Can't rescue a Kerbal stuck in Orbit!

[DONUTS]

Hello

I am having some real problems with doing this "rescue contract" I got. I have to save Irra Kerman from Low Kerbin orbit, and bring him/her back.

I launched my vessel, and adjusted the orbit so it's the same as Irra's, but...

There's always a 1,750KM difference (a lot), and for every turn it changes half a kilometer or so (I have limited Electric charge). I know there are a LOT of tutorials in rendezvousing (I think thats how you say it?) but No one seems to help me fix this problem, either that or im doing it wrong. Every time I change my orbit I fall into Kerbin, or it just doesn't change at all  We have the EXACT SAME orbit, just different locations.

Any help? The tutorials didn't help me at all  That's the only reason im bothering with this newbie question in the first place (Sorry)

Thanks, DONUTS

[Hupf]

On lower orbits, your orbital period (time it takes for one "turn") is smaller (you're going faster) than on higher orbits. So if your target is "ahead" of you if you watch the map view, you want to switch to a lower orbit. If you're ahead, you want to "slow down" by switching to a higher orbit until the target catches up with you.

To switch to a lower orbit, you lower your periapsis a little by orienting towards the retrograde marker (in "Orbit" mode on the navball, not in "Target" mode!) and doing a small burn, then repeating the same at the new periapsis to lower the apoapsis as well (though this circularizing is technically optional, it makes some things easier in the beginning). To switch to a higher orbit, you do the same but burn prograde instead of retrograde. So, a bit counter-intuitively, if your target is "in front" of you on the same orbit, you first have to burn "away" from it a little.

Once you are on a slightly lower/higher orbit, wait for a few turns until the target has gotten closer, then return to the same orbit as the target.

Once you upgrade your tracking station sufficiently, you'll be able to place maneuver nodes and preview the new orbits, as well as possible encounter locations with your target.

Edited October 6, 2016 by Hupf

[Chabadarl]

If you are ahead of your target :

- Find the angle between you and your target and calculate (or find directly) the time that it takes for your target to reach you. (using mechjeb or KER it's very easy) or by using a node and looking for the node ETA.
- Burn prograde so that your orbital period increase by exactly that time.
- After exactly one orbit, burn retrograde to reach the same orbit.

You should be close enough to follow your favorite tutorial (kill relative velocity go directly to the target, kill relative velocity again while approaching). (I think your mistake was to try that directly which is not efficient from far away).

 

If your vessel is behind, you can do the same by burning first retrograde then prograde but you have a risk to have a periapsis in the atmosphere.But as orbit are round you are always ahead ..... ;-)
If you have limited fuel, you can divide the time by 2 or 3 so you'll burn less and wait the same number of orbit. 

 

The burn is not intuitive because it seems that your burning away from the other ship but there is no direct line in orbit.

So you feel better the NASA made the same mistake until a guy named Buzz Aldrin  (you may have heard of :-) ) came up and explained the proper way.

Edited October 6, 2016 by Chabadarl
typos

[Aegolius13]

Once you get the hang of it, it's useful to launch when the target is just behind KSC in its orbit.  I usually do it when the ship is partway across the desert peninsula across the water from the KSC continent.  If you get it right, by the time you get to orbit you're close enough you don't have to do a full orbit adjustment.

[SinBad]

If your orbit is matched, you wont be getting any closer as you both take the same amount of time to go around kerbin.

You need to change your orbit so its faster or slower than your target, but so that some part of your orbits still touch. What you are looking for is an eccentric orbit, an oval.

Burn prograde for a bit and raise your apoapsis by 20 or 30km. The lowest part of your orbit should still touch your target orbit. Now make a manouver node where the orbits touch. Make sure you have the target selected as a target. Set the manouver to rematch yor orbit.

Now see the circle in the middle of your maouver node? Click on that and it should chane so it has 3 little circles in it, a red one for killing the manouver, a plus sign and a minus sign. Those two let you move the manouver node one whole orbit into the future, click on the plus and you should see your closest point of approach markers step around and converge. When they are within about 100km, then you can tweek the manouver node to try an get it within 1km.

Then you just warp to the burn (watch the time next to your navbal, you may need to do a few orbits) and do the burn. Now chane your navball to target mode (click on the speed) and burn retrograde until the speed is zero. You have matched orbits within 1km of your target. Now you can nudge yourself toward it. Slowly. If you try to do it fast, you will miss. I generaly stick to 1m/s per 100m range.

So, if you have stepped your manouver node around and not seen a good intercept, delete the node, and raise or lower your apoapsis by half of what you did last time.

Hope that helps.

[John Cochran]

I know you've mentioned the various tutorials on rendezvous, but for good measure you really can't beat Scott Manley. So take a look at this video for an example on how to do it. https://www.youtube.com/watch?v=8kJ-z0t_CY0

[Daveroski]

Something to notice.

If you point prograde (that's the direction you are going) and increase thrust, your orbit will belly on the other side of the planet (increase apoapsis.)

If you make it belly to about 150k and then watch the orbit of the ships, you will see that as your ship goes higher, it goes slower.

This can let the other ship catch you up.

To get close (Rendezvous) with another ship that is in a stable orbit in the shortest time it is better to start in a higher orbit than the ship you are trying to rendezvous with.

The ship you are trying to rendezvous with is probably at about 84k so set your initial orbit to 250k

Only two other things to watch for. You should be sure you are going the same direction and on the same plane.

From 250k you should be able to intercept the ship without having to go round and round the planet first.

Take note of where your ship is in it's orbit. Plot an intercept. Don't know how? ask me.

Remember that the skill with interception is being able to be going at the same speed when you get to the closest point.

As you head towards the intercept make sure that your navball is set for 'Target' and not 'orbit' or 'surface'

Turn your ship to retrograde and start to slow down as you get closer. Make relative speed as close to 0 as possible 0.something is good enough.

 

Turn your ship to point toward your target.

Apply enough thrust to move toward your target.

Turn your ship to retrograde again. Match speed before you pass the target.

Repeat the above three lines until you are close enough to get Irra out of their pod and safely to your ship.

The first time you do it, you will probably suck harder than the suckiest suck that ever sucked.

By the tenth, you should be getting the hang of it.

By the fiftieth, you will be as arrogant as the rest of us

[Starhawk]

Hello DONUTS.

This is a great place to ask newbie questions and there's no reason to be sorry.

KSP is very much a learning game and it takes time to learn many of the skills involved.

Among all the skills rendezvous may be the trickiest for many new players.

Learning how to rendezvous is built on several other skills.

1. You must understand the navball and the various markers on the navball.
2. You must understand how your orbit will change depending on which way your craft is pointing and where it is when you burn your engine.  (This is orbital mechanics.)
3. You need to know how to manipulate maneuver nodes.
4. You need to know about the intercept markers in map mode and how to use them to refine your intercept.
 

42 minutes ago, DONUTS said:

Every time I change my orbit I fall into Kerbin, or it just doesn't change at all

Your orbit will always change if you burn your engines.  One of the important things to understand is that you never want your periapsis (the lowest point of your orbit) to fall below 70 km if you are trying to stay in Kerbin orbit.  Thus, if you are in the same orbit as your target and low over Kerbin you want to make your orbit larger and set up a situation where you and your target end up in roughly the same place at the same time and then match your orbit to that of your target.  But what you actually do is match velocities with your target in flight mode once it gets very close to you.

I would recommend doing some trial and error playing around while in orbit.  Use your navball to point the ship different ways and do some burns.  Watch in map mode to see how burning in a particular direction changes your orbit.

I would also recommend seeking out information about orbital mechanics and about using the navball.  Whether you learn best by reading or by watching videos there are a number of resources available to help.  Youtube has a huge number of KSP videos and many of them can help you to learn the game.  The tutorials section of the forum here is chock full of info on these subjects, as well.
Most importantly, don't neglect to take a look around the KSP Wiki.  It is a wealth of information and an extremely valuable resource for a new player.

Happy landings!
 

 

[DONUTS]

Wow thanks everybody!!! Im learning a lot  and Im going to merge all the comments and see how i'll save Irra from her demise (I'll just assume a "her") and bring her safely back to kerbin. Thanks!!

[DONUTS]

2 hours ago, Daveroski said:

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2 hours ago, John Cochran said:

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2 hours ago, Aegolius13 said:

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3 hours ago, Chabadarl said:

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2 hours ago, Starhawk said:

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2 hours ago, SinBad said:

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3 hours ago, Hupf said:

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Thanks everybody!!! I managed to save Irra kerman. I got myself a 0.1km difference, and then just rushed to the pod, while leveling the relative speed! I got to get Irra (Which was in fact a girl! I was right yaaay ) into Kerbin. And yes, the Capsule/probe thingie with the ablator worked (I also only had 20 energy left from 460  ), So everything went okay in the end. Now Irra is taking a vac, and she's going to get sent to a mission very soon! This couldn't have been done without your tips and help, so thanks again