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Structural Dynamics Test of Spiral Tube Actuator for Controlled Extension / Retraction (STACER) Antenna Deployment in Microgravity

Completed Technology Project

Project Introduction

Structural Dynamics Test of Spiral Tube Actuator for Controlled Extension / Retraction (STACER) Antenna Deployment in Microgravity
The Trapped Energetic Radiation Satellite (TERSat) is an MIT satellite program sponsored by the AFRL University Nanosatellite program. The goal of TERSat is to understand how Very Low Frequency (VLF) waves interact with radiation particles and how VLF waves propagate in the plasma environment of the Van Allen Radiation Belts. A key component of TERSat payload is the STACER (Spiral Tube & Actuator for Controlled Extension/Retraction) antenna that will be used to transmit and receive VLF signals. This antenna is composed of a strip of beryllium-copper sheet metal coiled into a cylinder, which spring-deploys to a length of 2.5 meters. TERSat will use two STACERS to form a 5 m dipole. Only one 2.5 meter STACER is involved in the proposed test. A microgravity environment on a parabolic flight would enable testing of the deployment mechanism and antenna dynamics under flight-like load conditions, adding confidence in the STACER deployment system design. The STACER antenna poses two challenges to the TERSat mission: 1. The deployment mechanism has several possible modes of failure, some of which can be influenced by gravity. 2. It is important to understand the structural resonant frequency and behavior of the STACER for designing the satellite control algorithms, but STACER dynamics are difficult to measure on the ground. To test the deployment, a voltage will be applied to the Frangibolt actuator, which will release the STACER. The expectation for this test is that the release will occur within one parabola of microgravity, but if unforeseen difficulties occur with deployment, attempts during multiple parabolas may be necessary. The dynamics of the STACER will be tested over the rest of the parabolas of a single flight. A miniature shake table system controlled by a laptop will produce a sine sweep excitation through 100 Hz to 200 Hz per parabola, allowing engineers on-board to study the effects of the excitation. A high-speed camera will capture the motion for post-processing of data. A reference screen and clock will help to verify the eigenvectors and eigenvalues of the antenna motion. This information will enable the TERSat attitude control engineers to design the control algorithms to avoid exciting the antenna. Additional flights are desirable for statistical significance, but a single flight would be a valuable demonstration. The STACER deployment system development supports two Technology Roadmaps: the Science Instruments, Observatories, and Sensor Systems Roadmap (Technology Area 8) and the Materials, Structures, Mechanical Systems and Manufacturing area (Technology Area 12). The STACER antenna deployment and control dynamics are directly applicable to Structures and Antenna under 8.2.2 Observatory, which specifically calls out large deployable structures and control of large structures. These areas are addressed by the two goals of the TERSat STACER deployment system microgravity experiment. With respect to Technology Area 12, the restraint and release mechanisms under test fall in 2.3.1 Deployable, Docking, and Interfaces section of 2.3 Mechanical Systems in the listed Area 12 work breakdown structure. More »

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