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Old 05-31-2011, 04:16 PM   #31
Mister Mxyzptlk
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Chub, There is a "mod" button on sync orbit mfd. You need to click it til it is on "intersect one" or "intersect two" and then do a prograde burn until the orbits intersect. Then once they intersect you adjust your orbit when you are at the intersect point or when you are 180 degrees from the intersect point to get the Sh-Tor and the Tg-Tor countdown timers to read the same. Since there are 2 intersect points you can flip between them and use the one that has the closest set of readings. BUT, and this is a big but, you have to start the process when you still have 4 or more orbits til rendezvous/intersect. In the scenario you posted you are in your last orbit before rendezvous and it is too late get a good sync. Do you understand all of the salient points in my post?
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Old 05-31-2011, 05:52 PM   #32
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DTMin of 5.0 is actually 35 km distance (and thus perfectly close for doing a small correction to intercept the target) not 100 km. Are you sure you are not reading the instruments wrong, for example using the wrong intersection mode?
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Old 06-01-2011, 12:56 PM   #33
Chub777
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Quote:
Originally Posted by Mister Mxyzptlk View Post
 Chub, There is a "mod" button on sync orbit mfd. You need to click it til it is on "intersect one" or "intersect two" and then do a prograde burn until the orbits intersect. Then once they intersect you adjust your orbit when you are at the intersect point or when you are 180 degrees from the intersect point to get the Sh-Tor and the Tg-Tor countdown timers to read the same. Since there are 2 intersect points you can flip between them and use the one that has the closest set of readings. BUT, and this is a big but, you have to start the process when you still have 4 or more orbits til rendezvous/intersect. In the scenario you posted you are in your last orbit before rendezvous and it is too late get a good sync. Do you understand all of the salient points in my post?
I see. I was using the Sh-apoapsis mode. Also by "you have to start the process", do you mean the reducing of the DTmin?
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Old 06-01-2011, 01:17 PM   #34
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A quick reference when trying to dock
0.01 Rinc ~ 1 km distance at rendezdous
0.01 Dtmin ~ 80 m distance at rendezvous
1 DTmin ~ 8 km distance at rendezous

You need to be pretty accurate to fly a good approach.
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Old 06-01-2011, 01:35 PM   #35
Wishbone
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Or use TransX/KOST 0.75 to predict and minimize miss distance.
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Old 06-01-2011, 04:03 PM   #36
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Quote:
Originally Posted by Chub777 View Post
 I see. I was using the Sh-apoapsis mode. Also by "you have to start the process", do you mean the reducing of the DTmin?
That means "The time difference is measured at the apoapsis of your ship". This is NOT the same as the intersection with the target orbit.

before you have intersection, you should use Sh-Apoapsis because it is the closest available. You should better use "Intersection #1" or "Intersection #2" as reference, once your orbit crosses the target orbit. If you are at DTMin < 1.0 at one intersection, your distance will be less than 10 km.

You can correct the intersection easily...just switch to the next intersection, and use RCS for getting it to zero. if your future arrival is behind the target, you need to fire retrograde, so you do a bigger "semiloop" below the target. If you are arriving in front of the target, burn prograde to make the "semiloop" smaller.
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Old 06-01-2011, 04:14 PM   #37
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The process I mean is the process of doing prograde or retrograde burns to get the yellow Sh-Tor and Tg-Tor readings to be the same. Those readings represent the time in seconds till "Sh" your vessel, and "Tg" the target vessel will be at the intersect point. When both readings are exactly the same both vessels will be at the intersect point at the same time.

For now forget DTmin., Just make sure that Rel. inc. is 0. Right now I am going to explain a little more regarding Sh-ToR and Tg-ToR so you will understand how to do your burns to get them to be the same and stay the same.

If Sh-ToR is a larger value than Tg-ToR, your vessel is going to be late to the intersect point by however much the difference in value is, and conversely If Sh-ToR is a smaller value your vessel will be early to the intersect point. If Sh-ToR is a smaller value than Tg-ToR then you are early and must do a prograde burn till the values are equal at the intersect point.
Conversely if Sh-Tor is a larger value then you are late and must do a retrograde burn till the values are equal at the intersect point. To really fine tune the burn and get the numbers to coincide you will need to use the translation thrusters on fine control (hold "control" down on the keyboard) when the numbers are getting close.

Once you understand how to fine tune your your intersect time at the intersect point, which will most likely be your apoapsis or close to it, experiment with prograde and retrograde burns at your periapsis. Just make sure you don't use the translation thrusters that would cause you to move normal or antinormal as this will change your rel. inc.

Any questions?
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Old 06-01-2011, 04:34 PM   #38
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Quote:
Originally Posted by Chub777 View Post
 RInc is usually 0.0 but DTmin drifts to 0.1.
One problem I had when I was learning to rendezvous was that I would get the numbers all set, and then I'd time warp ahead to get to the rendezvous orbit ... and that would often be at least 3 or 4 revolutions, sometimes many more.

What I found was that during those revolutions, my DTmin and/or RInc would sometimes drift a bit. (I'm not entirely sure why since I don't have nonspherical gravity sources enabled.) But anyway, what I started doing was taking more time with the rendezvous effort.

Instead of blasting ahead several revolutions at a time, I would accelerate time 1 revolution at a time ... stopping at each Ascending/Descending node to RE-CHECK my RInc, and stopping at each rendezvous point to RE-CHECK my DTmin. I would also RE-CHECK the altitude of the ISS at my rendezvous point once per revolution and make sure that my ship's altitude was still aligned.

Since I started doing that, rendezvousing has become a total piece of cake. Now when I show up at the ISS, I am sliding in as smooth as silk.
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Old 06-01-2011, 06:05 PM   #39
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It sounds like you're not setting up your rendezvous point correctly. As I explained in my tutorial, you set your rendezvous point up by burning just after crossing orbital sunset so that the rendezvous point is actually on the other side of the planet in daylight:



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Old 06-02-2011, 08:50 AM   #40
Chub777
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Ok. Let me just try this.
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Old 06-02-2011, 08:53 AM   #41
Urwumpe
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If you need more help in the deep theory, look here:

http://www.orbiterwiki.org/wiki/Rendezvous

Of course, if you have any suggestions...write them yourself or wait for me to fix it...which can take a while, since writing the Skycrane Report has priority.
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Old 06-02-2011, 09:40 AM   #42
Chub777
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I just tried it and I have a DTmin of 32.27 (Sh-apoapsis and Intersect 2) and 31.60 (Intersect 1). What should I do now?
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Old 06-02-2011, 10:18 AM   #43
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wait until you are at the itnersection, then try mobing prograde using LIN RCS. if DTMin increases, stop and use retro-RCS (LIN) (press NUM 9) and it will get smaller, when it is close to 0, use CTRL-[RCS key] to use fine bursts, and you can get it to exactly 0 with some adjustment, then just coast to the correct orbit, wait until you are a half orbit away, then check plane alignment and DTmin are both 0.0, and perform orbit sync when appropriate

for a guide of orbit sync timing, use IMFD>Orbital>Velocity match, set the target, orient to the correct attitude (the + should be in the circle), then press AB when the time to intersection (shown on Sync MFD) is half of the required burn time (shown on IMFD), but allow a few 10ths of a second so you come a little short. then just approach it like in the sci-fi movies line up and dock, its easy when you know what youre doing

good luck!
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