SpaceX

Trevor Mahlmann

Trevor Mahlmann

Trevor Mahlmann

Trevor Mahlmann

Trevor Mahlmann

Trevor Mahlmann

Trevor Mahlmann

Trevor Mahlmann

Trevor Mahlmann

Trevor Mahlmann

Trevor Mahlmann

Trevor Mahlmann

Noon ET Update: In a series of tweets on Saturday, SpaceX chief executive Elon Musk said he personally called off the launch of a Falcon 9 rocket when the system was "green" for liftoff.

"All systems go, except the movement trace of an upper stage engine steering hydraulic piston was slightly odd," he tweeted. "If this is the only issue, flight would be fine, but need to make sure that it isn't symptomatic of a more significant upstream root cause. Btw, 99% likely to be fine (closed loop TVC wd overcome error), but that 1% chance isn't worth rolling the dice. Better to wait a day."

The "TVC" refers to thrust vector control, which helps steer the upper-stage engine. From these remarks it appears SpaceX will indeed try a second launch attempt on Sunday, during an instantaneous window that opens and closes at 9:38am ET.

10:08am ET Update: At T-13 seconds, the SpaceX launch team scrubbed Saturday morning's attempt. Engineers working the launch weren't comfortable with a "thrust vector control" issue on the rocket's second stage, which helps position the engine nozzle.

The company will probably try to launch again on Sunday at 9:38am ET, although a formal announcement is not likely until later on Saturday.

Original Post: NASA built two main launch pads during the Apollo program, 39A and 39B. The former was used for every Moon landing launch, except for Apollo 10, and most of the space shuttle missions. After the final space shuttle flight in 2011, NASA decided it needed just one of the pads for its future operations. So it leased Launch Complex 39A to SpaceX.

The company had intended to use Launch Complex 39A primarily for launches of its new Falcon Heavy rocket and commercial crew missions. However, on September 1, 2016, a static fire test accident at SpaceX's other Florida launch pad, Launch Complex 40, caused severe damage to facilities there (repairs may be complete later this summer, according to company president Gwynne Shotwell). This pushed SpaceX to expedite its refurbishment of Launch Complex 39A and to expand its use for all launches from the East Coast.

Now, after modifications and upgrades, the historic pad is finally ready for its second life. The first SpaceX launch from the historic pad is scheduled for Saturday at 10:01am ET (15:01pm UK). A Falcon 9 rocket will boost a Dragon spacecraft carrying about 2.5 tons of food, water, and scientific experiments to the International Space Station. About 10 minutes after launch, the first stage of the rocket will attempt to land back at Landing Zone 1, near the launch pad. So far, SpaceX is two for two with land-based returns of its rocket. The webcast will begin at about 9:40am ET:

Weather conditions are improving for Saturday morning's launch, with forecasters now estimating a 70-percent chance of "go" conditions during the instantaneous launch window. SpaceX is still working a technical issue with "tiny" helium leak within the rocket's upper-stage, and a final decision may not be made until a minute before launch.

Listing image by SpaceX