OrbitEta

OrbitEta is a special object that exists just to help you get the times from now to certain events in an orbit’s future. It operates on an Orbit, and can be obtained one of two ways:

  • Any Orbit contains an ETA suffix that will give you the ETA values for that orbit patch, for example:

    print SHIP:OBT:ETA:APOAPSIS.
print SHIP:OBT:NEXTPATCH:ETA:APOAPSIS.

  • With the ETA keyword: Just saying ETA gives the same thing as saying SHIP:OBT:ETA. Therefore this:

    print ETA:APOAPSIS.

    Is a shorthand for this:

    print SHIP:OBT:ETA:APOAPSIS
    structure OrbitEta

    Suffix

    Type

    Description

    APOAPSIS

    Scalar (s)

    Seconds from now until apoapsis.

    PERIAPSIS

    Scalar (s)

    Seconds from now until periapsis.

    NEXTNODE

    Scalar (s)

    Seconds from now until the next maneuver node.

    TRANSITION

    Scalar (s)

    Seconds from now until the next orbit patch starts.
ETA:APOAPSIS
Type

Scalar (s)

Access

Get-only

Seconds until the object in this orbit patch would hit its apoapsis. Note, that even hypothetical orbits created by CREATEORBIT which have no “object in orbit” right now, still have a hypothetical imaginary point along that orbit that represents where the “object” is “now”.

If the object is on an escape trajectory (hyperbolic orbit) such that you will never reach apoapsis, it will return the Very Big Number 3.402823E+38. (Largest non-infinity number that can be represented in a single precision float value, if you care why it’s that number.) A reasonable script test could simply be if eta:apoapsis > 100000000000000 you can assume it’s actually infinite, as that’s much bigger than any real elliptical orbit in the game would give you. (But a much better test for hyperbolic orbits is to look for the Apoapsis height being negative.)

Also be aware that in the stock KSP game (things may be different if you install a mod like Principia that changes the orbital calculation model) ETA:APOAPSIS can be decieving when looking at some large orbits. kOS will only return the fake bignum 3.402823E+38 for those orbits that are mathematically actual hyperbolic escape tragectories, not the orbits that are elliptical but the game still lets them escape anyway because of the limits of the Sphere of Influence model.

ETA:PERIAPSIS
Type

Scalar (s)

Access

Get only

Seconds until the object in this orbit hits its periapsis. If the ship is on an intersect with the ground, such that you’ll hit the ground first before you’d get to periapsis, it will still return the hypothetical number of seconds it would have taken to get to periapsis if you had the magical ability to pass through the ground as if it wasn’t there.

Note that in hyperbolic orbits (escape trajectories), if you are past the Periapsis, then you’ll never come back down to it. Rather than returning the Very Big Number (3.402823E+38) in this case to represent infinity, it will instead count time “backward” and show you a negative number, for how many seconds it’s been since periapsis.

ETA:NEXTNODE
Type

Scalar (s)

Access

Get only

Seconds until the next manuever node’s timestamp. NOTE this is the time shown on the navball for the maneuver node, and does not take into account the lead time shown on the navball.

This should give the exact same value as NEXTNODE:ETA with one important difference: NEXTNODE:ETA will throw an error if there is no next node, while this (ETA:NEXTNODE) will simply return a very big number representing the biggest floating point value (32-bit). (For various reasons, kOS does not allow the value “Infinity” in its Scalars, so “a really big number” is used in its place.)

ETA:TRANSITION
Type

Scalar (s)

Access

Get only

Seconds until the transition from this orbit patch to the next one. This ignores the effect of any intervening manuever nodes it might hit before it gets there. (This will be the path you would follow if you never execute any of those manuever nodes.)

If there is no next transition (you are on a closed loop that will not exit the current sphere of influence), this will return a very big number representing the biggest floating point value (32-bit). (For various reasons, kOS does not allow the value “Infinity” in its Scalars, so “a really big number” is used in its place.)