FDM® (Fused Deposition Modeling™) technology and ULTEM 9085 thermoplastic
Stratasys Direct Manufacturing (RedEye, Solid Concepts, and Harvest Technologies) Eden Prairie, MN
In 2006, a satellite mission called the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-1) was put into orbit. The purpose of the instrument was to collect global ionospheric and atmospheric data of temperature, moisture, and pressure, including hard-to-sample areas such as above oceans and polar regions. The project was led by the University Corporation for Atmospheric Research (UCAR), a consortium of more than 70 research universities in the US, and Meteorological Society of the Republic of China (Taiwan). Since its inception, the COSMIC-1 project has contributed to a wide range of scientific investigations and improvements in weather forecasting.
Due to COSMIC-1’s success, US agencies and Taiwan have been working on a follow-up project called FORMOSAT-7/COSMIC-2 that will launch six satellites into orbit in late 2016 and another six in 2018. NASA’s Jet Propulsion Laboratory (JPL) has developed satellite technology to capture a revolutionary amount of radio occultation data from Global Positioning System (GPS) and Russian GLONASS satellites that will benefit weather prediction models and research for years to come.
COSMIC-2 design and development began in 2011 at JPL. Critical components of the COSMIC-2 design are the actively steered, multi-beam, high-gain phased antenna arrays capable of receiving the radio occultation soundings from space. Traditionally, only large projects could afford custom antennas. COSMIC-2 was a medium-sized project that required 30 antennas, so minimizing manufacturing costs and assembly time was essential.
A standard antenna array support design is traditionally machined out of astroquartz, an advanced composite material certified for space. The team knew building custom antenna arrays out of astroquartz would be time-consuming and expensive because of overall manufacturing process costs (vacuum forming over a custom mold) and lack of adjustability (copper sheets are permanently glued between layers of astroquartz). The custom antenna design also contained complex geometries that would be difficult to machine and require multiple manufacturing, assembly, and secondary operations, causing launch delays. JPL turned to additive manufacturing technology to prototype and produce the antenna arrays.
The manufacturing technology chosen to build accurate, lightweight parts while maintaining the strength and load requirements for launch conditions was Stratasys’ Fused Deposition Modeling (FDM). FDM could produce this complete structure as a single, ready-for-assembly piece. This would enable quick production of several prototypes for functional testing and the flight models for final spacecraft integration all at a low cost. FDM can also build in ULTEM 9085, a high-strength, engineering-grade thermoplastic with excellent radio frequency and structural properties, high temperature and chemical resistance, and could be qualified for spaceflight.
Instead of purchasing an FDM machine to produce the parts internally, JPL turned to Stratasys Direct Manufacturing, which has the largest FDM capacity in the world, and project engineering experts who have experience with the aerospace industry and its requirements.
The antenna array support structures were optimized and patented for the FDM process. All shapes were designed with an “overhead angle” of 45 degrees at most to avoid using breakaway ULTEM support material during the build. JPL was also able to combine multiple components into one part, which minimized technician assembly and dimensions verification time and cost.
Although FDM ULTEM 9085 has been tested for in-flight components, it had never been used on the exterior of an aircraft, let alone in space. Therefore, in addition to standard functional testing, FDM ULTEM 9085 and the parts had to go through further testing in order to meet NASA class B/B1 flight hardware requirement, including susceptibility to UV radiation and atomic oxygen, and outgassing. Other testing included thermal properties tests; in particular, compatibility with aluminum panels. Aluminum has a slightly different coefficient of thermal expansion than non-glass-filled ULTEM. Vibration/acoustic loads standard to the launch rocket were tested, as well as compatibility with S13G high-emissivity protective white paint and associated primer.
Over 13 months, RedEye produced 30 antenna array structures for form, fit, and function testing. Throughout each design revision, RedEye’s project engineering team worked closely with JPL to process their STL files to ensure the parts met exact tolerances, and to minimize secondary operations. RedEye’s finishing department deburred the parts where needed, stamped each with an identification number, and included a material test coupon. They also reamed holes for fasteners that attach to the aluminum honeycomb panel and the small channels throughout the cones to the precise conducting wire diameter.
“Not only did NASA JPL save time and money by producing these antenna arrays with FDM, they validated the technology and material for the exterior of a spacecraft, paving the way for future flight projects,” said Joel Smith, strategic account manager for aerospace and defense at RedEye. “This is a great example of an innovative organization pushing 3D printing to the next level and changing the way things are designed.”
As of last year, the COSMIC-2 radio occultation antennas and FDM ULTEM 9085 were at NASA Technology Readiness Level 6 (TRL-6). RedEye was able to successfully enter the JPL Approved Supplier List, and delivered 30 complete antennas for final testing and integration. The FORMOSAT-7/COSMIC-2 mission will operate exterior, functional 3D printed parts in space for the first time in history.
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