Active surface
Encyclopedia
An active surface is a surface of a radio telescope
that is under active computer control of its shape.
Large (more than 10 m in diameter or length) radio telescopes always bend during operation, due to their enormous weight and the fact that even the strongest materials are not perfectly stiff. This bending, typically in the range of a few millimteres, does not affect 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.
The most notable examples of active surfaces are
Radio telescope
A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes...
that is under active computer control of its shape.
Large (more than 10 m in diameter or length) radio telescopes always bend during operation, due to their enormous weight and the fact that even the strongest materials are not perfectly stiff. This bending, typically in the range of a few millimteres, does not affect 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.
The most notable examples of active surfaces are
- Green Bank TelescopeGreen Bank TelescopeThe Robert C. Byrd Green Bank Telescope is the world's largest fully steerable radio telescope and the world's largest land-based movable structure. It is part of the National Radio Astronomy Observatory site at Green Bank, West Virginia, USA. The telescope honors the name of the late Senator...
- Large Millimeter TelescopeLarge Millimeter TelescopeThe Large Millimeter Telescope was inaugurated in Mexico on 22 November 2006. It is the world's largest and most sensitive single-aperture telescope in its frequency range, built for observing radio waves in the wave lengths from approximately 0.85 to 4 mm...
- Sardinia Radio TelescopeSardinia Radio TelescopeThe Sardinia Radio Telescope is a large, fully steerable radio telescope currently being completed near San Basilio, province of Cagliari in Sardinia, Italy. It is a collaboration among the Istituto di Radioastronomia di Bologna, the Cagliari Astronomy Observatory and the Arcetri Astrophysical...
- Noto Radio ObservatoryNoto Radio ObservatoryThe Noto VLBI Station is a radio observatory located on Sicily, southern Italy, outside of the city of Noto. The facility is operated by the Istituto di Radioastronomia di Bologna....