ISRO Satellite Center (ISAC), Bangalore has developed a satellite Bus Bar indigenously along with Indian industry. The Bus Bar makes the successful power distribution in high power satellites with minimum power loss and good thermal performance. This is one of the requirements for the realization of High Throughput Satellites (HTS), with more than 50 transponders per satellite, where power requirement is greater than 10 kW. Conventional harness for power distribution with twisted pair of wires cannot meet the low power and voltage drop specifications. Therefore, it is prudent to have an efficient and optimized power distribution system. Usage of Bus Bar in place of conventional power harness is noted to be an appropriate option. The main advantages are power and voltage drop reduction, better thermal design, and reduced Electro Magnetic Interference (EMI) compared to wire harnesses.
The development of indigenous materials and processes associated with the Bus Bar also have paved the way for spin-off applications in other subsystems and utilization for future satellite program. In addition, the indigenous development has derived the benefits of technology demonstration, technical expertise gain, in-house realization with adaptable and scalable designs for future application and saving of considerable foreign exchange. Development of insulation materials such as Poly Aryl Ether Ketone (PAEK), 3D printed Ultem and processes such as Micro Arc Oxidation and Epoxy Insulation coating are the new areas proven for space application while evolving this Bus Bar.
The development, realization and validation of first flight worthy indigenous Bus Bar is accomplished in GSAT-19 spacecraft. However, the specification of the Bus Bar is rated for handling power requirements of 100 A @70 V of HTS. The development of indigenous Bus Bar is multi-disciplinary activity.
The Bus Bar for GSAT-19 spacecraft is configured as 2xI type Bus Bar mounted on the equipment panel of the spacecraft as depicted in the Figures. The two 'I' bars are named live and return bars form the +70V and 0V potentials respectively. The assembly of Bus Bar measures about 54mm x 58mm x700 mm length and weighs about 1.3 kg. The live and return bars are separated by a rigid insulating fixation and four flexible insulating fixations spaced along the length of the bars. The raw bus power is carried on these two 'I' bars vertically separated with a gap allowing space for installation of connectors. The basic conducting material used is Al 6061 alloy having a cross-section dimension of 23 mm x 3 mm, specified for 100 A in vacuum with tolerable temperature rise.
The Bus Bar and its associated components are realized in-house at ISAC Mechanical Fabrication Facilities. Followed this, the Bus Bar is silver plated (12 ± 4 micron thickness) at connector locations for solderability. Subsequently, a Micro Arc Oxidation (MAO) coating of 100±20 micron thickness was performed as a first layer of insulation at Advanced Material Processing Lab. After that, a second layer of Epoxy coating (250 ± 50 micron thickness) is applied. MAO and Epoxy coating ensure a double layer of insulation all over the Bus Bars. Eight numbers of standard high power connectors each having eight contacts are used for connecting Bus Bars to different subsystems like Battery Discharge Regulator (BDR) package, Shunt Regulator, various loads like Core Power Electronics and Fuse Distribution Modules. High power connectors are soldered at Central Electronic Fabrication Facility using SN62 solder containing silver, followed by conformal coating and potting with RTV 3145 compound on exposed connector pins for double layer insulation. Every process, material and fabrication sequences are qualified for space environment by Reliability and Quality Assurance team.
The integrated Bus Bar assembly is successfully tested and qualified for a matrix of validation tests such as:
space qualification testing of all materials and processes,
electrical characterization for high power performance (high current 150 A and high voltage 140V),
mechanical characterization tests such as friction tests, curvature tests, and break load tests, etc.,environmental tests like thermal vacuum test, vibration test, shock test, etc.
The development of indigenous Bus Bar meets the requirements of ongoing programs and ensures the adaptability for forthcoming high power spacecraft program of ISRO. Further, ongoing developments of the Bus Bar at the anvil of ISAC include characterization and implementation of L-Junction for Multiple Bus Bar connection, flexible braids for inter panel connections, validation using straight pin connectors, etc.
The indigenous Bus Bar is replacing conventional harness to cater to the high power requirements of HTS Class of Satellites. The potential of Indian industry is utilized to realize Bus Bars at a remarkably competitive cost. For the first time, indigenous Bus Bars will be carried by GSAT-19 which is scheduled to be launched by GSLV-Mk III from SDSC, SHAR, Sriharikota.