The NASA Kennedy Space Centre's Shuttle safety chief, Tommy Holloway, has warned staff to be on the alert for breaches in safety as the pace of orbiting International Space Station (ISS) components increases over the next few years.

The warning to be extra vigilant about quality control and safety in the "challenging times ahead" came as the highly successful STS 88/Endeavour mission to assemble the first components of the station ended on 16 December.

More than 36 Shuttle missions and 150h of spacewalks will be required to complete the assembly over five years, with up to four Space Station-related Shuttle missions planned for 1999 in addition to two non-ISS flights.

To emphasise the potential dangers, Holloway cites three "close calls" involving the Shuttle between November 1997 and September 1998, which, although "minor", had the potential for causing a disaster.

In November 1997, during a ferry flight atop a Boeing 747, the Shuttle Atlantis was riding on three bolts attached to the carrier aircraft, one of which had a washer missing. Potentially, the Atlantis could have broken loose, potentially causing the loss of the Shuttle and the 747.

The Endeavour launch of a Mir mission in June 1998 could have ended in a return to launch site abort or something more serious when, at T+20s, a pressure sensor in a main engine failed because a broken piece of test equipment had been left in a cooling pipe.

John Glenn's historic flight aboard Discovery in September 1998 could have been a different story had the 5kg drag chute door which came loose damaged one of the main engines when it fell off during the ignition sequence. An on-pad explosion could have happened if the engine's nozzle had been pierced.

The Space Shuttle launch dates revealed for 1999 include: STS93/Columbia to deploy the Chandra X-Ray Observatory, no earlier than 8 April; STS96/Discovery, ISS, 13 May; STS101/ Atlantis, ISS, 5 August; and STS99/Endeavour, Shuttle Radar Topography Mission, 16 September. Two further ISS missions are planned.

The STS 101 launch date must be in doubt because a two-month delay (to September) to the launch of the Russian Service Module is likely.

Eight Shuttle flights are manifested for 2000, including the third Hubble Space Telescople service mission in July - which is becoming urgent because two of the telescope's three gyros are not working - and nine flights each in 2001 and 2002.

Source: Flight International