In its first launch in three months, ISRO will use its biggest rocket LVM-3 to send a communication satellite CMS-03 to space Sunday evening. This is the first time that ISRO will put a satellite weighing over 4,000 kg in the distant geosynchronous transfer orbit (GTO) from the Indian soil.CMS-03, a multiband communication satellite, weighing 4,410 kg will be placed in a transfer orbit of around 29,970 km x 170km from the surface of the earth. So far, ISRO had to contract out the launch of its heavier satellites to private space agencies from other countries. The current launch is a milestone towards the growing capability of the LVM3 rocket, a modified version of which will also be used under the Gaganyaan mission to put humans in space.Capability of LVM-3LVM-3, earlier referred to as Geosynchronous Launch Vehicle Mark 3 or GSLV Mk 3, uses solid, liquid, as well as cryogenic-fuel based engines to put up to 8,000 kg in low earth orbit (up to an altitude of 2,000 km from Earth’s surface) and up to 4,000 kg in geosynchronous orbit (about 36,000 km). ISRO’s initial plan was to use its workhorse PSLV for polar and low earth orbit launches — much closer to the surface of the Earth — and use GSLV II and GSLV Mk 3 to launch the satellites to the more distant geosynchronous orbits.The GSLV-Mk3 rocket was later adapted in 2022, amid the Russia-Ukraine war, to launch 72 OneWeb satellites in two launches to low earth orbit, prompting the change in name of the rocket. The GSLV name implied it was meant to deposit satellites only to the geosynchronous orbit, but the OneWeb missions showed that this rocket could be used for other purposes as well.At that time OneWeb, a global satellite internet company, was hard pressed to find a launch provider — Russia had stopped flying the internet constellation because its data was also being provided to Ukraine while the major European launcher Ariane-5 had retired with a replacement yet to be commissioned. During these two OneWeb missions, the rocket did carry a heavier payload of more than 5,700 kg but it was to a low earth orbit of around 450 km from the surface of the Earth.India’s previous heavy satellites — it does have a few communication satellites weighing more than 4,000 kg — were put in orbit by other private launchers. The 5,854-kg GSAT 11 and 4,181-kg GSAT-24 were launched by Ariane space. ISRO also used the service of Elon Musk’s SpaceX last year to put in orbit the 4,700-kg GSAT-20 satellite.For this launch, to accommodate a heavier satellite — over its capacity of 4,000 kg to GTO — the orbit has been lowered slightly, with the highest point being somewhere around 29,970 km. ISRO, however, is working on ways to increase the capacity of this launch vehicle.Story continues below this adChanges to be madeISRO has been working on increasing the carrying capacity of launch vehicle, especially considering it will be used for the country’s human spaceflight mission.One of the ways is to increase the thrust produced by the third or the cryogenic upper stage of the rocket, which accounts for nearly 50% of the velocity needed to place the satellites in the geosynchronous transfer orbits. The C25 stage presently being used in the launch vehicle can carry only 28,000 kg of the propellent producing a thrust of 20 tonnes. The new C32 stage will be capable of carrying 32,000 kg of fuel and produce a 22 tonne thrust.The space agency is also looking at using a semi-cryogenic engine instead of the liquid-propellent based second stage of the rocket. A cryogenic engine essentially uses liquified gases at extremely low temperatures as the fuel — in this case liquid oxygen and hydrogen. A semi cryogenic engine uses a liquified gas and a liquid propellent. ISRO plans to use a refined kerosene and liquid oxygen based second stage. This will not only increase the capability of the launch vehicle, it might also be cheaper.With the new engine, the vehicle is likely to become capable of carrying around 10,000 kg to the low earth orbit instead of the current 8,000 kg. The heaviest payload it has carried to low earth orbit is 5,800 kg for the OneWeb mission. The increased capability of the Kerosene will be enough to carry the first and the lightest module of the Bharatiya Antarish Station — India’s planned space station. A launch vehicle with a higher capability would be needed for the launch of the subsequent modules. The space agency is working on developing a new vehicle called Lunar Module Launch Vehicle (LMLV) that will be capable of carrying up to 80,000 kg in the low earth orbit — mainly being designed to carry out missions sending humans to the moon.Story continues below this adLaunches so farISRO’s heaviest launcher is also one of its most successful, with all seven of its flight putting satellites in the intended orbits.It is the launch vehicle that took both Chandrayaan-2 and Chandrayaan-3 to space, in addition to communication satellites GSAT-19 and GSAT-29. To compare, four of the 18 launches undertaken by its slightly less powerful cousin GSLV have failed. When it comes to ISRO workhorse PSLV, three of the 63 missions undertaken have failed, with most recent being in May this year, when the EOS-9 satellite could not be put in orbit after the third stage did not work as intended.The GSLV-Mk3, in its first flight in 2014, took to orbit a crew module for the country’s first ever re-entry test. This is very important, especially for human mission, where the space agency would have to make sure the astronauts safely return even through the massive heat generated due to friction in the atmosphere.