WARSAW, Poland — Europe’s Arianespace launch consortium won the largest commercial launch contract ever signed — a $1-billion-plus deal to launch between 650 and 720 of OneWeb LLC’s low-orbiting satellites aboard Russian Soyuz rockets —  by offering launch bases both at Europe’s spaceport in South America and Russia’s Baikonur Cosmodrome in Kazakhstan, OneWeb and Arianespace officials said June 25.

The Plesetsk Cosmodrome in northern Russia, which has a Soyuz launch installation, also may be used if needed, Arianespace said.

OneWeb Chief Executive Greg Wyler said that given the launch rhythm required to place some 650 satellites in orbit between late 2017 and late 2019, the prospect of having a launch failure shut down launch operations at a given launch pad was something OneWeb wanted to avoid at all costs.

Evry, France-based Arianespace signed a firm contract with OneWeb to launch 21 Soyuz rockets. The first launch, in late 2017, will be of 10 pilot satellites that will have the same Internet delivery capacity as the rest of the constellation, but will prove the new hardware in orbit.

The remaining 20 launches of Soyuz rockets managed by Arianespace will carry between 32 and 36 satellites each, depending on where the production, overseen by Airbus Defence and Space, ends up. The current thinking is that each satellite, using lighter-weight electric propulsion instead of chemical propellant, will weigh around 150 kilograms.

Wyler said OneWeb and Airbus continue to look at ways to pack the same amount of throughput and backup systems as are found in conventional, larger telecommunications satellites into a smaller package that would weigh less than 150 kilograms.

Arianespace Chief Executive Stephane Israel, in a June 25 conference call with reporters, said the OneWeb contract is valued at between $1 billion and $2 billion. One industry official said it is less than $1.5 billion.

Israel said a separate contract with OneWeb, not yet signed, will cover the cost of designing and building the dispenser system that will fit under the Soyuz fairing to carry the satellites into orbit and release them into a 500-kilometer orbit from which they will climb to their 1,200-kilometer operating location. It is not yet clear how long it will take the electric-powered satellites to reach their operating stations following launch.

Israel said that to meet the OneWeb schedule’s terms, Arianespace will contract with the Russian space agency, Roscosmos, this summer for an additional 21 Soyuz rockets or more. He said the two parties had agreed in principle to the new order during the Paris Air Show the week of June 15, and that a final signing therefore should not take long.

Arianespace has a long-standing Franco-Russian joint-venture company, called Starsem, which manages Arianespace-contracted Soyuz launches from the Baikour Cosmodrome. Given the demands on Soyuz in 2018 and 2019 by European governments, most of the OneWeb launches are expected to occur from the Baikonur facility, he said.

Israel suggested that the pricing arrangement for Soyuz launches between French Guiana, where Europe’s Guiana Space Center is located, and Baikonur are not a prime consideration in determining how many flights occur from the two spaceports.

The Samara, Russia-based company that is the Soyuz prime contractor has a well-demonstrated ability to produce two Soyuz rockets per month.

With 20 Soyuz vehicles to launch in 24 months, Israel sought to reassure Arianespace’s other Soyuz customers, notably the European Space Agency and the European Commission, that their missions would not take a back seat to OneWeb. The commission, which is the executive arm of the 28-nation European Union, notably plans to use the Europeanized Soyuz rocket – from the European spaceport only – for its Galileo positioning, navigation and timing constellation.

In addition to the French Guiana spaceport and Baikonur, Israel said the Soyuz launches could also occur from the Plesetsk Cosmodrome in northern Russia if further spaceport diversity were needed.

The OneWeb contract with Arianespace includes options for five more Soyuz rockets and three Ariane 6 vehicles. The Ariane 6 is scheduled to make its inaugural flight in 2020 and so presumably will not be used to lift the first-generation OneWeb constellation. Israel said it remains to be seen how many OneWeb satellites could be fitted onto an Ariane 6, and that even the choice of a lighter Ariane 62 or a heavier Ariane 64 had yet to be made.

With Russia’s Soyuz selected as the sole Arianespace rocket to be used by OneWeb, at least for now, an eventual role of France’s Coface export-credit agency is undetermined. Coface backing could be used in support of the European value added to Soyuz for the Guiana Space Center launches, but presumably at a much lower level than would be the case if an Ariane rocket had been selected.

Israel said the current Ariane 5 rocket could lift 60 OneWeb satellites, which given OneWeb’s constellation structure is less practical than a 32- or 36-satellite Soyuz, which can fill a single OneWeb orbital plane per launch.

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