Bet­ter Safe than Sorry

Though the glitch was mi­nor, ISRO sci­en­tists are un­will­ing to take any risk in en­sur­ing a per­fect launch for Chan­drayaan 2

India Today - - INSIDE - RAJ CHENGAPPA

At the launch of a space­craft, the most watched are the gi­ant dig­i­tal count­down clocks fit­ted in the con­trol room where the sci­en­tists are seated as well as in the me­dia gallery. For In­dia’s sec­ond moon mis­sion, Chan­drayaan 2, the clock be­gan count­ing down 20 hours be­fore the space­craft was slated to be launched at 2.51 am on July 15 at the In­dian Space Re­search Or­gan­i­sa­tion (ISRO) fa­cil­ity in Sriharikot­a in coastal Andhra Pradesh. The 5,000-odd vis­i­tors seated in the am­phithe­atre nearby watched the clock on a gi­ant mon­i­tor with an­tic­i­pa­tion.

For the count­down, ISRO had de­vel­oped a rig­or­ous re­view of ev­ery crit­i­cal com­po­nent of the space­craft, in­clud­ing its rock­ets, apart from the com­mu­ni­ca­tions and track­ing fa­cil­i­ties.

That’s be­cause space is un­for­giv­ing. A slight er­ror in cal­cu­la­tion or a mal­func­tion­ing valve could cause the

Rs 1,000 crore Chan­drayaan 2, which took over a decade to con­ceive and de­velop, to break up and tum­ble ig­no­min­iously into the Bay of Ben­gal.

There was much rid­ing on this launch for In­dia for even Pres­i­dent Ram

Nath Kovind to fly down to wit­ness it. Chan­drayaan 2 was a quan­tum leap in tech­no­log­i­cal ad­vance­ment and mis­sion ob­jec­tives from the first moon mis­sion In­dia suc­cess­fully sent up in

2008. Chan­drayaan 1 had an or­biter and im­pact probe. Its suc­ces­sor has not only a far more so­phis­ti­cated or­biter, but also a ro­botic lan­der equipped with a rover de­signed to tra­verse a ra­dius of half a kilo­me­tre on the lu­nar sur­face.

Equally im­por­tant is the heavy lift GSLV-Mark 3, In­dia’s most pow­er­ful launcher, de­vel­oped just five years ago and which has had only three flights so far. Ca­pa­ble of lift­ing over 4 tonnes of pay­load, GSLV-Mark 3 was de­signed not only to launch heav­ier com­mu­ni­ca­tion satel­lites into geosyn­chronous or­bits but also In­dia’s manned mis­sion Ga­ganyaan and the probes be­ing planned to visit the moon and other parts of the so­lar sys­tem.

The up­per stage of the moon launcher was fit­ted with an in­dige­nously built cryo­genic en­gine or one that uses su­per-cooled hy­dro­gen and oxy­gen as fuel. As com­pared to the solid mo­tor and the liq­uid fuel en­gine in the other two stages, the cryo­genic en­gine proved to be the most dif­fi­cult

for ISRO to master. That’s be­cause the tem­per­a­ture vari­a­tion to be han­dled ranges from mi­nus 253 de­grees centi­grade in which the hy­dro­gen fuel has to be main­tained to a blaz­ing 1,000 de­grees centi­grade when the en­gine fires. Apart from the en­gine be­ing built with spe­cial met­als to with­stand such great tem­per­a­ture fluc­tu­a­tions, it also re­quires an in­tri­cate net­work of pip­ing to not only fill the fuel tanks be­fore lift-off but also in­ject the su­per-cooled fu­els into the com­bus­tion cham­ber where these can be ig­nited.

The first in­di­ca­tion that some­thing was wrong came a lit­tle less than an hour be­fore lift-off, when the count­down clock stopped. It was fol­lowed by a terse an­nounce­ment from the ISRO spokesper­son that the launch had been post­poned. While sci­en­tists re­mained tight-lipped about what caused the hold-up, it was re­li­ably learnt that while the cryo­genic en­gine was be­ing fu­elled up, the mon­i­tors reg­is­tered an anom­aly. The pres­sure readings from the spher­i­cal he­lium bot­tles that main­tain the req­ui­site pres­sure and con­trol the valves sup­ply­ing fuel to the en­gine were be­low nor­mal. Sci­en­tists have sur­mised that the leak was mostly likely be­cause of a faulty plumb­ing in the he­lium con­tainer sys­tem.

ISRO sci­en­tists could have lived with some vari­a­tion in the pres­sure lev­els in these he­lium bot­tles, but pre­ferred to play it safe. The launch was post­poned to en­able them to de­tect the source of the prob­lem and rec­tify it. All indication­s are that the snag was not that se­ri­ous, as af­ter the ini­tial re­view, ISRO sci­en­tists were con­fi­dent of re­pair­ing the mal­func­tion­ing part with­out wheel­ing the space­craft back into the as­sem­bling work­shop at the com­plex. Given the rea­sons for the hold-up, when the space­craft is set for launch again, ISRO sci­en­tists will watch with great anx­i­ety how GSLV-Mark 3’s rocket en­gines func­tion. That’s only the first part—it will take an­other month and a half be­fore the pay­load reaches the moon and the lan­der and rover plonk them­selves on the lu­nar sur­face. K. Si­van, ISRO’s chair­man, calls these the most “ag­o­nis­ing mo­ments”. If In­dia suc­ceeds, it will be only the fourth na­tion to do so, next only to the US, Rus­sia and China. It is a sta­tus worth wait­ing for, not just for a week but even for a month or more, be­fore suc­cess­fully launch­ing Chan­drayaan 2.

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