Mechanical Engineering For The Stars: Atmospheric Challenges
Most astronomy is performed using ground based telescopes throughout the world. From the amateur astronomer using a small portable telescope, to the large optical telescope systems found at observatories, these optical instruments have a wide range of applications. There are also radio frequency telescopes, such as the ones located nearby at Stanford University.
One may easily access and adjust ground based telescopes, unlike space based telescopes. However, for optomechanical engineers, just because something is accessible doesn’t mean it’s easily adjustable.
One of the largest disadvantages to ground based telescopes is that the light (or signal) must pass through the atmosphere, which may degrade it. For this reason, astronomers place most large ground based telescopes in remotely located observatories with little light pollution. Astronomers favor mountain tops for their thinner atmospheres, because it results in less observational distortions. Although higher elevation locations aid in producing clearer observations, the temperature variations cause mis-alignment.
Before optomechanical engineers developed active optics, whenever there were shifts in temperature, astronomers had to adjust heavy observation mirrors using laborious and time consuming manual adjustments. Mechanical engineers perform extensive stress analysis, and vibration mode analysis, usually by finite element analysis (FEA), but the structures still suffer misalignment due to wind, vibration, temperature change, solar radiation, and other factors.
Active optics offers some relief by breaking up the large primary and secondary mirrors into a series of thinner and smaller mirror segments that resemble the shape of a honeycomb. Behind each mirror segment are actuators. Optomechanical engineers, with the help of electrical engineers and control systems engineers, design actuators and control systems, to compensate for misalignment. The computer software, developed by control systems engineers, collects the information, e.g. temperature, and sends out a series of commands to adjust the mirrors accordingly. The thinness of the mirrors paired with the sensory information gathered and adjusted by the actuators, provides observers with a more accurate method for obtaining images.
This new technology has been implemented into large telescopes built in the last decade, and is still evolving. Optomechanical engineers utilize better materials and methodologies, to obtain better results. Given the changes to active optics in the last decade, the saying, “the sky is the limit” takes on a whole new meaning.