Lesson plan
Active surface
An active surface is a surface of a radio telescope that is under active computer control of its shape. Large radio telescopes (more than 10 m in diameter or length) always bend during operation, due to their enormous weight and the fact that even the strongest materials are not perfectly stiff. This bending, in the range of a few millimetres, does not affect low frequency operation much, but dramatically reduces the efficiency of the telescope at higher frequencies where the wavelengths are comparable to the distortion. Typically, the efficiency of a telescope drops appreciably when the deviation from the desired shape is more than 1/10 of the considered wavelength. An active surface uses numerous small actuators to move the surface panels with respect to the underlying frame, and thus maintain the correct shape. An active surface can try to compensate for many different types of errors. The first is gravity—this is simplest since previous measurements, or even a mathematical model, can be used to predict (and correct) any bending. More difficult is correction for wind and thermal errors, since these require measuring and correcting in real time.…
Article summary
An active surface is a surface of a radio telescope that is under active computer control of its shape. Large radio telescopes (more than 10 m in diameter or length) always bend during operation, due to their enormous weight and the fact that even the strongest materials are not perfectly stiff. This bending, in the range of a few millimetres, does not affect low frequency operation much, but dramatically reduces the efficiency of the telescope at higher frequencies where the wavelengths are comparable to the distortion. Typically, the efficiency of a telescope drops appreciably when the deviation from the desired shape is more than 1/10 of the considered wavelength. An active surface uses numerous small actuators to move the surface panels with respect to the underlying frame, and thus maintain the correct shape. An active surface can try to compensate for many different types of errors. The first is gravity—this is simplest since previous measurements, or even a mathematical model, can be used to predict (and correct) any bending. More difficult is correction for wind and thermal errors, since these require measuring and correcting in real time.…
Key claims
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
Bibliography
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Key claims and bibliography are generated from the same tracked claims and sources as the article page.