Putting a satellite in polar orbit, longitude of ascending node

[Haukifile]

So I am trying to fulfill  a contract where I need to put a satellite in a polar orbit of Kerbin. Most comments about these contracts seem to suggest that I just need to make the orbit the same as the example, but even after doing that and getting the apoapsis and periapsis almost exactly at the expected values, my LAN node is 180 degrees, while the contract states it should be 277 deg. What can I do to fix this? A close look at the orbits at the periapsis is attached.

http://images.akamai.steamusercontent.com/ugc/356148425669801858/54964057647762F2E2F96F37D0D049052A5A3010/

[Snark]

If you have a case where your AN/DN are badly off from what they need to be, then the only way to fix it for a craft that's already in flight is to do a plane change, which is hellaciously expensive in dV.  By far a better option is to just launch the ship into the right plane in the first place, so that you don't have to do a plane change in orbit (or at least, only a minor correction).

When you get one of these "launch into a specific polar orbit" contracts, here's what you do:

1. Launch your craft, but don't take off yet-- let it sit on the launch pad.
2. Switch to map view.  By default it's centered on your ship.  Double-click Kerbin itself, so that the map view is focused on Kerbin instead of your ship.
3. Zoom out until you can see the target orbit (i.e. it fits comfortably on-screen).
4. Rotate the camera around until you're looking at the target orbit perfectly edge-on (i.e. it appears as a thin line running through the center of Kerbin, instead of an ellipse).
5. Now do time-warp.  You'll see your ship move across the screen as Kerbin rotates; the orbit you're looking at edge-on will stay stationary (as long as you don't move the map camera).
6. Let the warp continue until the ship moves right on the line.  This means that your ship, sitting on the launchpad, is now directly beneath the target orbit.
7. Now you launch your ship.  Instead of turning east as you usually do, go north or south (depending on which way the orbit over your head is going).  Since you're starting out with a bit of eastward motion due to Kerbin's rotation, you actually want to launch slightly west of due north or due sout.  Only slightly, though, like five degrees.
   • When you're deciding "north or south?", be sure to pick the right one!  Otherwise you could end up in a perfect orbit going exactly the wrong direction. 
8. Go ahead and complete your gravity turn and insertion to LKO.
9. You're now in a low circular orbit that is pretty close to the right inclination.  Go ahead and complete the orbital maneuvers needed to match the target orbit.  You'll likely need a small amount of plane change, but hopefully only a few degrees and it won't cost you much.

Edited January 5, 2016 by Snark

[Haukifile]

Wow, thanks for the detailed explanation! I don't completely get the concept but got it done quite easily with your advice. Is there an easy explanation how to perform the plane change?

[Snark]

3 minutes ago, Haukifile said:

Wow, thanks for the detailed explanation! I don't completely get the concept but got it done quite easily with your advice. Is there an easy explanation how to perform the plane change?

Well, that depends on which "plane change" you mean-- the whole point of the advice I give above is to try to avoid having to make a plane change in the first place. 

However, any time you're in the game and need to change your orbital plane-- either because you're trying to match a specific orbit for a contract, or you're just trying to make orbital rendezvous with another ship-- the principle is basically the same.  Do one of the following:

• Wait until your ship is at the descending node and burn normal (the direction of the purple pointing-up triangle on your navball)
• Wait until your ship is at the ascending node and burn anti-normal (the direction of the purple pointing-down triangle-with-tick-marks on your navball).

 

[Haukifile]

Thanks, I got it now. I just got confused by the terminology before. I actually managed to get the satellite in the right orbit by doing an incredibly wasteful plane change from an equatorial plane, but did it in the wrong direction, hence my nodes were flipped.

[Snark]

20 minutes ago, Haukifile said:

Thanks, I got it now. I just got confused by the terminology before. I actually managed to get the satellite in the right orbit by doing an incredibly wasteful plane change from an equatorial plane, but did it in the wrong direction, hence my nodes were flipped.

Makes sense.

By the way, if you haven't familiarized yourself with the care and feeding of maneuver nodes yet, it would be a Good Idea.    I bring it up because if you're making a big inclination change, it can be handy to set up a maneuver node for the inclination burn-- that way you can get it dialed in "just so" and can also see in advance just how excruciatingly expensive the maneuver will be.

[ElWanderer]

>>my LAN node is 180 degrees, while the contract states it should be 277 deg

There are two different things and I think you are conflating them. The Longitude of the Ascending Node (LAN) in the contract tells you where the contract orbit crosses the equator relative to an arbitrary fixed point in the sky box... that you can't see.  Unless you're using a mod that needs to know this value,  it is best ignored.  Just eyeball when the orbit is in the right place. When you look at the Ascending Node (An) in map mode, the number tells you your current orbit's relative inclination to the contract orbit.  The aim is to reduce this to 0 if possible. Sadly, a value of 180 indicates you are travelling in precisely the opposite direction to that which is required. 

 

 

Edited January 5, 2016 by ElWanderer
Trying to cut out extraneous blank lines.

[fourfa]

I have found it easiest to just eyeball these contracts in map view.  The LAN figures are just confusing and otherwise unnecessary (even with Mechjeb you can't seem to make them work out).  Fortunately, there's a fair bit of allowance in the contract orbit details - get it pretty close by eye, and the contract will complete.  I can't put a number on it for you though.

[FancyMouse]

I have a geostationary satellite right on top of KSC. Each time I want to launch at a particular time of a day, I just go to that satellite and put a maneuver node, and warp to the node.

[Haukifile]

7 hours ago, ElWanderer said:

>>my LAN node is 180 degrees, while the contract states it should be 277 deg

There are two different things and I think you are conflating them. The Longitude of the Ascending Node (LAN) in the contract tells you where the contract orbit crosses the equator relative to an arbitrary fixed point in the sky box... that you can't see.  Unless you're using a mod that needs to know this value,  it is best ignored.  Just eyeball when the orbit is in the right place. When you look at the Ascending Node (An) in map mode, the number tells you your current orbit's relative inclination to the contract orbit.  The aim is to reduce this to 0 if possible. Sadly, a value of 180 indicates you are travelling in precisely the opposite direction to that which is required. 

 

 

Yep, that's correct. When I first posted I thought that it showed the latitude there, which was kind of dumb thinking from my part. I did realize that it showed the difference between the expected orbit and my satellite's orbit when I did it according to Snark's advice.

[purpletarget]

3 hours ago, FancyMouse said:

I have a geostationary satellite right on top of KSC. Each time I want to launch at a particular time of a day, I just go to that satellite and put a maneuver node, and warp to the node.

If you want to get even more precise with that, warp to about 3 minutes before the node, and then switch and launch from KSC. The time it takes the gravity turn to get into the polar orbit should align even better with the target orbit, given the 3-4 minutes it generally takes to get into orbit. 

 

Although, a 3 degree plane change to adjust isn't too expensive...but the lead time can reduce that further.