PSLV-C61 Mission and the EOS-09 Satellite

1. ISRO launched the PSLV-C61 mission on May 18, 2025, aiming to place the EOS-09 satellite into a Sun-Synchronous Polar Orbit.
   • A Sun-Synchronous Polar Orbit (SSO) is a specific type of polar orbit where a satellite maintains a consistent relationship with the Sun.
   • This means the satellite always passes over a given point on Earth's surface at the same local time. SSOs are also known as helio-synchronous orbits.

2. The mission failed due to a malfunction in the 3rd stage of the rocket.
3. ISRO Chairman V. Narayanan confirmed that the failure was caused by a sudden drop in chamber pressure in the 3rd -stage solid motor casing.

What is PSLV?

 

1. PSLV stands for Polar Satellite Launch Vehicle.
2. It is an indigenously developed four-stage expendable rocket system by ISRO.
3. The PSLV is referred to as the "Workhorse of ISRO" due to its high success rate and operational reliability.

 

Legacy of PSLV

1. The PSLV achieved its first successful launch in October 1994.
2. It is known for launching multiple satellites in a single mission, often serving both domestic and foreign clients.
3. It Launches remote sensing, meteorological, navigation, communication, and scientific research satellites.
4. Notable missions:
   • Chandrayaan-1 (Moon, 2008)
   • Mars Orbiter Mission (Mangalyaan) (2013)
   • Aditya-L1 (Sun, 2023)
   • Astrosat (India’s first space observatory)

Key Technical Specifications of PSLV-XL

Feature	Details
Stages	4 (Solid-Liquid-Solid-Liquid)
Lift-off Mass (XL variant)	Up to 320 tonnes
Payload to SSPO (600 km)	~1,750 kg
Payload to Sub-GTO	~1,425 kg
Total Height	~44 meters
Launch Site	Satish Dhawan Space Centre, Sriharikota

Stage-wise Description of PSLV

1. Stage 1 (PS1) uses solid HTPB propellant and provides the initial thrust. It includes 6 strap-on boosters in the XL configuration.
2. Stage 2 (PS2) uses a liquid Vikas engine, powered by UDMH and N2O4, and operates after atmospheric exit.
3. Stage 3 (PS3) is a solid propellant stage using HTPB, designed to provide high thrust. This was the stage that failed in the C61 mission.
4. Stage 4 (PS4) is a liquid stage powered by two engines using MMH and MON. It is restartable and responsible for final satellite insertion.
    

What is EOS-09 Satellite

1. The EOS-09 is an Earth Observation Satellite designed for high-resolution remote sensing.
2. It supports various civilian applications including agriculture, water resource monitoring, urban planning, and disaster response.
3. It was intended to be deployed in a 600 km Sun-Synchronous Polar Orbit to ensure consistent lighting conditions.
    

PSLV Variants and Configurations

Variant	Description	Strap-on Boosters	Payload to SSPO
PSLV-CA (Core Alone)	No strap-ons; used for lighter payloads	None	~1,019 kg
PSLV-G	Standard with 6 boosters	6	~1,600+ kg
PSLV-XL	Extended; high capacity	6 (XL type)	~1,750 kg
PSLV-DL	Dual booster config	2	~1,200–1,300 kg
PSLV-QL	Quick launch, 4 boosters	4	~1,523 kg

Comparison: PSLV (Polar Satellite Launch Vehicle) and GSLV (Geosynchronous Satellite Launch Vehicle)
 

1. The PSLV and GSLV are both used by India to launch satellites, but they have different capabilities and purposes.
2. PSLV is primarily used for launching Earth observation and remote sensing satellites into lower orbits, while GSLV is designed for launching heavy communication satellites into Geosynchronous Transfer Orbit (GTO).
3. GSLV also utilizes a cryogenic stage, which PSLV does not, for more powerful launches.
   
    

Feature	PSLV	GSLV
Number of Stages	4	3
Propulsion Type	Solid and Liquid	Liquid and Cryogenic
Lift-off Mass	Approximately 320 tonnes	Approximately 420 tonnes
Primary Orbit Type	SSPO and Low Earth Orbit	GTO and High Earth Orbit
Maximum Payload	~1.75 tonnes (SSPO)	~2.25 tonnes (GTO)
Key Missions	Earth Observation and Scientific	Communication and Heavy Payloads
Notable Variants	CA, G, XL, DL, QL	Mk I, Mk II, Mk III

Implications of PSLV-C61 Failure

1. The PSLV-C61 failure is a rare setback in PSLV’s largely successful record.
2. It highlights the technical complexity of multi-stage launches, especially with solid propulsion systems.
3. ISRO’s quick diagnosis and public communication indicate transparency and institutional resilience.
4. The relaunch of EOS-09 will be crucial for maintaining confidence in the PSLV’s reliability.
    

Strategic Importance of PSLV

1. The PSLV has played a critical role in India’s space diplomacy, launching satellites for over 30 countries.
2. It has enabled India to become a low-cost, reliable launch partner in the global space market.
3. Despite occasional failures, the PSLV continues to be central to ISRO’s scientific and strategic missions.
    

Conclusion

The PSLV remains a cornerstone of India’s space program, known for its versatility, cost-effectiveness, and proven performance. The PSLV-C61 failure underscores the importance of continuous innovation and rigorous quality control. ISRO’s response demonstrates its maturity as a scientific organization, and the upcoming reattempt of EOS-09 will be an opportunity to reaffirm PSLV's legacy.