Card 6d - Earth

This optional card specifies the parameters and options for Earth view factor and albedo factor calculations.

Parameters: L, HR, ALB, THETAE, PHIE, TIME, PIR, PIRSUBSOLAR

L

L calculates albedo factor and Earth view factor.

  • L = EARTHN (or 12) computes albedo factor and Earth view factor with no shadowing.
  • L = EARTHS (or 13) computes albedo factor and Earth view factor with shadowing.

HR

HR is the H/R value, where H is the distance from the origin to the Earth's center, and R is the Earth's radius. The Earth's radius is equal to 3441 nautical miles, 3963 miles, or 6378 km.

ALB

ALB is the albedo value, typically 0.35. Albedo is the solar reflectivity (1–absorptivity) of the Earth.

If ALB = 0, no albedo factors or Earth view factors will be calculated, and the Earth cards will be used for solar eclipse calculations only.

THETAE

THETAE is the angle in degrees the Earth vector makes with the Z axis. The Earth vector is a unit vector at the origin pointing towards the center of the Earth.

PHIE

PHIE is the angle in degrees the projection of the Earth vector on the XY plane makes with the X axis (positive CCW).

TIME

TIME is the time at which the Earth's position is defined by the Earth card. TIME can be blank, or the flag CONSTANT.

PIR

PIR is optional, it defines the heat load per unit area leaving the planet. PIR overrides the Card 2a default PIR value. If PIR is blank, the Card 2a PIR value will be used.

PIRSUBSOLAR

PIRSUBSOLAR is optional, it defines the ratio of the IR emissive power of a planet at its subsolar point to its IR emissive power on the side opposite to the subsolar point. Alternatively, the PIRSUBSOLAR value can be defined on the Card 9 PARAM PIRSUBSOLAR Card. If neither is present, PIRSUBSOLAR = PIR will be used.

Code example

In this example, solar view factor, albedo factor, and Earth view factor calculations will be performed for all the elements TIME = 8.


 SOLSALL 0 30.0 40.0 8.0
 EARTHS 1.1 .35 20.0 30.0 8.0

Notes

The Earth Card defines the position and albedo of the Earth at a particular TIME. It is used for albedo factor, Earth view factor, and solar eclipse calculations. These are performed only for those elements that appear on Solar View Factor Request Cards 6b with the same TIME parameters as on the Earth Card. An Earth Card without a corresponding Solar View Factor Request Card will be ignored.

Earth is modeled with its center at a distance of .8E6 from the origin, with a radius of .8E6/HR.