Hed here HOUSTON As one group of Russian and American engineers breathe a sigh of relief after the Zvezda service module goes into orbit en route to the International Space Station, another will be gearing up for a tough challenge.
Its not enough to launch the 43-foot- (12.9-meter-) long service module; it has to dock with the parts of the International Space Station already there -- ideally this all happens robotically. No
astronauts.
| Zvezda Timetable and Contingencies |
| Click here for a timetable of launch and docking events designed to join the Zvezda module with the International Space Station. |
A two-man cosmonaut crew is waiting in the wings in case the robotic docking of Zvezda with the International Space Station fails. ? |
Ground controllers in Moscow will have 15 days after
Zvezda's launch aboard a Proton rocket to prepare the module for its rendezvous with the International Space Station (ISS). Among their tasks are extending the module's solar arrays, testing its docking system and performing engine burns to move it to the proper altitude.Controllers in Russia and at
Johnson Spaces Centers (JSC) ISS Mission Control Center have been going through the paces for some time now."Theres just a ton of activity going on. [Moscow engineers] are doing simulations every day in the month of June," said Mark Ferring, lead flight director at JSC. "We are doing a bunch of simulations ourselves."
Controllers in Houston are also practicing operation of the station after Russian controllers dock the two units together. Once docked, the modules computer systems must be linked together and engineers must electronically transfer control of the station from the Zarya module currently orbiting Earth to the newly added Zvezda.
Russian Mission Control in the hot seat
Before handing off to the U.S. side of the operation days later, controllers based near Moscow are in the hot seat to merge the two independent spacecraft -- Zvezda must join up with the Zarya and Unity modules, which already orbit Earth as one.
About two hours before
docking, Zvezdas computers will command it to make the first of two final engine burns to close in on the 50-foot- (15-meter-) long ISS. The thrusters also fire about 45 minutes before docking.Then the largely automated service module simply waits. Its solar arrays are pointed away from the ISS to prevent any propellant from damaging them.
"The ISS is the active vehicle during the final rendezvous and docking phase," Ferring said. "The Zvezda is basically sitting there waiting for something to come into contact with it."
At about 3 miles (5 kilometers) out, the KURS radar docking system aboard the ISS will begin communicating with Zarya to determine the closing rates, distance and the orientation of each craft.
The ISS has two KURS systems aboard. The first unit has showed some erratic behavior and will be saved as a back-up. Engineers have developed a software patch and will turn off unused electronic equipment that is suspected of causing the problem.
The KURS continues to exchange information as the ISS maneuvers to a position slightly above and about 220 yards (200 meters) from Zvezda.
Russian ground stations will be in range by now and will analyze the data sent by the vehicles. If all is well, controllers will command the KURS aboard the ISS to close in at about 6 feet (2 meters) per second and dock with Zvezda.
Once docked, the Zaryas solar arrays will begin tracking the sun again to provide power to the module.
More than one try is possible
Should the two craft be unable to dock on the first attempt, ground controllers will abort the effort and spend some time troubleshooting what went wrong.
Ferring said the ISS has enough propellant to make at least two docking attempts. He suspects there may be enough fuel for several more.
"All our calculations are worse-on-worse assumptions," he said. "Well know for sure after a couple of attempts if theres more fuel available.
'Crew Zero' standing by
If all attempts to dock the two craft fail, then a so-called Crew Zero swings into action about two weeks later.
A Soyuz with two cosmonauts aboard will lift off from the
Baikonur Cosmodrome in Kazakhstan to manually dock the ISS with Zvezda by using a Russian manual docking system."It will be possible to position the two space objects and provide the necessary parameters for docking," said veteran cosmonaut Yuri Malenchenko through a translator about the manual docking system.
The cosmonauts would dock the Soyuz to the rear of the Zvezda and spend two days setting up the docking system that uses a video feed and joystick system, much like a video game. They would then use the system to guide the ISS to the service module.
Malenchenko used the same system in 1994 while aboard Mir. A Progress supply vehicle failed to dock automatically and Malenchenko manually docked the craft. He said he is confident the cosmonauts are more than up to task for docking the spacecraft.
"Theyre well trained and have trained for a long time," he said. "We can be quite sure they will be able to perform the talks with quite [a] high probability of success."
As long as the cosmonauts are visiting the station, in effect the unofficial first crew, theyll spend a few weeks there after docking. The duo will prepare the station for the arrival of a Progress cargo ship and Space Shuttle Atlantis upcoming mission to outfit Zvezda.
Three become one
Once the two existing ISS pieces are joined with Zvezda, controllers at Johnson Space Center will begin the process of turning them into one spacecraft -- physically and electronically.
During the two to three days following docking, controllers are scheduled to pressurize the vestibule linking Zarya and Zvezda and check for leaks between the two craft. If leaks are detected, controllers will undo the latches and pull the craft together to reseat them.
Following the leak checks, about four days after docking, controllers will unify the computer systems of the three modules effectively turning them into a space station.
The next visitors will arrive aboard the shuttle Atlantis in September as the drive to finish outfitting the station for the first resident crews arrival in November continues.
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