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The Gist of Science Reporter: January 2015

India Makes it to Mars in the First Attempt (Free Available)
MOM’s Resounding Success (Only For The Subscribed Members)
Silence of the Bess (Only For The Subscribed Members)

India Makes it to Mars in the First Attempt

Tension writ large on his forehead, body stooped on the console, ISRO chief K. Radhakrishnan was in a pensive mood. So were the 60-70 odd engineers in the control room, who were intensely staring at the consoles. Everyone spoke in whispers, hustled around, stiff and anxious. The time ticked by, and in the tensed silence one could have heard heart beats.

At that instant, there was no radio link between the Mars Orbiter Mission (MOM) and the ground station as MOM was on the other side of Mars.

As the electronic clock on the wall silently flashed the time, one could feel an air of expectancy and anxiety. As soon as the clock struck 8.00 am, a broad grin appeared on ISRO chief Radhakrishnan’s countenance. Now relaxed, the chief swiftly reached for his phone. The broad smile and the abrupt change in the body language gave it away.

ISRO had made it - MOM had entered into the orbit of Mars! The journey that started about 10 months ago on a balmy Tuesday evening had succeeded. A new chapter in Indian space history had commenced.

MOM Gets Ready

India’s mission to Mars was conceived way back in 2010. After intense scrutiny, the final go-ahead was given by the Government on 3 August 2012. Within two days ISRO commenced the preparation of the Polar Satellite Launch Vehicle (PSLV) in Thiruvananthapuram and spacecraft fabrication at the ISRO satellite centre in Bangalore.

Working day and night, the launch vehicle, spacecraft and payloads were fabricated, tested, integrated and made ready, fit to fly in a record time of 15 months. All the components were moved to the Sriharikota-SHAR launch site for integration on 2 August 2013, well ahead of the scheduled initial launch date. MOM was mated with the launch vehicle, fuelling was commenced, and all was set for the launch on 28 October.

Route to Mars

The road to Mars is not a straight line. Indeed, H.G. Wells in his War of the Worlds speculated that when Mars and Earth were in inferior conjunction (same side of the Sun, therefore at the least distance from each other), a canon could be fired from Earth aimed at Mars enabling transportation. ‘Aim and Shoot’ could work well in science fiction, but in reality by the time the spacecraft nears the point where Mars was in space, it would have moved away in its orbit around the Sun.

Therefore, just like one shoots a flying bird by aiming ahead of its flight path rather than at its current location, it is imperative that the arrival of the spacecraft at the Mars orbit coincides with the arrival of Mars itself at the same location in space.

Towards Mars

Thankfully, the ships employed for their tracking facilities reached their scheduled places and the launch date was rescheduled to 5 November 2013. The PSLV rocket took the spacecraft to its initial 248 km x 23,500 km elliptical orbit. By performing several burns with its 440 N Liquid Apogee Motor (LAM) engine, when the spacecraft was closest to Earth (perigee), the altitude of the apogee (the farthest point of its orbit from Earth) was raised in succession. Although one of these orbit-raising manoeuvres faced a glitch, it was set right in the subsequent supplementary operation.

The PSLV rocket imparted a velocity of ‘9:’8 km/sec to MOM; the subsequent six orbit raising burns added a combined velocity of 0.873 km/ see second. Finally, on December lone more time the LAM was activated and this burn gave it a shove of 0.648 km/see. All the impulses combined to give the spacecraft a velocity of 11.4 km/sec, slightly larger than the escape velocity of 11.2 km/sec.

Even though in interplanetary space the Sun dominated, other planets and space objects also cast their influence, causing minor perturbations to the path of the spacecraft. In a long journey of 680 million km for 300 days, even a slight deviation of arc second could take the spacecraft many kilometres away from Mars. For successful Mars orbit insertion, MOM had to arrive 500+ or -50 km from Mars at the crucial time of 7:17 a.m. on 24 September. Therefore, en route, the path of the spacecraft was monitored and three corrections were made to ensure the spacecraft arrived precisely at its destination for the rendezvous with Mars.

Retro-firing

Having gained impulse from the LAM burn as well as gravity assist, during its interplanetary travel the spacecraft was speeding at 22.1 km/sec with respect to the Sun. When the spacecraft nears- the meeting point, if the spacecraft· has to be captured by Mars, the speed of the spacecraft had to be reduced by about 1.1 km/s, failing which Mars Orbital Insertion would fizzle out. Although MOM had completed more than 99.9% of its journey on 24 September, about 680 million km in deep space, the manoeuvres scheduled in the morning were crucial and pivotal.

Since the crucial operation on 24 September involved providing negative thrust, LAM had be retro-fired and rockets had to be used as a brake. If the negative thrust is more than anticipated, the resultant spacecraft velocity will be less and MOM will not enter into the projected orbit around Mars. The life of the spacecraft may be substantially reduced. If the negative thrust is less, the resultant velocity will be more making it impossible for gravitational capture by Mars - MOM would just flyby and be lost in space.

To enable autonomous manoeuvres ISRO had uploaded time-stamped codes prior to the crucial day. The additional concern was that four minutes into the crucial retro-burn the spacecraft would go behind Mars. So, even time-lag data would not be available. It was a blind date.

But ISRO’s maiden mission to Mars is essentially d technology demonstration mission; to demonstrate the capability of ISRO to innovatively launch a spacecraft towards Mars and then manoeuvre it into the Martian orbit.
Overcoming hurdles en-route, braving adverse space weather and radiation hazards, and maintaining reliable communication in deep “pace were the primary objectives of this mission. ISRO succeeded in this mission with aplomb putting India on a high pedestal among space-faring nations.