Have you ever wondered how one tiny node can affect a person’s life in orbit hundreds of kilometers away from the Earth? When we hear about space technology, we immediately think of giant rockets, rovers, or state-of-the-art orbital stations. However, behind each of these grandiose projects are thousands of details that seem quite mundane at first glance.
It would seem that an ordinary bearing is such an ordinary part that we rarely pay attention to it in our daily lives. However, when it comes to the complex mechanisms of a spacecraft or an astronaut’s spacesuit, the success of the entire mission can depend on the quality of these small rotating elements. After all, every detail, even the smallest, is crucial in a harsh vacuum and at extreme temperature fluctuations. Seemingly simple and invisible parts such as bearings are the basis of mobility for astronauts, and their service life is critical to human safety in orbit. That’s why even the simplest assembly turns into a complex engineering task that requires the teamwork of numerous specialists. In this article, we’ll look at the extensive and invisible work that engineers need to do to design bearings for spacesuits.
The key to developing innovations
Previously, spacesuits used mostly stainless steel bearings. A prototype bearing from the first iterations of the Apollo A6L space suit could even be bought at auction. These bearings were too bulky, which made it difficult for the astronauts to move in the limited space of the ship. Then, they decided to develop special prototypes that would meet the mission requirements. The option of using stainless steel had its advantages; it improved the astronauts’ mobility in the area of rigid tissue under pressure and served as reliable attachment points for safety connections. However, several problems arose.
Firstly, steel is heavier, which is crucial in space flights: every extra kilogram increases fuel consumption and complicates the life support system. Secondly, the placement of the safety joints caused uneven loading on the bearing housings, which increased internal stresses and wear on the components. All of this made it difficult to predict the durability and behavior of parts during operation.
The challenge of improving bearings in space environments is not only their ability to withstand extreme temperatures and lack of gravity but also the need to take chemical factors into account. According to the results of flammability tests, titanium in an environment with pure oxygen and high pressure did not cause ignition*, but under certain conditions, increased wear of parts was observed. This pointed to the need for additional engineering solutions, such as changing coatings, special lubricants, and closer control of the surfaces that interact with each other.
*Two main conditions are required for a metal to start “burning”: a sufficiently high temperature and access to oxygen. When the metal is heated to a certain temperature, an oxidation reaction begins: the metal actively reacts with oxygen and releases heat and light, which is the combustion process.
However, these risks do not diminish the benefits of titanium bearings. According to optimization studies (ICES-2017-242), this modernization can significantly reduce the weight of space equipment and spacesuits, saving about 10.4 kg (23 lb) in each suit without losing functionality.
Applications and operating conditions
In the process of developing new bearings, the main focus was on the Z series suits (Z1 and Z2), mainly for the lower part of the suit – in particular, for pelvic bearing models, as well as for the bearing in the waist area. They became the basis for tests and developments to improve the mobility, modularity, and efficiency of life support systems.
However, these models were not developed as final versions but served as prototypes for researching promising solutions. Further, NASA’s development program focused on xEMU, a more “complete” version that is to become a key element of the Artemis missions. It was in xEMU that many of the innovations incorporated in the Z-series were realized, including ideas for increased flexibility and improved ergonomics. The technology and test data from the Z1 and Z2 became the foundation for optimizing the new bearings at xEMU and were later passed on to Axiom Space and Collins Aerospace.
When walking on the surface of another planet or in outer space, mechanisms rotate cyclically with every movement. Previous versions of the bearings showed increased wear, but at the same time became a good “launching pad” for the creation of new, more wear-resistant parts. At the same time, it was important to preserve the basic geometric and functional parameters for compatibility with existing spacesuit components.
To determine the ultimate load levels, the researchers used Finite Element Analysis (FEA*) in combination with physical testing. In the first stage (described in ICES-2016-60), three different ball diameters and groove shapes in the titanium cages were tested. By varying the load and controlling the contact pressure between the ball and the cage, a benchmark was established: if the contact pressure does not exceed 115% of the yield strength of titanium**, the bearing is likely to withstand the required number of operating cycles.
*FEA is a way of “breaking down” a complex part or structure into many smaller and simpler parts (elements). Then we calculate the stresses, strains, displacements, etc. in each piece. As a result, we can see where overloads, cracks, or excessive deformations may occur in the structure and make changes to the design to avoid damage and reduce the weight or cost of the product.
**The yielding of a metal is its ability to take on a new shape, spreading or deforming, depending on the state (solid or liquid) in which it is.
In addition to finding the optimal geometry, different ball materials, clip coatings, and lubricant types were also tested. The best results were achieved with steel balls and lubricants that had already been used before, while a promising coating for titanium components was the pulsed plasma nitriding method*, which significantly improves wear resistance.
*Pulsed plasma nitriding is a method of creating a super-strong, wear-resistant layer on the metal surface by “embedding” nitrogen atoms there using a special plasma discharge with high voltage pulses.
The main focus was to increase the durability of the system to 200,000 cycles, which is the amount of walking that NASA estimates astronauts can do during long missions. One “cycle” involves rotating the bearing by a certain angle (from 30° for the belt to 45° for the hip assembly) forward and then doing the same in the opposite direction. Since these angles were determined based on the actual behavior of a person in a spacesuit, the test results are as close as possible to real-world loads.
Testing and selection of concepts
Developers have tested several approaches to modernizing bearings, primarily by changing ball size and surface height to reduce contact pressure. In the study (ICES-2017-242), the goal was to reduce the pressure between the balls and the shells to below 160 ksi (about 1103 MPa*).
*The pressure at the bottom of the Mariana Trench (≈11 km underwater) is about 108 MPa. That is, 1103 MPa is about 10 times higher than the pressure at the deepest point in the world’s oceans. This shows how significant the contact pressure can be in parts, such as bearings or other components with localized loads.
For this purpose, they used the FEA method, but it has its limitations: the very small contact zones between the ball and the track are often not determined with sufficient accuracy by conventional software. To get around this problem, the engineers created special models with very stiff elastic elements instead of balls. Each contact between the ball and the track returns a force value, which is then converted into a contact pressure value using the Hertz equations**.
**Imagine two parts colliding with each other with a certain force F. Because both surfaces are somewhat elastic, they press into each other, forming a small “spot” of contact. Hertz’s equations answer the question of how much and how exactly two elastic surfaces are “pressed” into each other under a given load, and what the maximum pressure and contact patch will be. These formulas are widely used to calculate loads in bearings, gears, machines, and mechanisms where it is important not to exceed the permissible contact pressure and avoid surface destruction.
To verify the results of the computational modeling, physical measurements were also carried out. A film was installed in specially designed clips that changed color under load, thus “visualizing” the peak contact zones. The resulting display was then analyzed using software that determined the load intensity.
The comparison of FEA and experiment showed that the distribution of forces by both methods coincided quite well, but physical measurements generally recorded slightly higher peak loads. For safety reasons, the engineers decided to “adjust” the results of the computational model to the higher values to leave an additional safety margin in real-world conditions. Next, each bearing variation was reviewed in terms of how the contact stresses would change: whether they would be higher or lower than the permissible limits.
In general, the method of adapting design models to test results is a common phenomenon in the engineering environment. This is especially useful and relevant for tasks where the object of calculation is subjected to ultra-high forces of various types under different vectors simultaneously. This means that building an accurate mathematical model can be difficult or take months of calculation.
In the process of developing the improved version of the belt bearing, the diameter of the ball was increased from 6.35 to 9.53 mm, and the height of the cage was increased by 4.32 mm. The difference between the original shape and the improved one can be seen in the comparison image.
Thus, by increasing the height, and diameter of the balls and several other improvements, it was possible to reduce the likelihood of premature wear and ensure the required compatibility with the rest of the structure. As you can see, the developers fought for tens of millimeters and grams. This is a prime example of how engineering decisions are made with a delicate balance between weight, size, and mechanical strength, which is critical for space missions.
Validation trials and test conditions
After completing the tests to verify the reliability and durability of the improved designs, during which each bearing completed 200,000 round-trip cycles, a detailed inspection revealed almost no signs of wear. Neither titanium chips nor dust were observed on the surfaces of the balls or raceways, which indicates the reliable operation of the lubrication system and the effectiveness of the pulsed plasma nitriding coating.
Throughout the test cycle, the temperature and torque remained stable, with no signs of overheating or sudden spikes, which confirms that the bearings remain functional even after a significant load. In the end, a comparison with the “legacy” design options showed a significant improvement: the previous models showed significant wear and torque increase under similar operating conditions. This time, the bearings proved to be very wear-resistant, with virtually no loss of performance, proving that they are ready to be used in the harsh conditions of space missions.
How to repair a worn bearing on Mars?
Suits and other equipment, including bearing systems, are bound to be subject to wear and tear during long expeditions, especially in the harsh conditions of the dusty Martian atmosphere and frequent extravehicular activities (EVA).
One possible solution to these problems is 3D printing directly on the surface of Mars. Researchers from the University of Maryland (College Park) and other scientific institutions are currently experimenting with technologies that allow them to produce rigid elements of spacesuits and their components (e.g., bearings and seals) by printing from metal and polymer “raw” material. In particular, they are checking whether it will be possible to “print” spare parts or even entire spatial mechanisms – from rescue elements to complex fragments of rigid suits – on site.
However, manufacturing or rebuilding a bearing using 3D printing has its challenges. As we’ve already seen, the normal operation of this assembly requires high precision, careful calibration of the groove and ball shapes, and strong and wear-resistant materials that can withstand sudden temperature changes and possible corrosion in an aggressive space environment.
Early attempts to “print” fully operational bearings revealed that most printers have insufficient resolution to produce a perfectly smooth ball surface. So now, experts are working on a combination of several technologies: from precision printing of the outer rims to the use of special inserts or separately printed balls made of harder metal alloys.
From all of the above, it is clear that a bearing – although it seems like an “ordinary” little thing – requires highly precise engineering work in the space environment. Many parameters and material nuances (from weight and geometry to resistance to extreme temperatures and vacuum) turn this seemingly simple assembly into a real challenge for engineers. This is just one of hundreds, if not thousands, of “invisible” elements of space technology that ensure the safety and comfort of astronauts and the efficiency of space missions.
Behind every successful launch, every functional system, and every reliable part are years of development, testing, and continuous improvement. Engineers, scientists, material scientists, programmers, additive technology specialists, and other experts join forces, spending thousands of hours working on a single component. And it is thanks to them that humanity is taking the next steps not only in exploring near-Earth space but also in preparing for the exploration of the Moon or Mars. Each such “little thing”, optimized and brought to perfection, brings us closer to the ambitious goal of becoming an interplanetary species.
