Super Heavy

The booster's story begins long before it had that name. In October 2012 SpaceX first publicly articulated its intention to develop a fully reusable launch system with far greater capability than the Falcon 9, and shortly afterwards mentioned the Mars Colonial Transporter concept, a vehicle meant to carry a hundred tonnes of cargo to Mars on methane-fuelled engines.

The concept acquired numbers on 27 September 2016, at the 67th International Astronautical Congress, when Elon Musk unveiled the Interplanetary Transport System: two stages, a reusable booster and a spacecraft, carbon composite tanks and liquid methane and oxygen as propellants. That first booster was to be 12 m in diameter and 77.5 m tall with 42 engines, and would land directly on the launch mount itself for immediate refuelling and reflight; grid fins to steer the reentry were already part of the design. A year later, at the 2017 congress, the project was renamed BFR and shrank to a somewhat more manageable scale.

The decisive turn came in December 2018, when SpaceX changed the structural material: out went carbon composites, in came stainless steel. Musk justified the switch by cost, ease of manufacture, the greater strength of steel at cryogenic temperatures and its tolerance of reentry heating. By 2019 the company was calling the complete system Starship and its first stage Super Heavy, and the design was essentially frozen: a 9 m steel cylinder built from welded rings.

Super Heavy is divided into four sections which, in ascending order, are the engines, the liquid oxygen tank, the liquid methane tank and the interstage. The two cryogenic tanks are separated by a common bulkhead, the same structural solution used on the S-II and S-IVB stages of the Saturn V, and each tank carries roughly seventy-four stringers for reinforcement. After the second flight test the common dome was redesigned to a more elliptical shape, slightly altering the capacity of both tanks.

The oxygen tank ends at the thrust puck, the part that gathers the load of the thirteen inner engines; the outer twenty are mounted on a ring attached to the vehicle's first steel ring. Large steel structures welded beneath the aft dome let that part carry the inner engines on its own while also providing routing paths for plumbing. The methane funnel sits partly inside the header tank, with the methane sump directly below it.

From Booster 7 onwards, four aerodynamic chines appeared along the outside of the oxygen tank. They are not decorative: they provide lift during descent and house batteries, composite overwrapped pressure vessels for spin start and carbon dioxide tanks for fire suppression.

The interstage carries four electrically actuated stainless steel grid fins weighing roughly three tonnes each. Unlike those of the Falcon 9 they do not fold: they stay extended throughout ascent to save weight, at the price of mild warping during stage separation. Between them protrude the hardpoints by which the tower lifts and catches the vehicle.

The process starts with rolls of stainless steel, unrolled, cut and welded along an edge into a cylinder 9 m in diameter, 1.83 m tall and 3.97 mm thick, with a mass of approximately 1600 kg. Each Super Heavy uses thirty-three such rings, plus four shorter 1.4 m rings for specific points in the structure.

The rings are stacked and robotically welded in the Starfactory into stacks of three or four, stringers are added, and cutouts are made for the grid fins and hardpoints. The domes are then installed inside the forward, aft and common ring stacks. Assembly proper happens in Mega Bay 1: first the methane tank, then the oxygen tank already integrated with the common dome, with the methane downcomer added before closing out. The vehicle is then rolled to the Massey's test site and cryogenically proof-tested twice, filling the tanks with non-flammable liquid nitrogen and sometimes liquid oxygen as well. Back at the production site the engines and their shielding go in, forming the aft bay, and static fire testing follows at the launch site.

The first prototype, BN1, was assembled in March 2021 as a production pathfinder and scrapped on 30 March without ever being tested. The next, BN3, was completed on 29 June 2021, passed the first cryogenic proof test of a Super Heavy on 13 July and performed on 19 July the only static fire of a Super Heavy conducted at the suborbital launch site; it was later partly scrapped.

Booster 4 was the first intended to fly. It was fully stacked on 1 August 2021 and had all twenty-nine engines — the configuration of the time — installed the next day; grid fins were added for atmospheric reentry testing, and it became the first Super Heavy to be stacked with a Starship on top. It never flew, being retired in favour of Booster 7 and Ship 24.

Booster 7 was placed on the orbital launch mount on 31 March 2022 and completed two cryogenic proof tests in April that ruptured the downcomer. Repaired, it went through a campaign of static fires and spin prime tests, one of which, on 11 July 2022, did significant damage to the vehicle. Booster 8, fully stacked on 8 July 2022 and moved to the launch site that September, was never tested there and was scrapped in January 2023.

After an attempt aborted on 17 April 2023, Booster 7 and Ship 24 lifted off on 20 April in the first integrated flight test. Three engines were disabled during the launch sequence and several more failed during ascent; the stack never separated and was destroyed. The launch also damaged the pad, forcing SpaceX to reinforce the tower foundation and to build a water-cooled flame deflector under the launch mount.

On 18 November 2023 Booster 9 and Ship 25 lifted off. All 33 engines kept running until staging, which for the first time was performed hot: the second stage lit its own engines and pushed itself away from the booster. Super Heavy completed its flip and began the boostback burn, but exploded after a run of successive engine failures.

The third flight left Starbase on 14 March 2024, coincidentally the twenty-second anniversary of the company's founding. Again all 33 engines lit and separation succeeded; Booster 10 performed the boostback burn, but the planned splashdown in the Gulf of Mexico failed and the vehicle exploded 462 m above the surface.

The fourth flight, on 6 June 2024, aimed to have the booster land on a "virtual tower" out at sea. Super Heavy achieved a soft splashdown — its first — and was destroyed only afterwards, when it tipped over on the water.

With that result in hand, Musk announced in April 2024 that the next step would be a tower catch attempt. Booster 12 and Ship 30 lifted off on 13 October 2024: the booster flew its boostback and landing burns without engine failures and was caught between the tower's chopsticks, which lowered it onto the launch mount. It was the first time an orbital-class booster had been recovered in mid-air, with neither legs nor a landing platform. Musk later reported minor and easily addressed damage, including warping of the outer engine nozzles. On the following flight the catch was aborted and Booster 13 splashed down at sea.

The second landmark came in 2025 with reuse. Booster 14 flew on 16 January 2025 with Ship 33: a nominal ascent burn and clean separation, though one engine failed to relight for the boostback burn. That same booster, now as B14-2, was integrated with Ship 35 on 25 May and lifted off on 27 May 2025, keeping all 33 engines lit until main engine cutoff and this time igniting all thirteen gimbaling engines for the boostback burn. Booster 15 also flew twice: it was caught on its first flight and returned to Mega Bay 1 on 8 March, passed through the Rocket Garden and on 6 September 2025 went back to the launch site for its second mission.

Block 3 is the booster's first deep redesign. It stands 72.3 m tall, integrates the interstage directly into the methane tank and cuts the grid fins from four to three, arranged in a 90/90/180 degree pattern. The new fins are roughly one and a half times the size of those on the earlier blocks and sit lower on the vehicle; according to SpaceX, the repositioning reduces the heat they endure during stage separation. The aft dome has been redesigned with metallic heat shield tiles mounted on it, and the engines move from Raptor 2 to Raptor 3, a change SpaceX applied from its first Starship flight of 2026.

Block 3 testing advanced through 2026: Booster 20 rolled out to Massey's on 5 June 2026 and passed a cryogenic test the next day, then performed a thirty-three engine firing on 10 July. On 7 May 2026 SpaceX had already fired all 33 Raptors of a V3 Super Heavy at full duration and full thrust at Starbase, the first successful full-up static fire of the variant; the same booster had earlier been used for a ten-engine trial in March and for further attempts cut short by ground equipment problems. Booster 19 began stacking on 27 November 2025, was completed on 24 December and became the vehicle assigned to Flight 12 in place of Booster 18.

Super Heavy and the ship are stacked on the launch mount and loaded with propellant through the booster quick disconnect and the ship quick disconnect arm. At nineteen minutes and forty seconds before launch, engine chill begins to protect the turbopumps from thermal shock; three seconds before liftoff the engine start sequence begins. After liftoff the engines burn for about one hundred and fifty-nine seconds, until the booster shuts down all but its three centre gimbaling engines at roughly 64 km altitude. It throttles the remaining engines down, the ship lights its own engines while still attached and pushes itself away, and Super Heavy then rotates and ignites ten additional engines for the boostback burn that sends it back toward the launch site. It descends under the control of the grid fins and of cold gas thrusters fed with residual ullage gas, vented through four perpendicular outlets in the interstage and others just below the common dome, angled slightly toward the engines.

Super Heavy has no independent existence: it is the lower half of a two-stage system whose upper half, the Starship spacecraft, is what reaches orbit, carries the payload and, in the planned architecture, is refuelled in flight. Roughly 58 per cent of the height of the stacked vehicle is booster. The flight cadence, the mission numbering and much of the booster's design direction follow what the ship needs, not the other way round.

That coupling also explains its institutional role. NASA selected a version of Starship as the crewed lunar lander for the Artemis programme, and the system's test flights — booster included — are assessed as progress toward that mission. Regulatory oversight of the programme rests with the Federal Aviation Administration, which licenses the launches from Boca Chica and has processed the environmental assessment of the site.