How to use protractor? Doesn't match Olex

[Elsig]

I'm only a few weeks "old" when it comes to KSP. Whenever I'm flying to other planets I've not used any calculators (or calculated it myself). I've just use the maneuver nodes and gotten to where I wanted by trial and error. Sometimes my kerbals have spent years (decades?) in space awaiting the right window.

Now I want to do things the right way. I'm not maths genius, nor do I have interest in calculating all this stuff so I'm using the tools that are available.

I'm attempting to get to Dres using the Protractor tool and the Olex calculator. I've been to Dres before but I must have orbited Kerbol about 20 times before the right windows occurred!

I'm currently sitting in orbit around kerbin at 110km. Olex is telling me I need to leave when Dres is at 82.06 and it gives me a picture which shows me that Dres needs to be about 1 o'clock.

However, when I use the Protractor mod it doesn't match what the Olex picture shows. As you can see the Protractor is currently showing 84.74 but it's at 10 o'clock.

I'm sure I'm doing it wrong so I'm asking the community for some help on how to use the tool.

Thank you

[creator1629]

actually the difference between these 2 measurements comes from the fact that the tools use slightly different ways to calculate the ideal angle. when i first started to use these tools as well, i experienced similar differences, sometimes up to 10 degrees difference for targets like moho. so i experimented and and tried using both values, and surprisingly they were both able to get me an intercept with the target planet (of course mid course correction burns were necessary, but not a lot). in the end, what i do usually though, is use ksp.olex.biz for the phase angle, while i use the protractor mod to determine the ideal ejection angle

[maltesh]

Protractor isn't telling you what the angle between your spacecraft's world and your target world is.

Protractor is telling you how far away from the ideal (circular, equatorial) hohmann transfer position you currently are.

You should be aiming to leave at about the time protractor shows you 0°.

[magnemoe]

Protractor isn't telling you what the angle between your spacecraft's world and your target world is.

Protractor is telling you how far away from the ideal (circular, equatorial) hohmann transfer position you currently are.

You should be aiming to leave at about the time protractor shows you 0°.

Yes, and an good advice is to always make an node who give you intecept or close pass and burn after this.

If you have to change orbital plane you can plan an new node on the projected pass just to make sure you have an Moho intercept or similar.

[Elsig]

Protractor isn't telling you what the angle between your spacecraft's world and your target world is.

Protractor is telling you how far away from the ideal (circular, equatorial) hohmann transfer position you currently are.

You should be aiming to leave at about the time protractor shows you 0°.

DOH! I thought Protractor gave me the current phase angle and I had to wait until it matched the Olex one. I get it now!! And I managed to use it to get to Dres on first try without doing multiple orbits.

Thanks for the help guys!

[Mr Shifty]

DOH! I thought Protractor gave me the current phase angle and I had to wait until it matched the Olex one. I get it now!! And I managed to use it to get to Dres on first try without doing multiple orbits.

Thanks for the help guys!

Note that the MechJeb Orbit Info panel does give you your current phase angle relative to your target. And it gives your angle-to-prograde for your current primary body that you can use for ejection burns. I use MechJeb far more for the information panels than for the automation.

[KerbMav]

I have only been to Mun and back again - at first try - so I do not understand why there are so many mods to navigate the system? Is the course plotting ingame that insufficient? (Please dont just answer with yes or no, I am a curious fellow. ^^)

[maltesh]

The Mun's SOI is close, and relatively large. Minmus is also fairly closeby. Navigation from Kerbin to reach either is fairly easily doable with ye olde "Munrise burn" technique.

With interplanetary destinations, their spheres of influence are /tiny/ compared to their orbital distances, they're moving around the sun in their own orbits, that are both inclined and eccentric, and hunting down the locations that the worlds will be at when you cross their orbits is kind of tricky /with/ maneuver nodes, and was even more difficult without maneuver nodes back in 0.17.

Most of the tools used for interplanetary travel date from around that time, and while most of them use simplified calculations to help you find launch windows, they're extremely useful for that sort of thing. Not using a Hohmann transfer launch window can cost you quite a bit in delta-V to chase down your target, or (if you really don't know what you're doing) can mean you spend /years/ of K-Time searching for the SOI of your target world.

[KerbMav]

OK, thank you, I will report back after my first attempt to place a probe in Duna's orbit.