A U.S. and Russian shuttle crew is prepared to deliver the second large component of the new international space station to Earth orbit this week, showcasing NASA's six-year strategy for assembling the sprawling research outpost with robotics and multiple spacewalks.
The shuttle astronauts have trained for more than two years to link the Russian-built Zarya control module launched from Central Asia on Nov. 20 with the Unity docking node that awaits liftoff on the shuttle Endeavour.
Endeavour is to blast off at 3: 59 a.m., EST Thursday from Kennedy Space Center in Florida.
The 11-day mission will feature more than 30 hours of precise operations with Endeavour's robot arm and at least three seven-hour spacewalks. Those activities must be carefully choreographed with the orbital rendezvous activities that NASA astronauts and ground control teams in the United States and Russia learned to execute so flawlessly during a three-year series of docking flights to the Mir space station.
"This easily ranks up there in complexity with any shuttle mission ever flown," said NASA's Robert Castle, who as the lead flight director will orchestrate the activities from mission control in Houston. "At the same time, it's one of the simpler space station assembly missions. It's an indication of things to come."
At least three dozen shuttle assembly missions combined with nine by unmanned Russian rockets will be required through 2004 to loft the more than 1 million pounds of hardware for the new 356-by-290-foot orbital outpost. At least 162 spacewalks, two-thirds of them by U.S. astronauts, will be required to join and maintain the hardware. Unity cost $300 million to build and Zarya cost $240 million.
The construction effort began with the launching of Zarya, a 41-foot-long, 42,600-pound module designed to furnish propulsion, electrical power generation, guidance and communications during the earliest phases of assembly.
Late last week, ground control teams completed a largely successful orbital check of Zarya. A series of post-launch maneuvers raised the module's initial elliptical orbit to a circular orbit of just under 250 miles in preparation for the shuttle's arrival. One of six large power storage batteries aboard Zarya was not discharging properly, and electronic gear to remedy the difficulty may be added to Endeavour so the shuttle crew can attempt a repair.
Unity, which is stowed in Endeavour's cargo bay, is 33 feet long and weighs 25,350 pounds. It is a cylinder with a half-dozen docking ports, four mounted radially and one at each end.
Together, the two modules will serve as a structural bridge between future Russian, U.S., European and Japanese segments.
The Russian service module, whose launch has been delayed repeatedly by that country's economic difficulties, is due to link with Zarya at the end opposite the node sometime after mid-1999, furnishing the living quarters for the station's first occupants.
The challenge begins with Endeavour's liftoff. It must be accurately timed to occur within a 10-minute period to ensure the spacecraft with its heavy payload achieves the velocity and altitude to rendezvous with the new station, in this case the already orbiting Zarya.
With a successful launch, the Endeavour crew should reach Zarya on Saturday afternoon.
Prior to doing so, however, astronauts will use the shuttle's robot arm to lift the Unity module from the cargo bay and reposition it. The task requires remote commands to the arm to align the node 4 inches above the shuttle's docking mechanism and air lock. The same docking device was used by the Russians and Americans to join the shuttle to Mir.
When correctly aligned and still in the arm's grasp, the node will become the target for the shuttle's docking assembly. Endeavour's pilots will fire thrusters fore and aft of their spacecraft, forcing it to dock with the node.
At that point, the shuttle is ready for its encounter with Zarya.
With Robert Cabana, commander of the six-member crew, and pilot Rick Sturckow at the controls, Endeavour will approach Zarya from below, pausing at a distance of 600 feet. The shuttle will then maneuver to a point 350 feet in front of the module as both race around the Earth at five miles per second.
The maneuvering will continue until the shuttle reaches 250 feet above Zarya. Endeavour's crew will then slowly descend toward Zarya with flight engineer Nancy Currie at the controls of the robot arm.
With the two modules aligned and separated by 6 inches, Endeavour's thrusters will be fired to drive the complementary docking mechanisms together.
Then it will be up to shuttle spacewalkers Jerry Ross and Jim Newman. During the first spacewalk, the two men will make nearly 40 power and data connections between the modules. Both men will be equipped with two safety tethers. Additionally, they will wear back-mounted jet packs that could steer them back to the modules if the tethers snap.
During the second spacewalk, Ross and Newman will install two communications antennas on Unity. The next day, when Cabana leads his crew into the two station modules for the first time, the astronauts will complete communications tasks that will permit mission control in Houston to monitor conditions aboard the node and Zarya.
During the third excursion, Ross and Newman will climb the two modules, at this point rising 80 feet out of the shuttle's cargo bay, to secure a bag of hand tools that will be used by a future spacewalk team, and they will inspect the docking mechanism that awaits the arrival of the Russian service module.
Pub Date: 11/29/98