Changing inclination while in LKO before transfer worth it?

[Liowen]

Been mulling this over in my head since last night and figured maybe someone could tell me if, or if not, possible to to set the inclination of a distant planet. Since most orbits are done in, roughly, an equatorial plain my thinking is that if I use Mun as my reference I could adjust my inclination to set up for my planetary transfer. I have not tried this yet but I figure it would not cost as much to do it this way vs doing it in a solar orbit. Am I wrong on this and if so why? I figure if it is close to the AN or DN of the planet in question it should all line up, but I have been known to be wrong from time to time.

Edited January 18, 2015 by Liowen

[Hannu]

It is no good idea to change inclination by separate burn if you are already on equatorial orbit. If you make inclination change during transfer orbit injection burn, velocities sums squared. If inclination change is small (few degrees), difference is typically negligible. In any case it is far less than separate burn.

But if you launch straight to inclined orbit you can benefit couple of tens of m/s. Or even more, if you need large inclination (Moho, Dres, Eeloo). In that situation you have to get right LAN. You can use (for example) angle to prograde -values which are given by Mechjeb and Alexmoon's transfer calculator.

Edit: I should read more carefully. You asked that is it better to make a transfer via single elliptic orbit or use plane change burn at orbital node. It depends. Most cases in KSP it is better to use single transfer, but not always. Especially it is sometimes better to make separate plane change burn with bodies I mentioned (they are on inclined orbits). However, it is more complicated to plan such a mission with KSP's tools and it may be difficult to prevent losing the benefit to inaccurate orbits.

You can use http://alexmoon.github.io/ksp/ to compare different transfer types.

Edited January 18, 2015 by Hannu
Good answer but wrong question

[GoSlash27]

Liowen,

You always want to perform inclination changes at low speed and as close as possible to the AN/DN. This will yield the most efficient conversion of DV into inclination change.

In the Kerbol inertial frame, you are moving slowest when you escape Kerbin SoI, so it makes more sense to match the inclination there.

Besides, your inclination WRT Kerbin isn't the same as your inclination WRT Kerbol.

Best,

-Slashy

[Spheniscine]

Launching into the right inclination for an interplanetary transfer is difficult with the tools the game gives you, as your inclination when you escape Kerbin's SOI is not equal to your inclination within Kerbin's SOI... it all depends on in which direction and how quickly you're escaping. You also need to make sure your ascending and descending nodes are at the right place.

I do have a particular process for this, but it's kinda complicated involving the use of two external programs and certain mods...

Edited January 18, 2015 by Spheniscine

[Liowen]

Thanks for that....I knew there was a reason but could not remember why it shouldn't be done. More trials for Moho then for me I guess LOL.

[Kryxal]

I'd probably just launch a satellite into an equatorial orbit then plot an escape trajectory for it ... then launch your actual vehicle to be in the same plane as the escape maneuver.

[LethalDose]

In the Kerbol inertial frame, you are moving slowest when you escape Kerbin SoI, so it makes more sense to match the inclination there.

Besides, your inclination WRT Kerbin isn't the same as your inclination WRT Kerbol.

This is only correct when you're dropping your PE below Kerbin's orbit (e.g. transferring to Moho or Eve).

In the Kerbol inertial frame, you're only moving slowest when you escape Kerbin's SoI heading "down" into the system. If you're transferring to a higher orbit (Duna, Jool, etc) you're at or near your orbital PE around Kerbol when you're leaving Kerbin's SoI, hence your orbital speed in the Kerbol frame of reference is greatest.

[StrandedonEarth]

I don't know how efficient this is, but this what I do:

When KAC says I'm at the window, I'll plot my escape maneuver out to the target planet's orbit. Then I'll set another node at the An/Dn and plot the plane change and whatever other finetuning I need to get the intercept I want. This is all before I do a single burn (aside from getting to orbit, of course). After I do the final burn I'll use RCS while focused on my destination to put the approach exactly where I want it

[Liowen]

I don't know how efficient this is, but this what I do:

When KAC says I'm at the window, I'll plot my escape maneuver out to the target planet's orbit. Then I'll set another node at the An/Dn and plot the plane change and whatever other finetuning I need to get the intercept I want. This is all before I do a single burn (aside from getting to orbit, of course). After I do the final burn I'll use RCS while focused on my destination to put the approach exactly where I want it

I may try this tomorrow for Moho, been having a heck of a time getting there for some reason. I have gotten a flyby before but never orbited or landed, usually I have burnt nearly all my fuel just to get a fly by. Getting better though....I think.

[LethalDose]

I don't know how efficient this is, but this what I do:

When KAC says I'm at the window, I'll plot my escape maneuver out to the target planet's orbit. Then I'll set another node at the An/Dn and plot the plane change and whatever other finetuning I need to get the intercept I want. This is all before I do a single burn (aside from getting to orbit, of course). After I do the final burn I'll use RCS while focused on my destination to put the approach exactly where I want it

This is a good general approach, it just doesn't work well for Moho, and is kind of mediocre for Dres.

I may try this tomorrow for Moho, been having a heck of a time getting there for some reason. I have gotten a flyby before but never orbited or landed, usually I have burnt nearly all my fuel just to get a fly by. Getting better though....I think.

The problem with approaching Moho is that you need much more dV to get captured than other planets. It's important to make plane changes efficiently to hold onto the dV for the approach.

Edited January 19, 2015 by LethalDose

[StrandedonEarth]

Yeah, my last trip to Moho seemed kind of expensive, dV-wise. Good thing I used a nuclear-powered transfer stage with plenty of dV

[Spheniscine]

Well, here is a summary of the process I was talking about; I've used it for inclined solar contract satellites, so it should work for Moho/Dres/Eeloo too:

1. Find your launch window using Alexmoon's planner (for aforementioned satellites I create a new "planet" with the orbital elements from the persistence file, and adjust "mean anomaly" to get a satisfactory balance between time and dV expense)

2. Enter the departure and arrival dates into "Compute Departure Burn" from KSPTOT. Reason I use Alexmoon's planner first is that I find its porkchop graphing much more convenient than KSPTOT's.

3. Take a note of the "Hyperbolic Departure Orbit from Kerbin", specifically, inclination, right ascension of AN (LAN), and argument of periapsis.

4. Use Hyperedit to move a "marker" satellite into that particular inclination and LAN. Also give it slight eccentricity so that the periapsis can mark the departure point. Hyperedit is technically cheating, but really the only way I know of to easily "visualize" those numbers in-game, and gives you something to target and make adjustments against. I just treat the marker as not "real" and just a hacky way of defining your own orbital waypoint.

5. Launch the vessel into inclination, using the marker as a guide. I've gotten good enough at it to usually come within 1 degree of the target orbit, which doesn't take too much dV to adjust.

Edited January 19, 2015 by Spheniscine

[Hannu]

Transfers to Moho need absolute accuracy. If your burn have an error of 1 m/s it may need 1000 m/s more dv at insertion. Inaccuracies of orbits and nodes are real problem. You shoud check orbit many times. Especially immediately after escaping Kerbin's SOI (SOI transitions cause errors to trajectroies). It is also good idea to put 1000-2000 m/s extra dv, if you are not experienced player who have strange passion to make accurate orbital maneuvers.

[Janos1986]

Merge the Hohman transfer with both altitude and inclination change to save some fuel.

[NASAHireMe]

If you want a great answer for this in regards to Moho, I highly recommend Metaphor's journey to Moho documented here. He/she managed to land on Moho with only 7217 dV, of which 4400 were launch to Kerbin orbit itself! Reading his discussion and the images of his gravity assists were the 'aha!' moments for me in which I really understood how gravity assists work in gameplay.