Orbit Reference Frames

•Earth Frames:

oInternational Celestial Reference System (ICRF)

oMean of J2000 Earth Equator

oMean of J2000 Earth Ecliptic

oCelestial Intermediate Reference Frame (CIRF)

oEarth Fixed

oTrue of Date Earth Equator

oTrue Equator Mean Equinox

oLocal Coordinates - Longitude

oLocal Coordinates - Longitude/Latitude

oMean of Date Earth Equator

oMean of 1950 Earth Equator

oTrue of Date Rotating

•Moon Frames:

oMoon Principal Axis - Inertial at J2000

oMoon Fixed (Principal Axis Rotating)

oMoon Principal Axis - Inertial at Epoch

oMoon Mean Earth - Rotating

oMoon Mean Earth - Inertial at J2000

oMoon Mean Earth - Inertial at Epoch

•Generic CelestialObject Frames:

oInertial Equatorial J2000

oBody Fixed

oInertial Equatorial At Epoch

•Axes: The directions of the axes are fixed with respect to a set of extragalactic objects. The celestial reference system is constructed such that its principal plane is as close as possible to the Mean of J2000 Earth Equator and that the origin of the principal plane should be as close as possible to the dynamical equinox of J2000.

•Origin: Spacecraft's Central Body

•Default reference frame.

•Inertial frame.

•This is the principal coordinate system used for computations in FreeFlyer.

1."IERS Conventions 2010," Luzum, B., & Petit, G., IERS Technical Note No. 36 (2010)

•Z-axis: Vector normal to the mean equatorial plane at Julian year 2000.0, pointing towards the Northern Hemisphere

•X-axis: Vector pointing from the center of the Earth to the mean vernal equinox at Julian year 2000.0

•Y-axis: Vector perpendicular to the x- and z-axes, forming a right-handed coordinate system

•Origin: Center of the Earth

•Inertial frame.

•Z-axis: Vector normal to the ecliptic plane at Julian year 2000.0, pointing toward the Northern Hemisphere

•X-axis: Vector pointing from the center of the Earth to the mean vernal equinox at Julian year 2000.0

•Y-axis: Vector perpendicular to the x- and z- axes, forming a right-handed coordinate system

•Origin: Center of the Earth

•Inertial frame.

•Z-axis: Celestial Intermediate Pole (CIP)

•X-axis: Celestial Intermediate Origin (CIO)

•Y-axis: Vector perpendicular to the x- and z- axes, forming a right-handed coordinate system

•Origin: Spacecraft's Central Body

•Non-rotating frame

•Z-axis: Points toward the true rotation axis at the current epoch

•X-axis: Vector from the center of the Earth to the intersection of the prime meridian with the true equatorial plane

•Y-axis: Vector perpendicular to the x- and z- axes, forming a right-handed coordinate system

•Origin: Center of the Earth

•Rotating frame.

•The Earth Fixed reference frame will also include polar motion effects if enabled:

•If polar motion modeling is not enabled, the Earth Fixed reference frame is equivalent to the True of Date Rotating reference frame (commonly known as Terrestrial Intermediate Reference Frame).

•Z-axis: Points toward the true rotation axis at the current epoch

•X-axis: Points toward the true vernal equinox at the current epoch

•Y-axis: Vector perpendicular to the x- and z- axes, forming a right-handed coordinate system

•Origin: Center of the Earth

•Directions of the coordinate system axes are time dependent

•The "true" reference frames include nutation and precession effects. The user can control when the nutation and precession matrices are updated using the FF_SolarSystem.CIRFEvaluationMode property (available only in the FF_SolarSystem object dialog).

•Z-axis: Points toward the true rotation axis at the current epoch

•X-axis: Points toward the mean vernal equinox at the current epoch

•Y-axis: Vector perpendicular to the x- and z-axes, forming a right-handed coordinate system

•Origin: Center of the Earth

•Z-axis: Points toward the true rotation axis at the reference epoch

•X-axis: Lies in the true equatorial plane at the reference epoch, pointing from the center of the Earth to the reference longitude (usually the longitude of the launch site)

•Y-axis: Vector perpendicular to the x- and z- axes, forming a right-handed coordinate system

•Origin: Center of the Earth

•Launch vehicle trajectory can be designed without regard to launch time and date

•In FreeFlyer 6.6 and earlier, this reference frame was referred to as "Launch Coordinates"

•Z-axis: Points from the center of the Earth to the reference longitude and geodetic latitude

•X-axis: Lies in the true equatorial plane at the reference epoch

•Y-axis: Vector perpendicular to the x- and z- axes, forming a right-handed coordinate system

•Origin: Center of the Earth

•Launch vehicle trajectory can be designed without regard to launch time and date

•In FreeFlyer 6.6 and earlier, this reference frame was referred to as "UVW Coordinates"

•Z-axis: Vector normal to the mean equatorial plane at the current epoch

•X-axis: Vector pointing from the center of the Earth to the mean vernal equinox at the current epoch

•Y-axis: Vector perpendicular to the x- and z-axes, forming a right-handed coordinate system

•Origin: Center of the Earth

•Z-axis: Vector normal to the mean equatorial plane at 12:00:00 on January 1, 1950

•X-axis: Vector pointing from the center of the Earth to the mean vernal equinox at 12:00:00 on January 1, 1950

•Y-axis: Vector perpendicular to the x- and z-axes, forming a right-handed coordinate system

•Origin: Center of the Earth

•Z-axis: Celestial Intermediate Pole (CIP)

•X-axis: Terrestrial Intermediate Origin (TIO)

•Y-axis: Vector perpendicular to the x- and z- axes, forming a right-handed coordinate system

•Origin: Spacecraft's Central Body

•Rotating frame.

•This is nearly equivalent to the Earth Fixed reference frame, but does not include polar motion effects.

•Commonly referred to as Terrestrial Intermediate Reference Frame (TIRF)

•The Moon PA frame evaluated at the J2000 epoch (Jan 01 2000 12:00:00.000 TDB). The frame is treated as stationary at the J2000 epoch and is not rotating.

•Origin: Center of the Moon

•Default reference frame.

•Inertial frame.

•The rotating Moon PA (Principal Axis) frame, as defined by the JPL planetary ephemeris.

•Origin: Center of the Moon

•Rotating frame.

•The Moon ME frame has a constant rotational offset with respect to the Moon PA frame. The rotational offset is defined in the JPL planetary ephemeris.

•This frame is based on the lunar principal axes, and differs from the Moon ME frame by about 1 km at the lunar surface.

•The Moon PA frame evaluated at a user-specified epoch. The frame is treated as stationary at the specified epoch and is not rotating.

•Origin: Center of the Moon

•Inertial frame.

•The rotating Moon ME (Mean Earth) frame, as defined by the JPL planetary ephemeris.

•Origin: Center of the Moon

•Rotating frame.

•The Moon ME frame has a constant rotational offset with respect to the Moon PA frame. The rotational offset is defined in the JPL planetary ephemeris.

•The Moon ME frame differs from the Moon PA frame by about 1 km at the lunar surface.

•The Moon ME frame evaluated at the J2000 epoch (Jan 01 2000 12:00:00.000 TDB). The frame is treated as stationary at the J2000 epoch and is not rotating.

•Origin: Center of the Moon

•Inertial frame.

•The Moon ME frame evaluated at a user-specified epoch. The frame is treated as stationary at the specified epoch and is not rotating.

•Origin: Center of the Moon

•Inertial frame.

•The CelestialObject body frame evaluated at the J2000 epoch (Jan 01 2000 12:00:00.000 TDB). The frame is treated as stationary at the J2000 epoch and is not rotating.

oFor the Earth, this maps to the ICRF frame.

oFor the Moon, this maps to the Moon PA - Inertial at J2000 frame.

oFor other CelestialObjects, this is defined based on the IAU/IAG Attitude model for that body.

•Origin: Center of the CelestialObject

•Default reference frame.

•Inertial frame.

•The identifier for this frame can be accessed using the syntax shown below. See the Celestial Object Reference Frame IDs summary for more information.

•The rotating CelestialObject body-fixed frame for the specified CelestialObject.

oFor the Earth, this maps to the Earth-Fixed frame.

oFor the Moon, this maps to the Moon-Fixed (Principal Axis rotating) frame.

oFor other CelestialObjects, this is defined based on the IAU/IAG Attitude model for that body. See the Modeling Solar System Objects section of the Solar System page for more information.

•Origin: Center of the CelestialObject

•Rotating frame.

•The identifier for this frame can be accessed using the syntax shown below. See the Celestial Object Reference Frame IDs summary for more information.

•The CelestialObject body frame evaluated at a user-specified epoch. The frame is treated as stationary at the specified epoch and is not rotating.

oFor the Earth, this frame is defined based on the Earth-Fixed frame, "inertialized" (not rotating) at the specified epoch.

oFor the Moon, this maps to the Moon PA - Inertial at Epoch frame.

oFor other CelestialObjects, this is defined based on the IAU/IAG Attitude model for that body.

•Origin: Center of the CelestialObject

•Inertial frame.

•The identifier for this frame can be accessed using the syntax shown below. See the Celestial Object Reference Frame IDs summary for more information.