To The Galileo Spacecraft Contents PageOne of the final subsystems installed on the spacecraft before launch--the thermal blanketing--is well along in its final design stages.
According to Hugh von Delden, cognizant engineer for the blanketing, there will be nearly 300 thermal blankets on the spacecraft covering virtually everything except for the radioisotope thermoelectric generators (RTGs), radio antennas, and selected radiating areas.
The blanketing serves several purposes. Not only does it retain heat to warm vital parts of the spacecraft, but it also protects against electrostatic discharge and micrometeoroid impacts. The blanketing on most of the spacecraft is spaced away from the surface of the equipment either by mylar standoffs or mechanical methods. This space provides a distance required to disperse the energy of an impacting micrometeoroid and thus prevent penetration of vital equipment. The blanketing serves as a breakup barrier against micrometeoroids up to 0.8 mm (1/32 of an inch) in diameter. Additional protection is provided in areas such as the fuel tanks, where one penetration could end the mission.
Blanketing on the retropropulsion module (RPM) will prevent the fuel and oxidizer from freezing. Excess power from the RTGs will be dissipated through shunt heaters in the RPM to maintain the necessary temperatures.
Thermal tests of the RPM have been performed on the 3-meter (10-ft) vacuum chamber at JPL. The "cold walls"--walls filled with liquid nitrogen--simulate the extremely cold temperatures of deep space, down to about 88.7 K (-300 deg F).
Thermal tests of the temperature control model (TCM) full-up spacecraft are currently scheduled for January 1984 in JPL's 7.62-meter (25-ft) space simulator chamber. Solar thermal vacuum tests of the flight spacecraft are scheduled for the summer of 1984.
Unlike Voyager's magnetometer boom, Galileo's mag boom will be covered with a single layer of black blanketing to protect it from electrostatic discharge and micrometeoroids. Prior to launch, the boom will be collapsed in a cylinder about 61 centimeters (2 feet) long . After release from the Centaur upper stage, the boom will be deployed, extending to its full length of 11 meters (36 feet). The single layer sock will be deployed with the boom structure.
The blanketing itself is a multilayer insulation (see figure). The portion nearest the spacecraft--its "thermal underwear"--consists of 10 to 20 layers of 6.3-micrometer-thick (1/4-mil) aluminized mylar and dacron net (see figure), explains von Delden. The final two-layer covering is a black outer layer (see figure) of 25.4-micrometer-thick (1-mil) carbon-filled polyester coating on 12.7-micrometer-thick (1/2-mil) Kapton® over a single layer of 25.4-micrometer-thick aluminized Kapton®. The black blanketing is conductive and grounded to meet the equipotential spacecraft requirements. Some spacecraft have been plagued by static discharge interpreted by the spacecraft as radio frequency signals. Unfortunately, this caused the spacecraft to do things they weren't supposed to do. The spurious signals were caused by electrical arcing resulting when a large differential charge exists between two surfaces. Galileo's blanketing has been designed so that there will never be more than 10V potential on the surface of the spacecraft at any time.
The blanketing process begins with a paper pattern that is fit to a model of the instrument or subsystem. The multilayer insulation is fabricated from these patterns and is installed on the spacecraft for a final fitting. Finally, the blanketing is laced into place--literally tied on in a time-consuming process. The final blanketing can be done only when the spacecraft has been fully assembled and prepared for launch at Cape Canaveral. A team of four to six people will work around the clock for two to three days to install the final blankets.
JPL's Instrumentation Section (351), Space Program Engineering Section (352), Applied Mechanics Technology Section (354), and Design and Mechanical Support Section (356) are involved in the design, development, and fabrication of the thermal blankets.
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