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A final order for a batch of 10 Ariane 5 rockets has been raised.

The vehicle, which has been the mainstay of European launcher activity for the past 20 years, will be phased out once its successor is in place.

ArianeGroup, the French-led industrial consortium, expects its new Ariane 6 to be flying no later than mid-2020, and in full operational service in 2023.

At that point, Ariane 5 can be retired. The last order ensures sufficient rockets are available for the handover.

ArianeGroup CEO Alain Charmeau commented: "This production kick-off of 10 new Ariane 5 ECA represents, for the European industry, a total of more than 1 billion euros.

"This also allows us to continue capitalising on the exceptional levels of quality and punctuality that have made Ariane 5 so successful, while being consistent with the rapid market introduction of Ariane 6."

After a couple of early-career failures, the Ariane 5 has become a super-reliable vehicle.

Its most recent outing in December was the 82nd straight successful flight.

However, the vehicle is now considered too expensive for the way the launcher market is developing. And this need for change is emphasised by the rising prominence of the American SpaceX company which is able to recover and re-fly rockets, gaining further price advantage on top of the more modern production methods it uses.

The Ariane 6, although not designed for reusability in the first instance, will nonetheless have a considerably cheaper ticket price than the Ariane 5.

This should be possible through a reduced workforce, more efficient production and the incorporation of advanced manufacturing techniques.

ArianeGroup and its subsidiary marketing company, Arianespace, hope this will keep the European offering competitive in the face of the American challenge.

With this latest order, there are now 23 Ariane 5 launchers in production or to be produced.

The current flight rate is about six missions a year. This gives an idea of how much longer the Ariane 5 will be available, given that its operation will soon dovetail with the Ariane 6.

2017 saw an Ariane 5 lift its heaviest payload to date when it put two geostationary satellites into orbit in June. The total payload mass was 10,865 kg, of which 9,969 kg was the net weight of the two passenger spacecraft.

SpaceX will soon debut its Falcon Heavy rocket, which should more than double this capability.

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: