structure LoadDistance

(The “on rails” settings)

LoadDistance describes the set of distances at which the game causes vessels to unload, and the distances that cause a vessel to become “packed”. This requires some explanation.

Before entering into that explanation, first here’s a list of example cases where you might want to use this feature to change these values:

• Trying to have one airplane follow another.
• Trying to have two rockets fly in formation into orbit together.
• Trying to have a rover race to a flag, with several rovers seeing who gets there first.

Basically, any time you might have more than just the current active vessel running a kOS script, this is a setting you probably will want to understand and tweak.

The explanation:

Most players of KSP eventually discover a concept called being “on rails”. This is a term used by the player community to describe the fact that vessels that are far away from the active vessel aren’t being micro-managed under the full physics engine. At that distance, changes in movement due to things like the atmosphere, are not applied. The vessel’s physics are calculated based only on orbital motion, much like the effects of using timewarp (not physics warp).

But the actual behavior in the game is a bit more complex than that, and understanding it is necessary to use this structure.

The term “on rails” actually refers to two entirely different things that are controlled by separate settings, as described below:

loaded : A vessel is LOADED when all its parts are being rendered by the graphics engine and it’s possible to actually see what it looks like. A vessel that is UNLOADED doesn’t even have its parts in memory and is just a single dot in space with no dimensions. An unloaded vessel is literally impossible to see on your screen no matter how much you squint because it’s not even being rendered on camera at all. Unloaded vessels only exist as a marker icon in space, with a possible label text.

packed : A vessel is PACKED when it is close enough to be loaded (see above), but still far enough away that its full capabilities aren’t enabled. A vessel that is loaded, but still packed will be unable to have its parts interact, and the vessel will appear stuck in the same location, unmoving. You can see a vessel that is loaded but packed, but the vessel won’t actually be able to do anything. In this state, the game is still treating the entire object as if it was one single part. It’s added all the graphic models of all the parts together into one conglomerate “object” (thus the term “packed”) that exists purely so you can look at it, even though it doesn’t actually work until you get closer and it becomes unpacked.

THE NEXT SENTENCE IS VERY IMPORTANT AND VITAL:

The kOS processor is able to run scripts any time that a vessel is loaded, but the script is not guaranteed access to all features when a ship is LOADED but not UNPACKED. KSP limits some features (like throttle control) to only vessels that are unpacked. You may check the UNPACKED suffix of the SHIP variable to determine if these features are available.

This structure allows you to read or change the stock KSP game’s distance settings for how far a vessel has to get from the active vessel in order for it to trigger its UNLOAD or PACK states.

The distance settings are different for different vessel situations. It’s important to first read the existing values before changing them, to see what the stock game thought were reasonable for them.

Some distances are very short. For example, the fact that the pack distance for a landed vessel is short is what allows landers to stay “parked” in place without tipping over when you leave them on a long distance EVA.

Each of these suffixes returns a SituationLoadDistance, which is a tuple of values for the loading and packing distances in that situation.

Wait between LOAD and PACK changes!

Due to a strange way the game behaves, it is unsafe to change both the load/unload distance and the unpack/pack distance at the same time in the same physics tick. If you are going to increase both, then increase the load/unload distances first, followed by a WAIT 0.001. to force a new physics tick and let the change take effect, then increase the unpack/pack distances after the wait is over.

Beware the space kraken when changing these:

There’s a reason the stock game has these distance limitations. Setting them very large can degrade your performance, and can cause buggy inaccuracies in the position and velocity calculations that cause the game to think things have collided together when they haven’t. This is the classic “space kraken” that KSP players talk about a lot. Computer floating point numbers get less precise the farther from zero they are. So allowing the game to try to perform microcalculations on tiny time scales using floating point numbers that have imprecision because they are large in magnitude (i.e. the positions of parts that are many kilometers away from you), can cause phantom collisions, which make the game explode things for “no reason”.

These distance limits were put in place by SQUAD specifically for the purpose of trying to avoid the space kraken. If you set them too large again, you can risk invoking the Kraken again. They typically CAN be enlarged some, because the settings are very low to provide a overly large safety margin, but be careful with it. Don’t go overboard and set the ranges to several thousand kilometers.

Also, don’t set the PACK distance to be higher than the LOAD distance, as that is undefined behavior in the main game. Always keep the LOAD distance higher than or equal to the PACK distance.

Members and Methods
Suffix Type Get/Set Description
ESCAPING SituationLoadDistance Get Load and pack Distances while escaping the current body
FLYING SituationLoadDistance Get Load and pack Distances while flying in atmosphere
LANDED SituationLoadDistance Get Load and pack Distances while landed on the surface
ORBIT SituationLoadDistance Get Load and pack Distances while in orbit
PRELAUNCH SituationLoadDistance Get Load and pack Distances while on the launch pad or runway
SPLASHED SituationLoadDistance Get Load and pack Distances while splashed in water
SUBORBITAL SituationLoadDistance Get Load and pack Distances while on a suborbital trajectory

Each of the above

structure SituationLoadDistance

SituationLoadDistance is what is returned by each of the above suffixes mentioned in the LoadDistance suffix list above.

Order Matters. - Becuse of the protections in place to prevent you from setting some values bigger than others (see the descriptions below), sometimes the order in which you change the values matters and you have to be careful to change them in the correct order, or else the attempt to change them will be denied.

Members and Methods
Suffix Type Get/Set Description
LOAD scalar, in meters Get/Set The load distance
UNLOAD scalar, in meters Get/Set The unload distance
UNPACK scalar, in meters Get/Set The unpack distance
PACK scalar, in meters Get/Set The pack distance
SituationLoadDistance:LOAD
Access: Get/Set scalar, in meters

Get or set the load distance. When another vessel is getting closer to you, because you are moving toward it or it is moving toward you, when that vessel becomes this distance or closer to the active vessel, it will transition from being unloaded to being loaded. See the description above for what it means for a vessel to be loaded.

This value must be less than UNLOAD, and will automatically be adjusted accordingly.

SituationLoadDistance:UNLOAD
Access: Get/Set scalar, in meters

Get or set the unload distance. When another vessel is becoming more distant as you move away from it, or it moves away from you, when that vessel becomes this distance or greater from the active vessel, it will transition from being loaded to being unloaded. See the description above for what it means for a vessel to be loaded.

This value must be greater than LOAD, and will automatically be adjusted accordingly.

SituationLoadDistance:UNPACK
Access: Get/Set scalar, in meters

Get or set the unpack distance. When another vessel is getting closer to you, because you are moving toward it or it is moving toward you, when that vessel becomes this distance or closer to the active vessel, it will transition from being packed to being unpacked. See the description above for what it means for a vessel to be packed.

This value must be less than PACK, and will automatically be adjusted accordingly.

SituationLoadDistance:PACK
Access: Get/Set scalar, in meters

Get or set the pack distance. When another vessel is getting farther away from you, because you are moving away from it or it is moving away from you, when that vessel becomes this distance or greater from the active vessel, it will transition from being unpacked to being packed. See the description above for what it means for a vessel to be packed.

This value must be greater than UNPACK, and will automatically be adjusted accordingly.

===Examples===

Print out all the current settings:

SET distances TO KUNIVERSE:DEFAULTLOADDISTANCE.

PRINT "escaping distances:".
print "  unpack: " + distances:ESCAPING:UNPACK + "m".
print "    pack: " + distances:ESCAPING:PACK + "m".
PRINT "flying distances:".
print "  unpack: " + distances:FLYING:UNPACK + "m".
print "    pack: " + distances:FLYING:PACK + "m".
PRINT "landed distances:".
print "  unpack: " + distances:LANDED:UNPACK + "m".
print "    pack: " + distances:LANDED:PACK + "m".
PRINT "orbit distances:".
print "  unpack: " + distances:ORBIT:UNPACK + "m".
print "    pack: " + distances:ORBIT:PACK + "m".
PRINT "prelaunch distances:".
print "  unpack: " + distances:PRELAUNCH:UNPACK + "m".
print "    pack: " + distances:PRELAUNCH:PACK + "m".
PRINT "splashed distances:".
print "  unpack: " + distances:SPLASHED:UNPACK + "m".
print "    pack: " + distances:SPLASHED:PACK + "m".
PRINT "suborbital distances:".
print "  unpack: " + distances:SUBORBITAL:UNPACK + "m".
print "    pack: " + distances:SUBORBITAL:PACK + "m".


Change the settings while flying or landed or splashed or on launchpad or runway, For the purpose of allowing more vessels to fly around the Kerbal Space Center at a greater distances from each other:

// 30 km for in-flight
// and PACK before UNPACK.  Otherwise the protections in
// place to prevent invalid values will deny your attempt
// to change some of the values:
WAIT 0.001. // See paragraph above: "wait between load and pack changes"
WAIT 0.001. // See paragraph above: "wait between load and pack changes"

// 30 km for parked on the ground:
// and PACK before UNPACK.  Otherwise the protections in
// place to prevent invalid values will deny your attempt
// to change some of the values:
WAIT 0.001. // See paragraph above: "wait between load and pack changes"
WAIT 0.001. // See paragraph above: "wait between load and pack changes"

// 30 km for parked in the sea:
// and PACK before UNPACK.  Otherwise the protections in
// place to prevent invalid values will deny your attempt
// to change some of the values:
WAIT 0.001. // See paragraph above: "wait between load and pack changes"
WAIT 0.001. // See paragraph above: "wait between load and pack changes"

// 30 km for being on the launchpad or runway