Make the Manoeuvring frame default to inertial of the current SOI

[ezsnackeur]

Given the amount of people on the discord channel not realizing that this feature exists at all, even if its clearly mentioned in the concepts page, i think that it would only make sense to make this behave closer to stock manoeuvre system.

It's also rare in my experience to have to use a different Manoeuvring frame other than inertial of the current SOI, the main use case being using ECEF for communication satellites positioning and MCMF for moon landings, so it would make sense to have to switch manually in these few cases rather than every time i'm using any Plotting frame that isn't inertial of the current SOI.

Might create a slightly unintuitive behavior when you are still orbiting a body thanks to principia but out of its SOI, but again its a super rare case.

[eggrobin]

Further discussion on the Discord, September 2025.

TL;DR: we should use the orbit that the analyser gives us for the coast preceding the manœuvre, not the SoI (which doesn’t exist in our C++ libraries anyway).

[05:28]Stupid Gay Furry: Is 6km/s realistic for LEO to LMO transfer at the optimal window? I feel like that's a lot
[07:12]kuzinat0r: Your manoeuvre frame is wrong. Set it to ECI. Mars transfer should be no more than 4k
[12:02]ezsnack - booster tank apologist: This feature needs to be changed asap lol
[12:04]Butcher: Why? There are valid uses for other frames, this is just user error.
[12:10]Nazfib: On the one hand, it's weirdly unintuitive if the default manoeuvre directions don't correspond to the trajectory you're looking at (e.g. tangent is not along the trajectory);
on the other hand, once you have some experience with manoeuvre planning, you learn that the body-centered inertial manoeuvre frame of the largest gravitational source at your current position is often the one you want, especially for large manoeuvres.
[12:10]ezsnack - booster tank apologist: Yea im not saying to remove it, i have a gh issue open about it, just make it default to the soi you are orbiting inertial
[12:57]Butcher: Oh I see, so on creation it defaults to whatever body you're in the hill sphere of instead of whatever your plotting frame is. 🤔
[13:00]ezsnack - booster tank apologist: no the opposite, and it should be like what you said
[13:00]ezsnack - booster tank apologist: because that is alot more alike to stock system, which people is used to, and they apparently refuse to read the concepts page or understand it :V
[13:01]ezsnack - booster tank apologist: so every single time you see someone struggling with an interplanetary transfer its because they are using target-sun-orbit manoeuvreing frame while plotting the ejection in LEO
[15:52]egg: Probably based on orbit detection rather than the hill sphere.
[15:53]sichelgaita: We'll assign an engineer to look into this issue.

[eggrobin]

Earlier discussion on the Discord in June 2023:

It is probably a good idea to change the default too, but while we are doing that we might as well make the message useful.

[13:26]test_account: i think it should warn if maneuver frame is not the inertial frame of current SOI body
[22:18]egg: We have orbit analysis, so probably if it is not the inertial frame of the primary of the detected orbit.
We don’t do red, we have orange for warnings.
I worry this might be too strong, because e.g. when planning adjustments in the vicinity of Lagrange points, the plotting frame is probably the least confusing option.
[22:19]test_account: Yes, the warning can't really cover all possible use cases
[22:20]egg: But certainly the current message is largely useless. In fact, it is conveying information that you can easily ascertain visually (the yellow thingy is not pointing forward). We could just replace it with a message—still informative (same colour)—saying that forward is not forward along the orbit.
[22:21]test_account: Would that work even if the player has never opened the orbit analyzer window?
[22:22]egg: The flight plan auto-analyses every coast, that is how you get the +1/-1 revolution buttons.
[22:26]test_account: Maybe the message could also point to the correct reference frame, saying something like "Choose ECI for a prograde burn along the orbit"?
[22:27]egg: That seems like a good idea, space permitting (and I think @al2me6 has ideas about making space permit anyway).
[01:29]Al₂Me₆: If we implement this we may as well have an 'infer manoeuvre frame' feature
[01:39]egg: Well, we have one already, when you create the manœuvre it comes with a frame. But it is the plotting frame by default. The inertial frame of the primary might be a better default, but this is really questionable for the more interesting trajectories, so I would not want to disrupt too much there.

[eggrobin]

Hm. the detected orbit of the previous coast is fine for an ejection from a parking orbit, but it is definitely going to be wrong choice for a capture burn (for an Earth-Moon transfer, the coast will be analysed as an Earth orbit).