Getting into Polar orbits...

[The Right Stuff]

Hey all. I'm having trouble getting into polar orbits- that is, making my orbit cross the north and south pole. I'll admit, being a new player, I'm not very efficient on fuel usage. So, if I'm in more or less orbiting around the equator, what is the best way to start crossing the poles without making my apoapsis or periapsis an insane altitude? Thanks.

[KvickFlygarn87]

That would be to start launching towards north/south. Hope this helps!

[Aethon]

Best answer would be to launch into a polar orbit, keeping in mind it will take more dv than an equatorial pro grade orbit.

Were I already there, I'd extend my apoapsis out as far as feasible and change my inclination at AP. Hope that helps

[Claw]

Yes, the best bet is (as has been stated) to set up your polar orbit during launch. Bear in mind that because Kerbin is rotating, you'll actually have to point a little west, in addition to either north or south. If you leave the navball in surface mode and point the "surface prograde" marker right on north (or south) you'll actually be a bit off once you reach orbit. However, if you manually switch your navball over to orbit mode, you can watch the prograde marker and get the "orbit prograde" right on north (or south) and you'll be all set.

Good luck.

[Kasuha]

However, if you manually switch your navball over to orbit mode, you can watch the prograde marker and get the "orbit prograde" right on north (or south) and you'll be all set.

There's no need to switch navball manually - it's pointless to do that in atmosphere so you can simply wait till you exceed 36 km and navball switches itself.

[Claw]

There's no need to switch navball manually - it's pointless to do that in atmosphere so you can simply wait till you exceed 36 km and navball switches itself.

I know it switches automatically. Personally I find it easier to switch to orbit mode earlier when aiming for polar orbits.

[Xavven]

I know it switches automatically. Personally I find it easier to switch to orbit mode earlier when aiming for polar orbits.

Agreed. It's easier and takes less delta-v if you switch your navball to orbit mode right when you start your gravity turn.

[Drew Kerman]

if you do start from an equatorial orbit for whatever reason, the most efficient thing to do is an oberth burn to raise your apoapsis far from Kerbin and then perform the plane change along that elongated orbit as the farther out you are from Kerbin the easier this will be. Then re-circularize when you drop back towards the planet

[BudgetHedgehog]

So, if I'm in more or less orbiting around the equator, what is the best way to start crossing the poles without making my apoapsis or periapsis an insane altitude? Thanks.

If you're going to enforce that ridiculous restriction, just keep burning normal or anti-normal (up or down. But remember that if you burn up long enough, you'll start creeping prograde so you'll need to gradually point your craft retrograde to compensate. Best way to do this is get the Enhanced Navball mod which displays it on your navball or just eyeball it and compensate as necessary.

Also, you say you're not so efficient on fuel usage - what I just suggested is far far more inefficient than if you were to do a bi-elliptic inclination change transfer

i.e. raising your AP to an insane altitude. For reference, that move in the picture saved me about 250 m/s delta-V overall. It'd would've taken me about 750 to just keep burning anti-/normal but overall, raising the AP, turning while I'm travelling much slower and then recircularising only took 500 m/s. And that's without aerobraking to help recircularise. So honest question, why would want to not raise your AP to an insane(ly useful) height?

Edited May 15, 2014 by ObsessedWithKSP

[cantab]

I assume what's been referred to is the way apopasis rises severely if you just try and do a normal/anti-normal burn. To clarify, the most fuel-efficient general way to make large inclination changes is:

1) Burn prograde to raise apoapsis as high as you like. If you're trying to rendezvous with something, make this burn at the ascending/descending node. (Target what you want to meet up with and you'll see the AN/DN markers appear).

2) At apoapsis, do a burn with a normal or antinormal component to match inclinations, and a retrograde component to lower periapsis to the desired altitude. (For aerobraking, make this in the atmosphere, but not too low! Try 40 km for Kerbin).

3) If not aerobraking, burn retrograde at periapsis to lower your apoapsis back down.

[michaelhester07]

I have 3 ways for you to do a polar orbit.

1. Launching into it: Obviously the easy one: do your gravity turn to the north or south. I recommend this method for asteroid interception.

2. Entering a system: Before you encounter a new system do some correction burns to lower your projected periapsis to the target to within 500km (50km for Minimus/Mun). Burn a small amount in each of the 6 major axes (pro grade, retrograde, left, right, up, down... as based on pro/retro trajectory) to see if it increases or decreases the projected periapsis. If it decreases keep burning until it stops decreasing or until the target altitude. Now when you enter the system you can do the blue and purple axes to adjust your orbit around the target without spending too much delta V to do so. Adjust until you have the desired axis of orbit then burn at the periapsis for system capture (or do an aerobrake if the target has an atmosphere).

3. In-orbit: If you're already in orbit of the target you can plan the burn. For whichever direction you drag the purple adjustment make sure you drag the retrograde green marker as well to maintain your orbit's shape. Drag purple and green until your orbit is the correct direction. Be wary as this type of burn can cost a bit of deltaV.

[ksbes]

There is a little bit more efficient way to transfere to polar orbit without using any navnodes. All you need is a control unit (e.g. docking port (the best) or spurnik) pointing 90 degrees to the major axis of you craft.

All yo need is to switch to control from this node, point it to the orbit vector, tilt your ship to north/south and burn. While burning yo should control 2 things:

1) control node must point orbital velosity vector all the way

2) your orbital speed shouldn't change (greatly): if it is increasing, tilt litle up (reletive to orbital velocity), if it is decreasing - down

your will need sqrt(2)*(orbital speed) to do the trick. E.g. for LKO your will need 3400 m/s deltaV

[Kasuha]

There is a little bit more efficient way to transfere to polar orbit without using any navnodes. All you need is a control unit (e.g. docking port (the best) or spurnik) pointing 90 degrees to the major axis of you craft.

All yo need is to switch to control from this node, point it to the orbit vector, tilt your ship to north/south and burn. While burning yo should control 2 things:

1) control node must point orbital velosity vector all the way

2) your orbital speed shouldn't change (greatly): if it is increasing, tilt litle up (reletive to orbital velocity), if it is decreasing - down

your will need sqrt(2)*(orbital speed) to do the trick. E.g. for LKO your will need 3400 m/s deltaV

For anything more than 60 degrees the most efficient method is bi-elliptic inclination change. Raise your apoapsis all the way up to SOI boundary, turn there, then circularize at periapsis again. Whether you do or don't use maneuver nodes for it is not very important.

[KerikBalm]

Couldn't you also use the Mun to get you into a polar orbit.... assuming that doesn't count as raising your apoapsis to an insane height (hey, its not like you're going to minmus!)

Like so:

http://en.wikipedia.org/wiki/PAS-22#Rescue_of_satellite

[Kasuha]

Couldn't you also use the Mun to get you into a polar orbit.... assuming that doesn't count as raising your apoapsis to an insane height (hey, its not like you're going to minmus!)

Like so:

http://en.wikipedia.org/wiki/PAS-22#Rescue_of_satellite

Yes you can. I remember someone even posting a screenshot of such maneuver. And yes, that lets you to do the maneuver spending even less dv.

[BudgetHedgehog]

Couldn't you also use the Mun to get you into a polar orbit.... assuming that doesn't count as raising your apoapsis to an insane height (hey, its not like you're going to minmus!)

Like so:

http://en.wikipedia.org/wiki/PAS-22#Rescue_of_satellite

Even better. Want to see the top of the sun? Slingshot off of Jupiter!

Also, yes, using the Mun to polarise your orbit (hell yeah that's a legitimate usage of polarise) is incredibly doable

Javascript is disabled. View full album

[phoenix_ca]

O.o

Is using the Mun for that any less costly than a plane change while in a circular orbit? My guess would be no, especially at higher altitudes (less Oberth effect when circularizing again).

[ksbes]

For anything more than 60 degrees the most efficient method is bi-elliptic inclination change. Raise your apoapsis all the way up to SOI boundary, turn there, then circularize at periapsis again. Whether you do or don't use maneuver nodes for it is not very important.

It's true. But question was about turning without raising apoapsis. As I understood it is all about time. If you want to do smth quicker you need to waste more fuel. I use this method for my kethane probes: they have 3000 dv (at 800 kg weight) and are expendables. So, in most cases saving fuel is not my concern. But time(ingame and real) is