Winston Scott was to be the second mission specialist, but NASA headquarters wanted an astronomer with experience with the inertial upper stage (IUS) that would deploy the AXAF. Steven Hawley was the only available astronaut who met both these requirements. Hawley was a very senior astronaut who had been selected with NASA Astronaut Group 8 in 1978, and had helped deploy the Hubble Space Telescope in 1990 and service it in 1996. Collins was apprehensive that Hawley would attempt to command the mission. Her fears proved groundless; Hawley offered wisdom and advice but made no attempt to interfere with Collins's command of the mission. The STS-93 mission was not routine. The had to be used because its airlock was inside the crew compartment instead of the payload bay. This meant that it was the only orbiter that could accommodate the AXAF and the IUS. Initially scheduled for January 1999, the launch date was delayed due to an investigation of a failed USAF Titan IV launch using the IUS and problems that were discovered during testing of the AXAF (now named the Chandra X-ray Observatory). This pushed the launch date back to April and then to July, when Columbia was scheduled for fifteen months' maintenance in Palmdale, California. Because the AXAF weighed and the IUS weighed , this was the heaviest payload ever launched by the Space Shuttle. To save weight, the crew was reduced to five members, and consumables to those needed for a five-day mission. This made it the shortest scheduled mission since 1990. Two of the five pairs of tanks holding hydrogen and oxygen for the fuel cells were removed, as was the robotic arm, so any problems had to be resolved in the payload bay, as the Chandra could not be retrieved. The large mass affected Columbias center of gravity, rendering a landing after an emergency abort extremely hazardous. The launch day of 20 July 1999, coincided with the thirtieth anniversary of the Apollo 11 Moon landing mission, so former astronauts Neil Armstrong, Buzz Aldrin and Michael Collins were at KSC to watch the launch. Observers also included Hillary Clinton and the United States women's national soccer team, who had recently won the 1999 FIFA Women's World Cup. The launch countdown proceeded smoothly until Columbias hazardous gas detection system highlighted an unacceptably high hydrogen concentration in the aft engine compartment, and the countdown was halted less than