Cannot reach ISS
- Thread starter tekinozbek
- Start date
Tommy
Well-known member
PeR is the distance above the center of the earth (radius of orbit) and PeA is the distance above the surface of the earth (altitude). From what I've seen i n your posts, I think you are in too much of a hurry to sync. Your velocity relative to the ISS is too high because you are trying to sync to soon. Depending on how far ahead/behind the ISS you are, it may take several orbits to acheive rendevous. After you've circularised your orbit and aligned your planes, See if you are Ahead of the ISS, or behind it.
First: If you are ahead, perform a very small retrograde burn (use partial throttle, or RCS in linear mode) to lower your PeA to a k or 2 below the ISS's. If you are behind it, do the opposite to get your ApA just a hair above the ISS's.
Second: If you are ahead of the ISS, burn prograde until your ApA is about 600k to 800k, no more. If you are behind it, burn retrograde to lower your PeA to no lower than 200k. Keep an eye on the list on the left of the Sync Orbit MFD (use intersect 1 or intersect 2 modes). The Orbit with the closest approach will be highlighted. It may be several orbits from now, and you may want to wait until a closer approach comes up (if the closest approach for the Orbits shown aren't very close). Once you find an orbit where the difference in times is 2k or less, you can try adjusting your orbit to get a lower DTmin. Watch the RVel line, you shouldn't have much more than 200k RVel.
Once you get close to the ISS, have your NAV1 frequency set to the ISS's transponder. Point the ship at the "cross in a ball" indicator. Watch the distance to the ISS, as long as it's decreasing you can just coast for now. Once the distance stops decreasing, or you get within 20k or so (whichever comes first) burn toward the "cross in a ball" until your relative velocity gets very lose to zero. When it gets close to zero the indicator will start moving around a lot, so be patient, use low thrust, and do your best to keep the indicator centered in the hud. Once it gets down to 2 or less you can stop.
Now, aim toward ISS. Burn until you see the negative RVel "cross not in a ball" indicator, and your RVel is 20k to 100k (depending on the distance to the ISS). Use translational RCS to keep the cross pointed at the ISS. If you get impatient, use short bursts of time acceleration - do NOT increase the RVel. Set your Docking MFD to the desired docking port and hit the HUD button. Use translational RCS to align the cross to the docking approach (rectangles shown on MFD), about halfway down the approach path. As you get near the approach path, use retro thrusters to lower the Rvel. You will also need to use translational RCS to maintain the cross in the path. Try to get the RVel down to .2 or less when you enter the path. Rotate towards the dock and orient as exactly as you can using the DockMFD. The, use translational thrust to move in and dock. Keep your speeds very low, 10 m/s or less, and use time accel if you get impatient. Patience is really the key to a successful rendevous and dock.
BTW, the positive RVel indicator (cross in a ball) is always directly opposite the negative RVel indicator. If you are pointing at the + RVel indicator, turning (or pitching) 180 degrees will point you at the - RVel indicator.
The tutorial you are following probably tells you to set the Sh-ToR(0) and Tg-ToR(1) equal because that is the best thing for those particular circumstances, where you are fairly close to the ISS, and slightly ahead of it. It is not always the correct way, and will only work in a very limited set of circumstances.
First: If you are ahead, perform a very small retrograde burn (use partial throttle, or RCS in linear mode) to lower your PeA to a k or 2 below the ISS's. If you are behind it, do the opposite to get your ApA just a hair above the ISS's.
Second: If you are ahead of the ISS, burn prograde until your ApA is about 600k to 800k, no more. If you are behind it, burn retrograde to lower your PeA to no lower than 200k. Keep an eye on the list on the left of the Sync Orbit MFD (use intersect 1 or intersect 2 modes). The Orbit with the closest approach will be highlighted. It may be several orbits from now, and you may want to wait until a closer approach comes up (if the closest approach for the Orbits shown aren't very close). Once you find an orbit where the difference in times is 2k or less, you can try adjusting your orbit to get a lower DTmin. Watch the RVel line, you shouldn't have much more than 200k RVel.
Once you get close to the ISS, have your NAV1 frequency set to the ISS's transponder. Point the ship at the "cross in a ball" indicator. Watch the distance to the ISS, as long as it's decreasing you can just coast for now. Once the distance stops decreasing, or you get within 20k or so (whichever comes first) burn toward the "cross in a ball" until your relative velocity gets very lose to zero. When it gets close to zero the indicator will start moving around a lot, so be patient, use low thrust, and do your best to keep the indicator centered in the hud. Once it gets down to 2 or less you can stop.
Now, aim toward ISS. Burn until you see the negative RVel "cross not in a ball" indicator, and your RVel is 20k to 100k (depending on the distance to the ISS). Use translational RCS to keep the cross pointed at the ISS. If you get impatient, use short bursts of time acceleration - do NOT increase the RVel. Set your Docking MFD to the desired docking port and hit the HUD button. Use translational RCS to align the cross to the docking approach (rectangles shown on MFD), about halfway down the approach path. As you get near the approach path, use retro thrusters to lower the Rvel. You will also need to use translational RCS to maintain the cross in the path. Try to get the RVel down to .2 or less when you enter the path. Rotate towards the dock and orient as exactly as you can using the DockMFD. The, use translational thrust to move in and dock. Keep your speeds very low, 10 m/s or less, and use time accel if you get impatient. Patience is really the key to a successful rendevous and dock.
BTW, the positive RVel indicator (cross in a ball) is always directly opposite the negative RVel indicator. If you are pointing at the + RVel indicator, turning (or pitching) 180 degrees will point you at the - RVel indicator.
The tutorial you are following probably tells you to set the Sh-ToR(0) and Tg-ToR(1) equal because that is the best thing for those particular circumstances, where you are fairly close to the ISS, and slightly ahead of it. It is not always the correct way, and will only work in a very limited set of circumstances.
Astronut409
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TSPenguin;78243 I highly recommend reading [URL="http://smithplanet.com/stuff/orbiter/orbitaloperations.htm" said:Orbital Operations[/URL] by Jared Smith. IMO the best tutorial for, well, orbital operations
(You might want to do some research along the lines of "What is an orbit" before proceeding...)
Happy Orbiting
Thank you so much for posting the link to the operations thing! It's exactly what I've been looking for, since docking, until about fifteen minutes ago, has eluded me like someone trying to find a living dinosaur. It was simple, easy to follow, and showed helpful screenshots.
ar81
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[ame="http://www.orbithangar.com/searchid.php?ID=3074"]Tutorial: DG to ISS[/ame]
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