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Is a gravity turn only used for rockets interested in orbit or a gravitational slingshot?

From this answer it sounds like Apollo 11 only used a gravity turn for the crew to maneuver.

Are there rockets that ascended straight into space with no gravity turns?

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Any rocket bound for Earth orbit will use some kind of gravity turn; orbit requires a lot of horizontal speed.

Interplanetary missions (almost?) always enter parking orbit around Earth before leaving for their destination (this allows them much more flexibility in launch timing). Thus they will use gravity turns.

I think you’re slightly misunderstanding the Apollo question you mention; the launcher rolls (rotates around its long axis) to a certain attitude for the convenience of the crew and to simplify the guidance program, but gravity turn is a pitch (tilting downward from vertical) maneuver not related to that.

Sounding rockets which are not trying to orbit go more nearly straight up. For the same amount of rocket, you can reach much higher altitude by going straight up, at the cost of immediately coming back down to Earth.

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  • $\begingroup$ So all that extra fuel and rocket mass for a bigger launch window? What if the stars are aligned, would they skip the gravity turn, or do it much later? Why is it done so soon? Why not wait till the rocket passes into space? $\endgroup$ – larry909 Feb 8 '18 at 14:00
  • $\begingroup$ Going into parking orbit increases the fuel requirements by less than 1%. The early turn is more efficient than going straight up and then turning. The ascent to orbit, and the interplanetary departure, are treated separately and the ascent trajectory isn’t altered based on the time within the launch window. $\endgroup$ – Russell Borogove Feb 8 '18 at 14:45
  • $\begingroup$ Why is the early turn more efficient? You'd think otherwise considering the atmosphere. Is it because of downward gravity vs lateral? $\endgroup$ – larry909 Feb 11 '18 at 0:04
  • $\begingroup$ One way to look at it is that you want to attain the horizontal velocity component as quickly as possible, because the curvature of the Earth gives you altitude for free when you're going sideways. That free altitude is how you stay in orbit -- at circular orbital velocity, the curvature of the Earth exactly matches the downward pull from gravity. Atmospheric losses for large launchers are only 1-2% of the total ∆v budget to orbit. $\endgroup$ – Russell Borogove Feb 11 '18 at 0:43
  • $\begingroup$ Note that the optimal trajectory varies with the shape of the rocket (which affects drag coefficient) and the changing acceleration of the rocket as fuel is expended. A properly initiated gravity turn is just a trajectory that's not painfully far from the optimum while also minimizing lateral aerodynamic forces on the vehicle. $\endgroup$ – Russell Borogove Feb 11 '18 at 0:47

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