Click the arrow to watch the abort of the CRS-10 launch at T-13 seconds. Video source: NASA YouTube channel.
Elon Musk personally called the hold that aborted today's SpaceX attempt to launch its first mission from Kennedy Space Center's Pad 39A.
Musk wrote in a series of Twitter posts:
All systems go, except the movement trace of an upper stage engine steering hydraulic piston was slightly odd. Standing down to investigate.— Elon Musk (@elonmusk) February 18, 2017
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— Elon Musk (@elonmusk) February 18, 2017
@Zybbby Not obviously related to the (very tiny) helium leak, but also not out of the question— Elon Musk (@elonmusk) February 18, 2017
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.— Elon Musk (@elonmusk) February 18, 2017
@Xuan_Thai System was green for launch. I called it off.— Elon Musk (@elonmusk) February 18, 2017
“TVC” refers to the Thrust Vector Control on the Falcon 9 upper stage. Earlier in the countdown, about fifteen minutes before launch, it was announced SpaceX was working an issue with the device. Another anomaly with the new automated flight termination system was resolved with a software update.
A thrust vector control actuator reportedly used on the Falcon 9. Image source: Jansen’s Aircraft Systems Controls Inc.
A page on the Jansen's Aircraft Systems Control web site states they produce the TVCs used on the Falcon 9. The page states, “Embedded within the single-ended piston is a dual-element LVDT, which provides two independent channels of position feedback to the external controller. A single D38999 Series III connector on the EFSV housing communicates all signals to and from the controller.”
“LVDT” is an acronym for Linear Variable Differential Transformer. According to the TE Connectivity web site, “LVDTs provide reliable position measurement for applications in subsea, power generation, industrial automation, aerospace, test and measurement, and more.”
A January 2015 SpaceX launch also was scrubbed due to a TVC actuator issue. According to the report by The Verge, “The launch was halted by the flight team because a thrust vector control actuator wasn't functioning correctly. The actuator was central to the landing mission and would have triggered an automatic abort if the team hadn't stepped in to stop the launch.”
As of this writing, a live video feed from SpaceflightNow.com shows the Falcon 9 has been lowered to the horizontal, out of view of the camera. This suggests it's either horizontal on the pad or back inside the integration hangar for inspection.
This mission will launch the SpaceX cargo Dragon to deliver payloads to the International Space Station. The next launch window is 9:38 AM EST tomorrow. According to Florida Today, a delay to Monday February 20 would require negotiating permission from Russia because that agency is scheduled to launch a Progress cargo ship to the ISS on February 22.