Using hydrogen as fuel for any land/sea/air vehicle (or as any kind of energy storage) is extremely bad idea because hydrogen is extremely explosive! Are we seriously thinking there will be never any leaks/ruptures that can easily cause massive explosions?

Motorcycles & cars & pickup trucks are already on their way to become battery powered & for all remaining large trucks & trains & ships & farm/construction/military vehicles we need to start global large scale production of biodiesel fuel (which maybe produced from many kinds of waste/biomass/crops/trash/sewage & can also be converted to jet fuel)!
Expanded Viewpoint
Oh good grief!! Yet another boondoggle of searching for "Zero emissions" by people who should know better! WHERE is it more beneficial for the environment to pursue hydrogen powered anything? HOW is it more economical to go with a vastly more expensive system like this? This must be the goal of teaching children that it's not the result of a math equation that matters, but how you FEEL about that result! If you feel that 2 plus 2 equals 5 is better than 4, then that's all just fine and well and you get a pass on it. So through some kind of bizarre virtue signalling to the world that it's better to use Hydrogen to power an airplane engine instead of a Hydrocarbon based fuel, nobody seems to ask where these copious amounts of Hydrogen come from!! Oh, it must just come out of the air by clapping our hands together!! Yes indeedy! We get just megatons of Hydrogen for FREEEEE!!! There's no cost for it, so why not use it? Yeah, right,
They are coming close to the innovation I've wanted to see: Make /some/ of the engines detachable while IN FLIGHT. This allows the extra power and fuel capacity needed for take-off and climb out to be put to better use than just idling along with the remainder of the flight.
The whole power-module drop-tank concept is something that I am surprised has not been tried before. I imagine it is not as efficient as conformal ~ integrated power but nonetheless... it would be an interesting model for regional airlines...
Love to see innovation and creativity in industry! Hydrogen has great potential as a fuel for direct burning as well as input to fuel cells. As for hydrogen sources, think nuclear power and solar.
Brian M
@FB36 Hydrogen is currently the most sensible for renewable fuel. As for the dangers, yes there are issues, but aviation fuel, petrol etc., are all highly combustible with a propensity to explode given the right conditions which are easy to achieve (unfortunately!).

It might be possible to produce a synthetic carbon based fuel using hydrogen, but its energy density would not be as good (pesky carbon atoms). As for biodiesel current technology would do more harm than good.

@Expanded Viewpoint
"nobody seems to ask where these copious amounts of Hydrogen come from!! "
Try taking a swim - Lots of Hydrogen there in the water! The technological processes for breaking that down to Hydrogen and Oxygen is getting better all the time using green elctricity.

Hydrogen could well be the go to energy force of the future - certainly more sustainable than current battery technology, but that is of course getting better as well.

The future of green energy sources is still to be written, but suspect it will be a mix of technologies.
Not going to happen as H2 sucks as a fuel. And the removable pod thing has little use other than major repairs just like any jet engine.
And ejecting $2mm pods isn't going to happen either.
Maybe do it with a liquid or low pressure synfue.l
Richard Poole
It seems strange that no mention was made of the noise reduction that could be possible with this approach.
A few little pesky details. Hydrogen is one of the few fuels that is explosive at ANYWHERE from 10-90% in air. The pods would have to be dropped in pairs to keep the aircraft stable. The pods would be similar to dropping a daisy cutter onto whoever is below. The plane would be slower since it would be a propeller airplane. And as several others have mentioned hydrogen doesn't come cheap.
@piperTom, they were using JATO 70 years ago to save fuel and launch heavier payloads. My father was a test pilot back then. The idea goes all the way back to the 1920s.