# How are orbit insertion changes in altitude and RAAN designed?

Assuming that desired inclination is achieved during the launch, how are the target altitude and RAAN usually achieved in satellite missions, if the launch could only place the satellite on a different orbit?

I understand that any change plane is cheaper at apoapsis, and that a change in RAAN without changing the inclination is only achievable at 90 degrees anomaly from the line of apses. I also believe that oftentimes the satellites are taken to much higher orbits (via Hohmann? Lambert?) where the plane change is cheaper, and then taken down to the desired orbit in a combined maneuver sequence.

Even if circular orbits were assumed, there seem to be a lot of different possible combinations.

How is this problem usually approached in preliminary mission design?

## 1 Answer

Altitude is usually via a burn at the apogee/ perigee, as you mentioned.

RAAN changes are usually done over time. If you are slightly over or under your target orbit, your RAAN will drift over time. This may take weeks to months, but you will eventually get there, without the expenditure of a lot of fuel.

Of some note is that there are some orbits that don't appear to have an RAAN drift, like sun-synchronous orbits. Those orbits actually require a specific altitude to achieve that no drift state, and thus if they are higher/ lower, they will actually still drift with time.

• How about orbits with no RAAN drift? Or a constellation where you need to fix the RAAN of only one satellite with respect to the others? I assume in those cases, if your launch doesn't place you at the right RAAN, you need to actively fix that Jun 4, 2020 at 11:55
• There is not an inclination that has no RAAN drift, you have to have an altitude and an inclination be in perfect sync to achieve no RAAN drift. Jun 4, 2020 at 12:21
• I see. What I was thinking about when I said "no drift" are Sun-synchronous orbits (I was wrong, they do drift, of course...), where you want a fixed RAAN or LTAN, since drifting it will always keep it in the wrong place with respect to the Sun. How would you correct the RAAN in such case? Jun 4, 2020 at 12:50
• Sun sychronous is only stable in RAAN at a given altitude for the inclination. See en.wikipedia.org/wiki/Sun-synchronous_orbit#Technical_details Jun 4, 2020 at 12:52
• Both of them can be changed in the same way. Jun 4, 2020 at 14:30