Last month, India completed tests of the first of two aerostat systems it is developing. The one that completed its tests employs a tethered (to a 1,000 meter/3,100 foot cable) unpowered blimp (aerostat) containing sensors and transmitters. India has been using imported aerostat radars for several years, and was satisfied enough to develop their own. It's not high tech, but requires effort to integrate all the existing technologies.
Over the last few years, India bought four Israeli EL/M-2083 Aerostat radars. Both India and Pakistan have been using radar aerostats (blimps) to fill in the many gaps in the radar coverage of their mutual border. The United States is providing aerostats to Pakistan. India bought its first EL/M-2083s three years ago, and is planning to deploy a total of six. India needs a total of 13 to cover all its borders. Pakistan is getting six L-88 Aerostat Systems.
Aerostat systems use a 32-85 meter (100-250 foot) long, helium filled, unmanned blimp equipped with radar and other sensors. The larger of these blimps are more than twice the size of the more familiar advertising blimps. An aerostat is designed to always turn into the wind and stay in the same place. An aerostat is unpowered, and secured by a cable that can keep the aerostat in position at its maximum altitude of 5,000 meters. India is now developing a larger aerostat that can operate that high. The cable also supplies power, which means the blimp can stay up for about 30 days at a time before it has to be brought down for maintenance on its radars and other sensors. Often, two radars are carried. One is a surveillance radar, the other is a precision track and illumination radar (PTIR). The surveillance radar provides long-range coverage (about 500 kilometers for the EL/M-2083), while the PTIR, which is a steerable system capable of tracking multiple targets, can focus in on items of interest.
Aerostat systems cost varies from $5 million, to over $100 million each, depending on the size of the aerostat and the capabilities of the radar and other sensors. Aerostats work. Kuwait had one in 1990, and the ground radar spotted the Iraqis as soon as they crossed the border. The U.S. uses dozens of aerostat systems in Iraq and Afghanistan, to guard bases. The EL/M-2083 costs about $20 million each. Israel itself is using six of them.
While aerostats stay in one place, they are up there, and in the way of aircraft that move. Some of the onboard sensors are used to alert moving aircraft that the aerostat is there, and to maneuver accordingly.