Spacecraft.PercentShadow(Variable) Method

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Description

Returns a numerical value representing the percentage-of-shadow the Spacecraft encounters in its orbit with respect to a specified CelestialObject's shadow. The calculation is based on percentage of shadow the Spacecraft encounters during penetration into the penumbral region. Once into the umbral region the percentage of shadow is 100%.

 

The three regions of the specified CelestialObject's shadow, the umbra, penumbra, and annular, are shown in the image below.  This method returns 100% when the Spacecraft is in the umbral shadow region, and 0% when the Spacecraft is in direct sunlight.

 

The three regions of a celestial body's shadow.

The three regions of a celestial body's shadow.

 

FreeFlyer's percent shadow calculation calculates percentage-of-shadow based on the area of the solar disk that can be seen by the Spacecraft.  The calculation is based on the following formulas:

 

                                                                                    (1)

                                                                                                                                    (2)

                                                                                                                                        (2)

 

 

Where:

= The percentage-of-shadow

= The apparent angular radius of the Sun, in radians

= The apparent angular radius of the occulting body, in radians

= The apparent angular separation of the centers of both bodies, in radians

 

 

(1) Equation 3.92, Page 83 of Montenbruck, Oliver and Gill, Eberhard, Satellite Orbits: Models, Methods, and Applications, Springer-Verlag Berlin Heidelberg 2000, Corrected 4th printing 2012

(3) Equation 3.93, Page 83 of Montenbruck, Oliver and Gill, Eberhard, Satellite Orbits: Models, Methods, and Applications, Springer-Verlag Berlin Heidelberg 2000, Corrected 4th printing 2012

 

Timing Precision Mode

This page describes functionality in millisecond timing precision mode. Millisecond timing precision mode is deprecated and will be removed in a future release. We recommend that you migrate your Mission Plans to nanosecond timing precision mode.

Click here to see the documentation for this object in nanosecond timing precision mode.

 

Method Signature

Spacecraft.PercentShadow(

Variable bodyID)

 

 

Arguments

bodyID

Description:

The id of the shadow body (either a pre-defined planet or user-defined CelestialBody) that may cast a shadow onto the Spacecraft. Body ID's 1-11 are assigned to the default Solar System objects, as shown below. Custom CelestialObjects will have body ID's starting at 12 and assigned in the order they are created.

Valid Range:

0 ≤ bodyID ≤ 281475000000000

Valid Values:

Celestial Object

Value

Mercury

Mercury.BodyID or 1

Venus

Venus.BodyID or 2

Earth

Earth.BodyID or 3

Mars

Mars.BodyID or 4

Jupiter

Jupiter.BodyID or 5

Saturn

Saturn.BodyID or 6

Uranus

Uranus.BodyID or 7

Neptune

Neptune.BodyID or 8

Pluto

Pluto.BodyID or 9

Moon

Moon.BodyID or 10

Sun

Sun.BodyID or 11

<Custom CelestialBody>

<Custom CelestialBody>.BodyID, starting at 12 and assigned in the order the custom CelestialObjects are created.

 

 

 

 

Return Value

Type:

number

 

 

Returns a numerical value representing the percentage-of-shadow the Spacecraft encounters in its orbit with respect to the specified CelestialObject's shadow.

 

Syntax

myVariable1 = mySpacecraft1.PercentShadow(myVariable2);

 

 

Example 1

This example demonstrates how to generate a report of a Spacecraft's passes through the shadow of a specified Central Body.

 

Spacecraft Spacecraft1;

 

Spacecraft1.Propagator.StepSize = TIMESPAN(1 seconds);

 

Step Spacecraft1 to (Spacecraft1.Epoch == "Jan 01 2020 00:06:55.000".ParseCalendarDate());

 

While (SC1.ElapsedTime < TIMESPAN(5 minutes));

 Report SC1.ConvertToCalendarDate(), SC1.PercentShadow(Earth.BodyID), SC1.PercentShadow(Moon.BodyID);

 Step SC1;

End;

 

 

Output:

 

SC1.ConvertToCalendarDate()

SC1.PercentShadow(Earth.BodyID)

SC1.PercentShadow(Moon.BodyID)

Jan 01 2020 00:06:55.000000000

Jan 01 2020 00:06:56.000000000

Jan 01 2020 00:06:57.000000000

Jan 01 2020 00:06:58.000000000

Jan 01 2020 00:06:59.000000000

Jan 01 2020 00:07:00.000000000

Jan 01 2020 00:07:01.000000000

Jan 01 2020 00:07:02.000000000

Jan 01 2020 00:07:03.000000000

Jan 01 2020 00:07:04.000000000

Jan 01 2020 00:07:05.000000000

Jan 01 2020 00:07:06.000000000

Jan 01 2020 00:07:07.000000000

Jan 01 2020 00:07:08.000000000

Jan 01 2020 00:07:09.000000000

100.000000000

100.000000000

96.020453805

87.304706783

76.399259848

64.236726691

51.462938425

38.629180358

26.278294165

15.023790236

 5.699908090

 0.062409792

 0.000000000

 0.000000000

 0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

0.000000000

 

 

 

See also

Spacecraft Object

Spacecraft.PercentShadow

Spacecraft Propagation Guide

Coverage and Contact Analysis Guide