Onmanorama explains | What does the launch of SSLV mean for the Indian space industry?

The Indian Space Research Organization (ISRO) is set to launch a smaller rocket that can place lightweight Earth monitoring satellites into low Earth orbits on demand. Called the Small Satellite Launch Vehicle (SSLV), it will lift off from the first launch pad at Satish Dhawan Space Center, Sriharikota, Andhra Pradesh on August 7.

SSLV is equipped to launch mini, micro or nano satellites (mass from 10 to 500 kg) in low Earth orbit (LEO), up to 500 km from the Earth. At 34 meters, the SSLV is shorter than the Polar Satellite Launch Vehicle (PSLV) of 44 meters.

It’s leaner too; if the diameter of the SSLV vehicle is 2 meters, it is 2.8 meters for the PSLV.

The former ISRO workhorse can carry payloads of up to 1750 kg up to 600 km. The smallest can only support smaller loads, from 10 to 500 kg, up to 500 km above the earth.

The SSLV is shorter than the Polar Satellite Launch Vehicle (PSLV) by 44 meters. Photo: ISRO website


If the take-off mass of PSLV (initial mass of a rocket) is 320 tons, it is only 120 tons for SSLV.

The mission of the launcher’s first development flight, SSLV-D1, is to place EOS-02 (Earth Observation Satellite-02), a 135 kg satellite, into low Earth orbit approximately 350 km from Earth.

There will also be a co-passenger satellite, AzaadSAT, which will also be placed in low Earth orbit (LEO).

What is LEO
Low Earth Orbit (LEO) extends 200-2000 km from the earth’s surface, after which Medium Earth Orbit begins.

Although called low earth orbit, this does not mean that the LEO is just an airplane flight distance from earth. The LEO exists far above the troposphere (up to 12 km from the earth, the edge of which is very rarely touched by commercial aircraft), the stratosphere (12-50 km) and even the mesosphere (50- 80km).

LEO is a region that straddles the thermosphere (80-700 km) and the exosphere (700-10,000 km).

The mission of SSLV-D1 is to place EOS-02 (Earth Observation Satellite-02) in low Earth orbit approximately 350 km from Earth. Photo: ISRO website


The SSLV was designed to place satellites up to the thermosphere.

What is the launch-on-demand capability?

Placing the EOS-02 on a LEO is just a show of force, like the military parade on Republic Day. The intention is to showcase ISRO’s on-demand launch (LOD) prowess. LOD is nothing but the expertise to place satellites into orbit on demand.

So far, PSLV (Polar Satellite Launch Vehicle) has placed satellites into orbits, including LEO, efficiently; 53 of its 55 launches were successful.

The problem is that the launch process takes time, a drawback at a time when the market for small satellite launches is growing.

US business consultancy firm Frost and Sullivan has estimated that the market for small satellite launch services will cross the $69 billion mark by 2030.

“Because PSLV rockets are fired by liquid propellant, their turnaround time (the time needed to assemble the different segments of the launcher, make the electrical connections and then transport them before launch) is at least a month. An SSLV launch , fired by solid rocket boosters, can be done in three days,” said S Unnikrishnan Nair, director of the Vikram Sarabhai Space Center (VSSC).

Liquid propellant rockets, unlike solid fuel vehicles, require more specialized knowledge and equipment. The three main propulsion stages of the SSLV are based on solid fuel; 87 tons, 7.7 tons and 4.5 tons. Solid propellants, unlike liquids, are easily stored, and are therefore easy to manage and integrate.

Does SSLV have a liquid stage?

However, SSLV has a fourth stage, a minor velocity trim module (VTM) powered by liquid propellant and weighing 0.05 tons.

“The vehicle must reach the precise speed to place the satellite in the specific orbit. A solid thruster cannot guarantee this, only a liquid thruster can help achieve the exact orbital parameters,” the VSSC director said.

SSLV has a fourth stage, a minor velocity trim module (VTM) powered by liquid propellant and weighing 0.05 tons. Photo: ISRO website


The PSLV, which launched India’s first Chandrayan-1 lunar mission in 2008 and Mars Orbiter Spacecraft in 2013, will now be reserved for larger domestic missions.

What does SSLV design mean for private industry
The SSLV has been designed in such a way that even small industry players can participate in its construction, unlike more advanced launchers like the PSLV or the geosynchronous satellite launcher (GSLV).

“We will only do two to three launches and after that we plan to transfer the technology to private players,” the VSSC director said. “We have developed a simple and user-friendly design that even small industry players can be part of building it,” he added.

He was referring to actors such as hardware manufacturers who can supply the metal casing of SSLV rockets or actors who design the electrical circuits or develop processors for critical operations within the launch vehicle.

Designing more advanced launchers like PSLV and GSLV requires highly skilled manufacturing processes that only big players like Hindustan Aeronautics Limited can adopt.

First payload of SSLV

EOS-02, which will be placed in an orbit of approximately 350 km, is an Earth observation satellite designed and produced by ISRO. It is an experimental optical remote sensing satellite, a microsat series satellite, providing advanced optical remote sensing operating in a high spatial resolution infrared band.

LEO satellites, such as EOS-2, are ideal for imaging and communication. Because it is closer to Earth, imaging satellites will be able to capture better and more detailed images.

Satellite voice and data services can also be useful in emergencies such as floods and other natural disasters.

The International Space Station, where large-scale remote sensing, medical, gravitational and space experiments are carried out, is in LEO, in an orbit close to that which EOS-2 will be released.

satellite powered by girls

AzaadiSAT is a Cubesat, a miniaturized satellite, weighing approximately 8 kg. It carries 75 different payloads each weighing about 50 grams and conducting femto experiments.

Female students in rural areas across the country received guidance in building these payloads. The payloads are integrated by the student team of “Space Kidz India”, an aerospace organization creating young scientists for the country.

Rifath Sharook, the Chief Technology Officer of Space Kidz India, tweeted on July 8 that AzaadiSAT was a special mission in which the organization had selected “750 female students from 75 government schools across all Indian states and provided training for build 75 experimental payloads”.

Payloads include a UHF-VHF transponder operating at amateur radio frequency to enable voice and data transmission for amateur radio operators, a solid-state PIN diode radiation meter to measure ionizing radiation in its orbit, a long range transponder and a selfie camera.

The ground system developed by ‘Space Kidz India’ will be used to receive data from this satellite.

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