<p>I'd like to start by quoting from the Wiki page on Nodal Precession you mentioned: </p>

<blockquote>
  <p>A non-rotating body of planetary scale or larger would be pulled by
  gravity into a sphere. Virtually all bodies rotate, however. The
  centrifugal force deforms the body so that it has an equatorial bulge.
  Because of the bulge the <strong>gravitational force on the satellite is not
  directly toward the center of the central body, but is offset toward
  the equator</strong>. Whichever hemisphere the satellite is in it is
  preferentially pulled slightly toward the equator. This creates a
  torque on the orbit. This torque does not reduce the inclination;
  rather, it causes a torque-induced gyroscopic precession, which causes
  the orbital nodes to drift with time.   </p>
</blockquote>

<p>(emphasis mine).  Note that this is a small force and the precession is slow compared with orbital speeds.  Precession towards (or coasting away from) the equator thus is a change in latitude compared with what would be expected, and this "twist" changes the expected longitude at a given point in time because the satellite's vector velocity changes (I believe in both direction and magnitude, but I'm not certain about the magnitude). </p>

CC BY-SA 4.0
2019-08-10T11:22:57.433Z
I'm pretty sure that only the direction changes, not the magnitude, since that would change the period of the orbit.
PM 2Ring
CC BY-SA 4.0
2019-06-11T17:55:50.690Z
2019-06-11T17:55:50.690Z
Carl Witthoft
<p>I've read that you can change the longitude of ascending node of a satellite (i.e. changing the orbital plane without changing the inclination) to change its orbital plane by using the torque imparted by the oblateness of Earth. How does this happen exactly? I mean how does the oblateness of Earth cause a <a href="https://en.m.wikipedia.org/wiki/Precession#Classical_(Newtonian)" rel="nofollow noreferrer">torque induced precession</a> of a satellite?</p>

<p>PS. I think I don't understand how torque induced precession works and that's why I am not able to understand this. So if any of you kind gentlefolk are willing to explain, I thank you in advance.</p>

<p>EDIT: I just came across <a href="https://en.wikipedia.org/wiki/Nodal_precession" rel="nofollow noreferrer">Nodal Precession</a>. And from what I understood that due to Earth's equatorial bulge, the gravitational force vector is offset from its center, thus producing torque. I can visualize how the longitude of ascending node will change, but can't visualise how will the change in the torque caused by slightly offset gravitational force vector will cause it.</p>

<orbit><orbital-mechanics><precession>
How can the oblateness of Earth impart torque to change the longitude of ascending node of a satellite?
TheReal_Skywalker
# How can the oblateness of Earth impart torque to change the longitude of ascending node of a satellite?

(Asked by: username_0 on 2019-06-11)

I've read that you can change the longitude of ascending node of a satellite (i.e. changing the orbital plane without changing the inclination) to change its orbital plane by using the torque imparted by the oblateness of Earth. How does this happen exactly? I mean how does the oblateness of Earth cause a [torque induced precession](https://en.m.wikipedia.org/wiki/Precession#Classical_(Newtonian)) of a satellite?

PS. I think I don't understand how torque induced precession works and that's why I am not able to understand this. So if any of you kind gentlefolk are willing to explain, I thank you in advance.

EDIT: I just came across [Nodal Precession](https://en.wikipedia.org/wiki/Nodal_precession). And from what I understood that due to Earth's equatorial bulge, the gravitational force vector is offset from its center, thus producing torque. I can visualize how the longitude of ascending node will change, but can't visualise how will the change in the torque caused by slightly offset gravitational force vector will cause it.

**Tags:** orbit, orbital-mechanics, precession


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## 1 answers

### Answer by username_1 on 2019-06-11. Score: 1 | Accepted answer

I'd like to start by quoting from the Wiki page on Nodal Precession you mentioned:

> A non-rotating body of planetary scale or larger would be pulled by
> gravity into a sphere. Virtually all bodies rotate, however. The
> centrifugal force deforms the body so that it has an equatorial bulge.
> Because of the bulge the **gravitational force on the satellite is not
> directly toward the center of the central body, but is offset toward
> the equator**. Whichever hemisphere the satellite is in it is
> preferentially pulled slightly toward the equator. This creates a
> torque on the orbit. This torque does not reduce the inclination;
> rather, it causes a torque-induced gyroscopic precession, which causes
> the orbital nodes to drift with time.

(emphasis mine). Note that this is a small force and the precession is slow compared with orbital speeds. Precession towards (or coasting away from) the equator thus is a change in latitude compared with what would be expected, and this "twist" changes the expected longitude at a given point in time because the satellite's vector velocity changes (I believe in both direction and magnitude, but I'm not certain about the magnitude).

> **Comments:**
> **username_2**: I'm pretty sure that only the direction changes, not the magnitude, since that would change the period of the orbit.  

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