2005 AGI Users’ Conference
1
Attitude Coverage Modeling in STK
FOR STK 6.2.1, STK/ATTITUDE, STK/COVERAGE, STK/PROFESSIONAL (STK/PRO) ESTIMATED COMPLETION TIME: 40 MIN
What You Will Do

Create a basic Attitude Coverage scenario

Use a basic Attitude Figure of Merit to measure performance

Investigate other Attitude Figures of Merit for more complex Coverage scenarios
What You Will Learn
The exercises that follow will teach you how to build an Attitude Coverage scenario and to use
Attitude Figures of Merit to analyze the results. You will learn about two new STK Objects, the
Attitude Coverage and the Attitude Figure of Merit. You will create Attitude Coverage to define
your directions of interest and assign assets and constraints. You will also create Attitude
Figures of Merit to calculate statistical data associated with the directions of interest and the
access to the assets. You will learn how to use, interpret and display several basic Attitude
Figures of Merit, including Simple Coverage, N-Asset, Coverage Time, Revisit Time, and
Access Constraint.
NOTES
NOTES
Attitude Coverage Modeling in STK
page 2
Introduction: What Is Attitude Coverage?
The Attitude Coverage object in STK calculates access from its parent object to one or more
assets. In addition, other types of objects, such as sensors, receivers, etc. can be the pointed
along the directions of interest affecting attitude dependent access times. Similar to
STK/Coverage, Attitude Coverage is designed for calculating statistical data about the amount
and quality of the total accesses, rather than simply determining if and when access exists.
Building an Attitude Coverage Scenario
The following exercise will take you through the basic process of building an Attitude Coverage
scenario in STK that allows you to determine when and how close the Sun will be to various
pointing directions.
Managing Sun Interference
A pre-existing scenario is provided for use with this exercise. The goal of this exercise is to
determine in which directions the Sun does not interfere with possible imaging opportunities.
The scenario contains all the necessary elements to achieve the above objective.
Creating an Attitude Coverage Definition Object

Open the UCAttCov scenario from the following directory:
C:\ training\UC05\CC.Intro_VGT_&_AttCov.Liepa.UC05.v1\AttCovScenario

Open up the properties for the ISS. Under the 3D Graphics/Model, set the Model Scale to 2.0.
Under the 3D Graphics/AttitudeSphere, set the AttitudeSphere scale to 4.0.

Highlight Satellite ISS, add to it a new Attitude Coverage object
NOTES
and rename it AttCov.
Attitude Coverage Modeling in STK
page 3

Double click on AttCov to open the Properties Browser.

The default Grid Definition type is set to Global. This definition results in a complete spherical
coverage region around the ISS Satellite.

On the Assets page select and Assign the Sun Planet.

Click OK.

Right click on AttCov, go to AttitudeCoverage Tools, and Compute Accesses. This will occur
instantly.
NOTES
Attitude Coverage Modeling in STK
page 4
Note: Without using a point definition object (see Using Point Definition Objects…) to apply
specific object properties, only directions through every point on the attitude coverage
grid are considered. This means that access intervals are the same for all directions
and are equal to those between the object at the center of the grid and corresponding
asset.
Using Attitude Figures of Merit to Evaluate
Performance
Now that all access data has been computed for the entire coverage grid, you can begin to
evaluate sun interference. This is done by adding a new sub-object, Attitude Figure of Merit, to
the attitude coverage object. Attitude Figures of Merit (FOM) allow you to qualify and quantify
coverage performance by applying various statistical measures to the visibility intervals already
computed. As noted in the previous section, attitude coverage in this scenario is created
without a point definition object, which makes access intervals in all directions the same and
equal to those between the ISS satellite and the Sun. Hence, while it is possible to compute
simple coverage and all access duration derived FOMs, their values will be the same for all the
points on the grid. However, there is another Attitude FOM that does vary from point to point
even when the access intervals do not. It is called AngleToAsset and is available as a special
constraint registered on the Attitude Coverage object itself. In this section you will be able to
apply this FOM and exercise some of the options for outputting data visually, graphically or in a
report format. Take some time to look at the different Attitude FOM’s as well.
AngleToAsset (Access Constraint) FOM

With AttCov highlighted, create a new Attitude Figure Of Merit object
NOTES
. Rename it AttFOM.
Attitude Coverage Modeling in STK
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Note: The default FOM is Simple Coverage. This FOM is a binary indicator of coverage. Its
value is 0 if a point is not covered and 1 if it is.

Animate the scenario and notice in 3D Window that the entire grid is re-colored whenever the
Sun rises above and sets below local horizon.

Open the Properties Browser for the AttFOM.

On the Basic Definition page, change Type to Access Constraint.

Constraints selector should be set to AngleToAsset. Change Compute to Minimum, Time step
to 30 sec and Invalid Data Indicator value to 180 deg.
NOTES
Attitude Coverage Modeling in STK
page 6

On the same panel go to 3D Graphics Contours page and enable Show Static graphics.

Input the following values as Levels for contours:
Field
Start
Stop
Step

Contour Level Adding
Value
0 deg
40 deg
20 deg
Click Add Levels and set Level Attributes if necessary.
Field
Color Method
Start Color
End Color
NOTES
Contour Level Attributes
Value
Color Ramp
Red
Blue
Attitude Coverage Modeling in STK
page 7

Click Ok. Notice the new contours on the 3D Graphics window.

Right click on the AttFOM, go to Tools, select Report from the AttitudeFigureOfMerit menu.

Select the Value By Point style and click Create.
NOTES
Attitude Coverage Modeling in STK
page 8

Close this report and the Report Tool window.

Open the Properties Browser for the AttFOM and select 3D Graphics Contours page.

Change Type to Animation

Enable Animation contours and set them to Use Static Contours.
NOTES
Attitude Coverage Modeling in STK
page 9

Change Type back to Static and disable it.

Click Ok.

Animate the scenario and notice in 3D Window that circular contours follow the Sun.
Note: Notice that the contours change whenever Sun crosses the local horizon line.
Review

Defined directions of interest using attitude coverage grid

Assigned Sun as asset

Evaluated access from attitude coverage parent satellite to Sun

Used AngleToAsset Access Constraint FOM to determine minimum Sun angle for all
directions of interest

Created report for minimum Sun angle for all directions over the entire computational interval

Used Static and Animation contour graphics to provide visual performance results
NOTES
Attitude Coverage Modeling in STK
page 10
Evaluating Performance Considering Multiple
Assets
Many types of FOMs including AngleToAsset Access Constraint supply Across Assets option for
performance evaluation. The following example will illustrate how to use this option when considering
pointing angle to multiple stars.

Open the Properties Browser for the AttFOM.

On Basic Definition page, select Maximum option for Across Assets and Maximum option for
Compute.

On the same panel go to 3D Graphics Contours page.

Change the type to Animation.

Input the following values as Levels for contours:
NOTES
Attitude Coverage Modeling in STK
Field
Start
Stop
Step
page 11
Contour Level Adding
Value
35 deg
50 deg
5 deg

Click Add Levels.

Change Add Method to Explicit.

Add Level at 0 deg.

Set Level Attributes if necessary.
Field
Color Method
Start Color
End Color
NOTES
Contour Level Attributes
Value
Color Ramp
Red
Blue
Attitude Coverage Modeling in STK
page 12

Click Ok.

Open the Properties Browser for the AttCov.

Select Assets page.

De-Assign Sun and assign all four stars as assets.

Click Ok.

Animate the scenario and notice in 3D Window changing contours.
Note: Contours in this case represent the largest angle from a given pointing direction to any
of the available stars at that moment in time.
Note, you can also change the contour type to static for further analysis.
NOTES
Attitude Coverage Modeling in STK
page 13
Review

Defined directions of interest using attitude coverage grid in different reference axes

Assigned multiple stars as assets

Evaluated access from attitude coverage parent satellite to stars

Used AngleToAsset Access Constraint FOM to determine maximum angle to any of four stars
for all directions of interest

Used Static and Animation contour graphics to provide visual performance results
Using Point Definition Objects for Direction
Dependent Access and Constraints
Point definition objects extend capabilities of STK/Attitude Coverage in the same way they
extend capabilities of STK/Coverage: they introduce additional object specific constraints into
the problem. These constraints can be used both to limit access to assets and to define
additional figures of merit. The following exercise will use sensor as a point definition object in
order to optimize its pointing as well as to maneuver the spacecraft for maximum coverage
across multiple targets.
Maneuver Planning and Sensor Pointing

Add sensor StarScope to the ISS satellite by inserting it from file: StarTracker.sn from the
following directory:
C:\ training\UC05\Introduction_to_Attitude_Coverage\Scenario
NOTES
Attitude Coverage Modeling in STK
page 14

With AttCov highlighted, from the AttitudeCoverage menu select Clear Accesses.

Open the Properties Browser for the ISS satellite.

Select Attitude page.

Make sue that Target Pointing is disabled.

Click Ok.

Open the Properties Browser for the AttCov.

On the Grid page click the Associate Class… button to open Point Definition Properties panel.

On Point Definition Properties panel select Use Object Instance, Use Actual Object on the
Grid Points, and highlight ISS/StarTracker sensor.
NOTES
Attitude Coverage Modeling in STK

Click Ok.

Click Ok to close Properties Browser

Open the Properties Browser for the AttFOM.

On the Basic Definition page, change Type to Coverage Time.

Select Total as Compute option.

Click Apply.
NOTES
page 15
Attitude Coverage Modeling in STK
page 16

On the same panel go to 3D Graphics Contours page and enable Show Static contours.

Input the following values as Levels for contours:
Field
Start
Stop
Step

Contour Level Adding
Value
0 sec
3600 sec
600 sec
Click Add Levels and set Level Attributes if necessary.
Field
Color Method
Start Color
End Color
Click Ok.
NOTES
Contour Level Attributes
Value
Color Ramp
Red
Blue
Attitude Coverage Modeling in STK
page 17

With AttCov highlighted, from the AttitudeCoverage menu select Compute Accesses. This will
take some time.

View static contours in 3D Window and notice color that corresponds to the longest coverage
time.

Open the Properties Browser for the AttFOM.

Select 3D Graphics Contours page and click on Legend… button. Click Ok.
Note: What is the approximate value for the longest possible coverage time?

With the AttFOM highlighted select Report from the AttitudeFigureOfMerit menu.

Select Grid Stats and click Create… to find the exact answer.

Close the report and the Report Tool.

With AttCov highlighted, from the AttitudeCoverage menu select Clear Accesses.
NOTES
Attitude Coverage Modeling in STK
page 18

Open the Properties Browser for the ISS satellite.

Select Attitude page.

Enable Target pointing. Click the Select Targets button. Select the four stars.

Click Ok.
Note: Targeted pointing attitude is configured to track the same four stars as the ones
selected as assets in AttCov. How would this change in attitude definition affect
coverage time? Also, note, while we would not see the ISS use this type of attitude,
other spacecraft could highly benefit from such an attitude.

With AttCov highlighted, from the AttitudeCoverage menu select Compute Accesses. This will
take some time.

View static contours in 3D Window and notice color that corresponds to the longest coverage
time.

With the AttFOM highlighted select Report from the AttitudeFigureOfMerit menu.

Select Grid Stats and click Create… to find the longest possible coverage time using target
pointing attitude.
NOTES
Attitude Coverage Modeling in STK
page 19
Note: Using 3D window identify direction of the longest coverage time. Is this direction along
the targeted boresight?

Close the report, but not the Report Tool.

Select Value by Point and Click Create… to find lat-lon values that correspond to the longest
coverage time.

Close the report and the Report Tool.

Open the Properties Browser for the StarTracker sensor.

Select Constraints Sun page.

Enable and set Solar Exclusion Angle constraint to 40 deg.

Click Ok. This will take some time.

View static contours in 3D Window and notice the change in their appearance.
Note: Is pointing direction of longest coverage time still along the targeted boresight?
NOTES
Attitude Coverage Modeling in STK
page 20
Review

Created sensor and assigned it as pointing definition object

Used sensor field of view constraint to limit access while pointing sensor in various directions

Used multiple stars as assets

Evaluated Coverage Time figure of merit to determine efficient attitude and sensor placement

Created report for overall Coverage Time statistics and for Coverage Time statistics for each
pointing direction

Used Static and Animation contour graphics to provide visual performance results
NOTES