A mild breeze was blowing across the Kapustin Yar launch site in the erst while Soviet Union when space scientists U R Rao and Satish Dhawan walked in.There was a sense of anxiety in the early-morning air as within 90 minutes a liquid-fuelled two-stage Kosmos 3M rocket was to blast off with a 360kg Aryabhatta, India's first satellite. That was April 19, 1975, when only a few dared to dream of making India a regular spacefaring nation.“The Russians were confident of our technology ,“ Rao recalled. But that was not enough.India was yet to build a rocket that would launch satellites. If Aryabhatta ushered in a new era for Indian space, the Polar Satellite Launch Vehicle ( PSLV ), a medium-class launcher, enabled Indian Space Research Organisation ( Isro ) to become self-sufficient in some ways.Isro's mastery in perfecting PSLV propelled this journey and its commercial arm, Antrix, ensured steady growth of customers and raked in the revenue. It is today the go-to organisation for several countries, translating into 10%-20% of Antrix's revenue.This February, Isro launched 104 satellites in one go beating Russia's record of 37. Barring the 714-kg Cartosat, all others were nanosatellites. For, when it comes to foreign launches, Isro's mantra has been 'small is beautiful'.Between May 1999 and June 2017, Isro launched 209 satellites from 28 countries with a combined weight of 6,694.70 kg. Contrastingly , the weight of three recent Indian satellites ­ GSATs 16, 15 & 18--launched by the French Ariane rocket, is 9,750 kg.But unlike the French Arianespace, or SpaceX of the US, Isro is not a commercial organisation. “Our country has a lot of demands.Commercial launches are secondary. That's why we offer spare space in the rocket to carry other satellites. There have been complete commercial launches for Singapore and the UK, but those were exceptions,“ Isro chairman AS Kiran Kumar told TOI.Antrix, which earned $76.5 million and $4.5 million - both must be added -by launching foreign satellites in the past two years, is hopeful of earning more in the future as Isro increases it PSLV launches from six per year to eight. In 2013, it earned $6.9m from foreign launches, and $18.2m and $55.5m in 2014 and 2015. “If we have two to three PSLVs to sell for dedicated launches to customers, we can look at earning more money , but with what we have now we can only offer space for co-passengers as India's needs are a priority ,“ Antrix chair man and managing director S Rakesh said.The PSLV's liquid propulsion system and liquid stages made it Isro's workhorse with whom development of liquid engines began.Isro used solid motor technology for SLV and ASLV , and scientists wanted a propulsion system that could give better specific impulse.“A solid rocket can have an impulse of 2,730 Nskg and liquid can have almost 2,900. Though liquid is complex with many parts for construction than solid, it can be stopped at any time and can control precise position or velocity ,“ said S Somanath, director, Liquid Propulsion Systems Centre.With PSLV a runaway success, Isro has begun work on its next generation vehicle -the Heavy Lift Vehicle or HLV powered by a semi-cryo engine that can lift nearly seven tonnes of payload.From one launch in 2007 to six in 2016, Isro has plans to increase its launch frequency to 10 per year. A new assembly centre in Sriharikota will help simultaneous work on PSLV and GSLV launches. Despite 90% of these resources being consumed for Indian needs, Antrix's growth graph is commendable, especially when a majority of the countries launching with Isro do not have bilateral space treaties with India.Rakesh explains: “There can never be a fixed cost. Commercial satellite launching is a fluctuating market based on many parameters like the space the payload occupies, the prime orbit, reliability of the rocket, the timing among others. We offer what they want otherwise we would not have these many customers.“Isro Satellite Centre director M Annadurai said India's cost competitiveness came from PSLV's reliability and Isro's quick turnaround time. “PSLV has a proven track record which makes customers insuring the satellites less expensive. We offer the best turnaround time given our frequency , which also adds to the cost factor,“ Annadurai said.Kiran Kumar said there were not many offering rockets in this class that could put small satellites into space, while Rakesh said Arianespace's Russian version operates in the same class but without PSLV's track record yet.