Need help docking 2 vessels

[coguar]

Hi everyone,

 

I just bought this game a month ago and still tied to it haha, here is my issue, I'm triying to complete the contract regarding dock 2 veesses arround kerbin, so 1st I launched one vessel, then send the other, after some time I managed to circularize the orbit and match both vessels in the same pattern (same AP and PA) however.... I don't how to make them encounter(see attached image) if I burn retrograde then the orbit will change and won't be able to reach any of the  vessels... to get the things worse....KSP saved automatically so all my pilots are outthere in kerbin orbit (I wish I could save a game before). I would like to know if anybody have some suggestions / advise on how to dock in this scenario.

 

Album a/SJ3UX will appear when post is submitted

Screens are in spanish(sorry)... but you should be able to understand velocity and distance meausures

 

Vessel1 have aprox = 3590 m/s DeltaV (remaining deltaV )

Vessel2 have aprox = 2506 m/s Deltav(remaining deltaV )

Hope anyone can provide some suggestions.

Edited March 1, 2018 by coguar
Images url was wrong

[bjerrang]

not possible to view photos. 

Step 1 match inclination.

The craft behind in orbit must have a smaller orbit to speed up , and if you want to control the one that if forward in orbit , make its orbit bigger to slow down

Edited March 1, 2018 by bjerrang

[Zhetaan]

@coguar:

Your links are were broken, but I was able to see the photos anyway.

Your problem is that you've matched orbits too soon; since both ships are in the same orbit, they orbit at the same speed; one will never catch up to the other.  You need to put one ship into a different orbit so that it can catch up or fall back to the other ship.

Think of it this way:  let's say you have two balls and want to throw them so that they hit the ground at the same time.  The problem is that you cannot throw them at the same time; nevertheless, they must still hit the ground at the same moment.  If you throw the first ball, and then you throw a second ball along the exact same path, would you expect the second ball to catch up to the first so both hit the ground at the same time?  Naturally, that won't happen.  The way to do it is to throw the first ball very high up so it takes a long time to fall; then you can throw the second ball so that they both hit the ground at the same time.

Therefore, the solution to your problem is to take one vessel (I recommend vessel 1 because it has more delta-V) and 'throw it high' by burning prograde.  Normally, the way to get an encounter is to burn prograde if you're ahead and need to fall back or retrograde if you're behind and need to catch up, but retrograde in this case might drop you into the atmosphere (which definitely keeps you from catching up), so we want to avoid that.

The amount that you need to burn prograde is something I can't guess from the picture, but we don't need to do that.  Your orbit is just about circular, so where you burn is unimportant.  Set a manoeuvre node some distance ahead of you (a few minutes at least, so you have time to plan properly) and, while still targeting the other vessel, pull on the prograde handle.  The intercept markers will move with the predicted encounter, so keep pulling until the intercept markers align.  You should be able to get an encounter under 5km very easily.  Make the burn and wait an orbit until you come back to your burn location.  When you do, your target will be there.

The next thing to do is to go back to your previous orbit; in theory, this would mean burning retrograde by the same amount that you burned prograde before, but because there's probably a bit of difference in how your two vessels are moving, your best course is to match with the other vessel directly.  You do this by clicking on the velocity readout at the top of the navball until it is in Target mode; this arranges the prograde/retrograde markers to align with your velocity relative to the target vessel.  Burn retrograde in target mode until the velocity difference is zero; you will then have matched orbits.

After that, it's simply a matter of closing the remaining distance and docking.  Simple may turn out to be relative; it depends on your fine control.  But at least you'll find out.

Edited March 1, 2018 by Zhetaan

[Snark]

On 3/1/2018 at 10:00 AM, coguar said:

I just bought this game a month ago and still tied to it haha, here is my issue, I'm triying to complete the contract regarding dock 2 veesses arround kerbin, so 1st I launched one vessel, then send the other, after some time I managed to circularize the orbit and match both vessels in the same pattern (same AP and PA) however.... I don't how to make them encounter(see attached image) if I burn retrograde then the orbit will change and won't be able to reach any of the  vessels... to get the things worse....KSP saved automatically so all my pilots are outthere in kerbin orbit (I wish I could save a game before). I would like to know if anybody have some suggestions / advise on how to dock in this scenario.

They don't meet now because you've got them in the same orbit.  That means they're in lockstep and stay the same distance apart.  It's like a clock that has two "hour" hands that are a few hours apart-- they never meet each other because they go around at the same speed.

To make them meet up, you're going to need to adjust one of them to be in a different orbit, so that it takes either less time to go around Kerbin (so that it catches up to the other ship), or else a little more time to go around (so that the other ship catches up to it).

"How much dV do I need?" I hear you ask.  The answer is:  as much or as little as you want.  It comes down to patience.  If you do a teeny-weeny adjustment that makes one ship take just 1% longer or shorter to orbit than the other one... then you'll have to wait dozens of orbits for them to come together.  If you are impatient and want it to match up sooner, you could do it in a single orbit... but that would be a bigger burn.

Basically, pick one of the ships and, for example, do a small burn.  That will raise its Ap.  This makes the ship take longer to go around Kerbin (because the bigger the orbit, the more time it takes).  Then start timewarping.  With each time you go around, the other ship will catch up some (how much it catches up will depend on how much you've adjusted the orbit).

Eventually, when it gets pretty close, you'll need to fine-tune the orbit so that they end up in the same place at the same time.

Here's a handy guide for getting a rendezvous:

Spoiler

Once you get a rendezvous set up (so that your ships will be in the same place at the same time, then you'll need to dock.  Here's an illustrated docking tutorial I wrote a while back, which you may find useful.

Hope this helps!

[Spricigo]

 

 

[GrouchyDevotee]

Scott Manley has a bunch of beginner instructional videos on youtube.

[Warzouz]

And BTW, don't panic, getting a rendezvous is one of the hardest things to do in KSP.

If you're have no clue, you can still install MechJeb, use the auto-rendezvous feature, check how it does it. Then try to redo it yourself using the same method.

Finally, you'll quickly understand how to do rendezvous more efficiently than MechJeb.

[Guest]

11 minutes ago, Warzouz said:

And BTW, don't panic, getting a rendezvous is one of the hardest things to do learn in KSP.

...just to be a bit more encouraging, as well as accurate. It's quite easy once you've got it figured out -- just like docking -- but it is one of the hardest things to learn. I was literally screaming in frustration when I was first trying to figure out how RV and docking worked.

BTW I would advice you to not use MechJeb to start with. It's great for taking out the chore with things you already know how to do, or executing complex flight plans, but if you use it before you understand what you're doing there's a big risk you'll end up just relying on it as if it was magic and never learning it yourself -- which will bite you later. 

[Warzouz]

Just now, Brikoleur said:

...just to be a bit more encouraging, as well as accurate. It's quite easy once you've got it figured out -- just like docking -- but it is one of the hardest things to learn. I was literally screaming in frustration when I was first trying to figure out how RV and docking worked.

BTW I would advice you to not use MechJeb to start with. It's great for taking out the chore with things you already know how to do, or executing complex flight plans, but if you use it before you understand what you're doing there's a big risk you'll end up just relying on it as if it was magic and never learning it yourself -- which will bite you later. 

You're right about learning. once you get it it's easy, but not because it's intrinsic easy, but because we become better at understanding orbital mechanic

As for MJ, I learnt a lot using it (probably more than watching vids). I remember using it for landing as I was overwhelmed by controls. I used it 2 or 3 times, then I didn't need it any more. Now I can land less than 1km from a chosen point on a vacuum world. Sure there are a lot of vids explaining KSP, but when you're in front of YOUR ship, which is going to crash soon, it's not easy. Watching MJ dealing with your ship in you mission made me understand more quickly, I think.

As I explained about MJ, I couldn't get how to do rendezvous. I use MJ, then I finally got it and find that MJ would waste a lot of fuel and there was better way to rendezvous, using less manoeuvres.

I don't use MJ much now.

[Kryxal]

On 3/1/2018 at 2:05 PM, Zhetaan said:

Your orbit is just about circular, so where you burn is unimportant.

Not really, this is a prelude to docking ... make your burn in a spot where you'll have lots of light to work with for a while when you get there again.  Maybe a minute after coming out of the planet's shadow should be great.