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Bug #10138

Target-relative velocity display for landed target

Added by Alchemist over 7 years ago. Updated over 5 years ago.

Status:
Confirmed
Severity:
Low
Assignee:
-
Category:
Controls and UI
Target version:
-
Start date:
07/20/2016
% Done:

10%

Version:
Platform:
Windows
Expansion:
Language:
English (US)
Mod Related:
No
Votes:
Arrow u r green
Arrow d r red

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 Anonymous, 12/16/2018 12:33 AM
40429

History

#1 Updated by Anonymous over 5 years ago

40429

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
} }

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