Indian Space Research Organisation (ISRO) on Sunday launched a smaller rocket that can place lightweight Earth-monitoring satellites on low earth orbits right on demand.
Called the Small Satellite Launch Vehicle (SSLV), it lifted off from the First Launch Pad of Satish Dhawan Space Centre, Sriharikota in Andhra Pradesh.
SSLV is equipped to launch mini, micro or nano satellites (10-500 kg mass) in the low earth orbit (LEO), up to 500 km from earth. At 34 metres, SSLV is shorter than the 44-metre Polar Satellite Launch Vehicle (PSLV).
It is leaner too; if the SSLV vehicle diameter is 2 metres, it is 2.8 metres for PSLV.
The old ISRO workhorse can take payloads up to 1750 kg up to 600 km. The smaller one can take only smaller loads, 10-500 kg, up to 500 km above the earth.
If PSLV's lift-off mass (initial mass of a rocket) is 320 tonnes, it is only 120 tonnes for SSLV.
The mission of the first development flight of the launch vehicle, SSLV-D1, is to place EOS-02 (Earth Observation Satellite-02), a 135 kg Satellite, into low earth orbit about 350 km from the Earth.
There will also be a co-passenger satellite, AzaadSAT, which will also be placed in a Low Earth Orbit (LEO).
What is LEO
The low earth orbit (LEO) spans 200-2000 km from the surface of the earth, after which the Medium Earth Orbit begins.
Though called low earth orbit, it does not mean that the LEO is just a plane-flying distance from the earth. The LEO exists far above the troposphere (up to 12 km from earth, the edge of which is touched very rarely by commercial planes), stratosphere (12-50 km) and even the mesosphere (50-80 km).
LEO is a region that straddles the thermosphere (80-700 km) and exosphere (700-10,000 km).
The SSLV has been designed to place satellites up to the thermosphere.
What is launch-on-demand capability
Placing EOS-02 on a LEO is just a show of strength, like the military parade on Republic Day. The intent is to showcase ISRO's launch-on-demand (LOD) prowess. LOD is nothing but the expertise to place satellites in orbit on demand.
Till now, PSLV (Polar Satellite Launch Vehicle) had been placing satellites on orbits, including LEO, efficiently; 53 of its 55 launches were successful.
Problem is, the launch process takes time, a disadvantage at a time when the market for small satellite launches is growing.
The American business consulting firm Frost and Sullivan has estimated that the small-satellite launch services market will cross the 69 billion dollar mark by 2030.
"Since PSLV rockets are fired by liquid propellants, their turnaround time (the time taken to assemble various segments of the launch vehicle, provide the electrical connections and then their transport before the launch) is at least a month. An SSLV launch, fired by solid propellants, can be done in three days," said S Unnikrishnan Nair, the director of Vikram Sarabhai Space Centre (VSSC).
Liquid propellant rockets, unlike vehicles using solid fuel, require more specialized knowledge and equipment. All the three main propellant stages of SSLV are based on solid fuel; 87 tonnes, 7.7 tonnes and 4.5 tonnes. Solid propellants, unlike liquid ones, can be stored easily, and therefore are easy to manage and integrate.
Does SSLV have a liquid stage?
However, SSLV has a fourth stage, a minor Velocity Trimming Module (VTM) fuelled by a liquid propellant and weighing 0.05 tonnes.
"The vehicle has to achieve the precise velocity to place the satellite in the specific orbit. A solid propellant cannot ensure this, only a liquid propellant can help achieve the exact orbital parameters," the VSSC director said.
The PSLV, which had launched India's first moon mission Chandrayan-1 in 2008 and Mars Orbiter Spacecraft in 2013, will now be reserved for bigger national missions.
What does SSLV design mean for private industry
The SSLV has been designed in such a manner as to make it easy for even small industry players to be part of its construction, unlike more advanced launch vehicles like PSLV or Geosynchronous Satellite Launch Vehicle (GSLV).
"We will be doing only two to three launches and after which we plan to transfer the technology to private players," the VSSC director said. "We have developed a simple and friendly design that even small industry players can be part of its construction," he added.
He was referring to players like hardware manufacturers who can provide the metallic case for the SSLV rockets or players who design the electric circuitry or develop processors for critical operations within the launch vehicle.
The design of more advanced launch vehicles like PSLV and GSLV calls for high-skill manufacturing processes that only big players like Hindustan Aeronautics Limited can take up.
SSLV's first payload
EOS-02, which will be placed at an orbit of about 350 km, is an earth observation satellite designed and realised by ISRO. It is an experimental optical remote sensing satellite, a microsat series satellite, offering advanced optical remote sensing operating in an infra-red band with high spatial resolution.
Satellites in LEO, like EOS-2, are ideal for imaging and communication. Because it is closer to the Earth, imaging satellites will be able to capture better and more detailed pictures.
Satellite voice and data services can also come in handy during emergencies like floods and other natural disasters.
The International Space Station, where remote sensing, medical, gravity and space experiments are conducted on a large scale, is in a LEO, in an orbit near the one EOS-2 will be dropped.
Satellite propelled by girls
AzaadiSAT is a Cubesat, a miniaturised satellite, weighing around 8 kg. It carries 75 different payloads each weighing around 50 grams and conducting femto-experiments.
Girl students from rural regions across the country were provided guidance to build these payloads. The payloads are integrated by the student team of “Space Kidz India”, an aerospace organisation creating young scientists for the country.
Rifath Sharook, the chief technology officer at Space Kidz India, tweeted on July 8 that the AzaadiSAT was a special mission in which the organisation had selected "750 girl students from 75 government schools from all the Indian states and provided training to build 75 experimental payloads".
The payloads include a UHF-VHF Transponder working in ham radio frequency to enable voice and data transmission for amateur radio operators, a solid state PIN diode-based Radiation counter to measure the ionising radiation in its orbit, a long-range transponder and a selfie camera.
The ground system developed by ‘Space Kidz India’ will be utilised for receiving the data from this satellite.
