Sun-Synchronous Molniya Orbit?

[Lime]

We know that polar sun-synchronous orbits are not possible in ksp. But highly elliptical orbits or Molniya orbit are possible. So if you would time a launch into molniya orbit would it be possibly to have it sun synchronous?

[Arkalius]

A Kolniya orbit, as it's called (It's official, I've gotten a contract to put a satellite into one) can be sun-synchronous but not continuously. Since KSP uses 2-body physics, and spherical gravity, there is no way to use gravity to precess the longitude of the ascending node so that the orbit stays continuously sun-synchronous.

[FancyMouse]

A Kolniya orbit, as it's called (It's official, I've gotten a contract to put a satellite into one) can be sun-synchronous but not continuously. Since KSP uses 2-body physics, and spherical gravity, there is no way to use gravity to precess the longitude of the ascending node so that the orbit stays continuously sun-synchronous.

Only equatorial orbits (i.e. with zero or 180 degree inclination) can be Sun-synchronous. In most cases a Sun-synchronous orbit needs a precession of 1 year, and as you mentioned, KSP doesn't model precession (because of absence of planet oblateness), so any orbit will have zero precession, so Sun-synchronous orbits are not possible unless precession doesn't matter. I don't know whether just coplanar to the planet orbital plane is a sufficient condition, but at least with the perfect condition of Kerbin's orbit, equatorial orbits around Kerbin do sound to me Sun-synchronous (but they're the only cases)

[Orbital Vagabond]

Only equatorial orbits (i.e. with zero or 180 degree inclination) can be Sun-synchronous.

This is inaccurate. Sun-synchronous orbits are highly inclined/polar orbits, not equatorial.

Sources:

http://satellites.spacesim.org/english/anatomy/orbit/sunsynch.html

[FancyMouse]

This is inaccurate. Sun-synchronous orbits are highly inclined/polar orbits, not equatorial.

Sources:

http://satellites.spacesim.org/english/anatomy/orbit/sunsynch.html

I'm talking about the Kerbin, not earth. For earth you do need inclination to get the proper precession, but things are different on Kerbin.

[Orbital Vagabond]

I'm talking about the Kerbin, not earth. For earth you do need inclination to get the proper precession, but things are different on Kerbin.

It doesn't matter. Equatorial orbits can never be sun-synchronous because they view the sun in different positions at any given latitude on each orbit since the position of the sun relative to the orbit changes on each orbit due to the planet's orbit around it's parent.

[Geschosskopf]

It doesn't matter. Equatorial orbits can never be sun-synchronous because they view the sun in different positions at any given latitude on each orbit since the position of the sun relative to the orbit changes on each orbit due to the planet's orbit around it's parent.

Kerbin's orbit has zero inclination, and Kerbin itself (and all other worlds in the game) has zero axial tilt. As a result, the sun is always directly over Kerbin's equator with no latitude changes (or seasons) over the course of the year. Also, in KSP, a ship's orbital plane doesn't change over time. Thus, if you put a ship into a polar orbit that's edge-on to the sun initially, then 1/4 of a year later the ship's orbital plane will be broadside on to the sun. The same thing happens to all inclined orbits. The orbit's LAN is fixed until you change it by maneuvering the ship.

For these reasons, you can't make a true sun-synchronous orbit (as in the ship crossing the equator at the same local time every orbit) in KSP. In KSP, an equatorial orbit is the closest you can do, and tehcnically this is actually sun-synchronouse because the angle of the orbital plane to the sun never changes, but it's of no real use and the altitude can be arbitrary.

[Lime]

Just did it when at apoapsis it's always in the sun.