Update 1: Added a marvelous photo of storm clouds approaching the Launch Pad 39A taken by Bill Ingalls
Today at 14:38 UTC, after postponing the tanking for 30 minutes, NASA scrubbed the launch of the Space Shuttle Endeavour (STS-127) to examine ground equipment and systems aboard Endeavour for possible damage from lightning strikes. 11 lightning strikes were recorded within 0.5km of the launch pad during last night’s “pretty spectacular electrical storm“. Although there were no direct hits to either the orbiter, the external tank or the solid rocket boosters (SRB’s), the Ground Lightning Monitoring System (GLMS) declared a “lightning event” at 06:00 UTC and additional checks are needed to reach 100% confidence that orbiter electronic boxes and the solid rocket booster circuitry are fully functional.
The launch window for STS-127 is only 10 minutes long because the launch pad needs to be in the plane of the space station’s orbit. The next window starts tomorrow at 23:08:55 UTC and NASA will attempt a launch at 23:13:55 UTC. Currently, the weather forecast for tomorrow’s launch predicts a 40 percent chance that weather will prevent a liftoff due to thunderstorms and electrically-charged clouds. If the conditions don’t allow launch on Sunday, there are windows opening at 22:46 UTC on Monday and 22:20 UTC on Tuesday. Tuesday is the last day for the STS-127 launch that would not interfere with the planned Progress mission to the ISS.
Today’s postponement comes a month after two earlier scrubs on June 13 and June 17 due to gaseous hydrogen leak on a vent line near the Ground Umbilical Carrier Plate (GUCP). After June 20, it was not possible to launch the shuttle before the beta angle cutout ended on July 10. The beta angle is defined as the angle between the orbit plane and the vector from the sun. It affects the percentage of time an object, such as a spacecraft in low Earth orbit (LEO), spends in direct sunlight, absorbing solar energy. To prevent the orbiter from overheating, the shuttle cannot dock with the ISS if its beta angle is more than 60 degrees.
With another delay in STS-127 mission it is now even more likely that the launch of the next space station assembly flight (STS-128), currently targeted for August 7, will be delayed in a downstream domino effect.