Dear all,

I am trying to estimate during a batch-least square over a series of position and velocity measurements the empirical accelerations one-cycle-per-rev (CRP) in radial, along-track and cross-track directions, for example for radial direction it would be:

Empirical_acceleration_R = a0 + a1 * cos(argument_of_latitude) + a2 * sin(argument_of_latitude)

I am not sure which AccelerationModel (HarmonicAccelerationModel or PolynomialAccelerationModel) to use to estimate the three parameters a0, a1, a2 per direction.

So far, this is what I was doing for example for the radial R direction constant term a0:

`AttitudeProvider attitudeProvider = new LofOffset(referenceSpacecraftState.getFrame(), LOFType.NTW);`

```
AccelerationModel a0 = new PolynomialAccelerationModel("aR_0", null, 0);
propagatorBuilder.addForceModel(new ParametricAcceleration(Vector3D.PLUS_I, attitudeProvider, a0));
```

In order to estimate also the coefficients a1 and a2 of the other two trigonometric terms, should I use the HarmonicAccelerationModel?

Is it fine to pass just once at the beginning the attitude provider instantiated with the initial (or reference) state? Are the proper radial, along-and cross-track directions then computed correctly at each epoch along the orbit?

Many thanks for your help.

Best regards.