The Indian Space Research Organisation (ISRO) has indigenously developed a power enhancing system for a class of communication satellites, that is said to be a crucial requirement for them to significantly increase the range of communication and digital services for citizens and the country’s defence forces. The ISRO Satellite Centre (ISAC) has developed what is called a ‘satellite bus bar’, which ensures successful power distribution in high power satellites with minimum power loss, and with good performance. The system would enable satellites to carry a much higher number of signal-enhancing transponders – which means, a wider range for services pertaining to television, wireless communication, digital services as well as dedicated surveillance and communication services for the defence and security organisations would be made available in the near future. According to ISRO, this is one of the most important requirements for the smooth and longer running of a category of high performance satellites, called High Throughput Satellites (HTS). An HTS is a satellite that can carry more number of transponders with many times the capacity of signals passing through as compared to the traditional fixed-satellite service (FSS) satellites for the same amount of allocated frequency in orbit. The satellite bus bar would enable these satellites to extend their mission life while continuing to provide the intended services for various categories of users in the country and subscribed users elsewhere. This category of satellites can carry more than 50 transponders each, wherein the power requirement per satellite is more than 10 kilowatts (kW). The highest number of transponders on a single satellite so far is 48 on board ISRO’s 11th communication satellite, the 3.18-tonne GSAT-16. It was launched on December 6, 2014 on board the Ariane-5 rocket by Arianespace from French Guyana. It has a 12-year mission life and is an advanced communication satellite, inducted into the INSAT-GSAT system. Now, the indigenously developed satellite bus bar will be installed on the GSAT-19E communication satellite, with the longest-planned mission life of 15 years. The satellite – heaviest of the ISRO satellites, weighing 3.2 tonnes – is scheduled to be launched in December 2016 from Sriharikota in Andhra Pradesh, 80 Km north of Chennai, on board ISRO’s geostationary satellite launch vehicle (GSLV) Mark III D1 on its maiden mission flight using a functional cryogenic engine. According to ISRO’s last annual report, the GSAT-19E satellite will act as a test-bed for the indigenously developed satellite bus bar, apart from trying out experimental technologies, including those for satellite manoeuvring and stabilisation. The successful working of the GSAT-19E satellite would open the gates to enhanced satellite services over more number of transponders, for longer mission lives than what present satellites offer.
HOW IT WORKS
In a communications satellite, a transponder receives signals over a range of uplink frequencies usually from a satellite ground station, amplifies them, and then re-transmits them on a different set of downlink frequencies to receivers on the ground. It does this without changing the content of the received signals. For instance, ISRO scientists explained, a satellites beaming signals for television channels, receive signals beamed from a large ground-based satellite uplink station. It then processes it, encodes it, amplifies it and then rebroadcasts the signal over a large region on earth from its high orbit up to 30,000 km. “It is like you being on the ground and wanting to sprinkle some powder on a much larger area. The best would be to throw the packet filled with powder to someone on the upper floors, from where that person would open the packet and sprinkle it over a much larger area than what you would have been able to do while standing on the ground,” an ISRO scientist explained. On reaching the ground, the signals are picked up by small satellite receivers and transmitted to the digital receivers in the customer’s living room, where it is decoded and displayed on a connected television screen. While in this example the signals are for television broadcasting, transponders can similarly process signals for mobile telephony, satellite communications, digital networks, defence applications, and so on. “The development of indigenous satellite bus bar meets the requirements of ongoing programmes and ensures the adaptability for forthcoming high power spacecraft programme of ISRO,” says ISRO on its website.