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abr35
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« Reply #15 on: June 25, 2011, 10:02:13 AM »

There is a pretty good description of rendezvous retrieval targeting maneuvers (CSI, CDH, TPI, TPM) in this document (http://www.ibiblio.org/apollo/Documents/HSI-208454.pdf) in a page 225 but but I have no idea what's CCM ?  Is that an apollo 7 specific maneuver of some kind ? Obviously, if you want to rendezvous the S-IVB then you have to move away from it at first by executing a few burns.


The Apollo 7 rendezvous procedure is documented in here: http://next.nasa.gov/alsj/a410/A07_PressKit.pdf on pages 9 and 12a.
Basically a phasing burn was performed shortly after separation to put some distance between the CSM and S-IVB. This burn put the CSM in front of the S-IVB at the same altitude, but the CSM needs to be behind it and below for a co elliptic rendezvous. So the CCM is a +dVo and -dVp burn just before the perigee. The CCM raises the apogee and lowers the perigee, placing the CSM behind and below the S-IVB at the next orbit.

From there it's no different then a Gemini/Agena or CSM/LM rendezvous. It looks like the CSI and CDH were one maneuver though.

Had look at the flight plans: CENTANG was always +13000, elevation angle was +02745 for Apollo 7 and +02660 for Apollo 11. I strongly believe that the elevation angle had the sole purpose to specify the pitch angle the CSM pointed to at TIG, so that the optics pointed at the SIVB (resp. the LM) and the burn could still be executed. This saves time, fuel and reduces the workload for the lonely CMP.

Great! If we have an elevation angle (called it LOS by accident) P34 will iterate a TIG, if it's provided with a starting point in N37. I'm not sure what the limits are on how far from the N37 it will look for a TIG, but I think it's about one orbit. I'll look it up.
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meik84
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« Reply #16 on: June 25, 2011, 12:18:14 PM »

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The Apollo 7 rendezvous procedure is documented in here: http://next.nasa.gov/alsj/a410/A07_PressKit.pdf on pages 9 and 12a.
An even more detailed doc is this:http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700025391_1970025391.pdf Note that the procedures regarding the CMC won't work - Apollo 7 flew with Sundisk, an early predecessor of the Colossus software we use.
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abr35
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« Reply #17 on: June 30, 2011, 03:48:23 PM »

I forgot to include this. A scenario starting just before the CCM is attatched.

* Apollo 7 RNDZ.scn (151.58 KB - downloaded 20 times.)
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Christophe
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« Reply #18 on: July 01, 2011, 08:37:28 AM »

Hi everybody!

I did not come around here for a long time and how I was surprised to see people still use EOCA, something I built a few years ago!
And the version I put online is a very early beta compare to the latest I have on my disk.

May be I should give you my point of view on all of this:

- I initially began EOCA due to the lack of MFD to compute 2 things:
1/ The position of a spacecraft in some time from present, in a stable way according to the gravity perturbations. Orbit MFD, for example, tell you where you are but not where you will be within one hour, 2 orbits or 2 days later. And situation has not really changed since almost no MFD can do that.
2/ The stars in sight in an attitude burn in order to perform the sextant star check in P40/P41.

- As I ran into the math for EOCA, Gauss equations and so on I realised that, if I could do the non spherical gravity field and perturbations calculations, I should be able to add a force on the spacecraft in almost the same way: I decided to enhance EOCA and to make it compatible with the computation for the delta V's required for any maneuver in a simple way for the user: for example, put the major axis orientation you want into EOCA and it will tell you which burn you have to do.

- As time passed it became obviously that the goal of EOCA overtook the excel spreadsheet capability. I always considered that this tool was more a demonstration of what we need and in which way, here in the NASSP community, in charge for the talented developers to further build the final tool.
This happened partially since IMFD5.5 is almost perfect for any basic maneuver . 
I’m happy to see that Jarmo came on this thread and ask some technical questions on the coelliptic RDV cause my experience says that it just means we’ll probably have a new feature on IMFD in a couple of time Wink. Just let’s be patient.

- As far as the accuracy of EOCA is concerned: I don’t remember exactly which version you use around here but I know that I’ve improved greatly the accuracy in the latest version I was working on. Unfortunately, all that files are less than beta and since I’m the worst developer of the world I wrote no commentary anywhere and today, I don’t understand exactly my own work!!!
I know that orbiter changed the state vector propagation and it probably does not match anymore the way EOCA did.
But may be I should see if I can put online one of the latest version I get if one is stable enough.

- About the purpose of this thread, the Apollo 7 RDV: Great question! Bangs Head

At the end, before I left the work on EOCA due to lack of time and a bit of discouragement I was trying to figure out the problem of coelliptic RDV in a general way to incorporate it in EOCA and especially the Apollo 7 and above all the Apollo 9 RDV that is quite the most beautiful amongst all.
I saw some members as well as Tschachim put here the links for some useful docs about RDV. I have many on my hard disk and since I’m back with orbiter and Apollo I’ll have a look on it again.
AFAIR, the coelliptic RDV itself is not so complicated, although CSI and TPI are not as simple as they look due to some operational constraints the NASA wanted to satisfy.
The biggest problem, I think, is the phasing.

I explain myself:

To consider how and when the different maneuvers occur in the whole RDV sequence, the best way is to depart from the end with the most important question:
Where do you want to dock?
Answering this question, you know the position of the target, and the time when final RDV should occur. That’s why the capability of position and time prediction for a vessel in orbiter is so important.
Then you know where and when the TPI should occur according one input: the delta H,  that is the difference of height between the target orbit and the chaser orbit. No other input is required since the constraint for the TPI is that the chaser attitude during the burn is such as the tgt is on the line of sight.
Normally, if you set a 15 nm delta H (if I remember correctly), the CENTANG is around 130°.
An opposite way is to depart from a 130° of CENTANG and then you compute a maneuver and the attitude burn is more or less with the tgt along the line of sight.
Then you know where and when the TPI should occur.
In the same manner you may find time and position for CDH and CSI and optionally a plane change between them, according to some operational constraint such as a min time of 10 minutes between 2 maneuvers. I know there is some other constraints I don’t remember exactly.

As soon as I get the CSI time and position I ran into the biggest problem for me:
Assuming the position of my vessel, which maneuver for which orbit should I do to get on the CSI burn at the right time?
In other words, I was in front of the problem of the phasing.
For a LM landed on the moon, about to lift off to rendezvous with the CSM: No problem: the orbit insertion is almost always the same and the phasing is only to wait on the surface the proper time for launch.
 For a vessel already in orbit (like the Apollo 7 CSM, the Apollo 9 LM or even the Apollo 10 LM) this problem is known as the Lambert problem and I found that I was on the edge of my knowledge as well as the limit of excel. Sure I know some methods to solve the Lambert problem but I was not really able to do it in a satisfactorily way with Excel.

I hope Jarmo will take time to incorporate tha coelliptic RDV feature in a further IMFD version.

Meanwhile, may be should I build a simplified spreadsheet to calculate and display a whole RDV sequence?
No need for maneuver calculation anymore. We can do that with delta velocity prog of IMFD.
The spreadsheet should give only the GETI and the orbit parameter.

May be you have some comments and request?

I’m open

And happy to be back again around here! Happy

Christophe


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Christophe
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« Reply #19 on: July 01, 2011, 09:41:03 AM »

Here are 2 screenshots of the last developement of EOCA with RDV.
The user page to build a whole RDV from separation mnvr (such as the one made by the CSM after the first formation flying with SIVB during Apollo 7) until final, including phasing, insertion and so on...



Uploaded with ImageShack.us



By cornu1911 at 2011-07-01
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eddievhfan1984
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« Reply #20 on: July 01, 2011, 09:56:30 AM »

Quote
Reading that it looks like we should cover the 2 RCS phasing burns before the SPS burns, too?
We could do that -but I don't think it's necessary. Both burns had the only purpose to bring distance between the CSM and the SIVB. Correction of plane misalignment etc. was done with the CCR.
As we talk about phasing: the EOCA is flawed somehow. I put in the right PeA and ApA, but what EOCA puts out is wrong: I get ApA/PeA which are up to 5 nm away from desired altitude when I burn with this data. This could also be the cause of the midcourse problems abr35 is talking about.

Not to be condescending, but I've made this mistake before, and it might cause the inaccuracy.

When Orbiter gives you state vectors, they are set to ecliptic frame of reference by default. EOCA calls for "reference equator, fixed" when gathering data. This screwed me up many times when doing calculations.

Also, when going through the Apollo 7 rendezvous documents I linked to you guys ages ago, it shows that the CSM only falls 20nm below and 50 nm above the SIVB during the procedure, so I'm using that to define my CCR orbital parameters. Since the LPe is changing constantly with orbital perturbation/rotating Earth, I just paused Orbiter, took the difference between both vehicles' LPe, and set the desired LPe in EOCA so as to make the variance from original the same as the delta-LPe. I should know more in the next few days about how that works out.

EDIT: Sorry, didn't notice Christophe's post while I was typing this. Well, hopefully that new EOCA release will be committed to CVS sometime in the near future. It's a godsend.
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jarmonik
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« Reply #21 on: July 04, 2011, 11:08:56 AM »

1/ The position of a spacecraft in some time from present, in a stable way according to the gravity perturbations. Orbit MFD, for example, tell you where you are but not where you will be within one hour, 2 orbits or 2 days later. And situation has not really changed since almost no MFD can do that.
This would have been implemented a long ago if someone would have asked. It's simple, no problem.

2/ The stars in sight in an attitude burn in order to perform the sextant star check in P40/P41.
It's possbile to choose a rotation of a vessel around the main axis for a burn. If that is enough then it should be possible to implement this feature.

As soon as I get the CSI time and position I ran into the biggest problem for me:
Assuming the position of my vessel, which maneuver for which orbit should I do to get on the CSI burn at the right time?
In other words, I was in front of the problem of the phasing.

I was asked to look into the RDV and I should have some time for that. I am not exactly familiar with the details of the Apollo 7 mission. But it sounds like you are talking about the -7.5ft/s burn around 00:03:20 GET in a case of Apollo 7. Based on my understanding of the RDV you are worrying about the CSI burn far too early. The RDV procedure must take you into a successful RDV with the target regardless of what ever is the initial orbit of the active vehicle. Therefore, the operation of the RDV procedure can't depend on the burns made before the CSI. Also, the CSI burn isn't a phase sensitive. As far as I understand the main purpose the CSI-CDH burns is to fix the phasing error of the active vehicle respect to the passive vehicle for a proper TPI.

I should have enough information to implement the RDV procedure into a MFD but since you are already invested a lot of efforts in the EOCA then what would you need to get it working ? I don't have Excel on my computer therefore I haven't been able to test the EOCA. Of course, it's not an expensive software so I can get it if there is a need.

If the screen shot is supposed to show Apollo 7 RDV then something is not right. The phasing burn should occur 3h 20min from liftoff. (It's 26h 14min in the screen shot) also the Delta-Vs makes no sense.
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meik84
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« Reply #22 on: July 04, 2011, 04:11:49 PM »

Quote
Based on my understanding of the RDV you are worrying about the CSI burn far too early. The RDV procedure must take you into a successful RDV with the target regardless of what ever is the initial orbit of the active vehicle.
That's my understanding of this, too. AFAIK the second phasing burn of Apollo 7 was just made because the SIVB didn't behave as expected and the distance between it and the CSM would have been too small. They wanted to have a bigger distance for a meaningfull test.
Quote
I should have enough information to implement the RDV procedure into a MFD but since you are already invested a lot of efforts in the EOCA then what would you need to get it working ?
When those little flaws are eliminated, EOCA will be a fine tool, no doubt. But it fills me with horror when I imagine that sometime later we might use it as a backup during lunar rendezvous: you've got to run the LGC, the AGS and copy around state vectors between orbiter and EOCA. Shocked Furthermore, we will need a orbital calculator for the LOI 2 burn of Apollo 8. Not to talk about the J missions when the CSM will do the DOI burn...
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abr35
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« Reply #23 on: July 04, 2011, 06:35:38 PM »

Being able to calculate the sextant/bore-sight stars for attitude reference would be awesome! I think that's the only part of a P30 PAD we don't have yet. I do have to agree though that having so many tools may become a problem down the line.
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Christophe
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« Reply #24 on: July 05, 2011, 06:36:57 AM »

Hi Jarmo, Meik84, abr35 and all guys!

1/ The position of a spacecraft in some time from present, in a stable way according to the gravity perturbations. Orbit MFD, for example, tell you where you are but not where you will be within one hour, 2 orbits or 2 days later. And situation has not really changed since almost no MFD can do that.
This would have been implemented a long ago if someone would have asked. It's simple, no problem.

Great news! That would be fine, not only for projectApollo, by the way.

2/ The stars in sight in an attitude burn in order to perform the sextant star check in P40/P41.
It's possible to choose a rotation of a vessel around the main axis for a burn. If that is enough then it should be possible to implement this feature.

I was thinking about a feature that could choose the 2 closest stars from the center line of sight of the sextant and then to compute their respective shaft and trunion, assuming that the burn is performed with roll 0°, as it is at usual (it means roughly heads down if the burn is posigrade and heads up if it is retro).
In the case of no stars are in the field view, the roll can be compute easily to “drift” the stars close to the line of sight.

I was asked to look into the RDV and I should have some time for that.

Great news!

I am not exactly familiar with the details of the Apollo 7 mission. But it sounds like you are talking about the -7.5ft/s burn around 00:03:20 GET in a case of Apollo 7. Based on my understanding of the RDV you are worrying about the CSI burn far too early. The RDV procedure must take you into a successful RDV with the target regardless of what ever is the initial orbit of the active vehicle. Therefore, the operation of the RDV procedure can't depend on the burns made before the CSI. Also, the CSI burn isn't a phase sensitive. As far as I understand the main purpose the CSI-CDH burns is to fix the phasing error of the active vehicle respect to the passive vehicle for a proper TPI.
And

If the screen shot is supposed to show Apollo 7 RDV then something is not right. The phasing burn should occur 3h 20min from liftoff. (It's 26h 14min in the screen shot) also the Delta-Vs makes no sense.

I do agree with you except a little bit confusion with the terms used in the EOCA screenshots (I admit that it is not very clear)

The -7.5ft maneuver you are talking about is not the phasing orbit displayed in the EOCA (the line in white). It should be what is called in the spreadsheet as the “initial maneuver” (not shown on the screenshot simply because it wasn’t yet implemented) displayed in orange colour on the graph.
The idea is simply that this (the “initial” maneuver and orbit) is the latest orbit followed by the active vessel before the phasing burn. That maneuver may be the LM DOI for a RDV following a lunar descent abort just before the PDI or, of course, may be a phasing, just like it was done in Apollo 7: the famous -7.5ft burn you are talking about.
I totally agree with you, the CSI/CDH depends only on the final RDV (time and position) you want to do. However, I don’t remember exactly but it seems that 2 types of CSI exist. I have to go in the doc again.
The phasing burn, strictly speaking is the orbit that relies the “initial orbit” and the insertion orbit from which the CSI occurs.
In the case of Apollo 7, this phasing burn was the first SPS burn expected to be performed at 26h24 GET (according to the presskit) and called: Corrective Combination Maneuver.

I should have enough information to implement the RDV procedure into a MFD but since you are already invested a lot of efforts in the EOCA then what would you need to get it working ? I don't have Excel on my computer therefore I haven't been able to test the EOCA. Of course, it's not an expensive software so I can get it if there is a need.

I wonder if it really worth the price of it. As meik84 already said:

When those little flaws are eliminated, EOCA will be a fine tool, no doubt. But it fills me with horror when I imagine that sometime later we might use it as a backup during lunar rendezvous: you've got to run the LGC, the AGS and copy around state vectors between orbiter and EOCA. Shocked Furthermore, we will need a orbital calculator for the LOI 2 burn of Apollo 8. Not to talk about the J missions when the CSM will do the DOI burn...

EOCA has the little advantage to simultate a bit a sort of RTCC at Mission Control Center, but the handling of it is too much heavy. Copying the SV, loading in EOCA, waiting for it to compute is time consuming. If you have it in the future project Apollo package that sim would require 10 people to run: one for the CSM, one for the LM and 8 for EOCA! ROTFL

If you, Jarmo has the time for that kind of effort, my opinion is that the best would be that all the navigation features would be included in IMFD and Apollo MFD.

However, I could continue the development of EOCA for the time interval, at least the RDV feature. 
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jarmonik
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« Reply #25 on: July 05, 2011, 09:35:15 AM »

However, I don't remember exactly but it seems that 2 types of CSI exist. I have to go in the doc again.

Yes, I ended up into the same conclusion a moment ago. It looks like the CSI (e.g. NCC1) burn of Apollo 7 isn't bound by the constraints set for the CSI. For an example one constraint is that the Z component of the delta velocity is zero. (i.e. restricted into a horizontal plane).  Also, It wouldn't be possible to archive that kind of "phasing" orbit (going 20nm below and 50nm above) with the CSI constraints.

The delta velocity for the CSI (NCC1) burn is:
X = 54.8
Y = -1.3
Z = 201.6

Also, it takes about 1h 30min to complete one orbit. If we look at the times of  NCC1, NSR, TPI burns. There seems to be about 360deg difference between the burns which will make the control of NSR position and delta-height problematic.
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Christophe
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« Reply #26 on: July 05, 2011, 10:06:19 AM »

I've just had a further look at my old EOCA and it seems that You were right and that I was wrong: in the Apollo 7 sequence the CSI is what they called as NCC 2 with a nominally delta V 0.

The problem is mainly that Apollo 7 is not a standard RDV as described in some doc. Naming has changed too.
Y'll try to figure out how it works.

Here in the attache a folder I've got with some pdf about RDV.
I guess you already have some but it may help you.

* folder01.zip (15330.5 KB - downloaded 19 times.)
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Christophe
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« Reply #27 on: July 05, 2011, 10:14:07 AM »

And another one...

* folder02.zip (11245.72 KB - downloaded 25 times.)
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jarmonik
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« Reply #28 on: July 05, 2011, 03:27:21 PM »

Thanks about the files and yes, you are right. It looks like the Apollo 7 RDV is a special case. The RDV done with the LM during Apollo 9 flight seems to be a standard RDV procedure like the one with the Apollo 10. The NCC1 burn is a problematic because the NSR burn will be execute about 360 degrees later in the same position in the space as the NCC1, so, how can you change the altitude (delta height) of the NSR with the NCC1 burn. If the difference of NCC1 and NSR is at least 10deg more or less than 360 then it might be enough to place the NSR burn in the right altitude.  It looks like the NCC1 burn is mostly rotating the line of apsides in other words it is changing the LPe.

As you mentioned above the NCC1 is a special burn but the NCC2 is technically the same as the CSI maneuver 120deg before the NSR (i.e. CDH). So, it looks like we have at least two different ways to solve the situation.

A)  Execute NCC1 and then proceed using a standard RDV procedure from NCC2
1. Execute NCC1 at 26:24 GET using External dV (P30) (54.8, -1.3, 201.6)
2. Execute CSI maneuver at 27:30 GET (Nominally zero but will most likely contain a significant dV component due to inaccuracy of NCC1 burn)
3. Execute CDH maneuver around 28:00 GET (dH and exact time will be know after computing the CSI)
4. Execute TPI around 29:22 GET

B)  Creating Apollo 7 specific and standard RDV program.
- Create Apollo 7 specific RDV program to compute NCC1 and NSR maneuvers accurately.
- Create an other program to compute a standard RDV procedure to be used with the other missions.

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Christophe
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« Reply #29 on: July 06, 2011, 03:54:43 PM »


I think you’re right.

. If the difference of NCC1 and NSR is at least 10deg more or less than 360 then it might be enough to place the NSR burn in the right altitude.  It looks like the NCC1 burn is mostly rotating the line of apsides in other words it is changing the LPe.

I didn’t found the parameters of the orbit following the NCC1, so I don’t know its period. But due to the fact that it seems that the Ap is rather high (the CSM overfly the SIVB more than 40 NM above) the period should be quite long, more than 90 min, so you can guess that the travel angle was less than 360° between NCC1 and NSR. In this case, conditions are satisfied for the NCC1 to adjust the Pe to the NSR height. But if I’m sure that the NCC1 shift the Lpe (it is mathematically almost mandatory) I’m not sure that the line of apside of the 2 vessels are aligned at that time. I’d rather think that this was done during the NSR.

As you mentioned above the NCC1 is a special burn but the NCC2 is technically the same as the CSI maneuver 120deg before the NSR (i.e. CDH)
Once again, I have the quite the same conclusion: In my mind the NCC1 places the CSM in the insertion orbit: the orbit from which the CSI occurs if we refer to the standard model. And the NCC2 is the CSI but due to the fact that this RDV is not following a lunar liftoff, there are no constraints about the insertion orbit. So they managed to compute a maneuver, the NCC1, so that the insertion orbit places the CSM in the proper way to directly perform the CDH. The result is that the CSI (NCC2) is nominally 0 and was eventually to be done only to null possible dispersion.

I spent most of the day (while I was at work!!! Embarassed) thinking on this problem and I remember having the same questions 2 years ago while trying to put this feature in EOCA. I remember having concluded that one of the standard maneuver was dropped from the Apollo 7 RDV but which one? By these days I balanced between the CSI, CDH or insertion.
Today I think things are a bit clearer.

B)  Creating Apollo 7 specific and standard RDV program.
- Create Apollo 7 specific RDV program to compute NCC1 and NSR maneuvers accurately.
- Create an other program to compute a standard RDV procedure to be used with the other missions.

May be it’s the solution.
I remember that while building this in EOCA, my goal was to put a feature to be versatile enough to do all the RDV for any mission including the abort procedure that could be made.
That’s the reason why I “started”  the RDV very early, considering the vessel formation flying like the beginning of a lunar descent followed by an abort an a RDV.
That means:
1/ The tgt separation mnvr. The only maneuver allowed by the target (the CSM in a lunar landing) in order to place the target on an equiperiodic orbit with an inward (or outward) delta V.
2/ The “initial” maneuver: nominally the LM DOI
3/ The phasing maneuver: Nominally the LM “go around” just after the decision of abort.
4/ The insertion maneuver: first of the standard RDV sequence.
5/ CSI
6/ CDH
7/ TPI . By the way the TPI is easily feasible with IMFD AFAIR.

Once this is include in the feature, any maneuver can either be programmed or ignored, depending the goal of the user and/or the mission the user is flying.

I don’t know whether this objective is too difficult or not if this is the right method  and even if it’s really possible.
I’m off duty within the next 3 days and I will try to get some result.
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