PARIS — The European Space Agency (ESA) has no intention of changing course for its future Ariane 6 rocket despite pointed criticism of the selected design by former ESA and European industry launch-vehicle experts, ESA Launch Vehicle Director Antonio Fabrizi said June 7.

Fabrizi said the current design, using two solid-fueled stages topped by a cryogenic upper stage, received the specific endorsement of ESA’s governments last November and cannot simply be set aside. He said the vehicle’s final design — both a single-block first stage and a multiblock cluster are being discussed — will be settled by early July.

Once ESA and the French space agency, CNES, freeze the Ariane 6 specifications, they will issue requests for information to European industry and then more-formal requests for bids on the Ariane 6 components.

These bids will be evaluated by the end of the year. ESA then will start the delicate procedure of asking governments where the winning bidders are located to invest in the Ariane 6 in proportion to the participation of their domestic industry. A final decision on the vehicle’s development would then be made at a late-2014 conference of ESA government ministers.

Europe’s Air & Space Academy in May wrote to ESA Director-General Jean-Jacques Dordain urging ESA to refrain from committing to the solid-fueled Ariane 6. The academy urged ESA to take four years to craft a more-powerful liquid-fueled alternative, and in the meantime to fund the 1.5 billion euros ($2 billion) needed to complete work on an upgrade of the current Ariane 5. 

The upgrade, called Ariane 5 ME, would increase the current Ariane 5’s payload-carrying power with a new, reignitable upper stage.

In an interview, Fabrizi specifically rejected the academy’s conclusion that a solid-fueled Ariane 6 is a dead-end technology incapable of adapting to future market conditions.

“I remember working on the Ariane 5 rocket’s solid-fueled boosters in 1985 when they were 170,000 kilograms of propellant,” Fabrizi said. “Then they grew to 210,000, then 230,000 and now they are 245,000 kilograms. Solid-fuel technology can evolve with the market.”

Backers of the Ariane 6 solid-fueled version say the Ariane program has never had issues with its solid-propellant stages. In addition, the synergies between the solid-fueled Vega small-satellite launcher, which ESA has flown twice, and the future Ariane 6 solid-fueled design will result in economies for both vehicles.

“We have done these trade offs over the past year or so and we went to our ministers [last November] with a specific design that they approved,” Fabrizi said. “We are now refining the specifics of it, but we cannot go against a design that has the endorsement of our ministers. We are moving according to plan and we are no more than a couple of weeks behind the schedule we set last November.”

The Air & Space Academy’s critique of the Ariane 6 as conceived by ESA and CNES included a second element: the role of Germany in Ariane 6. According to the academy, Ariane 6 will result in an upheaval of Europe’s rocket-industry landscape and create fractures among ESA governments that will not be easily healed.

The academy said that, to maintain its goal of building and operating the vehicle for 70 million euros per launch, the Ariane 6 design will have to rely on only a few ESA member governments, meaning the future Ariane program will lose its broad support in Europe.

Fabrizi said Germany’s likely leadership of the Ariane 6 cryogenic upper stage, plus work on the lower stages borrowing on what OHB AG’s MT Aerospace does for today’s Ariane 5, will enable the Ariane 6 program to promise 20-25 percent of its industrial share to Germany and ensure German backing.

Up to now, the German government and German industry have been skeptical about Ariane 6 and have focused their support on Ariane 5 ME.

Fabrizi said that 500 million to 600 million euros spent developing the Ariane 5 ME’s upper stage will be directly applicable to Ariane 6 because both will use the same Vinci restartable engine and share other components even if they do not use the same fuel tanks.

As to whether ESA governments in late 2014 will have a strong enough appetite for launch vehicle development to fund both Ariane 5 ME, scheduled to fly in 2017-2018, and a 10-year, 4 billion euro Ariane 6 development program, Fabrizi said it is too soon to tell.

“For both Ariane 5 ME and Ariane 6 we still need to receive final proposals,” Fabrizi said. “We will see what results from a real competition among bidders.”

More immediately, he said, ESA will ask its launcher program board the week of June 17 to consider improvements to the current Ariane 5 design to permit the vehicle to maintain its ability to find pairs of telecommunications satellites to launch at the same time.

Finding a smaller commercial telecommunications satellite to fit in the Sylda compartment of Ariane 5 ECA is becoming more difficult for the Arianespace commercial launch consortium.

Fabrizi said several options, both inside the Sylda and outside it under the Ariane 5 fairing, are being considered. One is a longer fairing, which Fabrizi said is an alternative that would take a couple of years to develop and qualify. Another is an enlarged Sylda structure to house the smaller of the two satellites Ariane 5 ECA carries into orbit with each flight.

Depending on the choice made, the governments whose industry stands to benefit from the work will be asked to finance it.

Peter B. de Selding was the Paris Bureau Chief for SpaceNews.