WASHINGTON — Satellite operator SES has selected Arianespace to launch a fifth set of O3b satellites as well as a large geostationary orbit communications satellite, the companies announced Sept. 12.

In one announcement, SES said that a fifth set of four O3b satellites will launch on a Soyuz rocket from French Guiana in 2019. The first 12 O3b satellites launched on Soyuz rockets in 2013 and 2014, with a fourth set of four due to launch in 2018, also on a Soyuz.

The O3b satellites, built by Thales Alenia Space, operate in medium Earth orbit at an altitude of 8,000 kilometers. These satellites are separate from the new O3b mPower system announced Sept. 11, which will feature seven Boeing-built satellites. SES has not disclosed launch plans for those satellites.

Separately, SES announced it will launch the SES-17 geostationary orbit communications satellite on an Ariane 5 in 2021. This satellite, also built by Thales Alenia Space, will weigh more than 6,000 kilograms at launch and carry a payload capable of producing 200 Ka-band spotbeams.

SES officials said in the announcements that the contracts with Arianespace were part of the Luxembourg-based company’s support for the European space industry. “Our commitment to Arianespace also underscores that SES continues to play a major role for the European space industry,” said Steve Collar, chief executive of SES Networks, in a statement on the O3b launch contract.

“We are satisfied to conclude two important contracts with Arianespace giving us the necessary and reliable access to space that we need to further develop and drive our business,” said Sir Martin Halliwell, chief technology officer at SES, in a statement.

SES is also in talks with Arianespace about future launches on the Ariane 6 vehicle in development. “SES’ continued trust in Arianespace is a clear demonstration that our Ariane 5 heavy-lift launcher is keeping pace with these changing technologies, prior to the advent of our new-generation Ariane 6 launch vehicle – for which discussions are underway to serve future SES missions,” Arianespace Chief Executive Stéphane Israël said in a statement on the SES-17 contract.