Bug #10138
Target-relative velocity display for landed target
10%
Description
Select a target that is on the surface of a planet. Then switch between navball modes and see how the velocity behaves.
If the target is in physics range, the target-relative velocity closely matches your surface-relative velocity, what is correct for a target practically doesn't move in relation to the surface.
However, if the target is outside the physics range, the displayed target-relative velocity matches your orbital velocity. That is, the unloaded target's orbital velocity is assumed 0, when it's surface velocity that should be so - the navigation forgets to account account for the planet rotating and the inertial-frame speed it gives to the target.
| TargetRelativeVelocity.jpg (218 KB) TargetRelativeVelocity.jpg | 100m/s approach, velocity becomes correct when close |
History
#1
Updated by Anonymous almost 6 years ago
- File TargetRelativeVelocity.jpg TargetRelativeVelocity.jpg added
- Status changed from New to Confirmed
- % Done changed from 0 to 10
The added launch-sites of Making History expansion provide a quick way to demonstrate this.
1) Launch Bug-E-Buggy (stock) at the Island Runway
2) Launch Velociteze (stock) at the KSC Runway
3) Use map view to target Bug-E-Buggy 33km away
The NavBall indicates 175m/s eastward velocity relative to the target, which is the surface rotation speed of Kerbin.
In fact, the planet rotation moves both Velociteze and Bug-E-Buggy at nearly the same velocity, with Bug-E-Buggy moving just 174m/s × 33km/600km = 10m/s downward in the (non-rotating) reference frame of Velociteze.
There is a very nice video https://youtu.be/VU-_InTkc54?t=681 warning new players about this, for aircraft landing. It also affects targeting bases on other bodies, whenever the body has noticeable rotational velocity.
Interestingly, going within the 2.25-km physics-loading distance to the target corrects the indicated velocity, and then after moving beyond the unloading distance, the velocity remains correct... until the next quicksave/quickload.
Workaround by increasing the physics-loading distance:
@PHYSICSGLOBALS { @VesselRanges { @landed {
@load = 60000
@unload = 70000
} }