National Aeronautics and Space Administration

Educational Product Educators Grades 5–12 & Students
EB-2001-12-019-JPL

Educational Brief
C A S S I N I S C I E N C E I N V E S T I G A T I O N

The Spinning World of Spacecraft Reaction Wheels
Objective
To demonstrate how reaction wheels (also known as momentum wheels) take advantage of Newton’s Third Law to control a spacecraft’s orientation. Time Required: 1 hour Saturn System Analogy: Cassini’s Reaction Wheel Assembly and its use during orbital operations at Saturn Keywords: Gyroscope, Interplanetary, Momentum, Orientation, Reaction
M AT E R I A L S

• D-cell battery. This will provide half of a 3-volt motor’s rated performance, which is just about right. • About 6 feet of thin wire pair, 28 gauge or so (available at electronics parts stores and hardware stores that carry a wide ranges of wire gauges). Use stranded rather than solid-conductor wire to provide flexibility. The thinner, longer, and more flexible, the better. • Optional: a switch or pushbutton, with a normally open circuit (available from electronics parts stores for a few dollars). If the switch is not used, the motor is controlled by touching the wire to the battery terminal. • Optional: a potentiometer (available from electronics parts stores) or other means to vary the voltage supplied to the motor

• Cassini spacecraft paper model (available through the Cassini web site at http://saturn.jpl.nasa.gov/ cassini/english/teachers/classroom.shtml/); also suitable are paper models of interplanetary spacecraft (available free from NASA at http://spacelink.nasa.gov); or commercially made models (an Internet search on “spacecraft models” will provide sources). • Small battery-powered electric motor (available at discount hobby stores); for example, the 3-volt miniature DC motor available for $4 at http:// www.ScientificsOnline.com/Products/ •