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When do you start your gravity turn


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Under stock I'll start turning slightly at 8km and aim to be at 45 degrees by about 24km, finally leveling off around 36km or so, right after hitting the dark blue band of atmosphere. Really depends on my TWR though; with a low thrust lifter I'll wait until 10km to start.

Under FAR/RSS, I start at around 1.5~2km and slowly pitch over until I'm level right after hitting the dark blue band of atmosphere. Mainly, though, I just watch my apoapsis and time-to, making sure I keep the time-to at 1 minute or more once I'm at the leveling off point.

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I tend to start turning over fairly low, just a few degrees at a time, as I find it tends to be more controllable and accurate for me. If I don't start my horizontal push fairly early to build up speed and instead wait till I'm very well clear of the bulk of atmospheric drag before I start, then I have a far harder time hitting my target orbits.

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Depends on the weight of my rockets. Normal well ballanced rockets, i start angling at 8-10k and be at about 45 degrees by 15k. On top heavy rockets that are not very controllable (aka space station modules) I start my turn at about 20k.

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The technique I developed (pre-FAR):

- Launch

- Switch to orbit frame of reference

- Watch the threshold efficiency indicator in KER and adjust throttle to not exceed ~115%. (requires Kerbal Engineer Redoux)

- Watch the prograde vector climb up from the horizon. When prograde vector approaches 45 degrees begin turning over so that the prograde vector doesn't go above 45. I would differ this a bit depending on the TWR, but generally target within 5-10 deg of 45. 45 is a bit arbitrary, so you can experiment to see if a different angle is more efficient.

- Continue until sufficiently out of the thick atmosphere, then point nose straight into prograde vector until desired apoapsis altitude is reached.

- Profit

But I recently added FAR so I'm back in diapers, so to speak...

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I do it based on speed, I've calculated and tweaked my TWR such that I should be reaching altitudes at about the same speed each time. I turn about 22 degrees for every 250 m/s. So the first turn is just after 10km. Once I hit 1000 m/s going almost flat to the horizon I switch to map view and wait until I get to 72km AP (or whatever AP I want) and cut engines for the coasting phase. It's not the kind of exact science that others have been using but it has resulted in my boosters performing well enough - on my last light mission I'm pretty sure that no matter how I did the numbers for ISP my booster was well short of 4500 m/s, yet I reached orbit on each attempt with a few drops of fuel to spare.

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Depends on the rocket, if I'm using my usual reliable lifter, I start a nice gentle turn as soon as I drop the SRBs, if I'm using some strut-laden floppy-topped abomination, I wait till I get into the dark blue part of the stratosphere.

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Usually @ 10Km because of consistent rocket construction, but depending on the TWR, I may wait later. I judge the angle at which I am tilted based on the shape of my orbit and my craft's location in that orbit, so I can't give you exact numerical values. What I can tell you is that I allow some space between my rocket in map view and the Apoapsis.

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A normal gravity turn starts with a pitch down by 15 degrees between 5000m and 7500m. Yes, that is slightly below the knuckle in the gravity-drag plot, but the delta-v requirements for starting late greatly outweigh the losses for starting early, especially with slower lifters. Science! :cool:

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Make sure your rocket has a decent TWR first.

On the vanilla drag model, its best to keep speed low and head directly up until you hit 10000m, then pitch 45 degrees as fast as you can without spinning whilst throttling up to full power.

The atmosphere on Kerbin decreases in density every 5000m above sea level. The first 2 "blocks" are quite thick so you want to spend as little time in them as possible, and waste as little fuel on drag

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