India's Mars Mission is a big leap

If the Polar Satellite Launch Vehicle (PSLV) lifts off on November 5 from Sriharikota as planned, it will be watched by more than a normal share of anxious eyes. It is a difficult mission, and fickle weather adds to the complexity.

But ISRO chairman K Radhakrishnan is not prone to fits of worry. "The PSLV is the best vehicle in its class," he says, "which is why many countries are using it now to launch their satellites." A mission to Mars will require taking into account the influence of earth, the moon, the sun and, of course, the destination planet, all of which keep changing positions with the day of the launch.

A small error in calculation will miss the target by tens of thousands of miles. "The spacecraft's arrival point on Mars has to be calculated to an accuracy of 60 miles about 280 days in advance," says Radhakrishnan. "It takes beyond textbook mechanics to achieve this precision." An excursion to the red planet does not come easy to even to the most experienced.

The Russians have a long history of failures in Mars missions. The Chinese have not yet attempted its own mission, and so Mangalyaan is extra special for India. "It will be a big leap for the country," says Goverdhan Mehta, space commission member. The Americans, Russians and Europeans have used larger rockets for their Mars missions. India is using the smaller PSLV, usually used to put small satellites into a low-earth orbit over the poles. The launch window to Mars is very small, the next one being available only in 2018. ISRO has already postponed the launch once due to bad weather.

If the PSLV does not go up before November 19, ISRO has to wait for another five years to get similar conditions. The PSLV is India's most mature rocket. ISRO has launched 35 satellites so far using PSLV and 10 are in waiting list for launch. The Mars mission will use PSLV in new ways, thereby adding new complexities. The trajectory of the spacecraft is very different to begin with.

The spacecraft’s arrival point on Mars has to be calculated to an accuracy of 60 miles about 280 days in advance,” says Radhakrishnan.

This new trajectory, the calculations for which are different for each launch date, requires a long coasting of the rocket between third and fourth stage. "The management of the long coast between third and fourth stage is a complex issue," says V Adimurthy, Satish Dhawanprofessor and senior advisor (interplanetary missions) of ISRO. There is only one time slot for lift-off- with five minutes leeway - available for launch during a specific day.

"The time of lift-off and required coasting duration is different for each day of launch; and one has to work out a series of different trajectory management strategies corresponding to each possible launch date," says Adimurthy. The satellite is first launched into an elliptical orbit at a velocity far less than what is required - over 11 km per second - for it to escape from the earth.

To make it come up to this velocity would require three to five manouevres using rockets in the spacecraft, depending on the velocity and position of the spacecraft when first injected. When it finally reaches Mars, not more than 60 km away from the intended spot, the spacecraft has to slow down for it to be captured into the Mars orbit. If this is not done with precision, the spacecraft will either fly by or crash into the Martian surface.

Some of the difficulty is in the constraints imposed by the need to lower energy use. "We have devised an orbit that reaches Mars with minimum use of energy," says Radhakrishnan. The more the energy required for the travel, the more the fuel the spacecraft has to carry, and hence the more the weight and more the cost. Other constraints were imposed by the harsh interplanetary environment like intense cold and high radiation.

Delay in communication is another problem as the spacecraft moves further and further away from the earth. The spacecraft has considerable autonomy to take decisions during critical periods.

When the Mangalyaan project was conceived, ISRO got 30 ideas for experiments. Out of these, nine instruments were possible to build and five were flyable. "So all the experiments possible were accommodated," says Radhakrishnan. One of this is a methane sensor. Finding methane conclusively on Mars would be a major achievement for Mangalyaan.

The Indian Space Research Organization completed integration of itsMars mission satellite on Sunday with therocket while the heat shield is expected to be closed in couple of days, an official said. 

"The 1,340 kg satellite was mated with the rocket today (Sunday). The heat shield will be closed in two or three days after tests. Everything is progressing normally on the rocket and the satellite side," an Isro official, who did not want to be identified, told IANS. 

On Saturday Isro chairman K Radhakrishnan told IANS that the Rs 450 crore Mars Orbiter Mission (MOM) will be delayed by a week as out of of the two ships — Nalanda and Yamuna — carrying rocket tracking systems, only the latter has reached Fiji. 

The Nalanda is expected to reach there October 21. From there, both the ships have to travel to their respective locations to track the rocket, Isro officials told IANS. 

The ships have terminals to track the rocket, which has a coasting period of around 20 minutes beyond the visibility of existing ground stations. 

The Malgalyaan mission was originally slated for October 28 from Isro's rocket launch centre in Sriharikota in Andhra Pradesh, around 80km from here. 

According to Isro officials, there is no problem as far as the mission is concerned. 

Radhakrishnan said as the launch window is between October 28 to November 19, the revised launch date will be decided October 22 after the ship reaches Fiji. 

Incidentally October 22 is seems to be a special date for Isro. It is a Tuesday and in Tamil, Mars planet is called Sevvai Graham and Tuesday is also called Sevvai. In Hindi, Mars is called Mangal and Tuesday is Mangalwar. 

India's first inter-planetary mission was to the Moon October 22, 2008 at an outlay of around Rs 390 crore.

No comments:

Post a Comment