Globalstar launched four new communications satellites Tuesday, replenishing the company's aging fleet in an effort to continue mobile telephone and data services through 2009.

The four craft were launched aboard a Russian Soyuz rocket at 2031 GMT (4:31 p.m. EDT) from pad 6 at the Baikonur Cosmodrome in Kazakhstan. The booster and its attached Fregat upper stage flew east away from the launch site and successfully guided the payload into a 572-mile-high orbit.

Spacecraft separation occurred at 2218 GMT (6:18 p.m. EDT). Ground stations soon established contact with all four satellites, according to a written statement.

"We are absolutely ecstatic about this success and pleased to make this announcement," said Jay Monroe, chairman and CEO of Globalstar.

The satellites will be added to Globalstar's constellation during the coming months to supplement the current flock of beleaguered first-generation spacecraft, which is due to be replaced beginning in 2009.

The current satellites are suffering from an anomaly with their S-band communications system that may cut off two-way communications services next year. The craft were launched between 1998 and 2000.

To join Globalstar's operational fleet, the spacecraft will raise their orbits to an altitude of about 876 miles with an inclination of 52 degrees.

The four satellites were designed by prime contractor Space Systems/Loral and kept on Earth as ground spares to be launched as needed. Four more identical craft will be sent into space later this summer.

"Globalstar considers these eight satellites to represent the beginning of our next-generation constellation because they will not only bridge the gap today, but last long into and seamlessly operate with our second-generation constellation," Monroe said.

Globalstar invested about $120 million in the two launches, according to Monroe.

Like the Globalstar satellites already in space, the four craft launched Tuesday are designed to operate for about seven-and-a-half years.

Each of the 992-pound satellites features an array of antennas mounted on the craft's Earth-facing deck.

C-band antennas are used to communicate with Globalstar gateways, ground-based centers that process and distribute phone calls to standard fixed and cellular networks. L-band and S-band antennas link the satellites with user phones, according to Globalstar.

Globalstar says using existing telephone networks simplifies the company's services and reduces operating costs. Ground-based gateways also house much of the system's critical software, decreasing spacecraft complexity.

The constellation originally consisted of 48 operational satellites and several in-orbit spares available to be added on short notice. After experiencing several hardware failures, Globalstar reduced the fleet to 40 active spacecraft plus orbital reserves.

The satellites are spread throughout six orbital planes, ensuring consistent service throughout the 120 countries covered by the company. The satellites can relay communications to and from more than 80 percent of the Earth's surface.

In February, Globalstar announced a serious problem with the S-band antennas aboard the existing spacecraft that may end the company's ability to maintain two-way communications services by next year.

Engineers have observed degradation in the performance of the antennas' solid-state power amplifiers, adversely affecting the quality of voice and data communications through the Globalstar system, according to a filing with the Securities and Exchange Commission.

"Despite a successful launch and optimized placement in orbit of the eight spare satellites in mid-2007, increasingly larger coverage gaps will recur over areas in which the company currently provides two-way communications services," the filing said.

Officials say Globalstar is working on plans to reduce the effects of the problem on its customers, who operate more than 250,000 activated voice and data units.

Globalstar is also racing to begin launching a new generation of satellites by 2009 to minimize the time without the capacity for two-way communications.

Thales Alenia Space will design and build the 48 new craft under a contract worth nearly $900 million announced in December. Launches are slated to begin in 2009, though the schedule could be accelerated, according to Globalstar.

The company expects to finalize launch plans later this year.

The satellites will be able to handle more call capacity, higher data transmission speeds, and video streaming through about 2025. The service upgrades are part of Globalstar's long-term business strategy.