best way to move your orbit from 90 back to 0

[Cerberus738]

Assuming 0 means equator. I have a ship in a polar orbit and I would like to get it back to the equator to pick up something. Is there an inexpensive way to do that? I'm trying a flyby of the Mun at the moment. I have a maneuver set up so the gravity of the Mun will pull my orbit up. is this a good or bad idea?

Edited January 30, 2014 by Cerberus738

[RSwordsman]

Sounds pretty good to me. It appears to my "wing-it" physics understanding that you're essentially raising your apoapsis veeeery high, making inclination changes much more fuel efficient. The gravity assist from the moon probably helps a ton as well.

[luizopiloto]

no need to go to the mun... just burn to Normal+ - at the down and Up nodes... if you don't have a mod that shows it, they are half way between Ap and Pe... normal + and - are the direction parallel to the ground but perpendicullar to you orbit. enhanced navball draws it at the Navball...

[TheDarkStar]

On the nav-ball, 90 is due west, so if you are going 90 or 270, you're equatorial.

However, you might be reading the values relative to a certain spacecraft. In this case, set it as a target and then burn at either point that it shows your orbital planes to intersect (but remember that the one further up is more efficient).

[Alistone]

If you did a direct burn to negate your appox 2000 m/s of N-S velocity and add approx 2000 m/s of W-E velocity you would have a dV of about 3000 dV.

Generally it is better to spend about 900 dV (while you are over the equator!) to enter a highly elliptical orbit (about minmus height at the far end). At the high and slow end (apoapsis) of the orbit you can spend another 50 m/s to kill your N-S velocity and add 50m/s of W-E velocity. Poof, your plane change is done.

At periapsis of your now equatorial then spend another 900dV circularizing (or dip into the atmosphere slightly to aerobrake maybe 55km?) and you can accomplish the maneuver using between 2000dV (or 1100 dV if you aerobrake). This compares to about 3000 dV if you try to do it directly.

Using the mun to do it seems much harder to me as it is likely to catapult you out of the kerbing SOI; and you still have to spend over 800dV to get out as high as the mun anyways...

Edited January 29, 2014 by Alistone

[tavert]

You have the right idea, using a gravity assist off the Mun is the most efficient way to make a large inclination change from low orbit. Will require careful tweaking of the maneuver and flyby to get it right. If the Mun weren't there or if you're having trouble finding a good flyby path, then a bielliptic inclination change is the next best thing for large changes (raise apoapsis to high altitude and close to the equator, change inclination at apoapsis, aerobrake to re-circularize).

[Capt. Hunt]

the best way is to not get in a polar orbit in the first place.

Point the rocket eastward (090) on lift off, that's more efficient anyway because you are using the rotation of Kerbin to your advantage, so it'll take less fuel then a polar launch trajectory.

[Kasuha]

the best way is to not get in a polar orbit in the first place.

There's no reason to stick to equatorial orbits. Polar orbits are useful, too. For instance, you can scan all biomes from them.

[wmheric]

Alistone is right: for a 90 deg plane change, the delta-V required is always smaller when you bright up the apoapsis and burn normal there, and it turns out that the amount of delta-V "saved" is smaller [EDITED: greater] for a higher apoapsis. The tradeoff is of course the total time (the period of the elliptical orbit) needed to finish the maneuver.

Gravity assist by the Mun is an challenging and an exciting idea

Edited January 29, 2014 by wmheric

[Legendmir]

Inclination changes are best done at slow speeds. So if you increase your orbit then warp out to the slowest point (apoapsis) and do the inclination change from there it will be less expensive then just going for it.

Grav assists are also a good idea but could require allot of fiddling with manover nodes. So for less game time id just go for increase orbit and then change inclination. for extra savings in sure a grav assist would work.

[Kasuha]

and it turns out that the amount of delta-V "saved" is smaller for a higher apoapsis

I guess this is a typo. From the dv perspective, the higher the more dv you save.

[SRV Ron]

You have the right idea, using a gravity assist off the Mun is the most efficient way to make a large inclination change from low orbit. Will require careful tweaking of the maneuver and flyby to get it right. If the Mun weren't there or if you're having trouble finding a good flyby path, then a bielliptic inclination change is the next best thing for large changes (raise apoapsis to high altitude and close to the equator, change inclination at apoapsis, aerobrake to re-circularize).

Extremely difficult to set up but most efficient.

[wmheric]

I guess this is a typo. From the dv perspective, the higher the more dv you save.

Derp. Thanks!

You save more delta-V by pushing the apoapsis higher.

[Cerberus738]

On the nav-ball, 90 is due west, so if you are going 90 or 270, you're equatorial.

However, you might be reading the values relative to a certain spacecraft. In this case, set it as a target and then burn at either point that it shows your orbital planes to intersect (but remember that the one further up is more efficient).

Yes i did have my space station targeted. its in an equatorial orbit and i can use it as a reference point for most things. i do always (except this case??) launch to the 90

Using the mun to do it seems much harder to me as it is likely to catapult you out of the kerbing SOI; and you still have to spend over 800dV to get out as high as the mun anyways...

you were so correct! it launched me out past minmus. however i did get a significant inclination change. i probably could have timed it better to be more efficient and get more change out of it but i was getting upset at my navball so i just went for it. ha ha

however with only needing 38m/s to correct it and getting within 3 degrees of inclination, i think i did pretty good!

new question... how is that SOI change going to affect me?

i want to try an aerobrake as i haven't done one before! should i set that up now? or wait till i pass through the Mun's SOI? and how deep into the atmosphere do i want to go?

There's no reason to stick to equatorial orbits. Polar orbits are useful, too. For instance, you can scan all biomes from them.

DING! DING! it was actually a mapping satellite. i figured it was the only way to map the poles?

just for fun here's the ship that's doing the performance

thanks everyone for your input!!

[Kasuha]

it launched me out past minmus.

Gravity slingshots are not about throwing yourself into some SOI and watching what happens. You can see what will happen up front in the map - and you can fine tune the outcome by minute corrections to your trajectory. Of course it also means passing SOI boundaries at low time warp to keep that fine tuning as close as possible and eventually issuing corrections.

i want to try an aerobrake as i haven't done one before! should i set that up now? or wait till i pass through the Mun's SOI? and how deep into the atmosphere do i want to go?

If you don't see Mun intercept in your map view, you're not going to intercept Mun in the next orbit. Probably.

To be safe, set your periapsis to about 40 km. It will not decelerate you enough in the first pass, but after you get to (now lower) apoapsis again, you can correct your periapsis and perform another pass. And repeat that until you're in orbit you want.

I believe even 38 km is still safe from that height. But I wouldn't go any lower without quicksave.

The lower you submerge to atmosphere the lower your periapsis will be after you get above it again. It will go down with each pass. And the lower it will be the higher you'll need to pull it up once you get your apoapsis at level you desire.

[Cerberus738]

Gravity slingshots are not about throwing yourself into some SOI and watching what happens. You can see what will happen up front in the map - and you can fine tune the outcome by minute corrections to your trajectory. Of course it also means passing SOI boundaries at low time warp to keep that fine tuning as close as possible and eventually issuing corrections.

If you don't see Mun intercept in your map view, you're not going to intercept Mun in the next orbit. Probably.

To be safe, set your periapsis to about 40 km. It will not decelerate you enough in the first pass, but after you get to (now lower) apoapsis again, you can correct your periapsis and perform another pass. And repeat that until you're in orbit you want.

I believe even 38 km is still safe from that height. But I wouldn't go any lower without quicksave.

The lower you submerge to atmosphere the lower your periapsis will be after you get above it again. It will go down with each pass. And the lower it will be the higher you'll need to pull it up once you get your apoapsis at level you desire.

I didn't get a capture of my original maneuver. that's a capture after already passing through the mun's SOI once. it worked but after switching SOI the orbit changed and shot me way out past minmus. i may have had warp going...

the maneuver set up there is me getting me PE back up. it just so happens that i pass by the mun again.

so this should work then?

Edited January 30, 2014 by Cerberus738
added picture