question regarding rendevouz

[Joe.L]

Good evening/morning everyone,

So I have recently managed to get into a co planer orbit with my temporary space station, however, I am co planer with it but at opposite sides of Kerbin. Watching the tutorials, it looks like I was meant to get co planer with it, but quite near it in order to rendezvous and then obviously dock.

 

Is there a way I can rendezvous with it currently or will I need to drop my orbit altitude in order to slow down and then rendezvous?

Many thanks,

Joe.

[Rhomphaia]

You need to raise your orbit altitude to slow down. dropping altitude speeds you up. unless your station is in a very high orbit then there is usually more room above it.

Easiest to plan would be to raise your apoapsis until you get a close encounter at periapsis.

Edited May 19, 2020 by Rhomphaia

[Joe.L]

so do I need to raise orbit to then have the space station come near me then get back onto the same orbit as the target?

[bewing]

If you burn exactly prograde to raise your Ap, then you will automatically remain co-planar. Once you've raised your Ap, you can wait multiple orbits until you are going to be pretty close -- then lower your Ap until your 'close approach' markers show an  extremely close rendezvous.

[Joe.L]

ok so tried all this and I have got within 10km of the target however, THIS GAME IS SO HARD and I seem to just either go flying past it (I don't really know how to slow down in orbit) or it keeps getting further and further away, i'm also struggling to stay looking at the target as the blue target marker on the navball doesn't appear (I have got my satellite set as target).

 

You know when I first got this game I didn't realise how fun but hard it was, i'm getting incredibly frustrated with this rendezvous docking thing...

[Vanamonde]

The good news is, this is considered the hardest part of the game by most people, so if you do figure it out, the worst will be behind you. 

If you're getting that close, you should be able to set the navball to target mode, then burn retrograde until you're at rest with respect to the target. Orbital mechanics will still mess with you a bit, but you should be able to fly more or less directly toward it and finalize the dock. 

[Joe.L]

ok thanks, the problem is, I set it to target mode in the navball but when I never see the blue target, I get pink icons in the nav ball, are they basically the same?

[Vanamonde]

The only blue marker on the navball is the maneuver burn indicator. Look for the retrograde marker. 

[Joe.L]

great, will try this out in a bit and let you know. Thanks for your help

 

[HebaruSan]

If you're somewhat close (10km isn't too bad) and the navball is in target mode, lining up the retrograde velocity vector  with the target retrograde vector  means that you're moving toward the target. You can do this while simultaneously slowing down your relative speed by burning  near them so as to "push" the two indicators together, like so:

   →  

 ←   

[HvP]

1 hour ago, Joe.L said:

ok so tried all this and I have got within 10km of the target however, THIS GAME IS SO HARD and I seem to just either go flying past it (I don't really know how to slow down in orbit) or it keeps getting further and further away, i'm also struggling to stay looking at the target as the blue target marker on the navball doesn't appear (I have got my satellite set as target).

 

You know when I first got this game I didn't realise how fun but hard it was, i'm getting incredibly frustrated with this rendezvous docking thing...

Don't feel bad. You're in good company. Even the Gemini astronauts and engineers had trouble figuring this out at first. The Gemini 4 mission failed to achieve rendezvous for the same reasons that beginners in KSP have. Orbital mechanics is very counter intuitive.

If you are able to get within 10km of the target then you are almost there. It's that last little bit that's the real fun.

When you are in target mode just remember this, burning retrograde will slow you down relative to your target, and burning prograde will speed you up relative to your target. When you close to about 10 km it's a good idea as @Vanamonde suggested to burn retrograde and bring your relative velocity to zero. Then, at that distance what you want to do is to practice moving that target marker on top of your prograde marker . This means that your direction of flight will carry you directly towards your target.

Watch what happens when you aim a little to one side or the other of your prograde marker . If you are burning prograde then the direction you are pointing will pull the prograde marker towards the direction you are pointing - and if you are burning retrograde then it will PUSH the retrograde marker away. You can use this technique to pull your prograde direction around until it lines up on top of that target marker . You can also reverse and burn retrograde to push that retrograde marker on top of the retrograde-target marker (that just means that when you are pointing at the target this is the direction 180 degrees behind you.)

As a little time passes and you move closer to your target the angle of difference between your path and where you cross your target will get wider and wider. Also, your curved orbit around the planet will start to change the angle too. This means that the two markers will start to separate again. Continue to nudge the two markers closer together again in small controlled bursts of no more than 10m/s at a time. Fine tuning things as you go, if you can.

With practice you can do this!

 

 

Edited May 19, 2020 by HvP
I said 10km/s - should be 10 m/s

[Joe.L]

yeah I am really struggling with these orbit mechanics, I just cannot get near the target without the periapsis dropping and then it all goes to...you know what I mean. everything acts differently in orbit than on the ground xD

[Joe.L]

I am nearly at a point now of giving up. The tutorials in this game are dreadful, I tried to follow the docking tutorial and nothing made sense. I have had to constantly revert back to being coplaner again, opposite sides of Kerbin because if I get near the station, my periapsis is around 30,000 so I just start to fall out of orbit, or I overshoot, or I get near then run out of fuel so have to use thrusters which then, they of course run out of fuel. I have watched countless tutorials and listened to every piece of advice on this page and I just feel like everyone else is understand it and I literally do not get it.

 

This game is so hard I just feel like giving up on ever trying to dock... 

Edited May 19, 2020 by Joe.L

[HebaruSan]

5 minutes ago, Joe.L said:

I just feel like everyone else is understand it and I literally do not get it.

Guarantee the difference is purely experience and practice. I didn't get it either for a long time. It just takes a lot of practice to get used to how everything works.

8 minutes ago, Joe.L said:

if I get near the station, my periapsis is around 30,000 so I just start to fall out of orbit, or I overshoot,

Yeah, it's important to always keep your periapsis above 70km. I'd recommend monitoring it on the map screen while doing burns, and if it gets too low, stop whatever you're doing and find another way. If your station is itself low, that can limit how much leeway you have, so some people prefer to put stations a bit higher than they otherwise might.

Usually while you're setting up a rendezvous, "another way" would mean raising your orbit instead of lowering it. This means that your ship will take longer to go all the way around the planet than the station does, so the station can "catch up".

[Joe.L]

so this is where I am currently at:

https://imgur.com/S4eFXbJ and don't really know what to do, not much fuel in the main tank so do I now just fly direct to pink target or prograde or?? (sorry for sounding so stupid as I know it's entirely me and you have all already answered this question)

 

I have raised my orbit to allow the station to catch up with me so should I collapse my orbit again to line up with the station?

Edited May 19, 2020 by Joe.L

[HebaruSan]

20 minutes ago, Joe.L said:

https://imgur.com/S4eFXbJ and don't really know what to do, not much fuel in the main tank so do I now just fly direct to pink target or prograde or??

It looks like you just missed a rendezvous, since the icons are close together. The time to start applying most of these tips is in the lead-up to the closest approach, as you're getting nearer to the target, so maybe 6 or so minutes ago.

20 minutes ago, Joe.L said:

(sorry for sounding so stupid as I know it's entirely me and you have all already answered this question)

Nah, there's a lot to this and it's hard to encapsulate all at once, since we don't know what problems you'll run into...

20 minutes ago, Joe.L said:

I have raised my orbit to allow the station to catch up with me so should I collapse my orbit again to line up with the station?

You can leave it as it is for a few orbits; it will move further counter-clockwise relative to your ship each go-around by approximately the current distance between the indicators, until it goes all the way around and gets close again (in maybe 5 orbits, looking at how far apart they are?). Just before that point you can try setting up some burns to make the closest approach as close as possible.

[overkill13]

Since you already raised your apoapsis to slow your orbit relative to your target, you can plan your intercept burn.

Place a maneuver node marker.  Click on the marker centre, then right click on it.  It should collapse into three icons.  The red x is a delete marker icon.  The other two are next and previous orbit. 

Click the next orbit button (the one with the plus sign) this will plan the maneuver on the next time you orbit around the planet, rather than the next time you pass the marker.  More importantly this will show your closest approach markers (the orange pointers) on the next orbit.   Keep adding orbits till they get close together.   Right click on the orange marker that shows intercept details, the distance to target and the relative speed difference.

Add a few delta-v prograde to the burn and then move the marker around the orbit and find the spot which gets your rendezvous closer together.  Add a few more delta v and move the marker to make the rendezvous closer again.  Keep doing this until your rendezvous will be within a km or two.  I have lots of practice and I use the fine maneuver controls but I like to get mine under 1km before I commit.  If the approach distance keeps getting further away, remove all planned burns from the maneuver, add or subtract an orbit and start again.  You can do this retrograde, and it might actually use less fuel, but you need to be very aware of your periapsis lest you reenter the atmosphere.

Once the maneuver is planned, perform it at the designated time, probably a few hours and a few orbits from now.  Then once you are close to the intercept, I usually start maneuvers 1 to 2 minutes before the closest approach, start using some of the other advise that's already posted to move the markers around and line everything up.  Trying to do this now (too late) or much too early will burn hellish amounts of fuel, and really mess with your orbit, as I suspect you are already aware.

For more advanced fun and reduced fuel use, you can place a maneuver node on your current orbit and a second one later.  Plan a small maneuver on your current orbit and advance the second one to see where the intercept will be several orbits later.  A smaller burn now could accomplish the same thing you just planned several orbits later.  Probably a bit advanced for right now, but keep it in mind when this all becomes second nature.

One more advanced technique is to plan a maneuver, advance the orbits till the intercept is close, then point you ship prograde and grab the maneuver node but don't actually add any delta-v to it yet.  While dragging it around a little bit start your engine at very low throttle.  Dragging the node will allow the intercept to recalculate.  If it gets further, point your ship retrograde and try again.  Once your approach is really close either leave it or actually plan a maneuver as above to bring the intercept together.  Again, be aware of you periapsis whenever you burn/plan retrograde.

Edited May 20, 2020 by overkill13

[HvP]

4 hours ago, Joe.L said:

so this is where I am currently at:

https://imgur.com/S4eFXbJ and don't really know what to do, not much fuel in the main tank so do I now just fly direct to pink target or prograde or?? (sorry for sounding so stupid as I know it's entirely me and you have all already answered this question)

 

I have raised my orbit to allow the station to catch up with me so should I collapse my orbit again to line up with the station?

You should be in a great position to plan an intercept. I think you might just be trying to make things happen too quickly.

Don't assume that you need to blast directly to the target right now. It's OK if your intercept happens on the other side of the planet as long as you get a close encounter somewhere in orbit that's what really counts.

Based on your screenshot it should be possible to lower your apoapsis so that your orbit encounters the target in less than 1/4 orbit. But if you are too aggressive, and lower it too much that might well drop you into the atmosphere. This is where you can use another handy trick that is often overlooked by newer players.

The light blue markers on the navball show you your radial-out and radial-in directions. Radial-out means that you are pointing outwards away from the center of the planet, and radial-in means that you are pointing inwards towards the center of a planet. These are extremely helpful when fine tuning an orbital rendezvous. Burning in the prograde and retrograde directions will move the opposite side of your orbit in and out. But, burning in the radial directions will pivot your orbit in a way that acts on the points 90 degrees around from those (3 o'clock and 9 o'clock positions if looking straight down on your orbit.)

For example, if you burn radial-in then you will see the part of your orbit 1/4 of the way in front of you (3 o'clock position) drop towards the planet, while the part of your orbit 1/4 behind you (9 o'clock position) will rise upwards away from the planet. The reverse of course happens if you burn radial-out. More importantly for a rendezvous, what this does is changes the time that your intercept happens by changing the point where you will eventually cross your target's orbit. For a beginner it would be best to use this technique once you have already lowered your orbit to a point that you have a close encounter less than one orbit away.

Edited May 20, 2020 by HvP

[Joe.L]

I can thank you all enough for your advice, I have been struggling to get into a stable orbit but now have that complete controlled so I know it's just a matter of practice for this to work so thank you for feeling me with confidence!

[Joe.L]

https://imgur.com/a/ZnUn4qC well it looks like all of what you said worked, now the next hard part...bloody docking the thing. 

 

I can't thank you all enough for your patience!!

ok, sorry again. As the image denotes, I have got even closer now at around 4 meters, however, I am now running quite low on monopropellant so getting close is proving to be very tricky. Is it still just a case of going prograde/retrograde in order to get close enough?

Edited May 20, 2020 by Joe.L

[Zhetaan]

43 minutes ago, Joe.L said:

I can thank you all enough for your advice, I have been struggling to get into a stable orbit but now have that complete controlled so I know it's just a matter of practice for this to work so thank you for feeling me with confidence!

Hello!  It's good to see that you're not giving up.  I don't know whether this will make you feel any better, but consider this:  you got the game for forty dollars; NASA had to figure this stuff out, when corrected for inflation, at over seven hundred million dollars per launch (and with no quicksaves, either!).

I looked at the image you posted:

2 minutes ago, Joe.L said:

https://imgur.com/a/ZnUn4qC well it looks like all of what you said worked, now the next hard part...bloody docking the thing. 

I have some advice for your next step:

Keep in mind that there's no hurry; it costs nothing to take things slowly, because KSP rewards you for doing things correctly, not quickly.  I don't know how much of a gamer you are, but I've noticed that a lot (perhaps most) of the frustration faced by more casual gamers trying to play KSP is caused by the fact that video games prefer to increase the difficulty by requiring you to perform tasks more quickly or with more precise timing--see, for example, the speedrun as a demonstration of skill.  That kind of thinking won't work here; KSP has very few situations that require quick reactions.  Instead, it presents the difficulty exactly as it is, and does not forgive you for making mistakes.  It's definitely an adjustment.

Remember that your camera view is two-dimensional and there's no sense of three-dimensional perspective, so once you have your docking ports aligned, be certain to move the camera to see whether you're aligned in all directions.  Also note that docking ports work best at a closing velocity of less than three tenths of a metre per second--that's .3 m/s or point three.

If you find that the station is drifting away from you, then remember that when you put the navball in Target mode, your prograde and retrograde markers show the direction of your relative velocity to the station.  This means that you can zero your velocity with a retrograde burn to stop the drift (though at this range, you're better off using RCS thrusters instead; you don't want to burn off parts of your station!).  You'll never make the drift exactly zero, but you can reduce it enough to give yourself time to dock.

If you find the station's docking port rotating away from you every time you get it lined up to your ship's port, that's because you're in a low-enough orbit that the curve of it is causing fast-enough relative rotation to cause a misalignment before you can close and dock.  To fix that, point the station's port in the normal direction and dock with it that way.

Good luck!

[Joe.L]

thanks a lot. I have played a lot of flight sim with PMDG etc and that was a struggle to understand but now can fly that plane easily (in simulator obviously) so I think taking it slow is the way forward like I did with PMDG.

 

The only trouble I find now is the low monopropellant, those tanks don't hold much fuel at all so I think if I had enough fuel this manoeuvre would be a lot easier.

[AHHans]

I can't believe that nobody has already mentioned @Snark's Illustrated guide to docking. It might be old but still applies, and it is IMHO (one of?) the best guide to docking around. (As in: it explains docking in the way I do it. (Except for the mod. Real men don't need mods to dock!)) It also has a section about rendezvous that might be useful.

[HvP]

2 hours ago, Joe.L said:

The only trouble I find now is the low monopropellant, those tanks don't hold much fuel at all so I think if I had enough fuel this manoeuvre would be a lot easier.

When you are close to your target and moving in for docking, try switching your camera view to "Locked" mode by toggling the "V" key. Then line up your camera looking forwards over the top of your craft. This will make it much easier to know exactly which direction you are moving when you fire your RCS thrusters and thus save on a lot of mono-propellant.

Also, you can toggle the CAPS-lock key on your keyboard to reduce the strength of your RCS thrust and balance your RCS more precisely. It could save you a lot of RCS propellant.

Edited May 20, 2020 by HvP

[Zhetaan]

4 hours ago, Joe.L said:

The only trouble I find now is the low monopropellant, those tanks don't hold much fuel at all so I think if I had enough fuel this manoeuvre would be a lot easier.

Once you have rendezvous, you don't need a lot of monopropellant, and often you can get by with just the on-board tank in the command pod.  Remember that docking is a lot like controlling a Kerbal on an EVA; you usually don't want to thrust hard and brake hard, but rather to use gentle taps and essentially drift to the docking port.  It doesn't take much monopropellant to move forward at .3 m/s, and provided that you are aligned, you don't need any monopropellant to stop because you'll dock, instead.

1 hour ago, HvP said:

Also, you can toggle the CAPS-lock key on your keyboard to reduce the strength of your RCS thrust and balance your RCS more precisely. It could save you a lot of RCS propellant.

Definitely don't overlook this.  It's called fine-control mode, and it can save a lot of frustration.  You can tell that you are in fine-control mode when the pointers for pitch, roll, and yaw in the lower left corner of the screen turn from orange to blue.