Spacecraft.CardinalPoints(CelestialObject, TimeSpanArray, Array) Method

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Description

Returns the times when the Spacecraft is at each of the cardinal points. The cardinal point calculations are based on the alpha angle, which is the angle between the Spacecraft's position and the target CelestialObjects's position with respect to the Spacecraft's central body when both vectors are projected onto the Spacecraft's orbit plane. Note that the target CelestialObject is modeled as a point.

 

 

The mathematical definition of the alpha angle is:

 

 

Below is a diagram depicting how the alpha angle is defined:

 

A visual representation of the Alpha angle.

A visual representation of the Alpha angle.

 

Timing Precision Mode

This page describes functionality in nanosecond timing precision mode.

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

 

Note: This is an interval method. See the Interval Methods page for more information.

Note: This method has a state. See the Methods and Properties with State page for more information.

 

Method Signature

Spacecraft.CardinalPoints(

CelestialObject target,

TimeSpanArray EventTime,

Array EventType)

 

 

Arguments

target

Description:

The target CelestialObject to be used in the CardinalPoint calculations. If no CelestialObject is specified, the Sun will be used.

 

 

EventTime

Description:

The time that the event occurred.

 

 

EventType

Description:

The type of the event that occurred.

Event Type == 1 is noon (alpha angle = 0).

Event Type == 2 is dusk (alpha angle = 90).

Event Type == 3 is midnight (alpha angle = 180).

Event Type == 4 is dawn (alpha angle = 270).

 

 

 

Return Value

Type:

number

 

 

Returns the number of elements filled into EventType and EventTime arrays.

 

Syntax

myVariable1 = mySpacecraft1.CardinalPoints(myCelestialObject1, myTimeSpanArray1, myArray1);

 

 

Example 1

This example demonstrates how to report times when a Spacecraft passes a cardinal point to a DataTableWindow using the Moon as the target CelestialObject.

 

Spacecraft Spacecraft1;

 

Variable i;

Variable numEvents;

TimeSpanArray EventTime;

Array EventType;

String scEventType;

String scEventTime;

DataTableWindow DTW({scEventType, scEventTime});

 

While (Spacecraft1.ElapsedTime < TIMESPAN(4 hours));

 

          numEvents = Spacecraft1.CardinalPoints(Moon, EventTime, EventType);

 

          If (numEvents > 0) then;

                      For i = 0 to numEvents - 1 step 1;

                                  Switch (EventType[i]);

                                              Case 1:

                                                          scEventType = "Passing Spacecraft Noon at";

                                                          scEventTime = EventTime[i].ConvertToCalendarDate();

                                                          Break;

                                              Case 2:

                                                          scEventType = "Passing Spacecraft Dusk at";

                                                          scEventTime = EventTime[i].ConvertToCalendarDate();

                                                          Break;

                                              Case 3:

                                                          scEventType = "Passing Spacecraft Midnight at";

                                                          scEventTime = EventTime[i].ConvertToCalendarDate();

                                                          Break;

                                              Case 4:

                                                          scEventType = "Passing Spacecraft Dawn at";

                                                          scEventTime = EventTime[i].ConvertToCalendarDate();

                                                          Break;

                                  End;

 

                                  Update DTW;

 

                      End;

          End;

 

          Step Spacecraft1;

 

End;

 

 

Output:

 

scEventType

scEventTime

Passing Spacecraft Noon at

Passing Spacecraft Dusk at

Passing Spacecraft Midnight at

Passing Spacecraft Dawn at

Passing Spacecraft Noon at

Passing Spacecraft Dusk at

Passing Spacecraft Midnight at

Passing Spacecraft Dawn at

Jan 01 2020 00:39:17.739257812

Jan 01 2020 01:04:00.747070312

Jan 01 2020 01:28:44.853515625

Jan 01 2020 01:53:29.619140625

Jan 01 2020 02:18:14.531250000

Jan 01 2020 02:42:57.612304687

Jan 01 2020 03:07:41.645507812

Jan 01 2020 03:32:26.484375000

 

 

 

See also

Spacecraft Object

Spacecraft.CardinalPoints

Spacecraft Propagation Guide

Coverage and Contact Analysis Guide