Matching orbits.

[Habalabam]

Hi. Several missions require me to match some specific orbit, either directly or indirectly (rendezvous missions).

I miss two things and I am wondering if there is some better way of achieving these things.

* The ability to target an orbit ("set as target", but targeting an orbit instead of an object).

* Navball should have "closest target orbit tangent prograde marker".

The latter marker would indicate the vector for matching velocity with the closest tangent of the target orbit. Thus you would be able to perfectly match orbit with a target even when the target itself is currently on the other side of the celestial body being orbited.

Any time you cross an orbit, it is only a matter of delta-V to enter the orbit. A navball indication for it would make it a lot easier than all those nav markers. With a pilot kerbal assisting for this marker, it would make matching orbits a breeze.

I find it weird that those two things do not appear to be in the game. Have I missed anything?

Edited April 28, 2015 by Habalabam
Clarification on use of "this".

[Kesa]

Do you know about manoeuver nodes?

[SRV Ron]

Do you know about manoeuver nodes?

As he is playing Career, that may not be available until he can upgrade Mission Control and Tracking. Even then, unless you download and use Kerbal Engineering for the orbital readouts, it will be next to impossible to place the satellite into the required orbit.

Edited December 23, 2014 by SRV Ron

[Anquietas314]

As he is playing Career, that may not be available until he can upgrade Mission Control and Tracking. Even then, unless you download and use Kerbal Engineering for the orbital readouts, it will be next to impossible to place the satellite into the required orbit.

Next to impossible? What? Kerbal Engineer is not even remotely required to do that. You have navball indicators and a map for a reason. You can totally just eyeball the whole thing by pointing pro/retrograde, (anti-)normal and (anti-)radial. I would highly recommend doing the orbiting tutorial if you don't understand the navball. It's been so long I forget whether it covers plane change and radial burns though.

[tsotha]

It's actually not that hard to put your sat in the right orbit without maneuver nodes. You have the reference orbit, after all, and you don't have to get it perfect. You can do it like this:

1. Get into a roughly circular orbit roughly with your apoapsis and periapsis roughly that of the target orbit's apoapsis. You may not be in the same plane, but that's okay. Just get it close. You really don't need to do this step, but it will save you a lot of fuel if you match your target's inclination at a lower speed.

2. Match inclinations by burning normal/antinormal (the pink symbols) to your orbit at an ascending or descending node until your target orbit and your own orbit are in the same plane.

3. Re-circularize your orbit, but this time be a bit more careful. Try to make get your apoapsis and periapsis within a few hundred meters.

3. Go to the opposite side of the target orbit's apoapsis and match it by burning prograde (forward) if you need to make your orbit larger or retrograde (reverse) to make it smaller. When you're done your orbit should be touching the target orbit at apoapsis, since you're in the same plane.

4. Go to the point where the orbits touch and use the same logic in step 3 to move the other side until it matches. If you've done everything right you'll be close enough to complete the contract.

It's a bit more difficult to rendezvous with a stranded Kerbal, since you not only have to be in the right orbit, but you have to be in the same place at the same time as your target. Still doable, though you should probably figure out how to do it with targeting and maneuver nodes in sandbox first, and when you're comfortable try it without.

[Xavven]

It's actually not that hard to put your sat in the right orbit without maneuver nodes. You have the reference orbit, after all, and you don't have to get it perfect. You can do it like this:

1. Get into a roughly circular orbit roughly with your apoapsis and periapsis roughly that of the target orbit's apoapsis. You may not be in the same plane, but that's okay. Just get it close. You really don't need to do this step, but it will save you a lot of fuel if you match your target's inclination at a lower speed.

2. Match inclinations by burning normal/antinormal (the pink symbols) to your orbit at an ascending or descending node until your target orbit and your own orbit are in the same plane.

3. Re-circularize your orbit, but this time be a bit more careful. Try to make get your apoapsis and periapsis within a few hundred meters.

3. Go to the opposite side of the target orbit's apoapsis and match it by burning prograde (forward) if you need to make your orbit larger or retrograde (reverse) to make it smaller. When you're done your orbit should be touching the target orbit at apoapsis, since you're in the same plane.

4. Go to the point where the orbits touch and use the same logic in step 3 to move the other side until it matches. If you've done everything right you'll be close enough to complete the contract.

It's a bit more difficult to rendezvous with a stranded Kerbal, since you not only have to be in the right orbit, but you have to be in the same place at the same time as your target. Still doable, though you should probably figure out how to do it with targeting and maneuver nodes in sandbox first, and when you're comfortable try it without.

This pretty much describes it! The only thing I would add is that you can burn radial in and radial out to rotate your orbit (like a hula hoop). This comes in handy when your inclination, apoapsis, and periapsis are all technically correct, but your orbit still doesn't match visibly. Hard to describe without using the technical term: your argument of periapsis mismatches.

[radonek]

1. Get into a roughly circular orbit roughly with your apoapsis and periapsis roughly that of the target orbit's apoapsis. You may not be in the same plane, but that's okay. Just get it close. You really don't need to do this step, but it will save you a lot of fuel if you match your target's inclination at a lower speed.

If you want to do a plane change at lowest speed, do it on top of hohmann BEFORE circularization burn. You only need to make soure your AP matches An/Dn with target orbit, which is conviniently shown in map view.

[RW-1]

I went to do my first sat launch and matched up the orbit within the tolerances just fine, even without tracking or SAS - What bugged me was the note about building it as a new ship after accepting the contract - WHICH I DID.

Accepted the contract, then went to VAB, New and built it, launched and put it up there. Tried it again, same thing.

Totally Stock, not sure why I'm having that issue.

- - - Updated - - -

This pretty much describes it! The only thing I would add is that you can burn radial in and radial out to rotate your orbit (like a hula hoop). This comes in handy when your inclination, apoapsis, and periapsis are all technically correct, but your orbit still doesn't match visibly. Hard to describe without using the technical term: your argument of periapsis mismatches.

+1 on mentioning that as well.

[Anquietas314]

If you want to do a plane change at lowest speed, do it on top of hohmann BEFORE circularization burn. You only need to make soure your AP matches An/Dn with target orbit, which is conviniently shown in map view.

Actually the most efficient way to do this is to combine the plane change with the circularization. The maths behind this is basically Pythagoras' theorem.

[tsotha]

If you want to do a plane change at lowest speed, do it on top of hohmann BEFORE circularization burn. You only need to make soure your AP matches An/Dn with target orbit, which is conviniently shown in map view.

You can do this if your target orbit is circular, or if you're really lucky. But if the target orbit is elliptical the nodes are usually closer to the planet.

[DelayedReaction]

had an awkward orbit contract yesterday. the orbit required actually put me on a direct intercept with the Mun (which after capture/escape completely screwed up all the Pe/Ap work i'd done... think I ended up cancelling the contract and taking another one. I also discovered that in the contract window when you are on-mission, you can click on the light-blue "note" for the orbit contract and it will give you every single parameter required for the orbit.

[Habalabam]

I apologize for not revisiting this thread until now. I thought I would get a notification if there were replies.

Yes, I know about maneuver nodes.

My grievence is two fold.

First is the fact that you cannot set an orbit as target unless you target an object that follows the desired orbit. In a rendezvous mission, there will be an object to target. In the missions that reads "put such and such an object into such and such orbit", then the orbit is indicated in the star map, but there is nothing to "set as target". Thus I will not get an indicator on Na/Nd. Furthermore I wont be getting the indication on orbit inclination match either (by having Na/Nd beginning to swap places).

Given enough time, you can always go back and forth between Ap/Pe to match orbits, but this can be time consuming and fuel inefficient to do this in stages. Any time you cross paths with your target orbit, you have an opportunity to completely match orbit. It is just a matter of delta-V. We have perfectly good navball indicators for that purpose to match speed of a target object. Why can't we have the same thing for target orbit? The targeted vector should be the velocity vector of the closest tangent of the target orbit.

If that was in place, then any time you intersected the desired orbit (no matter where), you could just burn to match velocity to the tangent of the orbit and you would immediately be in the desired orbit.

Of course you can perceivably do a docking operation without navballs indicators to match target object velocity, however I think we all agree that that would be needlessly hard.

Since such obvious navball indicators are absent, nor exist in any of the mods I have seen thus far, I was wondering if I was missing something obvious.

Thank you, all.

[Anquietas314]

I apologize for not revisiting this thread until now. I thought I would get a notification if there were replies.

You can actually set it to do that (note: I do not recommend this unless you enjoy sifting through lots of notifications )

Thus I will not get an indicator on Na/Nd.

I'm not sure exactly what you mean by that, but I'll assume you mean AN/DN. Those are shown on the target orbit when you're in the same SoI. Otherwise, yeah, the UI could be a little better.

We have perfectly good navball indicators for that purpose to match speed of a target object. Why can't we have the same thing for target orbit? The targeted vector should be the velocity vector of the closest tangent of the target orbit.

This is a good idea (post it in suggestions ), but it's not quite that simple I'm afraid; your orbits are almost never going to perfectly intersect, which means computing where that tangent point is (and consequently the relative velocity vector) is hard. You could of course just pick the closest point between the two orbits, but that's some fairly tricky maths to get right (WolframAlpha probably knows how to do that though, if you can figure out how to ask the question). The game technically does that already for getting near a target object's orbit, so I guess there shouldn't be too much left to do there

[Habalabam]

You can actually set it to do that (note: I do not recommend this unless you enjoy sifting through lots of notifications )

I'm not sure exactly what you mean by that, but I'll assume you mean AN/DN. Those are shown on the target orbit when you're in the same SoI. Otherwise, yeah, the UI could be a little better.

Yes, they are shown when you have a target orbit. Since we cannot set orbits that are part of objectives as target, we do not have the benefit of them.

This is a good idea (post it in suggestions ), but it's not quite that simple I'm afraid; your orbits are almost never going to perfectly intersect, which means computing where that tangent point is (and consequently the relative velocity vector) is hard. You could of course just pick the closest point between the two orbits, but that's some fairly tricky maths to get right (WolframAlpha probably knows how to do that though, if you can figure out how to ask the question). The game technically does that already for getting near a target object's orbit, so I guess there shouldn't be too much left to do there

Thank you. I don't see what your concerns are, though. Whenever you are close to another orbit, there will be a point on that orbit that is the closest point to you. All I am asking is that the navball should should have an indicator allowing you to match velocity with the tangent of that point.

Edited January 17, 2015 by Habalabam

[Lheim]

There's also the orbit details - required apoapsis, periapsis, etc, in an expandable note in the contract itself.

One tip: I find it useful to time my launch. Wait till the KSC is under the target orbit, then try to launch into the correct inclination right from the start - you can watch from map view and adjust your direction north, east, south, west, whatever, till you're at least nearly matching. Once it is matching, just keep ascending in the direction of your prograde vector; just make sure it's in orbit mode. It's slightly complicated by the fact that you have some eastward velocity already, but watching the map view you can correct it pretty close to what you want.

[Anquietas314]

Yes, they are shown when you have a target orbit. Since we cannot set orbits that are part of objectives as target, we do not have the benefit of them.

No, I mean there are already AN/DN indicators on the target orbit itself. Notice how there's 4 markers on them, not 2 when you're in the same SoI as the target orbit?

Thank you. I don't see what your concerns are, though. Whenever you are close to another orbit, there will be a point on that orbit that is the closest point to you. All I am asking is that the navball should should have an indicator allowing you to match velocity with the tangent of that point.

You slightly botched the quote btw - the second tag needs to be

[radonek]

Thank you. I don't see what your concerns are, though. Whenever you are close to another orbit, there will be a point on that orbit that is the closest point to you. All I am asking is that the navball should should have an indicator allowing you to match velocity with the tangent of that point.

Yeah, that would be handy. Actually, it would be too easy if you ask me. And probably not efficient anyway – getting intersection is not easy unless you make plane change first. I found it more efficient to do radial or planar maneuvers high-up. I did a lot of orbit jobs recently and found them rather trivial once you get hang of it.

1. Get to circular LKO

2. Open map view, center on Kerbin and move view until An/Dn nodes on target orbit overlap. Click on your orbit at point where they overlap and set up maneuver node. This is to project An/Dn on your orbit.

3. Burn at that node to raise Ap close to target orbit An or Dn, only a bit lower.

4. When close to Ap, do a plane change to match target orbit. (you may again do an/dn-overlap trick to better see point of intersection)

5. When you tackle inclination, immediately do a circularization burn until you get an intersection with target orbit.

6. Small radial burn slightly before intersection point will align both orbits.

7. Intersection point should now be Pe, small burn there will match eccentricity.

8. …

9. Profit.

Note its all done in map view. You don't even need to set up nodes, just burn at proper naball marks and see orbit move where you want it. Only initial Ap-rising need to be done with some accuracy, maneuvring high-up is cheap and its easy to pack up small sat with lots of spare delta-v, so don't be afraid to just try things. Its even possible to do several contracts with single craft once you get used to it.

Edited December 28, 2014 by radonek
clarification

[Superfluous J]

I did this on video recently for a nasty reverse-equatorial orbit that went through Mun's SOI twice per orbit. If my technique can work in that situation it can work in any situation.