ISRO’s Earth Observation Satellite (EOS) Program

Since its first remote‐sensing satellite (IRS-1A in 1988), ISRO has built up a large constellation of Earth observation satellites. These satellites carry instruments (optical cameras, radars, etc.) that monitor land, water and atmosphere to support agriculture, water management, urban and rural planning, mineral prospecting, environment and forest monitoring, disaster relief, oceanography and national security. In this context, the EOS (Earth Observation Satellite) series was initiated in 2020 to provide frequent, high-quality data for operational users. The EOS program’s goals are to deliver all-weather imaging of India and its surroundings, improve revisit rates for time-critical applications, and strengthen strategic surveillance.

EOS Missions (2020–2024)

• EOS-01 (Nov 7, 2020) – Launched by PSLV-C49 (2nd PSLV-DL flight) from Sriharikota, EOS-01 (~628 kg) carried an X-band Synthetic Aperture Radar (SAR) payload. It provides all-weather day/night imaging for applications in agriculture, forestry and disaster management. (EOS-01 is essentially RISAT-2BR2 and was injected into sun-synchronous low Earth orbit on 07 Nov 2020.)
• EOS-02 (Aug 7, 2022) – A ~130 kg microsatellite (IMS-1 bus) designed for advanced infrared optical remote sensing. EOS-02 was to be launched on the maiden SSLV flight (SSLV-D1), but that vehicle failed to achieve orbit. ISRO noted that the launcher fell short of inserting EOS-02 into its target orbit.
• EOS-03 (Aug 12, 2021) – A “state-of-the-art agile” Earth-imaging satellite (the first GISAT) intended for geostationary transfer orbit. It was launched on GSLV-F10, but the cryogenic third stage failed to ignite, so the mission “could not be accomplished as intended”. EOS-03 would have provided frequent coverage of India from a geo-stationary slot.
• EOS-04 (Feb 14, 2022) – A 1,710 kg radar-imaging satellite (sometimes called RISAT-2BR2R) launched by PSLV-C52. EOS-04’s SAR payload delivers high-quality images under all weather conditions for agriculture, forestry, plantations, soil moisture/wetness and flood mapping. The satellite generates 2,280 W and has a 10-year mission life.
• EOS-05 (planned) – (GISAT-2) A geosynchronous imaging satellite in development to complement EOS-03. (As of mid-2025 it has not yet launched.)
• EOS-06 (Nov 26, 2022) – Also known as Oceansat-3, this 1,117 kg satellite was launched by PSLV-C54. It carries four oceanographic payloads – an Ocean Color Monitor (OCM-3), Sea Surface Temperature Monitor (SSTM), Ku-band Scatterometer (SCAT-3) and ARGOS data-collection system. EOS-06 provides continuity of the Oceansat series, measuring chlorophyll/ocean color, sea temperature, wind vectors and related parameters for climate, ocean health and monsoon studies.
• EOS-07 (Feb 10, 2023) – A 156.3 kg microsatellite (Microsat-2B) launched on SSLV-D2. Its new payloads include an mm-Wave Humidity Sounder for atmospheric profiling and a spectrum-monitoring payload. EOS-07 demonstrated these technologies in a 450 km orbit; it was successfully injected into a 450 km circular orbit on 10 Feb 2023.
• EOS-08 (Aug 16, 2024) – A ~175 kg experimental microsatellite (Microsat-2C) launched on SSLV-D3. EOS-08 carries three novel instruments built on the IMS-1 bus: (1) an electro-optical/infrared (EOIR) imager that captures mid-wave and long-wave IR images by day or night; (2) a GNSS-Reflectometry (GNSS-R) payload that measures reflected GPS signals (for ocean winds, soil moisture, cryosphere/ice and flood monitoring); and (3) a SiC UV Dosimeter to measure ultraviolet/gamma dose (planned for Gaganyaan). These instruments serve disaster and environmental monitoring (wildfires, volcanoes, floods, etc.), marine and land moisture sensing, Himalayan cryosphere studies, and radiation monitoring. The SSLV-D3 flight was successful – EOS-08 was placed in a 475 km low-inclination orbit – completing the SSLV development program.

In summary, the EOS series has deployed multiple SAR and ocean-monitoring satellites (EOS-01, -04, -06) for operational imaging, along with a series of technology/demonstration microsatellites (EOS-02, -07, -08). These satellites have enhanced India’s remote sensing capabilities across agriculture, forestry, water resources, meteorology, and strategic surveillance.

EOS-09 Mission (May 18, 2025)

• Launch Vehicle & Orbit: EOS-09 was slated to be launched on 18 May 2025 at 05:59 AM IST aboard the PSLV-C61 rocket. This was the 63rd flight of PSLV (27th in the XL configuration). The plan was to inject EOS-09 into a 500–600 km Sun-synchronous polar orbit (SSPO) for consistent sunlight conditions. (The PSLV-XL vehicle is a 44.5 m, four-stage rocket with six solid strap-on boosters, lift-off mass ~321 tonnes.)
• Satellite & Payload: EOS-09 is essentially a follow-on to EOS-04 (and the earlier RISAT-1) built on the RISAT-1 heritage bus. It has a launch mass of 1,696.24 kg and carries a high-resolution synthetic-aperture radar (SAR) payload. The SAR operates in C-band and can image in any weather, day or night. The satellite is powered at ~2.4 kW and has a design life of 5 years. ISRO emphasized that EOS-09 would carry extra fuel for orbit lowering after its mission, to comply with debris-mitigation norms.
• Mission Goals: The primary goal of EOS-09 was to provide continuous, high-frequency remote-sensing data over India and nearby regions. With its SAR payload, EOS-09 was intended to bolster surveillance in strategic sectors (border and coastal monitoring), as well as serve civilian needs like agriculture, forestry, water resources and disaster response. (Economist Manish Purohit noted that EOS-09 “strengthens monitoring at borders and coasts,” and ISRO’s release highlighted its role in agriculture and disaster-relief imaging.)
• Anomaly and Setback: The EOS-09 launch lifted off nominally, but a serious anomaly occurred in the rocket’s third stage. ISRO reported that “PSLV-C61 performance was normal till 2nd stage. Due to an observation in 3rd stage, the mission could not be accomplished”. Specifically, post-launch telemetry showed a sudden drop in combustion chamber pressure in the solid-fuel third stage. This pressure loss meant the stage could not maintain thrust, and the rocket failed to reach the intended orbit. As a result, the EOS-09 spacecraft did not achieve its target orbit. In ISRO Chairman V. Narayanan’s words, “the third stage motor started perfectly but during the functioning of the third stage we are seeing an observation and the mission could not be accomplished…there was a fall in the chamber pressure of the motor case”. (Reuters and other reports confirmed a third-stage pressure drop that halted the 1,696.24 kg EOS-09 satellite.)
• ISRO Response: ISRO immediately began a thorough investigation. Chairman Narayanan stated that the performance data were under study and promised a report “at the earliest”. He convened an internal Failure Analysis Committee to determine the root cause. This is one of only a handful of PSLV anomalies in its long history (PSLV has had just three failures since 1993). ISRO emphasized that it would apply lessons learned to future flights. In public statements, ISRO also reiterated commitment to safe operations – for example, prior mission planning had included lowering the fourth stage orbit via its own thrusters to reduce space debris – underscoring that the rocket and satellite designs remain highly reliable overall.

Sources: Official ISRO mission pages and press statements, and contemporary news reports on the EOS-09 launch. These detail the EOS program’s history and objectives, the specifications of EOS satellites 1–9, and the EOS-09 launch anomaly and investigation. Each EOS mission summary above is drawn from ISRO announcements and mission documents.