PARIS — The European Space Agency (ESA) on Sept. 13 gave final go-ahead for development of the next-generation Ariane 6 heavy-lift launch vehicle, confirming a rendezvous that many thought impossible when it was set in December 2014.

Meeting at ESA’s headquarters here, the agency’s ruling council approved the release of the second and final tranche of funds for Ariane 6, with the transfer of funds to Ariane 6 prime contractor Airbus Safran Launchers to occur in late October.

The contract’s, whose financial contours have already been determined since its signature in August 2015, is for 2.4 billion euros ($2.7 billion) for the development of the Ariane 6 under Airbus Safran Launchers leadership.

A bit more than a quarter of that sum, 680 million euros, was paid out after the August 2015 signature. It is the remaining piece that was withheld pending a Program Implementation Review that ESA governments insisted on just to be sure they were not buying something they did not want. The funds’ release will now be validated by ESA’s Industrial Policy Committee, scheduled to meet in late October.

To these figures are added 600 million euros to be paid to the French space agency, CNES, to build the new Ariane 6 launch complex at Europe’s Guiana Space Center on the northeast coast of South America.

Another 400 million euros is coming from the principal industrial contractors building Ariane 6.

ESA’s Gaele Winters: Technical performance of Ariane 6 is clear

Gaele Winters, ESA’s outgoing director of launchers — his last day on the job was Sept. 13 — said the Ariane 6 is on track both in its technical design, performance requirements and schedule.

In an interview, Winters said the vehicle is still scheduled to fly in 2020. The current thinking is that the existing Ariane 5 would be operated in parallel until 2023. But the precise Ariane 5 phase-out schedule will be the subject of what Winters called an Exploitation Verification Key Point, to occur by the end of 2017.

Government guaranteed launch rate to be discussed later

Also to be determined then is whether and how European governments will guarantee to Airbus Safran Launchers five contract per year. The company has said it needs this minimum government guarantee to close the business case.

Winters said several ESA governments remain concerned that their industry will not receive contracts corresponding to the amount of their governments’ contributions to the Ariane 6 program. This issue, known at ESA as fair return or industrial return, is a pillar of ESA management.

Winters said he saw no serious issues there and that assuring the necessary return for all governments contributing to Ariane 6 will be part of the relatively easy adjustments to be made starting in 2017.

The biggest government customer for Europe’s Arianespace launch consortium is not ESA but the European Commission, the executive arm of the 28-nation European Union.

It is the commission that owns Europe’s biggest government space programs, the Galileo positioning, navigation and timing network and the Copernicus Earth observation system.

The commission is developing a space strategy for Europe that will not be published until late October. The consequences of this policy, and how to provide the Ariane 6 contractors a minimum annual government launches, will be a subject of debate starting in 2017.

Other details for Ariane 6 are not viewed as urgent but are nonetheless key to the program’s ultimate success. For example, it is not yet clear who has what responsibility in the event of an Ariane 6 failure.

“We are in a development phase now, and topics like this need to be addressed for the exploitation phase,” Winters said. “The exploitation review in late 2017 will treat aspects including the financial environment of the vehicle’s exploitation and other topics that do not need to be handled now.”

As a result of the Sept. 13 council decision, Ariane 6 will not be on the agenda for ESA governments when they meet in Switzerland in early December to discuss ESA’s mid-term budget and policy direction.

Once the funding complement is released, CNES is expected to proceed with the sale of its 35 percent share of Arianespace to Airbus Safran Launchers, a transaction valued at about 150 million euros.

ESA will remain a “censor” on the Arianespace board of directors, keeping at least a symbolic government hand in the launcher business despite CNES’s departure as an Arianespace shareholder.