In this research article, Iurii Bilubrov, a researcher the Centre for Collective Use of Scientific Equipment for National Academy of Sciences of Ukraine, takes a look at some of the factors that could have an effect on the development and research on the technology used for crystal production in space in the near future. In the article, we also propose certain new raw material sources for space additive manufacturing, such as mining asteroids or failed satellite parts to recycle. Below we provide an overview of these opportunities to extend the presence of AM, and humans, in future space and deep space missions.
For space research, the intermediate phases that require the temporary return of the in-space manufactured objects to Earth for studying result in a considerable increase in time and costs. In-situ research of substances in space (for instance, to determine optimum parameters of future space crystals production) demands an orbital laboratory with a complete set of equipment. Cost of instruments delivery increases in direct proportion to their mass. The limiting factor is the available volume in the launch vehicle payload fairing. There is a necessity to combine them into complexes with common uninterruptible power systems and common cooling systems (including, pipelines for circulation of cryo-coolers).
The most rational approach is to use new on-orbit opportunities. Extremely low values of residual pressure outside the spaceship remove several factors which limit the dimensions of vacuum chambers in the research instruments. Most bulky vacuum pumps and very thick walls are unnecessary for outside vacuum chambers. The increased dimensions may allow keeping in a vacuum a large number of samples prepared for measurements. It is a good basis to ensure continuity of the measurements without expenditures of time for replacement of the samples with concomitant operations (i.e. vacuuming, heating or cooling of instruments’ operational elements, etc).
A micro-g environment also gives specific opportunities to minimize the contact of the test substances with the instruments in the measurement bay. This is of the utmost importance for mid-IR region spectroscopy, in which selection of the material for windows is always compromised in terms of transmittance performance, ease of use, and price. The factors that limit the possibilities of utilizing the windows are as follows: low moisture resistance (NaCl, KBr, CsI), limited spectral range (MgO, α- Al2 O2, ZrO2 ), high toxicity (Thallium salt KRS‐5), non-transparency at high temperatures due to free thermal electrons (Si, Ge), extremely high cost (Diamond). Usage of composites, such as Germanium-coated KBr, addresses only part of the issues.
International space agencies are seriously considering the possibility of using rapid prototyping technologies in microgravity. The evolving projects for orbital and deep Space missions include 3D printers testing in orbit.
The National Aeronautics and Space Administration (NASA) is using material extrusion (FFF) technology in the microgravity environments of the International Space Station. The European Space Agency (ESA) has an analogous project called Additive Manufacturing Aiming Towards Zero Waste & Efficient Production of High-Tech Metal Products (AMAZE project).
The absence of vibrations from the rocket launch can simplify the construction of 3D printed structures, which in some cases are not even strong enough to support their own weight on Earth, yet are fully functional in microgravity. There are some parts of the spacecraft, which are very difficult to be compacted under rocket fairing. It is not always possible to decompose these structural elements in space. For instance, on the spaceship Galileo, a collapsible mirror did not open and communication with the spaceship was possible only with the help of a low-power reserve antenna. As a result, the ship control and data reception were considerably complicated due to the great distance from Earth.
There is enough time on Deep Space Missions to create irregular shaped parts (frame structure and parabolic antenna mirror) by additive manufacturing methods. The selection of raw materials for rapid prototyping technologies is very important and sets limits for future technological possibilities. The common titanium alloy Ti-6Al-4V has advantages due to its wide use in the space industry. However, instead of titanium powder as raw material, it may be more effective to use a brittle titanium hydride. It may in fact be possible to use hydrogen (from the fuel system, for example) to hydrogenate the broken titanium product for successful grinding.
Towards zero-waste production, a damaged titanium part from a satellite could be used as raw material to produce a 3D printed replacement, rather than having to wait for the arrival of the next supply ship. The large surface area of titanium hydride accelerates chemical reactions. This is good for the synthesis reaction of titanium nitride from TiH2 powder combustion in a nitrogen atmosphere. However, this creates problems during oxidation in the air. Therefore, the most successfully applied technology is dehydrogenation and sintering compacts in a vacuum. Powder sintered composite Ti-6Al-4V/LaB6, created for the nuclear industry using this technology, has reached the level of cast Ti-6Al-4V alloy. In general, the addition of 0.08 weight % boron in the weld seams and 3D printed details may be an effective hardening method, without loss of ductility of titanium alloys. The porosity issue can be solved by filling the pores with LaBxOy & TiB chemical compounds.
These compounds can also hinder the growth of grains within the alloy, which is important for casting alloys and powder metallurgy, as well as for welds and products created by additive manufacturing. Space 3D printing in a vacuum aboard a spaceship allows creating a metal product without an oxide film on the surface. This simplifies acoustic emission signal processing by reducing the amount of information coming from the sensors. The absence of overlay of signals from the oxide film cracking and the base metal destruction enhances the non-destructive testing of metal parts. Such opportunities for quality assurance are very important for titanium alloys and principled for aluminum alloys.
The full article is available here.