To The Galileo Spacecraft Contents PageCables composed of nearly 7.62 kilometers (25,000 feet) of electrical wire and over 700 connectors that will go into the Galileo Orbiter are currently in fabrication at JPL.
"It takes about four months to cable the despun section (see figure), and about six months to do the spun section," explains Galileo's flight cabling cognizant engineer Clyde King of JPL's Space Program Engineering Section (352).
The cabling design began several years ago, using spacecraft drawings to determine cabling needs. Fabrication began about a year ago.
The cabling task is exacting, requiring painstaking attention to details. Working with their hands and sometimes tweezers, the cabling team solders the wires to electrical contacts, routes the wires and ties them into bundles, and then sends the connectors to be potted--filled with a molding compound that holds the wires in place and provides electrical protection.
Quality assurance inspections take place at every step. In-process inspections are performed on every solder joint, and electrical inspections look for shorts, open circuits, or high-voltage breakdowns. Photographs are taken often to document each task.
A ring of cabling (see figure) will interconnect the electronics bays of the Orbiter's spun section. Cabling for this spun bus ring harness begins with prewiring at a workbench, making "pigtails" with 30 to 40 percent of the electrical leads dangling. The harness is then put on a mockup of the bus and the wires are routed. The routing takes many weeks, since some connectors have as many as 50 wires going eight to ten different places on the spacecraft (see figure).
Every wire and connector is completely shielded to protect against Jupiter's severe radiation. A major goal is to prevent any possibility of undesirable effects from electrostatic discharges on the spacecraft. Such ESD could cause component damage or upset the onboard computers. Voyager, on its quick sprint through the Jovian system, experienced some ESD problems. Galileo will spend many months in this hostile environment, compared to Voyager's few weeks.
Most of the wire insulation is Kapton®, chosen for its light weight and electrical characteristics. Teflon® is used in some areas of the spacecraft where different electrical characteristics are needed. Fiberglass sleeving is used on exposed cables for protection from micrometeoroids.
The cabling crew consists of about 15 experienced cable fabricators in the Fabrication Engineering and Services Section (357). The cablers have also gone to school at JPL to learn more about cable fabrication, soldering, potting, cleaning connectors, and crimping. They are currently working 60-hour weeks on a split-shift schedule in order to deliver the spun bus cables to JPL's Spacecraft Assembly Facility (SAF) about March 7. Delivery of the despun and science cabling will follow later this spring. Engineering liaison for the cable fabrication effort is under the cognizance of Art Prisk. Lead technician in the cable shop is Patricia Westerlund.
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