ISRO's EMISAT: Electronic Spy in Space

EMISAT is an advanced electronic intelligence (ELINT) satellite jointly developed by ISRO-DRDO. It has a basic architecture similar to HySIS (based on Small Satellite Bus-2) which was first used in SARAL satellite. The satellite has been under development for nearly 8 years. The ELINT payload of the satellite was developed under project KAUTILYA by Defence Electronics Research Laboratory (DLRL), Hyderabad. The project was first acknowledged in the Ministry of Defence annual report 2013-14.
EMISAT is a small satellite i.e. it weighs less than 500kg. It is likely to be placed in a highly elliptical orbit (signature SIGINT satellite orbit) so as to maximize dwell time over specific signal recording area.
Quick render of ISRO-DRDO ELINT Satellite EMISAT

What is SIGINT? 

Signal Intelligence (SIGINT) involves interception of signals broadcasted by communication systems, radars, and other electronic systems.
On the basis of the type of signal intercepted, SIGINT is divided into three subcategories 
  1. Electronic Intelligence (ELINT) :
  2. Communication Intelligence (COMINT)
  3. Foreign Instrumentation Signals Intelligence (FISINT) 

1. Electronic Intelligence (ELINT)  

Electronic Intelligence includes the collection (recording) and analysis of intercepted signals. It primarily deals with radars signals. An ELINT system intercepts radar signal and analyzes it i.e. determines the frequency of carriers and subcarriers, modulation, bandwidth, power level, beam footprint parameters, and emitter location and motion. Basically, it creates an RF signature of a radar which can be used for locating and quickly identify the radar in subsequent encounters. Furthermore, based on RF signature information of a radar, jamming techniques can be developed to counter the radar. This is the reason why IAF avoids using the radars of its fighters in joint exercises.

2. Communication Intelligence (COMINT) 

COMINT involved recording and analysis of communication signals. Intercepted COM signals are demodulated and the original data (audio, video, text) is extracted. Since military communications are usually encrypted, analyzing them requires more sophisticated equipment. Therefore, COMINT systems are more complex than ELINT systems.

3. Foreign Instrumentation Signals Intelligence (FISINT) 

FISINT is similar to TELINT (telemetry intelligence). It involves interception and analysis of non-communication signals (missile/UAV telemetry signals, missile tracking/arming/fusing commands, locator beacons). A FISINT system is more comprehensive in nature. It not only determines the configuration and capability of emitter but also the overall system emitter is a part of. 

Space-based SIGINT systems 

SIGINT satellites can be deployed in various orbits depending on the type of signals the satellite is designed for, e.g. To detect low power radar signals, the satellite has to be placed in low-earth orbit while high power early warning radars can be analyzed using a satellite stationed in geostationary earth orbit. The operational orbit of the satellite can be optimized to achieve optimum dwell time over a specific area. Another important factor determining the orbit of a SIGINT satellite is the size of the antenna and the sensitivity of receiving equipment.
HySIS and EMISAT - both satellites share same bus architecture 

The absence of large antenna (unless it has an unfurlable mesh antenna which isn't visible in render) indicates that EMISAT appears to be designed to intercept directed microwave transmissions. The microwave link between a satellite and ground station is highly directional. To intercept tight beam transmission, eavesdropper satellite has to be placed between the ground station and the target satellite. Another use of EMISAT is to determine the location of radar emitters (ground and naval) and command nodes. A single EMISAT will be able to determine the probable location of radio emitters, however, for increased DF (direction finding) accuracy multiple satellites are required.
American SIGINT satellite Orion has a 255 feet diameter unfurlable antenna which can detect signals from a wristwatch-sized radio. Orion satellites are used for intercepting missile telemetry/datalink signals and monitoring microwave traffic. SIGINT satellites like Orion are prohibitively expensive ($750 million each) for a country like India. EMISAT is a low-cost alternative. A cluster of EMISATs could mimic functions of a large satellite by sharing processing, communication and mission functions at a fraction of the cost.

satellites, earth
A cluster of four EMISAT satellites over an area-of-interest 

Advantages of Space-based intelligence satellites over conventional means 

Conventional SIGINT systems include ground stations, combat aircraft carrying specialized SIGINT equipment, unmanned aerial vehicles, dedicated SIGINT aircraft, and AEWCS. 
DRDO Netra AEW&C is equipped with a highly advanced SIGINT suite which covers all frequency band used on a battlefield, giving the user unprecedented situational awareness  (Image: Livefist)
Tapas BH201 AKA Rustom-2 UAV equipped with ELINT system (Image - Anantha Krishnan M)

  1. Ground-based SIGINT system, such as Samyukta, has a very limited visibility as SIGINT requires line-of-sight to the emitter. 
  2. Manned SIGINT aircraft are very expensive and prone to missile attacks. Losing even one AEWCS represents a huge blow - financial and strategic. Area of operation is limited. 
  3. UAV based SIGINT - prone to both missile and jamming attacks. Violation of airspace strains diplomatic relations.  
  4. Limited reach of conventional SIGINT systems, for example, a communication node in middle China/Russia can't be monitored by any of the conventional SIGINT systems mentioned above. 
24 hours a day, 7 days a week, 365 days a year, EMISAT along with upcoming GISAT and radar imaging satellites will provide India with an information edge over both Pakistan and China.