483 Tutorial STK/ Operations Sara Spangelo, March 27 · PDF file483 Tutorial STK/ Operations Sara Spangelo, March 27-28, ... We’re going to use a TLE to define the ... i.e. does

483 Tutorial STK/ Operations

Sara Spangelo, March 27-28, 2012

What did you guys want to learn?

Basically everything… so I’ll do my best to cover as much as possible!

0

10

20

30

40

50

60

70

80

90

100

Per

cen

tra

ge

of

Su

rvey

Res

ult

s

STK Skill

Yes + Absolutely

Needed for Project 2

Survey Results:

So… what are we going to do during this tutorial?

• Creating Scenarios – Model satellites with TLEs

– Model attitude geometries

– Model ground station networks

– Model GPS constellation

• Operational Analysis – Getting Eclipse times

– Getting Access times to ground stations and targets of interest

• Learn to use vector geometry – Model vectors, angles

– Verify attitude scheme

– Find angles between magnetic field, line of sight to sun, and satellite axis

• Link budget (focus on GPS) – Input antenna gain, losses, etc.

– Getting link budgets, making sense of the data

• Phobos / other bodies – Orbits about Phobos

So… what are we going to do during this tutorial?

Throughout this tutorial:

• RED Arrows and Boxes: pointing out instructions

• GREEN Questions: Homework questions to be filled out in this document:

483_STK2_Tutorial_Assignment

• BLACK Text: Normal Instructions

• RED “SAVE BREAK” Pages- very important- save at this point so I

don’t have to say “I told you so!”

Ask questions as you go! Not all the instructions are given such that you work

through things yourself. You should gain skills and confidence as you go, feel

free to turn back to old slides for refreshers!

Intro

Getting Set Up:

1. Open cmd.exe: To do this, click on the Windows "Start" button, type

"cmd.exe" into the search bar, and press enter.

2. Copy and paste the following command into the cmd.exe window.

net use W: \\afs\umich.edu\user\s\a\saracs\483_STK_Tutorial_2012

3. Open the tutorial “483_STK_Tutorial.ppt”

It will ask you to open a read-only version, and you will have to save it in one of your own folders.

4. You can start as soon as you want, and start the “homework” here:

W:\\hw\483_STK2_Tutorial_Assignment

It will ask you to open a read-only version, and you will have to save it in one of your own folders.

This homework is be submitted online (to CTools by Friday 3/30/2012 at 12 midnight) to

AEROSP483 001 W12 Resources / Homeworks & Midterm / STK-2 Tutorial Assignment

https://ctools.umich.edu/portal/tool/03cd62e0-ab27-4691-920d-7c988f9107aa?panel=Main






Create STK Scenario

– Start Date: 1 Dec 2011

– End Date: 1 Jan 2012

How to check basic scenario properties:

• Right click on RAX2 -> Properties

• Check Scenario/ Animation parameters

Creating RAX-2 Scenario

Input RAX-2 Satellite:

– Insert: New Satellite

– Define Properties


We’re going to use a TLE to define the orbit

1. Wait a second, what is a TLE? (hint: GOOGLE)

Open up your TLE, found here:

\\afs\umich.edu\user\s\a\saracs \483_STK_Tutorial_2012\TLE

By right clicking “Open with Notepad” or other text edit (I like jEdit)

1 37853U 11061E 11316.82156000 +.00010384 +00000-0 +84851-3 0 00355

2 37853 101.6969 253.5835 0254451 249.5696 107.8016 14.77774158002278

Inclination Eccentricity (0.0254451) Mean Motion


Go to Basic-> Orbit

– Change Propagator to SGP4

2. What is SGP4? What is its advantages over other propagators?


Input Two Line Element (TLE)

– Under TLE Source, click File, then Setup

– TLE File: search for correct file here:

\\afs\umich.edu\user\s\a\saracs \483_STK_Tutorial_2012\TLE

– Under TLE Selection, leave as Switching Method: Epoch


http://umich.edu/

Verify the TLE was loaded correctly

– in TLE Source: Click “Preview”

– Check out date of TLE epoch

3. Check out all of the orbital elements. Do they match the ones in the .tle?

(respond qualitatively, i.e. does the orbit have the major characteristics of the orbit?)


1 37853U 11061E 11316.82156000 +.00010384 +00000-0 +84851-3 0 00355

2 37853 101.6969 253.5835 0254451 249.5696 107.8016 14.77774158002278

Change Satellite Name to RAX2_TLE

4. Check out the orbit. Do the orbital elements seem right? Why?


Create another RAX2 using updated TLEs from AGI Server

– Copy and paste RAX2_TLE (right click or Ctrl-c, Ctrl-v)

– Rename RAX2_SSC

– Right click “RAX2_SSC” go to Basic-> Orbit

– Check out SSC Number- this distinguishes the satellite in the catalogue

– Under TLE Source, click “AGI Server”- this uses the SSC to always update with the most

recent TLE


OK, so what TLEs does this one use?

– In the TLE Source Window, Click “Preview”

5. Compare to original TLE we loaded- why/ when is it different?


1 37853U 11061E 11316.82156000 +.00010384 +00000-0 +84851-3 0 00355

2 37853 101.6969 253.5835 0254451 249.5696 107.8016 14.77774158002278

Change Satellite Color so we can tell them apart!

Use image below to figure it out… Don’t forget to hit “apply”


Now you should have two pretty satellites….

6. Why are they not exactly on top of one another? (we’ll investigate this more later)


We’ve done a lot of hard work….

SAVE BREAK


Let’s learn how to use the toolbar a bit

• Animations

Go to start of scenario, backwards, pause, forwards, slow down, speed up

• Take a picture (Snap Frame)

– This will ask you to save it (save as .bmp)

7. Take a picture of your simulation and copy and paste into your report


Review how to make a simple report

• Right click on (either) satellite, go to “Report & Graph Manager”

• Click “Create new report style”

• Name it “eclipse”

• Right click -> Properties

• Under Eclipse Times click the options below

• Click blue arrow and hit Apply and OK!


Generate report


8. Save report as a .csv, open in Excel and plot eclipse times for one week

Let’s model the attitude of the satellites.

RAX is passively magnetically stabilized

• What does this mean? (See figure below)

• Why do CubeSats use this orientation? Cheap, powerless, easy, flight heritage…


Right click on RAX2_SSC satellite, go to “Properties”

• Go Basic-> Attitude

• Under Basic Change Type to “Spin Aligned”

• Change Reference Vector to “IGRF” Magnetic Field Model

• Body Spins about the Z

• Spin rate: 10 deg/sec

• No Nutation angle

• HIT APPLY



SAVE BREAK


Check out the attitude to verify it’s correct…

We need to use VECTOR GEOMETRY TOOL

Check out all the stuff you can make….

A B C D

9. Identify what each of these buttons A-D can generate (hint…)

These can be very useful, but make sure you know what you’re constructing!


We need to make a vector!

• Right click on Satellite, hit “Vector Geometry Tool”

• Click insert vector (arrow box in top right)

• Name it “RAX2_SSC_Zaxis”

• Chose “Fixed in Axis” along Z axis

(since RAX spins this way)


Now we want to visualize this…

• Right click on satellite

• Go to “Properties” and click 3D Graphics-> Vector

• Click Add and add the new vector you created (click blue arrow) and “ok”


• Click the box under “Show”

• Cleck “Draw at Point” and make sure it’s your satellite!

• Change Common Options sizes as below:


10. Is the new vector pointed the direction you would expect it? Justify your

answer by taking picture and watching it through several orbits.


11. Find distance between two satellites. When are they the closest, why?

HINTs (see shots below)

– Add vector, (Use Vector Geometry Tool)

– Check it visually,

– Find the magnitude of the vector through representative orbits

(this should now appear under Vectors(Fixed) in Report Generator)

Creating vector Generating report


Now input the ground stations and target of interest from

\\afs\umich.edu\user\s\a\saracs \483_STK_Tutorial_2012\GSs

• Insert the facilities and target shown below (make sure you’re looking for the

correct type of file- a target (*.t) or a facility (*.f)


http://umich.edu/

Compute access times between satellites and ground stations

• Right Click on RAX2_SSC -> “Access”

• Access for RAX2_SSC

• Highlight all ground stations

• Hit “Compute”

• Under Reports-> “Access”

12. Make a report and rank the

ground stations in total access

time over the scenario.

Explain the order of the ground

stations’ access times.

Note: Access Reports can also be made using the conventional Report Generator.


13. Make a report that provides the access time from RAX2 to the Target of

Interest (Poker Flat) over the scenario.

– Compute the average access time per day

– Figure out the maximum/ minimum access time


OK, so now we’ve generated ….

14. Take a few pictures of your simulation capturing all of the ground stations/

targets and copy and paste into your report.



SAVE BREAK


Let’s put in a GPS Constellation!

– From top bar->Insert: Satellite from GPS Almanac

– Window->At top: Automatic- AGI Server

– Window-> On bottom left: Select All

– Window-> Click: Insert, it will take awhile for the constellation to load

– You should see the sweet constellation below (make sure to zoom out):


Reminder on Animation Toolbar



Run your sim a few times at different speeds. Have fun with it.



Let’s input a GPS “receiver” on RAX-2

• Go Insert-> New->Receiver-> From Saved Receiver File (*.r)

• Select RAX2_SSC


• Make sure “Files of type” is a receiver (*.r)

• Chose the GPS_receiver from the GPS file:

(You’re lucky- we’re giving you this receiver we’ve modeled)


• Right click ->Properties

• Check out the “Model Specs” and “Antenna” tabs:


15. What frequency does the receiver operate at?

Where does the antenna pattern come from? What is antenna gain pattern?

What’s your best guess of what the numbers in the antenna_pattern.txt file mean?

• In Properties, go to Graphics->Boresight

• Make sure this is checked and a Color is selected


• Check out your simulation. Does it look correct?



SAVE BREAK


• Now put a transmitter on your GPS satellites

(much like how we put a receiver on RAX-2)

• Hint is shown below:

• Make sure to hit Apply!


Now we’re going to compute the link budget!

• Right click on GPS_Receiver: “Properties”->Access

• Select options below and hit Link Budget

16. What is the maximum Eb/No (dB)?

What is the average Eb/No (dB) when the satellites are in view?


• Note that we have made a lot of assumptions in this link budget!

• I gave you the antenna gain pattern for the receiver- usually you will need

to find and model this.

• To perform a link budget for a real system, make sure to check all the

inputs (gains/ losses/ etc.)!

• This approach can be used to compute link budgets for communication

links too!



SAVE BREAK

Change of gears…. Next we’re going to model orbits about Mars and Phobos!

• Open a new STK Scenario (you can keep the old one open if you want)

• Now, select desired “Central body” (Mars/ Phobos/ whatever)

• Make sure to name scenario and chose desired analysis period

Creating Phobos Scenario

Check out Phobos- pretty cool!

Now let’s input a satellite using the Orbit Wizard. You know how to do this.

Make it “stationary” relative to Phobos


Personalize your satellite- change the name/ attitude/ orbit as you desire…

(Think about Project 2 and what type of orbit you might consider)


17. Compute the orbital period (about Phobos) for your satellite (you can do

this with reports). Compute the eclipse times for your satellite. What is the

maximum/ minimum/ average eclipse time per orbit? Watch a few orbits

and make sure your orbits make sense.


Extra Assignment 1:

• Compute the angle between the magnetic field line and the RAX-2 satellite

• Plot the results over several orbits

• Comment/ explain the results


Extra Assignment 2:

• Compute the angles between the line of sight to the sun and the RAX-2

+X, -X, +Y, -Y faces

• Plot the results over several orbits

• Comment/ explain the results


Extra Assignment 3:

Calculate average/ minimum/ maximum distance from:

• Earth to RAX-2

• Earth to GPS Constellation

• RAX-2 to GPS Constellation

Explain why does/ doesn’t make sense.


Extra Assignment 4:

Compute the average number of GPS satellites with Eb/No (dB) >35 dB (typical

minimum threshold required for GPS receivers) as a function of satellite latitude

for RAX-2. Does this make sense? Why or why not?


Extra Assignment 5:

Compute the average access time between your satellite in an orbit about Phobos

And the Deep Space Network (DSN). Discuss the general trends. How much

data could be communicated from your satellite to Earth at a 10 bps link? 100

bps link? 1kbps link?

Phobos Scenario

Documents

483 Tutorial STK/ Operations Sara Spangelo, March 27 · PDF file483 Tutorial STK/ Operations Sara Spangelo, March 27-28, ... We’re going to use a TLE to define the ... i.e. does