Planned orbital observatories would see satellites cross nearly all of their images.
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Planned satellite constellations may swamp future orbiting telescopes
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Beyond S/N ratio concerns associated with lots of short-duration exposures vs fewer long-duration ones, there are fixed costs in taking an exposure from a time perspective.
It takes time to sample the pixels from a sensor. You can try to go faster and speed up the process, but there's always a limit beyond which horrible things happen to the image produced. There are also a bunch of other overheads on every exposure unique to each system.
While reading out a sensor, the shutter typically must remain closed. For a CCD, the conversion process involves moving the charge around on the device, where an exposed object's accumulated charge is physically marched across the device's structure to one or more outputs where the voltage associated with the accumulated charge is then sampled into digital data. Leaving the shutter open results in trailed images as light falls on the sensor during the marching process, causing the charge to become smeared.
CMOS devices tend to have on-device active circuitry that are addressed and sampled without needing to slosh charge around, but leaving the shutter open while reading out would result in a non-uniform exposure time across the image.
IR devices tend to get even weirder in their operation and usage, but still have readout times that cannot be reduced past a certain point.
As a real-world example, the time to sample the complete image from the CCDs of Pan-STARRS' two Gigapixel cameras is about 7 seconds. Once converted, the digital pixel data can be more or less transferred within the shadow of the readout time (minus the last little chunk of pixels). The network is quite parallel and is largely not a bottleneck.
There's also another second and change of dead time per exposure associated with just physically moving the shutter blades. Other various smaller operations before and after the shutter actuation nibble a few tenths here and there, all of which add up.
(source: me)
Someone mentioned 600 1-second exposures vs a single 600-second exposure. In the former case, a 1-second exposure with about 10 seconds of operations that have to complete before the shutter can be opened again would be crippling from an efficiency perspective. The observatory would effectively spend all of its time doing nothing.
It takes time to sample the pixels from a sensor. You can try to go faster and speed up the process, but there's always a limit beyond which horrible things happen to the image produced. There are also a bunch of other overheads on every exposure unique to each system.
While reading out a sensor, the shutter typically must remain closed. For a CCD, the conversion process involves moving the charge around on the device, where an exposed object's accumulated charge is physically marched across the device's structure to one or more outputs where the voltage associated with the accumulated charge is then sampled into digital data. Leaving the shutter open results in trailed images as light falls on the sensor during the marching process, causing the charge to become smeared.
CMOS devices tend to have on-device active circuitry that are addressed and sampled without needing to slosh charge around, but leaving the shutter open while reading out would result in a non-uniform exposure time across the image.
IR devices tend to get even weirder in their operation and usage, but still have readout times that cannot be reduced past a certain point.
As a real-world example, the time to sample the complete image from the CCDs of Pan-STARRS' two Gigapixel cameras is about 7 seconds. Once converted, the digital pixel data can be more or less transferred within the shadow of the readout time (minus the last little chunk of pixels). The network is quite parallel and is largely not a bottleneck.
There's also another second and change of dead time per exposure associated with just physically moving the shutter blades. Other various smaller operations before and after the shutter actuation nibble a few tenths here and there, all of which add up.
(source: me)
Someone mentioned 600 1-second exposures vs a single 600-second exposure. In the former case, a 1-second exposure with about 10 seconds of operations that have to complete before the shutter can be opened again would be crippling from an efficiency perspective. The observatory would effectively spend all of its time doing nothing.
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