Coordinate Systems for ACE

A good description of how to make transformations between the different coordinate systems can be found in a paper by M. A. Hapgood, "Space physics coordinate transformations: A user guide", in Planetary and Space Science, Vol. 40, No. 5, pp. 711-717, 1992.

J2000 GCI

Geocentric inertial reference frame using the Julian Epoch of Jan. 1, 2000.
At the Julian Epoch,
X = First point of Aries (Vernal Equinox, i.e. from Earth to the Sun in the first day of Spring)
Z = Earth's mean spin axis

RTN - Radial Tangential Normal

Spacecraft centered coordinate system.
R = Sun to Spacecraft unit vector
T = (Omega x R) / | (Omega x R) |
where Omega is Sun's spin axis (in J2000 GCI)
N completes the right-handed triad

GSE - Geocentric Solar Ecliptic

X = Earth-Sun Line
Z = Ecliptic North Pole

GSM - Geocentric Solar Magnetospheric

X = Earth-Sun Line
Z = Projection of dipole axis on GSE YZ plane

HSEa - Heliocentric Solar Ecliptic (Inertial)

X = First poin tof Aries (Vernal Equinox, i.e. to the Sun from Earth in the first day of Spring)
Z = Ecliptic North Pole

HSEb - Heliocentric Solar Ecliptic (Earth Oriented)

X = Sun-Earth Line
Z = Ecliptic North Pole

HS - Heliocentric Solar

X = Intersection between solar equator and solar central meridian as seen from Earth
Z = North Pole of solar rotation axis

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Last Updated: Sep 15, 1998

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