How the heck do I match this orbit?

[Durzan]

 

How the heck do I get my satellite to come close to matching this stupid orbit?

Heres a pic.

 

I've managed to get get the orbit to approximately 1 or two degrees, but everything I do to try to adjust and match the green orbit only seems to make things worse.

Edit: Here's a bit more info:

Its totally a polar orbit.Thats how I got into this predicament in the first place. The issue is that I have no clue how to fine tune to match the objective orbit as closely as possible, even with mechjeb. I kinda am a bit dense in the head when it comes to these things.

When It comes to fuel, I think I got plenty. I've got two stages on the satellite you see in the picture. ~2400 m/s of dV on stage 1 and about ~2360 m/s of dV on the Final Stage. Unless I do something really stupid, I should have plenty to match the orbit, and possibly a bit left over in case I decide to do anything else with this satellite (not likely)

Also, I got the picture uploaded. 

Thanks in advance!

Edited March 5, 2018 by Durzan
Adding picture.

[Ten Key]

8 minutes ago, Durzan said:

How the heck do I upload a screenshot?!?

Welcome to the forums Durzan.

Unfortunately, you cannot upload a screenshot directly to the forum. You'll need to host your screenshot on a third party site and then link it back here. Imgur is a popular choice for this sort of thing. 

Without seeing the orbit I can only guess, but one common thing that trips people up is a retrograde target orbit. You get your satellite to match the orbit perfectly. . .and then realize it's orbiting in the wrong direction. 

[bewing]

I suspect that your target orbit is actually in the same orbit as some body like the Mun or Ike? Maybe retrograde?

To match the orbit, you have to do it quickly. You can match a target orbit from a safe orbit in less than 1/4 of a revolution if you do it right. Start in the safe low orbit. Time it so that the interfering body has just passed the opposite side of your safe orbit. Raise the Ap to just barely inside the target orbit. Look for the point where your orbit is closest to the target orbit. Burn prograde just before you get there, until your new "closest point" is significantly closer than it was before. Then repeat.

 

[Snark]

8 hours ago, Durzan said:

How the heck do I upload a screenshot?!?

1. Take an in-game screenshot using F1.  It gets saved to the "Screenshots" folder of your KSP installation.
2. Go to www.imgur.com.  (You don't need to make an account or anything, this works fine anonymously.)
3. Click on the green "new post" button up top.
4. Drag your image into the "drop image here" box that it pops up.
5. As soon as the post is complete, right-click on the image on the imgur page and choose "Copy Image Location".
   • Important, not the URL of the page on Imgur.  You need the URL of the image, i.e. it should end in ".png".
6. Paste that URL into your forum post here.  It'll get automagically converted into an in-line image.

[Capt. Hunt]

if it's an extreme inclination (ie. Retrograde, polar, etc) I've found it easier to launch direct into that inclination than to try to change it while in orbit.

Edited March 6, 2018 by Capt. Hunt

[Guest]

To riff off @Capt. Hunt, the trick with Kerbin polar orbits especially is to wait until the target orbit passes over the KSC, then launch directly that way. You'll get the inclination within a few degrees, and can then fine-tune it as usual. Note that it'll cost more than than the regular equatorial orbit because you won't get the kick from Kerbin's rotation.

[Durzan]

5 hours ago, Brikoleur said:

To riff off @Capt. Hunt, the trick with Kerbin polar orbits especially is to wait until the target orbit passes over the KSC, then launch directly that way. You'll get the inclination within a few degrees, and can then fine-tune it as usual. Note that it'll cost more than than the regular equatorial orbit because you won't get the kick from Kerbin's rotation.

Yep. Its totally a polar orbit.Thats how I got into this predicament in the first place. The issue is that I have no clue how to fine tune to match the objective orbit as closely as possible, even with mechjeb. I kinda am a bit dense in the head when it comes to these things.

And I got plenty of fuel. I've got two stages on the satellite you see in the picture. ~2400 dV on stage 1 and about ~2360 dV on the Final Stage. Unless I do something really stupid, I should have plenty to match the orbit, and possibly a bit left over in case I decide to do anything else with this satellite (not likely)

Also, I got the picture uploaded. 

Thanks in advance!

Edited March 5, 2018 by Durzan

[Guest]

That's an expensive orbit all right.

MechJeb won't really help here, it'll do your burns more precisely but you still have to plan them. Here's the simplest way to match an orbit like that which isn't incredibly inefficient (although there certainly are more efficient ways):

(1) Wait until the KSC is under your target orbit. Then launch due north (or south, depending on which way the orbit is), more or less. Aim for a pretty high Ap, this will make things easier. Say 150 km.

(2) Once you're past the risky part of the ascent (Ap is well in space), start watching the An and Dn markers on your target orbit as you continue to burn towards orbit. If Dn is on the same side of the orbit as you are, steer a bit towards the ascending node on your navball (the triangle). If An is on the same side as you are, do the opposite. Watch the numbers on the An/Dn go down. Don't sweat it if you don't get it exactly right, there will be plenty of time to correct it later -- if it's less than 5 degrees, awesome, if it's less than 10 degrees, it's fine, if it's 20 degrees or over, it's gonna get expensive.

(3) Once you're in orbit, it's time to fine-tune. Rotate the map view so you line up the An and Dn markers on the target orbit, and draw an imaginary line through them. Put a maneuver node on your orbit where that imaginary line intersects it (if you want to be more efficient, pick the side which is lower, but it won't make a huge difference most of the time). Then rotate the map view so you see the target orbit edge-on. Pull the Ascend or Descend markers until your orbital planes line up (the brown dotted line of your orbit "merges" with the target orbit). Move your maneuver node if necessary.

(4) Execute the burn. As you're doing so, watch the An and Dn markers again. The numbers should go down. If they start "escaping" from you before they're at 2 degrees, stop, and repeat the exercise with the new position of the markers. When you see the An/Dn markers read zero (0), stop burning and ignore them from here on out.

(5) Put a maneuver node at your Pe. Pull the prograde marker until your orbits nearly touch. Then pull the Radial In/Radial Out markers until your Pe and Ap line up with the target orbit's; pull back the prograde marker if this makes your orbit shoot past the target. The objective is that your orbit touches the target orbit at its Ap, and both orbits' Ap markers overlap.

(5b) Alternative approach: put a maneuver node at your Pe. Pull the prograde marker until your orbits nearly touch. Then drag the marker around your orbit until your and the target orbit's Ap markers are lined up. Push or pull the prograde marker to keep your orbits touching until they're where you want (your orbit touches the target orbit at both orbits' Ap).

(6) Execute the burn.

(7) Put a maneuver node at your Ap. Pull the prograde marker until your orbits match. Now the Ap and Pe markers should both overlap.

(8) Execute the burn. As you're burning, watch the target orbit: at some point, it will disappear. That means you're close enough for the contract, so cut your burn.

(9) Wait ten seconds and collect your pay.

Edited March 6, 2018 by Guest

[Starman4308]

2 hours ago, Brikoleur said:

That's an expensive orbit all right.

MechJeb won't really help here, it'll do your burns more precisely but you still have to plan them. Here's the simplest way to match an orbit like that which isn't incredibly inefficient (although there certainly are more efficient ways):

(1) Wait until the KSC is under your target orbit. Then launch due north OR SOUTH, more or less. Aim for a pretty high Ap, this will make things easier. Say 150 km.

Very important clarification: for contracts, you need to be going the right direction*. If you head north while passing under an orbit going southbound... you're 180 degrees off target.

*This is specified by longitude of the ascending node: where your orbit passes the equator going northbound. If you launch north under the equatorial ascending node, or south under the descending node, you're golden. Mix them up, and you're 180 degrees off-target. Note that LAN (Longitude of the Ascending Node) is defined with respect to the fixed sidereal frame of reference, not the rotating frame of reference of Kerbin's surface.

You'll also wind up burning slightly west of south/north to cancel out Kerbin's rotation.

Personally, I'd launch south, just so I'm not launching over land. There's no in-game reason not to launch north, but I like to play with imagined azimuth restrictions that don't drop used rocket stages on peoples' heads.

Edited March 6, 2018 by Starman4308

[Capt. Hunt]

3 hours ago, Starman4308 said:

Very important clarification: for contracts, you need to be going the right direction*. If you head north while passing under an orbit going southbound... you're 180 degrees off target.

*This is specified by longitude of the ascending node: where your orbit passes the equator going northbound. If you launch north under the equatorial ascending node, or south under the descending node, you're golden. Mix them up, and you're 180 degrees off-target. Note that LAN (Longitude of the Ascending Node) is defined with respect to the fixed sidereal frame of reference, not the rotating frame of reference of Kerbin's surface.

You'll also wind up burning slightly west of south/north to cancel out Kerbin's rotation.

Personally, I'd launch south, just so I'm not launching over land. There's no in-game reason not to launch north, but I like to play with imagined azimuth restrictions that don't drop used rocket stages on peoples' heads.

the direction of the orbit should also be indicated by the animation of the required orbit in the map screen.  it will appear to rotate in the direction of the orbit.

[GrouchyDevotee]

It looks like the target orbit and your orbit actually do intersect twice...

At one of those points drop a manoeuvre node and mess around with the Blue "Radial In" and "Radial out", you might have to make a couple different burns

[HvP]

Judging by your screenshots you're going in the right direction, that's half the battle.

If you have the inclination right then all that's left to do is put your apoapsis and periapsis in the right place. But, it's important to understand what the directions on the NavBall do when you burn your engines in different directions.

Burning prograde raises the opposite side of your orbit, and burning retrograde lowers it.

Burning normal inclines the half of the orbit in front of you "upwards" in relation to a line passing from the midpoint of your burn through the center of mass of the body you are orbiting. Burning anti-normal of course reverses the incline of that half of your orbit. (Most people make the mistake of assuming the inclination changes are relative to the equator, but that's just how they are measured. The effect on your orbit is always in relation to the direction of your orbit, we just usually do them to adjust our relation to the equatorial plane.)

Burning radially-out will raise the part of your orbit 1/4 away around in front of you and lower that part of the orbit 1/4 of the way behind you (reversed for radial-in.) It has the effect of sliding the whole circle of your orbit one way or the other. THIS is the best way to fine tune your orbit quickly. The advantage this has is that it allows you to change your apoapsis and periapsis without actually being at either.

I suggest you experiment with burning radially. Look for that blue circle on your navball and see what burning in that direction does to your orbit. You can also point some degrees between the prograde/retrograde and radial markers to further fine tune the orbit if you're up for a lot of practice.

And as @GrouchyDevotee said, these maneuvers should be done at the points where your orbits intersect. Because you won't be able to move the exact point you are at in any significant way you should start in a place this is already at the right height (at the height of the target orbit.)

Edited March 6, 2018 by HvP

[Guest]

6 hours ago, Starman4308 said:

Very important clarification: for contracts, you need to be going the right direction*.

Thanks fro the correction, I added it to my answer.

[bewing]

When you are approaching a Descending Node (DN) you burn gently in the Normal direction to make the DN value go to zero. When you are approaching the AN point, you burn Anti-normal to do the same thing. This corrects your inclination.

To get the right orbit shape, it's easiest if your starting orbit is entirely inside or outside the target orbit. Then you just burn gently prograde or retrograde a little before you get to the closest point.

In your case, your orbits cross. For those, as said above -- the crossing points are the key, and you want to burn either radial in or radial out, right at the crossing point.

 

[Kryxal]

In contrast, it's entirely reasonable to make two burns to match AP and PE ... one to make your orbit just touching on the other side, the second when you're at the intersect point, all done prograde/retrograde (except maybe a small correction on the second burn).  Do whichever you like.