SpaceX's Upgrade Everything On Starship's Welding&Flap, Unlike any other...

Starship V2 is here and it brings new improvements. One of the most noticeable is the change in the welds. The welding technique that Starship uses has always been an important aspect of its development. I mean, it's the technique that turns Starship from looking like a patched together metal water bottle into a real spaceship. So, what is the purpose of this new V2 change? Well, turns out, SpaceX's welding method contains even more genius than you think. While everyone is making their own theories about the use of these new welds, I think we need to look back at the evolution of SpaceX's welding techniques to make the most accurate judgment. Starships were originally intended to be built with carbon fiber because of its light and strong properties. However, while carbon fiber is highly durable, it begins to degrade at approximately 200 degrees. Because of that, a very thick heat shield would be necessary to withstand the 1600 degree temperatures during multiple re-entries. Furthermore, carbon fiber is expensive at around $150 per kilogram, making it harder to turn the ship into a commercial vehicle like SpaceX wants. Stainless steel is different, although it is a bit heavier than carbon fiber. It has a better ability to withstand extreme temperatures, both hot and cold, making it more suitable for the harsh conditions of re-entry into Earth's atmosphere. With the price of only $3 per kilogram, stainless steel is also significantly cheaper and easier to manufacture in large quantities. Although stainless steel possesses outstanding advantages, there are difficulties when working with this material, especially when welding. Stainless steel retains heat very efficiently. It has a higher rate of thermal expansion compared to mild steel and aluminum alloys, which makes welding it a bit more difficult, especially for novice welders. When faced with excessive welding heat, stainless steel can warp from the high temperatures and even distort during the cooling process. Additionally, stainless steel has a higher tendency to form heat-affected zones, or chaisees, which can lead to loss of corrosion resistance and weakening of the weld. To overcome these challenges, specialized welding techniques and filler metals must be used when welding stainless steel. The initial Starship prototypes employed a welding technique known as flux-cored arc welding. This technique, also known as dual-shield welding, is a semi-automatic arc welding process that is similar to metal-active gas, MAG welding. Flux-cored arc welding uses heat generated by an electric arc to fuse base metal in the weld joint area. This arc is struck between the metallic workpiece and the continuously fed tubular cord consumable filler wire, with both the wire and the metallic workpiece melting together to form a weld joint. A type of FCAW, known as dual-shield welding, uses an external shielding gas. Developed for welding structural steels, using a flux-cored electrode and an external shielding gas, typically a 75% argon, 25% carbon dioxide blend, this method is ideal for thicker, out-of-position metals and produces welds with easy-to-remove slag. It offers better mechanical properties and fewer defects, along with a higher production rate since operators don't need to change electrodes frequently. However, it is unsuitable for windy environments due to potential weld porosity. Back then, SpaceX did not have the complete facilities like now. The first Starship models were mostly stored outdoors. Because of this, unlike the sleek, shiny version of today's Starship, Mark 1 is more like a Frankenstein's monster version. The welds on the first prototype were severely corroded, featuring cracks and rough edges on the surface. In an effort to improve those welds, SpaceX grinds them so they're flush with the surface, which eliminates the possibility of weld cracks growing larger as the spacecraft is put under pressure. However, this effort is not enough. On November 20, 2019, Mark 1 blew apart during a pressure test when one of the horizontal welds failed and sent the bulkhead flying. Since Mark 2, SpaceX switched to using the TipTig welding method. TipTig is a variation of gas tungsten arc welding, GTAW, that uses filler wire agitation to improve the dynamics of the molten weld pool. This agitation enhances the fluidity of the weld puddle, helps release evolving gases, reduces the risk of inclusions and porosity, and aids in separating impurities. TipTig systems are essentially GTOW systems with wire feeding, which introduce a vibratory motion to the wire and apply hot wire current to the filler metal before it enters the weld pool. The vibration is generated by a custom wire feeder system, while the secondary power source provides the hot wire current. This technique resulted in much thinner welds with less warping of the surrounding metal. The effectiveness of using this method has been confirmed by SpaceX founder Elon Musk. In his tweet, he mentioned that along with the change in dome forming method, the change from flux core welding to TipTig improved accuracy, stronger welds, and reduced overall weight by up to 20%. To further boost production, SpaceX began purchasing robotic welding machines from companies like Liberty and KUKA. These machines are highly automated and specialized in performing precise welding tasks, which results in cleaner and more precise welds. By utilizing robotic welding, SpaceX has scaled production, accelerated workflow, and enhanced consistency. Not stopping there, SpaceX is taking advantage of another modern welding method, laser welding. Rex Alexander, the former senior welding engineer at SpaceX and principal engineer at the Handheld Laser Institute, recently recounted his journey into handheld laser welding at the OEM Collision Repair Technology Summit during the 2024 SEMA show in Las Vegas. Alexander's entry into the world of handheld lasers was anything but typical. It began when Elon Musk saw a TikTok video and sent him a handheld laser from Amazon. Initially intimidated by the device, Alexander later recognized its potential and began applying the technology at SpaceX, where he successfully used it to create welds that ended up in rockets launching into space and returning safely. By now, SpaceX has likely moved on to laser welding for many of Starship's sections. This technique concentrates heat more precisely and penetrates deeper into the metal, enabling the ring segments to be welded in a single pass. For Starship to be what it is today, the welding method is one part, and materials also play a very important role. The first Mark 1 prototypes were built using 3-O-1 stainless steel. Stainless steel type 3-O-1 is an austenitic chromium nickel stainless steel available in annealed and cold work conditions. In the annealed condition, type 3-O-1 offers the highest level of stretch formability of any stainless steel, and in the heavily cold worked condition, it offers the highest strength level of any 300 series stainless steel. Type 3-O-1 is non-magnetic in the annealed condition, but becomes magnetic as a result of cold working. Then in the SN series, SpaceX switched to using grade 3-O-4-L stainless steel in many parts. While both 3-O-1 and 3-O-4-L stainless steel use iron as their main ingredient, the two alloys have a couple of key differences in their chemical composition. In mildly corrosive environments at typical ambient temperatures, the corrosion resistance of grade 3-O-1 and grade 3-O-4-L stainless steel is quite similar. However, grade 3-O-1 is generally somewhat less resistant to corrosion than grade 3-O-4-L due to its lower chromium content and higher carbon levels. At higher temperatures, the difference in corrosion resistance is more pronounced. For instance, if you were to weld or laser cut a piece of 3-O-1 stainless steel, you would be more likely to observe corrosion in the heat affected zones, compared to a piece of 3-O-4 stainless steel treated in the same manner. This is due to the precipitation of chromium carbide, which depletes the chromium content in the affected areas. Another advantage Elon mentioned when talking about the reason for changing from 3-O-1 to 3-O-4-L stainless steel is its toughness at cryogenic temperatures. Grade 3-O-4-L is more than four times stronger than grade 3-O-1 at cryogenic temperatures. Because Starship is welded from multiple steel rings, the welds are often the weakest points, so using a material that is stronger at extreme temperatures is extremely important. Although under normal conditions 3-O-1 stainless steel seems to be stronger than 3-O-4-L, switching to 3-O-4-L significantly improves its corrosion resistance, ease of welding, and ability to withstand extreme temperatures of the weld. In addition to switching to a different type of steel, SpaceX also used an additional step to increase the strength of its material. When Starship's stainless steel is manufactured in its factory, it undergoes a process known as cold rolling. This involves passing the metal through a series of rollers, which compress it down and stretch out the grains in the metal, which increases the strength via strain, hardening up to 20%. It also improves the surface finish and holds tighter tolerances. However, when Starship is welded, the heat causes the metal in that region to soften once more. This is where SpaceX's massive planishing machine plays a crucial role. Planishing involves using a hammer or a planishing tool to strike the welded joint gently but firmly. During welding, the heat-affected zone, CHAZ, around the weld may become softer or harder than the base metal. Hammering and compressing the weld ensures that the hardness of the welded area is consistent with the surrounding material, reducing the risk of stress concentration and making the metal stronger overall. Planishing also helps smooth the surface of the welds. The process of hammering the weld gradually smooths out these imperfections, making the weld blend more seamlessly with the surrounding metal, ultimately improving the aesthetic of the Starship. Unlike previous steel plates that were cut into rectangles and welded together, SpaceX uses steel coils to form a complete steel ring with a diameter of 9 meters. These rings significantly reduce the surface area that needs to be welded. In mechanics, simpler is more durable. We need 20 of those steel rings to make a complete Starship. These rings are then stacked into stacks of varying heights. These pre-installed stacks will reduce the time required for installation in the high bay, freeing up that area for other tasks. Next, the domes are sleeved with the ring stacks to form the methane tank, oxygen tank, and payload bay. These are then stacked together with the nose cone equipped with the headed tank. Flap and heat shield were then added to form a complete non-engine Starship. SpaceX has been experimenting with different thicknesses of stainless steel for the Starship, but the company must be careful not to make the same mistakes NASA made in the past. Back in the 60s, NASA made an Atlas rocket out of incredibly thin stainless steel. On May 11, 1963, the Atlas Agena D rocket sat on its launch pad at Vandenberg Air Force Base on California's beautiful Central Coast for various tests. During fueling, a gas bubble developed in the propellant fill and drain system for the rocket. This created a hydraulic ram effect that shook loose the connection inside the vehicle where liquid oxygen flowed into the Atlas. The launch pad crew hunkered down in the blockhouse and drained all of the liquid oxygen in the upper tank. The Atlas rocket was unique because it derived its structural strength from pressurization. Imagine a full soda can. If you place it on the ground, you can likely stand on it. But if it's emptied, it will collapse under your weight, especially when the Atlas is so thin. And that's what happened. The Atlas Agenda rocket depressurized on the pad, collapsed, and tore itself to pieces. The lessons learned from history form the foundation for refining and enhancing current technologies. The Starship of today represents the fusion of past innovations and modern advancements. From the meticulous selection of materials to the precision of welding techniques, Starship demonstrates that in engineering, no detail is too small. Every element must be thoughtfully considered to achieve greatness. Even knowing the process, as someone who has followed Starship's development from the early days, I still find it hard to believe that Starship has evolved to what it is today. Well, as Elon always says, engineering is the closest thing to magic that exists in the world. The flaps of SpaceX's Starship rocket play a crucial role in controlling its aerodynamics during various flight phases, particularly during re-entry and landing. It consists of two components, forward flaps positioned on the payload bay, and aft flaps located on the sides of the engine bay and LOX tank. In Starship Block 1, the old flap design clearly showed its shortcomings. Flight 4 marks the first time both booster and ship made them all the way to a soft landing in the ocean. This allows us to take a closer look at the performance of the flaps. During Ship 29 re-entered, plasma got into the portside forward flap hinge, nearly melting it off. Ship 30 in Flight 5, although has the heat shield fairing much better than Ship 29, still had some burn marks on the forward flaps. Then on Flight 6, SpaceX challenged Ship 31 even more by flying at higher angles of attack to test the limits of flap control and future landing configurations. Prior to launch, the flaps and flap fairings got the new ablative layer, and gap filler material was added to the flaps. As a result, there was once again a burn through on at least one of the forward flaps of Ship 31. It's safe to say that the Block 1 flap design had a major weakness related to its ability to withstand extreme heat during re-entry. This indicates that while design upgrades have already proven beneficial, further refinements are still needed. That is where the second version comes in which will incorporate more significant upgrades. So, what differentiates the Block 2 flap design from the previous design? Let's start off with the forward flaps. Beyond a space shuttle-style heat shield of blankets and ceramic tiles, the Starship upper stage is meant to achieve that re-usability by descending through the atmosphere and landing unlike any other spacecraft, plane, or rocket ever flown. Instead of flying, gliding, or knifing through the atmosphere nose or tail first, Starship free falls perpendicular to the ground for the last few dozen kilometers before aggressively flipping into a vertical orientation at the last second and landing propulsively on its tail. Now, according to Elon Musk, two of the four flaps that largely make that exotic maneuver possible are set for a small but significant redesign. I'm so glad we finally fixed the forward flap design. The old one was killing me. It was too large and heavy, positioned at 180 degrees, which caused issues during the high-heating hypersonic phase of flight. The new design solves those problems. The new, smaller flap design is a game-changer for Starship. These changes will not only improve maneuverability during flight but also boost overall reliability. While the version 2 forward flap is significantly smaller, reducing the static aerodynamic demands that affect navigation and the critical flip maneuver during descent, this design minimizes the risk of damage during flight and simplifies manufacturing, which will increase operational flexibility. In Block 1, the forward flaps had a design where the lower edge ran parallel to the ground and was perpendicular to the outboard edge, creating a distinct 90-degree angle at the lower corner. In contrast, the new flaps have a much more swept shape compared to the Block 1 design and will no longer have the bottom edge parallel to the ground when deployed. Additionally, the new flaps appear thinner, which helps reduce dead weight. Both faces of the new flaps are parallel, simplifying the heat shield design significantly. In contrast, the old flaps had non-parallel faces due to their thicker construction near the hinge, tapering toward the outboard edge. This tapered design introduced additional complexity to the heat shield. All the way back in August of 2021, SpaceX CEO Elon Musk noted that there was a slight error with the forward flap design. While the moving section of the flap is essential for control, the passive section was deemed counterproductive as it pushed the nose of the spacecraft backward. This passive section comprises parts of the flap and a component called static arrow, which always extends from the ship, increasing drag. The static arrow serves to protect the hinge and fill the gap between the nose cone and the flap. This flap configuration adversely affected the spacecraft during descent, as it continuously attempted to lift the forward end, requiring compensation from the aft flaps. To address this issue, Musk suggested rotating the forward flaps to leeward and further forward to improve the moment arm. Maybe roughly 120 degrees apart, and now the flaps are now situated about 120 to 140 degrees apart from each other, rather than the 180 degrees on the older design. It means it shifted higher and closer to the leeward side. This repositioning offers better protection during atmospheric re-entry, reducing the potential for damage like what was observed in Flight 4. As a result of these changes, the static aerodynamic system is largely shielded from airflow, and when the flaps are retracted, they are almost completely hidden behind the nose tip. While the forward flaps have undergone significant redesigns, the structure of the aft flaps appears to remain unchanged, and the reasons for this are unclear. The aft flaps on Starship share many characteristics with the previous forward flap design. There is no discernible difference between the aft flaps of the older and updated ship models. They maintain the same shape and internal structure, indicating they are essentially carryovers from the previous generation. The aft flaps continue to be spaced 180 degrees apart. At this point it seems SpaceX has chosen not to modify its design. The thickness and shape of these flaps have remained consistent. Like the former forward flap design, the aft flaps feature a tapered profile that narrows toward the outboard edge, causing their two faces to be non-parallel, which contrasts with the new forward flaps. The flap design of SpaceX's Starship significantly differs from that of NASA's Space Shuttle. The Shuttle features a vertical stabilizer, with wings attached to the mid-fuselage, while SpaceX opts for a design without large wings to minimize dead weight and enhance safety and efficiency. The Shuttle's oversized wings limit its capabilities, confining it primarily to low Earth orbit and hindering its potential for missions to Mars or the Moon. This design not only makes launches less efficient, but also increases the risk of debris collisions during ascent. SpaceX's approach focuses on creating a more streamlined spacecraft. The Starship employs body flaps that play a crucial role in controlling its trajectory, especially during landing. These flaps are designed to dissipate energy during atmospheric entry and are positioned to optimize performance. Unlike the Shuttle, which relies on the lift generated by its wings for a gradual descent, Starship uses a high-drag strategy, presenting its broadside to the airflow to slow down rapidly during re-entry. This design philosophy allows Starship to manage heat dissipation more effectively, reducing the risk of thermal damage. The differences in their re-entry mechanisms highlight the distinct operational goals of each spacecraft, with Starship prioritizing rapid deceleration over lift and glide capabilities. Overall, SpaceX's innovative flap design reflects its commitment to creating a fully reusable spacecraft, capable of ambitious missions beyond low Earth orbit. To achieve the current flap design of Starship, SpaceX invested years in research, testing, and modifications, particularly evident during the dynamic early development phase when annual changes were common. In the initial 2017 design, known as the Big Falcon Ship ABFS, the upper stage featured a small delta wing at the rear with split flaps for pitch and roll control. This delta wing was intended to enhance the spacecraft's flight capabilities, allowing it to land in various atmospheric conditions, whether in a vacuum, thin atmosphere, or dense environment, thus enabling landings anywhere in the solar system. By 2018, this design evolved into what Elon Musk referred to as the final version of SpaceX's Big Falcon Rocket. The updated model replaced the single delta wing with three larger wings, two actuated aft fins and one landing pad. Additionally, it included two forward-actuated flaps. The forward fins were positioned near the nose to aid in steering, slowing down, and stabilizing the spacecraft during atmospheric entry. The aft wings not only facilitated flight on Earth and Mars, but also served as landing pads, moving away from previous designs that featured pop-out landing legs. This iteration could accommodate a significant amount of cargo, equivalent to a double-decker bus, for easier access post-landing. The evolution continued into 2019, when further redesigns reduced the number of aft flaps from three to two, primarily driven by concerns about vehicle mass. Musk noted that this change was based on analyses suggesting that two rear fins with separate airframe-mounted legs would be lighter. The design also included smaller fins at the top of the vehicle for added control, with features like forward-movable fins and cold-gas-attitude-control thrusters, aimed at balancing the mass of the Raptor engines and fins at the base. Since then, the number and structure of flaps have been mostly maintained, except for the fact that SpaceX only made a few tiny changes for Starship version 2, as we stated. Similar to any other part of Starship, the flap design development process was based on an iterative approach. This methodology emphasizes rapid prototyping, allowing SpaceX to quickly build, test, and refine each version of the spacecraft. By embracing a cycle of build-test-analyze-improve, the company can swiftly identify flaws and implement necessary changes based on real-world data, rather than relying solely on theoretical models. This approach contrasts sharply with traditional aerospace practices that often involve extensive upfront planning and lengthy development timelines. Over the years, SpaceX has produced multiple prototypes of Starship, each serving as a learning platform for subsequent iterations. The iterative process not only accelerates development, but also enhances cost efficiency by reducing the man-hours required to address issues as they arise. Moreover, this flexibility allows SpaceX to adapt designs in response to test results, ensuring that each iteration is better suited for its intended mission. The iterative design strategy has proven particularly effective in addressing challenges associated with developing a fully reusable spacecraft capable of interplanetary travel. As a result, Starship is on track to revolutionize space travel by making it more accessible and sustainable.