It needs to be remembered that an aerostat is not a balloon. As the name suggests it is a lighter-than-air vehicle that is so constructed that its aerodynamics keep the structure always pointed into the wind, that is, from the direction in which the wind is blowing.
It swings on an axis created by the tether/cable by which it is anchored to the ground. The intention is to overcome the limitations to detection of airborne objects and suspicious movements on the ground those are otherwise masked by the curvature of the earth and terrain features like mountains and tall buildings.
India’s requirement for aerostats has recently been highlighted by Pakistan testing a short-range nuclear-capable missile known as the Nasr. It is a multi-barrel rocket system with a range of about 60 km and its flattened trajectory makes it extremely difficult for ground-based radars to detect because it can come in at treetop level and allows for a very short reaction time.
An aerostat can detect the transporter, erector, launcher (TEL) vehicle well before it can arrive at battle station and prepare for launch. Since the Nasr is a tactical or local area weapon, the means for detecting it too need to be localized and counter-measures like the Prithvi air-defence interceptor or high rate of fire anti-aircraft guns used to neutralize it.
India procured its first aerostat from Israel about five years ago but its projected requirement of 15 to cover the gaps in the air defence ground environment system (ADGES) may need to be revised upwards given the new kinds of threats.
These threats require a denser radar coverage than the currently deployed long-range reconnaissance and observation system (LORROS), INDRA for detection of low-flying aircraft and the airborne warning and command systems (AWACS) aircraft.
Tethered by an umbilical cord-like cable at 15,000 feet the aerostat can cover ranges of up to 500 km and depending on the onboard sensors can scan the electromagnetic spectrum for electronic and signals intelligence.
This is extremely useful in detecting and pinpointing sources of terrorists’ conversations. Or it can scan the spectral medium for day and night imagery in all weather conditions. Very high winds can pose a threat to the system but it can be lowered and fastened to a strong steel framework close to the ground if the weather becomes stormy.
Made out of an ultra-light fabric that can retain the helium that makes the aerostat lighter than air, the larger sized aerostats of about 250 ft in length are able to take aloft a payload of up to two tones comprising systems that cater to national security needs be it intelligence gathering or providing early warning of approaching threats.
The reason why it is suggested that more may be required than the projected 15 at the moment is that the nature of warfare on the subcontinent is changing both in its conventional execution as well as in its sub-conventional application that new methods need to be evolved for battlefield surveillance, target acquisition and engagement more particularly in the mountainous terrain all along the Himalayas.
The Kargil conflict underscored the inadequacy of weapons locating radars in the Indian arsenal. This was not just because of the technical specifications of the equipment but also caused by the serrated-edged nature of the terrain that had closely spaced deep valleys and high crests that made it difficult to adequately plot the trajectory of a warhead so as to ensure effective counter-bombardment.
A weapons locating radar taken aloft above the crest-line can make a faster and more accurate calculation of which of the many valleys separating the battle-lines from which the gunfire originated. A counter-barrage of artillery would, therefore, be more effective than any input from a sensor operating from ground level.
Taking sensors aloft has already proved to be a better option as is seen in the many different kinds of unmanned aerial vehicles (UAV) deployed for low-level observation to medium and high level surveillance and attack capabilities as in the US Predators.
The aerostats being static reduce the cost of operations in that there are no recurrent expenditures as in fuel for the UAVs. Once a month or so they need to be brought down and serviced to ensure optimum efficiency of the onboard systems and sensors.
The DRDO has created an indigenous aerostat for surveillance of the electromagnetic spectrum from which can be garnered electronic and signals intelligence generically called communications intelligence (COMINT).
Named as Divya Chakshu the indigenous aerostat is to undergo more tests with other types of sensors before it can be said to be fully validated for deployment in a military role.
The current tests have been conducted at a height of 1000 ft and it remains to be seen how well it can deliver in terms of resolution of infrared imagery as well as in ELINT and SIGINT collection when deployed at its full length of 15,000 ft.
While India is well up in equipment manufactured by Bharat Electronics designed to distinguish friend from foe there are other sensors like the LORROS that it will need to be imported to make the indigenous aerostat a worthy platform for homeland security.
The recent failures by institutions entrusted with the task of maritime defence to detect pirates close to the Indian shoreline or even ensure that no vessel can be deliberately run aground to cause oil spillage and ecological disaster has spurred authorities to look for more failsafe means of surveillance and detection.
Nonetheless, the creation of a stable airborne platform indigenously has given hope that eventually, with greater public-private sector participation even the sensor package can be developed indigenously.
The Israeli aerostat purchased earlier has not been very effective. In the maritime role, the ability to scan up to a range of 500 km would be of considerable assistance to the Indian Coast Guard, the jurisdiction of which covers the 200 nautical mile Exclusive Economic Zone.
Aerostats on the Gujarat coast would be able to keep under surveillance the fishing grounds that are so often the scene of detention of fishing boats that enter Indian waters. It needs to be remembered that the Pakistani terrorists who attacked Mumbai on 26/11 came from the seaward side.
In a separate development the National Aerospace Laboratory, the Bangaluru-based affiliate of the Council for Scientific and Industrial Research has developed a smaller blimp which it says will be useful in internal security duties like counter-insurgency and counter-terrorism.
Among the first requirements of such a system would be that it is not amenable to destruction by ground fire. Given instances where the Indian Air Force helicopters have been fired at (in which some personnel were killed or injured) this is a palpable threat.
If it can be lofted to 500 meters it would be out of range of most rifles that are in the hands of the Maoists who have shown a penchant for destruction of cellphone towers to disrupt communications nodes in their attempt to stay one jump ahead of security forces. There is this constant clash between contending capabilities.