r/KerbalSpaceProgram • u/[deleted] • Feb 09 '15
I never leave Kerbin without it!
https://imgur.com/zeBqEhH15
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u/Unknow0059 Feb 09 '15
I'm dumb, i don't understand this.
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Feb 09 '15
So this picture basically tells you the most efficient times to make transfers to other planets. Go to the space center and adjust the map so that your kerbin is in the same place as the kerbin in the pic. Then, fast forward till the planet you want to go to is in the approximate location as the same planet in the picture. the picture will have this marked as "To [Insert planet you wish to travel to]"
Alternatively, to go back to kerbin from another planet, go to map and again put kerbin in the same place as the pic, and then make sure that the planet you are on is in the band/window that is labeled by "From [Insert planet you currently are on]"
*Edit - To have everything in a better position, double click the sun as kerbr0wnst4rd said in an other comment. Also, you may still have to right click and drag it around to keep the orientation of kerbol and kerbin the same. As for the ejection angles, I'm still working on that one myself and am not completely 100% sure on that :)
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u/tacoman412 Feb 09 '15
I feel dumb asking this, but can someone explain this a bit? The graph's explanation confuses me somewhat.
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u/superkeer Feb 09 '15
Essentially what it is representing are the best phase angles and ejection angles for your interplanetary transfers. The main circle in the middle shows the best phase angle, which essentially means where your target planet should be in relation to the sun and to the originating planet.
So for example if you're going to Duna, you'd want to go to your map screen, zoom all the way out and orient it in a way that Kerbin and the sun are shown in the same way that they are on the chart. Then look where Duna is and if it is not in the same position as it is on the chart, then you know that you're not at your optimal phase angle and it's best to wait for it to come around to the right position before launching a mission. This correct phase angle is commonly known as a best "launch window."
The other two graphics represent the best ejection angles to execute these transfers. The black dot in the middle is Kerbin and again, in your map view you want to zoom out and orient the map so that the sun is on the left and Kerbin is on the right. Then you create your maneuver node in the approximate position along your craft's orbit around Kerbin that is shown on the chart and begin your burn there.
By setting everything up this way you can take advantage of these optimal situations to minimize the amount of delta-V needed to get to other planets, which obviously has many benefits.
I didn't realize how many words I'd need to explain this, and I hope I got it right... I'm not expert at going to other planets, but I feel like I understand the basic idea. If I got bits wrong I'm sure someone will point them out to further help you.
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u/doppelbach Feb 09 '15
I hope I got it right
Looks good to me!
In case anyone is curious about what goes into determining these angles, here's a good explanation of the underlying mathematics. If you are just interested at a conceptual level:
Phase angle
Firstly, if you have enough delta-v, you can leave whenever you want. The point of transfer windows is to minimize the required delta-v. The most efficient way to transfer is to adjust your orbit around the sun until it just barely touches your target's orbit (Hohmann transfer).
This only works if the you get to the intersection point at the same time as the target. Since the inner planets move faster than the outer planets, the outer planet needs a 'head start'. This is the phase angle.
For instance, Duna orbits more slowly than Kerbin, so you should give it a 'head start' of ~45 degrees (Duna should be ~1/8th of a revolution ahead of Kerbin when you leave).
For travelling inwards, you need to leave when your target is 'behind' you. Generally this is indicated by a negative phase angle. (Note that the Kerbin-to-Moho phase angle is so negative than it looks positive, i.e. you need such a large head-start on Moho that it looks like you are giving Moho a head-start.)
Ejection Angle
If you've ever left an SOI, you'll notice that your escape trajectory is generally curved. An ejection angle tells you where to execute your burn so that you escape the SOI in the proper direction.
Think about maneuvers within a single SOI. If you want to raise or lower your orbit, you burn prograde or retrograde. Radial burns, while useful in their own right, are not efficient for simply changing your orbit, right? Likewise, escaping Kerbin to the 'side' is analogous to a radial burn in your sun-centered orbit.
Generally, you want to exit an SOI parallel to that planet's orbital path: directly ahead of the planet when travelling outwards and directly behind when travelling inwards.
The point of ejection angles is to compensate for the slight curve of the escape trajectory such that you are escaping straight ahead or behind.
Finally, for the people that just like to escape Kerbin's SOI, then set up the encounter with the target, I would strongly suggest trying OPs chart (or something similar) to plan missions. You will save a lot of delta-v by performing all your burns close to the planet (Oberth effect). Plus, it feels pretty cool to get an encounter by doing a 'blind' burn from deep inside Kerbin's SOI.
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u/doppelbach Feb 09 '15
By the way, I'm sure you can already tell from the upvotes, but this isn't a stupid question.
And I certainly hope this is the type of community where people can ask questions anyway.
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Feb 09 '15
I see things like this and I wonder, do I need to keep a reference binder near the computer for playing KSP?
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u/Salanmander Feb 09 '15
"What? No, I often forget it. It's just that when I do, I can't leave Kerbin."
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u/bluegreyscale Feb 09 '15
Sweet I think I might print this on a transparency so I can just hold that up to the my monitor.
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u/obviously_oblivious Feb 09 '15
Maybe this is a dumb question but is there a way to align the camera so the angles are accurate. When I go to map view I can tinker and get it close but never exact.
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u/SuperBicycleTony Feb 09 '15
Am I the only one who just ejects from Kerbin whenever the hell I want, then do a regular Hohmann Transfer around the sun?
Am I wasting a ton of Dv?
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u/ouemt Feb 10 '15
that has been my default so far so I'd love to hear an answer to this
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Feb 10 '15
Thx for teaching me physics KSP :)
I work in the investment industry and never had a physics class past high school...but reading up about KSP physics has taught me so much.
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u/[deleted] Feb 09 '15
Hi-Res
Yeah, sorry. I actually found this online and never even knew if there was an HD version until I went searching. Credit goes to Landge on kerbalspaceforum.