The Naval Research Laboratory's Tether Electrodynamics Propulsion CubeSat Experiment (TEPCE) underwent successful deployment tests on March 19 and March 23, 2010.
TEPCE is a tethered spacecraft being built by NRL to demonstrate electrodynamic propulsion in space. Electrodynamic propulsion holds the promise of limitless propulsion for maneuvering spacecraft without using expendable fuel. The spacecraft, in its orbital configuration, will consist of two CubeSat end masses attached to the end of 1 kilometer of electrically conducting tether.
Electrodynamic propulsion works on electromagnetic principles similar to an electric motor. The magnetic field in an electric motor attracts an electric current that flows through the windings of the armature causing the armature to spin. In space, the earth has a naturally occurring magnetic field and for TEPCE, the tether wire serves the purpose of the armature. By inducing an electric current to flow along the tether, a mutual attraction between the earth's magnetic field and the tether will occur. This electromagnetic attraction can propel TEPCE to higher altitudes or to change the orientation of its orbit.
NRL researchers conducted the deployment tests in the Naval Center for Space Technology's high bay facilities at NRL. The tests exercised a spring deployment mechanism, called a stacer, which pushes the two CubeSats apart at a relative velocity of 4 meters per second. The tests were conducted in free fall that simulated the weightlessness of space. The CubeSats were instrumented with angular rate gyros and accelerometers that measured rotations and accelerations.
The TEPCE deployment tests determined the effectiveness of the stacer mechanism to produce the required separation velocity while holding tip-off rotations to an acceptable level. The deployment experiment was a milestone in the development of the first tethered spacecraft to demonstrate electrodynamic thrusting for orbit maneuvers using energy derived from the sun instead of from expendable fuel, explains NRL's Dr. Shannon Coffey, TEPCE program manager.
Figure 1 shows the integrated TEPCE spacecraft immediately before the deployment tests. The end masses are designed to be nearly identical. Visible in this picture are the batteries, partially complete electronics boards and antennas to the radio receivers. The white cylinder in the middle eventually will house the tether. Figure 2, shows a nearly vertical orientation of TEPCE immediately after deployment. The pictures and rate gyros proved that sidewise rotations will not be a problem during deployment in space.