# Reference to understand the notation of orbital charts

To address various orbital evolutions of spacecrafts, some particular orbital charts are taken into account. For example, the following is used to depict how a chaser reaches a target:

The only thing that I know about this notation is its frame definition, based on which +X is the horizontal axis toward left, and +Z is downward. But I have no idea about the rest, say, the curves, their size variations, those black squares, etc.

Does anyone know any reference in which the interpretation of this graphical notation is thoroughly discussed?

• That diagram is cartoonish, perhaps overly so. Commented Jun 8, 2019 at 23:45
• @DavidHammen, perhaps that's because said diagram was used to train flight crew...FYI, they are referred to as "relative motion diagrams", as referenced in Organic Marble's answer (see below). Commented Jun 10, 2019 at 16:08

Since you are specifically asking for a reference, I'll refer you to the Appendices in History of Space Shuttle Rendezvous, where these topics are covered in some detail.

Appendix G describes the relative frame used in the diagram.

Appendix H describes the burn nomenclature (the squares in the picture are burns, and this appendix decodes their names). For example:

NSRn – Slow Rate maneuver places the chaser in a co-elliptic orbit with the target, aligning the lines of apsides of both vehicles. NSR burns can be used to meet lighting requirements on the day of rendezvous.

You can also look at this paper, which plows much of the same ground in less words (it's written by the same guy).

This picture (from the Shuttle Rendezvous Training Manual, sadly not online, although it's where your picture in the question came from originally) tries to show how the relative motion diagram syncs up with an orbital diagram.

• Cool links! factoid: there's a squiggly line in this answer as well.
– uhoh
Commented Jun 8, 2019 at 22:20
• @uhoh those guys loved their squiggly lines, they are on their patch imgur.com/a/URQwzY5 Commented Jun 8, 2019 at 23:03
• googling "rendez-vous, prox-ops training" + "NASA yields all kinds of interesting things!
– uhoh
Commented Jun 9, 2019 at 10:19

To add more information to this thread, this paper (On-Board Rendezvous Targeting for Orion - https://ntrs.nasa.gov/api/citations/20100026547/downloads/20100026547.pdf) provides a slightly more satisfying (at least to me) expansion of the acronyms (NC, NH, NSR, etc.). The N in these acronyms stands for "Nominal."

NSR Nominal Slow Rate (Coelliptic Maneuver)
NPC Nominal Plane Change
NH  Nominal Height Adjust (Altitude Raising Maneuver)
NC  Nominal Catchup (Phasing Maneuver)


I hope this information adds some clarity.

Cheers, Andy

• Originally the N did not stand for Nominal, as explained in Appendix H of the link in my answer. Calling it N-for-Nominal is a backronym. "The names NC , NH , NPC , and NSR represented the Nth crossing of the chaser line of apsides, the point where the burns were typically performed." Commented Feb 1, 2023 at 20:13