SpaceX Super Heavy

Super Heavy is the first stage of the SpaceX Starship super heavy-lift launch vehicle, which it composes in combination with the Starship second-stage. As of 2024, Super Heavy prototypes are being flight tested. Super Heavy flew for the first time on April 20, 2023, during the first orbital launch attempt of the Starship rocket.

Manufacturing
The manufacturing process starts with rolls of stainless steel, which are unrolled, cut, and welded along an edge to create a cylinder of 9 m diameter, 1.83 m in height, and 3.97 mm thick, and approximately kg (undefined kg) in mass.

These rings are stacked and welded along their edges to form the outer layer of the rocket. Domes are added early on in the assembly process, before final assembly of the tank sections begins.

Usually before final assembly of the vehicle, grid fins are added to the interstage, and chines are added after stacking the sections. After cryogenic pressure testing, engines are installed, followed by the vented interstage.

Design
Super Heavy is 71 m tall, 9 m wide, and is composed of four general sections: the engines, the fuel tank, the oxygen tank, and the interstage. Elon Musk stated in 2021 that the final design will have a dry mass between 160 t and 200 t, with the tanks weighing 80 t and the interstage 20 t.

Tanks
The propellant tanks on Super Heavy are separated by a common bulkhead, similar to the ones used on the S-II and S-IVB stages on the Saturn V rocket. The oxygen tank has four chines attached, which protect the COPVs and tanks for fire suppression, as well as providing lift during descent. The LOX tank also contains a header tank, which is used for the landing burn. A central transfer tube through the oxygen tank supplies methane to a distribution manifold just above the engines.

The booster's tanks hold 3400 t of propellant, consisting of 2700 t of liquid oxygen and 700 t of liquid methane.

Engines
Super Heavy v1 has 33 raptor engines, which are arranged in three concentric rings, with the outer ring of 20 engines lacking gimbal actuators and onboard startup hardware to save weight. These engines are started using ground support equipment on the launch mount and are not reignited for subsequent burns.

Raptor uses a full-flow staged combustion cycle, which has both oxygen and methane-rich turbopumps. Before 2014, only two full-flow staged-combustion rocket engine designs had advanced enough to undergo testing on test stands: the Soviet RD-270 project in the 1960s and the Aerojet Rocketdyne Integrated Powerhead Demonstrator in the mid-2000s.

At full power, all engines produce a collective 74.4 MN of thrust as of 2022 (more than double that of the Saturn V first stage), however, Raptor 3 may increase thrust to 90 MN at sea level. Boosters lack an engine skirt, and without engines, boosters are about 3 meters shorter. The 33 individual closely-spaced plumes can interact to produce gigantic shock diamonds in the exhaust.

Interstage
The interstage is also equipped with four electrically actuated grid fins, each with a mass of 3 t. Adjacent pairs of grid fins are only spaced sixty degrees apart instead of being orthogonal (as is the case on Falcon 9) to provide more authority in the pitch axis. Unlike Falcon 9, the grid fins remain extended during ascent, rather than retracted as on Falcon 9. During unpowered flight in the vacuum of space, control authority is provided by cold gas thrusters fed with residual ullage gas. The interstage also has protruding hardpoints, located between grid fins, allowing the booster to be lifted or caught by the launch tower. 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 3 of its engines, while the second stage fires its engines before separating, thus the second stage "pushes off" from the first stage giving added lift. The vented interstage contains a dome to shield the top of super heavy from the second stage's engines. Elon Musk has claimed that this change might result in a 10% increase in the payload to low Earth orbit.

After IFT-3, SpaceX has jettisoned the Vented Interstage after the boostback burn, in order to save mass. As of June 2024, SpaceX does not plan on expending the Vented Interstage after the debut of the V2 booster.

Planned mission profile
About forty two minutes before flight, propellant load of the booster begins. At the T – 19:40 mark, engine chill begins on the booster. This is to protect the engine's turbopumps from thermal shock. At three seconds before a flight, the thirty-three engines startup sequence begins. After liftoff, the engines burn for 162 seconds, at which point 30 of its engines shut off, leaving only the center three engines running at 50% thrust. The ship ignites its engines while still attached to the booster and separates, while the booster rotates for the boostback burn. The boostback burn uses all 13 central engines and lasts for 54 seconds. About seven minutes after launch, the 13 engines reignite before again dropping back to the innermost three, and the booster is caught by the "chopsticks" on the launch tower.

BN1
BN1 was the first Super-Heavy Booster prototype, a pathfinder that was not intended for flight tests. Sections of the ~66 m tall test article were manufactured throughout autumn 2020. Section stacking began in December 2020. BN1 was fully stacked inside the High Bay on March 18, 2021, and was scrapped on March 30, 2021.

B3
Booster 3 completed stacking in the High Bay on June 29, 2021, and moved to the test pad without engines. A cryogenic proof test was completed on July 13, 2021. Three engines were subsequently added.

A static fire test was conducted on July 19, 2021. BN3/Booster 3 was partially scrapped on August 15, 2021, while the LOX tank remained welded to the Test Stand. The LOX tank was taken off the Test Stand on January 13, 2022.

B4–B6
Booster 4 first became visible on July 3, 2021. Musk ordered several hundred SpaceX employees at Hawthorne to relocate to Boca Chica to accelerate the development of SN20, BN4, and the Orbital Launch Platform in an attempt to put the Starship system on OLM A by August 5, 2021. BN4 was fully stacked on August 1, with a full complement of 29 engines installed on August 2, 2021. Grid fins were added to support atmospheric reentry testing.

SN20 was stacked on top of Booster 4 on August 6, 2021 for a fitting test, making it the tallest rocket ever fully integrated, until September 5, 2023, when S25 was stacked onto B9. Booster 4 was then returned to the High Bay for secondary wiring. On September 9, 2021, Booster 4 came again to the launch site on top of the Orbital Launch mount. B4 completed its first cryogenic proof test (17 December 2021), and a pneumatic proof test on December 19, 2021. It underwent another cryogenic proof test and a full-load cryogenic proof test. B4 and Ship 20 were then retired.

On March 6, 2024, B4s grid fins were removed. It was moved to the Mega Bay on March 21, 2024, where it was scrapped on March 22, 2024.

Parts for B5 were observed as early as 19 July 2021. Stacking for BN5 completed in November, although on 8 December 2021, B5 was retired alongside SN15 and SN16. It was later scrapped.

B6 was converted into Test Tank B6.1.

B7–B8
Parts for B7 were first spotted on September 29, 2021. B7 was placed on the orbital launch mount on March 31, 2022. After completing a cryogenic proof test on April 4, 2022, it was placed onto the new booster test stand on April 8, 2022. B7 completed another cryogenic test on April 14, 2022, but the downcomer suffered a failure and ruptured. On April 18, 2022, B7 returned to the production site for repairs. On May 5, 2022, B7 was again placed on the orbital launch mount. B7 completed two cryogenic tests on May 9 and May 11, 2022, before being moved back to Mega Bay 1 for engine and grid fin installation. On July 11, 2022, B7 experienced an anomaly during an attempted 33 engine spin prime test, resulting in a detonation underneath the engines. The booster then rolled back to Mega Bay 1. On August 4, 2022, B7 was transported back to the orbital launch pad with 20 outer Raptor engines, and completed its first single-engine static fire test on August 9, 2022. B7 completed a 20-second static fire on August 11, 2022, the longest static fire on a Starship prototype to date. Following these successful tests, it returned to the production site to receive the remaining 13 engines. B7 was lifted back onto the launch mount August 23, 2022. This was the first lift of a booster using the chopsticks. It underwent further testing including its 13 inner engines on August 26, 2022. On August 31, 2022, B7 completed a multi-engine static fire. This was followed by multiple spin prime tests, and a seven-engine static fire on September 19, 2022. B7 again returned to the Mega Bay on September 21, 2022. After receiving additional upgrades it was again lifted on the launch pad on October 8, 2022. Ship 24 was stacked on top B7 on October 12, 2022, and was removed after completing multiple cryogenic load tests. B7 then completed a spin prime test of multiple engines on November 12, 2022, and a 14 engine static fire test on November 14, 2022, and finally an 11 engine static fire in an autogenous pressurization test on November 29, 2022. On December 9, 2022, B7 rolled back to Mega Bay 1 for further shielding. In January 2023, Booster 7 was rolled back to the launch site where it was stacked with Ship 24 on the Orbital Launch Mount (OLM) for partial and full Wet Dress Rehearsals before Ship 24 was detached and sent to the Rocket Garden for final TPS work. On February 9, 2023, Booster 7 attempted a 10-second duration 33-engine static fire where 31 of the 33 engines successfully fired for the full duration. One of its engines was disabled just before testing, and one engine shutdown prematurely. On April 20, 2023, Booster 7 was launched on Integrated Flight Test 1, being destroyed before stage separation after a fire in the aft section severed connections between its engines and flight computers, resulting in a loss of attitude control and FTS activation.

The first part of B8, the engine thrust puck, was spotted on October 5, 2021. Other parts for B8 were observed on February 3, 2022. The booster was fully stacked on July 8, 2022. It was moved to the launch site on September 19, 2022, though it was not tested there. Booster 8 was scrapped in January 2023 in favor of Booster 9. Booster 8's hydraulic power units were used to replace Booster 7s, along with several other parts, including the engine shielding.

B9–B12
B9 finished stacking in late 2022, and was moved to the OLS cryogenic station on December 15, 2022. Two cryogenic proof tests were conducted on December 21 and December 29, both of which were successful. B9 was rolled back to Mega Bay 1 on January 10, 2023 for engine installation. Among several other upgrades, Booster 9 was the first to feature an electric thrust vector control (ETVC) gimbaling system of the raptor engines. This system replaced the hydraulic power units that were used until Booster 8. On July 20, 2023 Booster 9 was rolled to the launch site, and lifted onto the Orbital Launch Mount (OLM) in preparation for its testing campaign. On July 23 Booster 9 performed a cryogenic proof test on the OLM. This was followed by a spin prime test on August 4.  On August 6, Booster 9 fired 29 engines for 2.7 seconds, instead of the planned 33 engines for 5 seconds. It was then moved off of the OLM and rolled back to Mega Bay 1, where its vented interstage was added on August 16. B9 was moved back onto the OLM on August 22 and underwent another spin prime test the next day. On August 25, Booster 9 underwent a static fire of all 33 engines, lasting around 6 seconds. Two engines shut off early during the test. On September 5, Ship 25 (S25) was lifted onto B9 for the first time. On September 14, S25 was removed from B9, followed one week later by the vented interstage. On September 26, the vented interstage was lifted onto B9, only to be removed on October 9. It was lifted back onto B9 on October 16, along with S25. S25 was removed on October 17, and then lifted back onto B9 on October 20. On October 22, B9 underwent two partial cryogenic tests, while S25 was not tested. On October 24, B9 and S25 completed a wet dress rehearsal (WDR). On October 26, S25 was removed from B9 for flight termination system (FTS) installation. This was followed by the removal of the vented interstage one day later. The vented interstage was then placed back on B9 on October 28. On November 9, B9's FTS was installed, followed by S25 being restacked onto B9, and then destacked on November 11. The vented interstage was removed the next day. On November 15, the vented interstage was reattached to B9, followed by the stacking of S25 for Integrated Flight Test 2. Due to a failed grid fin actuator, S25 was destacked on November 16, and restacked on November 17. The following day, November 18, Booster 9 and Ship 25 lifted off with all 33 engines lit at 7:02 am CST. Following the successful separation from S25, B9 was destroyed after several engine failures during the boost-back burn.

B10 was fully stacked in March 2023. B10 was moved to Massey's for cryogenic testing on July 7, undergoing a cryogenic proof test on July 18. It was moved to the rocket garden on July 21, and was then moved to Mega Bay 1 on August 17. On September 10, B10 was moved back to Massey's for additional cryogenic testing. A cryogenic test was performed on September 13, followed by a second on September 15 and a third on September 17. It was moved back to Mega Bay 1 on September 19 for engine and interstage installation. On December 4, B10 received its vented interstage, and was moved to the Rocket Garden on December 5. SpaceX confirmed that B10 would be used for IFT-3 shortly after that. On December 18, B10 was moved to the orbital launch site, followed by a lift onto OLM A the next day. A static fire test was attempted on December 21; however, it was aborted for unknown reasons. On December 29, B10 conducted a 33-engine static fire test, followed by its removal from OLM A on December 30. On January 2, 2024, B10 was moved back to the Production Site. B10s vented interstage was removed on January 15 and reinstalled on January 26. On February 8, B10 was removed from Engine Installation Stand 3, before being transported to the Orbital Launch Site for a WDR. On February 9, B10 was lifted onto OLM A, and on February 10, Ship 28 (S28) was lifted onto B10. S28 was destacked on February 12, potentially due to an issue with the Vented Interstage. On February 13, S28 was restacked onto B10. On February 14, a WDR was aborted. A second WDR was attempted on February 16, and it was also aborted. On February 18, S28 was destacked, followed by B10s removal from OLM A on February 19. On February 20, B10 was moved into the Mega Bay, where it was lifted onto Engine Installation Stand 3. On February 28, B10 was moved back to the Launch Site, before being lifted onto OLM A. S28 was stacked on B10 on March 1. On March 3, B10 and S28 completed a WDR, followed by a destack for FTS arming on March 5. The FTS was armed on March 8, followed by S28 being restacked on March 10. On March 14, B10 was launched with S28 on IFT-3, completing the ascent burn with zero engine failures. Six engines failed during the boostback burn. During its landing burn, only three engines started up with two failing shortly thereafter. In June 2023, B11 was fully stacked. On October 12, B11 was moved to Massey's test site on a Thrust Simulator Stand, where it was cryo-tested two days later. It was then tested on October 18. On November 19, B11 was moved back to Mega Bay 1 for engine and interstage installation. On February 2, 2024, SpaceX released an image of B11, with multiples engines being visible. It was moved to the Launch Site for static-fire testing on April 4 before being lifted onto OLM A. It conducted a 33-engine static-fire on April 5. On April 7, it was removed from OLM A, and rolled back to Mega Bay 1 for pre-flight modifications. On April 28, B11's Vented Interstage was rolled into Mega Bay 1. B11's vented interstage was installed between April 28 and May 7. On May 10, B11 was rolled out of Mega Bay 1, and rolled to the Orbital Launch Site. It was lifted onto the OLM on May 11. On May 15, Ship 29 (S29) was lifted onto B11 for Wet Dress Rehearsal testing, with the combined vehicle completing a partial cryogenic test on May 16. A full Wet Dress Rehearsal was conducted on May 20, followed by S29 being destacked for tile work on May 21. S29 was restacked on May 26, followed by a second Wet Dress Rehearsal on May 28. On May 29, S29 was destacked for final tile work and Flight Termination System (FTS) Installation, with FTS installation occurring on May 30. S29 was restacked on June 1, followed by a third destack on June 4. S29 was stacked onto B11 for the fourth and final time on June 5. On June 6, B11 and S29 launched on IFT-4, with a single engine failure occurring shortly after liftoff. The boostback burn saw no engine failures, though a second engine failed during the landing burn. B12 began assembly in June 2023. On December 11, 2023, B12 was moved onto engine installation 1. On December 28, 2023, B12 was moved onto a thrust simulator stand before being moved to Massey's for cryogenic testing. On January 10, 2024, B12 underwent its first cryogenic test, and a second test on January 12, 2024. B12 was moved to the rocket garden in mid-January 2024, and on January 24, 2024, B12 was moved into Mega Bay 1, presumably for engine and interstage installation. On February 2, 2024, SpaceX released an image showing the process of engine installation on B12 had begun. B12 rolled out to the launch site on July 9 for static fire testing, followed by a lift onto OLM A the same day. On July 11, B12 underwent a pressurization test. On July 12, B12 conducted a 33 engine spin prime, followed by a 33 engine static fire on July 15. B12 was rolled back for vented interstage installation on July 16, 2024.

B13–B16
B13's assembly was completed on February 3, 2024. It was rolled to Massey's test site for cryogenic testing on April 25. B13 completed its first cryo-test on April 26, and a second cryogenic test on April 29. It was then moved to Mega Bay 1 on May 3, and lifted onto Engine Installation Stand 3.

On May 11, SpaceX released an image showing that B14 had been assembled.

Test articles
BN2.1 was rolled out on June 3, 2021 for cryogenic tests. It conducted two tests, the first on June 8, 2021, and the second on June 17, 2021.

B2.1 (not BN2.1) conducted three cryogenic tests on December 1, 2021, December 2, 2021, and December 3, 2021.

B6.1 was originally intended to be the third flight-worthy super heavy, but was repurposed as a test tank. In May 2023, it was used to test the modified FTS system, after the FTS on B7 and S24 failed to destroy the vehicle.

Liquid Oxygen Landing Test Tank (LOX LTT) was based on the LOX Landing tank on the Booster. It was cryo tested at Mcgregor in early 2022.

B7.1 was first cryogenically proof tested on 28 June 2022, and tested again on 19 July 2022. During a suspected pressurize to failure test two days later, it received minor damage. After repairs, it underwent a fourth cryogenic proof test on July 27, 2022, a fifth on September 1, 2022, and a sixth five days later. It then rolled back to the production site on September 16, 2022. B7.1 was then moved to the Massey's test site in September 2022, and then scrapped in December 2023.

Hot Stage Load Head (HSLH) was a test article designed to verify the structural integrity of the interstage of Super Heavy Boosters 9+. It was transported to the Massey's test site on July 30, 2023, before being loaded onto the Can Crusher testing device. In mid-October 2023, it was moved back to the production site, where it was disassembled.

B14.1 is a test article consisting of a booster common dome and a forward section. After structural testing at Masseys, it was moved to the launch site on June 21, 2024, and lifted onto OLM A. It was tested on June 26, followed by additional testing on June 27. It was then removed from OLM A on June 28, and rolled to the Rocket Garden.