The European Space Agency (ESA) has settled on the basic design of the Ariane 6, the next-generation launch vehicle that will succeed Europe’s heavy-lift Ariane 5.

Known as the “Multi P Linear” concept, the launch vehicle will comprise four solid-fueled boosters that make up the rocket’s first and second stages, topped by a cryogenic third stage based on the Vinci engine, which is being developed by the Snecma motors division of France’s Safran as part of a midlife upgrade to the current Ariane 5, known as Ariane 5ME.

ESA says it expects the rocket to loft 3,000-6,500 kg (6,600-14,000 lb.) to geostationary transfer orbit (GTO) — 500 kg less than French space agency CNES had targeted earlier this year, after ministers from ESA’s 20 member states approved funding for early design work on the rocket at a November 2012 budget meeting in Naples, Italy.

Although less capable than the Ariane 5 — which delivers around 9,000 kg to GTO — Ariane 6 is designed to be more affordable to produce and operate.

Over the past six months, project teams at ESA and CNES had been weighing two concepts for the Ariane 6 design: one based on a large, single, solid-fueled booster to serve as the rocket’s first stage, and a second design based on a cluster concept involving three solid-rocket boosters as the core, topped by a fourth solid booster to function as the second stage.

Both designs were to incorporate a cryogenic third stage based on an adapted version of the Vinci engine.

In June, ESA Director of Launchers Antonio Fabrizi said the cluster option appeared to be more affordable than the single-booster concept.

“The cluster provides higher production rates for the motors, with a lower cost for each motor,” he said on the sidelines of the June 5 launch of Europe’s Automated Transfer Vehicle (ATV-4) from Europe’s Guiana Space Center in Kourou. “But there are integration complications with building the cluster, so we have to make the trade.”

Having settled on the cluster concept, ESA says each of the four lower-stage boosters will be loaded with around 135 metric tons of solid propellant, and that the design choice is expected to afford synergies with future evolutions of Europe’s new Vega light launcher.

In addition, the Ariane 6’s 5.4 meter-dia. payload fairing will be able to accommodate the same volume of satellites as Ariane 5.

The next step for ESA is to consult with competing industry teams that will produce work packages for the new launch system, with a preliminary requirements review slated for October. By early next year, Fabrizi said ESA will propose the best concept to its member states ahead of a 2014 budget ministerial for which no date has been set.

“We’ll have to propose to member states the best concept we can get from competition,” he said. “Only in the second half of next year will we have the proposal ready for the ministers.”