Effect of TemperatureAt 90 degrees centigrade the fatigue susceptibility parameter is significantly higher than that at 25 degreesFibre strength decreases by 25% at 90 degrees compared to 25 degrees
It's an interesting idea, but the TRL for doing such a thing is far lower than that of just landing on Venus Aka, 1) short lifespan probes, or 2) bellows or phase-change balloon probes that can rise back up, or 3) high-temperature-operation probes; all are more mature than dangling 30km fibre optic cables on Venus, and give you a lot broader range of things you can do rather than just use it as a nephelometer / photometer. Concerning the fiber withstanding those temperatures (not just material properties, but optical properties as well, including run length between repeaters), do you have a reference?
http://www.electronics.dit.ie/staff/tfreir/ft220/ME%201.7%20Bending%20Loss%20&%20Fibre%20Stress%20and%20Reliability%20web%20version.pdfQuoteEffect of TemperatureAt 90 degrees centigrade the fatigue susceptibility parameter is significantly higher than that at 25 degreesFibre strength decreases by 25% at 90 degrees compared to 25 degreesIf that's happening at 90°C, then what's happening at 450-500°C? Googling for "heat resistant" silica optical fibers I find things like:http://global-sei.com/technology/tr/bn74/pdf/74-10.pdfApparently "high temperature" is considered to be 200°C - a far stretch from Venus surface conditions. You're presenting a rather large surface area to mass ratio, too, so you're amplifying any corrosion issues. As Mike Lepage pointed out, there is shear, although not as much as at the cloud level (I'm not sure what paper he's referring to as it loads to a dead link to me and there's not enough info in the URL to figure it out), so comparisons to space tethers and tethers laid out on the bottom of the ocean aren't really apt. At least there's (probably) little turbulence in the lower atmosphere. I admittedly don't follow the lower atmosphere as much as the the cloud decks (mainly the middle cloud), but if I recall correctly the layering goes:0-~10km: possibly somewhat convective~10-~20km: fairly stable~20-~30km: convective~30-~48.5km: quite stable... and then you're well in the cloud layers, which are convective to varying degrees. The middle cloud layer for example is surprisingly reminiscent of Earth's troposphere, with 20-30km convection cells (average size on Earth = 24km). The atmosphere again becomes quite stable above ~60km.Still, good to think outside the box
https://pure.strath.ac.uk/portal/files/18200068/Mechanical_strength_of_silica_fiber_splices_after_exposure_to_extreme_temperatures.pdfwas the reference I found which suggested things would be reasonable below 500c.
This also looks interestinghttp://suboptic.org/wp-content/uploads/fromkevin/program/TU1A.4%20Optical%20Fibre%20Fatigue%20And%20Submarine%20Networks%20Reliability%20-%20Why%20So%20Good.pdfAs does thishttp://www.escm.eu.org/docs/eccm13/posters/2619.pdfI was looking for data on the breaking strain of a Silica fibre to see what length a fibre could carry before snapping under its own weight.
The data on repeater distances came from a 2012 on a planned FO cable between UK and Japan reported in Popular Mechanics.
Keep in mind that atmospheric drag is the largest force on a satellite around the Earth below 1000Km and the space tether that the YES2 project tested for ESA was much more like a bare optical fibre than an electric cable.
This looked like an approach that could supply continuous data quite deep into the atmospheres of various bodies, rather than being confined to short dives deep into the atmosphere and longish recovery periods.