Basic Satellite Design Using the Orbit Wizard

STK Pro, STK Premium (Air), 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.

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 capability of the Ansys Systems Tool Kit® (STK®) digital mission engineering software:

  • STK Pro

Problem statement

Engineers and analysts require a way to design, test, and analyze satellite orbits. They need to simulate multiple orbits of different types quickly and efficiently.

Solution

Use the Orbit Wizard to design nine (9) standard orbits. You will model two kinds of satellite orbits: satellite orbits used to view the Earth's surface and satellite orbits used to communicate with a ground site.

What you will learn

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

  • The Orbit Wizard
  • Orbit Wizard orbit types

Creating a new scenario

First, you must create a new scenario, 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 New Scenario Wizard:
    4. Option Value
    Name OrbitWizard
    Location Default
    Start Default
    Stop + 2 days
  4. Click OK when you finish.
  5. Click Save () when the scenario loads.

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

  6. Verify the scenario name and location when the Save As dialog box opens.
  7. Click Save.

Modeling the ground site

The basis for your comparison is a ground site, for which you will determine access times to your Sensor objects.

Inserting a Facility object

Insert a Facility object into your scenario.

  1. Bring the Insert STK Objects () tool to the front.
  2. Select Facility () in the Select An Object to Be Inserted list.
  3. Select Define Properties () in the Select A Method list.
  4. Click Insert....

Selecting the location of the Facility object

Place the Facility object near the geographic center of the contiguous United States.

  1. Select the Basic - Position page when the Properties Browser opens.
  2. Enter the following coordinates in the Position panel:
    3. Option Value
    Latitude 39.8281 deg
    Longitude -98.5795 deg
  3. Click OK to confirm your changes and to close the Properties Browser.
  4. Right-click on Facility1 () in the Object Browser.
  5. Select Rename in the shortcut menu.
  6. Rename Facility1 () US_Center.

Using the Orbit Wizard

The Orbit Wizard is a satellite-level tool designed to assist you in either creating any one of several standard orbits or designing your own satellite orbit. The configurable options available depends on the orbit type selected.

Inserting a Satellite object

Insert a Satellite object using the Orbit Wizard method.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Satellite () object using the Orbit Wizard () method.

Using the Circular orbit type

You will start with a Circular orbit type. Circular orbits have a constant radius. Place this satellite in a medium Earth orbit (MEO) that's similar to that of a GPS satellite.

  1. Leave the default Type set to Circular when the Orbit Wizard opens.
  2. Enter MEO_Circ_Sat in the Satellite Name field.
  3. Enter the following values in the Definition panel.
    4. Option Value
    Inclination 54.8 deg
    Altitude 20000 km
    RAAN 336 deg
  4. Click OK to propagate MEO_Circ_Sat () and to close the Orbit Wizard.

If you ever need to adjust an orbit your created with the Orbit Wizard, you can select a Satellite object in the Object Browser, then select Orbit Wizard... in the Satellite menu on the Menu Bar to reopen the Orbit Wizard for that satellite.

Inserting a Sensor object

MEO_Circ_Sat in this scenario will be used for low-gain communications. In this instance, you want to use a Sensor object to cover the entire sky hemisphere using a Simple Conic sensor definition. The sensor's field of view is simply being used to visualize the expected area from which a receiver at a ground site should be able to obtain some information from the satellite's transmitter.

  1. Insert a Sensor () object using the Define Properties () method.
  2. Select MEO_Circ_Sat () in the Select Object dialog box.
  3. Click OK to confirm your selection and to close the Select Object dialog box.
  4. Select the Basic - Definition page when the Properties Browser opens.
  5. Enter 14 deg in the Cone Half Angle field in the Simple Conic panel.

    6. At this altitude, the full cone angle of 28 degrees will provide good visualization of your expected communication reception on the ground.

  6. Click OK to confirm your changes and to close the Properties Browser.
  7. Rename Sensor1 () MEO_Circ_Sens.

Viewing the Circular orbit

View the Circular orbit in the 2D and 3D Graphics windows.

  1. Click on the 2D Graphics window.
  2. Select the Window menu on the Menu Bar.
  3. Select Tile Vertically in the Window menu.
  4. Use your mouse to obtain a good view of the Circular orbit type in both windows.

    5. circular orbit

  5. Clear MEO_Circ_Sat's () check box in the Object Browser.

Using the Critically Inclined orbit type

Critically inclined orbits maintain perigee at a fixed latitude. Their lines of apsides do not change over time. This satellite will be used view the surface of the Earth.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Satellite () object using the Orbit Wizard () method.
  3. Open the Type drop-down list when the Orbit Wizard opens.
  4. Select Critically Inclined.
  5. Enter Crit_Inclined_Sat in the Satellite Name field.
  6. Use the default values.
  7. Click OK to propagate Crit_Inclined_Sat () and to close the Orbit Wizard.

Inserting a Sensor object

You will use a Rectangular sensor type. Rectangular sensor types are typically used with satellites or aircraft for modeling the field of view of instruments such as pushbroom sensors and star trackers. Rectangular sensors are defined according to specified vertical and horizontal half-angles.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Sensor () object using the Define Properties () method.
  3. Select Crit_Inclined_Sat () in the Select Object dialog box.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Select the Basic - Definition page when the Properties Browser opens.
  6. Open the Sensor Type drop-down list.
  7. Select Rectangular.
  8. Enter the following values in the Rectangular panel:
    9. Option Value
    Vertical Half Angle 15 deg
    Horizontal Half Angle 5 deg
  9. Click OK to confirm your changes and to close the Properties Browser.
  10. Rename Sensor2 () Crit_Inclined_Sens.

Viewing the Critically Inclined orbit

View the Critically Inclined orbit in the 2D and 3D Graphics windows.

  1. Use your mouse to obtain a good view of the Critically Inclined orbit in both windows.

    2. Critically Inclined orbit

  2. Clear Crit_Inclined_Sat's () check box in the Object Browser.

Using the Critically Inclined, Sun Sync orbit type

Critically inclined, Sun-synchronous orbits combine the features of both basic types of orbits. The orbit uses a retrograde inclination of 116.565 degrees. A satellite in a critically inclined, Sun-synchronous orbit will pass overhead at the same local mean solar time for each revolution and it has a perigee, which remains at a fixed latitude. This satellite will be used view the surface of the Earth.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Satellite () object using the Orbit Wizard () method.
  3. Open the Type drop-down list when the Orbit Wizard opens.
  4. Select Critically Inclined, Sun Sync.
  5. Enter Crit_Inclined_SunSync_Sat in the Satellite Name field.
  6. Enter -80 deg in the Longitude of Ascending Node field in the Position panel.
  7. Click OK to propagate Crit_Inclined_SunSync_Sat () and to close the Orbit Wizard.

Reusing Sensor objects

To save time, all of your satellites viewing the surface of the Earth will use Crit_Inclined_Sens. You can simply copy and paste this sensor to other satellites performing the same type of mission.

  1. Select Crit_Inclined_Sens () in the Object Browser.
  2. Click Copy () on the Object Browser toolbar.
  3. Select Crit_Inclined_SunSync_Sat () in the Object Browser.
  4. Click Paste () on the Object Browser toolbar.
  5. Rename Crit_Inclined_Sens1 () Crit_Inclined_SunSync_Sens.

Viewing the Critically Inclined, Sun Sync orbit

View the Critically Inclined, Sun Sync orbit in the 2D and 3D Graphics windows.

  1. Use your mouse to obtain a good view of the Critically Inclined, Sun Sync orbit in both windows.

    2. Critically Inclined, sun sync orbit

  2. Clear Crit_Inclined_SunSync_Sat's () check box in the Object Browser.

Using the Geosynchronous orbit type

A satellite in a geosynchronous orbit will remain fixed in the sky above the specified fixed longitude. This satellite will be used for communications.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Satellite () object using the Orbit Wizard () method.
  3. Open the Type drop-down list when the Orbit Wizard opens.
  4. Select Geosynchronous.
  5. Enter GEO_Sat in the Satellite Name field.
  6. Enter -120 deg in the Subsatellite Point field in the Definition panel.
  7. Enter 2 deg in the Inclination field.
  8. Click OK to propagate GEO_Sat () and to close the Orbit Wizard.

Inserting a Sensor object

Since GEO_Sat in this scenario will be used for Ku-band communications, use a Half Power sensor type to simulate the approximate field of view of a parabolic antenna.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Sensor () object using the Define Properties () method.
  3. Select GEO_Sat () in the Select Object dialog box.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Select the Basic - Definition page when the Properties Browser opens.
  6. Open the Sensor Type drop-down list.
  7. Select Half Power.
  8. Use the default values in the Half Power panel.
  9. Click Apply to confirm your selection and to keep the Properties Browser open.

Pointing the sensor's boresite

Point the Sensor object's boresite in a fixed direction in the vicinity of US_Center by updating its Pointing properties.

  1. Select the Basic - Pointing page.
  2. Set the following values in the Fixed panel:
    3. Option Value
    Azimuth -66.1 deg
    Elevation 83.3 deg
  3. Click OK to confirm your changes and to close the Properties Browser.
  4. Rename Sensor3 () GEO_Sens.

Viewing the Geosynchronous orbit

View the Geosynchronous orbit in the 2D and 3D Graphics windows.

  1. Use your mouse to obtain a good view of the Geosynchronous orbit in both windows.

    2. Geosynchronous orbit

  2. Clear GEO_Sat's () check box in the Object Browser.

Using the Molniya orbit type

Molniya orbits are highly eccentric, meaning that there is a large difference between the altitude at apogee and the altitude of perigee. Molniya orbits are also critically inclined. This keeps the perigee of the orbit in the Southern Hemisphere. Molniya orbits also have a long dwell time in the extreme latitude regions of the Northern Hemisphere. This satellite will be used for communications.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Satellite () object using the Orbit Wizard () method.
  3. Open the Type drop-down list when the Orbit Wizard opens.
  4. Select Molniya.
  5. Enter Molniya_Sat in the Satellite Name field.
  6. Click OK to propagate Molniya_Sat () and to close the Orbit Wizard.
  7. Copy and paste MEO_Circ_Sens () to Molniya_Sat ().
  8. Rename MEO_Circ_Sens1 () Molniya_Sens.

Viewing the Molniya orbit

View the Molniya orbit in the 2D and 3D Graphics windows.

  1. Use your mouse to obtain a good view of the Molniya orbit in both windows.

    2. Molniya orbit

  2. Clear Molniya_Sat's () check box in the Object Browser.

Using the Orbit Designer orbit type to create a Tundra orbit

With this option, you can create any orbit you wish. Use the Orbit Designer to create a Tundra orbit, which has a an apogee dwell. This orbit is well-suited for communication satellites in high-latitude regions.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Satellite () object using the Orbit Wizard () method.
  3. Open the Type drop-down list when the Orbit Wizard opens.
  4. Select Orbit Designer.
  5. Enter Designer_Sat in the Satellite Name field.
  6. Enter the following parameters in the Orbital Elements panel:
    7. Option Value
    Semimajor Axis 42164 km
    Eccentricity 0.2
    Inclination 63.4 deg
    Argument of Perigee 270 deg
    RAAN 119 deg
    True Anomaly 0 deg
  7. Click OK to propagate Designer_Sat () and to close the Orbit Wizard.
  8. Copy and paste MEO_Circ_Sens () to Designer_Sat ().
  9. Rename MEO_Circ_Sens1 () Designer_Sens.

Viewing the Tundra orbit

View the Orbit Designer orbit in the 2D and 3D Graphics windows.

  1. Use your mouse to obtain a good view of the Orbit Designer orbit in both windows.

    2. tundra orbit From Orbit Designer

  2. Clear Designer_Sat's () check box in the Object Browser.

Using the Repeating Ground Trace orbit type

Orbits with a repeating ground trace are useful when identical viewing conditions are desired at different times to detect changes. The ground trace may be caused to repeat every day or to interweave from day to day before repeating. This satellite will be used view the surface of the Earth.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Satellite () object using the Orbit Wizard () method.
  3. Open the Type drop-down list when the Orbit Wizard opens.
  4. Select Repeating Ground Trace.
  5. Enter Repeat_Sat in the Satellite Name field.
  6. Enter -88 deg in the Longitude of First Ascending Node field in the Definition panel.
  7. Click OK to propagate Repeat_Sat () and to close the Orbit Wizard.
  8. Copy and paste Crit_Inclined_Sens () to Repeat_Sat ().
  9. Rename Crit_Inclined_Sens1 () Repeat_Sens.

Viewing the Repeating Ground Trace orbit

View the Repeating Ground Trace orbit in the 2D and 3D Graphics windows.

  1. Use your mouse to obtain a good view of the Repeating Ground Trace orbit in both windows.

    2. Repeating Ground Trace orbit

  2. Clear Repeat_Sat's () check box in the Object Browser.

Using the Repeating Sun Sync orbit type

Sun-synchronous orbits with a repeating ground trace are useful when identical viewing and lighting conditions are desired at different times to detect changes. The ground trace may be caused to repeat every day or to interweave from day to day before repeating. The orbit repeats the ground coverage cycle and passes overhead at approximately the same local mean solar time for each revolution. This satellite will be used view the surface of the Earth.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Satellite () object using the Orbit Wizard () method.
  3. Open the Type drop-down list when the Orbit Wizard opens.
  4. Select Repeating Sun Sync.
  5. Enter Repeat_Sun_Sat in the Satellite Name field.
  6. Enter 13 deg in the Lon. of First Ascending Node field in the Definition panel.
  7. Click OK to propagate Repeat_Sun_Sat () and to close the Orbit Wizard.
  8. Copy and paste Crit_Inclined_Sens () to Repeat_Sun_Sat ().
  9. Rename Crit_Inclined_Sens1 () Repeat_Sun_Sens.

Viewing the Repeating Sun Sync orbit

View the Repeating Sun Sync orbit in the 2D and 3D Graphics windows.

  1. Use your mouse to obtain a good view of the Repeating Sun Sync orbit in both windows.

    2. Repeating Sun Sync orbit

  2. Clear Repeat_Sun_Sat's () check box in the Object Browser.

Using the Sun Synchronous orbit type

Sun-synchronous orbits are designed to utilize the effect of the Earth's oblateness, causing the orbit plane to precess at a rate equal to the mean orbital rate of the Earth around the Sun. Sun-synchronous orbits have the property that their nodes maintain constant local mean solar times. This satellite will be used view the surface of the Earth.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Satellite () object using the Orbit Wizard () method.
  3. Open the Type drop-down list when the Orbit Wizard opens.
  4. Select Sun Synchronous.
  5. Enter Sun_Sync_Sat in the Satellite Name field.
  6. Enter 11:44:00.000 HMS in the Local Time of Descending Node field in the Node Definition panel.
  7. Click OK to propagate Sun_Sync_Sat () and to close the Orbit Wizard.
  8. Copy and paste Crit_Inclined_Sens () to Sun_Sync_Sat ().
  9. Rename Crit_Inclined_Sens1 () Sun_Sync_Sens.

Viewing the Sun Synchronous orbit

View the Sun Synchronous orbit in the 2D and 3D Graphics windows.

  1. Use your mouse to obtain a good view of the Sun Synchronous orbit in both windows.

    2. Sun Synchronous orbit

  2. Save () your scenario.

Viewing all nine orbits simultaneously

It's interesting to compare all nine (9) orbit types simultaneously in the 3D Graphics window.

  1. Using the Ctrl key and left mouse button to multi-select all the Satellite () objects in the Object Browser.
  2. Click on one of the Satellite () object check boxes to make them all visual in the 2D and 3D Graphics windows.
  3. Click Properties () on the Object Browser toolbar.
  4. Select the 3D Graphics - Model page when the Properties Browser opens.
  5. Move the Details - Maximum Viewing Distance - All slider all the way to the right in the Detail Thresholds panel.
  6. Click OK to confirm your changes and to close the Properties Browser.
  7. Bring the 3D Graphics window to the front.
  8. Zoom out so that you can see all nine (9) orbits.

    9. viewing all orbit types

  9. Click Start () on the Animation toolbar to animate the scenario.
  10. Click Reset () when finished.

Using the Access tool

You can analyze access times for all Sensor objects simultaneously to determine which orbit type accesses US_Center the longest by using the Access tool to create a Access report.

  1. Right-click on US_Center () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Expand () Crit_Inclined_Sat () in the Associated Objects list when the Access tool opens.
  4. Right-click on Crit_Inclined_Sens ().
  5. Select Select All Sensors in the shortcut menu.
  6. Click .
  7. Click Access... in the Reports panel.

Viewing the access data

You can use the Access report to determine which orbit type will access US_Center the longest and shortest amount of time, and if any of your Satellite objects don't have any accesses.

  1. Scroll through the Access report.
  2. Answer some questions based on the access report:
    • Which orbit type has the longest Total Duration access time?
    • Which orbit type has the shortest Total Duration access time?
    • Do you have any orbit types with No Access Found?
  3. Close the Access report when finished.

Generating an Access graph

When viewing multiple accesses using different orbit types, an Access graph can provide a quick snapshot in one view.

  1. Click Access... in the Graphs panel.

    2. access graph

    Your image may differ from the one shown above. In this image, GEO_Sat has the longest total duration time compared to the other orbit types. Something interesting is to compare your non-geosynchronous communications satellites access times to each other and your Earth viewing satellites to each other.

  2. Close the Access graph and the Access tool when you are finished.

Saving your work

Clean up your workspace and close out your scenario.

  1. Close out any open reports and tools that are still open.
  2. Save () your work.
  3. Close the scenario when you are finished.

Summary

This scenario was designed to provide an overall understanding of the Orbit Wizard and the orbit types that are provided for your use. All of the Earth-observing satellites used rectangular sensor types. All the communication satellites (expect the geosynchronous satellite) used sensor objects viewing from horizon to horizon. The geosynchronous satellite instead used a half power sensor type, which focused its view in the vicinity of the ground site. Using the Access tool, you created an Access report to determine with Sensor object accessed the ground site the longest during the two-day analysis period. Finally, you created an Access graph, which provided a snapshot of all the accesses at one time.

On your own

You mostly used the default values for your satellite orbits. Some of your sensors had low to no access durations. Change some of the orbital parameters and see if you can increase access times for those satellites.