Corrective Optics Space Telescope Axial Replacement

Once it had been identified in 1990 that the primary mirror in the recently launched Hubble Space Telescope (HST) was defective due to it having been ground to the wrong shape, engineers at NASA came under immense pressure to fix the problem.

However, the loss of light to the large, out-of-focus halo severely reduced the usefulness of the telescope for faint objects or high-contrast imaging.

[2] When launched, the HST carried five scientific instruments: the Wide Field and Planetary Camera (WFPC), Goddard High Resolution Spectrograph (GHRS), High Speed Photometer (HSP), Faint Object Camera (FOC) and the Faint Object Spectrograph (FOS).

Since it was too difficult to bring the HST back to earth for repairs the engineers considered everything from replacing the telescope's secondary mirror by sending a spacewalking astronaut into the telescope's optical tube, to installing a circular shade around the opening of the tube, which would reduce the aperture and improving the focus by blocking out the outer regions of the primary mirror.

[3] It was eventually determined that with the HST still in orbit that they could replace the WFPC with the improved Wide Field and Planetary Camera 2 which would incorporate corrective optics.

[4] Once back in America he explained his idea, which was immediately taken up by other engineers who began to develop what by 1990 had become the Corrective Optics Space Telescope Axial Replacement, or COSTAR.

[5] 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, which was the least important of the four axial detectors.

[2] The final design which is the size of a telephone booth consisted of small correction mirrors radiating out horizontally out from an extendable tower.

[4] In January 1991 Ball Aerospace Corp. was selected by NASA as the prime contractor to undertake the entire development, production and verification of COSTAR, a process which took 26 months.