Jump to content
  • 0

How to get two orbiting rockets close to them?


janq0
 Share

Question

3 answers to this question

Recommended Posts

  • 1

It also helps to set the other rocket as the target (you can do this in map mode) because that will give you a set of markers which show you the point of closest approach.  They look a lot like the Ap and Pe markers, but they are different colours and they have a vertical line down the centre rather than lettering.  The orange set shows the next point of closest approach (the one pointing down is your position, and the one pointing up is the target's position), and the magenta set shows the point of closest approach on the orbit after that.

What you will want to do is modify your orbit (generally, you want to lower your orbit if the target is ahead of you and raise it if it is behind you, but if you're orbiting at low altitude, you will have to go higher either way to avoid grazing the atmosphere and re-entering) and then wait until the separation gets close.  For these sorts of approaches, it sometimes makes sense to circularise at the modified orbit because it makes the rendezvous go more quickly, but for small changes, it usually works better to keep one apsis at your target's orbit and stay elliptical.  As the markers get closer, that is a visual indication of how much your target is catching up to you (or vice versa).

Eventually, the target-position marker (the one pointing up) will skip over the closest-approach marker.  This indicates that your target will pass you on the next orbit.  That's how you know that it is time to change your orbit back towards the target orbit.  However, you don't want to change it the whole way:  you want to get to the same place as the closest-approach marker and slowly thrust to move the orbit back while watching in map mode.  What you will see is that the target-position marker will slide along its orbit:  what you will want is to slide it to align with your closest-approach marker.  When that happens, shut down your engines.  Your orbits aren't yet matched, but you won't want to fully match until you have actually rendezvoused.  You can check the separation distance on the closest-approach marker; it ought to be under 2.5 km and ideally under 1 km.  Closer is better to a point; I usually try for 0.2 km because I don't want to have any collisions and because 200 metres is quite close enough for orbital rendezvous.  Collisions aren't likely but I had a nasty surprise once when I tried to rendezvous with a station, so I stay safe.

Now you have to wait one more orbit, and once you get to the point of closest approach, you ought to see the target floating next to your rocket.  Now is the time to fully match.  The way to do this is to set the navball to target mode (do this by clicking on the speed display at the top of it) and thrust retrograde until the target velocity equals zero.  Retrograde when you're in target mode is defined with respect to the target's relative velocity; so making it zero means that you and your target have matched orbits.  The match isn't perfect (and it won't be unless you dock) so the target velocity will start to rise as you drift apart, but a good rendezvous will give you a fairly stable match for at least five minutes, which is plenty of time to do most anything.

If you are more visually-inclined, Scott Manley does a better job of explaining it than I do, because he has pictures:

And the second part:

 

Edited by Zhetaan
Link to comment
Share on other sites

  • 2

Moving this question about how to play the game to Gameplay Questions.

42 minutes ago, janq0 said:

I have two rockets. they are orbiting ~ almost same path about kerbin but they are at the opposite ends how to get them together?

You need to alter one of them to either speed up or slow down its orbit, so the other one can catch up to it.  This will involve either burning :prograde: to raise its orbit (thus making it slower), or else burning :retrograde: to lower its orbit (thus making it faster).

The precise amount to burn depends on how patient you are (e.g. how many orbits you're willing to wait until the one rocket catches up to the other one).  If you're patient and only want to spend a little bit of fuel, you can make the orbit only slightly bigger or smaller than the other rocket's, then just timewarp and watch them go round and round as they gradually get closer to one another.

Link to comment
Share on other sites

  • 0
On 14. 11. 2017 at 8:28 PM, Snark said:

Moving this question about how to play the game to Gameplay Questions.

You need to alter one of them to either speed up or slow down its orbit, so the other one can catch up to it.  This will involve either burning :prograde: to raise its orbit (thus making it slower), or else burning :retrograde: to lower its orbit (thus making it faster).

The precise amount to burn depends on how patient you are (e.g. how many orbits you're willing to wait until the one rocket catches up to the other one).  If you're patient and only want to spend a little bit of fuel, you can make the orbit only slightly bigger or smaller than the other rocket's, then just timewarp and watch them go round and round as they gradually get closer to one another.

 

On 15. 11. 2017 at 3:29 PM, Zhetaan said:

It also helps to set the other rocket as the target (you can do this in map mode) because that will give you a set of markers which show you the point of closest approach.  They look a lot like the Ap and Pe markers, but they are different colours and they have a vertical line down the centre rather than lettering.  The orange set shows the next point of closest approach (the one pointing down is your position, and the one pointing up is the target's position), and the magenta set shows the point of closest approach on the orbit after that.

What you will want to do is modify your orbit (generally, you want to lower your orbit if the target is ahead of you and raise it if it is behind you, but if you're orbiting at low altitude, you will have to go higher either way to avoid grazing the atmosphere and re-entering) and then wait until the separation gets close.  For these sorts of approaches, it sometimes makes sense to circularise at the modified orbit because it makes the rendezvous go more quickly, but for small changes, it usually works better to keep one apsis at your target's orbit and stay elliptical.  As the markers get closer, that is a visual indication of how much your target is catching up to you (or vice versa).

Eventually, the target-position marker (the one pointing up) will skip over the closest-approach marker.  This indicates that your target will pass you on the next orbit.  That's how you know that it is time to change your orbit back towards the target orbit.  However, you don't want to change it the whole way:  you want to get to the same place as the closest-approach marker and slowly thrust to move the orbit back while watching in map mode.  What you will see is that the target-position marker will slide along its orbit:  what you will want is to slide it to align with your closest-approach marker.  When that happens, shut down your engines.  Your orbits aren't yet matched, but you won't want to fully match until you have actually rendezvoused.  You can check the separation distance on the closest-approach marker; it ought to be under 2.5 km and ideally under 1 km.  Closer is better to a point; I usually try for 0.2 km because I don't want to have any collisions and because 200 metres is quite close enough for orbital rendezvous.  Collisions aren't likely but I had a nasty surprise once when I tried to rendezvous with a station, so I stay safe.

Now you have to wait one more orbit, and once you get to the point of closest approach, you ought to see the target floating next to your rocket.  Now is the time to fully match.  The way to do this is to set the navball to target mode (do this by clicking on the speed display at the top of it) and thrust retrograde until the target velocity equals zero.  Retrograde when you're in target mode is defined with respect to the target's relative velocity; so making it zero means that you and your target have matched orbits.  The match isn't perfect (and it won't be unless you dock) so the target velocity will start to rise as you drift apart, but a good rendezvous will give you a fairly stable match for at least five minutes, which is plenty of time to do most anything.

If you are more visually-inclined, Scott Manley does a better job of explaining it than I do, because he has pictures:

And the second part:

 

Thank you!

Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Answer this question...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...