STK 6.0 Session 3: Newton’s Second Law Revision 1.0 Aug 9, 2005
Preparations for the Instructor
This session contains three main tasks.
Given a pair of orbiting satellites, students determine the amount of thrust generated by a rocket engine
prepared by the instructor.
Given the Satellite Properties window, students generate one gee (9.8 m/s
2
) of thrust.
Given a target range of 10. km, students compute and execute maneuvers to reach and stay close to the
target range in the least time. The maximum acceleration is limited to one gee.
Task 1: Measure the force (thrust) of the provided rocket engine.
A real rocket engine expends a significant amount of mass as it generates thrust. Beginning physics
students have just learned Newton’s Second Law: F =ma. You will have to edit STK to create a custom
rocket engine that generates thrust without expending mass, allowing students to apply F = ma without
having to learn the rocket equation.
Launch STK, create a new scenario, rename it 03Newton, and save it to a new folder named 03Newton.
Under View, select Astrogator Browser. Click on the directory folder named Engine Models.
Highlight the entry named Constant Thrust and Isp (which is specific impulse – the number of seconds one
pound of rocket fuel can generate one pound of thrust). Click on the button named Duplicate.
When the Field Editor comes up, rename the engine as Newton engine #1. Under User Comment, type
“unknown thrust and zero mass loss.” When you close the Field Editor, you will see your new engine
displayed in green in the Astrogator Component Browser.
Double click on your (green) Newton engine #1 to edit its values. Double click on Isp to change its value.
The allowed upper limit is claimed to be 1.79 x 10
308
. This is a slight lie. Enter 1.7e307 and it will be
accepted. This large value effectively reduces the mass flow rate for the engine to zero.
Double click on the Thrust parameter. The default value is 500. N. Change it to some new value of your
choosing, such as 800. N (or 815 N). Be aware the value you enter can be found by the students if they
follow in your footsteps and launch the Astrogator browser. During the classroom session monitor the
students to ensure they do not look up the thrust value – they are to calculate it, not look it up.
Hit Okay to close out the Astrogator browser window and save the scenario. You should enter a different
thrust value on each computer your students use. Keep a table of your engines such as the one shown.
Computer ID Engine # Thrust (N)
_________ ________ _________
_________ ________ _________
_________ ________ _________
_________ ________ _________ End of Preparations for the Instructor
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