26 July 2017

Red challenge

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Isro has meticulously prepared for its ambitious Mars mission. Scientists have equipped the orbiter with all possible solutions for many anticipated problems. Yet, the flight’s real test will begin once it leaves the comfort of the Earth’s atmosphere

India’s first mission to Mars which is set to take off on November 5 from Srharikota on a Polar Satellite Launch Vehicle (PSLV-XL) at 2:36 pm faces technological challenges from the word go. November 30 is the day of reckoning, when the Mars orbiter would have to leave the Earth’s orbit, because if it doesn’t, the Indian Space Research Organisation (Isro) would have to wait two more years (2016) to launch again and if that is missed, the launch can happen only in 2018. This is because the alignment of Mars and Earth has to be favourable for the launch from Earth to reach Mars. Therefore, for reasons of time and of proving that India has the technological wherewithal to make it to Mars, the November 2013 launch is crucial.

The first test for the mission is to get injected into the Earth’s orbit, circle around it and then hit the trajectory to Mars, leaving the Earth’s atmosphere. Isro officials involved with the mars mission told Deccan Herald that India’s orbiter will first circle the Earth in an elliptical orbit. Six engine firings will raise the spacecraft’s orbit, which will remain in Earth’s grip for about 25 days. A final firing on November 30, 2013 will send the Mars orbiter on to an interplanetary trajectory. The journey to Mars will take close to 300 days after the orbiter travels 400 million kilometres approximately. All these operations have to be precise and timed to the second. The orbiter must demonstrate the capability to survive and perform Earth-bound manoeuvers.

Then arises the question of the journey itself. The orbiter has to last around 280 to 300 days, get past obstacles along the way and most importantly withstand the Van Allen radiation belt in the first part of its journey.The radiation belt named after US scientist James Van Allen, who discovered it, exists at an altitude of 6,000 kilometres to 60,000 kilometres above the surface of the Earth, but well within the earth’s magnetosphere.

“Prolonged exposure to the radiation belt will burn the spacecraft, which has to withstand the heat and pass beyond this sphere. The spacecraft has been provided with augmented radiation shielding to protect it when it passes through the belt,” Isro Chairman K Radhakrishnan had told a scientific gathering recently. Mars being 400 million kilometres away, communication between Earth and Mars would be 20 minutes each way. Isro has set up a self-health checking system within the orbiter to monitor its own health all along the 280-300 day journey as an alternative to commands from Earth. But this option has also been kept open. During the journey, if the spacecraft develops a problem, it has to be put into a safe mode so that ground controllers can set it right.

After it begins it’s a nearly 300-day journey, the liquid apogee motor of the orbiter will shut down. It will restart on its own after 11 months for the Mars orbit insertion. It is important that the engine sleeps while it has to and wakes up and fires when it has to. The former is crucial to save fuel and the latter is crucial to be injected into the mars orbit. Isro has developed software to track the orbiter’s positions along the journey and to also assess influence of other planets and the sun on the orbiter.
To ensure onboard autonomy, 68 software modules have been developed.
Another crucial aspect to the journey is to track the orbiter at all times. Isro doesn’t have the technology to track it in certain phases of the journey when the orbiter becomes invisible. Precisely at that time, NASA will help manage the communication and navigation through its deep space network featuring three international data receiving stations.

A major challenge is to track the rocket in its flight and ensure correct flight path. The time between the third and fourth stage in the Mars flight, what is called the coasting period, is long — the fourth stage ignites almost 1,500 seconds after it has separated from the third stage, which is almost 25 minutes, while a regular PSLV flight takes a few minutes. Then the separation of spacecraft from the fourth stage will take nine minutes. The rocket has to perform both functions flawlessly. Error in calculating the separation and ignition processes will end the mission instantly. While a regular PSLV flight takes 20-22 minutes, the Mars flight will take 42 minutes approximately. And because there is no ground station at the location where the fourth stage separates from the third (over Fiji islands and South America), Isro has to track the flight path from two ships in the pacific ocean close to Fiji islands. The ships have tracking terminals on board and are positioned 2,000 kilometres apart.

The Mars mission will help Isro develop technologies for design, planning, management and operations of interplanetary missions. The challenges, says an Isro official, are design and realization of the Mars orbiter, capability of the orbiter to survive and perform earth-bound maneuvers, last the 280-300 day journey to mars, Mars orbit insertion and capture, lasting the on-orbit phase around Mars, deep-space communication, navigation, incorporating autonomous technologies in the orbiter to handle emergencies and the overall inter-planetary mission planning and management. The scientific objectives include exploration of Mars surface, morphology, mineralogy and Martian atmosphere through five indigenous scientific instruments.

Compared to Chandrayaan-I, which Isro launched in 2008, the Mars mission involves a longer flight and a different trajectory that reduces fuel usage to transfer the orbiter from an Earth orbit to a Martian one. But both launches are on PSLV-XL rocket and have elliptical orbit for the spacecrafts.

The spacecraft is expected to enter the Mars orbit on September 21 next year. Globally, the success rate of mars missions is just 33 per cent. Isro has its fingers crossed. On reaching Mars, the spacecraft with a six-month lifespan will operate in the 363 km x 80,000 km orbit. This means its nearest point to the Martian surface will be 363 kilometres, while the furthest will be 80,000 kilometres

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