The International Space Station is a modular space station located in low Earth orbit. This feat of engineering was accomplished through collaboration between the National Aeronautics and Space Administration (NASA), Boeing, Space X, Northrup Grumman Corporation, Sierra Nevada Corporation, Roscosmos (Russia), the Japan Aerospace Exploration Agency, the European Space Agency, and the Canadian Space Agency. In addition to these prime contributors, many machine shops manufactured machined high-complexity components to build the ISS. Its purpose is to enable long-term exploration of space and provide benefits to people on Earth through research and technological developments [1]. Its basic anatomy is shown below.
ISS Structure & Components
Structurally, the backbone of the ISS is the system of trusses attaching solar arrays, radiators, cargo, and living quarters. This is a frame with connecting joints for structural cross members and mating interfaces for connecting the trusses to other elements of the ISS.
Shown above is a central truss segment manufactured as a test specimen for the ISS. Nine of these segments make up the 360-foot-long truss of the International Space Station that hold four solar arrays. These arrays are the primary power source of the ISS [3]. From a space station manufacturing perspective, this part was cut out of one large aluminum sheet with a water jet table. The pockets and holes were later bored out with a 3-axis CNC mill. Aerospace designers use pockets to achieve weight savings, and all holes are for assembly of the truss system in space. Since the holes must mate up with other components in space, it is crucial that these features are precisely located and then matched drilled.
The above-mentioned features are critical to the design of parts for space projects due to the extreme cost of moving materials to space. As an example – SpaceX Falcon 9 rockets, which are the current means of transporting materials up to and resupplying the ISS, cost a premium of $2,720 per kg of material for transport to the space station. Weight saving cutouts that do not sacrifice the structural integrity of a part can potentially save thousands of dollars.
Primus Aerospace has the capacity to make parts like this truss segment completely in-house. Our Omax 120x Abrasive Water Jet Cutting Machine has a work footprint of 21’8” x 17’3” which is more than large enough to cut out most structural frame outlines. Our 3 axis and 5 axis CNC mills are precise enough to maintain the extremely tight tolerances associated with mating surfaces.
Primus Aerospace manufactured various precision components that were used to assemble nodes and sub-assemblies of the International Space Station. Manufactured space components were composed of either high-grade plastic or metal. These components contributed to primary structures, secondary structures, robotic machinery, and life support systems. One particularly interesting part that was manufactured by Primus was for the mounting structure of the robonaut (seen above).
International Space Station Assembly
How were the international space station (ISS) components assembled while circling the Earth at 17,500 MPH? This engineering feat was accomplished with the station’s Mobile Servicing System. The MSS is comprised of a series of robotic arms that travel along the truss scaffolding of the International Space Station. The most notable of these arms, the Canadarm, is controlled remotely by astronauts in the Cupola Module. This is an observation deck that was specifically designed in a joint project with NASA, ESA, and Thales Alenia Space Italy to monitor and control the robotic arm [4]. The robotic arm itself has seven degrees of freedom, and all seven of its joints can rotate 540 degrees. The Canadarm can travel the entire length of the space station and is capable of large assembly tasks [5]. More intricate tasks are handled by the Special Purpose Dexterous Manipulator, or Dextre for short. This is a two-armed robot that was primarily designed for performing external maintenance on the International Space Station and is precise enough to use tools and manipulate cargo from visiting spacecrafts [6]. The vast system of robotic arms aboard the ISS makes the seemingly impossible task of extraterrestrial machine assembly possible.
The truss system provides the structure to which modular laboratories and nodes are attached to. Destiny is the primary United States lab for research and has 24 equipment rack interfaces for research and experiments. These interfaces house International Standard Payload Racks, modular units that contain an experiment or a set of lockers that each contain individual projects. These racks and lockers are usually purchased by governments or corporations for experimental purposes [4]. Some other research laboratories on the ISS are the European Columbus Laboratory and the Japanese Hope Laboratory.
Aside from laboratories, the ISS also consists of a series of nodes. These structures perform a variety of distinct functions. The Unity node connects the US and Russian sections of the ISS. Harmony connects the US, European, and Japanese laboratories and contains several ports for spaceship docking. Tranquility provides accommodation for the inhabitants of the ISS such as living space and workout equipment.
These nodes and laboratories are manufactured in the same way. The individual nodes are composed of machined space components that are then assembled into the final node. They are all cylindrical pressure vessels with linear axial and radial ring supports. This backbone is filled in with panels to form the basic structure of these compartments.
Shown above is the Destiny Laboratory. Here, you can clearly see the cylindrical structure and precision machined space panels. The structural rings and axial members were either forged or extruded aluminum that were later CNC machined with a large 3 axis CNC mill to meet tolerance. The panels have a swept profile, making them impossible to manufacture on a 3-axis machine. The x-shaped cutouts shown above were milled using a 5 axis CNC mill. Primus utilizes gantry driven 5 axis CNC machines to be able to machine complex parts like the panels of the Destiny module. 5 axis machines allow the part in question to be machined on multiple different faces from complex angles without the need for re-fixturing. This allows Primus to machine parts from multiple orientations without running the risk of incorrectly locating the part during re-fixturing. With this capability, we can hit complex geometries such as coaxial holes, parallel surfaces, and tight form tolerances with precision and reliability.
The ISS is a multinational effort to sustain human existence in space and its primary purpose is to positively contribute to the lives of people living on Earth. It does this through research. Because the lack of gravity in space contributes negatively to human bone and muscle mass, resistive exercise devices have been developed to keep astronauts in shape while aboard the space station. These same techniques have been used to treat people with osteoporosis domestically. In addition, protein crystals can be grown far more efficiently and to greater extents in the absence of gravity, enabling researchers on board the ISS to analyze protein microstructures to a greater degree than was ever possible on Earth. This can lead to breakthroughs in the development of new drugs to treat diseases such as muscular dystrophy and cancer [10]. Futuristic technologies, such as biomaterial 3D printing and cold welding of microscopic electronic devices, are also being developed in space at a rapid pace.
Biomaterial 3D printing has the potential to replace injured body parts at a fully customizable level. Bio-3D printing technology will revolutionize the medical field if done successfully. Cold welding allows for the perfect welding of two metals in contact with one another without sacrificing mechanical or electrical properties. This phenomenon is possible because the presence of a vacuum allows the electrons of two metal pieces in contact to flow freely between the two specimens without a layer of air or oxidized material hindering their motion. The free transport of electrons welds the two pieces together without any porosity, warping, or denaturing of either material. If this technique can be developed in space and used on Earth, it will further catalyze the influx of complex electrical devices and computers seen in the 21st century.
We at Primus are extremely proud to know that our aerospace manufacturing efforts are contributing to the International Space Station, and the development of humankind.
Sources
[1] http://www.pbs.org/spacestation/station/purpose.htm
[2] http://www.issnationallab.org/iss360/the-iss-engineering-feat-design/
[3] https://www.nasa.gov/multimedia/imagegallery/image_feature_444.html
[5] https://www.nasa.gov/mission_pages/station/structure/elements/subsystems.html
[6] https://ntrs.nasa.gov/api/citations/20170002575/downloads/20170002575.pdf
[7] https://eoportal.org/web/eoportal/satellite-missions/i/iss-mss
[9] https://commons.wikimedia.org/wiki/File:ISS_Destiny_Lab.jpg
[10] https://theconversation.com/five-key-findings-from-15-years-of-the-international-space-station-51540
