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Space Forum / Space Flight / November 2003Cathodic protection of spacecraft
Good news: inert metal compounds such as platinum coated titanium rods are sometimes used as the anodes. They do not corrode in marine environment, so they may survive in the aft end of the spacecraft. > Good news: inert metal compounds such as platinum coated > titanium rods are sometimes used as the anodes. They > do not corrode in marine environment, so they may > survive in the aft end of the spacecraft. ..Maybe I'm missing part of the conversation. Why is cathodic protection of spacecraft needed? Especially if you're using titanium or platinum, both of which are pretty corrosion resistant already. Mike Miller, Materials Engineer MM> ..Maybe I'm missing part of the conversation. Here is the entire message: The outer shell of atmospheric reentry spacecraft is made of expensive and frail materials. It may be possible to replace the expensive materials with cheap tungsten if we can protect the tungsten shell with cathodic protection. Description of the cathodic protection: http://www.teamworknet.com/resourcelibrary/educational/CathodicProtection The cathodic protection works well in a conductive environment, for example marine environment. When the spacecraft reenters the atmosphere, it is in contact with electrically conductive plasma. Inert metal compounds such as titanium rods coated with platinum are used as anodes in the marine environment and are very durable. It is not known if these platinum anodes would survive in the aft end of the spacecraft. Empty fuel tank trailing the spacecraft may be used as a cheap, sacrificial anode. MM> Why is cathodic protection of spacecraft needed? MM> Especially if you're using titanium or platinum, MM> both of which are pretty corrosion resistant already. Titanium nose cone will not survive without cooling. Platinum may survive, but it is expensive. I guess that tungsten with cathodic protection would be cheaper than platinum without the cathodic protection. > MM> ..Maybe I'm missing part of the conversation. > [quoted text clipped - 12 lines] > When the spacecraft reenters the atmosphere, > it is in contact with electrically conductive plasma. [...] > Titanium nose cone will not survive without cooling. > Platinum may survive, but it is expensive. > I guess that tungsten with cathodic protection > would be cheaper than platinum without the > cathodic protection. You are confusing the _ELECTROLYTIC CORROSIION_ of disimilar metals immersed in salt water with high-velocity plasma erosion; these two processes have _ABSOLUTELY NOTHING TO DO WITH EACH OTHER_. One is the result of chemistry, while the other is the purely thermo-physical result of ridiculously high temperature atoms striking a material at ridiculously high velocities. Please _do_ try to learn some basic physics and chemistry, so that you will not make quite so many utterly false analogies. -- Gordon D. Pusch perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;' > Titanium nose cone will not survive without cooling. > Platinum may survive, but it is expensive. > I guess that tungsten with cathodic protection > would be cheaper than platinum without the > cathodic protection. If you're going to use a tungsten heat shield (especially with platinum anodes), you can afford to coat the tungsten with a flash of iridium for passive oxidation protection. You don't need to get into sacrificial cathodic protection (requiring replacement) or impressed currents (electrical equipment that can break down). A few grams of iridium per square meter of tungsten will be affordable, even if you need exotic deposition processes to put it down. Figure 28 grams of iridium per square meter and the raw material cost is only around $400 for the iridium (per square meter.) Heck, you might end up beating out carbon-carbon heat shields on price for an iridium-plated tungsten heat shield. (I recommend tungsten-rhenium alloys, actually, for their low temperature toughness). Mike Miller, Materials Engineer MM> ..Maybe I'm missing part of the conversation. Here is the entire message: The outer shell of atmospheric reentry spacecraft is made of expensive and frail materials. It may be possible to replace the expensive materials with cheap tungsten if we can protect the tungsten shell with cathodic protection. Description of the cathodic protection: http://www.teamworknet.com/resourcelibrary/educational/CathodicProtection The cathodic protection works well in a conductive environment, for example marine environment. When the spacecraft reenters the atmosphere, it is in contact with electrically conductive plasma. Inert metal compounds such as titanium rods coated with platinum are used as anodes in the marine environment and are very durable. It is not known if these platinum anodes would survive in the aft end of the spacecraft. Empty fuel tank trailing the spacecraft may be used as a cheap, sacrificial anode. MM> Why is cathodic protection of spacecraft needed? MM> Especially if you're using titanium or platinum, MM> both of which are pretty corrosion resistant already. Titanium nose cone will not survive without cooling. Platinum may survive, but it is expensive. I guess that tungsten with cathodic protection would be cheaper than platinum without the cathodic protection. How many people read the subject as 'Catholic' protection of spacecraft? :-| :-)  SignatureSteve. > How many people read the subject as 'Catholic' protection of spacecraft? I thought they didn't believe in it. > How many people read the subject as 'Catholic' protection of spacecraft? Who's the patron saint of space travel? Peter >Who's the patron saint of space travel? > >Peter St. Christopher? :+) James >>Who's the patron saint of space travel? > > St. Christopher? AIUI, Christopher was "de-sainted" (or whatever you'd call it) in the 1960s, so probably not. I've found one reference to Joseph of Cupertino as a patron of astronauts & aviators in general, if that's any help... Signature-Andrew Gray shimgray@bigfoot.com |
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