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Polar orbit with specific LAN; do I just wait?


whoshotdk
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I'm well into my new 1.3 career save and have decided at long last to do some "Stick some hardware in orbit with specific longitude of ascending node" missions. I've got two polar orbit contracts that require a specific LAN each.

My question is; in a polar orbit, does the LAN continuously change as the planet rotates beneath me? If so, is it just a case of launching to a polar orbit and waiting for the LAN to come 'round?

I'll be testing this out myself anyway, but I'd quite like to hear some other's opinions/thoughts.

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Space coordinates are defined according to the celestial sphere, ie: they don't change as the planet rotates around its axis or the Sun. A LAN of 36.4° on Y1D1 00:00:00 will be the same as a LAN of 36.4° on Y80D129 01:07:44, or any other random date you can come up with.

This means that you need to launch at the right moment to get in the right orbit, since it won't "drift into position" as Kerbin rotates. The easiest (and most efficient) way to do it is to launch when the target orbit is right over the KSC.

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Ah I totally missed that on the Wiki, I tend to skim. So apparently on Earth we use the "First Point of Aries" as the origin of longitude. I'll have to check through MechJeb/FlightEngineer to see if they can tell me that info for Kerbin et al.

Anyhow, I'll follow your advice and just more-or-less eyeball it. :)

Thanks!

Edited by whoshotdk
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5 hours ago, whoshotdk said:

Ah I totally missed that on the Wiki, I tend to skim. So apparently on Earth we use the "First Point of Aries" as the origin of longitude. I'll have to check through MechJeb/FlightEngineer to see if they can tell me that info for Kerbin et al.

Anyhow, I'll follow your advice and just more-or-less eyeball it. :)

Thanks!

Mechjeb and KER both can display the LAN for the current orbit. KER for post burn too, not too sure about mechjeb.

For a kerbin target orbit, it's easier to just eyeball it. if you launch when the orbit line passes directly over the KSC, you'll be able to get a LAN very close to target, which means small maneuvers to fix it later.
Might even manage to hit it perfectly on the way up.

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