What is the Fixed Reference Frame of the Moon?

The default fixed reference frame for the Moon is the MeanEarth reference frame.

Verifying the reference frame
To test which reference frame STK is using, follow these steps:

1. Create a Place object at Geodetic Lat-Lon-Alt = 0-0-0.
2. Create a new custom report style, expand Points Choose System, and select the X, Y and Z data providers, making them the content of the report. 
3. Run this new report and, in the Select System window, filter by Primary Central Bodies. Select the Moon by clicking it, and then select the MeanEarth reference frame and click OK.
4. The result should be 1737.400000, 0.00000, 0.00000 for X, Y, and Z, respectively, where 1737.4 is the radius of the Moon. If the report returns a different result, then you are using a different reference frame than the default.

Changing the default reference frame

1. Open the <STK install folder>\STKData\CentralBodies\Moon\Moon.cb. file. This file is read only for general users, so you need administrator rights to change it.
2. Change the Central Body definition in the Moon.cb file from the MeanEarth reference frame to PrincipalAxes_430. To do this, comment out the MeanEarth line with a # before it and remove the comment marking on the  FixedFrame PrincipalAxes_430 line by deleting the # in front of it. When you are finished, the opening lines of the Moon.cb file should appear as illustrated below:

BEGIN   Moon   #FixedFrame                     MeanEarth   # By default, the Fixed frame for the Moon is the MeanEarth (ME) frame. # Previous to STK 9 and ODTK 6, the Fixed frame for the Moon was defined by # the PrincipalAxes_403 frame if the user was using the DE 403 or DE 405 file # or by Analytic if using the DE 200 file.  You can uncomment a line below # to set the Fixed frame to another frame.   # The Fixed_IAU2003 frame uses the RotationDefinitionFile MoonAttitude2000.rot   # FixedFrame                    Fixed_IAU2003 # FixedFrame                    Fixed_NoLibration # FixedFrame                    PrincipalAxes_403 # FixedFrame                    PrincipalAxes_418 # FixedFrame                    PrincipalAxes_421 FixedFrame                        PrincipalAxes_430

4. Close STK, verify that there are no processes left running, and then restart STK.
5. With the changed Fixed-frame Moon (430) reference frame, regenerate the report that you created in the first section of this article, using PrincipalAxes_430 as the reference frame. You should get 1737.400000, 0.000000, 0.000000, and for MeanEarth you will now get 1737.399780, 0.570560, -0.662286.