PARIS — European commercial satellite fleet operators, including the world’s four largest by annual revenue, have written the European Space Agency urging that it find immediate ways to reduce Ariane 5 rocket launch costs and, in the longer term, make the next-generation Ariane 6 vehicle more attractive for smaller telecommunications satellites.

In an April 8 letter to ESA Director-General Jean-Jacques Dordain, the seven companies comprising the European Satellite Operators Association (ESOA) said the industry is about to be transformed by the arrival of satellites with all-electric propulsion, which for a given amount of capacity are as much as 50 percent lighter than satellites carrying conventional chemical propellant.

Signed by the chief executives of Intelsat, SES, Eutelsat, Inmarsat, Hispasat, Telenor Satellite Broadcasting and HellasSat, the letter says Europe cannot wait for an Ariane 6 early in the next decade before attacking its current launch cost problems.

“What is sure is that Europe deserves and requires a [reorganized launcher sector] ahead of 2019,” the letter says. “[C]onsiderable efforts to restore competitiveness in price of the existing European launcher need to be undertaken if Europe is [to] maintain its market situation.

“In the short term, a more favorable pricing policy for the small satellites currently being targeted by SpaceX seems indispensable to keeping the Ariane launch manifest strong and well-populated.”

ESA governments are scheduled to decide in December whether to proceed with full development of an Ariane 6 rocket, to fly starting in 2021. The rocket’s principal design objective is that, by its 15th launch, it can be built and launched for a cost of no more than 70 million euros, or $96 million at current exchange rates.

The target cost would be assured even if the rocket is only launched nine times per year, said Guy Pilchen, head of Ariane 6 planning at the 20-nation ESA, although Ariane 6 plans are based around an annual launch rate of 12 vehicles per year.

The vehicle will be able to carry a 6,500-kilogram satellite to geostationary transfer orbit, the destination of most commercial telecommunications spacecraft.

ESA and CNES, the French space agency, which are co-managing the Ariane 6 work, have said using identical solid-fueled stages for the vehicle’s strap-on booster and first and second stages, topped by a cryogenic upper stage, will assure a large enough production volume of components to meet the 70 million-euro target.

But several satellite fleet operators have lamented what they say is the vehicle’s lack of modularity, and the fact that ESA and CNES appear to have focused Ariane 6 on launching one satellite at a time. For a 6,500-kilogram satellite, they have said, the target cost may be competitive. But if operators must pay the same price to launch a 3,500-kilogram or 5,000-kilogram satellite, Ariane 6 will lose market share.

“Satellite operators believe electric propulsion, full or hybrid, will lead to a potentially sharp reduction in the mass of satellites in the years to come,” the ESOA letter says. “[A]ny future launcher should be designed bearing in mind the fact that the share of the small satellite class, typically plus or minus 3,500 kilograms, is likely to grow in the years to come.”

Hawthorne, Calif.-based Space Exploration Technologies Corp. has already begun to win customers that, up to now, would have been all-but-certain clients of Europe’s Arianespace launch consortium, with prices that are $60 million or less.

Addressing the Space Access conference here April 9, organized by Astech Paris Region, Pilchen ran into sharp questioning from a satellite operator representative, who demanded to know what it might cost to place a lighter-weight satellite on the Ariane 6.

Pilchen said different Ariane 6 designs are being investigated to better attract owners of satellites weighing between 3,500 and 5,000 kilograms. But he declined to be cornered on whether these Ariane 6 variants, which may not benefit from the same scale economies, would be less expensive than the core design.

Satellite operators have long pushed ESA and Evry, France-based Arianespace to drop their dual-launch model and design a next-generation vehicle that carries one satellite at a time.

The difficulties, and frequent launch delays, associated with having to wait for two compatible satellites to be placed on the same vehicle are not worth whatever savings there may be, operators have said.

They appear to be changing their minds for Ariane 6 if the vehicle’s designers and operators are able to slash the 70 million-euro price per satellite.

“We expect alternative service providers to offer launch services at approximately $60 million [for a 3,500-kilogram-class spacecraft],” the ESOA letter says. “In that respect, satellite operators consider that dual launches, even though they produce additional requirements, are a viable solution … if they represent the strongest lever to deliver enhanced competitiveness in price.”

Pilchen said ESA has reviewed, many times, the chosen design for Ariane 6, including adding liquid propulsion. “Yes, we have reopened the files,” he said. “We’re used to doing that. But the element we have always to remember is the vehicle’s recurring cost.”

The mainly solid-fueled design, he said, continues to offer the best hope for meeting this requirement and for meeting the inaugural-flight date of 2021.

Peter B. de Selding was the Paris bureau chief for SpaceNews.