Problem DG to ISS Tutorial missing a step?

[Flux]

Hey,

I've been reading the Orbiter manual and am currently working my way through the steps required to dock with the ISS using the DG. I've got it right on the money until it comes to intercepting the ISS. Following the steps in the manual, the ISS is orbiting on the inside track which makes it impossible to get the RVel down to 0 in order to make an approach.

Am I missing something or shouldn't there be a step in which a burn is performed to match the orbits so that they line up completely, making you and the target stationary relative to one another? and not just have a close approach at Periapsis?

Flux

 

[Cras]

The easiset way to dock is to tune to the port frequency on nav 1, then press "h" until you bring up the docking HUD. This will show your velocity vector, how fast you are closing in on the ISS, where the ISS is (outlined in a green box), and then a path leading out from the docking port. When you get close, as in about 5k meters, point your ship to your v-bar and fire retro to slow yourself down to something more managable, a closing rate of 20 or so, then switch your RCS to translation and move your velocity vector to the beginning of that route the HUD is giving you.

This is not a very fuel effecient way, and you will have to preform a lot of corrections to you need to stay on top of it, but eventually you will get there.

If you want to try and meet up with the ISS like the real life space vehicles do, like when the space shuttle does, use Rendezvous MFD. It will help you perform an R-Bar approach, which means you will approach the station from behind and underneath.

 

[fireballs619]

Your orbits don't necessarily have to be exactly the same, they must just intersect at a point such that both the ships reach that point at the same time. The step in the tutorial that begins with 'Fire main engines until Sh-ToR(0) matches Tg-ToR(1).' This makes it so you get pretty close to the ship in question. Once you have reached the point where you are closest to the target as you will get in your current orbit, you take matters into your own hands.

Assuming you have your MFD all set, you switch to the docking HUD and you will see a circle that has within it a cross. That is the relative velocity marker. If you fire towards that, you will see RVel drop down until it is close to zero. Now it's just a matter of getting your velocity vector pointed towards the target, and you should begin to close in on it.

 

[Flux]

When I fire towards the crosshair the RVel increases. There is another circle though, with a dot in the middle. It has a -V next to it. When I fire towards that the RVel decreases but only to about 4 or 5 then begins to get too hard to chase and starts to climb again as it speeds by on the inner track. I'm very confused as to what I'm doing wrong. During this whole process I don't even get a visual sighting on the ISS.

 

[PhantomCruiser]

Tex has made a very good video using the DGIV, you can get/watch it here...
http://www.orbiter-forum.com/showthread.php?t=2055

 

[Flux]

OK, I've had some success with that! I managed to get within docking distance but some errors in my orbit started to push my DTmin past 0.00 and I took too long on the approach and missed the closest approach of ISS and ended up chasing it down, unsuccessfully! I guess practice makes perfect! ;-)

 

[PhantomCruiser]

Right, practice, practice and more practice. With a good amount of study with the manuals (http://www.amcsorley.dsl.pipex.com/play_in_space.htm is a good one to have).