DRDO Expands Space-Based ELINT and RF Geolocation Technologies for Future Defence Surveillance

India’s Defence Research and Development Organisation is expanding work on space-based electronic intelligence, radio-frequency geolocation and multisensor surveillance technologies, laying the foundation for a more persistent defence intelligence architecture extending from terrestrial emitters to low-Earth-orbit platforms.

Official DRDO technology-foresight documents identify several relevant areas under development, including geolocation techniques for Electronic Intelligence, high-gain beam-steering antennas for LEO platforms, AI and machine-learning-based multisensor data fusion for space surveillance, and space-qualified software-defined radio payloads. Together, these technologies point towards a future system capable of detecting, locating and analysing electronic activity across large geographical areas from space.

DRDO has not publicly announced a standalone operational “RF surveillance constellation” with a defined satellite count or deployment schedule. The present work is better understood as the development of the enabling technologies required for future military space-based electronic surveillance.

Space-Based ELINT Emerges as a Priority Technology

DRDO’s official Space Technologies roadmap specifically identifies geolocation techniques for Electronic Intelligence, or ELINT, as an area of interest within electronic warfare.

ELINT focuses on detecting, characterising and locating non-communications electromagnetic emissions, particularly those associated with radars and other electronic systems. A space-based ELINT capability can observe emitters over large areas and help determine where those transmissions originate, giving defence forces another layer of situational awareness beyond conventional imagery.

Unlike an electro-optical satellite, which must capture a visual or infrared image of a target, an RF surveillance payload can detect the electromagnetic activity associated with a radar or transmitter. This makes electronic intelligence particularly useful when the signal itself provides more information than the physical appearance of the system producing it.

DLRL Focuses on Locating Radio Emitters from Low Earth Orbit

One of the clearest official indications of DRDO’s direction comes from a research problem issued through the DRDO Industry Academia Centres of Excellence.

The Defence Electronics Research Laboratory, or DLRL, has sought research on “Geolocation of Terrestrial Radio Emitters from RF Payloads on LEO Satellites.” The stated objective is to develop practically implementable algorithms capable of determining the location of terrestrial transmitters using radio-frequency payloads carried aboard low-Earth-orbit satellites.

DRDO identifies possible target signals including Automatic Identification System transmissions, ADS-B signals, military radios and radar emissions. The research is explicitly described as an enabling technology for future projects, making clear that DRDO is building the computational and orbital foundations required for more advanced electronic-surveillance missions.

Multiple Satellites Can Geolocate a Single RF Emitter

Space-based RF geolocation typically becomes more accurate when several satellites observe the same transmitter from different positions.

DRDO’s published research problem refers to techniques based on Time Difference of Arrival and Frequency Difference of Arrival, commonly known as TDOA and FDOA. TDOA measures minute differences in the time at which a signal reaches different satellites, while FDOA measures frequency variations caused by relative motion between the satellites and the emitter.

When these measurements are combined with accurate knowledge of satellite position, the system can estimate the location of the transmitter on the ground or at sea. This requires precise timing, reliable orbital navigation and tightly coordinated processing across the participating spacecraft.

The challenge is not simply detecting a signal. The system must also separate the desired emission from background electromagnetic activity, identify its characteristics and calculate location accurately enough to make the information operationally useful.

Formation Flying Is Central to Accurate RF Surveillance

DRDO’s research documentation examines coordinated groups of satellites operating in formation.

The reference concept includes clusters of three or four spacecraft arranged in different orbital geometries, allowing the same emitter to be observed simultaneously from several locations. Such configurations improve the geometry required for geolocation and can increase the frequency with which a region is monitored.

Formation flying also introduces demanding technical requirements. Each satellite must know its own position precisely, maintain accurate timing and coordinate data collection with the rest of the group while travelling at orbital velocity.

These requirements explain why RF surveillance from space is as much a problem of navigation, synchronisation and computation as it is one of antenna design.

Ground Processing Remains an Important Part of the Architecture

DRDO’s research problem envisages RF payloads collecting digitised signal data as satellites pass over areas of interest and transmitting that information to ground stations for detailed processing.

The processing chain can include signal detection, parameter estimation, geolocation calculations and correlation with other sources of intelligence. The expected research therefore extends beyond the spacecraft itself to include satellite geometry, RF payload characteristics, communication links, orbital data and ground-based computing.

This architecture allows relatively compact orbital sensors to work with powerful terrestrial processing systems, reducing the amount of computation that must necessarily be performed aboard each spacecraft.

Over time, greater use of onboard processing and artificial intelligence could shift more of this analysis into orbit, but the official DRDO material currently places strong emphasis on the complete space-to-ground surveillance chain.

AI and Multisensor Fusion Expand the Intelligence Picture

RF geolocation forms only one part of DRDO’s broader space-surveillance technology effort.

The organisation’s roadmap also identifies AI and machine-learning-based multisensor data fusion for space-based surveillance as an area of development. Data fusion allows information from different sensors to be combined into a single operational picture rather than being analysed separately.

An electronic emitter detected by an RF satellite could, for example, be correlated with imagery from an electro-optical satellite, information from synthetic-aperture radar or data from terrestrial surveillance systems. Such correlation can reduce uncertainty and help analysts distinguish isolated signals from broader military activity.

This becomes particularly valuable when a platform attempts to reduce its visual signature but continues to operate radar, communications or other electronic equipment.

High-Gain Beam-Steering Antennas Support Focused Surveillance

DRDO also lists high-gain beam-steering antennas suitable for low-Earth-orbit platforms among its priority space technologies.

Beam-steering antennas allow radio-frequency sensitivity to be concentrated towards selected directions or regions without requiring the entire spacecraft to be physically reoriented for every observation. This can improve efficiency when surveillance needs to focus on particular geographical zones or specific emitters.

DRDO has also identified spaceborne unfurlable antennas as an enabling technology. Such antennas can provide larger apertures after launch while remaining compact enough to fit inside a launch vehicle during ascent.

For RF surveillance, antenna aperture and sensitivity directly influence how weak a signal can be detected from orbit.

Software-Defined Radio Adds Mission Flexibility

DRDO’s communication-technology roadmap also includes space-qualified software-defined radio-based satellite communications payloads with regenerative transponder capability.

Software-defined radio replaces many fixed hardware functions with configurable digital processing. This allows a radio system to adapt to different frequency bands, waveforms and mission requirements through software rather than requiring extensive hardware redesign.

Although DRDO lists this particular capability under communications rather than ELINT, the development of space-qualified SDR technology has wider relevance to future RF payloads. Flexible digital radios can support systems that must detect, classify or process many different types of electromagnetic signals.

This adaptability will become increasingly important as modern radars and communication systems use more agile and complex waveforms.

India Is Expanding Its Wider Defence Space Architecture

DRDO’s technology work is progressing alongside India’s broader expansion of military space capabilities.

The Defence Space Agency has already begun integrating space-based assets more closely into military operations. In November 2024, it conducted Antariksha Abhyas, India’s first dedicated space table-top exercise, examining threats to and from space assets while improving coordination among the three armed services.

The exercise covered emerging technologies, space situational awareness and the protection of critical military space infrastructure. It also reflected the growing importance of space as an operational domain rather than merely a supporting communication or navigation layer.

This broader institutional development provides the environment within which future RF surveillance and ELINT capabilities can be integrated.

Space-Based Surveillance Programme Adds Persistent Coverage

India has also moved forward with the third phase of its Space Based Surveillance programme, SBS-III.

Official DRDO-linked material describes SBS-III as the successor to earlier surveillance programmes involving Cartosat electro-optical satellites and RISAT synthetic-aperture radar spacecraft. The programme is intended to strengthen persistent monitoring over strategically important land and maritime regions.

The Defence Space Agency is expected to play a central role in implementing this capability under the wider national security structure, with new satellites introduced over several years.

RF and ELINT technologies being developed by DRDO can complement such imaging systems by adding information about electronic activity that cameras or radar imagery alone may not reveal.

RF Surveillance Complements Optical and Radar Satellites

Different satellite sensors answer different intelligence questions.

Electro-optical satellites can provide highly detailed imagery but are affected by cloud cover and lighting conditions. Synthetic-aperture radar can operate through clouds and at night, making it valuable for all-weather observation of physical targets and terrain.

RF surveillance works differently. Instead of observing the appearance of a target, it listens for electromagnetic emissions produced by radars, communication equipment and navigation transmitters.

A radar installation that is visually concealed may reveal its location once it begins transmitting. A ship attempting to reduce its physical signature may still generate electronic emissions associated with navigation, communications or onboard radar.

Combining optical, radar and RF surveillance therefore produces a richer intelligence picture than relying on any one sensor type.

Maritime Surveillance Could Become a Major Application

The Indian Ocean is particularly well suited to space-based RF surveillance.

Commercial ships routinely emit Automatic Identification System signals, while aircraft transmit ADS-B information. Military ships and aircraft may use radar and communications equipment that produces more complex electronic signatures.

A space-based RF system can monitor these emissions across areas too large for continuous observation by individual ships or aircraft. This would complement India’s maritime patrol aircraft, coastal radar chains, satellites and naval surveillance networks.

For a country with extensive interests across the Indian Ocean, the ability to monitor electronic activity over large maritime areas has obvious strategic value.

Military Radar Detection Is a More Demanding Mission

Detecting cooperative civilian transmitters is technically easier than locating military radars designed to resist surveillance.

Military emitters may use frequency agility, short transmission periods, directional beams, low-probability-of-intercept techniques and electronic countermeasures to make detection more difficult.

Space-based sensors must therefore possess sufficient sensitivity, bandwidth and processing capability to capture signals that may be brief, weak or deliberately difficult to characterise.

Accurate geolocation becomes even more demanding when emitters transmit intermittently. Coordinated observations from several satellites can improve the probability of detection and reduce location uncertainty.

DRDO’s focus on formation geometry, synchronisation and signal-processing algorithms directly addresses these challenges.

Space-Based ELINT Reduces Dependence on Airborne Collection

Electronic intelligence has traditionally been collected using ground stations, ships and specialised aircraft.

These platforms remain valuable but face geographical and operational limitations. Aircraft require access to suitable airspace and may be exposed when operating close to contested regions, while ground stations are constrained by geography and the curvature of the Earth.

Satellites offer a different advantage because they can observe large areas without entering another country’s airspace. Repeated orbital passes can also provide surveillance over regions that may otherwise be difficult to access.

A distributed constellation can increase revisit rates and eventually create a level of persistence that is difficult to achieve with airborne platforms alone.

DRDO Is Building Enabling Technologies Rather Than Announcing a Finished Network

The distinction between research, technology development and operational deployment remains important.

DRDO has officially confirmed work on ELINT geolocation, RF payload concepts, formation-flying algorithms, space-based multisensor fusion and related antenna technologies. It has not publicly announced a dedicated operational RF surveillance constellation with a disclosed satellite count, launch schedule or frequency architecture.

The current effort should therefore be understood as the construction of the technological foundation needed for future systems rather than the unveiling of an already operational network.

This makes the programme strategically important even before a specific constellation is announced, because the difficult underlying technologies must exist before a sovereign space-based RF surveillance architecture can be fielded.

India’s Defence Space Architecture Is Becoming Multi-Sensor

The significance of DRDO’s work becomes clearer when viewed as part of a larger system.

High-resolution optical satellites provide visual intelligence. Synthetic-aperture radar offers all-weather imaging. Infrared sensors can support missile warning and thermal detection. RF payloads add a separate layer by locating electronic activity that may remain invisible to traditional imaging systems.

Artificial intelligence and multisensor fusion can then combine these streams into a more coherent operational picture.

This is the direction in which modern military space surveillance is increasingly moving: not towards dependence on one exceptionally capable satellite, but towards networks of specialised sensors contributing to a shared intelligence architecture.

Indigenous RF Intelligence Strengthens Strategic Autonomy

Space-based ELINT demands expertise across satellite engineering, orbital mechanics, radio-frequency electronics, precision timing, antennas, digital signal processing, artificial intelligence and secure ground infrastructure.

Building these capabilities domestically reduces dependence on foreign intelligence feeds and gives India greater control over how surveillance systems are designed for its own strategic requirements.

DRDO’s work on RF geolocation therefore represents more than the development of a single payload. It is part of the technological foundation for an indigenous defence-space ecosystem capable of detecting, analysing and correlating activity across the electromagnetic spectrum.

As India expands its wider military space architecture, space-based ELINT and RF geolocation can add a powerful new dimension to surveillance over land and the Indian Ocean. The convergence of electronic intelligence, multisensor fusion and low-Earth-orbit technology is steadily strengthening India’s ability to build a more persistent, sovereign and integrated defence-surveillance network.

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References

Defence Research and Development Organisation — Space Technologies: Technology Foresight.
https://drdo.gov.in/drdo/en/offerings/technology-foresight/space-technologies

Defence Research and Development Organisation — Research Problems for DRDO Industry Academia Centres of Excellence: Geolocation of Terrestrial Radio Emitters from RF Payloads on LEO Satellites.
https://drdo.gov.in/drdo/sites/default/files/form_formats/ResProblemsDIACoEsOct2024Latest.pdf

Defence Research and Development Organisation — Communication Technologies: Technology Foresight.
https://drdo.gov.in/drdo/en/offerings/technology-foresight/communication

Defence Research and Development Organisation — Space Situational Awareness: Technology Foresight.
https://drdo.gov.in/drdo/en/offerings/technology-foresight/space-situational-awareness

Press Information Bureau, Ministry of Defence — First Ever Space Exercise Antariksha Abhyas 2024 Hosted by Defence Space Agency, November 11, 2024.
https://www.pib.gov.in/Pressreleaseshare.aspx?PRID=2072518

Press Information Bureau, Ministry of Defence — Defence Space Agency Successfully Conducts Maiden Exercise Antariksha Abhyas 2024, November 13, 2024.
https://www.pib.gov.in/PressReleasePage.aspx?PRID=2073082

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