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Four satellites designed to broadcast high-speed Internet signals to the developing world are mounted on top of a Russian-made Soyuz rocket for liftoff Thursday from the Guiana Space Center in South America.

Launch of the Soyuz ST-B booster — under the joint management of Arianespace and Russian rocket engineers — is set for 1837 GMT (1:27 p.m. EST) from a purpose-built launch facility in French Guiana.

The photos below chronicle preparations of the O3b satellites, including their fueling with toxic hydrazine fuel, attachment to a dispenser, and encapsulation inside the Soyuz rocket’s 13.4-foot diameter payload fairing atop the launcher’s Fregat upper stage.

Built by Thales Alenia Space, each O3b satellite is about the size of a car and weighs 700 kilograms, or about 1,543 pounds, fully fueled for liftoff. The Soyuz rocket’s Fregat upper stage will deploy the spacecraft about two hours after launch into an orbit 5,000 miles over the equator. From that vantage point, the satellites will beam broadband Internet to O3b’s customers, which include maritime users, companies in the oil and gas exploration industry and national operators.

The satellites will join eight O3b satellites launched in June 2013 and July 2014 on two previous Arianespace-run Soyuz flights from French Guiana.

The O3b satellites were attached to the Soyuz rocket Monday evening after the three-stage rocket rolled to the launch pad from its integration building earlier in the day.

Follow Stephen Clark on Twitter: @StephenClark1.