NASA explores manufacturing parts in space

Materials World magazine
,
30 May 2019

NASA is exploring the feasibility of producing items in orbit, with a series of projects that could rapidly accelerate the capabilities of manufacturing methods.

’Some day’ technologies stand a greater chance of reaching coveted trusted status when adopted by major industry players, particularly when they are used in cutting-edge concept projects. For instance, while space exploration may seem a fantastical and tenuous field of research, it presents many opportunities to refine technologies to meet extreme demands in other industries, such as the adverse and isolated environments of polar research and very long journeys in shipping.

The Made in Space event held in Coventry, UK, on 6-7 May 2019, had a clear focus on the work required to extend the success of additive manufacturing (AM). To a degree, AM is still viewed by some as a solution looking for a problem, but the diverse range of projects presented demonstrated a focus on going beyond the broad or even trivial uses of modern day AM to bring it to all industries that use manufacturing. It is commonly used to print precise or bespoke parts, but this process would need to undergo significant refinement if it were to be used for space missions.

Several key trends underpinned the space event, cropping up as recurring themes across presentations – the need for better accuracy and flexibility with more materials, to enable inspection and maintenance of 3D-printed parts, and to establish quality standards and regulations to propel the use of AM towards high-risk, high-cost applications.

‘It is the reliability we’re going to need, especially when we go to deep space with manned spaceflight,’ said NASA Technical Fellow for Materials, Rick Edwards. ‘The big thing for additive is the replacement parts as you are not going to have the ability to make replacement parts, so reliability is most important.

‘AM is not mature enough for the high life-performance of space requirements that we need for our safety-critical structures, so we need a framework to integrate our design, from design to production and quality assurance.’ Edwards confirmed that NASA is well into preparations for setting standards for powder bed fusion of metal, but that they are extending this to encompass other materials including polymers and ceramics. Also, NASA is in discussions with the ESA to set consistent international standards for AM.

Airbus Materials and Process Engineer, Ernest Allswell, said, ‘A lot of our projects are funded by the ESA […] but at the moment there is no standard for AM in the space industry in Europe.

‘The ESA is drafting a standard for metallic powder bed fusion and in the future it is hoped that more standards will become available. It will be important to standardise the materials and processes between end-users like ourselves and machine manufacturers.’

Setting it up

Several years ago, NASA started work on the Evolveable Mars Campaign, a study to prime the organisation for the needs of deep space exploration, specifically with the intention of going to Mars. Although the campaign was later de-funded, a dedicated team continued to assess the requirements of such a mission and to what extent manufacturing items in space would improve projects.

In-space manufacturing could bring a plethora of benefits, including financial, logistical and societal. Firstly, let’s look at the real-world successes. NASA Deputy Manager of the Science and Mission Systems Office at the Marshall Space Flight Center, Dr Raymond Clinton, gave an overview of the trials run onboard the International Space Station (ISS), and how these have helped steer researcher projects.

Clinton explained that the ISS is required to store an exorbitant amount of spare parts and supplies – on the station and on Earth – but the study revealed that up to 95% of these parts have never been and are unlikely to be used. This represents thousands of kilograms of dormant, but essential, weight. However, for such a sensitive environment as living in orbit, chances cannot be taken on the need for critical parts.

Supply trips to the ISS are relatively frequent and it has fast abort-to-Earth and fix-and-fly capabilities. ‘So, if something breaks, we can bring it down, which we have, fix it and fly it again,’ Clinton said. ‘Now for a deep space mission, you don’t have the abort-to-Earth capability, you don’t have a periodic resupply and you don’t have a fix-and-fly capability. So clearly, the space station maintenance logistics model is not something that’s going to work for deep space exploration.’

The ISS model performs well, but this can still be improved upon through smarter logistics. ‘In-space manufacturing can address some of the issues that we find here,’ Clinton added.

‘It can provide spares on-demand, it can recycle materials and reduce the mass that is required. It can also respond to the flexibility to unanticipated circumstances, thereby contributing to addressing astronauts’ safety by having adequate spares onboard’.

Getting AM to work

AM is ideal for printing drop-in replacement parts, and the team on the ISS used a commercial 3D printer to successfully print 21 parts in November 2014, which were returned to Earth for destructive and non-destructive testing. Clinton explained how the tensile and flexure of flight articles were stronger than on-ground ones, while compression was the opposite. They attributed this to the Z-cal difference [z axis calibration] between the tip-to-tray.

A second run with an optimised Z-cal difference showed improved tensile results. After aged feedstock was tested, the second-generation AM facility was made to help reduce crew time and increase the range of materials being used, which was originally only ABS high-density polyethylene.

In trial two, the crew printed a range of practical items, urine funnels and medical splints, as well as technical tools including an air sampling adapter, a radiation shield for the radiation monitors, a tow hitch for the autonomous spheres that fly around the space station and an antenna feed horn. Clinton said, ‘The next time we get an opportunity to print on space station, we’re going to characterise the ABS material’. The team is also developing better fabrication tools and custom inks.

Recycling and repair

US tech company Tethers Unlimited won several tenders to work on various NASA AM trials, such as developing a machine to recycle Ultem 9085 and use it to print test items. Initial tests were not successful enough to warrant recycling material with a fabricator on the current mission, but Clinton said tests are continuing on making this a viable option.

‘We will be using a recycled feedstock so we can swap out the cartridge for [this] and print some recycled material that was ground-based on orbit, bring them back and take a look at them as well as dissecting this problem and understanding what we need to do to improve the performance next time,’ he said.

Tethers Unlimited also worked on the second stage of the refabricator system, Erasmus. ‘It expanded on the refabricator by applying a dry heat steriliser because a fair amount of the waste and trash on the space station comes from food and medical products. So we’re going to take advantage of the trash that is produced to turn it into usable feedstock, again, lowering the mass take on deep space missions,’ Clinton said.

As the majority of waste is from packing material, NASA contracted companies Tethers Unlimited and Cornerstone to help turn it into thermal feedstock. ‘Tethers took the problem and sort of turned it inside out,’ Clinton said. ‘Instead of taking what you got from packaging material, they said we’re going to create a new packaging material from feedstock we know we can recycle, so they did. They created the [protective foam for equipment in trunks]. And you can tailor the vibration characteristics, the mechanical properties for whatever you need to provide for your particular payload.

‘Cornerstone took a different approach. They are adding a reversible thermal suck copolymer to the materials used in packing, and they added the copolymer and have been able to control the viscosity to the point that they can print with it.’

The projects encompass a whole series of manufacturing tools for space missions, that include wire arc technology, a CNC machine and mill, Ultratec to bond thin films together, and a refabricator wire feed that has inductive heater to soften wire, finish it and consolidate the part using a low-powered laser.

Electrical problems

Clinton said the most common problem in space is failed electronics, so NASA started working with its Ames Research Centre, which specialises in robotics and printed electronics.

During this R&D they developed several sensors in-house, including the composite pressure temperature sensor, a number of gas sensors for environmental control and life support systems – including ammonia, carbon dioxide, carbon monoxide, hydrogen and humidity – and patented several inks. One was Inconel 718, in partnership with Oakridge.

Additionally, they worked on aluminium and aluminium-tin for random access memory sensors and batteries, alongside other technologies such as a power source coupled with the sensors to have a self-contained unit, and flexible electronics. These are intended to help crew health monitoring as the astronauts could wear the body sensors at all times.

In terms of printing, the next phase of development will be enabling the refabricator to print with a wider range of materials, including aerospace-grade metallics to realise these products.

Several tipping point projects are currently ongoing to make in-space robotic manufacturing and assembly – IRMA – a reality. For two years NASA has been working on building major equipment in orbit, based on starting with gossamer structures. This would remove the need for launchers and packing equipment, and is especially useful for satellite maintenance. Two projects are running in parallel. For the first they printed an 850mm composite, a copolymer blend, its PEI polyetherilid and polycarbonate in a thermal vac system.

The second was to explore the ability to service satellites, manage communications and reconfigure
RF antennae. Under this work, NASA could build a solar array in space with no need for rocket launcher systems, saving significant equipment and energy costs. Clinton said onground risk reduction tests have so far proven successful for good results in space.

Inspection and CT scanning

According to Clinton, no matter if a part is plastic, ceramic, or metal, ‘we want it to be highly autonomous, we also want it to be in line with inspection and quality control because, as everybody knows, we don’t have NDE [non-destructive examination] equipment on the space station’.

‘We have to have some way to validate the parts that we’re going to create, particularly on long-range deep space missions. We have to know those parts were built correctly. NDE is still in its infancy for certifying parts on space station. Certified parts on the ground – well it is a huge problem for the entire community. Now imagine taking that problem and putting it on a space station. We face additional challenges on how we are going to certify the quality of the parts that we prep off planet surface.’

NASA is currently working on phase one of a solution to inspection and examination limitations with results to be announced later this year.