How the maiden flight of ISRO’s SSLV went awry
Context:
- The first developmental flight of the SSLVD1/EOS2 mission failed to place the payload (satellites) in their required orbits, and the satellites, as they were already detached from the launch vehicle, were lost.
- The Small Satellite Launch Vehicle (SSLV) D1/EOS2 mission was carrying two satellites — the Earth Observation Satellite 2 (EOS2) and AzadiSAT. The mission aimed to place the EOS2 in a circular Low Earth Orbit at a height of about 350 km above the Equator and inclined at an angle of 37 degrees.
Purpose of the SSLV D1/ EOS 2 mission:
- The EOS 2 which was designed and developed by ISRO, offered advanced optical remote sensing operations.
- It would have operated in the infrared region and could have served many purposes, from imaging for climate studies to simply keeping an eye on Earth.
- AzadiSAT, on the other hand, was a collective of 75 tiny payloads weighing around 50 grams each, which were integrated by students.
- It carried tiny experiments which would have measured the ionising radiation in its orbit and also a transponder which worked in the ham radio frequency to enable amateur operators to access it.
Stages of the event:
- The SSLV was composed of three stages powered by solid fuels and these three performed their function as planned.
- However, when it came to the stage when the satellites had to be set in orbit, there was a glitch which resulted in the satellites being lost forever. Due to a malfunctioning of a sensor, the satellites were put in an elliptical orbit, rather than a circular orbit.
Difference between circular and elliptical orbits:
- Mostly objects such as satellites and spacecrafts are put in elliptical orbits only temporarily. They are then either pushed up to circular orbits at a greater height or the acceleration is increased until the trajectory changes from an ellipse to a hyperbola and the spacecraft escapes the gravity of the Earth in order to move further into space — for example, to the Moon or Mars or further away.
- Satellites that orbit the Earth are mostly placed in circular orbits. One reason is that if the satellite is used for imaging the Earth, it is easier if it has a fixed distance from the Earth. If the distance keeps changing as in an elliptical orbit, keeping the cameras focussed can become complicated.
Launch vehicles:
- Launch vehicles are rockets that take and put payloads (eg, satellites) in the intended place or orbit in space.
- The 2 main types of launch vehicles of ISRO- PSLV (Polar Satellite Launch Vehicle) and GSLV (Geosynchronous Satellite Launch Vehicle) – can carry huge loads but GSLV is more powerful than PSLV.
PSLV:
It is a third-generation launch vehicle. It is termed as the ‘Workhorse of ISRO‘.
There is a total of 4 stages in this launch vehicle:
1. First Stage – PSLV uses the S139 solid rocket motor that is augmented by 6 solid strap-on boosters.
2. Second Stage – PSLV uses an Earth storable liquid rocket engine for its second stage, known as the Vikas engine, developed by Liquid Propulsion Systems Centre.
3. Third Stage – It is a solid rocket motor that provides the upper stages high thrust after the atmospheric phase of the launch.
4. Fourth Stage – The uppermost stage of PSLV comprising two Earth storable liquid engines.
Payload capacity:
1. 1750 kg to sun-synchronous polar orbits (SSPO) (Altitude – 600 Kms).
2. 1425 kg to Geosynchronous and Geostationary Orbits (GTO).
PSLV has launched Indian Remote Sensing (IRS) Satellites, among others.
GSLV:
The largest launch vehicle developed by India. It is a fourth-generation launch vehicle.
It has three stages:
1. First stage – The 138-tonne solid rocket motor is augmented by 4 liquid strap-ons.
2. Second stage – One Vikas engine is used in the second stage of GSLV.
3. Third Stage – Developed under the Cryogenic Upper Stage Project (CUSP), the CE-7.5 is India’s first cryogenic engine, developed by the Liquid Propulsion Systems Centre.
It also has four liquid-engine strap-ons.
Payload capacity:
1. 2500 kgs INSAT class of communication satellites to GTO
2. 5000 kgs heavy satellites to multiple smaller satellites in LEO.
About Small Satellite Launch Vehicle (SSLV):
- Recently ISRO is using (SSLV) to launch smaller payloads, by making it more efficient than PSLV. Now, those payloads with masses up to 500 kilograms can be sent up using the SSLV instead.
- The SSLV has been promoted as the next workhorse rocket of ISRO after the PSLV.
- Measuring just 2 metres in diameter and with a height of 35 m, it is indeed smaller than the PSLV which has been used to place satellites of a wide range of masses.
Advantages of SSLV:
- The SSLV can easily carry small to medium loads from 10 kg to 500 kg. It is also less expensive.
- The three stages being powered by solid fuel is another advantage. Solid fuel is easier to handle, whereas handling the liquid propellants used in the PSLV and GSLV is more complex.
- SSLV has the flexibility to launch multiple satellites, and satellites can be launched on demand — as the rocket requires minimal launch infrastructure. All these features make it very attractive for commercial earth observation and communication.
Conclusion :
One failure should not be used to evaluate the future use of SSLV which is likely to remain a workhorse of ISRO. On the other hand, ISRO also needs to look at alternatives, especially reusable rockets.
