6
$\begingroup$

Does Starship perform a launch tower avoidance maneuver? If yes, is this accomplished using gimbaled raptor engines or RCS rockets? How far laterally is the Starship axis shifted by this maneuver and how are related stresses managed?

https://ntrs.nasa.gov/api/citations/20190033307/downloads/20190033307.pdf describes “an initial small tower avoidance maneuver” of Saturn V. It also states

Problems in vehicle control arise because Saturn vehicles cannot be considered rigid but must be treated as distributed masses connected by an elastic structure. Forces acting on these masses resulting from atmospheric perturbations or active control of the vehicle excite the complex spring-mass system and cause body bending. Since the structure possesses low damping, oscillatory bending modes of considerable amplitude can be produced; the control sensors may be subjected to these large amplitude oscillations at their particular location. Thus incorrect information about the total vehicle behavior may cause self-excitation and instability of the vehicle control system.

This description makes it sound like the Texas Two-Step required to yaw, then straighten, the rocket’s course in the first seconds of launch could produce significant bending moments in the stack.

$\endgroup$
1
  • $\begingroup$ I cannot find the quote in the linked article, but I think it should relate to motivation as to why Saturn V didn't use closed-loop control in the ascent. $\endgroup$
    – Ludo
    Commented Apr 22 at 12:09

1 Answer 1

5
$\begingroup$

The SuperHeavy/Starship does yaw before clearing the tower in a manner analogous to the Saturn V.

In the picture below (shamelessly stolen from here), the early tilt of the Saturn V away from the tower (in the y-direction) is a yaw maneuver to avoid the tower. It's designed to nudge the vehicle away from any arms on the tower that have failed to retract.

yaw

The Saturn V, like most rockets, then heads in an Easterly direction after takeoff (the z-axis in the next picture, from the same site), which means the vehicle also has to pitch in the z-direction soon after launch.

This may account for the "Texas-Two Step". The tilt of the vehicle in the z-direction then starts to increase with altitude in the direction of its intended orbital inclination. There are also roll maneuvers about the x-axis.

Coordinates

The SpaceX launch platform is to the East of the launch tower, not South as is the case with the Saturn V. It's clear from this video of the Starship launch on its 3rd integrated test flight that the vehicle begins to yaw only a few metres above the platform - see the graphical images at the base of the footage. At a tilt of a few degrees, the yaw slows, or perhaps stops, until it resumes with the first kilometre.

This diagram shows a similar tilt in the second Starship test flight in November 2023:

Starship second test flight

(NB: I can't find SpaceX documentation or an Elon explanation, but it's hard to interpret the yaw in any other way.)

$\endgroup$
3
  • 1
    $\begingroup$ I added a diagram that I made for a similar question which illustrates the Starship tilt during liftoff. $\endgroup$ Commented Apr 22 at 12:17
  • $\begingroup$ Thank you @StevePemberton. That's perfect! $\endgroup$
    – Galerita
    Commented Apr 22 at 14:11
  • 1
    $\begingroup$ That it Perfect. No better answer than this $\endgroup$ Commented Apr 28 at 13:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.