PARIS — Daniel Neuenschwander, director of space transportation at the 22-nation European Space Agency (ESA), is not one for dramatic declarations.

So when he says that the 40-year model Europe has used to develop rockets is facing its greatest crises since a 2002 Ariane 5 failure came close to ending the program, it’s worth noting.

What Neuenschwander knows is this: Europe’s Ariane program has been the only large space-launch system whose survival depends mainly on the commercial-launch market, not government business.

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