Circularizing orbit from Kerbin

[thewhitemetroid]

When I did circularization maneuvers from Kerbin in KSP 1 I always attempted to get as circular and specific about my altitude as possible every time, and managed to get very good at it, to the point where I did not need to rely on the maneuver planner to do this. I am having a hard time doing that in KSP 2. My AP keeps going into HKO while PE is barely scraping the atmosphere. For you knowledgeable players out there what's going on here. Is the maneuver node buggy in this specific instance as well or is the calculation just more realistic than KSP 1. My current hypothesis, if this is not a bug, is that it's my current vertical velocity vector that is impacting my final result. I'm burning prograde on the maneuver icon but do to my ascent I still have latent vertical velocity. Did KSP 1 not calculate the orbital circularization maneuver in this way?

[LameLefty]

KSP2 seems to calculate the resultant orbit based on estimating the burn over time (which is much more realistic than stock KSP1, which assumes a simplistic instant acceleration applied at a point). So to get better circular orbits, you will have to add some radial component, either radial in or radial out, depending on your initial apoapsis altitude and whatever periapsis altitude you ended up with when you stopped your burn. The higher your initial Ap, the easier it is to get a good final orbit because it is likely to require less radial component to get close Ap and Pe values. 

Edited March 5, 2023 by LameLefty

[thewhitemetroid]

Hmm, Thanks. I have been adding a radial component to compensate, but have not tried a higher initial apoapsis. I don't mind increased complexity especially if it is more driven by what occurs in real life, but if that's the case the maneuver node system needs a lot of tweaking because right now it seems very fiddly.

[Streetwind]

You shouldn't really need to make a node for this at all, assuming you managed to go fast enough sideways during ascent. You should aim to reach a speed of 2000m/s by the time your apopasis reaches the correct height and you cut your engines and coast. You can still circularize without a node with 1900m/s or even less than that, but the lower you go, the more difficult it becomes.

The general approach: coast until you are about 10 seconds before apoapsis, then throttle up. I recommend using the mouse to click and drag the throttle for this, as it offers unparalleled precision control. Try to figure out how high you have to throttle so that the time to apoapsis neither decreases nor increases. Once you have found that point, start backing off the throttle slowly and gradually. You'll find that the closer you get to circularizing, the less thrust you need. If you feel comfortable in your control, let the apoapsis come even closer, to just a few seconds. Then just hold it there with your manual throttle control until the periapsis has climbed up to where you want it.

If you are going too slow, and have a weak engine, you may find that even at full throttle, the apoapsis won't stop coming closer if you start the burn at 10 seconds off. In that case, you'll want to start burning earlier. Use your judgement; you'll soon get a feel for how well your rockets accelerate after you've done this a few times.

And, of course, going faster sideways during ascent makes this easier. meaning, tip over a little sooner/harder. Just be careful not to go too flat. Each individual rocket will be slightly different with how flat a trajectory it can fly without falling out of the sky. The more TWR, the flatter you can go. It also helps if you gradually throttle down the upper stage as your apoapsis climbs above 55km, thus delaying the point in time until you have to cut your engines entirely.

5 hours ago, thewhitemetroid said:

I'm burning prograde on the maneuver icon

Oh, additional info: the SAS Hold Maneuver mode is buggy, and tends to veer off the marker. If you use nodes, try following the marker manually, or just use SAS without any of the Hold X modes.

 

Edited March 5, 2023 by Streetwind

[Scarecrow71]

What I have been doing is to create the node and then slide it around on the planned trajectory to get the Pe I want.  Then you'll have to pull retrograde to lower the Ap, then slide some more, then pull, then slide, then...you get the idea.  My issue with this is that you can't do this when the game is paused, so you have to be pretty fast to get this done.

Alternatively, just push an HKO orbit and, after circularizing, go retrograde to pull that Ap down a bit.  Not optimal, but it should work.

[thewhitemetroid]

I would normally just shoot from the hip to go orbital from Kerbin, it's easy enough but this is EA and I wanted to yank the chains on this this to see how it has "improved"...ahem. To further delve down into this I just did an orbital ascent maneuver and used the nodes to plan it. When using the horizontal component to circularize, at just about the moment PE reaches LKO it decays and the AP goes nuts, as if I'm adding a radial component at the same time, hence my question in the opening of this thread. It is confusing because my AP is peaked at (enter LKO # here) and I'm applying a horizontal vector. The orbital planner seems to be including a vertical vector in as well because the orbit starts to behave that way. I don't have too many problems getting into orbit considering the circumstances of the game, but I'm trying to understand if this is a bugged instance of the maneuver node or an aspect of orbital mechanics that I do not understand yet.

[LameLefty]

I want to add, too, that is *is* possible, just about, to fly very close to a direct-assent orbit in KSP2, much like most rockets do it in the real-world today, and do it completely manually.

The method is, once you see your Ap getting very close to what you want your final circular orbit to be, point your craft nose down toward and then below the horizon. Keep pitching down while you burn until the Ap is no longer increasing, or at worst increasing very slowly. At this point, you are adding velocity and shaping your orbit further and further oblong, pushing your IIP (initial impact point) of your Pe on the surface of Kerbin ever further downrange, until eventually your Pe goes positive and starts climbing rapidly. 

You will have to pay close real-time attention to the Ap numbers as you fly, and control your pitch up and down while you climb to keep that Ap more or less constant. It's been many years (pre-MechJeb circa version 0.19) since I had to do this regularly, but I've gotten reasonably good at it again. Yesterday I flew an ascent like this that required under 100 m/s to properly circularize a 110 km circular orbit.  And since the ascent is nearly direct, the time to Ap was almost half an orbit around, so plenty of time to carefully craft a maneuver node for that final burn.