Interplanetary Tutorial

Topics: Orbit, Ecliptic, Moon Pages: 21 (7071 words) Published: March 12, 2013
Trajectories in STK in a
Few Hundred Easy

(*and to think that last year’s students thought some guidance would be helpful!)

Satellite ToolKit Interplanetary Tutorial
STK Version 9

1) Open STK. Choose the “Create a New Scenario” button.

2) Name your scenario and, if you would like, enter a description for it. The scenario time is not too critical – it will be updated automatically as we add segments to our mission.

3) STK will give you the opportunity to insert a satellite. (If it does not, or you would like to add another satellite later, you can click on the Insert menu at the top and choose New…) The Orbit Wizard is an easy way to add satellites, but we will choose Define Properties instead. We choose Define Properties directly because we want to use a maneuver-based tool called the Astrogator, which will undo any initial orbit set using the Orbit Wizard. Make sure Satellite is selected in the left pane of the Insert window, then choose Define Properties in the right-hand pane and click the Insert…button.

4) The Properties window for the Satellite appears. You can access this window later by right-clicking or double-clicking on the satellite’s name in the Object Browser (the left side of the STK window). When you open the Properties window, it will default to the Basic Orbit screen, which happens to be where we want to be. The Basic Orbit screen allows you to choose what kind of numerical propagator STK should use to move the satellite. Since we want to perform maneuvers, choose Astrogator from the Propagator pull-down menu. This changes the Basic Orbit window to look like the one below.

5) Notice at the top that the Central Body is the Earth. This is good since we are starting at Earth. If you were modeling only heliocentric orbits or those about other planets, you could change the central body for the scenario by making sure that “Planetary Options” is checked on the View menu at the top of the STK window, then using the pull-down on the New Scenario button at the top left of the STK window to create a new scenario around a different central body. 6) Set the Initial State of the satellite to be the initial circular orbit. You can do this most easily by selecting Keplerian in the Coordinate Type pull-down menu. Set an initial circular orbit (Eccentricity = 0) with a 300 km altitude (Semi-major Axis = 6678 km). The Inclination should be 28.5 degrees, and probably already is by default. The Orbit Epoch time at the top tells you at what time the satellite will have the True Anomaly specified at the bottom. 7) The left pane of the Basic Orbit window lists the pieces of your trajectory, called Mission Control Segments, or MCS. After the Initial State, there should already be a segment called Propagate. Clic k on the Propagate segment.

8) The first option available to you is which type of propagator to use to numerically integrate the equations of motion. Click the “…” button next to the Propagator name to choose from the available options. To match the calculations you have done by hand, choose Earth Point Mass as your propagator. (The others will include contributions from the oblateness of the Earth or gravitational effects from third bodies and will show how your orbit would drift given these effects.) 9) There are many options for how long to allow the satellite to continue in its origina l orbit. These are called Stopping Conditions. Time is always selected by default, and is always set to 43200 seconds, or 12 hours. Click the Insert… button next to Sto pping Conditions to choose other options.

10) If you want to allow the satellite to orbit three times before performing its next maneuver, a good stopping condition is counting how many times the satellite passes the Ascending Node. Choose AscendingNode from the Stopping Conditions list, and click OK. 11) Now your Propagator window has two Stopping Conditions. Click the line for Duration, then the...
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