Globalstar's satellite fleet has four new members after a Russian Soyuz rocket launched the replacement communication platforms Saturday to bolster the company's aging constellation.

The Soyuz launched at 2012 GMT (4:12 p.m. EDT) from Complex 31 at the Baikonur Cosmodrome in Kazakhstan. The three-stage booster and an attached Fregat upper stage rocketed into space and released the four satellites about 100 minutes after liftoff.

The rocket was shooting for a circular orbit about 572 miles high with an inclination of 52 degrees. The Fregat upper stage fired two times to reach the targeted orbit, according to Starsem, the international marketing firm for the Soyuz rocket.

The satellites will use their own maneuvering thrusters to raise their orbits to an altitude of 876 miles over the next few weeks before eventually placing themselves into open slots in Globalstar's operational fleet.

Globalstar satellites provide voice and data communications to more than 275,000 activated fixed and mobile units in more than 120 countries.

The satellite fleet consists of 40 active spacecraft plus additional orbital reserves, and the company's communications relay service can reach more than 80 percent of the Earth's surface. The craft are spread throughout six orbital planes to ensure customers always have a satellite overhead.

The four satellites launched Saturday, in addition to another quartet launched earlier this year, were the last in the company's original batch of spacecraft that were deployed beginning in 1998.

The 992-pound craft were built by prime contractor Space Systems/Loral and kept on Earth as ground spares until Globalstar needed to replenish its constellation. The satellites are designed to last for at least seven-and-a-half years.

The company invested about $120 million in the two launches, according to a Globalstar written statement.

"Although they represent the completion of our current generation space segment, these satellites along with the four launched earlier this year, will also facilitate a seamless transition into our second-generation constellation beginning in 2009," said Tony Navarra, president of global operations for Globalstar.

C-band antennas mounted on each satellite's Earth-facing deck communicate with Globalstar gateways, ground stations that distribute satellite phone calls to conventional terrestrial telephone networks.

The gateways help reduce the company's operating costs because they use existing telephone networks and house many critical systems, reducing the satellites' complexity, officials said.

Globalstar satellites also feature an array of L-band and S-band antennas to link with user telephones and modems.

Globalstar announced in February that engineers discovered a serious problem with S-band antennas on satellites already in orbit. The company said the issue could hinder two-way communications services beginning next year, according to a filing with the Securities and Exchange Commission.

Engineers observed degradation in the performance of the antennas' solid-state power amplifiers, which was decreasing the quality of two-way communications, the SEC filing said.

Officials believe the eight replacement satellites launched this year will extend the current fleet's lifetime through 2009, when the first of eight launches is scheduled to deliver upgraded satellites to space.

Globalstar awarded the satellite development contract to Thales Alenia Space in December, followed last month by the selection of Arianespace as the launch services provider. Launches are slated to begin in mid-2009 aboard Soyuz rockets launched from a new launch pad at the European spaceport in French Guiana.

The second-generation constellation will provide faster data speeds to facilitate video communications and additional call capacity through 2025, Globalstar said.