ixf
Joined 8 years ago
Joined 8 years ago
Hearing protection always talks about attenuation in terms of dB(A) (A-weighting being a sensible thing to do when measuring perceived sound levels). 30dB(A) is a significant attenuation (logarithmic scale, don't forget). 35dB(A) is quite an improvement over 30dB(A).
For long-term use, ear plugs aren't great. But ear defenders can be had cheaply which will work well; I know of some people who use ear defenders atop in-ear active-noise-cancelling headphones as a double-whammy.
The correct answer is to work/sleep in quiet places, though, but I realise this is fast becoming a luxury.
Most telecoms applications use an ePRTC source which tends to be implemented as a GPS/GLONASS/Galileo redundant frequency source, plus a local rubidium source or cesium reference. High-end telecoms applications use a hydrogen maser.
You can't stuff that over an unmanaged network and get the performance you need. Hardware needs to support it hop-to-hop.
Case in point, this recent restoration of Morecambe and Wise by BBC R&D: http://www.bbc.co.uk/rd/blog/2017-12-morecambe-wise-video-fi...
They laser cut the film apart, then used X-ray microtomography to scan the film and some very clever software to unwarp layers from the 3D data produced by the X-ray microtomography process. Not exactly something we could've done 5 years ago.
The required precision for construction of telescopes is incredible, and doesn't translate to space well, especially once you start talking about apertures that even folded won't fit into even the largest Starship SpaceX is proposing.
Ground-based astronomy is here to stay and with good reason. SpaceX needs to avoid or minimise the harms to these users of the night sky.
There is another aspect of harm, too - the casual observer. The night sky is a precious resource and shared by all. Introducing huge constellations which in many parts of the world will be visible year-round (and in some quite heavily populated areas like northern Europe, even through the night at some times of year) is like building a huge mobile phone mast outside someone's window and expecting them not to complain, but on a much larger scale.
Light pollution is a huge issue, and satellites can pollute just as well (if not more effectively) than ground based sources - it needs to be an ecological consideration of any launch.