Next stop Mars

The PSLV-C25 launch vehicle puts the Mars orbiter into an earth orbit in a mission that has gone according to the script down to the last detail.

Published : Nov 13, 2013 12:30 IST

The PSLV-C25 rocket carrying the Mars orbiter blasting off from the launch pad at Sriharikota on November 5.

The PSLV-C25 rocket carrying the Mars orbiter blasting off from the launch pad at Sriharikota on November 5.

INSCRUTABLE was the expression on the face of M.S. Pannirselvam as he held a microphone in his hand. Seated next to him was V. Seshagiri Rao. As Pannirselvam readied himself to make an announcement over the microphone, Seshagiri Rao leaned forward and was obviously curious to know what the former was going to say. “Spacecraft separation achieved. It has been successfully put into orbit,” came the brief statement from Pannirselvam, Range Operations Director, Polar Satellite Launch Vehicle (PSLV-C25). Seshagiri Rao, Associate Director, Satish Dhawan Space Centre (SDSC), Sriharikota, then leaned back in his chair and smiled broadly.

The announcement marked the end of 44 minutes of tense wait on the afternoon of November 5 at the SDSC’s swanky Mission Control Centre (MCC) and the beginning of India’s ambitious interplanetary mission to Mars, christened the Mars Orbiter Mission (MOM). It signalled that the Indian Space Research Organisation’s (ISRO) PSLV-C25 had successfully put its Mars orbiter into an earth orbit. The spacecraft had taken its very first step in its voyage of 300 days to Mars, whose distance from the earth varies between 20 crore kilometres and 40 crore km. In fact, in its curving trajectory, the Mars orbiter will travel 65 crore km as it voyages through deep space to rendezvous with the red planet. If everything goes well, the orbiter will be captured into the Martian orbit on September 24, 2014 (See “Mission to Mars”, Frontline , November 15).

As soon as the success of the PSLV-C25 flight was announced, applause erupted in the MCC. As the applause continued, K. Radhakrishnan, Chairman, ISRO, turned around, ran up a couple of steps and acknowledged, with folded hands, his colleagues’ cheers. “The PSLV-C25 has placed the Mars orbiter spacecraft precisely into an elliptical orbit around the earth. This is the 25th flight of the PSLV,” said Radhakrishnan. Against the predicted perigee of 250 km from the earth and the apogee of 23,500 km, the PSLV-C25 put the Mars spacecraft into an earth-bound, elliptical orbit with a perigee of 247 km and an apogee of 23,566 km. He called it “a new and complex mission”.

About an hour later, S. Arunan, Project Director, Mars Orbiter, proudly announced that the orbiter’s primary and secondary panels, as well as the high-gain antenna, had been deployed. Arunan, who led the team that integrated the five scientific instruments into the spacecraft bus, called the flight “an exciting mission”.

Two days later, around 1-22 a.m. on November 7, there was as much joy in the ISRO Telemetry, Tracking and Command Network (ISTRAC) station in Bangalore, 345 km from Sriharikota, when the first of the six manoeuvres to raise the spacecraft’s orbit was successfully accomplished. The orbit-raising manoeuvre began when ISTRAC sent a tele-command to the spacecraft for firing up the 440 newton engine on board the spacecraft. The firing up of the engine began when the spacecraft was at its perigee and incrementally increased the apogee, making the orbit even more elliptical. At the end of five minutes, the apogee was boosted to 28,814 km from the earth and the perigee went up to 252 km. The sixth and a prolonged firing on December 1 will catapult the spacecraft out of the earth orbit into a heliocentric (sun-centric) orbit. During the next 300 days, the spacecraft will coast around the sun and will finally be captured in the Martian orbit on September 24, 2014.

ISTRAC successfully accomplished the second orbit-raising manoeuvre of the Mars spacecraft on November 8. After ISTRAC sent the command to the 440 newton engine on board the spacecraft to fire, the engine sizzled with life for about 570 seconds from 2-19 a.m. and the orbiter’s apogee was boosted from 28,814 km to 40,186 km.

On November 6, ISTRAC did a full-fledged rehearsal of these six orbit-raising manoeuvres. “We did the rehearsal of everything except firing the engine,” said M. Annadurai, Programme Director, Indian Remote-sensing Satellites (IRS) and Small Satellites Systems (SSS), ISRO. But the entire sequence of the six orbit-raising operations was rehearsed and everything was monitored by the ground stations, Annadurai said.

On November 5, after the PSLV-C25 successfully delivered the Mars spacecraft into the orbit, an array of ISRO top brass, both present and former, emphasised that India’s Mars spacecraft reaching the earth-bound orbit was only the “first and crucial step” in its “long voyage in time and space” to the red planet.

A.S. Kiran Kumar, Director, Space Applications Centre (SAC), ISRO, Ahmedabad, congratulated the launch vehicle team on “putting our baby [the Mars orbiter] in space”. He said he was proud that “the first job has been successfully done but a tremendous job awaits ISRO” in the coming months in navigating the Mars orbiter through deep space and finally putting it in a Martian orbit. (India’s Mars orbiter has five instruments to study Mars’ atmosphere, mineralogy, morphology, and so on. The SAC built three of these instruments, including a key payload called the Methane Sensor for Mars.)

S. Ramakrishnan, Director, Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram, explained why the PSLV-C25 putting the Mars orbiter into the earth-bound orbit amounted to “the first but difficult step” in its journey towards Mars. He said, “Several systems have to work precisely to take the object from the earth into the orbit. Energy-wise, what the spacecraft takes to go from the orbit to Mars is only a fraction of the percentage that it took to go from the earth into the orbit.” While the PSLV-C25 used up 250 tonnes of propellants to take the Mars orbiter from the earth to the earth-bound orbit, the spacecraft will use only 850 kg of liquid propellants to navigate its way to Mars, the VSSC Director said.

Ramakrishnan called it “a historic mission” that “symbolises India’s assured access to space”. “With meticulous planning and teamwork, we can be confident that no mission is beyond our capability,” he added.

The challenges before the mission include navigation of the spacecraft from the earth orbit to Mars in deep space; restarting the 440 newton engine after it has idled for 300 days (it was fired up six times when the spacecraft was in the earth orbit); communicating with the Mars orbiter with a “round-trip delay” of 40 minutes (it will take 20 minutes for the signal from the Mars orbit to reach the ground stations and another 20 minutes for the tele-commands from the ground stations to reach the spacecraft); and providing on-board autonomy to the spacecraft so that it can take decisions by itself if any system on board malfunctions, in order to obviate the communication delay of 40 minutes.

Several highlights marked the mission. This was the 25th flight, or the silver jubilee lift-off, of the four-stage PSLV. The workhorse did not fail ISRO, and it turned out to be the 24th successful PSLV flight in a row. It was a totally indigenous mission. ISRO had built the launch vehicle and the spacecraft with its five payloads. The five instruments were readied and integrated into the orbiter bus within a tight schedule of about 18 months. The mission had the longest flight duration of 44 minutes: previous PSLV flights lasted about 18 minutes. The flight saw a long coasting phase of 25 minutes between the third-stage burn-out and the fourth-stage ignition. It was only 37 seconds after the fourth-stage burn-out that the spacecraft was injected into orbit.

P. Kunhikrishnan, Mission Director, explained why there was a deliberate delay of 37 seconds in injecting the spacecraft into orbit after the fourth-stage cut-off. “Before the injection, certain conditions have to be met. The spacecraft needs some orientation. We were manoeuvring [the spacecraft] for 37 seconds after the fourth-stage separation,” he said.

He gave a break-up on the performance of the PSLV-C25’s four stages. The first stage, in fact, over-performed, he said. The stage-two burn-out took place as planned. The third-stage performance was excellent. “There was excitement” after the fourth-stage ignition, and applause rippled through the MCC after the two ship-borne radar terminals in the South Pacific Ocean, off Fiji, acquired the data about the Mars spacecraft entering the orbit. Kunhikrishnan described “the silver jubilee flight” as an “excellent mission”.

Despite the enormous complexity of the mission, a relaxed atmosphere prevailed on the vast SDSC premises on October 30, when ISRO took a team of reporters to the spaceport in Andhra Pradesh. On that day, the 44.4-metre-tall rocket, weighing 320 tonnes, stood fully integrated inside the Mobile Service Tower (MST) on the first launch pad on the beachfront by the Bay of Bengal. The Mars orbiter, encased in the heat-shield, had been coupled to the rocket’s fourth stage. The rocket was an XL version of the PSLV, that is, it had extra large strap-on booster motors fuelled by more solid propellants.

“We are ready for the launch,” said B. Jayakumar, Vehicle Director. He and R. Hutton, Associate Vehicle Director, explained to reporters how the four stages were assembled in the 76-metre-tall MST, which was made of steel and weighed more than 2,500 tonnes. It is called the MST because it will be wheeled 150 metres away on its 32 wheels about 54 hours before the lift-off. The MST can withstand cyclonic conditions, and the PSLV-C25 itself is “a rain-proof vehicle”.

“We are relaxed,” declared the dapper M.Y.S. Prasad, Director, SDSC. “Don’t get perturbed,” he advised reporters. For, no blip will appear, he said, on the monitor for about 100 seconds in the gap caused by the second ship-borne terminal taking over from the first ship-borne terminal. This was the first time that ISRO was deploying ship-borne terminals because the flight profile—the long coasting phase between the third-stage burn-out and the fourth-stage ignition—demanded it. The ship-borne radars, named Nalanda and Yamuna, borrowed from the Defence Research and Development Organisation (DRDO), were to monitor the fourth-stage ignition and burn-out, and finally the spacecraft injection.

The sophisticated MCC, built like a flying saucer, boasted a bank of 80 computers and five wide screens. Six ground radars at Sriharikota and telemetry stations at Port Blair, Brunei, and so on, and the two ship-borne radars would continuously track the vehicle, and its positional information would be known every 100 milliseconds, said Seshagiri Rao.

The 56.5-hour countdown, which began at 6-08 a.m. on November 3, proceeded smoothly and the PSLV-C25, with the Mars orbiter aboard, lifted off majestically at the appointed time of 2-38 p.m on November 5. The flight was flawless, with each stage igniting and falling off on the dot and the heat-shield encasing the spacecraft splitting down its seams and falling into the Bay of Bengal. At the end of 44 minutes, the Mars orbiter was precisely injected into orbit and applause echoed through the MCC.

However, all the top ISRO brass were quick to issue a word of caution. S.K. Shivakumar, Director, ISRO Satellite Centre, Bangalore, said, “We have a long way to go in time and space” before the spacecraft reached Mars and was inserted into its orbit in September 2014. Prasad called the orbiting of the spacecraft “a first important step in the long mission”.

“The long journey has started,” said Professor U.R. Rao. He was proud that the spacecraft had “excellent instruments on board”.

While “the primary objective” of the mission, according to Radhakrishnan, was to put the spacecraft into a Martian orbit, its scientific objective was the empirical observation of Mars. The five instruments on board the orbiter are the methane sensor, which will look for the presence of methane on Mars because methane is a possible indicator of microbial life; a thermal infrared imaging system to study its geological activity; a colour camera for optical imaging of Mars’ surface; a Lyman Alpha Photometer, from the Laboratory for Electro-Optic Systems (LEOS), Bangalore, to study the Martian atmosphere; and the Martian Exospheric Neutron Composition Analyser (MENCA) from the Space Physics Laboratory, VSSC, to investigate the neutral composition of the planet’s upper atmosphere.


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