PARIS—Mobile satellite services provider Inmarsat has entered into a multi-year contract with Telenor Satellite of Norway to lease a large piece of the mobile Ka-band broadband capacity on Telenor’s Thor 7 satellite, industry officials said.

The agreement will allow London-based Inmarsat to bolster its growing aeronautical broadband portfolio over Europe and the North Atlantic air routes beyond Inmarsat’s own Global Xpress satellite, and without waiting for Inmarsat’s European air-to-ground network to deploy.

Inmarsat and Oslo-based Telenor officials declined to comment on the issue, but industry officials said the deal was concluded several months ago.

Telenor’s Thor 7, launched in June 2015, carries a conventional Ku-band payload for Telenor’s established television broadcast and maritime business, and a Ka-band spot-beam payload designed for the maritime broadband market.

Industry officials said that under the terms of their agreement, Inmarsat would not use Thor 7 capacity to compete directly with Telenor in the maritime market, which has historically been Inmarsat’s core business. Instead, Inmarsat will use Thor 7 for its fastest-growing business, which is aviation connectivity.

Inmarsat’s three Global Xpress Ka-band satellites, carrying both military and commercial Ka-band payloads for mobile customers, are in orbit.

The company is also building its European Aviation Network, to feature a network of ground-based terminals to provide high-speed connectivity in European aeronautical markets too concentrated for a satellite alone. The company has an S-band satellite payload under construction to serve the same market alongside the air-to-ground technology.

Inmarsat is also building two Inmarsat-6 L- and Ka-band satellites to continue its heritage L-band mobile connectivity business and expand its Ka-band broadband portfolio. Finally, a fourth Inmarsat Global Xpress satellite is nearing completion. Inmarsat is mulling where to place it.

For a time, it looked like Inmarsat would position the fourth Global Xpress satellite over Asia to appeal to the Chinese market. Inmarsat has yet to disclose its final decision.

That means three satellites with Ka-band mobility payloads under construction for Inmarsat. But Leo Mondale, head of the company’s aviation division, let slip that a fourth payload was also on the way.

“In addition to the three Ka-band payloads we have in orbit today, we ‘ve committed to four additional ones that are being built. They are under contract, and will be launched an operated, and there could be more by 2020,” Mondale said March 8 at the Satellite 2016 conference in National Harbor, Maryland.

Mondale made his comments during a debate with competing Ku- and Ka-band mobile satellite providers, especially Carlsbad, California-based ViaSat Inc. ViaSat is designing a terabit-per-second-throughput ViaSat 3 satellite, with one each to be placed over the Americas and Europe around 2020.

Mondale’s point was that 2020 is a long way off and the market landscape could change substantially by then. He declined to identify the additional Ka-band capacity, saying only: “There is a payload that we are not disclosing the details of, that we have secured in addition” to the fourth Global Xpress and the two Inmarsat-6 spacecraft, he said.

Telenor has scheduled an event in London on May 11 to unveil its Thor 7 Ka-band maritime business, which has been in beta testing in the months since its mid-2015 launch.

Inmarsat has gone so far as to acquire an existing maritime satellite service provider and to transition what is now an installed base of Ku-band VSAT-equipped ships to Global Xpress’s Ka-band, at substantial cost to Inmarsat.

It is unclear what strategy Telenor will use to wean its Ku-band maritime customers to Ka-band, or whether the company feels the need to do so. It could let existing customers migrate from Telenor Satellite-provided Ku-band to Ka-band at their own pace, without forcing the switch to Ka-band.

In a series of presentations in February, Telenor said less than 5 percent of current maritime commercial vessels are equipped with VSAT terminals, leaving a large greenfield market available for Ka-band.

The company said it moved to Ka-band because Ku-band orbital slots over Europe are difficult to acquire, with most of them occupied with serving the highly profitable broadcast market.

“We can offer higher bandwidth through smaller antennas,” Telenor’s Julian Crudge said during the presentation.

Tore Morten Olsen, head of Marlink, a maritime satellite services provider that is the former Telenor Satellite Services, said tests of Thor 7 in the North Sea and other rough-weather maritime areas where Telenor operates have shown that rain-fade from Ka-band is manageable.

“During rain, the receive signal dropped compared to cloudy conditions, but the system still kept high performance,” Olsen said. “Heavy rain at [Telenor’s] Nittedal hub [in southern Norway] did not degrade the signal. Seamless beam switching between the Nittedal teleport and the diversity teleport seemed to work well.”

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