payload of 10 Iridium satellites into a good orbit. Then the first stage booster fired its engines for home. SpaceX founder Elon Musk had warned that landing conditions were marginal due to extreme weather, and that the droneship had had to be relocated as a result. But no matter, the first stage booster hit the mark on Just Read the Instructions all the same. Also, it appeared the new grid fins performed well, with little evidence of charring.

Original post: Chances are, if you're a SpaceX employee, you've had a busy weekend. On Friday, the company successfully launched its second "used" Falcon 9 rocket from Kennedy Space Center in Florida. Now, two days later, the company will attempt to launch a new Falcon 9 from California's Vandenberg Air Force Base. The instantaneous launch window opens at 4:24pm ET.

This is a fairly conventional launch for SpaceX except for one novelty, revealed by SpaceX founder Elon Musk on Saturday night. After lifting 10 Iridium NEXT satellites to low Earth orbit, the Falcon 9's first stage will attempt to return to a droneship with a new, more durable set of grid fins, which help to stabilize the rocket as it descends back to Earth.

During prior missions these grid fins, manufactured from aluminum with added thermal protection, have caught fire due to atmospheric heating. To address this problem the company has forged new grid fins from titanium. "Flying with larger & significantly upgraded hypersonic grid fins," Musk tweeted. "Single piece cast & cut titanium. Can take reentry heat with no shielding." The new fins are a bit heavier, but are designed for multiple re-uses as SpaceX seeks to more toward rapid reuse of its first stage booster.

The Falcon 9 rocket's first stage being used for Sunday's mission is a good candidate for future reuse. Friday's launch of BulgariaSat-1 employed the Falcon 9 rocket first used in January to launch 10 satellites for Iridium's new constellation. This rocket will have a similar flight profile to January's launch, and therefore will have enough fuel reserves for a smoother return with less heating during atmospheric reentry.

The webcast embedded below should begin about 20 minutes before the scheduled liftoff. Due to the narrow launch window, if there are any problems Sunday's attempt will have to be scrubbed, with another attempt likely Monday. Weather conditions for a launch from southern California are ideal.