Interesting Fact
March 2024
Interesting Fact: Manufacturing in Space
Space is a dangerous place for humans: Microgravity sets our fluids wandering and weakens muscles, radiation tears through DNA and the harsh vacuum outside is an ever-present threat.
But for materials that show incredible strength, transmit information with barely any loss, form enormous crystals or even grow into organs, the harshness of space can be the perfect construction zone.
And as the cost of spaceflight goes down, more of these materials may become cost-effective to make or study in space. And soon, more and more people might be carrying around objects built off the planet.
There are many aspects of space we can’t mimic on Earth,” says Dr. John Charles of NASA’s Johnson Space Center in Houston. “We can turn down air pressure in laboratory vacuum chambers and bombard samples with space-like radiation. But we can’t turn off gravity, or look down on Earth from above.”
Some experiments simply can’t be done on Earth. The space environment offers unique vacuum, temperature, pressure, radiation and gravity characteristics. Gravity of one-g is the natural environment for all terrestrial processes. And while higher g load levels can easily be produced and are common processing means, as in centrifugal separation, it is different with processing in a lower than one-g environment or weightlessness, because this condition can only be produced during free fall motions and is restricted to durations from fractions of seconds to about 30 seconds during the free fall trajectory flight in an airplane.
On earth only very few but remarkable manufacturing processes of very short processing cycle are able to use the lower than 1g level. An example is the free fall casting of lead shot, which was utilized centuries ago by pouring liquid lead through a screen atop the shot towers. Another example is the “atomizing” of metals and nonmetals to powders, tiny glass spheres and even hollow spheres called “microballoons”. However there is no process possible where a true equilibrium condition is reached until the free fall duration is extended to great length. This happens only in orbit where the satellite or complete manufacturing facility is consistently free falling around the earth.
The major importance of the sustained weightless environment lies in the fact that materials in liquid state become objects in their own right. From our terrestrial experience, liquids alone practically do not exist. They always need a container. The ever-present action of gravity causes buoyancy, separation and thermal convection during the interaction with other liquids, solids and gases, and is overshadowing and preventing many processes. Furthermore, on a macroscopic scale, molecular forces such as cohesion and adhesion do not play a large role, while in zero gravity they represent process controlling factors.
One example of the problems which arise during development in the weightless environment, was postulated to be the making of precise hollow spheres. It became obvious that the concentricity of the original gas pocket in the sphere is not self-adjusting because gas bubbles in a liquid in weightless environment stay where they are. It was found that application of acceleration will equalize the wall of the sphere. Acceleration of the wall mass generates a hydraulic pressure which causes the thicker portion to run into the thinner portion of the wall until the sphere has a uniform wall thickness. Radial acceleration can be caused by pulsing the environmental pressure which causes expansion and contraction of the sphere. Also, angular or translatory accelerations over two axis or planes will cause symmetric wall distribution. The spinning or translation can be induced during the electromagnetic container-less suspension of the material.
According to NASA’s In-Space Manufacturing (ISM) program, the ability to perform In-Space Manufacturing provides a solution towards sustainable, flexible missions (both in-transit and on-surface) through in-situ fabrication, repair, and recycling capabilities for critical systems, habitats, and mission logistics and maintenance. ISM is developing these capabilities by leveraging the highly disruptive technologies being developed terrestrially and adapting them for operations in the space environment.
According to Forbes magazine, innovators should not be limited to the tools they are given — or the planet they are on. On earth, we are limited to what we can engineer according to gravity, as well as the laws of nature and physics. But what can be manufactured in an environment that is not constricted in those ways?
Let your imagination take flight.
“We generally make things by subjecting them to a different environment,” said Andrew Rush, president and CEO of Made In Space, an in-space manufacturing company. “We make food by cooking it in fire, heating it up and causing chemical reactions. We make steel by heating things up at high temperature and maybe, depending on the steel, in a high-pressure environment. We can quench things; we can make things cold to make different materials or improve on those materials. Really, space-enabled materials are just another version of that, but instead of throwing something in a furnace and heating it to 1,000 degrees Fahrenheit [540 degrees Celsius] or something, we take it to space. In space, microgravity lets materials grow without encountering walls, and it allows them to mix evenly and hold together without traditional supports. And a nearby ultrahigh vacuum helps things form without impurities.”
Made in Space, Inc. has been delivering next-gen manufacturing capabilities in orbit to support exploration objectives and national security priorities. The company sent the first ceramic manufacturing facility to the International Space Station with the goal of demonstrating the ability to make turbine components with “higher strength and lower residual stress, due to a reduction in defects caused by gravity.” If successful, this effort will dramatically increase the commercial value of space manufacturing.
Manufacturing in microgravity and in manufacturing environments with unique gaseous compositions improves the manufacturing of metal alloys, for example, as elements can combine more consistently and efficiently to yield superior products with novel structures and properties.
Other manufacturing innovators envision a move to space as an excellent strategy for extending supply chain resiliency beyond current global boundaries. Bringing in a steady supply of electronic components and materials from earth to outer-space manufacturing plants is an opportunity to expand current footprints without the risk of climate-changing pollutants that are impacting earth. There’s also a great deal of interest in harnessing limitless solar power, as well as greater security and care using nuclear energy to further transform manufacturing in space.
And consider this:
When Galileo arrived at Jupiter in 1991, NASA scientists could not launch the spacecraft’s antenna completely, and several studies led them to conclude that cold welding had fused the antenna’s main mobile structure. What is cold welding?
If two pieces of the same type of metal touch in space they will permanently bond. This incredible fact is also known as “cold welding” and it happens because the atoms of two pieces of metal have no way of knowing they are separate. This doesn’t happen on Earth because of the air and water found between the pieces.
There are 3 kinds of bonds: covalent, ionic and metallic. In metallic bonds, metal atoms are kept close to each other so electrons can freely move between them. The attraction between these electrons and all of the metal nuclei keeps them held together. Metallic bonds are also responsible for the conductivity of metals. On earth, metals are almost always covered by a very thin film of oxide making metal-to-metal contact rare. In space there is no atmosphere to provide oxygen, which would renew the oxide coating. When the oxide wears off and metals are pressed together, there is true metal-to-metal contact. Since the metal surfaces are not microscopically smooth, the pressure is all taken out on a small number of microscopic high spots and the metals simply unite at these points.
You can try a similar effect in your own kitchen. Take a couple of ice cubes, let them warm up a bit, then press them together. They will weld into a single lump. Water already has all the oxygen in its molecule that it can accept, so it cannot oxidize further.
The effect has a lot of implications for spacecraft construction and the future of metal-based construction in vacuums.
Future human deep space exploration will be faced with the challenges of long mission endurance, as well as demand for robust surface infrastructure, increased solar power generation, and reliable high data rate communications, just to name a few. In-space manufacturing (ISM) can potentially address these challenges, and thus revolutionize human spaceflight.
Thanks and attribution:
https://www.nasa.gov/oem/inspacemanufacturing
https://www.sciencebyxanth.com/post/cold-welding-in-space
https://science.nasa.gov/science-news/science-at-nasa/2003/16jan_sts107/
Canaveral Society of Technical Societies, Space Congress Proceedings, Technology Today and Tomorrow,“Unique Manufacturing Processes in Space Environment”, 1970
https://www.space.com/40552-space-based-manufacturing-just-getting-started.html
