STK Session 10: Transferring a Satellite between Circular Orbits Rev 1.1 24 Sept 2003
Name 1: ___________________________ Name 2: _________________________________
In this session you are tasked with transferring a satellite from an inner circular orbit to an outer circular
orbit. This requires two firings of a rocket engine aboard the satellite. This is called a Hohmann transfer,
as it uses the least amount of energy to transfer the satellite.
Transfer orbit
Inner
orbit
orbit
orbit
v1
v2
Outer orbit
The central body is the Earth. The radius of the Earth is 6378.137 km
G = 6.672 x 10-11 N-m2-kg2  = 3.986005 x 1014 m3/s2
Inner orbit radius = _______________
Outer orbit radius = _______________
Calculate the velocity of the satellite in the circular inner orbit:
___________________
Calculate the velocity of perigee of the transfer orbit:
____________________
Calculate the delta vee to enter the transfer orbit from the inner orbit: ___________________
Calculate the velocity of apogee of the transfer orbit:
_____________________
Calculate the velocity of the satellite in the circular outer orbit:
_____________________
Calculate the delta vee to enter the outer orbit from the transfer orbit: ___________________
Calculate the time of flight along the transfer orbit:
______________________
Launch STK.
Create a new scenario named Hohmann. Set its time duration to three days.
Create a new satellite.
Highlight the satellite, select basic properties, and change the propagator to Astrogator.
Segment 1: inner orbit
Right click on Initial State. Select Properties. Change the name from Initial State to inner orbit.
Change the element type to Modified Keplerian. Set the radius of periapsis to the value you used above.
Set the Eccentricity to 0.000. Set the Inclination to 28.5 degrees. Click on Satellite properties, and change
the fuel mass to 5000 kg.
More on back 
STK Session 10: Transferring a Satellite Between Circular Orbits page 2 Rev 1.1 Sept 24, 2003
Option: Use STK without detailed step by step instructions.
On your own, add additional segments to the Astrogator propogator. Show the satellite initially located in
the inner orbit for a duration of two hours, followed by an impulsive maneuver that sends the satellite along
the transfer orbit. After that, a second impulsive burn sends the satellite into the outer orbit. Propagate the
final orbit for at least one day.
Rotate your view of the satellite to look down from above the North Pole region of the Earth. Zoom out to
see the full trajectory.
Show your completed animation to your instructor.
If you do this without additional help, you will receive seven bonus points.
STK Session 10: Transferring a Satellite Between Circular Orbits page 3 Rev 1.1 Sept 2003
By using this sheet you are forfeiting seven bonus points.
Segment 2: propagate
Right click on inner orbit, and Insert After: Propagate. With this segment highlighted, change the
Propagator to Earth Point Mass. Set the trip duration to 7200 sec.
Segment 3: delta vee 1
Right click on the propagate segment, and Insert After: Impulsive Maneuver. Right click on this new
segment, select properties, and change the name to delta vee 1. (That represents the first change in velocity
maneuver.) Select Thrust Vector for Attitude Control. Select Cartesian for Vector Type. Select VNC for
Thrust Axes. Set the X (Velocity) component to the value you had calculated. Turn ON the Decrement
Mass Based on Fuel Usage option.
Segment 4: Transfer Ellipse
Right click on delta vee 1, and Insert After it a propagate segment. Right click on this new segment, select
properties, and rename it Transfer Ellipse. Change its color to white. Select Earth Point Mass as the
propagator. Then change the duration to the value you had calculated above.
Segment 5: Delta vee 2
Right click on the Transfer Ellipse segment and Insert After: Impulsive Maneuver. Right click on this new
segment, select properties, and rename it delta vee 2. Select Thrust Vector for Attitude Control. Select
Cartesian as the Vector Type. Select VNC as the Thrust Axes. Set X (Velocity) to the value you had
calculated above. Turn ON the Decrement Mass Based on Fuel Usage option.
Segment 6: propagate
Right click on delta vee 2, and Insert After: propagate. Right click on this new segment, and rename it as
outer orbit. Set its color to blue. Select Earth Point Mass as the propagator. Set the Duration to at least
86400 sec.
At last, you are ready to animate your satellite. Click the green Run button labeled, “Go.” Animate the
scenario. Rotate your view of the satellite to look down from above the North Pole region of the Earth.
Zoom out to see the full trajectory.
Show your completed animation to your instructor.
Teacher Notes for STK Training Session #10 Rev 1.1 Sept 24, 2003
Session 10 is a test. Students are paired up for this test. They are assigned an inner orbit radius and an
outer orbit radius by the instructor. Generally, use values that are at least 100 km greater than the radius of
the Earth.
Typical values:
Inner radius (km)
Outer radius (km)
6570
7000
6700
8000
6800
8400
6900
8800
7100
9500
7300
10700
Really, you can use any pair of values you want – but don’t go beyond geosynchronous orbit -- just to keep
the numbers realistic.