Of these, iron asteroids are relatively rare (about 8%). Carbonaceous asteroids account for about 75%, the overwhelming majority, and silicacaceous about 17%.

The Mitsuboshi Starframes approach to mining and refining has two key points, one in the asteroid belt for collection and preparation, and the other at L-4 for refining, alloying and actual fabrication. The facility at L-4 is the L-4 Plant of the Metals and Materials Division (generally known merely as The Yard), while the facility in the asteroid belt is officially Kachikachiyama Plant, Metals and Materials Division. (It is generally known as "Catch," which derives from the "kachi" part of its official name, which in turn was taken from a nursery song about Mt. Kachikachi.)

The catalyst is added to the polymer making up the bag, which contracts and hardens to a relatively hard material. This forms a relatively compact, semi-solid mass which can be easily handled, a refining system attached, and the container pumped full of carbon monoxide manufactured at Catch from asteroidal carbonaceous material. The refining system is then injected onto a trajectory which will carry it (usually) around the sun and back to a position close to L-4, using one of many trajectories (depending on the relative positions of the asteroid and the moon) with a flight duration between 3 and about 25 years. Iron-nickel asteroids are normally injected into a circumsolar orbit, but asteroids with major platinum-group content may be sent directly toward L-4. While coasting from the asteroid belt past the sun and back on a parabola to L-4, the robotic refining system optimizes the carbon monoxide and bag internal temperature (through the use of parabolic mirrors) while refining the ore.

Based on the Mond metal carbonyl reaction, the refining system utilizes stored, pressurized carbon monoxide and hydrogen to first exclusively form Ni(CO)4 in a pure CO atmosphere. After the reaction stabilizes, indicating that the majority of available nickel has been absorbed, the gaseous nickel compound is pumped into a solar-powered separator which recovers the CO, leaving extremely pure nickel powder for storage. The CO from the separator is mixed with stored hydrogen gas, and in this new environment Fe(CO)5 is exclusively formed. Again, the resulting Fe (iron) is captured and stored. The entire process is repeated once again, driven entirely by the high energy levels available close to the sun during the swing-around.

When the bag finally reaches the pick-up point near L-4, the carbon monoxide and hydrogen are recovered for use in the steel refining process, the residuals (carbon-based organics, non-ferrous metals such as platinum, stony matter) passed to various other processing systems, and the mined nickel and iron passed to the smelting facility. The refining system is refurbished and eventually sent back out to the asteroid belt for another load.

While the time from belt to L-4 can be decades, there is a continuous flow of asteroids "in the pipeline," so that the Mitsuboshi facility is in continuous operation. Excess asteroids which reach the L-4 facility are processed and stored in orbit, formed into massive radiation shields for the L-4 colony and the Mitsuboshi Starframes plant.

Each refining system, by the way, is fitted with three individually-powered beacons. They don't get lost, and while theft is certainly possible it is quite difficult to "hide your tracks" while radar is watching. The speeds of the asteroids are kept deliberately low and their mass is generally between 2000 and 6000 metric tons each to ensure that they can be safely caught by the waiting mining tugs at L-4 when they arrive.

• Carbon steel is by far the most commonly-used type of steel. Its properties depend primarily on the amount of carbon it contains, which is usually less than 1 percent.
• Alloy steel also contains some carbon, but its properties are mostly due to other chemical elements, each of which improves some properties. Manganese increases hardness, toughness, and wear resistance; nickel increases toughness, especially at extremely low temperatures; molybdenum increases hardness and corrosion resistance, and tungsten increases heat resistance. Other types of alloy steel use aluminum, chromium, copper, silicon, titanium, and vanadium.
• Stainless steel resists corrosion better than any other type of steel, and the primary alloying element is chromium, although many also contain nickel. All stainless steel contains at least 12 percent chromium, and some as high as 30 percent.

The Bolt, as it is generally known, was discovered on an asteroid which reached the Mitsuboshi Starframes L-4 Plant on May 14, 2284. While it appears to be a common hex-headed bolt, in fact there are a number of peculiarities about it, namely (1) it was electrocoated with a vanadium-based coating which prevented it from being dissolved during the refining process, and which (though easy enough to duplicate) has never been used by Man as far as anyone knows, (2) the size of the hexagonal head (face to face) cannot be expressed as an integer of any unit of length known to Man, likewise for the shaft diameter and the thread pitch, (3) the glyph (possibly a character, possibly a picture of some sort) on the top surface of the head is wholly unknown, (4) laser spectroscopy indicates that the bolt is made of a steel alloy which has never been used by Man, as far as anyone knows, although, again, it is not difficult to duplicate. It is generally assumed to be an alien artifact, although cries of clever forgery have also been heard. No other alien artifacts have been reported in the Solar asteroid belt.