I'm looking for a more economical and efficient method of making steel for my project Death Star Unlimited, a mega infrastructure orbiting Mars with a mass of 500,000,000 metric ton give or take 1%. Is there any good way to make steel in space within a time frame of a decade at most given immediate future tech? I will accept alternative to steel as long as it has similar or better properties and value for money. Currently my team is salvaging from the man-made debris encircling Earth but my engineer told me this is slow and the amount of steel recycled won't be promising.
Makre your own. The asteroid belt has about 3x1021kg of mass. 10% of the asteroid belt is made up of metallic-stype asteroids. Quite how much actual metal there is in there is hard to say, but lets go for 50%. So that's 1.5x1020kg. You need about .3% carbon in structural steel. About 75% of the belt are carbonaceous-type asteroids. These have a bulk carbon content of about 2%, so that's a good 4.5x1019kg of carbon right there... more than enough. You could probably get more than enough for your needs from dismantling phobos or deimos. There's an outside chance you'll get a decent amount of metal from them too, but I couldn't guarantee that.
Anyway, you've got the raw materials for 150 petatonnes of steel... not quite enough for a trillion of your "death stars", but enough to be getting on with. You've got more than enough solar power to keep you going, other elements in the asteroids you mine will provide for the rest of the material of your deathstar and for your mining fleet and there'll be enough ice out there to help run rockets and fusion reactors.
Oh, and if your engineer says this will be too slow, throw them out of an airlock and get someone capable of running a scale-up enterprise. Remind them that you are making a death star, after all. Parallelising your mining, refining and fabrication facilities should be straightfoward. Your material needs are sufficiently modest that you might even be able to get all you need without treading on any existing mining operations, if you felt the need to be at least minimally restrained or even surreptitious.