Normal changes could take into account planetary spin

[DannyD]

I was thinking about why normal plane changes are more effective when done far away from the planet and it seems to me that a planets spin would make it so that the plane change was more affected by the rotation of the planet if done from further away.

When looking at this effect on the map, it wouldn't be a laterally flat oblong around the planet that the craft would take when it did the plane change, but would be a lateral logarithm that pulls the craft along the direction of the planets spin most when at periapsis.

 

[dmsilev]

I’m not sure I understand what you’re getting at. The cost of a plane change is proportional to the orbital velocity of a craft, so for a given change of inclination, it’ll be cheaper to do it at high altitude than at low simply because the velocity of a high orbit is lower. The spin of the underlying body doesn’t have any effect.
Put another way, consider a craft in an elliptical 90 degree inclination orbit, with PE and AP at the equator.  The dv costs to switch to a 0 degree (aligned with spin) or a 180 degree (anti-aligned with spin) orbit are the same, but doing the change at periapsis costs more than at apoapsis.

[Jeq]

On 2/18/2024 at 8:08 PM, DannyD said:

I was thinking about why normal plane changes are more effective when done far away from the planet and it seems to me that a planets spin would make it so that the plane change was more affected by the rotation of the planet if done from further away.

When looking at this effect on the map, it wouldn't be a laterally flat oblong around the planet that the craft would take when it did the plane change, but would be a lateral logarithm that pulls the craft along the direction of the planets spin most when at periapsis.

 

It is easier to change direction of orbit because you are traveling slower. if you go straight 2200m/s, you need  to burn 2200m/s left/right to get angle of 45degrees. If you go straight 100m/s you only need 100m/s to change angle to 45.

If you are not moving anywhere, you would instantly get to direction of burn.

Edited February 20 by Jeq

[Hotel26]

On 2/19/2024 at 2:08 AM, DannyD said:

a planets spin

has no (non-relativistic) effect on an orbiting craft.

The speed of the orbiting craft in a circular orbit at a particular altitude ("outside the altitude") is determined by the mass of the body it is orbiting and the craft's altitude (actually, orbit radius).

Vorb = sqrt( G * M / r )

Elliptical orbits are similarly independent of planetary spin.

See also Mean Orbital Speed in Wikipedia. 

Welcome to the forum!

Edited February 21 by Hotel26

[magnemoe]

Now having an landing indication like mechjeb has in KSP 1 would be nice. This shows where you intercept the ground taking into account the rotation, now you kind of have to update your burn or rater burn.
Mechjeb indicator also worked in atmosphere but it was inaccurate here, more so as orientation would change drag, but if you knew your craft you could land withing KSC. 
 

[Turbo Ben]

On 2/26/2024 at 6:18 PM, magnemoe said:

Now having an landing indication like mechjeb has in KSP 1 would be nice. This shows where you intercept the ground taking into account the rotation, now you kind of have to update your burn or rater burn.
Mechjeb indicator also worked in atmosphere but it was inaccurate here, more so as orientation would change drag, but if you knew your craft you could land withing KSC. 
 

I use the Trajectories mod with KSP1. It does a good job of predicting your trajectory through atmosphere and where your impact ... I mean landing site will be. It takes into account planet rotation and also adjusts as you change orientation and/or drag (I use airbrakes on my returning rockets to slow down and for fine tuning the landing location). It's not perfect, took a few attempts at first, but now I'm able to land most of my craft within a Km of the KSC, though I haven't managed to nail the launchpad yet.

Something like this would be a great addition to KSP2, espescially if we are going to need to do precision landings when colonies are introduced.