SpaceX has a successful second launch of its Block 5 rocket

Update: At the top of its launch window, the Falcon 9 rocket took off early Sunday at 1:50am ET (05:50 UTC) and lofted its large satellite payload into geostationary transfer orbit. Meanwhile, the first stage of the rocket made a safe landing on a drone ship in the Atlantic Ocean. One wonders how many times we will see this core fly.

Original post: Having worked through its fleet of used Block 4 rockets, SpaceX will now transition into flying its more advanced Block 5 variant of the Falcon 9 rocket full time. As early as 1:50am ET (05:50 UTC) Sunday, SpaceX will attempt to launch the Telstar 19V satellite from Cape Canaveral Air Force Station in Florida. The mission has a four-hour launch window.

This will be the second launch of the new version of SpaceX's Block 5 rocket. The first one had a flawless debut on May 11, and the first stage made a safe return to a drone ship, as expected. Since then, SpaceX engineers have been assessing how that Block 5 core, optimized for reusability, actually performed during that flight.

“We are going to be very rigorous in taking this rocket apart and confirming our design assumptions to be confident that it is indeed able to be reused without taking apart,” SpaceX honcho Elon Musk said in May, at the time of the first Block 5 flight. “Ironically, we need to take it apart to confirm it does not need to be taken apart.”

SpaceX has not said how many new Block 5 cores it will build before beginning to re-fly these first stages. However, the company does intend to only fly Block 5 first stages of the Falcon 9 rocket from this point forward.

Sunday’s launch should be a fairly standard mission for the Falcon 9 rocket, delivering the Telstar communications satellite to geostationary transfer orbit. After its mission, the first stage will attempt to land on the Of Course I Still Love You drone ship off the Florida coast.

For those up late tonight, the webcast below should begin about 15 to 20 minutes before launch. Weather is a concern, with thick clouds and upper-level winds combining to provide just a 60-percent chance of favorable conditions for launch. However, with a four-hour launch window, there will be some time to find good-enough weather to fly. A back-up window is available on Monday morning, also at 1:50pm ET.