In a space mission, many things can go wrong, and often something will. Now, as the Chandrayaan-2 mission prepares to take to the skies and beyond, veterans remember some tense moments in its predecessor.

Chandrayaan-1 was launched on October 22, 2008. The 4-stage PSLV rocket was chosen to take the satellite to the low earth orbit — it would be eventually and gradually pushed to the moon. In a PSLV, the second and fourth stages are powered by liquid propellants, while the first and third have solid propellants.

On the eve of the launch — October 21 — the mission was filling liquid propellants to the second stage. The propellant consists of fuel and oxidiser, which in this case were the chemicals UH25 and nitrogen tetroxide, respectively. Nitrogen tetroxide is a highly toxic chemical — inhale a little and you are gone. Twenty-five tonnes of the stuff was to go into the rocket.

The filling of the fuel, handled by computers, was being supervised by a team headed by the Director-Operations, M. Y. S. Prasad, some 10 km away from the rocket. Around 3 pm, the team noticed on the CCTV monitors a sudden incursion of thick, pink-coloured smoke, which completely engulfed the standing rocket.

The only way to find out what had happened was by going inside the toxic fumes. Two people – one Mr Annamalai and Prasad – took a jeep and drove in heavy rain to the rocket, wearing gas masks. To their relief they found that the problem was a leaky joint that connected the oxidiser tank and a pipe on the rocket. The rocket itself was fine.

It took several hours for the experts to repair the coupling, but the team realised that to prevent a recurrence of the leak they would have to slow down loading of the oxidiser. They did, but that didn’t help much because, later, another leak occurred at the same spot.

So, once again a small team was sent to do the repair. This set the clock back by another three hours or so. And, as luck would have it, the leak occurred a third time, around midnight.

“The entire world was watching us, there were phone calls from all over,” recalls Prasad, who is today the Vice-Chancellor of Vigyan University, Guntur, Andhra Pradesh. If the mission was aborted, it would be a national shame.

However, by that time, 23.5 tonnes of the oxidiser had been loaded, only a little remained to be put in. Dr K Sivan (the current ISRO Chairman) was in charge of computer simulations — he did some quick calculations and said it was okay if no further oxidiser was loaded — the rocket was good to go.

That was also the time when the fuel had to be loaded. The team faced a vexing dilemma. If a similar leak occurred while loading the fuel, it would come in contact with the leaked oxidiser hanging around, the result would be an explosion.

Prasad decided that they would first blow away the oxidiser clouds, using compressed air kept behind the rocket, for some other purposes. And so, another expert was sent to handle the operation — he flushed out the Nitrogen tetroxide with the compressed air. Fuel loading began.

In the meantime, it was also decided that other operations, such as charging of the satellite batteries, would go on simultaneously, rather than sequentially, to save time. In the end, PSLV-C11 took off carrying Chandrayaan-1, and the mission was a resounding success.