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PRACTICE NO. PD-ED-1229 PAGE 1 OF 6

PREFERRED RELIABILITY PRACTICES

SELECTION OF ELECTRIC MOTORS FOR AEROSPACE APPLICATIONS

Practice: Careful attention is given to the specific application of electric motors for aerospace applications when selecting motor type. The following factors are considered in electric motor design: application, environment, thermal, efficiency, weight, volume,life, complexity, torque, speed, torque ripple, power source, envelope, duty cycle, and controllability. Brushless direct current motors have been proven to be best all-around type of motors for aerospace applications because of their long life, high torque, high efficiency, and low heat dissipation. Benefit: Selection of the optimum electric motor for space flight operations results in a safe,reliable, effective, efficient and economical electric motor power source for space flight. Brushless direct current motors provide the lightest weight alternative for most applications. Programs That Certified Usage: Tethered Satellite System (TSS), Solar Max Mission (SMM), Infra Red Telescope (IRT), Saturn 1B (S1B), Saturn V (SV), Skylab, High Energy Astronomy Observatory (HEAO), Lunar RovingVehicle (LRV), Hubble Space Telescope (HST), Advanced X-Ray Astrophysics Facility (AXAF), and other MSFC projects. Center to Contact for More Information: Marshall Space Flight Center (MSFC) Implementation: Four principal types of electric motors are suitable for in-space applications, AC Induction Motors, Brush Direct Current (BDC) Motors, Brushless Direct Current (BLDC) Motors, and Stepper Motors.Table 1 shows the most predominant applications for each type of motor. Generally AC Induction Motors are used for constant speed applications where a fixed frequency power source such as 60 Hz or 400 Hz is available in the spacecraft. Typical applications are fans and pumps. Motor construction consists of windings on the stationary part of the motor and copper shorting bars on the iron laminationsof the armature. The AC voltage applied to the windings induces a current in the armature

MARSHALL SPACE FLIGHT CENTER

PRACTICE NO. PD-ED-1229 PAGE 2 OF 6

SELECTION OF ELECTRIC MOTORS FOR AEROSPACE APPLICATIONS
of the rotor, creating a magnetic field. This field reacts with the field in the stationary part of the motor to create torque. These motors are rugged, with no wear outmechanisms other than the bearings. Table 1. Uses of the Four Principal Types of Electric Motors for Space Applications A.C. Induction Motor 1. Thrust Vector Control (TVC) Actuators 2. High torque and high RPM applications Brush D.C. Motor 1. Limited-life applications 2. Low RPM applications 3. High torque applications Brushless D.C. Motor 1. TVC actuators Stepper Motor 1. Optic drives

2. Fuel valvecontrol actuators 3. Solar array deployment 4. Control moment gyroscopes 5. High RPM applications 6. Light weight applications 7. Low thermal emission applications

2. Solar array deployment 3. Gimbal positioning 4. Low torque applications 5. Open loop micropositioning 6. Timer switching

The BDC motors use commutators and carbon brushes to apply current through the windings as the motor rotates.The BDC motor utilizes wound elements in the rotor and permanent magnets attached to a stationary stator ring. In a BDC motor, electrically separated motor windings are connected to the commutator ring. Current is carried by spring loaded brushes, through the commutator into the windings of the rotor. The current in the windings creates magnetic fields, which react with the stator’s permanentmagnetic field. The magnetic repulsion causes the rotor to rotate. This rotation causes the brushes to make and break connections through the commutator with different winding pairs. The moving magnetic field provides the torque necessary to rotate the motor’s armature.

PRACTICE NO. PD-ED-1229 PAGE 3 OF 6

SELECTION OF ELECTRIC MOTORS FOR AEROSPACE APPLICATIONS
The BLDC motor uses electronic...
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