From the days of having a church as control room, the bishop's house as office, a bicycle as ferry, naked eyes to track the smoke plume at Thumba in Kerala, converting a toilet into a satellite data receiving centre in Bangalore, the Indian space odyssey has come a long way to launching lunar probes, working on a Mars mission and ferrying foreign satellites up for a fee.

On Sunday, ISRO will touch a major milestone, the 100th space mission with the launch of two foreign satellites.

"During those days infrastructure was not available and we used what was available. In Bangalore we even converted a toilet into a data receiving centre for our first satellite Aryabhata," U.R. Rao, former chairman of Indian Space Research Organisation (ISRO) told IANS.

Today India is reckoned as a serious emerging player in the global satellite launch and manufacturing industry and the market leader in vending images sent by its remote sensing/earth observation satellites.

Ferrying 27 foreign satellites till date, ISRO Sunday would carry a 715 kg French satellite (heaviest foreign payload to be carried by an Indian rocket) and a 15 kg Japanese micro satellite signalling the increased confidence in the space agency's rocket Polar Satellite Launch Vehicle (PSLV).

The space agency has also jointly built two heavy satellites - 3,453 kg W2M and 2,541 kg Hylas - for the French agency EADS Astrium.

India's high point in its space odyssey was its moon mission in 2008 when it launched Chandrayaan-1 and Chandrayaan-2 is slated for 2014. The government has also sanctioned a mission to Mars which is expected to happen next year.

But the achievement that ISRO started notching up in rocket and satellite launches since 1990s were due to the trials and tribulations that the ISRO's founding fathers underwent.

Though ISRO has been flying sounding rockets (experimental rockets) from Thumba since 1963, its efforts to launch a rocket with a heavier payload actually started with Satellite Launch Vehicle-3 (SLV-3) in 1980.

However by that time ISRO had already built and launched two satellites - 358 kg Aryabhata and 444 kg Bhaskara-1.

"Starting from the scratch was the challenge before us while we began the Aryabhata project. Majority of the team members were new to this field. The time given was just two and half years so that it could be flown in a Russian rocket. Building clean room, thermo vacuum room and other facilities were all new," recalled Rao.

After Bhaskara-1 the Indian space agency built the APPLE communication satellite laid the ground for the INSAT series satellites possessing multiple capabilities - telecom, television, meteorological and imaging.

"Building the four-in-one satellite was a challenge. While we designed the INSAT-1A satellite it was made by Ford Aerospace and was launched by an American rocket. The satellite had a short life," Pramod Kale, the first project director for INSAT now retired, told IANS.

Success started smiling at ISRO from INSAT-1B onwards which according to Rao ushered in communication revolution in India.

There was no looking back for the space agency on the satellite side. From one tonne satellites, the INSAT series started growing in weight to become three tonne and ISRO later started making satellites for others.

Meanwhile scientists at Vikram Sarabhai Space Centre (VSSC) in Thiruvananthapuram, were initially toiling to get the rocket right as the SLV and Augmented SLV (ASLV) missions gave mixed results.

"The two ASLV failures were the real test beds for perfecting the PSLV rocket. Issues like rocket tumbling, monitoring of rocket's main forces, detailed profiling of wind and other issues were done," S.C. Gupta, former director of VSSC, told IANS.

The third ASLV with Stretched Rohini Satellite Series (SROSS) turned out to be successful but the result of the first PSLV flight in 1993 was negative owing to a software error, which was later sorted out.

Since then there was no looking back for ISRO as far as PSLV rocket is concerned. The space agency has now three PSLV variants.

"As technology was not available we developed our own navigational systems, propellent and all the elements of the launch vehicle with help of Indian industry," Gupta recalled.

But the serious issue before ISRO now is perfecting the technology for its heavier rocket Geosynchronous Satellite Launch Vehicle (GSLV) so that heavy communication satellites can be launched.

"The challenge before ISRO is to perfect its own cryogenic engine that would power the final stages of GSLV rocket. Otherwise the rocket has the same reliability like PSLV," B.N. Suresh, former director of VSSC and now retired, told IANS.