Part 18: Ground-Based Space Situational Awareness with EOIR

STK Premium (Space) or STK Enterprise
You can obtain the necessary licenses for this tutorial by contacting AGI Support at support@agi.com or 1-800-924-7244.

Required Capability Install: For versions 12.10 and earlier of the STK software, this lesson requires the installation of the EOIR capability. For these versions of the software, the EOIR installer is included in the STK Premium software download, but requires a separate installation process. Read the Readme.htm found in the STK software install folder for installation instructions. You can obtain the necessary install by visiting https://support.agi.com/downloads or calling AGI support.

This tutorial requires version 12.9 of the STK software or newer to complete in its entirety. If you have an earlier version of the STK software, you can view a legacy version of this lesson.

The results of the tutorial may vary depending on the user settings and data enabled (online operations, terrain server, dynamic Earth data, etc.). It is acceptable to have different results.

Capabilities covered

This lesson covers the following capabilities of the Ansys Systems Tool Kit® (STK®) digital mission engineering software:

  • STK Pro
  • Electro-Optical Infrared Sensor Performance (EOIR)
  • STK SatPro

Problem statement

Engineers and operators require a fast and easy way to model and simulate the detection, tracking, and imaging performance of electro-optical and infrared sensors. Such sensors are used in wide variety of applications, including space situational awareness (SSA). You want to simulate a ground-based long-wave infrared (LWIR) sensor system that monitors and tracks space objects from its location at an observatory in Hawaii. You want to be able to visualize its field of view and analyze its performance metrics as it tracks a satellite that is tumbling in a polar low Earth orbit (LEO). You need to model the sensor system from known specifications and to consider atmospheric effects, temperature, emissivity, and radiance in your analysis.

Solution

Use the STK application and the Electro-Optical Infrared Sensor Performance (EOIR) capability to model and simulate a synthetic sensor scene as viewed from the ground site of the satellite in its orbit. Use data providers installed with the EOIR capability to generate a custom graph showing specific target metrics related to the target satellite. Finally, use the SatPro capability to model the attitude profile of a tumbling satellite and review the changes to your custom graph to understand the effects.

What you will learn

Upon completion of this tutorial, you will understand how to do the following:

  • Configure Sensor objects to use the EOIR sensor type
  • Generate a synthetic EOIR sensor scene
  • View scene pick information in the EOIR Scene Visual Details dialog box
  • Use EOIR data providers to create a custom EOIR signal-to-noise (SNR) graph
  • Select different satellite attitude profiles

Creating a new scenario

First, you must create a new STK scenario, and then build from there.

  1. Launch the STK application ().
  2. Click Create a Scenario in the Welcome to STK dialog box.
  3. Enter the following in the STK: New Scenario Wizard:
    4. Option Value
    Name STK_EOIR
    Location Default
    Start 1 Aug 2026 15:00:00.000 UTCG
    Stop + 10 min
  4. Click OK when you finish.
  5. Click Save () when the scenario loads.

    6. The STK application creates a folder with the same name as your scenario for you.

  6. Verify the scenario name and location in the Save As window.
  7. Click Save.

Save () often during this lesson!

Modeling the ground site

You are modeling the 1.6-meter Advanced Electro-Optical System (AEOS) telescope at the Air Force Maui Optical Station (AMOS) observatory, which is located at the Maui Space Surveillance Complex (MSSC) in Maui, Hawaii.

Inserting a Facility object

Use the Insert STK Objects tool to insert a Facility from the Standard Object Database. A Facility object models a ground station or other facility on the surface of the central body.

  1. Bring the Insert STK Objects tool () to the front.
  2. Select Facility () in the Select An Object To Be Inserted list.
  3. Select the From Standard Object Database () method in the Select A Method list.
  4. Click Insert....

Selecting the MSSC 1.6-meter telescope

Select the Maui Space Surveillance Complex in Maui, Hawaii.

  1. Clear the Data Sources: Online check box when the Search Standard Object Data dialog box opens if you have online operations enabled.

    2. This will ensure you only search for the MSSC facilities available in your local object database.

  2. Enter MSSC in the Name field.
  3. Click Search.
  4. Select MSSC 1.6m in the Results list.
  5. Click Insert.
  6. Click Close to close the Search Standard Object Data dialog box.

Modeling the EOIR sensor system

The Electro-Optical Infrared Sensor Performance (EOIR) capability models the detection, tracking, and imaging performance of electro-optical and infrared sensors. You can use the EOIR capability to support concept development, design, field-testing, and operations. The STK software takes this modeling to the big picture by considering electro-optical and infrared performance in conjunction with sensor platform dynamics, communications, and other mission architecture elements to assess integrated performance. The EOIR capability has the ability generate performance metrics such as signal-to-noise ratio and sensor images with both Earth and space in the background.

To generate an EOIR sensor scene and obtain performance metric data, you must first create a Sensor object and specify the EOIR properties for both it the other objects in the scene. Start with the Sensor object.

Inserting a Sensor object

Attach a Sensor object to MSSC_1_6m to model the 1.6-meter AEOS telescope.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Sensor () object using the Insert Default () method.
  3. Select MSSC_1_6m () when the Select Object dialog box opens.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Right-click on Sensor1 () in the Object Browser.
  6. Select Rename in the shortcut menu.
  7. Rename Sensor1 () Telescope.

Selecting the EOIR sensor type

Select the EOIR sensor type on the sensor's Definition page to begin modeling the LWIR sensor system. The EOIR sensor type is used to model electro-optical and infrared sensors. The EOIR capability supports up to 24 sensors and up to 36 bands per sensor. Bands share a common location and line of sight, but otherwise can have different parameters. You can simulate both multiband sensors and different image magnifications, as with the different settings of a zoom lens.

  1. Right-click on Telescope () in the Object Browser.
  2. Select Properties () in the shortcut menu.
  3. Select the Basic - Definition page when the Properties Browser opens.
  4. Open Sensor Type drop-down list.
  5. Select EOIR.
  6. Click Apply to confirm your selection and to keep the Properties Browser open.

Setting the sensor's spatial properties

By default, an EOIR sensor is set up with a single band. Select the Spatial tab on the Definition page to specify the spatial properties for each band. Keep the default single band and update its spatial properties to more accurately model the AEOS telescope by defining the angles that make up its total field of view.

  1. Select the Spatial tab.
  2. Note that Field-of-View and Number of Pixels is selected as the Input method by default.
  3. Enter the following parameters in the Field of View panel:
    4. Option Value
    Horizontal Half Angle 7.5 deg
    Vertical Half Angle 7.5 deg

    The EOIR capability uses these half angles to determine the full angular extent of the sensor field of view.

  4. Review the settings in the Number of Pixels panel.

    5. These specify the number of sensor pixels in the field of view in the horizontal and vertical directions. The default value is 128 pixels for each dimension.

  5. Click Apply to confirm your changes and to keep the Properties Browser open.

The Related Detector Parameters and Instantaneous Field of View values on this tab are based on the sensor spatial and optical properties. These are read-only fields and are automatically updated when you apply your changes.

Setting the sensor's spectral properties

The AEOS telescope observes the long-wave infrared waveband. Specify the sensor's spectral properties to model this spectral band range.

  1. Select the Spectral tab.
  2. Enter the following values (in microns) in the Spectral Band Edge Wavelengths panel:

    3. You must set the High value first.

    Option Value
    High 1.0
    Low 0.7
  3. Leave the Number Of Intervals set at 6.000000.

    4. The sensor model samples your spectral band using the number of intervals you define. The more intervals you have, the higher the accuracy of the analysis. However, more intervals mean longer computation times.

  4. Leave the Spectral Shape set to the Use Optical and Radiometric Response option.

    5. This leaves the spectral shape to the individual optical transmission and quantum efficiency spectral characteristics.

  5. Click Apply to confirm your changes and to keep the Properties Browser open.

Setting the sensor's optical properties

Next, specify the sensor's optical properties by choosing which two optical parameters will serve as the inputs used to calculate a third parameter.

  1. Select the Optical tab.
  2. Open the Input drop-down list.
  3. Select F-Number and Entrance Pupil Diameter.
  4. Enter the following input parameters:
    5. Option Value
    F/# 200
    Entrance Pupil Diameter 367.00

    The Entrance Pupil Diameter is measured in centimeters.

  5. Open the Image Quality drop-down list in the Image Quality panel.
  6. Select Negligible Aberrations.

    7. The EOIR capability models aberrations based on a root-mean-square wavefront error. The Negligible Aberrations setting introduces a 7% wavefront error.

  7. Click Apply to confirm your changes and to keep the Properties Browser open.

Setting the sensor's radiometric properties

The sensor's radiometric properties define its noise floor and its saturation ceiling.

  1. Select the Radiometric tab.
  2. Note that the Irradiance option is the default selection in the Units for Saturation and Sensitivity panel.

    3. Irradiance is better suited for sensors that are observing point sources like stars.

  3. Leave the Input set to High Level.

    4. With high-level radiometric parameters, you can populate and edit sensor performance data with measurements from an actual sensor or estimates for a sensor being developed.

  4. Set the following Reference Noise Equivalent Irradiance (NEI) vs. Integration Time (msec) Pairs options in the Sensitivity panel:
    5. Option Value
    Integration Time 100
    Equivalent Value 1e-16

    When preparing to take measurements with the sensor model, you specify an integration time. This is the time interval over which a radiant signal is collected before generating an image. The longer the time, the more photons that get collected. This field is equivalent to the "exposure time" setting on an analog film camera. You can also define a set of points that relate Integration (Exposure) Time to NEI/SEI (noise equivalent irradiance / saturation equivalent irradiance). The STK application linearly interpolates between the points to get correct NEI/SEI for the integration time you set. The Sensitivity defines the "noise floor" of the sensor. The sensor will not detect signals below this level.

  5. Click Apply to confirm your selection and to keep the Properties Browser open.

Updating the sensor-level properties

You can define certain properties that apply to the EOIR sensor in general, including all its bands. These sensor-level properties all appear below the band-specific tabs (Spatial, Spectral, Optical and Radiometric) on the Definition page.

  1. Scroll down below the band-specific tabs.
  2. Note that the Processing Level defaults to Sensor Output.

    3. The processing level enables you to visualize the geometric information in the sensor scene or the sensor output image. The Sensor Output processing level produces analog output energy in units of electrons.

  3. Leave LOS Gaussian selected for the method in the Jitter panel.

    4. Vibrations of a sensor's parent object can cause its line of sight to move during integration time, blurring the image. This tells the EOIR capability to apply a Gaussian probability distribution around the center beam to model line-of-sight (LOS) motion.

  4. Enter 1 in the Line of Sight Jitter field in the Jitter panel.

    5. This introduces a Gaussian vibration of one milliradian along the sensor boresight.

  5. Click OK to confirm your changes and to close the Properties Browser.

Opening the EOIR toolbar

To get started using the EOIR capability with your sensor, you must first display the EOIR toolbar. You can use the EOIR toolbar to access the EOIR configuration and EOIR sensor scene for a particular sensor.

  1. Select View in the Menu Bar.
  2. Select Toolbars in the View menu.
  3. Select EOIR in the Toolbar submenu to show the EOIR toolbar ().

Viewing the EOIR configuration

View the default EOIR configuration.

  1. Click EOIR Configuration... () on the EOIR toolbar.
  2. Review the information in the EOIR Configuration dialog box when it opens.

    3. The STK application automatically adds EOIR pattern sensors and their parent objects to the EOIR configuration. All central bodies and objects, except for the source sensor, that are part of the EOIR configuration are listed in the Available STK Objects list.

  3. Click Cancel to close the EOIR Configuration dialog box without making any changes.

Generating an EOIR sensor scene

Now you are ready to generate an EOIR sensor scene. There are two sensor scene images generated: an internal image passed to a Sensor Model and a displayed image (or sensor scene). The displayed image is different from the internal image in that the dynamic range is compressed to fit the display’s RGB capabilities, it has automatic gain control and brightness/contrast settings, and it has pixel value mapping for false color display. The EOIR line of sight and field of view are synchronized to the STK Sensor object.

  1. Select Telescope () in the Object Browser.
  2. Click EOIR Sensor Scene... () on the EOIR toolbar.

EOIR Sensor SCENE in Grayscale

The Sensor Scene Generator generates an image in the EOIR Sensor Scene window that represents the sensor's output based on material optical properties, object shape models, and thermal models of the objects in the scene. You should see some white dots and gray dots representing stars against the black background of space. The scene represents the analog world by digitally sampling the "modeled universe" at four times the sensor's pixel's spatial frequency, 16 spatial samples per sensor pixel, and over the passband and at wavelengths defined by the sensor model. The scene is thus a "box" of floating point numbers of dimension (horizontal spatial resolution × vertical spatial resolution × spectral resolution). These scenes accurately portray sensor images for the processing level selected.

Displaying visual details about the sensor scene

Use the EOIR Scene Visual Details dialog box to set the color map, determine the resolution of the Earth map using the scene detail box, adjust the brightness and contrast, change the file output settings and return back information on the pixel clicked inside of the sensor scene.

  1. Right-click on the sensor scene when the EOIR Sensor Scene window opens.
  2. Select Details... in the shortcut menu.
  3. Move the EOIR Scene Visual Details dialog box when it opens so that it's not sitting on top of the sensor scene.
  4. Select the BGRY option in the Color Map panel.

    5. The EOIR capability uses false color to bring out details in the image data that are often lost when displayed on a monitor with less resolution than the EOIR sensor. For instance, a typical monitor can display only 256 levels of grayscale, whereas an EOIR sensor might have 4096 levels of grayscale resolution. Color mapping is only for visual effect and does not change any of the internal data values.

    EOIR Sensor SCENE with BGRY color map

  5. Click on one of the stars to show more details about it in the Scene Pick Information panel.

    6. You can click to display information for each pixel in the sensor scene, including stars, assigned target objects, and the background. Stars are pure point sources with effective temperatures derived from catalog data. Clicking on a star will display the catalog number of the selected star, based on the Star Collection databases selected for the scenario's default databases.

  6. Note that the AGC check box is selected.

    7. AGC is Automatic Gain Control. When this option is selected, the EOIR capability automatically calculates brightness and contrast such that the brightest scene detail fits within the brightness resolution of the monitor.

  7. Click Close to close the EOIR Scene Visual Details dialog box when finished.
  8. Close () the EOIR Sensor Scene window.

For the Sensor Output processing level, the raw sensor data and image can be saved out at every animation step. You can save the data in each sensor click to a file by selecting Pixel Spectral Data on the EOIR Scene Visual Details page. You can then compound these images to create a movie or run through external image processing software for further analysis.

Inserting the satellite

Insert a Satellite object using the Orbit Wizard method to model a satellite in a polar low Earth orbit.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Satellite () object using the Orbit Wizard () method.
  3. Set the following options when the Orbit Wizard opens:
    4. Option Value
    Type Circular
    Satellite Name LEO_Sat
    Altitude 700 km
    RAAN 359 deg
  4. Click OK to confirm your changes, propagate LEO_Sat (), and to close the Orbit Wizard.

The orbit will take LEO_Sat through Telescope's field of view.

Viewing LEO_Sat and the ground site in the 3D Graphics window

View LEO_Sat and the Facility in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Right-click on LEO_Sat () in the Object Browser.
  3. Select Zoom To in the shortcut menu.
  4. Pan and zoom around so that you can view both LEO_Sat () and MSSC_1_6m ().
  5. Click Decrease Time Step () on the Animation toolbar until the Time Step is set to 1 sec.
  6. Click Start () to animate the scenario.
  7. Click Reset () when finished.

Although this tutorial is a ground-to-space example, it is possible to host an EOIR sensor on both air and space vehicles. The workflow of setting up an EOIR sensor model is similar for all supported STK objects.

Adding LEO_Sat to the EOIR configuration

To see LEO_Sat in the EOIR sensor scene, you must first select it as a target in the EOIR configuration.

  1. Click EOIR Configuration... () on the EOIR toolbar
  2. Select Satellite/LEO_Sat () in the Available STK Objects list when the EOIR Configuration dialog box opens.
  3. Move () Satellite/LEO_Sat () to the Selected Targets list.
  4. Click OK to confirm your selection and to close the EOIR Configuration dialog box.

Viewing LEO_Sat's EOIR Shape properties

When you include an object as a target in the EOIR configuration, you can then specify the EOIR properties for that object. For Satellite objects, you can select shapes and specify corresponding dimensions to represent them, as well as temperature and material data (which together create a thermal model of the spacecraft) by updating its EOIR Shape properties. Examine LEO_Sat's default EOIR Shape properties.

  1. Open LEO_Sat's () Properties ().
  2. Select the Basic - EOIR Shape page when the Properties Browser opens.
  3. Examine the following options:
    • Shape
    • Radius
    • Body Temperature
    • Temperature
    • Material
  4. Click Cancel to close the Properties Browser without making any changes.

Viewing LEO_Sat in the EOIR sensor scene

An EOIR sensor will take images of objects that fall within the sensor's field of view if they are sufficiently bright, either in reflected light or from self-radiance, at wavelengths that the sensor can detect. When LEO_Sat passes over the AMOS facility, AMOS is in darkness while LEO_Sat is illuminated. This scenario gives good lighting conditions for imaging.

Computing access between Telescope and LEO_Sat

Use the Access tool to compute access between Telescope and LEO_Sat. You will use the access for further analysis.

  1. Right-click on Telescope () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Select LEO_Sat () in the Associated Objects list when the Access tool opens.
  4. Click .

Setting the animation time from an Access report

Target satellites can appear in an EOIR sensor scene during the interval between their orbit start and stop times. Generate an Access report. You will use the time of the first access to set a viewing time for your sensor scene.

  1. Click Access... in the Reports panel.
  2. Right-click on the first access' Start Time when the Access report opens.
  3. Select Start Time in the shortcut menu.
  4. Select Set Animation Time in the Start Time submenu.

    5. This sets the Current Scenario Time to the time when LEO_Sat first enters the telescope's field of view.

  5. Close () the Access report.
  6. Click Close to close the Access tool.

Creating the EOIR sensor scene

Generate the EOIR scenario scene featuring LEO_Sat.

  1. Select Telescope () in the Object Browser.
  2. Click EOIR Sensor Scene... () on the EOIR toolbar.
  3. Right-click on the sensor scene when the EOIR Sensor Scene window opens.
  4. Select Details... in the shortcut menu.
  5. Move the EOIR Scene Visual Details dialog box when it opens so that it's not sitting on top of the sensor scene.
  6. Select the Gray Scale option in the Color Map panel when the EOIR Scene Visual Details dialog box opens.

Performing EOIR sensor scene analysis

View the EOIR sensor scene details.

  1. Click Decrease Time Step () on the Animation toolbar to set the animation Time Step to 0.50 seconds.
  2. Repeatedly click Step Forward () until you see LEO_Sat () come into the scene.

    3. The dot that represents LEO_Sat moves across the scene while the stars stay relatively still.

  3. Click on LEO_Sat's dot in the EOIR sensor scene to get more details about it.

    4. Note that, in addition to the name of the Satellite object (LEO_Sat), other information about the satellite is displayed in the Scene Pick Information panel, including the distance to it in kilometers, its relative azimuth and elevation, and the thermal model temperature and material type of the surface location as specified in LEO_Sat's EOIR Shape properties, which you viewed earlier.

  4. Click Close to close the EOIR Scene Visual Details dialog box when finished.
  5. Close () the EOIR Sensor Scene window.

Creating a custom EOIR graph

The EOIR capability does more than simulate scenes created by an EOIR sensor. It can also calculate metrics a sensor would receive from a target's signal. The following will familiarize you with some of the available EOIR data providers that are part of the EOIR sensor model.

For more information on the relationships among the modeled STK objects, the sensor scene generator, and the sensor model, refer to the EOIR Technical Overview.

Creating a custom graph style

Create a custom graph style called Sensor to Target Metrics.

  1. Right-click on Telescope () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the My Styles () folder in the Styles panel when the Report & Graph Manager opens.
  4. Click Create new graph style () on the Styles toolbar.
  5. Name the graph style Sensor to Target Metrics.
  6. Select the Enter key to set the graph's name and to open its Properties ().

Selecting the graph's data providers

You will use the EOIR Sensor To Target Metrics data provider's In-band target irradiance and Signal to noise ratio elements.

  1. Select the Content page when the Properties Browser opens.
  2. Expand () the EOIR Sensor To Target Metrics () data provider in the Data Provider list.

    3. These are time dependent metrics for a unique EOIR Sensor-Band / Target pairing.

  3. Select the In-band target irradiance () data provider element in the Data Provider list.

    4. This is the irradiance at the sensor aperture from a target object whose angular extent is smaller than the effective instantaneous field of view — that is, a point source target.

  4. Move () the In-band target irradiance () data provider element to the Y Axis list.
  5. Enter In-band Target Irradiance to the Axis field in the Y Axis panel.
  6. Select the Signal to noise ratio () data provider element in the Data Provider list.

    7. This is the ratio of the difference in sensor response between target-containing pixel(s) and the local surrounding pixels to the total noise. For point source targets, the background is assumed to be uniform (spatial clutter is neglected) and the target is assumed to be exactly centered on a pixel.

  7. Move () the Signal to noise ratio () data provider element to the Y2 Axis list.
  8. Enter Signal To Noise Ratio (SNR) to the Axis field in the Y2 Axis panel.

Updating the In-band target irradiance unit of measure

You can change the units of measure for a report style. In this case, change the units of the In-band target irradiance data to watts.

  1. Select EOIR Sensor to Target Metrics-In-band target irradiance in the Y Axis list.
  2. Click Units... below the Y2 Axis panel to open the Units dialog box.
  3. Clear the Use Defaults check box when the Units dialog box opens.
  4. Select Power in the Dimension column.
  5. Select Watts (W) in the New Unit Value list.
  6. Click OK to confirm your changes and to close the Units dialog box.

Setting the step size

Set the graph's step size to one second.

  1. Enter 1.0 sec in the Step Size field in the Step Size panel.
  2. Click OK to confirm your changes and to close the Properties Browser.

Setting the Time properties

Set the time properties so the data is reported over the first Access interval.

  1. Select the Specify Time Properties option in the Time Properties panel.
  2. Open () the Start and Stop times drop-down menu.
  3. Select Interval Component... in the shortcut list.
  4. Select Facility-MSSC_1_6m-Sensor-Telescope-To-Satellite-LEO_Sat () in the Objects list when the Select Time Interval dialog box opens.
  5. Expand () AccessIntervals (), located in the Installed Components () folder, in the Intervals for: Facility-MSSC_1_6m-Sensor-Telescope-To-Satellite-LEO_Sat list.
  6. Select First ().
  7. Click OK to confirm your selection and to close the Select Time Interval dialog box.

This limits the analysis period to the interval when LEO_Sat is visible in the EOIR sensor scene and decreases the computation time needed for the analysis.

Generating the custom graph

Generate the custom graph over the first Access interval.

  1. Select Sensor to Target Metrics () in the Styles list.
  2. Click Generate....
  3. Look at the graph.

    4. In-band target irradiance versus SNR graph

    This graph shows the signal is small relative to the noise, however using gray scale color mapping, you are able to see the target satellite in the EOIR sensor scene.

  4. Keep the Sensor to Target Metrics graph open.

Viewing the effects of EOIR atmosphere modeling

By default, the EOIR capability applies neither an atmosphere model nor an atmosphere parameter setting when generating a sensor scene. You will apply a Simple Atmosphere model and adjust its parameters to view the effects the atmosphere has on your data.

Selecting the Simple Atmosphere model

Set the EOIR atmosphere model.

  1. Click EOIR Configuration... () on the EOIR toolbar.
  2. Click Atmosphere and Textures... when the EOIR Configuration dialog box opens.
  3. Take a minute to view the different atmosphere models when the EOIR Atmosphere, Clouds, and Texture Maps dialog box opens.
    • Simple Atmosphere: This model calculates the atmospheric properties at the wavelengths corresponding to the Spectral Band Edges, and at a spectral resolution specified by the Number of Intervals set on the Sensor's Spectral Properties page. The Simple Atmosphere model only uses variations of atmospheric properties with altitude. It does not calculate the horizontal variations — which constitute weather — nor clouds. You can use the EOIR capability, however, for modeling clouds.
    • MODTRAN Derived Lookup Table: MODTRAN (MODerate resolution atmospheric TRANsmission) is a community standard, and the MODTRAN Derived Lookup Table atmosphere model is one of the highest-fidelity atmospheric models available in with the EOIR capability.
  4. Select the Simple Atmosphere option in the Modes panel.
  5. Open the Aerosol Models drop-down list in the Parameters panel.
  6. Select Maritime.

    7. This selects the type of aerosol model for the Simple Atmosphere model to use. Aerosols are tiny particles in the air that cause whitish haze visible to the human eye. Each aerosol model comprises a distribution of particles of different sizes and how light interacts with them. For instance, in a Maritime atmosphere, such as in Hawaii, salt crystals from wind and wave action are a major contributor to aerosols.

  7. Enter the following options in the Parameters panel:
    8. Option Value
    Visibility 40
    Humidity 70

    Visibility specifies the meteorological visibility in kilometers. Meteorological visibility is the greatest distance at which a black object of suitable dimensions, located near the ground, can be seen and recognized when observed against a bright background. Humidity specifies the relative humidity as a percentage from 0.0 to 100.0.

  8. Click OK to confirm your changes and to close the EOIR Atmosphere, Clouds, and Texture Maps dialog box.
  9. Click OK to confirm your changes and to close the EOIR Configuration dialog box.

Refreshing the custom graph

Refresh the open graph to see the changes.

  1. Return to your Sensor to Target Metrics graph.
  2. Click Refresh (F5) () on the graph toolbar.

    3. graph showing effects of atmospheric degradation

    Note the changes. The degradation is due to atmospheric effects. The "bumps" coincide with LEO_Sat passing over the facility's zenith.

  3. Keep the Sensor to Target Metrics graph open.

Turning off the atmosphere model

Now that you have seen the effects the atmosphere has on your data, turn the atmosphere off.

  1. Click EOIR Configuration... () on the EOIR toolbar to open the EOIR Configuration dialog box.
  2. Click Atmosphere and Textures... to open the EOIR Atmosphere, Clouds, and Texture Maps dialog box.
  3. Select the Atmosphere Off option in the Modes panel.
  4. Click OK to confirm your change and to close the EOIR Atmosphere, Clouds, and Texture Maps dialog box.
  5. Click OK to confirm your change and to close the EOIR Configuration dialog box.

Viewing the effects of a custom EOIR shape

When you include an object as a target in an EOIR configuration, you can specify the EOIR properties for that object. Earlier, you viewed LEO_Sat's basic EOIR Shape properties. Now, update some of those properties to more closely model LEO communications satellite.

Redefining LEO_Sat's EOIR shape and surface material

The EOIR capability models material types for aircraft, missiles, ships, ground vehicles, and satellites. The source for these material property models is NASA Reference Publication 1121, Apr 1984, "Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (PDF)." The STK application uses thermal models plus material emissivity to calculate each object's self-radiance via the Planck function and allows you to specify a fixed temperature and a composite shapes as built into the shape definition. Update the EOIR Shape properties of LEO_Sat to change its shape and surface material.

  1. Open LEO_Sat's () Properties ().
  2. Select the Basic - EOIR Shape page when the Properties Browser opens.
  3. Open the Shape drop-down list.
  4. Select LEOComm.

    5. The LEOComm shape is a composite shape based on the iridium.glb 3D model file. This based model can be found in <Install Dir>\STKData\VO\Models\Space. You don't have to update LEO_Sat's 3D Model File to match, as this is for illustrative purposes only.

  5. Leave Static selected for the Body Temperature.
  6. Enter 400 K in the Temperature field.

    7. The STK software applies this temperature to the entire shape. This then applies for the entire EOIR sensor scene's time period.

  7. Open the Material drop-down list.
  8. Select Aluminum MLI.

    9. Aluminum MLI specifies aluminum multi-layer insulation. Each surface material has optical properties used in the sensor scene calculation. One of these is reflectance. Light bouncing off a surface is selectively reflected by wavelength; that is, some wavelengths are absorbed instead of reflected. In the visible wavelengths, this is what gives objects color. Each surface material has a table of its reflectance versus wavelength.

  9. Click OK to confirm your changes and to close the Properties Browser.

Regenerating the EOIR sensor scene

Regenerate the EOIR sensor scene with LEO_Sat's updated EOIR Shape properties.

  1. Right-click at the beginning of the Sensor to Target Metrics graph.
  2. Select Set Animation Time in the shortcut menu.
  3. Select Telescope () in the Object Browser.
  4. Click EOIR Sensor Scene... () on the EOIR toolbar.
  5. Right-click on the sensor scene when the EOIR Sensor Scene window opens.
  6. Select Details... in the shortcut menu to open the EOIR Scene Visual Details dialog box.
  7. Move the EOIR Scene Visual Details dialog box when it opens so that it's not sitting on top of the sensor scene.

Viewing LEO_Sat in the EOIR sensor scene

You can view how LEO_Sat now appears in the EOIR Sensor Scene window.

  1. Repeatedly click Step Forward () on the Animation toolbar to see LEO_Sat move across the scene.
  2. Click on the dot representing LEO_Sat () to view information about it.

    3. Note that LEO_Sat's updated EOIR Shape properties, including the temperature and material, are now displayed in the EOIR Scene Visual Details dialog box's Scene Pick Information panel.

  3. Click Close to close the EOIR Scene Visual Details dialog box when finished.
  4. Close () the EOIR Sensor Scene window.

Refreshing your custom graph

Refresh your custom Sensor to Target Metrics graph to see how the updated properties affect it.

  1. Return to your Sensor to Target Metrics graph.
  2. Click Refresh (F5) () on the graph toolbar.

    3. graph showing effects of EOIR shape changes

    The curve is showing a single minimum rate in in-band target irradiance and SNR that coincides with LEO_Sat passing near the facility's zenith.

  3. Keep the Sensor to Target Metrics graph open.

Analyzing the light signature of a tumbling satellite

In your previous analysis, LEO_Sat was holding the default nadir-pointing attitude profile. Because of this, the EOIR sensor sees a near-constant satellite cross-section during its overhead pass. Now, you will analyze the light signature of a satellite that is tumbling through space.

Updating LEO_Sat's Attitude properties

Update LEO_Sat's attitude profile to be that of a precessing spin, one of several predefined attitude profiles included with the SatPro capability.

  1. Open LEO_Sat's () Properties ().
  2. Select the Basic - Attitude page when the Properties Browser opens.
  3. Open the Type drop-down list in the Basic panel.
  4. Select Precessing Spin.

    5. This type of attitude profile describes attitude motion as a composition of two rotations: spin and precession.

  5. Set the following Body Spin Axis options:
    6. Option Value
    Type Cartesian
    X 0
    Y 1
    Z 0
  6. Enter 30 revs/min in the Rate field in the Precession panel.
  7. Enter 30 revs/min in the Rate field in the Spin panel.
  8. Click OK to confirm your changes and to close the Properties Browser.

Viewing LEO_Sat in the 3D Graphics window

View LEO_Sat spinning in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Zoom To LEO_Sat ().
  3. Click Decrease Time Step () on the Animation toolbar to set the animation Time Step to 0.1 seconds.
  4. Repeatedly click Step Forward () to see LEO_Sat () tumble.

Updating the custom graph

Refresh the Sensor to Target Metrics graph and update its step size to better show the effects of the tumbling satellite.

  1. Return to the Sensor to Target Metrics graph.
  2. Enter 0.1 sec in the Step field.
  3. Select the Enter key to regenerate the graph.

    4. Be patient, this may take a while.

    graph showing tumbling satellite

As the spacecraft rotates, its various panels and surfaces reflect varying amounts of light. The plot is jagged, thus confirming that the spacecraft is tumbling.

Saving your work

Clean up your workspace and save your scenario.

  1. Close your Sensor to Target Metrics graph, the Report & Graph Manager, and any open reports and tools.
  2. Save () your work.

Summary

This was an introduction to the STK software's EOIR capability. You modeled, simulated, and analyzed the MSSC's 1.6-meter AEOS telescope at the AMOS observatory in Maui, Hawaii, that tracked a polar satellite in LEO. You set your Sensor object attached to the ground site to use the EOIR capability. You defined its spatial, spectral, optical, and radiometric properties. Using a synthetic EOIR sensor scene, you obtained data on stars and the satellite in LEO. You became familiar with satellite EOIR shape configurations and attitude issues. Using the EOIR configuration, you applied atmospheric changes to your analysis. Finally, you created a custom graph and graphed the various changes as part of your analysis.