It's a bit tricky because the non-spherical gravity is causing the orbital elements to jump up and down. That shouldn't be a problem after I implement a mean elements display in LTMFD.
Thatís sounds great because itís really needed.
BTW that was one of the goals of EOCA. Iím not sure I did that very well according to some posts here on this thread, reporting some differences between the EOCA versus DSKY Pe and Ap values. At least I think that the computations Iíve implemented was not the same than the AGC uses.
An other point is the major axis secular shift due to the non spherical gravity field as a function of J2, Rt, a, i and e.
This seems to be a ignored by NASA doc. In my mind, this is because the target and the chaser are on similar orbits: Inclinations i are equals, of course Rt too, a and e are very closed and may be they consider that the 2 major axis shift at the same rate so they are fix relatively.
What do you think about that?
Also the advanced op-mode of the LOI program of LTMFD is almost exactly the CDH. It allows to set PeA, ApA and LPe.
I noticed that!
what constraints are there for CDH ?
AFAIK the CDH constraints are:
- 180į away from the CSI: since the CSI delta V is always horizontal (+/- X in the local horizontal frame) it means that the CSI occurs at an apside cross (Pe or Ap) otherwise the X impulse would make an undesired major axis shift.
So the CDH should occurs at the next apside cross after CSI (180į)
More exactly, the CDH occurs at a number N of apside cross after CSI. BTW itís an input the astronauts enterd into the AGC during P32, V06N55, line 1.
N could be:
. 1: (1 half of orbit: 180į) or 3 (1 orbit and one half: 540į) for a so called ďunconstrained delta HĒ CSI
. 2 or 4 (1 or 2 full orbits: 360į or 720į) that means that the CDH occurs at the same place than the CSI and CSI must be done at the coelliptic delta H. Thatís why such a CSI is called ďconstrained delta HĒ CSI. Note that in this case, CSI is just a phasing.
- At least 10 minutes after the CSI (with a travel angle of 180 į itís not a problem) and 10 minutes before the TPI.
- The CDH set Ap and Pe to the target oneís minus the delta H and shift the chaserís orbit major axis parallel to the targetís orbit major axis
I canít guarantee Iím totally right because I discovered yesterday that Iíve made a mistake in the RDV with EOCA: I thought the CDH occurs when the chaser crosses the targetís line of apsides and that was wrong.
So if I have made one mistake I can make another one!
The IMFD is based on a conic solution and it's not accurate enough. Also, the IMFD can't handle transfer angles greater than 360. There is a numeric lambert solver in the LTMFD but currently it is only used as an sub program for the other programs. There is no user interface for it but it shouldn't be difficult to create one.
So may be a spreadsheet for the RDV would be useful in order to present a synoptic page on a graph in the curvilinear coordinates. It would help the simmer to build the whole sequence.
Then, to perform the burns he would only use the AGC and or IMFD/LTMFD without requiring to go back again to any spreadsheet.