May 17, 2012: An Israeli SkyStar 180 observation balloon was recently brought down in southern Israel when the balloon's power and control cable were hit by a crop duster aircraft. The crop duster was damaged but landed safely. The SkyStar was also brought down and checked out, the cable was replaced and the balloon was sent back up. The SkyStar normally floats at 300-400 meters (910-1240 feet) altitude and uses its cameras, radars, and thermal sensors to spot hostile activity in northern Gaza.
These helium filled balloons are as important as UAVs in keeping an eye on the battlefield. As popular as UAVs are, blimps provide most of the aerial surveillance over Afghanistan and many other trouble spots (like Gaza, the West Bank, and southern Lebanon). The larger UAVs are popular mainly for their mobility and persistence (the ability to stay in the air, over a particular area, for a long time). Predator and Global Hawk can stay in the air for over 24 hours at a time. Controllers and observers, operating via satellite link from bases in the U.S., see that the video and radar images get passed on to the people that need them. But the military has found that "stationary UAVs" (helium filled aerostats or tall towers) not only do the job but do it a lot cheaper (under $1,000 an hour, mostly for maintenance, repairs, and personnel to monitor the sensors) and stay airborne nearly all the time. Compare this to Predator, which costs $6,000 an hour to fly, and Global Hawk, which is 4-5 times more than that. Global Hawk is so expensive partly because of the high end sensors used. Not everyone needs the high flying Global Hawk or even a Predator. They just need a way to keep an eye on a large area (like a chunk of the Syrian, Iranian, or Pakistani border or the area surrounding a base) 24/7. Americans call these PTDS (Persistent Threat Detection Systems) and mount the sensor package on aerostats or towers as a much cheaper alternative to mobile UAVs.
All this is a recent development. Eight years ago the U.S. Army sent 22 blimps (aerostats, actually) to Iraq and Afghanistan for the first time. The most common model of aerostats float at about 330 meters (a thousand feet) up, tethered by a cable that provides power and communications to the day and night cameras up there. The big problem was ground fire from rifles and machine-guns. Hostile gunmen liked using the aerostats as targets. Rifle fire would not destroy the aerostats but did cause them to be brought down more frequently for repairs. Normally, the aerostats can stay up for 30 days at a time but the bullet hole repairs have some of them coming down every few days. The PTDS surveillance systems mounted on tall steel towers also suffer gunfire damage but rarely any that disables the equipment.
The first army aerostats sent to Iraq in early 2004, were used to help defend offshore oil facilities from attack by terrorist speedboats. Those early systems used a 75.2 meter (233 foot) long, helium filled, unmanned aerostat equipped with radar and other sensors. These aerostats were about 2.5 times the size as the more familiar advertising blimp. Aerostats are blimp like vehicles designed to always turn into the wind and stay in the same place. These larger aerostats were originally designed to detect cruise missiles but were soon replaced by smaller and cheaper aerostat systems currently in use. The Israeli SkyStar looks more like a spherical balloon, but it does have a special shape to it that helps keep it stable in winds.
These smaller PTDS systems were much cheaper, less than five million dollars each, and the army has bought several hundred of them. These PTDS systems use aerostats as well as towers. The aerostat, operating at 330 meters, could see out to about sixty kilometers. The smaller towers shorten that range quite a bit. The 30 foot tower can see out to eleven kilometers, the 60 foot tower out to 16 kilometers, and 84 foot tower out to 20 kilometers. The 30 foot tower is adequate for most situations, which usually involve guarding a base.
Israel also produces the larger EL/M-2083 Aerostat radars. These systems can hover at 3,000 meters altitude and carry up to two tons of sensors. These blimps can stay up for about 30 days at a time before it has to be brought down for maintenance on its radars. 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 system costs vary 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 has bought six of them.