Thermal expansion coefficient of a telescope tube prepared for observations on the Moon

Details Thermal expansion coefficient of a telescope tube prepared for observations on the Moon Thermal expansion coefficient of a telescope tube prepared for observations on the Moon

Apr 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004rnaoj...7....1m&link_type=abstract

Report of the National Astronomical Observatory of Japan (ISSN 0915-6321), Vol. 7, No. 1 - 2, p. 1 - 7 (2004)

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Moon, Telescopes

Scientific paper

To investigate lunar origin and evolution, ILOM (In-situ Lunar Orientation Measurement) project is proposed, which launched a polar lander equipped with an optical telescope for observations on the Moon. The telescope is to be set on a polar area of the Moon, where the only one side of the tube is exposed to the Sun. Hence there occurred a temperature difference between the side exposed to the Sun and the opposite side. The temperature difference may lead to the thermal distortion of the tube, which may cause a tilt of the optical axis of the telescope. Hence the development of a telescope tube of low thermal expansion is required. In this article, measurements of the thermal expansion coefficient β of a thermal model of the telescope tube were made to obtain β = (1.5±0.2)×10-6K-1, while the coefficient was obtained as (1~2)×10-7K-1 about three years ago. These results suggest that the tube changed its characteristics because of being kept in natural circumstance for three years. We also suggest that it is essential to study a cause of the change, e.g. humidity or others. However, this value of β is considered to satisfy a minimum condition of tilt of the optical axis, several hundred seconds. This article also proposes a method which realizes zero thermal distortion of a telescope tube without utilizing materials of zero thermal expansion, but by design.

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