A Proton rocket hauled three new satellites into orbit Thursday to replenish Russia's space-based navigation system, marking the heavy-lift booster's second flight in less than a week.

The Proton rocket launched from the Baikonur Cosmodrome in Kazakhstan at 0849 GMT (4:49 a.m. EDT) Thursday. The rocket's three lower stages completed their burns in the first nine minutes of the mission, and the Block DM upper stage fired twice to propel the three Glonass satellites into a medium-altitude orbit.

The 3,000-pound satellites were released in a circular orbit nearly 12,000 miles high with an inclination of 64.8 degrees, completing the Proton's seventh flight of the year.

The Glonass constellation, Russia's counterpart to the U.S. Global Positioning System, currently includes 16 satellites.

One spacecraft is undergoing maintenance and another is being decommissioned, leaving 14 satellites available for daily operations, according to an update posted on the Russian Space Agency's Web site this week.

Maintained by the Russian military, Glonass satellites transmit two navigation signals for armed forces and civilian users. The civilian channel can provide positioning data within about 200 feet, according to the Russian Space Agency.

A constellation of 18 satellites spread among three orbital planes is required to provide blanket coverage of Russia, while 24 spacecraft can reach users worldwide. Russian officials want to achieve a full Glonass constellation of 30 satellites, including spares, by 2011.

Three more Glonass satellites are scheduled for launch in December, following by more additions next year.

The satellites launched Thursday are expected to operate for at least seven years, Russian officials said.

Thursday's launch was the second Proton mission in six days.

Another Proton rocket blasted off Friday with the Nimiq 4 communications satellite. That launch, conducted under the auspices of International Launch Services, used a Breeze M upper stage to deliver the 10,692-pound payload into an elliptical geosynchronous transfer orbit.

Nimiq 4 will broadcast direct-to-home television services to Canadian customers for Bell TV, a leading direct broadcasting firm in Canada.

The spacecraft, which includes Ku-band and Ka-band transponders, will be operated by Telesat Canada. The communications payload is geared toward specialty, foreign language and high-definition television programming.

Nimiq 4 was manufactured by EADS Astrium and will be located along the equator at 82 degrees west longitude.

The next Proton launch is scheduled for late October or early November with the ASTRA 1M communications satellite.