Thursday 13 September 2007

PSLV Crash -Failure Analysis

Business India, January 17-30, 1994

What went wrong?

The Failure Analysis Committee's report

Shivanand Kanavi

The Failure Analysis Committee headed by N. Pant, to probe the failure of the PSL V -Dl flight launched from Shriharikota, on 20 September 1993, has submitted its report. Three factors have been identified as having caused the failure.

First is the time gap between switching off the second stage engine and switching the third stage engine. Second, some retro-rockets failed to get fired after the second stage separated from the third stage, leading to an imbalance. And third, there was an error in the control software. How these three factors com­bined to plunge the Rs.45crore PSLV ­D1 into the Bay of Bengal is a revealing tale of the technological complexities of such a mission.

Theorising, modelling, and simu­lating possible scenarios started in ISRO in earnest right after the mission failed. Simultaneously, the Space Commission launched an independent probe, through the Failure Analysis Committee, ploughing through the 100,000 pages of telemetric data from the launch vehicle.

Control systems
To understand what went wrong it is essential to understand how the vehicle is controlled. The rocket is under con­trol only when the main thrust motors are firing. Any deviations from the flight path due to disturbances in the pitch, yaw or roll of the vehicle, are then set right by firing the control systems.

In the period between one stage being shut down and another being ignited there is no control. This gap is unavoidable due to the number of operations required for a clean separation of the stages.

The second and third stages are sepa­rated by exploding a ring of explosive embedded in the casing that shears the alu­minium alloy. At that time, though sepa­rated, the second and third stages will still be moving with more or less the same velocity. If there is even a small imbalance in velocities, the jettisoned second state can hit the third stage.

To prevent such a mishap retro-rockets are fitted to the jettisoned part and are fired along with the separation explosion so that the jettisoned part is slowed down slightly. It is in order to complete these operations smoothly, that a small gap is kept between shutting one stage's engine and firing the next. If liquid propellants are used, the engine can get hiccups when the fuel is over. So it is advisable to shut it off before the fuel gets exhausted.

Earlier ground simulations had given ISRO grounds to believe that if there was a three-second gap between the separation of stage two and three, nothing drastic would happen. But now, in the light of PSLV-Dl having failed, it is felt that the three-second gap may have been too large, allowing errors to multiply dangerously. Hence, the committee suggests this gap should be reduced.

The second flaw was that all the retro-­rockets did not ignite to slow down the jettisoned stage. This caused a slight imbalance in the jettisoned stage, and could have hit the third stage before ignition. It is conjectured that the firing circuits of the two retro-rockets got so dis­turbed by the explosive separation that they did not fire. Hence, further isolation and protection of these circuits from the shearing explosion has been recom­mended.

Error compounded
The third problem with PSLV-D1 was a software error caused by the 'overflow' in a control parameter. What it means is that the control software in the mother console was designed to handle variations in a par­ticular parameter, between, let us say, plus (+) or minus (-) 99.99. Now when that parameter crosses, say, -99.99 and reaches -100.00, the seven characters in ­100.00 could not be recognised and so the software ignores the bit representing the ‘-’ (minus) sign. The result was that in the flight a control command geared to correct a parameter of say -99.99 was suddenly changed by default to that required for + 100.00, while the system was actually suffering from a deviation of -100.00.

Thus the control command from the computer instead of correcting an error, actually compounded it. ISRO is debug­ging the control software to remove any other such glitches. Some believe that despite the problems created by the retro­rockets, etc, the vehicle could still have been controlled if the correct command had reached the control systems. (Incidentally, such software errors are not unusual. NASA's space shuttle mis­sion had to be grounded in 1988 when similar software errors were found and all the five on-board computers had to be debugged.)

The rocket motors for the second flight, PSLV-D2, in 1994, are under con­struction. The corrections required will not lead to any major design changes. In fact, but for this mishap in the separation of stage two and three, all other systems (including many new technologies) have worked remarkably well. Thus, despite the truism in space flights anything less than 100 per cent success is a failure', the PSLV-D1 flight is considered a 90 per cent success.

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!"

ISRO men in global space industry

Business India, February 8-21, 1999

Career launchpad

ISRO has launched the career of many a senior executive in the global satellite industry

Shivanand Kanavi

If one were to organise an Indian Space Research Organisation (ISRO) alumni reunion, it could easily be mistaken for a conference of the global satellite industry. There would be high-level executives from Inmarsat, PanAmSat, World Space, Agrani, ICO­ Global, Lockheed Martin, Matra Marconi, and Loral, in essence, every player that counts in the bird business (see table).

"We are proud that a single Indian organisation has contributed so much talent to the global satellite industry. It is an acknowledgement of ISRO'S talent pool and capabilities," says Dr Kasturirangan, chairman, ISRO. He maintains that the talent flight has not affected the organisation. "While we do regret losing such highly trained and capable people, we cannot stop this. We have enough depth to replace such people; hence overall the space programme does not suffer."

ISRO alumni in the global satellite industry

Inmarsat: D V Ramana
ICO-Global: P Ramachandran, Y N Bhushan
Agrani: Jai P Singh, K Narayanan
World Space: M G Chandrasekhar, D Venugopal
Matra Marconi: Mrinal Saha
MTSat: K P M Bhat
Loral: P Damodaran, Devendra Verma
Intelsat: S Manoharan,
Discovery: Kiran Karnik

Every year ISRO loses about 150 people, mainly to the software industry. Besides new recruits, people who have been with ISRO for 10 years and who have taken on inde­pendent responsibilities also start looking for opportunities outside.

"We continue to recruit from regional engineering colleges and other good colleges. It depends on the projects on hand, but about 300-350 scientists and engineers are recruited every year," says Kasturirangan. ISRO is increasingly targeting MTechs rather than BTechs as many private sector companies are doing, and encourages them to do an in-house PhD as well in a specialised field.

Nonetheless, thanks to the Fifth Pay Commission, ISRO'S packages at the entry level are now as good as in the private sector, except probably for software. A new recruit gets above Rs.15,000 on a monthly cost-to­-company basis, though at the senior level people do not find it very attrac­tive monetarily. For example, the chairman himself gets a pay package of around Rs30,000 and a few perks like housing and car.

Jai Singh, CEO of Agrani Satellite Communications and an ISRO alum­nus, concurs that the organisation has very good depth in its management ranks. Singh left ISRO in 1988 after a 15-year stint. Says he: "The work, albeit hi-tech, was getting a bit routine. I had no other problems at ISRO. It was for personal reasons- I wanted my family to get an interna­tional environment and so on -that I took on the Inmarsat assignment."

K. Narayanan, who was Insat programme director and director of satellite communications at the Department of Space and is now executive vice-president at Agrani, suggests: "ISRO people should be allowed to work in Indian industry for a couple of years and join back. That will help both sides. The hi-tech devel­oped within ISRO will get transferred to industry and they will bring back industry practices in cost-cutting, customer service, and so on."

Kasturirangan is all for lateral movement of professionals into ISRO. "Already an MS or PhD from a decent university abroad with some experience is taken in directly. They can send in their CVs any time. Professionals working in India are also taken in through advertisements."

Some engineers feel ISRO restricts their career mobility. Being a govern­ment organisation, it discourages
employees with over 10 years of service from taking voluntary retirement and joining the private sector, by stipulating a two-year 'cooling off' period. Such a rule makes sense in cases where, for example, a bureaucrat might award a government contract to a private sector company and then leave to join the same company as a quid pro quo. But engineers today would turn down any company that restricts their mobility.

ISRO is an organisation with over 18,000 personnel and has been successful in a hi-tech area on a shoe­string budget. Naturally it has become a favourite for headhunters. It should be given a free hand by the govern­ment to formulate a liberal HRD policy which takes cognisance of market real­ities. However, ISRO would benefit by networking the wider ISRO parivar. Almost all of them hold fond memo­ries, and would help ISRO gain an entry into the $60-billion global space industry.