The NASA delays are due primarily to problems completing software development and final assembly of the complex U.S. laboratory module, Destiny, the scientific heart of the orbital outpost.
With the December flight now expected toward the end of January, only two shuttle missions will remain on the books for 1999: A mission to map Earth's surface using high-resolution radar and a high-profile flight to service the Hubble Space Telescope.
NASA originally intended to launch the Shuttle Radar Thematic Mapper - SRTM - mission aboard shuttle Endeavour on September 16. The shuttle Discovery then would be launched October 14 to service the Hubble Space Telescope.
But a short circuit during the shuttle Columbia's launch in July has thrown a wrench into the near-term shuttle schedule as engineers carry out time-consuming inspections to make sure Endeavour and Discovery are safe to launch.
The work will delay the SRTM mission - flight STS-99 - from September 16 to at least October 10, according to the latest internal NASA manifest. Under that scenario, sources say, the Hubble repair mission would be delayed from October 14 to early November.
But NASA managers are assessing a second option that calls for launching Discovery on its original October 14 launch date. Under that scenario, the SRTM mission would slip to around November 21, after the potentially hazardous Leonids meteor shower earlier in the month.
It's not yet known which option ultimately will be approved, but a decision is expected by the end of the week.
All of the launch options under discussion show mission STS-101, also known as space station assembly flight 2A.2, slipping from December 2 to January 22. Station flight 3A (STS-92), a mission to deliver an integrated truss segment, gyroscopes and other equipment, is expected to slip from February 24 to around March 23.
The station's first permanent crew - commander Bill Shepherd, Yuri Gidzenko and Sergei Krikalev - had been scheduled for launch atop a Soyuz rocket on March 12. That flight now is expected to slip into early April.
Launch of the station's initial set of solar arrays, the major element of assembly flight 4A (STS-97), is expected to slip from March 23 to around April 27. Finally, the U.S. lab module, the major element of flight 5A (STS-98) is expected to be delayed from April 20 to around May 25. Downstream flights will slip four to six weeks accordingly.
The truss, solar arrays and other elements of flihts 3A and 4A generally are on schedule. But NASA wants to carry out end-to-end tests of all the initial station components to make sure the elements will work together in orbit as planned.
The Destiny lab module is several weeks behind schedule, primarily because of problems completing software development and testing. Assembly flights 3A and 4A will be delayed to permit integrated testing with the lab module when it's finally ready for such tests.
By William Harwood