Help with matching orbit given in satellite contract

[eatU4myT]

I've launched a satellite to fulfil a satellite contract mission, and have matched the given orbit to within what I would expect to be acceptable error margins (as close if not closer than others I've succesfully matched in the past).  However, the contract is not being marked as complete.  What have I not done?!

 

I've got a screenshot to attach, but I'm new to the forum and not sure how to do this, perhaps someone can advise?

 

Thanks!

[Val]

You can find instructions on how to attach screenshots here.

 

[klesh]

Welcome to the forums!  My pre-screenshot guess is going to be that you've matched orbits but are going in the wrong direction.  Very common with these satellite orbit contracts.

[PrvDancer85]

What does your ascending or decending note read? If its 180 or -180 than it is an retrograde orbit

Edit thats the same thing as @klesh said.

Edited August 3, 2018 by PrvDancer85

[OhioBob]

An ascending node between 0-90^o is prograde, and between 90-180^o is retrograde.  Looking down on the orbit, prograde is counterclockwise motion, and retrograde is clockwise motion.  The orbit animation in the tracking station or map view also show the direction of movement.

[eatU4myT]

4 hours ago, klesh said:

Welcome to the forums!  My pre-screenshot guess is going to be that you've matched orbits but are going in the wrong direction.  Very common with these satellite orbit contracts.

This is it, thanks! Obviously got lucky the half dozen times I've done this before, as I didn't realise  it mattered!  Hmm...  Anyone care to advise on the most dV efficient way to fix this?!

[bewing]

Are you sure you want the most dV efficient way? See, there is a fast way, and a dV efficient way.

The fast way is to realize that you are already in exactly the right place, going in exactly the wrong direction, at precisely the right speed. So to fix it fast, you point retrograde (then set it back to "stability mode") and burn exactly twice your current orbital velocity and you're done.

The dV efficient way is called a bi-elliptic transfer and takes a lot longer -- but I'm sure these other guys will explain that one to you.

 

Edited August 3, 2018 by bewing

[eatU4myT]

5 hours ago, bewing said:

Are you sure you want the most dV efficient way?

 

Unfortunately, yes. I used this satellite to complete two contracts, so I gave myself some dV to transfer from one orbit to the second, and it turns out it was a bit more than I needed - however, it's almost certainly not enough to correct my mistake here! I suspect I'm doomed, but if there is a super efficient way, it might just work...!

[klesh]

I'm not a KSP math kinda guy, but if I were faced with doing it and needed an efficient method, I would boost my AP up very high, wait till I get to AP, burn retro till I flip the orbit and my PE is back to where I want it, coast to PE and lower AP back to original orbit parameters.  Should save you some amount of dV over just slamming on the brakes down low in the orbit.

[OhioBob]

1 hour ago, klesh said:

I'm not a KSP math kinda guy, but if I were faced with doing it and needed an efficient method, I would boost my AP up very high, wait till I get to AP, burn retro till I flip the orbit and my PE is back to where I want it, coast to PE and lower AP back to original orbit parameters.  Should save you some amount of dV over just slamming on the brakes down low in the orbit.

That is the best way to do it, but it can still take a lot of delta-v depending on how high the initial orbit is.  Starting out in low Kerbin orbit, and boosting the apoapsis all the way out the sphere of influence, will cost over 1900 m/s to complete all the maneuvers.  Of course it will cost nearly 4600 m/s to reverse the orbit without raising the AP, so it's a big savings.  The higher the initial orbit, the less delta-v it takes for both methods.  It's always better to raise the AP, but the savings we get by doing so diminishes.  For instance, suppose the initial orbit is 3000 km.  Doing a simple orbit reversal right from there takes 1980 m/s, and by raising the AP we can reduce it to 880 m/s.