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# orbital nodes for interplanetary transfers

## Question

after some bad experiences trying to get to moho, i realized that i can't just ignore the difference in orbital plane when going to orbit other planets. it results in higher intercept speeds, and i end up paying the cost anyway.

so i decided i should preferably start my journey when the starting planet is already in a node. this way, i can pay the plane change manuever together with the ejection burn, and pitagora's theorem will save me some fuel (this will likely be outside of a transfer window, but i can get an intercept by burning when intercepting the target's orbit. if done correctly, what i spend there is mostly saved in minor intercept speed)

problem is, i can't seem to find a way to find those nodes, besides eyeballing them. the game does not show them. it only shows nodes when you are orbiting the sun; but then, i'd  have made the injection burn already, and trying to make a big prograde/retrograde burn there would make me lose all the oberth effect.

so, is there a way to see those nodes? or perhaps some greater trick for interplanetary transfer that will make my experiment with nodes moot?

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Check out this thread for Moho's AN. It happens every year around Day 82. Keep in mind that the odds of Moho being there when you reach its orbit are low, so you'll have to treat it like a rendezvous - burn retrograde at Pe until you get an intercept on the next go round.

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1 hour ago, Grogs said:

Check out this thread for Moho's AN. It happens every year around Day 82. Keep in mind that the odds of Moho being there when you reach its orbit are low, so you'll have to treat it like a rendezvous - burn retrograde at Pe until you get an intercept on the next go round.

i'm not asking specifically for moho. i'm asking as a general rule. and in fact, i'm going to moho starting from eve, from refueling at gilly to be exact, so those dates would be moot. i even figured out for myself the trajectory, since that trajectory is much cheaper than having to make a 1500 m/s plane correction burn midway, and it's very rare to have the transfer window fall naturally on an orbital node.

but the thread does answer this: no, there is not another way with the in-game tools.

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9 hours ago, king of nowhere said:

...and it's very rare to have the transfer window fall naturally on an orbital node.

This is true. However, when people talk about the apoapsis transfer from Kerbin to Moho (the aforementioned day 82 date), they generally accept this.

In other words, people prefer to just make the transfer at apoapsis, even if that is not a transfer window and that burn does not get them an encounter. What they do instead is burn until their transfer orbit's periapsis touches Moho's orbit, then travel to said periapsis. There they make a retrograde burn in solar orbit to lower their apoapsis to some place between Kerbin and Moho. Just like with a rendezvous, this lets them phase into an encounter with Moho over several solar orbits.

This might mean that it may take anywhere between three to ten times as long as an in-window Hohmann transfer to reach Moho. Many players are fine with this, so long as it is cheaper dV-wise. After all, an in-window Hohmann transfer to Moho not only requires the highest precision of all transfer burns in the game, but is also the most expensive transfer in the game as well. Even more expensive than Eeloo.

So if you want to make transfers at planar intersection nodes, you will likely have to accept the fact that you will afterwards be doing a solar orbit rendezvous with your chosen destination planet. You pay for the reduction in dV cost with a large increase in travel time.

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6 hours ago, Streetwind said:

This is true. However, when people talk about the apoapsis transfer from Kerbin to Moho (the aforementioned day 82 date), they generally accept this.

In other words, people prefer to just make the transfer at apoapsis, even if that is not a transfer window and that burn does not get them an encounter. What they do instead is burn until their transfer orbit's periapsis touches Moho's orbit, then travel to said periapsis. There they make a retrograde burn in solar orbit to lower their apoapsis to some place between Kerbin and Moho. Just like with a rendezvous, this lets them phase into an encounter with Moho over several solar orbits.

This might mean that it may take anywhere between three to ten times as long as an in-window Hohmann transfer to reach Moho. Many players are fine with this, so long as it is cheaper dV-wise. After all, an in-window Hohmann transfer to Moho not only requires the highest precision of all transfer burns in the game, but is also the most expensive transfer in the game as well. Even more expensive than Eeloo.

So if you want to make transfers at planar intersection nodes, you will likely have to accept the fact that you will afterwards be doing a solar orbit rendezvous with your chosen destination planet. You pay for the reduction in dV cost with a large increase in travel time.

yes, i know. i've been using that manuever for a while now.

in fact, since i'm here, i may as well ask how i get to see the intercept with this manuever, since the game does not show. even when i know (having calculated the orbital times) that i will have a close approach in two orbits, the game does not show that as closer approach, instead showing me some crazy point where the planet is on the opposite side of the orbit that i don't know how the game can consider a close approach. i have to mostly find the SoI blindly.,

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Well, it stands to reason that there is a single-orbit solution. In other words, a burn you can make at periapsis that results in an encounter after looping around once post-burn. It will be ridiculously expensive, but you do get close approach markers for that one. So go find it, and look at how many days away that encounter is.

You now know how many days exactly it takes for Moho to return to periapsis (and thus your encounter point) after you make your burn.

You also know Moho's orbital period. Add that period to the number of days you have just measured. You receive a span of time after which Moho will be at periapsis again, but during the orbit after its current one.

Now all you need to do is to set your maneuver node dV in such a way that your orbital period after the burn will be exactly that span of time.

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8 hours ago, Streetwind said:

Well, it stands to reason that there is a single-orbit solution. In other words, a burn you can make at periapsis that results in an encounter after looping around once post-burn. It will be ridiculously expensive, but you do get close approach markers for that one. So go find it, and look at how many days away that encounter is.

You now know how many days exactly it takes for Moho to return to periapsis (and thus your encounter point) after you make your burn.

that seems more practical that my current solutions to this, which are

1) eyeballing it, or

2) saving the game, fast-forwarding time and seeing which day it will be when moho moves in position, then reloading.

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On 8/20/2020 at 4:33 PM, king of nowhere said:

that i will have a close approach in two orbits, the game does not show that as closer approach,

The game shows you the closest encounter during your next orbit after the Maneuver Node.

In oder to see encounters in 2, 3, n orbits, you have to lay down another maneuver and use the "+- one orbit" clickies.

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