If you're building a space ship you have very tight tolerances and specifics needed for the alloying of the metals you use. The aluminum in aircraft is full of strange things that need to be removed for general use aluminum and definitely need to be removed for building new aircraft.
You're right that melting and re-casting aluminum is really cheap and efficient for beer cans, it's not so much the same for aerospace aluminum.
When it comes down to spaceships, the energy used to produce them is usually a very small portion of the total cost of the mission and we don't make very many of them – recycling isn't and shouldn't be a priority.
The Falcon 9 burns 110,000 liters of kerosene every launch, if it were made of carbon fiber, maybe it wouldn't matter how the structure was disposed.
[0] Aircraft grade aluminum alloy's composition roughly includes 5.6–6.1% zinc, 2.1–2.5% magnesium, 1.2–1.6% copper, and less than a half percent of silicon, iron, manganese, titanium, chromium, and other metals.
[1] Aluminum cans are typically 1% magnesium, 1% manganese, 0.4% iron, 0.2% silicon, and 0.15% copper.
There are a lot of metrics that determine the appropriate use of various grades of aircraft level alloys [2]. I guess from the outside some big considerations are how the metal reacts to temperature change and how well a metal cylinder can handle stress while staying light.
[0] https://en.wikipedia.org/wiki/7075_aluminium_alloy [1] http://www.madehow.com/Volume-2/Aluminum-Beverage-Can.html [2] https://en.wikipedia.org/wiki/Aluminium_alloy
Are we talking beer cans or rockets? Maybe they are the same after all :)
All spot on. There are lots of alloys used for lots of different things and economics and availability play their part too. When you're designing your airplane every slight detail matters.
"Dilution is the solution" was an unfortunate attitude on Earth. It will work for millions of years in space, and hydrocarbons are pretty abundant.
In recycling the fibers get shorter..
Could not that be re-applied to a different industry as far as re-using the carbon fiber? Body Armour for soldiers as the shorter fibers would be of use there?
The carbon fiber is then chopped and used as reinforcement in other material likes plastics. SGL Group, who supplies/partners in production with BMW, even uses reclaimed and production waste in it's production process for the new 7-series.
A more technical breakdown and state of the industry can be found here: http://www.compositesworld.com/articles/recycled-carbon-fibe...