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 swath
1. 4 km by 2.5 km
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Build the A Train Constellation using STK
The swath dimensions must
be translated into angles.
sin( ) 
RE
sin( )
(eq 2)   90     (eq 3)
(eq 1) cos( ) 
RE  H
sin( )
RE =
C=
H=
=
=
=
=
Swath width =
=
=
=
Swath width =
6378
40,075
705
64.2
89.89
0.101528
0.011222
2.5
km
km
km
degrees
degrees
degrees
degrees
km
radius of the Earth
Earth's circumfrence
altitude
angular radius of the Earth
elevation angle
nadir angle
Earth central angle
given
given
input
determine
input
determine
determine
given
Use equation 1 to determine
Based on how big you want your “swath” to be
Use equation 2 to determine
Use equation 3 to determine
89.94
0.056855
0.006285
1.4
degrees elevation angle
degrees nadir angle
degrees Earth central angle
km
input
determine
determine
given
Two “nadir angles” entered into STK for
Vertical and Horizontal Half Angles
embedded spreadsheet
http://www.smad.com/store/bookstore/stl/smad3err.pdf
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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
0.5 miles
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.
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 on the picture
to see the scenario.
Click to see
measurement
of the swath size
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