I am doing North-South manuever for GEO satellite. My purpose is to reduce the inclination. My initial inclination is 0.07 deg, and my target inclination is 0.0002 deg. I have tried the maneuver in GMAT. I tried to do maneuver in ascending node and descending node. Both of them seems work. But I still confused, should I do the maneuver in the ascending node or descending node? Thank you.

  • 3
    $\begingroup$ the node closest to apogee should be more fuel efficient, but both will work $\endgroup$
    – user20636
    Mar 21, 2020 at 14:41
  • $\begingroup$ thank you very much for your answer. I found the value of dV (deltaVelocity) was a little different between both of the node. Now, I understand the reason. Thank you. $\endgroup$ Mar 21, 2020 at 14:56
  • $\begingroup$ It's always okay to answer your own question. If you think you have a solution I'd say go ahead and write it up as an answer. That way future readers will benefit. $\endgroup$
    – uhoh
    Apr 4, 2021 at 22:14

2 Answers 2


Although it has been already answered briefly, I would like to add some extra information (increasing the inclination) about on the N/S maneuvers.

Well the location of the thruster firing is highly depends on the maneuver type. If the maneuver is:

  • North, then you should fire your thrusters while the satellite passes from ascending node in order to do more efficient maneuver. Since satellite already starts to ascending, less fuel will be used.

If it is:

  • South, then you should fire your thrusters while the satellite passes from descending node in order to do more efficient maneuver. Since satellite already starts to descending, less fuel will be used.

Basically with this approach, you will not waste your fuel and you let part of the job to do by orbital mechanics (celestial mechanics).

  • $\begingroup$ Hmm... this is interesting but is it true? Can this be supported with links or sources or mathematics? Thanks! $\endgroup$
    – uhoh
    Apr 4, 2021 at 12:30
  • 1
    $\begingroup$ It's definitely not true in the case of the maneuver the asker wants: to decrease orbital inclination. Burning north at the ascending node, or south at the descending node will increase orbital inclination. $\endgroup$
    – notovny
    Apr 4, 2021 at 12:43
  • $\begingroup$ Well yes you are right! I just wanted to add extra information about the N/S maneuvers. But question is emphasizes to reduce inclination, so the most efficient time to perform maneuver where the satellite is slowest. Thus the place needs to be close as much to apogee. $\endgroup$ Apr 4, 2021 at 13:01
  • $\begingroup$ The problem probably refers to a circular orbit, so there won't be an apogee. $\endgroup$
    – uhoh
    Apr 4, 2021 at 22:13
  • $\begingroup$ There is no perfect circular orbit (even though the GEO satellites are have an eccentricity like 0.00000xxx) in the universe. I know it is very close to "0" but it is NOT "0". So even the GEO satellites are have apogee and perigee. Of course it is up to you to add this very small eccentricity in your calculations but it is highly depends on your mission and wanted resolution. For example T4A has the 35781 km perigee and 35808 km apogee even it is a GEO satellite that I worked with. In our case it was very crucial to add those numbers into our calculations. $\endgroup$ Apr 5, 2021 at 5:54

You can get the same efficiency in the ascending or descending node, it's just that you would need to apply the force in the opposite position if you wanted to switch from ascending to descending and vise versa.

  • $\begingroup$ This seems like the right answer to me; the definition of which node is ascending and which is descending is arbitrary; in this problem there's complete symmetry about the equator. $\endgroup$
    – uhoh
    Apr 6, 2021 at 22:49

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