This was the 63rd PSLV launch. Since their introduction in the 1990s, PSLVs have only failed twice – the first during the inaugural flight in 1993 and in 2017, when the C-39 mission was unsuccessful. Here is why PSLVs have become reliable for India’s Space agency and what happened during the two failed missions.

First, what is a PSLV?

Satellites deployed for navigation, mapping, or other purposes must be carried to Space by launch vehicles, or rockets, like the PSLV. The rockets have powerful propulsion systems that generate a huge amount of energy, required to lift heavy objects like satellites into Space, overcoming the Earth’s gravitational pull.

Satellites, or payloads as they are often called, sit inside the rocket and are ejected once they reach near their intended orbit in Space.

ISRO has three main types of launchers: the PSLV, the Geosynchronous Satellite Launch Vehicle (GSLV), and the Geosynchronous Satellite Launch Vehicle Mk-III (LVM3). Variants are chosen based on the payload weights and the orbit they are to reach.

The ISRO website notes that PSLV has been a “versatile launch vehicle deployed for launching all the three types of payloads viz. Earth Observation, Geo-stationary and Navigation. It has got highest success rate and considered as work horse of ISRO.” Further, it has launched two spacecraft, Chandrayaan-1 in 2008 and Mars Orbiter Spacecraft in 2013.

The PSLV has four parts — PS1, a solid rocket motor augmented by 6 solid strap-on boosters; PS2, a storable liquid rocket engine, known as the Vikas engine; PS3, a solid rocket motor that provides the upper stages high thrust after the atmospheric phase of the launch; and PS4, the uppermost stage consisting of two Earth storable liquid engines.

It has also carried satellites from other nations into Space. Apart from its reliability, the PSLV is also more affordable than the launch vehicles of many countries. In 2023, the PSLV-C37 launched a record 104 satellites in one mission from Sriharikota.

Why did the PSLV fail in 1993 and 2017?

In September 1993, the PSLV-D1 was launched from Satish Dhawan Space Centre in Sriharikota to place the remote sensing IRS-1E Satellite in the Lower Earth Orbit (altitude of 2,000 km or less).

However, the launch vehicle failed to achieve orbit because of problems in the onboard software, leading the mission to crash into the ocean.

In 2017, the 41st PSLV flight was supposed to launch IRNSS-1H, the eighth satellite of the Indian Regional Navigation Satellite System (IRNSS), into a Sub-Geosynchronous transfer Orbit (Sub-GTO). Here, instead of directly placing a satellite into an orbit, transfer orbits are first targeted. From here, the satellites go to another orbit by using energy from onboard motors, according to the European Space Agency.

However, the mission failed. ISRO said a heat shield failed to separate, preventing the satellite from being deployed in Space by PSLV-C39, the launch vehicle. As The Indian Express reported at the time, the performance of PSLV-C39 went to plan up to the point when the satellite had to be inserted into orbit. Due to the separation failure, the rocket lost velocity.

The heat shield is a protective cover around the satellite to help it withstand the adverse temperatures when a rocket is launched into Space. Separation of the heat shield occurs mid-flight when the rocket leaves Earth’s atmosphere and reaches an altitude of around 120 km. ISRO declared the mission unsuccessful shortly after the final stage of the launch, making it the first mission failure after the 1993 developmental flight.

A PSLV Heat Shield Model at HAL Aerospace Museum in Bengaluru. (Wikimedia Commons)

And what was the mission this time?

ISRO planned to put the 1,700-kg Earth observation satellite at an altitude of about 597 km in a sun-synchronous polar orbit — meaning the satellite was to pass over a given place at the same time every day.

The EOS-09 satellite carried a Synthetic Aperture Radar (SAR) payload, capable of providing images of the Earth in all weather conditions. This was the second consecutive failure for the Space agency after its GSLV could not place the NVS-02 satellite in the correct orbit during ISRO’s 100th mission in February this year.