Six next-generation satellites for the Globalstar mobile communications network will launch from Kazakhstan on a Soyuz rocket Tuesday, the first of four missions to replace the company's aging space fleet.

Artist's concept of Globalstar satellites in orbit. Credit: Thales Alenia Space

The launch is the first phase of a $1 billion investment to restore Globalstar's beleaguered two-way voice and data service and extend satellite operations beyond 2025.

Globalstar's duplex voice and data service fell victim to a problem with the existing fleet's S-band antennas. First announced in 2007, the issue severely limits reliable satellite coverage for users on the ground.

The launch of 24 second-generation Globalstar satellites will gradually bring back the curtailed two-way communications services.

"There will be an immediate improvement after each of the launches," said Tony Navarra, president of global operations at Globalstar Inc. "A month or two after this first launch, they will start to see improved services."

The antenna degradation does not affect Globalstar's simplex service used for data relay and asset tracking applications.

The Soyuz rocket is scheduled to launch at 1710:59 GMT (1:10:59 p.m. EDT) Tuesday from the Baikonur Cosmodrome in Kazakhstan. The booster is flying in the Soyuz 2-1a configuration with an advanced digital command and telemetry system and upgraded injectors in the first and second stage engines.

"It's moving according to schedule," Navarra said Monday in a phone interview from Baikonur. "The Soyuz rocket is on the pad now."

Towed by a train, the four-stage rocket left its Baiknour assembly building at 6:30 a.m. local time Saturday. The Soyuz arrived at the pad and was hoisted upright on the launch pad later Saturday morning.

The Russian launch team will load the Soyuz with liquid oxygen and kerosene propellants about four hours before liftoff.

The Soyuz rocket poised on the launch pad at the Baikonur Cosmodrome. Credit: Roscosmos

The Soyuz will ascend above Baikonur and turn east, surpassing the speed of sound moments after liftoff and consuming all of its first stage propellant two minutes into the mission.

The rocket's four first stage boosters will separate at T+plus 1 minute, 58 seconds. A single second stage core engine will fire for another three minutes, before giving way to the Soyuz third stage.

After shedding a bulbous ST-type payload fairing, the third stage engine will shut down and release the Fregat upper stage. The Fregat main engine will ignite to place itself in a low parking orbit, then fire a second time to reach the Globalstar separation orbit at an altitude of 572 miles and an inclination of 52 degrees.

The Fregat will deploy the six satellites in range of Globalstar's ground station at Aussaguel, France. Clustered on a cone-shaped payload dispenser, the first two 1,543-pound satellites are scheduled to separate at T+plus 98 minutes, 36 seconds.

The rocket will release the other four payloads less than two minutes later, completing the mission at T+plus 100 minutes, 20 seconds. The Fregat will later fire a third time to guide itself to a destructive re-entry over the Pacific Ocean.

The satellites' power-producing solar panels will deploy between four and six minutes after separation, according to Navarra.

Controllers will test each satellite's systems before placing the spacecraft in Globalstar's constellation.

Six Globalstar satellites are mounted on a payload dispenser during launch preparations. Credit: Arianespace

Navarra said two of the satellites launched Tuesday will enter the constellation in about one month. It will be early 2011 when the other four spacecraft drift to their assigned locations.

Another Soyuz rocket will dispatch six more Globalstar satellites between January and March of 2011. Two more flights are planned at two-month intervals next year to finish launching the 24 second-generation satellites, Navarra said.

"I would say in the second quarter of 2011 Globalstar will be back and providing the high-quality voice and data service that we had in the 2004 to 2006 timeframe," Navarra said.

Built by Thales Alenia Space, each new Globalstar satellite is trapezoidal in shape and features 16 transponders in C-band and S-band and 16 recievers in L-band and C-band. The second-generation craft are designed to work for 15 years, twice the design specification of the existing satellites, most of which have exceeded their planned lifetimes.

Globalstar's first launch campaign orbited 48 satellites on Delta and Soyuz rockets between 1998 and 2000. The company launched eight more spare satellites on two Soyuz flights in 2007.

According to Navarra, there are about 40 satellites left in Globalstar's space fleet. Officials are retiring the remaining satellites as new ones arrive in orbit.

The eight payloads launched in 2007 will join the 24 brand new spacecraft in the next incarnation of the Globalstar constellation.

"We're going to marry the 24 satellites with the eight already in orbit to have a 32-satellite constellation," Navarra said.