![]() ![]() How does that stabilize the satellite? Imagine the satellite as a hand trying to excite a wave in a string by moving up and down. Because the spring is (deliberately) imperfectly elastic, these waves are damped to heat and dissipate. Because the boom is attached to a large mass (the payload) at one end, the angular oscillations tend to cause a whipping motion in the spring that excite waves along the spring. How do they work? There are several types, but one is a long helical spring. Passive Gravity-Gradient Libration Dampers, SP-8071. ![]() Tubular Spacecraft Booms, Extendible, Reel Stored SP-8065 DODGE is mentioned 14 times.There are some interesting, if slightly dated NASA monographs about these: Passive damper booms dissipate energy internally so that oscillations around the stable orientation gradually damp down. Question: What are damper booms, and how do the the "passive and semipassive techniques" to achieve triaxial gravity gradient stabilization work in this case?īonus points: How did a boom almost 46 meters long " get out of DODGE" by such a long distance? The cylinder itself is only about 1.6 meters long. The satellite was placed in an operational off mode in early 1971. Early in 1971, problems with the batteries on board limited operation to only solar acquisition periods. The satellite operated for over 3 years and took thousands of black-and-white and color pictures of the earth. The mission was a success and proved the feasibility of achieving triaxial gravity-gradient stabilization at synchronous altitudes using passive and semipassive techniques. It was oriented with its base and mast directed toward the center of the earth's disk. The satellite was successfully stabilized 12 days after launch by means of the gravity-gradient booms and libration dampening systems. ![]() The telemetry system included two directional antennas mounted on the mast, two 38-channel commutators for housekeeping data, and a dual transmitter system that transmitted analog data at a frequency of 240 MHz and TV data at 136.8 MHz. ![]() The command system consisted of a dual command receiver, dual command logic, and power switching circuitry. The remaining seven booms were contained in the satellite body along with a two-camera (one color and one black-and-white) vidicon camera system. The cylindrical mast housed a 4.6 m boom that extended through the end of the mast, two 15.25 m long damper booms that extended in the x-y plane, and triaxial vector magnetometer sensors. Upon radio command, these booms could be independently extended or retracted along three axes to various limits out to 45.75 m. A total of 10 knobbed booms were carried on board. The satellite body was 2.41 m long and 1.22 m in diameter. The satellite was in the form of an octagonal aluminum shell with a truncated pyramid at the top and a 25.4 cm-diameter cylindrical mast extending 1.57 m from the satellite base. Secondary objectives included obtaining measurements of the earth's magnetic field at near-synchronous altitudes and black-and-white and color TV photography of the entire earth disk. The DODGE (Department of Defense Gravity Experiment) satellite was orbited primarily to study a number of advanced biaxial and triaxial gravity-gradient stabilization techniques at near-synchronous altitudes. The spacecraft's primary function however was to experiment with gravity gradient stabilization for high orbits near GEO. I'd never heard of DODGE until I saw it mentioned this answer as the source of the first full color "full Earth" image. ![]()
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