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More Details for 1999-05-13

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The International Space Station will await its first visitors of the year for at least one more week as Shuttle managers elected to move Discovery back to its hangar for repairs to its external fuel tank insulation caused by a recent hail storm.

The launch delay has no impact on ISS operations as flight controllers in Houston and Moscow have completed systems testing and attitude maneuvers to ensure the complex's overall health whenever Discovery shows up on the first logistics flight of the year. The shuttle is carrying logistics and supplies that will be used by the first crew that will live aboard the ISS beginning early next year.

In preparation for the shuttle's arrival, the ISS team conducted a dress rehearsal of the docking earlier this week by maneuvering the station from its present orientation - a slow spin with the Unity module pointing to Earth and Zarya toward space - to an orientation that is horizontal to Earth's surface, with Zarya pointed in the Station's direction of travel.

The Station remained in the horizontal orientation for about three hours while the Zarya module's guidance system was calibrated using the horizon of Earth as a point of reference. The station then was maneuvered to an orientation again perpendicular to Earth's surface, but without any spin and with Unity pointing to space and Zarya to Earth - the same orientation required for Discovery's docking.

Following the docking test, the station was placed back into the normal orientation with Unity pointed toward Earth and the spin rate verified at about three-tenths of a degree per second.

Meanwhile, Zvezda (Star) - the service module - is on its way to the launch site, riding on a train from Moscow to Kazakhstan. The departure from Moscow was mid afternoon Eastern time Wednesday and the trip takes about five days. Once at the Baikonur Cosmodrome launch site, testing on the module will be completed over the next several months prior to its launch this fall. Zvezda provides the living quarters, for the first crew scheduled to arrive on a Soyuz rocket early next year.

Flight controllers have finalized plans to changeout a suspect power distribution box of the Early Communications System on Unity that appears to be the culprit in preventing a return link from the module. Commanding through the system up to the station works through the low gain antenna, allowing controllers to use the system to send commands up to the station. But the return link still does not work and replacement hardware is loaded aboard Discovery to hopefully alleviate the problem. In the meantime, commanding through Russian ground stations and the Zarya module continue as the primary means of commanding to the ISS. The problem with the Unity system has not hampered operations of the Station and poses no problems for the docking with Discovery.

When Discovery arrives at the station, it will be carrying 3,600 pounds of supplies and hardware that will be stowed away on board for use by the first resident station crew.

The International Space Station is in an orbit with a high point of 252 statute miles and a low point of 238 statute miles, circling the Earth once approximately every 92 minutes. The Station has completed more than 2,719 orbits of Earth since its launch. As it passes overhead at dawn or dusk, the station is easily visible from the ground, and it will become even brighter once Discovery has docked. S