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Build the A Train Constellation using STK

To build the “ideal” A Train constellation we will use STK - Satellite Tool Kit by AGI

Next we will add a Ground Stations at Fort Wayne, add a sensor to CloudSat and adjust the swath of the CloudSat CPR sensor.

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Build the A Train Constellation using STK

Lets add Fort Wayne to our A Train scenario. Select Insert>Facility From City Database.

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Build the A Train Constellation using STK

Type in and search for Fort Wayne and then select insert.

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Build the A Train Constellation using STK

Fort Wayne now shows up on the globe.

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Build the A Train Constellation using STK

How about if we wanted to determine when the satellites can communicate with the Fort Wayne ground station?

Select Access

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Build the A Train Constellation using STK

Select all the satellites and then hit the “Compute” button.

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Build the A Train Constellation using STK

When the satellite can communicate to the Fort Wayne ground station a line appears between the satellite and Fort Wayne

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Build the A Train Constellation using STK

Let remove all the reference grids and vectors and add the CPR instrument to CloudSat

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Build the A Train Constellation using STK

To add an instrument select Insert>Object Catalog

The Object Catalog form will pop-up and select “Sensor”

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Build the A Train Constellation using STK

The new sensor “footprint” or swath defaults to a Simple Conic, 45 degrees.

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Build the A Train Constellation using STK

CloudSat’s CPR actually has a rectangular swath.

CloudSat swath1. 4 km by 2.5 kmCloudSat swath

1. 4 km by 2.5 km

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Build the A Train Constellation using STK

http://www.smad.com/store/bookstore/stl/smad3err.pdf

HR

R

E

E

)sin(

)sin(

)sin()cos(

90

Use equation 1 to determine

Based on how big you want your “swath” to be

(eq 1) (eq 2)

Use equation 2 to determine

Use equation 3 to determine

(eq 3)

RE = 6378 km radius of the Earth given

C = 40,075 km Earth's circumfrence givenH = 705 km altitude input = 64.2 degrees angular radius of the Earth determine = 89.89 degrees elevation angle input = 0.101528 degrees nadir angle determine = 0.011222 degrees Earth central angle determine

Swath width = 2.5 km given

= 89.94 degrees elevation angle input = 0.056855 degrees nadir angle determine = 0.006285 degrees Earth central angle determine

Swath width = 1.4 km given

embedded spreadsheet

The swath dimensions must be translated into angles.

Two “nadir angles” entered into STK for Vertical and Horizontal Half Angles

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Build the A Train Constellation using STK

STK has some additional information of creating a rectangular sensor pattern in the STK help area.

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Build the A Train Constellation using STK

Entered the full angles not the half angles. It should get a swath that is twice as wide and twice as long?

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Build the A Train Constellation using STK

Width is 1.4 km?

Using this tool measure the width and length of the swath.

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Build the A Train Constellation using STK

Length is 2.5 km?

Swath size is 1.4 by 2.5 for the angles entered. Conclusion, if you use the spreadsheet “nadir angles” you do not need to divide by two.

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Build the A Train Constellation using STK

6 ft

1/8 inch

By comparison using the calculated swath size (1.4 km) divided by the CloudSat altitude (705 km), a six foot man looks like 1/8 inch tall from a half a mile away and would be hard to see. Therefore, we will scale the size of the swath.

We will scale the swath width and length by 50 times so we can see it better.

0.5 miles

We will make the swath 2.84° by 5.07°

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Build the A Train Constellation using STK

First we will change the Sensor Type to “Rectangular”

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Build the A Train Constellation using STK

With the Vertical Half Angle to 2.84°and the Horizontal Half Angle to 5.07°. Actually, is will make our swath area 2500X larger than the actual swath size for CloudSat’s CPR.

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Build the A Train Constellation using STK

Swath area increased by 2500X times or 8,740 km2

Click to see measurement of the swath size

Click on the picture to see the scenario.