The second of two groups of cosmonauts and astronauts returned to Moscow from Baikonur Friday, May 26 following a training session on the all-but-flight-ready Zvezda service module.

If everything goes as planned, the next time the space travelers visit the module it will be in orbit. A crucial element of the International Space Station (ISS), Zvezda will provide propulsion capabilities and living quarters to the fledgling outpost. Long-delayed launch of the module is currently scheduled for July 12.

The astronauts and cosmonauts who went through Baikonur training in two separate sessions on Tuesday and Thursday represented four different international crews:

• Vladimir Dezhurov, Mikhail Turin and Kenneth Bowersox are the backup crew for the first resident expedition to the ISS.
• Bill Sheppard, Yuri Gidzenko and Sergei Krikalev, members of the station's first resident crew, are expected to take off to the ISS on October 30.
• Edward Lu, Daniel Burbank, Yuri Malenchenko and Boris Morukov expect to visit the station in September aboard a space shuttle during the STS 106 mission, after Zvezda docks with the ISS.
• Genadi Padalka and Nikolai Budarin, a contingency crew, sometimes referred to as the "Zero" crew, will be launched into orbit to manually dock the Zvezda module to the ISS in case the planned automatic rendezvous fails.

Zvezda Service Module

The STS 106 crew members had a chance to review the route on the exterior of Zvezda they expect to take during spacewalks planned for their mission. The astronauts and cosmonauts reviewed handrails that can help them to get to their destination on Zvezda's skin, as well as various antennas and targets that can slow them down.

The future spacewalkers were also expected to review possible repair scenarios, for example, deploying jammed latches of the solar arrays on the module.

As cosmonauts and astronauts walked through the maze of access platforms enveloping Zvezda, the engineers in Baikonur were literally putting finishing touches on the module. One of the last chores for the processing team this week was painting bilingual labels on the exterior and the interior of the module, which will help the future residents of the station. Some of the labels had to be sewn onto the fabric of the module insulation, while others were spray-painted through NASA-provided templates. As of Friday, 95 percent of the labels have been completed.

The biggest obstacle that could delay the Zvezda launch schedule is the Proton rocket. The crash last October of the booster pushed Zvezda's launch dateback from the beginning of the year.

The only major hardware element yet-to-be installed on the module is two large solar arrays, which will provide it with electricity. On May 15, Zvezda was removed from a vacuum chamber in Baikonur after successful tests.

During the next four weeks, Zvezda should go through its final cleaning, its tanks will be filled with water and its hatches closed. The processing teams will then weigh the spacecraft and determine its exact center of gravity.

The formal go-ahead for the Zvezda launch is expected around June 23 during the so-called General Design Review, GDR. This critical meeting will review the important issues of the mission:

• History of Zvezda testing
• Current status of the module
• The module's test results
• Readiness of the Baikonur Cosmodrome launch facilities
• Readiness of Mission Control in Korolev, near Moscow
• The Progress cargo ship's readiness (The launch of a Progress M 1 spacecraft carrying fuel to the ISS is scheduled for July 31.)
• Contingency- (Zero-) crew readiness (If Zvezda's automatic linkup with the ISS fails, the cosmonauts will have carry out a manual docking within two weeks.)
• NASA's assessment of the currently orbiting ISS Zarya and Unity modules

If no potential problems arise, the green light will be given to prep Zvezda for launch by fueling of its tanks with toxic propellants. The operation might take place around June 27 or 28.

The biggest obstacle that could delay the Zvezda launch schedule is the Proton rocket. The crash last October of the booster pushed Zvezda's launch date back from the beginning of the year. Although the rocket returned to service in February, the Russian Aviation and Space Agency (Rosaviacosmos) decided to use modified engines, known as Phase 2 engines, on the second and third stages of the booster that will carry Zvezda. The agency announced that two or three Protons with the modified engines carrying less important payloads should first complete successful flights before the Zvezda launch.

The first Proton launch carrying Phase 2 engines is scheduled for liftoff June 6, and it appears on track. The rocket will carry the Gorizont 45 communications satellite. The second rocket with modified engines is also ready. However, its payload, the Geyzer relay satellite for the Russian Ministry of Defense, which was expected to ride this booster into orbit, is not.

According to the sources within Russian space program, the Express A-3 communications satellite, previously scheduled for launch on June 8, might replace Geyzer as the Proton passenger. The Express launch then may take place around June 20 -- just in time to give Zvezda the go-ahead to launch. Rosaviacosmos plans yet another Proton shot on June 29. The rocket with older engines will carry a U.S. Sirius 1 communications satellite.

A formal decision on the Proton schedule is expected on May 31.