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Roughly by how many degrees does the strongback tilt back during liftoff? does the angle have any significance other than avoiding collision?

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    $\begingroup$ Which one? There is more than one strongback. $\endgroup$ Sep 21, 2021 at 14:15
  • $\begingroup$ Well generally, because this link - nasaspaceflight.com/2015/11/spacex-conducts-rollout-39a-te mentions that the strongback for Falcon heavy will be tilted by just 2.5 degrees away, but in other launches, the tilt appears more than that. So lets say, how much does Falcon 9 strongback tilt? $\endgroup$
    – suzi Venus
    Sep 21, 2021 at 16:31
  • $\begingroup$ Which one? The ones in Florida and the ones in California are different. $\endgroup$ Sep 21, 2021 at 18:03
  • $\begingroup$ Starts connected, then releases and leans back a few degrees, then at launch leans way back rapidly. Its purpose? Extra crispy fried T/E is more expensive to repair, they prefer medium rare. $\endgroup$ Sep 21, 2021 at 18:43

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Roughly by how many degrees does the strongback tilt back during liftoff?

For the Falcon 9 at Kennedy Space Center LC-39A and Cape Canaveral Space Force Station SLC-40:

  • "Arms" open at about T-00:04:05
  • Leanback to about 2.5° from T-00:03:45–T-00:03:15
  • Fallback to about 45° from T-00:00:00–T+00:00:05

For the Falcon 9 at Vandenberg Space Force Base SLC-4E:

  • "Arms" open at about T-00:04:15
  • Leanback to about 20° from T-00:03:45–T-00:03:15
  • No fallback at liftoff

For most other launch vehicles: it doesn't tilt back during liftoff. It tilts back long before liftoff. For example, the livestream for the Astra LV0006 flight test started at T-01:00:00 and at that time, the strongback was already retracted about 15°–20°, and it does not move during liftoff. Firefly Alpha's strongback and Electron's strongback also don't move.

does the angle have any significance other than avoiding collision?

The smaller the angle, the shorter, lighter, and less complex the umbilicals for the second stage and the payload are.

The bigger the angle, the less damage the upper portions of the strongback take from the exhaust gases and flames.

Hence the peculiar way the Falcon 9 works: Falcon 9 does a "load and go" fueling, which means fueling goes right up until T-00:02:00, only two minutes before liftoff. Therefore, it makes sense to keep the strong back as close to the rocket as possible, to make fueling easier.

At the same time, SpaceX wants to support a rapid launch cadence: in the beginning of the year, SpaceX launched almost every two weeks. The fastest turnaround times on the same launch pad I found during a quick search was Transporter-1 (January, 24th 2021) to Starlink 18 (February, 4th 2021) to Starlink 19 (February, 16th 2021) for SLC-40: that's 11 and 12 days. For LC-39, I even found one faster: Starlink 17 (March, 4th 2021) to Starlink 21 (March, 14th 2021): 10 days. The fastest turnaround across pads was Starlink 20 from SLC-40 on March, 10th 2021 to Starlink 21: 4 days. (And 3 launches from 2 pads within 10 days.)

Such a cadence would simply be impossible if you toast the strongback every time.

Note that the launch cadence from Vandenberg is much lower, hence why they can risk more damage to the strongback there. Also note that we might see a steep ramp up in Launches from Vandenberg for the high inclination and polar orbits of Starlink. Therefore, I would not be surprised if SpaceX were to upgrade the strongback in Vandenberg to the new configuration at some point, but as of February 2022, that has not happened.

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  • $\begingroup$ Thanks that helps.. $\endgroup$
    – suzi Venus
    Sep 22, 2021 at 11:04

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