There are some things electric power cannot achieve, like lifting that 787. But that doesn’t mean big jets can’t go green, or at least greener. Several fuel refiners and airlines are experimenting with Sustainable Aviation Fuels, known as SAFs. These fuels, which burn just like the common “Jet A” fuel, can be made from waste such as used cooking fats. Some companies, like Neste, use hydrogen in refining its SAF fuel.

Although aviation safety organizations allow commercial aircraft to use fuel containing 50 percent or less SAF, in demonstrations, existing jets have burned 100-percent SAF, “and the engines are very happy with it,” Ms. Simpson of Airbus said.

But SAF may be seen as a stopgap, as larger planes have flown happily burning emissions-free pure hydrogen. In 1957, a Martin B-57B powered part of a flight using hydrogen as fuel. In 1988, a Soviet TU-155 airliner flew on hydrogen fuel alone.

For Senator Spark Matsunaga, a Democrat of Hawaii who died in 1990, it was a missed opportunity — as significant as Soviet’s Sputnik satellite beating the United States into space. “Once again we’ve missed the boat,” he said, “and we can only hope that the next administration will be more interested in hydrogen than this one has been.”

Any mention of hydrogen aircraft means addressing the zeppelin in the room. Although hydrogen has been used in ballooning since 1783, its aeronautical future dimmed on May 6, 1937, when the zeppelin Hindenburg very publicly burned in Lakehurst, N.J. killing 36. It is still debated if the flames, immortalized on radio and in newsreels (and a Led Zeppelin album cover), were caused mostly by hydrogen or the incendiary paint used on the airship’s fabric skin. Regardless, the damage to hydrogen’s reputation lingers today.

More recently, ZeroAvia experienced a bad news/good news scenario when its hydrogen-fuel-cell-powered Piper Malibu Mirage M350 crash landed last April. The good news was that no one was hurt, despite the plane losing a wing. Better still, with no fuel to leak and no hot engine to ignite it, there was no Hindenburg-like conflagration.

“The hydrogen system itself all held up perfectly,” Mr. Miftakhov said. “The emergency crew said if it were a fossil-fuel plane it would have been a major fire.”