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Achieving orbit witch low twr


kiwiak
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I sometimes have trouble witch achieving nice round orbit, when my twr is low and i cant just burn for fef seconds exactly on apo.

Often, when apo passes and i keep burning, apoapsis start to rise, along witch peryapsis.

I suspect that in such cases, you have to point little radially, to compensate for fact that you are not in apoapsis anymore.

Do you have any advices?

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Don't wait until you're at Apoapsis to burn towards the horizon.

You may need to pitch up to keep your craft from falling down again. Exactly how much going to depend on the craft, but with practice you should be able to keep the prograde marker on the horizon line - if you can do that, you can actually "surf" the Apoapsis all the way to a circular orbit.

Check out the video below starting at around the 3:50 mark. TWR < 1.0, just have to ride the apoapsis. Note the navball shows I'm pitched upwards quite a bit...

https://www.youtube.com/watch?v=D3Y3e_TciAE

=Smidge=

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What I do is set up a maneuver node at apoapsis right when I get to 70,000 (this with the Ap around 100,000 as a rule). I go ahead and pull prograde and then set a little bit of radial as the two apses get close to one another, then continue slow prograde pulls until they're relatively close to one another (that's probably not efficient at all, but it does work). I then split the burn - however long of a burn is indicated, I figure up half of it and begin my burn that many seconds ahead of the node. For short burns, I might multiply the time by three before splitting it, and then pull the burn at 1/3 thrust. I usually wind up with the apses within 500-800 meters of one another, probably more precise than what's absolutely necessary for most cases.

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Also, if you have a really low TWR, have the time and aren't worried about falling back into the atmosphere (i.e. you are already above it), you can circularize over several orbits. Just do your burn near the Ap, wait till the next Ap, and burn again.

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When you reach apoapsis, even with TWR < 1.00 you can circularize your orbit. When you plan you maneouvre node, for example your burn is 60 seconds, point your nose in the node direction, and at -30 start to burn. if you have a 2:00 minutes burn, at - 1:00 minute to node start to burn. To be precise, you have to consider that in that period of time you burn fuel, so your vessel gets lighter, and you accelerate linearly faster as you burn fuel (your TWR slightly raises). For a 60 s burn, for example, start the burn at more or less -25 s, not -30s, because as you burn fuel, you go faster and you estimated burn time variation slightly drops. I usually go full throttle, then when I get 20 m/s ÃŽâ€V i cut off the engines (X) and i fine tune the remaining ÃŽâ€V at 10% thrust. Doing this you don't raise your apoapsis and you get a nice round (with an error of maximum 500 m between apoapsis end periapsis if you do it correctly). If you get periapsis = apoapsis you was lucky as hell, so don't expect to get a perfect orbit at first burn.

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