A return to wind in their sails is out of the question. So how are we to reduce the emissions footprint of the global shipping industry — which accounts for about 90% of the world’s goods movements, and about 3% of global greenhouse-gas emissions?

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Among the pioneers working to enable this transition is Padmini Mellacheruvu, a cryogenic rocket systems engineer who helped write the first “class rules” for hydrogen-powered ships in June. These rules, issued by the UK-based ship-classification society Lloyd’s Register, aim to help shipowners retrofit, design and operate hydrogen-powered ships safely.

Lloyd’s, incidentally, is among a handful of ship-classification societies that set the standards for global ship-building, in a tradition that dates to 1760 (when Lloyd’s was founded, as the Register Society). No ship can be insured, for instance, unless it has been “classed” by such a body.

When it came to drafting rules for hydrogen-powered ships, though, Lloyd’s hit a roadblock. Because the use of hydrogen to power commercial vehicles is so new, they couldn’t find scientific experts within the maritime industry to define and design propulsion and safety systems.

That expertise existed — in an entirely different industry that has been using hydrogen to move very, very large objects across extensive distances: Aerospace.

When it comes to hydrogen propulsion systems in space, Mellacheruvu stands out.

When Lloyd’s approached her in 2022, she had been with the Indian Space Research Organisation (ISRO) for seven years, working on both liquid hydrogen and compressed hydrogen gas cryogenics systems. She had helped launch rockets and the moon orbiter mission Chandrayaan-2.

It was a tough decision to leave for a completely new industry, she says. What eventually tipped the scales was the opportunity to help pioneer a green transition in something as large and vital as global shipping.

“We take knowledge about hydrogen and cryogenics for granted in the aerospace world, but such systems are very rare in the marine and automotive industries,” she says. “So I wanted to share that knowledge and play my part in reducing greenhouse gas emissions. I think that’s what future generations need from us.”

Growing up in Guntur, Andhra Pradesh, Mellacheruvu — the daughter of an optometrist and a school headmistress — fell in love with science-fiction as a child. She was in school when “missile man” APJ Abdul Kalam (who helped design the Prithvi and Agni missiles, among others) became President of India in 2002.

“He inspired me to explore engineering and aerospace,” she says. After studying mechanical engineering at BITS Pilani, she worked at a Tata Technologies car crash analysis unit in Pune for a year. Then, in 2015, she got the offer to work at ISRO’s Satish Dhawan Space Centre in Sriharikota.

“I was ecstatic,” says Mellacheruvu, who made the most of the opportunity to work on everything from the cryogenics systems on rockets to control systems, fire and personnel safety, and post-launch data analysis.

“It’s a very ‘systems-engineering’ approach there. You cannot be pigeonholed into one thing at ISRO. Everybody has to learn about everything that goes on. It was a great experience. Every day, I learned something new.”

Her first rocket launch was the Polar Satellite Launch Vehicle (PSLV) C29 flight in December 2015. She was 22. “I was still very green, but the organisation and the senior scientists trusted me to actually work on the launch vehicle and learn on the job,” she says.

She worked on the 2017 launch of the Geosynchronous Satellite Launch Vehicle (GSLV) Mark III, on the Reusable Launch Vehicle Technology Demonstrator, and perhaps most excitingly, on Chandrayaan-2.

Mellacheruvu remembers tense moments in the control room before its first scheduled launch on July 13, 2019. Senior scientists analysed a technical glitch and debated whether to proceed with the launch or put it off, aware that the whole country was watching.

Once the decision was made to delay the launch, they immediately got to work fixing the problem. “Within a couple of days, we were able to identify the issue and take corrective action,” Mellacheruvu says. “We worked around the clock. Even outdoors and in the middle of a cyclone, everyone was completely focused on the job at hand.”

Chandrayaan-2 was finally launched, successfully, nine days later, on July 22.

Lloyd’s Register is exciting in a different way. It allows her to work on a very different aspect of the future, Mellacheruvu says.

She is bullish about hydrogen’s potential as a green fuel, and as an energy carrier that can be used to store, move and deliver energy produced via other sources. “One of the interesting things about hydrogen is that you can blend it with most conventional fuels. Studies show, for instance, that with a 50-50 blend of hydrogen and marine gas oil, we could reduce emissions by 43% per tonne per km travelled. This means that even if one doesn’t opt for full hydrogen transition — which comes with costs in terms of comprehensive ship redesign — one can opt for some amount of blending and reduce carbon emissions,” she says.

Small, short-distance hydrogen-powered tug boats are already running in European waters. Mellacheruvu says some medium-distance goods-shipping firms, luxury cruise-liners and passenger ferries have expressed an interest too. If the current spate of projects and experiments on medium-sized freight ships is successful, she believes the world really could begin to decarbonise shipping.

Here’s to wind in their sails.