Monday, October 21, 2013

3D Printing … in space

Although 3D printing has existed for years, originating in the 1970s, only recently has it caught the imagination of the public. Numerous optimistic claims have been made about how 3D printing will change the face of manufacturing. One of the more optimistic beliefs regarding 3D printing is how it will change the nature and planning of space colonization, especially prospects for colonizing Mars and the Moon. While on some level such excitement is understandable, it is not appropriate to presume that the inherent problems with incorporating 3D printing into a colonization mission will be solved in the near future or even at all.

For example the most overplayed aspect of 3D printing in a colonization mission is its versatility. Proponents argue that the idea of rationing and scarcity are eliminated in the world of 3D printing. Unfortunately such hopes are rather confusing when compared against reality. The biggest concern for 3D printing is this perceived greatest strength. The versatility of 3D printing is drawn from a blank canvas, but that canvas requires more material than is needed for the particular design in question because what will be needed overall is not known.

Granted the additive process of 3D printing is more efficient at reducing waste than subtractive processes, but waste will exist unless all material is used. At the current stage of launch technology weight is the most important aspect of mission planning as it relates to cost and design. Additional material that will not be used for anything creates additional deadweight costs for the mission. Compare this deadweight cost against a properly planned mission with appropriate organization and logistics and costs should be reduced.

Another problem with costs associated with blank canvases is the volume constraints. Both cost and time exponentially increase to the third power relative to the size of the manufactured product. Basically if one wants to double the size of the product it will cost eight times to produce and take eight times as long to print. The cost and weight issue relative to the canvas also assumes 100% efficiency/reusability when producing an item otherwise the costs and weight required will increase further.

There has been some interest in foregoing the use of Earth-derived source materials and incorporating local surface regolith in the development and maintenance of a lunar or Martian colony.1 While this idea is promising there are still numerous elements that need to be considered before implementation and even if studied may never come to pass (note all of the scientific desires/predictions of last century that failed to culminate into reality even those that attained laboratory success). There is reason to hope though as the European Space Association is teaming with various private corporations to continue to study the necessary processes.

Regolith structure is the chief problem for its use as a source material for while one can create a binding ink that interacts with metallic oxides in the regolith to initiate a crystallization process, regolith on both the Moon and Mars (especially Mars) is heterogeneous with shards of glass, sand and other particles. Also most of the regolith is inert, thus it will have to be doped to form an anhydrous characteristic to increase efficiency.1 The size and surface area of regolith particles is also important, for particles that are too large or too small will create structural inefficiencies and weaknesses, especially if initial results from vacuum reticulation are to be believed.1 Therefore, some mechanism will have to be utilized to filter out particles of inappropriate size.

Somewhat ironically the advantage of the 3D printer in colonization is that of a safety tool versus an efficiency tool. When constructing and expanding an off-Earth colony almost all of the materials will be in-situ limiting the need for inter-planetary resources. Therefore, the additional material designated for use in a 3D printer originating from Earth will largely be utilized in quasi-emergency situations to manufacture semi-critical life support parts. The reason for this limited niche (at this time) is due to the accuracy, power and speed limitations of 3D printing. Common use items will not be created through 3D printing because it is simply easier to provide them during transit reducing costs. Emergency items will typically not be printed because of the time constraints associated with manufacture of the item, especially speed because the most important factor influencing manufacture time is the chemical properties of the utilized material, not the structure/design of the 3D printer.

Additional concerns that will hopefully be addressed in the future are how micro-gravity, inconsistent air pressure and greater temperature shifts will affect the manufactured products. Made In Space has conducted some small short-term tests, but the range of tests does not produce much practical information for long-term utility. Also the biggest current problem for 3D printing is the limited ability to manufacture an item derived from only a single source material, at the moment plastic is typically used. The principle reason combining materials is not applicable at the moment is most materials of significant structural difference (various metals, plastics, etc.) have melting temperatures hundreds to thousands of degrees apart creating structural problems in alloy creation. Some small advances have been made in regards to incorporating electronics, but this type of manufacturing is still in its initial prototype stage. In space colonization some of the other concerns with 3D printing like required CAD blueprints and prototyping are not significant, but it does limit the usefulness of 3D printing largely to the expected “unexpected”.

However, another significant concern for creating quasi-emergency parts is the inaccuracy of 3D printing. Most popular news stories about 3D printing fail to mention that currently 3D printing has a common error rate of about +/- 0.1 mm for various materials. For critical smaller life support parts such error rate may be too costly. Also this error rate may increase due to changes in post-build cooling temperature and micro-gravity environments, which will be more prevalent in colonization missions. Finally current 3D printing commonly produces products that have inferior tensile strength versus standard manufacturing. The additive methodology through the layered construction creates a laminate weakness due to incomplete bonding between the Z-axis and X and Y planes.

Overall at the moment the idea that a 3D printer can revolutionize space colonization should be more reserved. Part of the problem is the limitations of 3D printing, especially with the costs associated with the blank canvas materials that currently need to originate from Earth. The niche role of 3D printing also may need to be expanded to justify its inclusion in colonization missions. Additionally most 3D printer colonization enthusiasts forget that the rise of 3D printing has not occurred alone, but in consort with casting, laser cutters, mills, lathes and routers as an entire manufacturing process. Finally more than likely years of testing will need to be conducted in space type environments like on the International Space Station to gauge the effectiveness and problems with 3D printing in these environments, including situations of very low power. Therefore, 3D printing in space may require such a culmination of various operating and manufacturing elements versus just a single 8’ x 8’ rapid prototyping unit.
Citations -

1. Ceccanti, F, et Al. “3D printing technology for a moon outpost exploiting lunar soil.” 61st International Astronautical Congress. Prague. 2010. IAC-10-D3.3.5 1-9.

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