Thursday 13 September 2007

PSLV Success

Business India, October 24-November 6, 1994

The great leap forward

The successful launch of the PSLV puts India’s satellite launch capacity on a firmer footing

Shivanand Kanavi

The countdown started at 10:02, thirty minutes prior to launch (T­-30:00). As the minutes ticked away, each of the hundreds of scientists and engineers manning different stations reported to the mission control about the health of the sub-system he was monitoring.

Suddenly, as the launch sequence was being initiated, at T -14:50, the Precision Coherent Monopulsed C band (PCMC) Radar that would track the launch reported 'carrier loss' - it was not receiv­ing signals from the C band transponder placed in the PSLV. The countdown was immediately stopped, raising the spectre of an aborted launch.

The tension in the mission control cen­tre, and even in the press room 7 kill away from the launch pad, was palpable. Three minutes passed in attempts to restore the connection; then, the mission director Madhavan Nair gave the go ahead for the launch, despite the problem. In a complex space mission, the risk of mission failure due to malfunction of a single component or subsystem is extremely high; hence there is redundancy built in, so that if something fails, then its back up can take over. And that is exactly what happened . Another channel was switched on, the mission director saw that minimum con­figuration was achieved and gave the all important go ahead.

The countdown was, resumed and, step by step, the rocket was detached from the launch pad as the internal systems took over. The power was cut from the ground and the internal bat­teries switched on. Twelve minutes before launch the automatic launch sequence was initi­ated and the onboard computers took charge.

At 10:35 precisely, amidst billowing clouds of smoke, the first stage assisted by two strap-on boosters appeared to a novice's eye to be struggling to lift the mammoth 300-tonne rocket and start it on an accelerating trajectory that would achieve speeds up to 25,000 km per hour before injection into orbit. Then, with an ear-splitting roar, it roared up and as the ignition, separation and success of each stage was announced, cheering broke out in the control room .

But it was clearly still too early for self-congratulations. The mission would not be complete till the injection of the satellite into its designated orbit nearly 17 minutes after lift off. The grim memories, of the first developmental fligt of PSLV plunging into the Bay of Bengal into the Bay of Bengal a few minute after lift-off in last September, were too fresh. It was only when the on-line data showed that the fourth stage had sepa­rated from the satellite and steered itself out of orbit, that the tension gave way to elation and an overwhelmed Kasturi Ran­gan, chairman of the Space Commission, hugged his colleagues.

Later, when a galaxy of space scientists including Kasturi Rangan, Satish Dhawan, Yash Pal, Abdul Kalam, S.C. Gupta, N.S. Pant, Deekshithalu, P. Kale and Madhavan Nair addressed thousands of ISRO scien­tists and technicians in an open air audito­rium, words seemed superfluous. Twelve years of toil had finally paid off and the bit­ter disappointment of a failed launch was overcome. Every one to a man had a proud smile on his face.

The drama of the PSLV's successful launch is worth recording at some length. Mere description of the payload, orbital characteristics, thrusts generated by dif­ferent stages and myriad other details do not bring out a living picture of our space programme or the significance of the PSLV. After the failure of PSLV D-1. ISRO personnel and the fault analysis committee had ploughed through 100,000 pages of data, to discover an overflow error in the control software. Instead of correcting a deviation in the course caused by the failure of retro rock­ets during the separation of second and third stages, this overflow aggravated the tilt, which made the rocket tumble uncontrollably into a suborbital flight and plunge into the Bay of Bengal.

In PSLV D-2, this overflow error was corrected, the positioning of the actuator for the flex nozzle of stage three was altered, and the time gap between the burn-out of the second stage and ignition of the third stage, during which the rocket coasts along without control, was cut down. Even after all these improvements, if the desired 817 km-radius, sun-sychro­nous, circular-polar orbit was not achieved then a fall-back programme on the onboard computer would allow the satellite to be injected into a lower, 770 km orbit. No wonder, some ISRO top guns were so sure of success that one of them, who could not be present at the launch; left a post-dated congratulatory message! ,

The remote sensing satellite IRS P-2 that was launched had also undergone some improvements. It carries two Linear Imaging Self Scanner-II (LISS-II) cameras connected to a single optical unit, thus saving on costs and weight. In satellite technology, anything that saves weight of the payload is a most welcome development, since each kg added to the payload requires tones of added thrust at the lower stages. That is why multistage rocket design, where each stage provides a certain thrust and falls off, is so popular. Once the fuel is exhausted, the empty motors and casing need not be carried along into orbit.

The PSLV incorporates a number of new technologies, as compared to the earlier SLV and ASLV. It is the first rocket in Indian space programme, where liquid ­fuelled engines have been used for pri­mary propulsion. The first stage comprises third largest solid-fuelled booster in the world, after the American space shuttle and the Titan boosters. New technologies include the gimbaled motors for the liquid-fuelled second and fourth. stage, flex nozzle for the solid fuelled third stage, the Redundant Strap- down Inertial Navigation System, and the heat shield, which protects the satellite and the fourth stage from the atmosphere and opens at an altitude of about 120 km.

A number of new materials like the super alloy maraging steel for the giant first stage casings, new propellants for all stages and Kevlar and Titanium alloy for the third and fourth stages, were also developed. In short, PSLV was ten times more complex than the earlier generation ASLV.

Though ISRO has a vast network of centres in Bangalore, Thiruvananthapuram, Sriharikota and Ahmedabad, it has constantly endeavoured to transfer technology to industry and involve them as suppliers. Thus Larsen & Toubro and Walchandnagar Industries precision- machined the motor casings made of maraging steel for PSLV stage one. NOCIL manufactured hundreds of tonnes of Hydroxyl Terminated Poly Butadiene, the high powered solid propellant for the main booster rocket. The liquid-fuelled engine for the second stage named Vikas was an engineering marvel jointly manufactured and assembled by Hyderabad based MTAR and Godrej. When PSLV: D-1 failed, ISRO'S 150-odd vendors were naturally concerned that the systems sup­plied by them had been the cause. They heaved a collective sigh of relief when the software error was detected.

But does the successful launch mean we are ready to offer PSLV as a commercial vehicle to launch remote sensing satellites in polar orbits? The answer is: not yet. The next developmental, flight of PSLV is sometime next year and a new series of three more flights are being planned. Work has already started in ISRO to increase the payload to reach the magic figure of one tonne so that large remote sensing satellites like the coming IRS 1-D can be launched indigenously. So far, IRS 1-A and 1-B have been launched from the Russian cosmodrome at Baikanour, as will 1-C be in late 1995.

Interestingly, the existing rocket can launch a payload weighing a little over one and a half tonnes into a polar sun-syn­chronous orbit. But as the trajectory from Sriharikota crosses Sri Lanka" and no country allows a rocket to over fly its terri­tory, the rocket has to accomplish a com­plicated yaw manoeuvre, before it reaches the desired orbit. This limits the weight of the payload.

It is important to note that India's most ambitious space programme yet, the GSLV, which can provide it capabilities to launch -2.5 tonne communication satel­lites, is largely made up of stage one and two of PSLV. Only a third cryogenic stage needs to be developed. A few cryogenic engines have been bought from the Rus­sians to start the programme. By building on its own INSAT 2-A and 2-B, India has already demonstrated its ability to build world class communication satellites. Thus, in a real sense, PSLV's success is a stepping stone to the ambitious GSLV.

Can the PSLV be used to launch Motorola’s Iridium network, the global cellular phone network based on 77 low earth orbiting satellites? The answer is 'yes' but again 'not yet'. Iridium consists of a large number of polar satellites weighing around 400 to 600 kg and orbiting at about 600 km. Thus, once the tech­nology to launch independently targeted multiple satellites is mastered then PSLV can launch a cluster of 3-4 low earth com­munication satellites for Iridium type of projects. Since there are not enough launch vehicles in the world to launch 77 satellites in quick succession, one can, expect PSLV to play a role in this.

Another question normally asked is whether the PSLV can be use to launch reconnaissance satellites. Technically, the answer is 'yes'. After all, they are small satellites orbiting at an altitude of around 300 km altitude. They need to orbit at low altitudes to get good resolution, that is the ability to discern small objects. However, due to friction with rarefied atmosphere, their life is shortened.

Can PSLV technology be used for developing inter-continental ballistic missiles? Technically, "yes'. In fact, the Americans were barking up the, wrong tree when they twisted Russian arms to renege on the cryogenic deal. Cryogenic engines cannot be used for missiles of any kind, as it will take months to prepare them for flight and great expense to main­tain them in readiness. There is no single missile in the world in which cryogenic engines are being used. The most popular rocket is a solid-fuelled "booster. Although ISRO is not involved in military applications, DRDO is. Technically India can build ICBMS. It is a different issue that India can, ill afford to misspend vast resources in militarisation.

The timing of the flight and the unprece­dented invitation to the press to witness the, flight seems to have been a decision origi­nating in PMO - the obvious reasons being India’s pitch in the UN to be made a permanent member of the Security Council and secondly, the need to redeem ourselves in international eyes after the ignominy of the recent 'plague' outbreak. As a scribe exclaimed after the launch, "If we were Chinese, we would call 1994 the Year of the Prithvi, Plague and the PSLV!"

No comments: