Flight Question Spherical Apoapsis Rendezvous

[RonDVouz]

Normally I have been rendezvousing with the ISS with Sp Perigee and got pretty good at that, so I started trying the Sp Apogee rendezvous but at the point of rendezvous I misjudge the velocity and flat out miss getting into the ISS's vector. I don't speed up enough. The tutorial only uses Sp Perigee, which I've memorized to a T, but the Sp Apogee is the Russian "fast track" orbit and I want to get good at that too.

What do I do?

 

[meson800]

point of rendezvous I misjudge the velocity and flat out miss getting into the ISS's vector

One general docking/rendezvous tip is to use Docking MFD. Target the ISS, and then hit the "Copy to HUD" button on the docking MFD.

Now, you will have relative velocity vectors to the ISS. Just find the retrograde indicator on the HUD, and burn towards it to reduce your relative velocity to zero.

 

[RonDVouz]

One general docking/rendezvous tip is to use Docking MFD. Target the ISS, and then hit the "Copy to HUD" button on the docking MFD.

Now, you will have relative velocity vectors to the ISS. Just find the retrograde indicator on the HUD, and burn towards it to reduce your relative velocity to zero.

I got all that, what you're describing works for the Sp Perigee rendezvous, with the Sp Apogee I have to increase my velocity as I'm reaching the slowest part of my orbit and usually the ISS is at perigee and it's moving its fastest. Burning into the velocity isn't quite cutting it as far as matching speeds, I'm not catching up. I think if I started burning into the velocity before reaching the actual rendezvous point. I'm going to try later after I've finished downloading all the new textures.

 

[Deleted Orbinaut]

I got all that, what you're describing works for the Sp Perigee rendezvous, with the Sp Apogee I have to increase my velocity as I'm reaching the slowest part of my orbit and usually the ISS is at perigee and it's moving its fastest. Burning into the velocity isn't quite cutting it as far as matching speeds, I'm not catching up. I think if I started burning into the velocity before reaching the actual rendezvous point. I'm going to try later after I've finished downloading all the new textures.

It works either way. Once you get close to intercept (<50km or so), you ignore your Earth-relative velocity and focus only on ISS-relative velocity. The easiest (though not most efficient) way to get close is to burn off your ISS-relative velocity by burning toward the retrograde velocity marker (looks like a cross with -V[ISS] next to it) on the docking HUD until the relative velocity (the number next to -V[ISS]) is 0. Then, burn toward the target marker (looks like a square with D[ISS] next to it) until your relative velocity is comfortable for approach. Then slow down as you get closer. (I like to use retro-jets for this, if they're available.) It doesn't matter whether you approach at apogee, perigee, or in between. As long as you have a close intercept and can slow down fast enough, this will work.

 

[RonDVouz]

Mmm, maybe I'm not being clear.

This isn't about the type of rendezvous they used in the tutorial, and doing the exact opposite of Sp Perigee RV doesn't exactly work. The one time I was able to get into the velocity from Sp Apogee the ISS whizzed past me, almost hitting it. So being ahead of the ISS (as preferred in Sp Perigee) isn't a good thing, so I tried coming up from behind and under (just like the ATV did in real life) it but this gives me very little time to burn into the velocity. So what I'm coming up with is to burn into the velocity, but ISS is moving so fast ahead I miss the window to get into the +V.

 

[Deleted Orbinaut]

I feel like you're still not using relative velocity. Use a rule of thumb. For example, keep your relative velocity in m/s equal to about 10x the distance from the ISS in km, so at 20km, you want a closing speed of about 200 m/s, and at 1 km, you're closing at 10 m/s. It's also important that your relative velocity vector points directly at your target: on the docking HUD, this means that the circle+crosshairs with V[ISS] next to it will be inside the square with D[ISS] next to it. This ensures that your relative velocity is in the direction of the target. It really doesn't matter whether your vessel's orbital speed is faster or slower than your target's as long as you are approaching it.

 

[RonDVouz]

So actually there wasn't anything wrong with my approach, it's that the base program wasn't working right. I re-loaded it and now it works fine.

Apparently as I was downloading and adding the new texture files the base program got messed up and the velocity meter on the docking HUD just wasn't registering the change, or moving.

Sorry for the confusing post.