03-17-2016, 04:45 PM
This is just the usual pahoated abusive rant when his errors are pointed out. It's sometimes amusing, but I suspect in most cases he simply doesn't understand the subject well enough to know when he's posting utter bollocks. As for DSPs (digital signal processors), I've been working with them for the last couple of decades at UKIRT, so I really don't know why he decided to bring that up.
Tink - both ground-based and space based optical/infrared telescopes use guide stars to remain pointing precisely at whatever object they're observing. For ground-based telescopes the guide signal is fed to a computer controlling the mount (i.e., the main part of the telescope that controls telescope slews and positioning) and a computer that controls the secondary mirror (the mirror at the top of the telescope). Although the mount drives tend to be very accurate in tracking a target, small errors build up and changes in the guide signal will be sent to the mount computer to correct the pointing. These errors build up slowly so it's easy for the whole telescope to make small corrections. The signal sent to the secondary is generally used to correct for aberrations caused by the atmosphere. The secondary mirror is much smaller than the primary and can therefore be moved much faster. Our system typically operates at 50-100 Hz, i.e., 50-100 corrections are made every second - it improves our delivered image quality by a factor of two compared to uncorrected observations.
For orbiting telescopes, the same principle applies, but they don't have to correct for atmospheric conditions, so the guide signals are used to make small corrections in the satellite's pointing. You might be interested in how the Hubble does this:
http://goo.gl/rlI17M
The Hubble uses "reaction wheels" to make these corrections. Essentially, it uses basic physics to keep pointing accurately and to slew to new targets. If the telescope needs to move, the computer/gyroscope system instructs the wheels to spin. As a wheel spins in one direction, Newton's 3rd law takes over and the telescope moves in the opposite direction. Hubble has four such wheels aligned in different directions so it can move in any direction.
Hope that helps.
Tink - both ground-based and space based optical/infrared telescopes use guide stars to remain pointing precisely at whatever object they're observing. For ground-based telescopes the guide signal is fed to a computer controlling the mount (i.e., the main part of the telescope that controls telescope slews and positioning) and a computer that controls the secondary mirror (the mirror at the top of the telescope). Although the mount drives tend to be very accurate in tracking a target, small errors build up and changes in the guide signal will be sent to the mount computer to correct the pointing. These errors build up slowly so it's easy for the whole telescope to make small corrections. The signal sent to the secondary is generally used to correct for aberrations caused by the atmosphere. The secondary mirror is much smaller than the primary and can therefore be moved much faster. Our system typically operates at 50-100 Hz, i.e., 50-100 corrections are made every second - it improves our delivered image quality by a factor of two compared to uncorrected observations.
For orbiting telescopes, the same principle applies, but they don't have to correct for atmospheric conditions, so the guide signals are used to make small corrections in the satellite's pointing. You might be interested in how the Hubble does this:
http://goo.gl/rlI17M
The Hubble uses "reaction wheels" to make these corrections. Essentially, it uses basic physics to keep pointing accurately and to slew to new targets. If the telescope needs to move, the computer/gyroscope system instructs the wheels to spin. As a wheel spins in one direction, Newton's 3rd law takes over and the telescope moves in the opposite direction. Hubble has four such wheels aligned in different directions so it can move in any direction.
Hope that helps.