instead of the intended 1.00230.[60][61] The same number was also derived by analyzing the null corrector used by Perkin-Elmer to figure the mirror, as well as by analyzing interferograms obtained during ground testing of the mirror.[62]Because of the way the HST's instruments were designed, two different sets of correctors were required. The design of the Wide Field and Planetary Camera 2, already planned to replace the existing WF/PC, included relay mirrors to direct light onto the eight separate CCD chips making up its two cameras. An inverse error built into their surfaces could completely cancel the aberration of the primary. However, the other instruments lacked any intermediate surfaces that could be figured in this way, and so required an external correction device.[63]The Corrective Optics Space Telescope Axial Replacement (COSTAR) system was designed to correct the spherical aberration for light focused at the FOC, FOS, and GHRS. It consists of two mirrors in the light path with one ground to correct the aberration.[64] To fit the COSTAR system onto the telescope, one of the other instruments had to be removed, and astronomers selected the High Speed Photometer to be sacrificed.[63] By 2002 all of the original instruments requiring COSTAR had been replaced by instruments with their own corrective optics.[65] COSTAR was removed and returned to Earth in 2009 where it is exhibited at the National Air and Space Museum. The area previously used by COSTAR is now occupied by the Cosmic Origins Spectrograph.[edit] Servicing missions and new instruments[edit] Servicing Mission 1Astronauts Musgrave and Hoffman installing corrective optics during SM1Improvement in Hubble images after SM1Astronauts replacing gyroscopes during SM3AHubble on the payload bay just prior to release during SM3BMain article: STS-61The telescope had always been designed so that it could be regularly serviced, but after the problems with the mirror came to light, the first servicing mission assumed a much greater importance, as the astronauts would have to carry out extensive work on the telescope to install the corrective optics. The seven astronauts selected for the mission were trained intensively in the use of the hundred or more specialized tools that would be needed.[66] The Space Shuttle Endeavour mission STS-61 took place in December 1993, and involved installation of several instruments and other equipment over a total of 10 days.Most importantly, the High Speed Photometer was replaced with the COSTAR corrective optics package, and WFPC was replaced with the Wide Field and Planetary Camera 2 (WFPC2) with its internal optical correction system. In addition, the solar arrays and their drive electronics were replaced, as well as four of the gyroscopes used in the telescope pointing system, two electrical control units and other electrical components, and two magnetometers. The onboard computers were upgraded, and finally, the telescope's orbit was boosted, to compensate for the orbital decay from 3 years of drag in the tenuous upper atmosphere.[50]On January 13, 1994, NASA declared the mission a complete success and showed the first of many much sharper images.[67] At the time, the mission had been one of the most complex ever undertaken, involving five lengthy periods of extra-vehicular