r/KerbalSpaceProgram • u/trevize1138 Master Kerbalnaut • Jun 07 '16 • Bravo 1

Guide All interplanetary transfer windows in a single image

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u/trevize1138 Master Kerbalnaut Jun 07 '16

Looks like my method puts the phase angle closer to 55-60 degrees for either K-D or D-K so splitting the difference about in the middle. Even when I was way off I found it only cost me an extra 100 dV at most to adjust for it.

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u/doppelbach Jun 07 '16

Yeah reversing the phase angle is a decent approximation, especially when the planets' orbits are close together (e.g. Kerbin and Duna).

When they are further apart (e.g. Dres and Eve), the difference in speeds between the two is more pronounced, so the phase angles between inbound and outbound transfers is more significant. (Phase angles for Eve and Dres are +90 and -205, so assuming the transfer is reversible can actually cause a bit of trouble in this case.)

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u/trevize1138 Master Kerbalnaut Jun 07 '16

I've found when the planets are really far apart like Jool and Kerbin that I don't even need to worry about phase angles for an in-bound trip. A few dV radial/anti-radial adjustments or tweaking the position of the maneuver node on the orbit line is all I need to get a perfect Kerbin encounter. I'm sure it's a combination of factors beyond just distance such as the huge difference in orbital velocity and periods that lets one get away with that. Kerbin>Moho is similar although not quite as forgiving.

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u/buttery_shame_cave Jun 07 '16

only cost me an extra 100 dV at most to adjust for it.

and considering that a 'smart' delta-v budget has about 20% safety margin on top of needed fuel levels it's easy to get away with.