OrbitMFD Some data is missing??

[bande]

hi everyone.
i'm working on doing a rendez-vous with ISS using Dan's DeltaGlider IV, and i need some help with OrbitMFD: as you surely know, in order to choose an encounter-point, we have to know the target's altitude when its angular position is = to our periapsis' longitude. I usually check "LPe" (Longitude of periapsis), and, when LPe matches with target's TrL, i take note of target's altitude. my question is: if i want to know my APOAPSIS' longitude, what do i have to do? MFD doesn't display it, so i thought that if apoapsis and periapsis are always opposite to the centre, then LAp (longitude of apoapsis) must be LAp = LPe - 180°, but i don't know if it's true.

can anybody help me?

 

[the.punk]

For the insertion burn to a rendezvous with a station you can't use OrbitMFD. SyncMFD helps you with that. OrbitMFD gives you only info about your currently orbit and the one of the target.
Here is a good video tutorial by tex for a rendez vous with a DGIV to ISS: DG4 to ISS: Orbiter Tutorial on Vimeo

 

[bande]

For the insertion burn to a rendezvous with a station you can't use OrbitMFD. SyncMFD helps you with that. OrbitMFD gives you only info about your currently orbit and the one of the target.
Here is a good video tutorial by tex for a rendez vous with a DGIV to ISS: DG4 to ISS: Orbiter Tutorial on Vimeo

i know, in fact i can dock a DG to an orbiting station, but before using syncMFD i have to fix a rendez-vous point, so i take note of the target's altitude when it crosses my apoapsis/periapsis, then i make ApA/PeA = Alt of the target in that point. then, when i have an intersect, i switch on syncMFD and dock.
all i want to know is if apoapsis and periapsis are always opposite to the centre, so that longitude of apoapsis = longitude of periapsis - 180°

 

[TJohns]

Always opposite

...all i want to know is if apoapsis and periapsis are always opposite to the centre, so that longitude of apoapsis = longitude of periapsis - 180°

By definition, yes they are

 

[bande]

By definition, yes they are

ok thank u guys!:thumbup::thumbup:

 

[TSPenguin]

Should you have nonspherical gravity enabled, there are fluctuations to be expected.

 

[Tommy]

but before using syncMFD i have to fix a rendez-vous point,

Not really. SyncMFD can do that for you. For instance, say you are in a 200km parking orbit. There are a couple ways to use SyncMFD to establish the rendezvous.

The easiest is to use Intersect 1 or Intersect 2 mode. When you select this mode, there won't be a list of orbits. Burn prograde until the list appears, and you have established an intersection point. Orbit and make adjustments until a low DTmin is established. It's a good idea to check the ISS's PeA and reduce thrust or use RCS when your ApA gets close.

A slightly more efficient method is to use Target - Pe mode, and in this case - yes, the Ap is about (exactly if non-spherical gravity sources is disabled) 180 degrees from the Pe in any non - polar orbit. However, unless you are trying to be super efficient you can simply "eyeball" that using SyncMFD, and use OrbitMFD to match your ApA with the target's PeA. If you have "non - spherical gravity sources enabled, this will likely result in you making the rendezvous point a bit below the target since it's Pe will have moved and your intersection will no longer be at the target's lowest point. Still, for a target with a fairly low eccentricity (and high eccentricity orbits don't have "wandering" Pe's) that will still put you within 10 to 20 kilometers from your target, which is plenty close for an initial approach.

 

[bande]

Not really. SyncMFD can do that for you. For instance, say you are in a 200km parking orbit. There are a couple ways to use SyncMFD to establish the rendezvous.

The easiest is to use Intersect 1 or Intersect 2 mode. When you select this mode, there won't be a list of orbits. Burn prograde until the list appears, and you have established an intersection point. Orbit and make adjustments until a low DTmin is established. It's a good idea to check the ISS's PeA and reduce thrust or use RCS when your ApA gets close.

A slightly more efficient method is to use Target - Pe mode, and in this case - yes, the Ap is about (exactly if non-spherical gravity sources is disabled) 180 degrees from the Pe in any non - polar orbit. However, unless you are trying to be super efficient you can simply "eyeball" that using SyncMFD, and use OrbitMFD to match your ApA with the target's PeA. If you have "non - spherical gravity sources enabled, this will likely result in you making the rendezvous point a bit below the target since it's Pe will have moved and your intersection will no longer be at the target's lowest point. Still, for a target with a fairly low eccentricity (and high eccentricity orbits don't have "wandering" Pe's) that will still put you within 10 to 20 kilometers from your target, which is plenty close for an initial approach.

that's great, until now i always used perigee method, 'cause the better tutorial i found explains very well how things work by that. i'm not anxious to be extra fuel efficient, i
only try to reach ISS in a reasonable short time (docking refuelling rules), in fact my next step will be a direct ascent to ISS. anyway, thank you for your advice :thumbup: