In: Physics
For the equations of motion to be correct, the coordinate reference frames must be inertial. Is the geocentric-equatorial coordinate system, commonly used for spacecraft, a truly inertial reference frame? Why or why not? If not, why can we use it?
Geocentric equitorial coordinate system uses the Earth's equitorial plane as the X-Y plane and the north pole of the Earth as the vertical axis.
Origin of the coordinate system is located at the center of the Earth and X-axis is towars the First point of Aries (intersection of Earth,s equitorial plane and the ecliptic plane, also called as vernal equinox).
This coordinate system do not rotate with Earth's rotation, however slowly drifts over time with the motions of precession, which makes it non-inertial.
However, it is the most convenient coordinate system to specify positions of spacecrafts, as it fixed with respect to distant stars. Due to the fact that it is a non-inertial sysytem, equations of motioal get second order changes, which can be corrected by specifying the date (or called as epoch).