On ISRO and the failure of the Chandrayaan-2 lander
ISRO has set up a Failure Analysis Committee (FAC) to identify the root cause of the problem that caused Vikram to crash-land on the moon.
It was a few years ago that a senior reporter from Doordarshan and this writer were at Satish Dhawan Space Centre (SDSC), Sriharikota, to cover the lift-off of a launch vehicle; the conversation turned to the Indian Space Research Organisation’s (ISRO) track record of successes and failures. The Doordarshan reporter, who had covered many launches from Sriharikota, tersely summed up the issue when he said, “ISRO always had a problem accepting its failures.” Today, ISRO might claim that its Chandrayaan-2 mission to the moon was a “95 per cent success” but the fact remains that the mission failed. For the mission’s centrepiece was to softly touch down a lander called Vikram on its four legs on the South Polar region of the moon at 1.55 a.m. on September 7, 2019, and a rover called Pragyaan was to emerge from Vikram four hours later and roll on to the moon’s surface. These did not happen. After a controlled descent of 28 km from above the moon’s surface, the lander spun out of control when it had only another two km to descend and it crashed on the moon’s surface. It was a hard landing on its side and not a soft landing on its four legs. In the process, Vikram was damaged. Till September 13th night, Vikram had not responded to ISRO’s sustained efforts to communicate with it from the ground. But ISRO’s top officials claimed that the mission was “a 95 per cent success” because the orbiter had been put into a perfect orbit around the moon and that it was one of the high-resolution cameras on board the orbiter that had taken thermal images of Vikram lying close to the spot where it was to soft-land.
It was in 1980 that this writer first encountered a top ISRO engineer, who refused to come to terms with a mission failure in 1979. The first experimental launch of Satellite Launch Vehicle-3 (SLV-3) on August 10, 1979, had ended in failure. It, therefore, could not put a 35-kg Rohini satellite into orbit. The four-stage vehicle had dived into the Bay of Bengal when the nitric acid in one of its solenoid valves leaked. “A rocket trying to go up without nitric acid is like your trying to driving a car without petrol,” Dr. Vasant Gowariker, then Director, Vikram Sarabhai Space Centre (VSSC), Thumba, Thiruvananthapuram, had explained to this writer in July 1980 (repeat July 1980). A few days later, when this writer tried to discuss the failure of the SLV-3 with a top ISRO rocket engineer, he brusquely said, “Don’t remind me about that failure. I don’t want to discuss it with you.”
Members of the Indian media cover the developments at ISRO Telemetry Tracking and Command Network (ISTRAC) facility in Bangalore, on September 6, 2019, as the countdown for the soft-landing of Vikram lander of Chandrayaan-2, on the surface of the moon was expected to happen in the early hours of September 7. MANJUNATH KIRAN/AFP/Getty Images
When another SLV- 3 in 1981 and an Augmented Satellite Launch Vehicle (ASLV) in 1987 put their satellites into a lower orbit than targeted and the satellites, therefore, burned up after some days, ISRO would glibly call the missions “partial successes.” When Chandrayaan-1 failed in August 2009 after it was in orbit around the moon for only 312 days instead of its planned life of two years, ISRO’s top brass repeatedly called the mission “a success.” They claimed that the mission was a great success because the orbiter had sent thousands of pictures of the moon and that it was Chandrayaan-1 which discovered water-ice on the moon. Failed missions were always a sore issue with ISRO’s top brass and they would often gloss over them.
Having said that, one should also argue that ISRO always has this extraordinary trait in its genes: failures have always galvanised it to spectacular successes. We will come to this later. Despite the failure of the Chandrayaan-2 mission to achieve its core objective of soft-landing Vikram on the South Polar region of the moon and bringing the rover out of Vikram, it should be noted that nobody poured scorn over the failure. Perhaps, there was no scientific mission other than Chandrayaan-2 which had fascinated the entire country, with which crores of people had identified themselves with, rooted for it, and into empathised with ISRO when it did not meet its core objective. For the man on the road knew what kind of risks this 3.84 lakh km, 48-day perilous journey to the moon entailed. And what was deeply chagrining about the mission was that it came so close to achieving success. As Professor U.R. Rao, then ISRO Chairman, said after the failure of the very first Polar Satellite Launch Vehicle (PSLV) on September 20, 1993, “In space, even 99.99 per cent does not help. It has to be 100 per cent. Nothing less.”
Let us go back in history to see how failures have always spurred ISRO to go back to the drawing boards, identify what led to the failures, take corrective action, and achieve successes in different classes of vehicles it built, be it the SLV-3, the ASLV, the PSLV, and the GSLV. After the first flight of the SLV-3 on August 10, 1979, from Sriharikota was a failure, the project team led by the late A.P.J. Abdul Kalam did systematic reviews and simulations and ISRO got back on its feet within a year. On July 18, 1980, the second flight of SLV-3 turned out to be a major success and it put a 35-kg Rohini into its orbit. India thus became a member of the exclusive space club of the US, the USSR, France, the UK, and China. But the third flight of the SLV-3, that is, its first developmental flight was only “a partial success.” The vehicle put the Rohini satellite into a lower orbit than targeted because the vehicle had developed snags in its fourth stage. Rohini burnt up in orbit nine days after the launch. What was redeeming about the mission was that the rocket did not break into pieces. ISRO analysed the failure and the next SLV-3 flight on April 17, 1983, which incorporated modifications, was a big success. It smoothly hoisted a 40-kg Rohini satellite into a perfect orbit. Prime Minister Indira Gandhi was at Sriharikota to watch the launch. After the mission’s success, she exulted, “Even though I am past 60, I am thrilled and excited…”
The SLV-3 programme thus ended on a happy note and ISRO graduated to a five-stage ASLV. What was important about the ASLV was that ISRO was using two strap-on motors around the core for the first stage. The two strap-on booster motors would help the ASLV to put a 100-kg satellite into orbit compared to 35 kg to 40 kg Rohini satellites put into orbit by its predecessor rocket, the SLV-3. However, to ISRO’s great disappointment, the first two ASLV flights from Sriharikota on March 24, 1987, and July 13, 1988, ended in failures. It was a high visibility let-down for the first ASLV flight on March 24, 1987. Prime Minister Rajiv Gandhi and Andhra Pradesh Chief Minister N.T. Rama Rao were present at the Mission Control Centre (MCC) at Sriharikota when the ASLV lifted off. The two strap-on motors had ignited and jettisoned on time. But the vehicle’s core first stage failed to ignite. The command for the first stage to ignite did not register. So the rocket, with a Stretched Rohini satellite, plunged into the Bay of Bengal. Even as the ISRO engineers looked crestfallen, Prime Minister Rajiv Gandhi told them: “Do not lose heart. It is only when you stumble that you can get up and walk better. I have no doubt that ISRO will get up and not only become more dynamic but also stronger. ISRO would analyse what went wrong, correct it and move on to Polar Satellite Launch Vehicle and further progress.” The then ISRO Chairman, Professor U.R. Rao assured the Prime Minister that the setback “will only push us forward.”
However, the second ASLV flight on July 13, 1988, was also a failure. It crashed into the Bay of Bengal 150 seconds after its lift-off. Although the strap-on motors and the first stage fired, the strap-on motors did not jettison. So the first stage developed anomalies because it had to carry the extra weight of the burnt-up strap-on motors. The vehicle dived into the sea. “This is certainly disheartening,” said Professor U.R. Rao. “But we have to get over that.”
There was bad news again for ISRO when the third ASLV flight achieved only “a partial success” on May 20, 1992. The satellite went into a lower orbit than targeted. It burned up after it remained in orbit for only 55 days instead of the projected life of 100 days.
The fourth ASLV flight on May 4, 1994, was a great success with the vehicle putting the 113-kg Stretched Rohini satellite into a perfect orbit. The then ISRO Chairman Dr. K. Kasturirangan noted, “Each of these [ASLV] missions depended on the experience of the previous missions…The uniqueness of this mission is that we have tried to incorporate whatever we have learned from the previous missions. It is a process of continuous upgradation.”
With the fourth ASLV flight ending on a triumphant note, the ASLV series came to an end. Although three ASLV missions failed, ISRO learned valuable lessons from them. As R. Aravamudan, who was Director of SHAR and later became Director, ISRO Satellite Centre, Bengaluru, says in his book “ISRO, A Personal History”, “…In my opinion, ASLV provided ISRO with invaluable experience in rocket technology…The strap-on technology, inertial navigation, closed-loop guidance system, digital autopilot, real-time decision-making, bulbous heat shields, S-band TTC (telemetry, tracking, and command), vertical integration and so on, all tried out and perfected in the ASLV, could be used in the PSLV. Also, most importantly, the teams learned that rocketry is unforgiving and called for a totally disciplined approach to ensure quality and reliability.” (R. Aravamudan with Gita Aravamudan in their book, “ISRO, A Personal History”, 2017, HarperCollins Publishers India).
As in the case of SLV-3 and the ASLV, the PSLV’s first flight on September 20, 1993, too failed because of a software implementation error when there were disturbances during the separation of the second stage from the third stage. The two stages collided with each other. The vehicle “capsized” and fell into the Bay of Bengal. A Failure Analysis Committee delved into the problem and suggested corrective steps to overcome the software implementation problem. Subsequently, 38 PSLV flights were successful in a row. Today, the PSLV is ISRO’s most trusted workhorse. By May 2019, the PSLV had launched 297 satellites belonging to 33 countries. It was the PSLVs which successfully put Chandrayaan-1 orbiter and ISRO’s spacecraft to Mars in their initial earth-parking orbits on October 22, 2008, and November 05, 2013 respectively. On February 15, 2017, a PSLV put as many as 104 satellites into orbit – a stellar achievement by world standards. What was important was the complexity that the mission entailed – the 104 satellites had to be shot into orbit in a sequence and without their colliding with each other. A.S. Kiran Kumar, then ISRO Chairman, said, “It is not about setting records. It is primarily about improving our capability to maximise our returns.” K. Sivan, then Director, VSSC and ISRO Chairman now, said at that time, “Even to separate one satellite from the vehicle is complex, to put 104 satellites into orbit was not an easy job.” They had to be rifled into orbit in 600 seconds before the vehicle reached the South Pole, he said.
The Geo-synchronous Satellite Launch Vehicle (GSLV-Mark I) flights with a Russian cryogenic engine and the GSLV-Mark II with an indigenous cryogenic engine had their failures on July 10, 2006, December 25, 2010, and April 15, 2010, respectively.
It was GSLV-Mark III which broke the jinx of the first flight of each class of vehicle of ISRO failing. The GSLV-MK III is the most powerful rocket that ISRO has built so far, with an indigenous cryogenic engine that uses 25 tonnes of liquid oxygen and liquid hydrogen, and produces 20 tonnes of thrust. Besides, it uses 400 tonnes of solid propellants and 110 tonnes of liquid propellants. It weighs 640 tonnes and is 44 metres long. Its debut flight on June 5, 2017, was a remarkable success. At the end of more than 16 minutes of flawless flight, it put the GSAT-19 communication satellite into orbit. The GSLV-MK III’s second flight on November 14, 2018, was a success and the vehicle put the GSAT-29 satellite into a perfect orbit. Its third flight was the cynosure of attention on July 22, 2019, when it put Chandrayaan-2 into a perfect earth-bound orbit. Chandrayaan-2 comprised an orbiter, the lander Vikram, and the rover Pragyaan ensconced inside the lander. The orbiter, the lander, and the rover together constituted the composite module.
BENGALURU, INDIA - AUGUST 26: Dr K Sivan, widely known as the Rocket Man of India, is a 62 year old home grown aerospace engineer, currently Chairman of the Indian space agency and head of the Indian Space Research Organisation (ISRO) who is pictured here posing with a moon globe on August 26, 2019 in Bengaluru, India. The Indian space agency successfully lofted its second mission to the moon named Chandrayaan-2 or Moon Vehicle. The successful launch took place on July 22, 2019 from the Island of Sriharikota.(Photo by Pallava Bagla/Corbis via Getty Images)
It looked as if nothing would go wrong with the Chandrayaan-2 mission. During a 48-day journey, the composite module travelled 3.84 lakh km towards the moon. On August 20, 2019, the composite module was inserted into an orbit around the moon. On September 2, 2019, the lander Vikram, sitting on top of the orbiter, detached itself from the orbiter. Two objects were going round the moon now: the orbiter and the lander with the rover inside. On September 7, at 1.40 a.m. when Vikram was at an altitude of 30 km above the moon, it began its descent to land softly in the South Polar region of the moon. Vikram’s four throttleable engines began firing in unison to control the velocity of Vikram’s descent in stages. The descent would take 15 minutes and Vikram would touch down gently on the moon’s surface at 1.55 a.m. Four hours later, Pragyaan would emerge from Vikram and roll on to the lunar soil. Vikram had come down 28 km and it had only 2.1 km to go in the next three to four minutes before landing softly on the moon. But Vikram tumbled out of control and crashed on the moon’s surface. It was a hard landing instead of a soft landing. In the process, Vikram got damaged. It lay on its side.
An ashen-looking K. Sivan, ISRO Chairman, walked up to Prime Minister Narendra Modi, who was present in the Mission Operations Complex, Bengaluru and broke the bad news to him. Modi told ISRO personnel, “There are ups and downs in life. This is not a mean achievement. The nation is proud of you…I am with you. Move forward bravely.” Some minutes later, Sivan read out a brief statement, which said, “Vikram lander’s descent was as planned and normal performance was observed up to 2.1 km. Subsequently, communication from the lander to the ground station was lost. Data is being analysed.
ISRO has set up a Failure Analysis Committee (FAC) to identify the root cause of the problem that caused Vikram to crash-land on the moon. Vikram’s descent over 30 km consisted of four phases: rough braking (repeat braking) phase, absolute navigation phase, fine braking phase, and terminal, vertical descent phase. Informed ISRO officials blamed an error in software, that is, error in the formulation of the algorithm, for Vikram’s crash-landing. They explained that with its four throttleable engines firing in a balanced manner, Vikram’s downward journey during the rough braking phase was smooth. But during the transition from the rough braking phase to the fine braking phase, an anomaly occurred in one of the four throttleable engines. This engine produced a higher thrust than required. So instead of turning 90 degrees to touch down on its four legs, the lander turned 180 degrees and fell on its side. “So instead of travelling in its planned, fine trajectory, Vikram deviated from its trajectory. It did so very fast and crash-landed”, said an ISRO engineer. “The twist” from 90 degrees to 180 degrees led to the loss of communication with the lander, he said.
Another ISRO engineer said everything worked perfectly during the lander’s descent: the propulsion system (the four throttleable engines) worked well; the sensors did their job; navigation was alright and Vikram’s attitude (repeat attitude) was perfect. But when Vikram was getting into the fine braking phase, a problem in Vikram’s control occurred. There was a large disturbance. The software, produced by the U.R. Rao Satellite Centre, Bengaluru, could not take care of the disturbance, the engineer said. The formulation of the algorithm was not done properly. It was a [computer] coding error. Vikram, therefore, crashed on the moon’s surface.
It will take some time for ISRO personnel and crores of countrymen to come to terms with the sense of loss that the Chandrayaan-2 mission has engendered.