 |
| Bryan Versteeg / Spacehabs.com |
In 2011 German designer Markus Kayser built a machine called a Solar Sinter. It concentrates sunlight via a 3 foot by 5 foot fresnel lens onto a box containing sand. The box moves a layer of sand in programmed patterns, allowing the 1600 degree Celsius beam to melt the sand in a controlled design. Once that pattern, or layer, is complete, another layer of sand is added and the process is repeated until a 3D object is created from fused sand.
A very similar machine could 3D print objects in orbit around the Earth or Moon or anywhere in space sufficient sunlight can be collected to melt stuff. It would have to be highly modified over Mr. Kayser’s design. For one thing, you don’t have the convenience of gravity holding down your bed of sand. Another thing … you don’t have sand.
Plastic grocery bags prefer this as their second career.
The fresnel lens will have to be replaced with mirrors simply because mirrors are cheaper, more rugged, and more flexible. The bed of the printer will have to be inside a centrifuge affair producing artificial gravity. Envision a large cylinder 80 feet in diameter and 300 feet long. It spins around its long axis. The printer head can travel the length of the cylinder or in a circular path inside the cylinder, or a flat path on a chord of some arc of the cylinder that is still far enough from the central axis of the cylinder to have enough “gravity” for the system to work. Flexible light pipes will take the sunlight collected by the mirrors at the center of one end of the cylinder and feed it to the printer head. A lens at the printer head will further control the acuity of the beam that hits the medium to be melted.
Ideally, the centrifuge portion would be attached to an asteroid placed in orbit at one of the Lagrange points L4 or L5 in the Earth-Moon gravity system. That would simplify spinning it without the worry of compensating for precession like a top or anything else that spins. It would be attached to the relatively massive asteroid with brackets that extend to the ends of the cylinder where bearings and electric motors provide smooth, stable rotation with a minimum of fuss and bother. The asteroid is acting like a good work bench, providing stabilizing mass to carry out projects in space.
If a suitable mass isn't available, the cylinder would simply be set spinning by tangential thrusters with any precession also controlled by swiveling thrusters at each end of the cylinder.
If a suitable mass isn't available, the cylinder would simply be set spinning by tangential thrusters with any precession also controlled by swiveling thrusters at each end of the cylinder.
 |
| Centrifugal 3D printer attached to asteroid. Drawing by Glen Hendrix. Click to Enlarge |
If we’re not talking about sand as a printing medium, what are we talking about? There are really only two practical sources for meltable medium to be used in our 3D printer. One is lunar regolith and the other is ground up asteroid. The asteroid option is cheaper if you discount the getting it there part. Lunar regolith would have to be transported from the Moon’s surface. Asteroid material is already in orbit. So far, two good reasons asteroid mining will complement our travel to space and our ability to stay there for any length of time.
Use those plastic grocery bags again. Save money. Save the world. Here’s how.
The disadvantages of using asteroid material are that it has to be excavated from the asteroid, sorted by material, and milled into a powder. This will call for the invention of robotic excavators that drill into the asteroid much as tunnel borers do their job on Earth. One of the first jobs to be done in mining an asteroid will be to make safe, comfortable housing for personnel during the project. The asteroid excavator can hollow out tunnels which will be outfitted for habitation safe from any stray cosmic rays.
 |
| Asteroid mining - courtesy NASA |
The Moon’s regolith, on the other hand, is already a fine powder. So fine, it was a problem on the lunar landing missions. It is also fairly uniform in composition. Although it would have to be transported from the surface of the Moon, the one sixth Earth gravity should make that a cheaper solution than bringing material from Earth, especially if water can be found on the Moon in sufficient quantity for use as fuel. A lot of regolith can be hauled into orbit for the cost of moving an asteroid.
 |
| 3D printed Lunar base - courtesy European Space Agency |
Let’s say we use another, more traditional method of 3D printing whereby a small, sticky glob of substance is deposited out of a nozzle and the nozzle moves on. Mixing our asteroid or lunar powder with water and some other adhering substance to hold everything together gives us a paste to use similar to what concrete printers use now, perhaps thicker to cut down on explosive evaporation of the paste as it comes out of the printer nozzle.
Imagine a large steel plate as the print bed. It could be a light gauge steel sheet with stiffeners on the bottom. Without gravity and its attendant forces, the print bed is just a place holder and starting point. The printing side is coated with Teflon for easy removal of the printed object. The edges of the plate are rounded to fit pulleys. Four pulleys with bearings, two on each side of the print bed and aligned with each other, roll continuously along the edges of the printer bed in the plus or minus “x” direction. From the centers of these pulleys extend upwards four shafts in the “y” axis direction. These shafts go through a stabilizer frame that holds everything together. This whole stabilizer frame moves in the plus or minus “y” direction. Mounted through this stabilizer frame is another shaft with the printer head and motor to drive that head in the plus or minus “z” direction. A large tank for mixing, storage, and pumping floats around, making sure there is no binding or interference with the umbilical delivering print medium to the printer head.
 |
| Free-floating 3D printer. Printing volume about 300' x 60' x 15'. Drawing by Glen Hendrix Click to Enlarge. |
This type of printer might be good for producing parts for habitats in orbit or insulating cladding for equipment or personnel tunnels in an asteroid. The cold of space will seep into the deepest parts of an asteroid and must be dealt with.
Whether we bring an asteroid into Earth’s orbit or not, I predict 3D printing of large objects in space will become a reality. It may or may not look and work like what I’ve described here, but they will be an integral part of a robotic fabrication milieu in outer space. Human workers will be at a premium. Machines will have to fill the gap.
The human race is on a course of infinite growth in a finite environment. The push into an infinite environment with infinite space, materials, and energy is inevitable and desirable if a global catastrophe is to be avoided. The sooner we start, the better chance we have of surviving our immature macro-societal tendencies.
Other articles you may enjoy:
Other articles you may enjoy:
No comments:
Post a Comment