,TC Although the shuttle Discovery's current mission will take it as far north as Newfoundland over the next six days, Marylanders will not get a chance to see the spacecraft as it streaks over the state.
NASA officials said none of the orbiter's passes over the continental U.S. will occur when the shuttle is in sunlight and the ground below is in darkness -- conditions needed for ground observers to see the shuttle.
The shuttle was spotted all along the East Coast of the United States during the first eight minutes after its launch Thursday morning. That was because the spacecraft's main engines and booster rockets were burning, making it appear like a fast-moving star brighter than the planet Jupiter.
In orbit, those engines are shut down, and the spacecraft can be spotted only when it is reflecting sunlight to observers in darkness.
Discovery's mission to measure atmospheric chemistry and ozone depletion in the Northern Hemisphere is taking it much farther north and south than most shuttle flights -- as far as 57 degrees north and south latitudes. This orbit will carry it over such frosty places as southern Sweden, much of Canada, the former Soviet Union and below the southern tip of South America.
Most shuttle missions are launched to the southeast over the Atlantic and get no farther north than their launch point at Cape Canaveral, Fla., at 28.5 degrees north latitude. Baltimore, at 39.3 degrees north latitude, is too far north for residents to spot the shuttle during most missions. But this one would have been well within view -- if the timing of its orbits and sunlight had worked out.
The shuttle's carefully calibrated ozone studies are needed to help check the accuracy of data transmitted by unmanned satellites, whose instruments degrade over time in space.
Stratospheric ozone absorbs much of the destructive ultraviolet solar radiation that strikes Earth. Scientists say its thinning may lead to higher rates of human skin cancer, reduced crop yields and reduced production of ocean plankton, which forms the base of the ocean food chain.