In MaxQ and in SPICE, the term “Reference Frame” describes a particular orientation (of coordinate system axes). This does not include the spatial position of a coordinate system’s origin, only the orientation.
A majority of the time either an inertial (non-rotating) or rotating (fixed, attached to a body) Reference Frame is used, although there are other types.
A few common reference frames:
|Reference Frame||It is|
|J2000||Aligns XY in Earth’s Equatorial plane, Z: North Pole.
X points to the Sun at J2000 Epoch.
Y = Z x X
Does not rotate with Earth.
|ECLIPJ2000||As above, but aligned to the Ecliptic plane.|
|IAU_EARTH||Normally ITRF93, rotates as if attached to earth|
|IAU_MOON, etc||As above, but for other bodies|
J2000 as a reference frame is related to, but different than the J2000 Ephemeris Time Epoch. J2000 as an epoch is defined as “12:00 Terrestrial Time January 1, 2000”.
J2000 as a reference frame is a coordinate system orientation. It aligns the coordinate system’s Z-axis with Earth’s North Pole and XY plane with Earth’s equator as of the J2000 time Epoch. The X axis points towards the Sun from Earth’s location at the Vernal Equinox.
The J2000 reference is convenient for objects in Earth’s orbit, such as the Hubble Space Telescope. Earth-Centered “Intertial” frames are referred to by the TLA “ECI”.
ELCIPJ2000 is similar to J2000, but aligns the XY plane with the Ecliptic plane.
ECLIPJ2000 is a convenient Reference Frame for objects orbiting the Sun, such a Space Probe traveling through the solar system on its way to Mars.
IAU_EARTH is attached to and rotates with Earth.
IAU_EARTH is a convenient Reference Frame for objects on Earth’s Surface, such as Deep Space Network radio antenna stations. “Earth-centered, Earth-fixed” frames are often referred to as “ECEF” frames. IAU_EARTH is often defined as the ITRF93 frame through kernel FK frame assignments, and often “high precision” binary “PCK” kernels are used to obtain/predict the orientation of this frame with very high precision.