It is my understanding that the Falcon 9 thrust vector control (TVC) actuators use RP-1 as hydraulic fluid and use the fuel turbopump energy to drive the hydraulic pump for the TVC.

How do you do a preflight test of actuators since the turbo pumps are not running?


Before every flight, SpaceX do a static fire test where the rocket is placed on the launch pad and the first stage engines are fired. That's an opportunity to test the gimbaling system.

According to the Falcon 9 user manual, the gimbaling system doesn't seem to be tested during the launch countdown (where you'd have a few seconds to do the tests between ignition and release):

Engine ignition occurs shortly before liftoff, while the vehicle is held down at the base via hydraulic clamps. The flight computer evaluates engine ignition and full-power performance during the prelaunch hold-down, and, if nominal criteria are satisfied, the hydraulic release system is activated at T- 0.

  • $\begingroup$ That might work for first stage tests, but in case of CRS-10 the second stage TVC was one of the reasons for a scrub iirc. $\endgroup$ – jkavalik Feb 26 '17 at 14:12
  • $\begingroup$ Yes, it was the second stage test prior to launch that forced the scrub. I'm curious on how it was actuated. $\endgroup$ – BobK99 Feb 26 '17 at 22:00
  • $\begingroup$ Los, for obvious reasons, the static fire doesn't test the second stage engine $\endgroup$ – oefe Feb 26 '17 at 22:13
  • $\begingroup$ The Falcon 9 user manual referenced above states that the second stage uses cold nitrogen gas (GN2) for attitude control so it was possible they tested it prior to launch . Thank you for passing on the user manual. $\endgroup$ – BobK99 Feb 26 '17 at 22:36
  • 3
    $\begingroup$ Yes you are correct my mistake. A MIT student asked my question during a tour of Space X and his response:They basically said that the pressure in the fuel tanks is sufficient to test the actuators, and that the turbopump pressure is only needed when they're actually steering the full mighty rocket engine. When it's sitting on the pad they can make little pivots without much "convincing" so the pressure that they pressurize the tanks with is enough to make sure the thing is working. $\endgroup$ – BobK99 Mar 4 '17 at 21:34

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