SpaceX Super Heavy
Super Heavy is the reusable first stage of the SpaceX Starship super heavy-lift launch vehicle, which it composes in combination with the Starship second stage. As a part of SpaceX's Mars colonization program, the booster evolved into its current design over a decade. Production began in 2021, with the first flight being conducted on April 20, 2023, during the first launch attempt of the Starship rocket.
The booster is powered by 33 Raptor engines that use liquid oxygen and methane as propellants. It returns to its launch site after propelling the second stage toward orbit, landing vertically by being caught by the launch tower.
Design
Super Heavy is tall, wide, and is composed of four general sections: the engines, the oxygen tank, the fuel tank, and the interstage. Block 3 Super Heavy is 72.3 meters tall.Tanks
The two cryogenic propellant tanks on Super Heavy are separated by a common bulkhead, a similar structural design to the S-II and S-IVB stages on the Saturn V rocket. After Starship's second flight test, the common dome's design was changed to be more elliptical, altering the propellant capacity of both tanks by a small amount. Each tank possesses roughly 74 stringers for structural reinforcement, attached to their interior walls. The booster's two tanks hold a combined of propellant: of liquid oxygen and of liquid methane. Fuel is fed to the engines via a single liquid funnel, and channeled into distribution manifolds of the engines. This system was upgraded on Block 3 boosters, featuring a substantially larger transfer tube connecting the engines and the methane tank. Block 1 and 2 boosters both have a single booster quick disconnect, along with multiple quick disconnects for the outer engines, while Block 3 boosters have two quick disconnects. One disconnect feeds liquid oxygen into the vehicle, the other feeds liquid methane.The oxygen tank ends at the thrust structure of the vehicle. While the outer twenty engines are mounted to the walls of the aft bay, the inner thirteen are mounted onto the thrust puck, a part of the aft dome. Large steel structures are attached to the bottom of the dome, reinforcing the puck sufficiently to fully support the inner thirteen engines, and at the same time providing pathways for methane and oxygen into the engines. In addition, large filters were added in this region beginning on Booster 10. Liquid oxygen is supplied by a header tank during landing burn for the inner thirteen engines. On Booster 15, the header tank had at least nine additional tanks attached, increasing capacity for the landing burn. The added tanks may have been present on Boosters 12, 13, and 14, though this was unconfirmed as of February 2025. Booster 5 was the only 29-engine booster to receive a header tank, mounted to the side of the oxygen tank instead of being integrated with the thrust puck.
The methane funnel is partially contained within the header tank, as the methane sump is directly below it. On Booster 7 and all subsequent vehicles, four aerodynamic chines are located on the outside of the oxygen tank, providing aerodynamic lift during descent, as well as housing batteries, composite overwrapped pressure vessels for spin start, and tanks for fire suppression. On vehicles with hydraulic power units, COPVs dedicated to engine ignition, batteries, and communication antennae were located within the HPU cover instead of the chines.
Propulsion
Super Heavy is powered by 33 Raptor engines, which on Block 1 and 2 vehicles are housed within a dedicated shielding compartment. This compartment is not present before engine installation, thus boosters are roughly three meters shorter prior to engine installation. The outer 20 engines, arranged in a ring, are fixed in place. To save weight, the 20 engines are started using ground support equipment on the launch mount and cannot be reignited for subsequent burns. The inner thirteen engines are equipped with gimbal actuators and reignite for the boostback and landing burns. After Starship's first flight test, this gimbaling system was switched from a hydraulic system to an electric one, enabling the removal of the hydraulic power units. This change was made to the upper stage after the second flight test. During the ascent and boostback burns, the engines draw propellant from the main tanks, with the liquid oxygen being drawn from a dedicated header tank during the landing burn. Like the thrust vector control system, the engine shielding, which isolates individual engines in the event of a failure, was upgraded after Starship's first flight test, alongside the fire suppression system. The aft bay has eighteen vents visible on the outside of the booster, which are believed to be connected to the outer 20 engines, while the center engines vent directly below the launch pad.The Raptor engine uses a full-flow staged combustion cycle with oxygen and methane-rich turbopumps. Before 2014, only two full-flow staged-combustion rocket engine designs had advanced enough to undergo testing: the Soviet RD-270 project in the 1960s and the Aerojet Rocketdyne Integrated Powerhead Demonstrator in the mid-2000s. To improve performance, the engines burn subcooled propellant; i.e. the propellants are cooled below their respective boiling points to further increase their density and the engine mass flow rates.
The Block 1 version of the booster produced a total of just over twice that of the NASA Saturn V first stage, with this total being expected to increase to for Block 3 boosters and later up to with the Block 4 vehicle. The thirty three engines collectively produce large shock diamonds in the exhaust jet, visible during ascent and descent.
During unpowered flight in the upper atmosphere, control authority is provided by cold gas thrusters fed with residual ullage gas. Four perpendicular vents are located within the interstage. Additional vents are located just below the common dome, pointing down toward the engines at a slight angle.
The Block 3 booster contains an updated aft dome, with metallic heat shield tiles mounted upon it.
Interstage
The interstage is equipped with four electrically actuated grid fins made of stainless steel, each with a mass of roughly. The fins remain extended during ascent to save weight, though this results in mild warping during stage separation. The interstage also has protruding hardpoints, located between grid fins, allowing the booster to be lifted or caught by the launch tower. The ability to lift a booster from these hardpoints was proven on August 23, 2022, when Booster 7 was lifted onto OLM A. The first catch of a booster occurred on October 13, 2024, using Booster 12.After the first Starship test flight, all boosters have an additional 1.8 m tall vented interstage to enable hot staging. During hot staging, Super Heavy shuts down all but the three center engines, while the second stage fires its engines before separating, thus the second stage "pushes off" from the first stage, giving added thrust. The vented interstage contains a dome to shield the top of Super Heavy from the second stage's exhaust. Elon Musk in 2023 claimed that this change might result in a 10% increase in the payload to low Earth orbit. Beginning with Booster 11, the vented interstage is jettisoned after completion of the boostback burn, to reduce mass during descent. As of December 2025, SpaceX does not intend to jettison the interstage when flying Block 3 boosters, as the vented section will be directly integrated into the vehicle.On Block 3 boosters, the interstage is directly integrated into the methane tank, and the number of grid fins is reduced from four to three, in a 90/90/180 degree arrangement. These grid fins are roughly one and a half times the size of the Block 1 and 2 grid fins, and are positioned lower on the vehicle. According to SpaceX, the repositioning reduces the heat experienced during stage separation. Additionally, the fins are integrated with the catch pins.
Manufacturing
The manufacturing process starts with rolls of stainless steel, which are unrolled, cut, and welded along an edge to create a cylinder of diameter, tall, and thick, and approximately kg in mass. Thirty-three such rings are used in the Super Heavy Booster, while four rings are tall. These shorter rings are used exclusively in the aft section. A and a tall ring are used to construct the liquid oxygen header tank. These rings have a significantly smaller diameter than the main rings.The forward dome is constructed out of two segments: the "dome knuckle" and the "dome frustum". The aft dome has a third component: the "thrust puck", which supports the inner thirteen engines, while the common dome is composed of a single part, and is more elliptical than the forward and aft domes.
These rings are stacked and robotically welded along their edges to form stacks of three to four rings in the Starfactory. Stringers are then added to the ring stacks, improving the structural strength of the booster. Cutouts are made for the grid fins and hardpoints for the forward section. Following this, the domes are installed within the forward, aft, and common ring stacks. The forward ring stack consists of three rings, and the common ring stack consists of four. The aft section is constructed solely from the four rings. Tank vents and external piping are added at this stage, followed by the COPVs and header tank.
Following the completion of each of the ring stacks, the stacking of these sections begins with the assembly of the methane tank. This process occurs in Mega Bay 1. Once the methane tank is completed, the oxygen tank is assembled, already integrated to the common dome. Before assembly of the oxygen tank is finished, the methane downcomer is added, along with final stringers to the weld lines. When both tanks are complete, the methane tank is stacked onto the oxygen tank, completing the primary tankage assembly. Chines are added after this stage.
The vehicle is then rolled to the Massey's test site and cryogenically tested twice. These tests fill both tanks with liquid nitrogen, which is nonflammable, though liquid oxygen may be loaded as well. After returning to the production site, the engines are installed, alongside their shielding, which forms the aft bay. This is followed by static fire testing at the launch site. Once this test is completed, the vented interstage is added to the vehicle.