German Aerospace Center (DLR)

Backed by European and UK research programs, Rolls is evaluating “vast unknowns’’ posed by the future move to hydrogen-fueled propulsion.

Arianespace’s workhorse Ariane 5 rocket closed out 27 years of operations on July 5 with its 117th mission.

The mission, which is intended to deliver two European government communications satellites into orbit, had been targeted to launch on June 16.

Arianespace is delaying the launch of its final Ariane 5 rocket due to a possible technical issue with the booster.