General Question 2010-P1 Docking HUD, Velocity Indicators

[Havner]

In two documents I've been learning Orbiter with (the official documentation and Orbital Operations Manual) it's been written something that doesn't fit with my Orbiter instalation.

When I approach ISS after syncing our orbits there are 2 points showing me relative (to ISS) velocity vector.

Let's call it the "prograde" one which is the one where you have to point your ship and run main thrusters to decrease the speed towards the station.
And the "retrograde" one which is the one where you have to point the nose and run retro thrusters to decrease the speed between you and the station.

In the two mentioned documents the prograde point is marked with a circled cross and the V[ISS] and the retrograde point is marked with a cross and -V[ISS]. The prograde is also the one that is marked with an arrow when none of those points is visible.

On my orbiter the prograde is marked with a circled dot and -V[ISS] and the retrograde is marked with a circled cross and V[ISS]. Which is more or less inverted comparing to the docs. Also this time the retrograde is the one that is marked with an arrow when no point is visible.

I even launched the 2006 version on my quicksave and it fits the manuals. My 2010 doesn't. This change is not mentioned anywhere in the orbiter changelog, the manual states that it should be as it was in 2006. Am I missing something? I'm not using any mods (but the official textures) and I'm flying the default DG.

I'm wandering whether there is something awkward happening or it's just the way it's supposed to be since 2010-P1.

 

[statickid]

They are velocity vectors relative to the target (ISS). Accelerating towards the circled cross will increase your velocity relative to the target, accelerating towards the circled dot will decrease your velocity relative to the target. Your vector may be taking you in any direction, not just towards or away. You can think of a line segment connecting the center of a sphere to ANY point on its surface.

These are NOT the same as prograde and retrograde, which have to do with your orientation to your own orbit, or can also describe the type of orbit you are in (clockwise or anticlockwise) as viewed from the "top", above the ecliptic plane.

You are only traveling DIRECTLY towards or away from the station IF and only IF one of the circled indicators is resting exactly on top of the station, visually. Unfortunately if you try to fly straight at it, you have to constantly adjust your trajectory. In an optimum rendezvous, your circled cross will need to be pointed to one side of the target, and eventually drift together with less corrections than if you fly directly at it in a straight line.

 

[Ripley]

Here I am closing in towards the ISS, at 28 km distance, with a positive closure speed of 40.99 m/s..

When I'll be closer I'll need to point my nose "- Λ -" over the velocity vector (the cross in the circle) and "brake" with retro engines/RCS LIN (keypad 9).

Or, if I turn 180° and point my nose over the other velocity vector (the point in the circle), I will brake with main engines/RCS LIN (keypad 6).

 

[Havner]

Sorry for the confusion. I know exactly what this vector is and I know exactly what a prograde and retrograde attitudes are in relation to the orbit.

I just called those direction so I could relate to them in the post (I think they were called like this in some tutorial). I could have named them "point A" and "point B" just as well. It's just a name.

My original question was not about the physics or how to use them but about their markings and markings only.

Why did they change between 2006 and 2010 and why they where inverted (markings). And why this is not mentioned in the changelog and what was the cause of this change. Also why the documentation doesn't reflect this change.

To put it simpler:
A: circled cross (2006) changed into circled dot (2010).
B: cross (2006) changed into circled cross (2010).

In 2006 the arrow pointed at A, in 2010 the arrow points at B.

 

[statickid]

Who knows? :shrug:

Probably for visual clarity. I remember noticing this when it changed, I think it has to do with the way the symbols overlap. It's easier to align their centers now.

Edit: The arrow still points at the forward velocity vector. I could be wrong, but I seem to remember having to guess where the rearward velocity vector was in the old version. :hmm: or was it the indicator towards the target... whatever the case, I think there is more information on the new HUD than the old HUD that makes docking quite a bit easier.

 

[Havner]

Edit: The arrow still points at the forward velocity vector. I could be wrong, but I seem to remember having to guess where the rearward velocity vector was in the old version. :hmm: or was it the indicator towards the target... whatever the case, I think there is more information on the new HUD than the old HUD that makes docking quite a bit easier.

The arrow points at a different point than in 2006. I just checked that. It now points where you have to use the retro thrusters which makes docking easier only if you have a spaceship that have them.

And the most confusing thing is that every 2006 tutorial tells you to follow the arrow and run the main thrusts towards a circled cross you find there. And if you follow that in 2010 you get exactly the opposite result.

 

[statickid]

Well it looks like the documents just need updating. I can see why that would be confusing. That's the way it's supposed to be, nothing awkward is happening.

It's a feature not a bug!