The Principles of Astronomical Telescope Design by Jingquan Cheng

Author:Jingquan Cheng
Language: eng
Format: epub
Publisher: Springer New York, New York, NY

5.3 Space Telescope Projects

5.3.1 Hubble Space Telescope

The first major space telescope project was the Hubble Space Telescope (HST). The project, also named the Large Space Telescope (LST) and Space Telescope (ST), was proposed by the National Aeronautics and Space Administration (NASA) in the 1960s. In the beginning, the telescope size was not fixed. An early test tube structure made by Boeing Inc. had a 3 m aperture size. The 2.4 m aperture size was finally selected in 1975 as a result of cost analysis. At that time, the budget for a 3 m telescope was $334 M, for a 2.4 m one $273 M, and for a 1.8 m one $259 M. The space telescope plan was formally approved by the US Congress in 1977 with a total budget of $425 M to $475 M. The European Space Agency (ESA) also joined the project and shared 15% of its cost.

Along with the project development, the cost went up rapidly. By 1985, the HST budget reached $1.175B. The cost reached $1.6B when the telescope was ready for launch. The HST launch was delayed because of the space shuttle disaster in 1986. The HST was put into a low earth orbit in 1990 with a total cost of $2.35B. The HST operational cost is about $230 M per year (Petersen and Brandt, 1995).

The HST telescope optics was made by the Perkin-Elmer Company. The company won the contract with a very low bid of $95 M. However, when the optical components finished in 1984, the company submitted a claim of $300 M, a number far above the bid price. The company also claimed that the components reached a much better accuracy than the specification required.

However, it was just this optics which gave the telescope a very poor image quality after launch. The HST optics suffered from serious spherical aberrations. During the manufacture of the HST primary mirror, a combined primary and secondary mirror test was not performed. The primary mirror was tested simply using nulling lens optics. Unfortunately, the primary null-corrector was misplaced by a very small distance of 1.3 mm so that the outer edge of the primary mirror was over-polished. The solar panels of the HST also had thermal caused vibration problems.

Immediately after launching of the HST, a special panel was formed to investigate this spherical aberration problem. In 1993 special correction optics was added to the HST during the first shuttle service mission for compensating spherical aberrations. In this mission, new solar panels were used in the telescope. To date, three additional service missions in 1997, in 1999, and in 2002 were performed for the HST. During these missions, three guiding gyros, new focal instruments, and a cooler system were installed.

The HST is a 2.4 m space telescope with a honeycomb fused silica primary mirror of 829 kg. The mirror was formed by fusing together five mirror components, the upper and bottom plates, the inner and outer rings, and the honeycomb grid (Figure 2.18). It is light in weight and high in stiffness.

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