STK LAB 5 - Laboratory Mission 0: Installing STK PDF

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Laboratory Mission 0: Installing STK...

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Laboratory Mission 5: Predicting Orbits Mission Objective - Develop an understanding of orbital predictions - Use STK to predict the future location of an orbiting object - View the International Space Station based on STK predictions

Resources/Requirements For this laboratory mission, you must have; Successfully installed STK and borrowed a license for a period covering the class in which this mission is to be executed (unless using the computer lab) Read Chapter 8.1 & 8.2 of Understanding Space

Mission Planning DEVELOP AN UNDERSTANDING OF ORBITAL PREDICTIONS 1.

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SATELLITE TWO LINE ELEMENTS (TLE): The Space Control Center in Cheyenne Mountain’s Operation Center (CMOC) collects and maintains general orbital element sets on all space objects. These Two Line Element (TLE) sets are periodically updated to maintain a reasonable predictive capability on all space objects. From the knowledge of a spacecraft’s classical orbital elements, the position and velocity of an object at a given time in the future can be predicted. A sample TLE for the International Space Station (ISS) is given below.

ISS (ZARYA) 1 25544U 98067A 02166.25000000 .00022749 00000-0 30765-3 0 5637 2 25544 51.6332 62.6174 0006804 238.6710 31.2451 15.57611327203721

The general format of the TLE is: OBJECT NAME

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[IDXXXU] [Int Desig] [Epoch] [FTD MM] [STD MM] [drag] [Eph T] [Ele #] [IDXXXX]

[Inc]

[RA AN]

[Ecc]

[AOP]

[MA]

[Revs]+[ON]

A. Line 0 is an eleven-character name. [ISS (ZARYA)] B. Line 1 • Satellite Number [25544U] •

•

• • •

International Designator • Last two digits of launch year [98067A] • • Epoch •

Launch number of the year [98067A] Piece of launch [98067A] Year (Last two digits of year) [02166.25000000]

• Day number and fractional portion of the day [02166.25000000] First Time Derivative of the Mean Motion divided by 2 or Ballistic Coefficient (Depending on ephemeris type) [.00022749] Second Time Derivative of Mean Motion divided by 6. (Blank if N/A) [00000-0] BSTAR drag term if GP4 general perturbation theory was used. Otherwise, radiation pressure coefficient. [30765-3]

• Ephemeris type [0] • Element number [5637] C. Line 2 • Satellite Number [25544] • • •

Inclination [51.6332 Degrees] Right Ascension of the Ascending Node [62.6174 Degrees] Eccentricity [0006804 (decimal point assumed)]

• •

Argument of Perigee [238.6710 Degrees] Mean Anomaly [31.2451 Degrees]

• • •

Mean Motion [15.57611327203721 Revs per day] Revolution number at epoch [15.57611327203721 Revs] Check Sum [15.57611327203721]

Notice that this TLE set has an epoch (reference point in time for the orbital elements) on the 166th day of 2002 (15 JUN 2002). The actual time at which these orbital elements were valid was 06:00:00.00 UTC. Based on this data, future positions and velocities of the ISS can be estimated. Due to orbital perturbations (including orbital drag), the ISS TLE is updated periodically. An updated TLE is given below: ! ISS (ZARYA) 1 25544U 98067A 04251.47151402 .00013051 00000-0 11370-3 0 6336 2 25544 51.6353 265.7194 0005624 120.5009 34.2494 15.69386100331241

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! Figure 1: STS-114 (Discovery) onboard photograph of the ISS in orbit on 06 Aug 2005.

2.

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DOWNLOAD THE LATEST TLE FOR THE ISS USING STK a) In this section, you will be required to download the latest TLE from for the ISS through STK. In order for STK to connect to the Internet, you will need to set the proxy server. To do this, follow these steps: • Open STK. • Select the Tools menu from the tool bar. • Select Options from the menu (see Figure 2). • Select the Online tab. • Click on the Allow Online Operations box. • Click on the Use Proxy box. • Type in “DRENPROXY.USAFA.AF.MIL” in the Server box. • Type in “80” in the Port box. • Click OK. • If this doesn’t work, open your internet explorer, go to tools, click on internet options, click on connections, click on LAN settings, and check what you are using for proxy and port on your internet connection. Enter these into the HTTP Proxy boxes.

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! Figure 2: Setting Your Proxy Address

b) While connected to the USAFA Intranet, launch STK and create a new Scenario. c) Add a Satellite object (cancel the Orbit Wizard) and open the Properties Browser for the new Satellite. d) Select the Basic/Orbit page and change the Propagator to SGP4. • This Propagator allows STK to use the TLEs for a given spacecraft. e) In the SSC Number block, enter the satellite number for the ISS (25544). f) Under the TLE Options at the bottom right, click on the Load button. • On the popup window, under Load Method select Online Load (See Figure 3). • Check the Load Newest box. • Click on the Go Online button. • Under the TLE Selection box, make sure the SSC number 25544 is highlighted and click OK. g) Back on the Orbit/Basic Property Page, click Apply. h) Select the 3D / Data Display Property Page. • Check the box for the Classical Orbital Elements. • Click OK. i) Open the 3-D Graphics Window and record the six COEs displayed for the ISS in Table 1.

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Figure 3: TLE Selection menu.

! Table 1: COEs for the ISS based on the most recent TLE available.

Orbital Element

Value

a

km

e i

degrees

Ω

degrees

ω

degrees

ν

degrees

! j) Rename the Satellite “ISS” in the Object Browser. k) Save the scenario in a folder on your desktop named “ISS_View”. You will refer to this file during the in-class Mission Execution. What type of orbit is the ISS in? What is the orbital period of the ISS? What is the approximate altitude of the ISS orbit?

Mission Execution Having downloaded the most recent TLE for the ISS, predict future visible passes over the Air Force Academy using STK.

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PREDICT FUTURE PASSES OF THE ISS OVER USAFA 1.

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Open the saved Scenario file ISS_View in the folder that you saved during Mission Planning. The image canno t be displa yed.

Change the scenario dates a) Open the Properties Browser for the Scenario b) Open the Basic / Time Period page. c) Enter the word “Today” in Start Date field and the Epoch field. d) Enter “+14 days” in the End Date field. e) Click OK.

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Create a city viewing location a) Under Insert in the top menu, select City from Database b) Check the City Name box and enter “Colorado Springs” (see c) Figure 4).

Figure 4: City Database menu

d) Click Perform Search. A Search Results window will appear as shown in Figure 5.

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Figure 5: City Database search results

e) Highlight Colorado Springs and click OK. • Notice that a ground station icon named Colorado_Springs has appeared in the Object Browser. f) Close the City Database window and open the 3-D Graphics Window • Confirm that the ground station is located at the appropriate point on the Earth. 4.

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Set up the constraints for viewing the ISS at USAFA a) Open the Properties Browser for the Colorado_Springs ground station. b) Under Constraints in the left column, select Sun. c) Check the Lighting box and change the pull down menu to Umbra. d) Click OK. • This constraint tells STK to only report on ISS passes that occur when the ground station is in darkness. e) Open the Properties Browser for the ISS Satellite f) On the Constraints/Sun page, check the Lighting box and change the pull down menu to Direct Sun. g) Click OK. • This constraint tells STK to only report on ISS passes that occur when the ISS is in direct sunlight.!

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Create a Report of potential ISS viewing opportunities from USAFA a) Right click on the Colorado_Springs ground station in the Object Browser. b) In the popup menu, select Facility Tools and open the Access tool. • Note: You may also click the Access icon ( ) from the toolbar. c) Highlight the ISS Satellite icon in the Associated Objects box. d) Click Compute at the bottom of the box. e) Under Reports, select AER.

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This report gives the time, azimuth, and elevation of visible ISS passes from USAFA. The times are UTC which is +6 hours MDT. You will have to subtract 6 hours from the times given in the report to obtain the local viewing time. • Note: As you are subtracting 6 hours, keep in mind the DATE may change also. For example, 00:50:00 UTC on 2 Oct, is actually 18:50:00 MDT on 1 Oct.

• •

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Changing AER report to local time: a) Click on Custom under Reports in the Access for Colorado_Springs menu. b) Select AER in the window that opens. c) Click Customize under the Style menu to the right. d) In the right box of the popup menu that opens, select Time under Report Contents. e) Select Units below the menu. f) Un-check the box for Use Default Report Units and select Gregorian LCL (LCLG) in the box to the right. g) This will change the AER report time units from UTC to MDT. h) Click OK to close the open menus until you return to the Access for Colorado_Springs menu. i) Select AER under Reports.

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Copy and paste this report into a word processing program and save the file for the Mission Debrief and to enjoy watching the ISS pass over the Academy From the scenario start date, when is the first opportunity from USAFA to view the ISS? What is the maximum elevation of this pass? Will this pass be visible above the “horizon mask” (i.e. above the mountains and buildings in the local area)? At the maximum elevation, what is the azimuth?

NOTES ON OBSERVING THE ISS: First, start in an open location free of trees and large buildings. A dark location is also preferred. Timing is important, so make sure you have a watch with the accurate local time. Select a pass from your STK data that has a maximum elevation (degrees above the horizon) greater than 15 or 20° so that the ISS clears the local buildings and landscape. Recall that the azimuth is measured from true North; therefore, an azimuth of 0° implies that the ISS is due North (90° = East, 180° = South, 270° = West). You can also visit http://www.heavens-above.com. This site estimates the relative brightness (Magnitude) of the ISS for each pass. A smaller (i.e. negative) Magnitude implies a brighter pass (the Magnitude of the brightest star in the Northern sky, Sirius, is -1.46). For morning passes in the Fall, Sirius (in the constellation Canis Major) will be visible and the brightest star in the sky. For evening passes in the Fall, Vega (in the constellation Lyra) is the brightest star in the sky with a magnitude of 0. The website also provides star maps with the ISS crossing paths for Colorado Springs; however, if you select a negative magnitude pass, finding the ISS will be very easy. Figure 6 shows the geometry of a typical ISS pass.

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! Figure 6: A typical ISS pass showing maximum elevation (directly overhead would be an elevation of 90°) and a departure point. Departure refers to a loss of elevation or sunlight illuminating ISS; thus, departure may occur before the ISS reaches the local horizon.

! Figure 7: Amateur ground-based telescope view of the ISS.

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Use the star maps provided below to sketch the trajectory of the ISS over-flight. 1. EVENING PASSES IN THE SPRING

In the evening sky (late Winter and early Spring), three bright stars to the southwest form the Winter Triangle. The brightest of these stars is Sirius (the brightest star in the Northern Hemisphere) in the constellation Canis Major. Betelgeuse in Orion and Procyon in Canis Minor finish the Winter Triangle. Orion with its collection of bright stars is unmistakable in the early evening hours. Betelgeuse in Orion and Aldebaran in Taurus (just above Orion) are characteristically red in color. A grouping of seven stars is just above Taurus known as the Pleiades (or seven sisters, not to be confused with the “Little Dipper” due to its shape). The twin stars of Castor and Pollux are in Gemini to the West of Orion. The constellation LEO is over head, and the familiar “Big Dipper” in Ursa Major is also prominent to the North. In the early evening, Venus might be visible to the West. If it is, it will be much brighter than Sirius (the dog star) and will not appear to “twinkle” like Sirius and other stars do. Mars will also be visible in the West after about 2000 hrs.

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2. MORNING PASSES IN THE SPRING.

In the morning sky (early Spring), the three bright stars overhead form the Summer Triangle. The brightest of these stars is Vega in the constellation Lyra. The other two members of the summer triangle are Deneb in Cygnus and Altair in Aquila. Off to the west is another bright star Arcturus (slightly orange in color) in the constellation Bootes. To the south is Scorpius and its familiar red star Antares. Cassiopea, the large “W” in the sky is to the east of the North star, Polaris, in Ursa Minor. In the early morning, the planet Venus might be visible to the east. If it is, it will be the brightest object (besides the moon) in the morning sky.

NOTES ON THE USE OF THE ABOVE STAR MAPS: At first glance, it appears that East and West are on the wrong side of the map. However, the map was made to be correct when they are held over your head with North pointing in the right direction.

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