It was a black Thursday for Indian space programme as it suffered a serious setback after its workhorse rocket Polar Satellite Launch Vehicle (PSLV) failed to deliver India's eighth navigation satellite in its intended orbit. The 1,425 kg Indian Regional Navigation Satellite-1H (IRNSS-1H), which was launched at 7 p.m. on board the PSLV, was declared unsuccessful after its heat shield failed to separate. Indian Space Research Organisation (ISRO) Chairman A.S. Kiran Kumar said: "The mission was unsuccessful." "The rocket heat shield didn't separate. The satellite is inside the heat shield," he added. Speaking to the media, Kiran Kumar said the rocket engines performed well but only the heat shield did not get separated. "The satellite was seen rotating inside the heat shield enclosure," he said. Queried about the impact of the mission failure on getting commercial launch prospects, the ISRO Chairman said the issue has to be studied. The rocket's heat shield should have separated some three minutes into the launch, but it failed to. The scientists waited for some 19 minutes to see if it would separate, and then declared the mission unsuccessful. The IRNSS-1H satellite was to have been slung into orbit at around 507 km above the earth. Rocket scientists are perplexed at the failure. "It is really perplexing that such a thing has happened. Normally the PSLV rocket has several redundancies built into it," R.V. Perumal, a former ISRO scientist, told IANS. He said all the commands are pre-planned and built into the computers. "There cannot be any manual command," he added. Earlier, at around 7 p.m. the rocket PSLV standing around 44.4 metres tall and weighing 321 tonnes with a one-way ticket hurtled towards the skies ferrying the IRNSS-1H. With a rich orange flame at its tail, the rocket ascended towards the evening skies amidst the resounding cheers of ISRO scientists and media team assembled at the launch centre. Space scientists at ISRO new rocket mission control room were glued to their computer screens watching the rocket escaping the earth's gravitational pull. The IRNSS-1H is a substitute for IRNSS-1A as the three rubidium atomic clocks of the latter has failed. The launch failure has shocked the Indian space community as PSLV has a good record of success missions since 1993 and has been a major revenue earner for Antrix Corporation, ISRO's commercial arm. PSLV is a four stage (engine) rocket powered by solid and liquid propellants alternatively. The first and third stages are fired by solid propellant and the second and fourth stages are fired by liquid propellant. The rocket that failed on Thursday is the much powerful variant called PSLV-XL. But for two failures - one in 1993 and the other on Thursday - the PSLV has an excellent success record launching several Indian and foreign satellites. Incidentally the launch of the first navigation satellite IRNSS-1A was also postponed from its original launch date. The launch had to be put off initially after finding a problem in one of the electro-hydraulic control actuators in the rocket's second stage/engine. The second stage had to be dismantled to replace the actuator, which is an assembly of several components. It weighed around 20 kg. ISRO also had earlier dismantled a fully assembled PSLV rocket to check a component in the rocket's second stage. In 2010 a fully assembled PSLV rocket was dismantled to replace a gas motor in its second stage/engine with an uprated one. The gas motor powers the rocket's second stage control actuators for manoeuvering the engine's nozzle - the process is called gimballing. The process enables the rocket to maintain a steady course on its way up. The failure of PSLV on Thursday is expected to impact ISRO's prospects in the global small and medium sized global satellite launch market.