How to measure when the Mun is at opposition?

[LambdaCactus]

I\'m playing around with the awesome KSP Orbit Mechanic calculator and trying to work out how to apply it in the game. So if I want to time my orbit insertion, I need to know when the craft-Kerbin-Mun are lined up (conjunction) or when the mun is directly overhead from Kerbin orbit (opposition).

Is there a trick for measuring the syzygy events (even semi-accurately), or do you just eyeball it (rule of Jeb) in the map? 8)

[Xivios]

I take it your trying to insert yourself into Mün orbit. Apparently, and I\'ve tried this and it works, well enough for me to have done a direct descent from to the moon from Kerbin orbit, in a single burn out of Kerbal orbit until slowing for landing, is to time your TLI until the mün is just rising over the horizon while in an orbit of about 100,000 to 150,000 meters.

You could eyeball in the map when the mün will be opposite your craft fairly well, but the mün won\'t be there by the time you get there. Your hugely elliptical insertion orbit does not have nearly the same period as the müns circular one, so it won\'t be around when you get there.

For some reason, the horizon method means your ship will usually arrive in the prescribed location a bit before the moon will, but travelling far slower than the mün and close enough to enter the müns SOI and be pulled towards it, usually on either a collision course, or one that will swing just outside the far side of the mün and sling you back towards Kerbin. Either one can be made into a succesful orbit, if it\'s a collision course, I usually push the orbit a bit out until it turns into the 'sling to kerbin' orbit, wait for periapsis on the far side, and then burn retrograde to pull into a nice, low altitude orbit around Mün.

[ThaineFurrows]

I\'m playing around with the awesome KSP Orbit Mechanic calculator and trying to work out how to apply it in the game. So if I want to time my orbit insertion, I need to know when the craft-Kerbin-Mun are lined up (conjunction) or when the mun is directly overhead from Kerbin orbit (opposition).

Is there a trick for measuring the syzygy events (even semi-accurately), or do you just eyeball it (rule of Jeb) in the map? 8)

I had the same thought. Would be nice to have some more info on the map. As for example angles between different objects from your position, etc... Maybe we can collect some useful data to show and post it in the development section. Maybe something useful comes up with the mission control center and flight planning. I\'m quite excited about the flight planning thing anyhow.

[LambdaCactus]

time your TLI until the mün is just rising over the horizon while in an orbit of about 100,000 to 150,000 meters.

Yes, I\'ve done this successfully a number of times, looking at the map and adding throttle until the orbit apogee stretches to the Mun\'s orbit, but using the map is too easy! I\'d like to try how it\'s done using the calculator (i.e. timing the orbit and accelerating to the determined velocity) which is more like how it\'s done in the real world. (I know, calculating is so not Kerbal!)

Anyway, I did find that eyeballing the map works quite well (Apollo astronauts had little more than window sights for alignment too!):

1. Press TAB to focus on Kerbin

2. Zoom to fill the screen with the globe of the planet

3. Align the view so the Mun icon sits at the bottom of the planet (behind it)

Assuming you have a nice round equatorial orbit (I tried this with 100km), your craft will point to the top of the planet when it passes in front. This is conjunction. For opposition, your craft will pass behind Kerbin, and you can spot when it passes the Mun, about a quarter of the way from the bottom of the planet\'s globe.

Would be nice to have some more info on the map.

Agreed, maybe a measuring tool or something!

[WX_Echo]

I\'m playing around with the awesome KSP Orbit Mechanic calculator and trying to work out how to apply it in the game. So if I want to time my orbit insertion, I need to know when the craft-Kerbin-Mun are lined up (conjunction) or when the mun is directly overhead from Kerbin orbit (opposition).

Is there a trick for measuring the syzygy events (even semi-accurately), or do you just eyeball it (rule of Jeb) in the map? 8)

I\'m glad to hear you like the calculator.

When designing this feature, I would just eyeball the syzygy conditions you\'ve specified. In the absence of more precise in-game orbital tools, it\'s the best we can manage.

The trick when using the calculator is to know what type of syzygy you\'re dealing with. Most users will be performing a low-to-high Hohmann transfer where the Mun is at opposition. My recommendation is to zoom out just far enough to be able to estimate when your spacecraft will move between Kerbin and the Mun such that all three are along a single line extending radially from Kerbin out to the Mun (and beyond). Different syzygy geometries will require a bit more understanding from the user, but are still very easy to estimate.

FYI: this feature originally required the user to estimate angles like 83 deg. I received some great feedback from one of my beta testers that indicated syzygy events (e.g. conjunction or opposition) were much easier to estimate (precisely) without additional in-game tools.

Happy orbiting!