IMFD IMFD losing reference body

[Andy632]

So I've been trying to follow the Artemis I mission plan and on approach to the Moon (exiting the DRO and getting ready for the perilune burn to get back home), IMFD's map program loses its data on the Moon, displaying as reference only 'Earth (weak)'. I've got my ship about an hour from 80km perilune and still IMFD is giving me nothing; it gives the present position of the Moon but not the hypothetical. I'm fairly sure I've got the program configured correctly.

Could it be something to do with my inbound trajectory, and IMFD is predicting that after perilune (without the burn) my course is going to carry me too far away from the Moon for any relevant data to be displayed?

 

[BrianJ]

Hi Andy,
could you post your scenario? Might be possible to see what's happening with IMFD.
Have you checked your IMFD Map "REF" is "Moon" ? (if not click REF and enter Moon).
Have you tried changing any of the Map config settings : Period Limit / Hyper Limit ?
Cheers,
Brian

 

[Andy632]

Hi Brian, thanks for the reply. I'd read somewhere about the period limit setting and per your suggestion finally found and changed both it and the hyper limit to 'no'. Interesting to see what it does to the map view, great way to learn about orbital mechanics.

There's still an issue with the map program though that I don't understand, which is that sometimes while sharing with delta velocity, it drops the plan as I change the velocity components, returning to display the current trajectory; this can happen even when making the smallest incremental change to say lower the periapsis by a few kilometres. So I revert to transx, do the burn and then sort out the residuals by viewing IMFD map in real time. Perhaps it's a limitation of the MFD or it might be my computer hardware introducing too much lag.



Going a little off topic, I've decided to do a whole re-run of the mission, this time with the powered lunar flybys - it turns out I had an incomplete grasp of the flight plan first time round. This time it's going beautifully, I have the real PeA altitude and MJD and I'm approaching the first flyby. But I don't know the dv components for the flyby burn to DRO altitude. I'm wondering if there's a place this kind of thing can be found, perhaps it'll only emerge in a post-mission report.

 

[BrianJ]

Hi Andy,
one more thought I had re:IMFD DeltaVelocity + Map - have you checked that your planned burn is actually in the future? If the IMFD DeltaVelocity burn countdown goes to 0, the Map no longer shows resultant trajectory (unless burn is in progress).

Have fun with Orion and DRO - I don't know if the flight notes I put in the SLS for Orbiter2016 for EM-1 are any help.
I like to use LagrangeMFD "rotating frame" to plan and visualise the DRO insertion burn.

Cheers,
Brian

 

[Andy632]

Ah! That must be it, thank you. I had thought that when TEj = 0, delta velocity program is just ready for you to do the burn anytime you want, with the ignition time being the current MJD. Perhaps it still means that, but the map program doesn't know it and just assumes the burn though planned never took place.

I didn't know about Lagrange MFD, I'll have to check it out. Just came back to Orbiter this year and really into it this time, probably too much!

 

[Andy632]

I went back to trying this out and was wondering how one actually went about using Lagrange MFD to set up a DRO around the Moon. "Rotating frame" and then?

It's a little difficult trying to find information on DROs that isn't just the basic idea of it. In addition to being high altitude, retrograde etc, could it be said to be an orbit that runs through the L1 and L2 points, hence its stability?

 

[BrianJ]

I went back to trying this out and was wondering how one actually went about using Lagrange MFD to set up a DRO around the Moon. "Rotating frame" and then?

Hi,
its been a while since I tried to get my head around going to a DRO.
I don't know if my "EM-1 Flight Notes.pdf" is any help - attached to this post.
Also, there is this thread: https://www.orbiter-forum.com/threads/target-a-vessel-in-dro-around-moon.36385/
@MontBlanc2012 and @dgatsoulis are probably the guys who have the best handle on this type of thing

It's a little difficult trying to find information on DROs that isn't just the basic idea of it.

More infos:

Degenerate Conic | Distant Retrograde Orbits

degenerateconic.com

http://www.mdpi.com/2226-4310/3/4/37/pdf

In addition to being high altitude, retrograde etc, could it be said to be an orbit that runs through the L1 and L2 points, hence its stability?

I don't think that is correct (but don't take my word for it!)

Cheers,
BrianJ