Card 6t - ORBDEF4 Orbit Parameters for CLASSIC, SUNSYNC, SHUTTLE OR MOLNIYA options

ORBTYPE

ORBTYPE is the flag to specify the type of orbit.

ALTOPT1

ALTOPT1 is the first of two flags necessary to specify the elliptical shape of the orbit.

ALT1

ALT1 is the orbit shape parameter value corresponding to ALTOPT1.

ALTOPT2

ALTOPT2 is the second of two flags necessary to specify the elliptical shape of the orbit.

ALT2

ALT2 is the orbit shape parameter value corresponding to ALTOPT2.

ORBINCL

ORBINCL is the orbit inclination angle in degrees, which is the angle between the North vector and the normal to the orbit plane.

When the orbit is so viewed that the spacecraft travels in the counterclockwise direction, the orbit normal points towards the viewer. If it travels in the clockwise direction, the orbit normal points away from the viewer.

The ascending node is the point in planet’s equatorial plane where the spacecraft crosses the equator moving from South to North.

ORBINCL is positive counterclockwise when looking towards the planet’s center from the orbit ascending node. The orbit ascending node is the point where the orbit crosses the equatorial plane going Northwards. Refer to the diagram in Card 6l - Additional Orbital Parameters ORBADD.

ANGPER

ANGPER is Periapsis angle in degrees, which is the angle in the plane of the spacecraft's orbit between the ascending node and the perigee of the orbit, measured in the direction of motion of the spacecraft.

It is positive in the direction of motion of the spacecraft. Refer to the diagram in Card 6l - Additional Orbital Parameters ORBADD.

ANOPT

ANOPT is the flag specifying the nature of the ascending node value.

If ANOPT = LTIME, ANVAL is the local time value in hours (0-24) at the ascending node position in the orbit.

If ANOPT = LNOON, ANVAL is the angle in degrees of the ascending node from local noon. It is measured in the equatorial plane from the reference line to the ascending node, and is positive in the counterclockwise direction when the equatorial plane is viewed from the North Pole. It is the same as the angle OMEGA on the diagram in Card 6l - Additional Orbital Parameters ORBADD Card.

The reference line is the projection of the sun vector onto the equatorial plane. Refer to the diagram in Card 6l - Additional Orbital Parameters ORBADD Card.

The sun vector points towards the sun. If ANOPT = RAAN, ANVAL is the right ascension angle of the ascending node in degrees. Refer to the diagram in Card 6l - Additional Orbital Parameters ORBADD Card – Optional.

The right ascension angle is the angle measured Eastward from the vernal equinox axis in the Earth's equatorial plane to the ascending node.

The vernal equinox is the time when the apparent position of the sun crosses the equator moving from south to north. The vernal equinox axis is a line from the Earth's center to the point where the sun crosses the equator moving from South to North.

The ascending node is the point in planet’s equatorial plane where the spacecraft crosses the equator moving from South to North.

If ANOPT = LONGAN, ANVAL is the geographic longitude of the ascending node in degrees, measured from the Prime Meridian. The Prime Meridian is the line longitude at which longitude is 0 degrees.

If ANOPT = LONGSAT, then is the longitude of the spacecraft in degrees at the time specified in fields SV1-SV6 of the ORBDEF3 Card. This option is valid only if SOLOPT = GMT on the ORBDEF3 Card.

ANVAL

ANVAL is the ascending node value corresponding to the ANOPT option.

ORBDEF4: Orbit Parameters for BETA option

BETAOPT is the flag specifying the nature of ALRADVAL.

ALRADVAL is the altitude or radius value corresponding to BETAOPT.

BETAANGLE is the beta angle value in degrees. The beta angle is the minimum angle between the orbit plane and the sun vector.

BETAANGLE must be between -90 and +90 degrees.

BETAANGLE > 0 occurs when the spacecraft travels in the counterclockwise direction in its orbit when viewed from the sun, and BETAANGLE < 0 occurs when it travels in the clockwise direction.

ORBDEF4: Orbit Parameters for GEOSYNC option

LONGVALUE is the sub-spacecraft longitude value when SOLOPT = GMT on the ORBDEF3 Card. Otherwise, it should be 0. The rationale for this is that for the geosynchronous option there is no ascending node value, LONGVALUE is used only for the orbital display option.