NEW YORK A string of winter storms in North America has provoked execution of new tactics for improving airline flight safety in ground-icing conditions, giving regulatory and airline officials the chance to test the effectiveness and uncover the weaknesses of those plans.

WASHINGTON A competitive selection of either the Patriot multi-mode missile or Erint (Extended-Range Interceptor) to upgrade U. S. theater ballistic missile defenses is expected in 1993 after the Army determined that developing both weapons would be too expensive.

WASHINGTON An international X-ray astronomy satellite has discovered what appears to be a huge concentration of so-called dark matter—a finding that may mean the universe will stop expanding and eventually collapse upon itself. Observations by the Roentgen Satellite (Rosat) were the first to point to any area of the universe in which "dark," or unseen, matter seems to be in large enough proportions to visible matter to confirm the leading theory of the Big Bang.