Card 6t - ORBDEF2 Planet Parameters

This optional card defines the planet parameters for a spacecraft orbit.

Parameter Value Description
ORBDEF2 ORBDEF2 or 42 Mnemonic
ID integer ID number
PLPERIOD real Planet period value
STATIONARY The planet does not rotate
PLRADIUS real Planet radius value
PLGRAV real Planet gravity constant value
PLIRFLAG OFF Planet albedo and IR radiation are not calculated
ON Planet albedo and IR radiation are calculated
ALB real Albedo value. Alternatively, ALB may be of the form Tn, where n is a table number, referencing a TABTYPE Card, or an array number, referencing an ARRAYTYPE Card. The dependent variable on the TABTYPE Card must be ALBEDO, and the independent variable LATITUDE, LONGITUDE, or TIME. The dependent variable on the ARRAYTYPE> Card must be ALBEDO, and the independent variables LATITUDE and LONGITUDE. Latitude and longitude must be defined in degrees. If a table is specified, the Card 9 PARAM EXEARTH flag must also be set.
IROPT1 FLUX Sunlight side planet IR radiation is specified as flux
TEMP Sunlight side planet IR radiation is specified as temperature
IRVAL1 real Sunlight side planet IR radiation value. Alternatively, if IROPT1 is set to FLUX, IRVAL1 may be of the form Tn, where n is a table number, referencing a TABTYPE Card, or an array number, referencing an ARRAYTYPE Card. The dependent variable on the TABTYPE Card must be PIR, and the independent variable LATITUDE, LONGITUDE, or TIME. The dependent variable on the ARRAYTYPE Card must be PIR, and the independent variables LATITUDE and LONGITUDE. Latitude and longitude must be defined in degrees.
IROPT2 FLUX Dark side planet IR radiation is specified as flux
TEMP Dark side planet radiation is specified as temperature
IRVAL2 real Dark side planet IR radiation value. Alternatively, if IROPT2 is set to FLUX, IRVAL2 may be of the form Tn, where n is a table number, referencing a TABTYPE Card, or an array number, referencing an ARRAYTYPE Card. The dependent variable on the TABTYPE Card must be PIR, and the independent variable LATITUDE, LONGITUDE, or TIME. The dependent variable on the ARRAYTYPE Card must be PIR, and the independent variables LATITUDE and LONGITUDE. Latitude and longitude must be defined in degrees.
IROPT3 LN Local noon is the longitude from which the prime meridian for the selected celestial body is referenced
ME March equinox is the longitude from which the prime meridian for the selected celestial body is referenced
AN Ascending node is the longitude from which the prime meridian for the selected celestial body is referenced
IRVAL3 real Angle from the reference longitude to the prime meridian
IROPT4 CCW Counterclockwise rotation orientation for the generic planet
CW Clockwise rotation orientation for the generic planet

PLPERIOD

PLPERIOD is the period of the planet's rotation, i.e., the time in seconds for a complete rotation around its axis of rotation. For Earth, this value is 86400 seconds. If you set PLPERIOD to STATIONARY, the planet does not rotate.

PLRADIUS

PLRADIUS is the planet radius value. For Earth, this value is 6370.32 km.

PLGRAV

PLGRAV is the planet surface gravity value. For Earth, this value is 9.81 m/s².

PLIRFLAG

PLIRFLAG is the flag to indicate whether the planet IR and albedo are to be calculated or not.

ALB

ALB is the planet albedo value. For Earth, the average value is 0.3.

IROPT1

IROPT1 is the flag to specify how the planet IR radiation value is specified (flux or temperature).

IRVAL1

IRVAL1 is the IR radiation value (in flux or temperature units) for the sunlight side of the planet.

IROPT2

IROPT2 is the flag to specify how the planet IR radiation value is specified for the dark side of the planet (flux or temperature).

IRVAL2

IRVAL2 is the IR radiation value (in flux or temperature units) for the dark side of the planet. The interpolation between the dark and sunlight side is done according to the algorithm described on the Card 9 PARAM PIRSUBSOLAR Card.

IROPT3

IROPT3 is the flag to specify the longitude from which the prime meridian for the selected celestial body is referenced.

IRVAL3

IRVAL3 is the angle from the reference longitude defined by IROPT3 to the prime meridian. The angle should be between 0 and 360 degrees, and it is measured counterclockwise.

IROPT4

IROPT4 is the flag to specify the generic planet rotation for longitude-dependent calculations.

Notes

All fields are required on all the Cards, except for the FRONTGRP and REVGRP on ORBDEF1, which may be blank. If the value in a field is to be ignored, specify 0.

A simpler alternate method is available in Cards 6k and 6l.

It is helpful to reference the diagram in Card 6l - Additional Orbital Parameters ORBADD when perusing these cards.

ID is the orbit and attitude modeling request number. ID is an integer value common to all associated ORBDEF Cards.

For the Sun Planet Vector orbit type, the independent variable can only be time. It cannot be longitude and/or latitude.