PARIS — Mobile satellite services provider Inmarsat on May 16 told investors that the failure of Russia’s Proton heavy-lift rocket earlier in the day made it “now likely” that Inmarsat’s Global Xpress Ka-band broadband network will miss its scheduled in-service date.

The company said a Russian government-managed board of inquiry, called the Failure Review Oversight Board (FROB), is being assembled to investigate the May 16 failure and is likely to report its conclusions within two months. The Proton has experienced six launch mishaps since late 2010, all on Russian government missions.

“We believe a delay in the planned launch of both the Inmarsat-5 F2 and F3 is now likely, which would delay the launch of [Global Xpress] services on a global basis,” Inmarsat said in a statement to investors. “However, the start of commercial [Global Xpress] services on a regional basis using the F1 (and F2 in due course), as well as existing customer commitments to purchase [Global Xpress] services, will not be impacted by any delay in global service availability.”

London-based Inmarsat had been counting on launching the second and third Global Xpress spacecraft on International Launch Services commercial Proton vehicles this year.

The first satellite was launched in December and is now being tested by U.S. special forces in Africa, among other early users. The launch of the two remaining spacecraft would provide global coverage outside the polar regions.

The May 16 Proton failure, tentatively attributed by the Russian space agency, Roscosmos, to a third-stage anomaly, is all but certain to push one, if not both, Inmarsat launches into 2015.

The Proton 2014 manifest, with both Russian government and commercial missions, had already been stretched tight. Most recently the next ILS commercial launch, of the Astra 2G satellite for SES of Luxembourg, was moved from June to September to accommodate Russian government missions.

The next Inmarsat Global Xpress spacecraft would have been launched after Astra 2G, meaning perhaps in October.

The May 16 failure is almost certain to change the calculus. Russian Federal missions, including satellite launches for the Russian Satellite Communications Co. (RSCC), which operates a fleet of commercial telecommunications spacecraft, are obliged to use Proton.

While Inmarsat’s Global Xpress satellites are compatible with Europe’s Ariane 5 rocket, they would need a place in Ariane 5’s upper position, reserved for heavier spacecraft, with the lower position given to the lighter of the two passengers carried on each Ariane 5 commercial mission.

An official with Evry, France-based Arianespace on May 16 said that because of a July 2013 Proton failure, many owners of heavy satellites rushed to Arianespace to book upper-berth launches. The company booked contracts for 11 heavy telecommunications satellites in 2013, equivalent to two years’ worth of Ariane 5 launches.

“Because of this large influx of orders, we are booked through mid-2017,” the official  said May 16. “There is always the possibility of a new order being able to slip into the manifest if an existing customer’s satellite experiences major delays. But our natural inclination is to keep these slots open for customers that have given us their confidence.”

Sea Launch AG of Switzerland, which competes with Proton and Arianespace to launch heavy telecommunications satellites, has said it will have a vehicle available as soon as late this year.

But Sea Launch has had reliability issues of its own and even a customer under pressure to find a launch is unlikely to book with Sea Launch until after the company’s scheduled May 26 launch of a telecommunications satellite owned by Eutelsat of Paris.

Industry officials said the Proton failure will almost certainly make Inmarsat one of the first calls Sea Launch will make after a successful Eutelsat launch.

The latest Proton failure resulted in the loss of RSCC’s Express AM4R satellite, which according to Roscosmos never reached orbit. The satellite, built by Airbus Defence and Space Group of Europe, was intended to replace the Express AM4 satellite that was lost in a 2011 Proton failure.

The heavy-lift Proton has now had six mishaps since late 2010 — five outright failures and one in which a satellite was left in the wrong orbit but was able to reach its proper orbit using onboard fuel.

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