Starship is a two-stage fully reusable super heavy-lift launch vehicle under development by American aerospace company SpaceX. On April 20, 2023, with the first Integrated Flight Test, Starship became the most massive, tallest, and most powerful vehicle ever to fly. SpaceX has developed Starship with the intention of lowering launch costs using economies of scale, aiming to achieve this by reusing both rocket stages by "catching" them with the launch tower's systems, increasing payload mass to orbit, increasing launch frequency, mass-manufacturing the rockets and adapting it to a wide range of space missions. Starship is the latest project in SpaceX's reusable launch system development program and plan to colonize Mars.

Starship's two stages are the Super Heavy booster and the Starship spacecraft. Both stages are equipped with Raptor engines, the first flown and mass-produced full-flow staged combustion cycle engines, which burn liquid methane (natural gas) and liquid oxygen.

As of 2024, Starship is in development with an iterative and incremental approach, involving test flights of prototype vehicles. As a successor to SpaceX's Falcon 9 and Falcon Heavy rockets, Starship is intended to perform a wide range of space missions. For missions to further destinations, such as geosynchronous orbit, the Moon, and Mars, Starship will rely on orbital refueling; a ship-to-ship propellant transfer demonstration is expected to occur in 2025. SpaceX also plans other versions of the Starship spacecraft, such as cargo (deploying SpaceX's second-generation Starlink satellite constellation) and human spaceflight (the Human Landing System variant will land astronauts on the Moon as part of the Artemis program, starting in 2027).

When stacked and fully fueled, Starship has a mass of approximately 5,000 t (11,000,000 lb), a diameter of 9 m (30 ft) and a height of 121.3 m (398 ft). The rocket has been designed with the goal of being fully reusable to reduce launch costs; it consists of the Super Heavy booster and the Starship upper stage which are powered by Raptor and Raptor Vacuum engines.

The bodies of both rocket stages are made from stainless steel and are manufactured by stacking and welding stainless steel cylinders. These cylinders have a height of 1.8 m (5 ft 11 in), a thickness of 4 mm (0.16 in) and a mass of 1,600 kg (3,500 lb) each.

Domes inside the spacecraft separate the methane and oxygen tanks. SpaceX has stated that Starship, in its "baseline reusable design", will have a payload capacity of 100–150 t (220,000–331,000 lb) to low earth orbit and 27 t (60,000 lb) to geostationary transfer orbit.

Super Heavy is 71 m (233 ft) tall, 9 m (30 ft) wide, and is composed of four general sections: the engines, the oxygen tank, the fuel tank, and the interstage. Elon Musk stated in 2021 that the final design will have a dry mass between 160 t (350,000 lb) and 200 t (440,000 lb), with the tanks weighing 80 t (180,000 lb) and the interstage 20 t (44,000 lb).

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. After Starship's second flight test, the common dome's design was changed to a more elliptical dome, which changed the propellant capacity of both tanks by an unknown, but likely negligible, amount. Both tanks are heavily reinforced, with roughly 74 stringers attached to the interior walls of the tanks. The booster's tanks hold 3,400 t (7,500,000 lb) of propellant, consisting of 2,700 t (6,000,000 lb) of liquid oxygen and 700 t (1,500,000 lb) of liquid methane.

The methane tank has a camera installed in the forward dome, enabling images of the tank's interior. Fuel is fed to the engines via a single downcomer, which terminates in a large distribution manifold above the engines. The design of this manifold was changed when Super Heavy was upgraded from 29 engines to 33, with the more modern design featuring a dedicated methane sump instead of a direct distribution manifold.

The oxygen tank terminates with the thrust structure of the vehicle. While the outer 20 engines are mounted to the walls of the aft bay, the inner thirteen are mounted directly to the thrust puck, which is part of the aft dome. A large steel structure is mounted at the bottom of the dome, reinforcing the thrust puck enough to enable its support of the inner thirteen engines, while also providing pathways for methane and oxygen to flow into the engines. Large slosh baffles were added in this region as well, beginning on Booster 10. A header tank is used to supply liquid oxygen during the landing burn for the inner thirteen engines. On Booster 15, the header tank has at least nine additional tanks attached, increasing total propellant supply during the landing burn. These tanks may have been present on Boosters 12, 13, and 14. However, this is unconfirmed. As of November 2024, Block 2 boosters are expected to have significantly larger header tanks, which may be used for the boostback burn in addition to the landing burn. Booster 5 was the only 29-engine booster to receive a header tank, which was mounted to the side of the oxygen tank. It is unknown whether or not the top of this tank was ever completed, as a forward dome was never spotted during the assembly or scrapping of the vehicle.

The methane downcomer 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 composite overwrapped pressure vessels (COPVs) and CO₂ tanks for fire suppression.

Super Heavy is powered by 33 Raptor engines housed within a dedicated shielding compartment. This compartment is not present before engine installation, thus, boosters are roughly three meters shorter before engine installation. The outer 20 engines, arranged in a single ring, are fixed. To save weight, these engines are started using ground support equipment on the launch mount and cannot be reignited for subsequent burns. The inner thirteen engines are attached to an adapter, which rests directly against the thrust puck/aft dome assembly. These 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. This system uses CO₂ tanks to purge the individual engine compartments during flight, as well as a nitrogen purge while on the launch pad. 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 super cooled propellant.

The Block 1 version of the booster (used through November 2024) produces a total of 73.5 MN (16,500,000 lb_f) just over twice that of the Saturn V first stage, with this total being expected to increase to 80.8 MN (18,200,000 lb_f) for Block 2 boosters and later up to 98.1 MN (22,100,000 lb_f) with the Block 3 vehicle. These later versions may have up to 35 engines. The combined plume of the engines produces large shock diamonds in the exhaust during the ascent burn.

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, placed at a 45-degree angle from the hardpoints. Additionally, four "cowbell" vents are located just below the common dome, which point down towards the engines, though at a slight angle.

The interstage is equipped with four electrically actuated grid fins made of stainless steel, each with a mass of roughly 3 t (6,600 lb). These grid fins are paired together, with the fins in each pair being 60 degrees apart from each other, differing from the Falcon 9 booster, which has titanium grid fins mounted 90 degrees from each other. This is done to improve control in the pitch axis. The fins remain extended during ascent to save weight. 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 3 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 engines. 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 interstage is jettisoned after completion of the boostback burn, to reduce mass during descent. As of June 2024, SpaceX does not intend to jettison the interstage when flying Block 2 and Block 3 boosters, as the interstage will be directly integrated into the vehicle.

The Block 2 version of Starship is 52.1 m (171 ft) tall, 9 m (30 ft) wide, and is composed of four general sections: the engine bay, the oxygen tank, the fuel tank, and the payload bay. The retired Block 1 was constructed in a similar manner, though it was only 50.3 m (165 ft) tall. Elon Musk stated in 2021 that the vehicle has a dry mass of roughly 100 t (220,000 lb). The windward side is protected by a heat shield, which is composed of eighteen thousand hexagonal black tiles that can withstand temperatures of 1,400 °C (2,600 °F). It is designed to protect the vehicle during atmospheric entry and to be used multiple times with minimal maintenance between flights. The silica-based tiles are attached to Starship with pins and have small gaps in between to allow for heat expansion. After IFT-4, SpaceX added a secondary ablative layer under the primary heat shield, though this was only added to the flaps of the IFT-6 vehicle. The total mass of the heat shield and ablative layer of a Block 1 ship is 10.5 t (23,000 lb).

The propellant tanks on Starship are separated by a common bulkhead, similar to the ones used on the S-II and S-IVB stages on the Saturn V rocket. While Block 2 vehicles uses an elliptical dome, the common and forward domes of the Block 1 design was more conical. Both tanks are heavily reinforced, with roughly 30 and 48 stringers attached to the interior walls of the methane and oxygen tanks, respectively. Block 1 vehicles lacked any reinforcement to the methane tank, and the oxygen tank only had 24 stringers. The vehicle's tanks hold 1,500 t (3,300,000 lb) of propellant, consisting of 1,170 t (2,580,000 lb) of liquid oxygen and 330 t (730,000 lb) of liquid methane. Running along the sides of the tanks are the "raceways", which support the transfer of pressurization gas and electrity throughout the vehicle. Beginning with Block 2 vehicles, these are covered by dedicated aerocovers.

The methane tank has a camera installed in the forward dome, enabling images of the interior of the tank. There are three baffles located inside the tank to prevent sloshing of the propellant during flight. Fuel is fed to the engines via four downcomers, with three smaller downcomers feeding the Vacuum Raptors/RVacs and the central downcomer feeding the inner three engines. The central downcomer connects to a large sump, instead of directly to the methane tank itself. The original design only featured a single downcomer, which terminated in a distribution manifold, directing propellant to the three sea level engines and the individual RVacs. Inside this tank are two additional downcomers, which provide oxygen and methane to the central three engines from the header tanks. A camera is located on the walls of the tank, near the flight termination system.

Like the methane tank, the oxygen tank also has three baffles to prevent sloshing. The oxygen tank terminates with the thrust structure of the vehicle. The RVacs are mounted directly to the aft dome, which has reinforcements mounted inside of the tank. The three sea level engines are mounted on the thrust puck, which forms the bottom of the aft dome. A conical steel structure is mounted inside the bottom of the dome, reinforcing the thrust puck enough to enable its support of the inner three engines, while also providing pathways for methane and oxygen to flow into the engines. The outer wall of the aft dome is covered in an insulation material, presumably to prevent frost from building up inside the engine bay during propellant load.

The propellant lines on the vehicles are all vacuum jacketed, reducing boiloff while in orbit. Block 1 vehicles used more conventional insulation, though only on the header tank's propellant lines.

Starship is powered by 6 Raptor engines, which are housed within a dedicated shielding compartment. This compartment is present before engine installation, and contains several critical systems. These includes some of the motors for the aft flaps, the quick disconnect interface, and at least one battery. A camera is mounted inside of this bay, enabling images of the engines during flight. Until Starship flight test 3, this section held the hydraulic power unit, which provided the three sea level engines with thrust vector control capability. The first Block 1 vehicle, S20, had multiple composite overwrapped pressure vessels (COPVs) mounted in this region as well. These components are all protected by the engine shielding.

The 3 Rvacs, which are arranged in a single ring, are in a fixed position. An additional three RVacs will be added to the Block 3 ship design. The inner three engines are attached to an adapter, which rests directly against the thrust puck/aft dome assembly. These engines are equipped with gimbal actuators, and reignite for the landing burns. After Starship's second 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 booster after the first flight test. During the ascent burn burns, the engines draw propellant from the main tanks, with all subsequent burns drawing propellant from dedicated header tanks. 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. This system uses CO₂ tanks to purge the individual engine compartments during flight, as well as a nitrogen purge while on the launch pad. The aft bay has fifteen vents visible on the outside of the ship.

The Raptor engine 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: 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 super cooled propellant.

The Block 1 version of the ship (used through November 2024) produces a total of 12.25 MN (2,750,000 lb_f) almost triple the thrust of the Saturn V second stage, with this total being expected to increase to 15.69 MN (3,530,000 lb_f) for Block 2 boosters and later up to 26.48 MN (5,950,000 lb_f) with the Block 3 vehicle.

During unpowered flight in orbit, control authority is provided by cold gas thrusters fed with residual ullage gas. Four of these thrusters are located on the methane tank. Another four are located just below the payload bay, and two on the oxygen tank. Near the top of the nosecone, there are four vents connected to the header tanks, as well as two others located on the tip of the payload bay. In the aft bay, two engine chill lines double as thrusters near the base of the vehicle. There are an additional ten vents in the aft bay, likely for preventing an overpressure in the engine shielding compartment. Beginning with S25, the Block 1 design had 14 such vents. Finally, three large liquid oxygen (LOX) vents are located in the aft bay of the vehicle, enabling the ship to dump LOX as needed. For Block 1 ships, these vents terminated in a singular large nozzle, with Block 2 vehicles, each vent splits into two smaller nozzles.

The payload bay hosts the nosecone, header tanks, forward flaps, multiple COPVs, and the "pez dispenser". The header tanks provide propellant for all burns after SECO, and are mounted at the tip of the payload bay. These tanks only connect to the sea level engines. The LOX header tank forms the top of the nosecone, with the methane header tank attached directly below it. These tanks terminate in a conical sump, which are attached to the downcomers. Block 1 vehicles lacked this sump, reducing propellant capacity. Fourteen COPV's are mounted in the space around the methane header tank, providing the startup gas for the engines, as well as six near the pez dispenser.

The nosecone has substantial internal reinforcement, mainly around the forward flap attachment points and lifting points for the chopsticks. The number of internal stringers was increased between Block 1 and Block 2 vehicles. Additional reinforcements are used to support the pez dispenser on ships equipped with one. Located along the sides of the nosecone are four Starlink antennas. Another two are placed at the bottom of the payload bay.

The pez dispenser is used to deploy Starlink satellites into LEO. It was first added to S24, though it was permanently sealed until flight 3. It consists of the dispenser mechanism and the door. The door is actuated, folding up into the payload bay to open, and lowering to close. Its approximately 0.8 m (2 ft 7 in) tall and 7.3 m (24 ft) wide. In order to account for the door, significant structural reinforcements are added around it. During assembly, additional reinforcements are added to the door. The door has substantial reinforcements added to its interior, helping prevent deformation. The door is capable of maintaining a seal during flight, so long as it is not opened.

The dispenser itself is mounted directly to the forward dome. It has a truss structure for its base, with solid steel used elsewhere. A mobile track is used in the base, enabling the dispenser to push the satellite out of the vehicle. After dispensing a satellite, the next payload is lowered onto the base, and is deployed. The opposite occurs during loading, with the dispenser raising its payloads to receive another satellite. In order to prevent the satellite from floating out of the mechanism during zero-g operations, the dispenser locks the satellites in position using a "retention frame". This is lowered alongside the satellites during operation. On Block 1 vehicles, beginning with S24, the dispenser was made from stainless steel, with SpaceX potentially changing this to aluminum on Block 2.

Starship controls its reentry with four flaps, two aft flaps mounted to the sides of the engine bay and LOX tank and two forward flaps on the payload bay. Significant structural reinforcement is added to the flap attachement point and within the flaps themselves. According to SpaceX, the flaps replace the need for wings or tailplane, reduce the fuel needed for landing, and allow landing at destinations in the Solar System where runways do not exist (for example, Mars). The flap's hinges are sealed in aerocovers because they would otherwise be easily damaged during reentry.

Despite this, damage to the forward flaps was observed on flights four, five, and six, with near complete loss occurring on flight 4. Beginning with Block 2, the design of these forward flaps was significantly changed, becoming thinner and angled. This sets them at an approximately 140 degree angle between the forward flaps, compared to the 180 degrees of the aft flaps. On Block 1 vehicles, the forward flaps were also parallel to each other. This change was made to prevent the damage observed on the last three flights of the Block 1 ship. There are two cameras located at the bottom of the flaps, with another providing images of the flap itself. Both sets of flaps feature cameras in their hinges as well.

Raptor is a family of rocket engines developed by SpaceX for use in Starship and Super Heavy vehicles. It burns liquid oxygen and methane in an efficient and complex full-flow staged combustion power cycle. The Raptor engine uses methane as fuel rather than kerosene because methane gives higher performance and prevents the build-up of deposits in the engine from coking. Methane can also be produced from carbon dioxide and water using the Sabatier reaction. The engines are designed to be reused many times with little maintenance.

Raptor operates with an oxygen-to-methane mixture ratio of about 3.6:1, lower than the stoichiometric mixture ratio of 4:1 necessary for complete combustion, since operating at higher temperatures would melt the engine. The propellants leave the pre-burners and get injected into the main combustion chamber as hot gases instead of liquid droplets, enabling a higher power density as the propellants mix rapidly via diffusion. The methane and oxygen are at high enough temperatures and pressures that they ignite on contact, eliminating the need for igniters in the main combustion chamber. The engine structure itself is mostly aluminum, copper, and steel; oxidizer-side turbopumps and manifolds subject to corrosive oxygen-rich flames are made of an Inconel-like SX500 superalloy. Some components are 3D printed.

A Raptor 2 engine produces 2.3 MN (520,000 lbf) at a specific impulse of 327 seconds (3.21 km/s) at sea level and 350 seconds (3.4 km/s) in a vacuum. Raptor vacuum, used on the Starship upper stage, is modified with a regeneratively cooled nozzle extension made of brazed steel tubes, increasing its expansion ratio to about 90 and its specific impulse in vacuum to 380 seconds (3.7 km/s). The main combustion chamber operates at a pressure of 350 bar (5,100 psi) exceeding that of any prior operational rocket engine. The Raptor's gimbaling range is 15°, higher than the RS-25's 12.5° and the Merlin's 5°. SpaceX has stated they aim to achieve a per unit production cost of US$250,000 upon starting mass production.

Performance

Starship metrics	Block 1	Block 2	Block 3
Payload to orbit (t)	N/A	100+	200+
Booster prop load (t)	3,300	3,650	4,050
Ship prop load (t)	1,200	1,500	2,300
Booster liftoff thrust (tf)	7,500	8,240	10,000
Ship initial thrust (tf)	1,250	1,600	2,700
Ship SL engines	3	3	3
Ship VAC engines	3	3	6
Booster height (m)	71	72.3	80.2
Ship height (m)	50.3	52.1	69.8
Total height (m)	121.3	124.4	150

On April 4, 2024, Elon Musk provided an update on Starship at Starbase, where two new versions of Starship were announced, Block 2 and Block 3.

Block 1 upper stage vehicles have been retired but were used for the first 6 Flight Tests. As of January 2025, Block 1 boosters are still being used.

Block 2 upper stage vehicles feature a thinner forward flap design, its flaps are positioned more leeward, a 25% increase in propellant capacity, integrated vented interstage, redesigned avionics, two "raceways", and an increase in thrust. The integrated vehicle will be a total of 3.1 m (10 ft) taller than the previous Block 1 vehicle and is planned to have a payload capacity of at least 100 tons to orbit when reused. Additionally, Block 2 vehicles will use Raptor 3, removing the need for secondary engine shielding. However, the first Block 2 vehicle, S33, received Raptor 2 engines. Initial Block 2 upper stage vehicles will use a Block 1 booster. Block 2 will be first flown on the seventh flight test.

As of June 2024, the Block 3 final configuration is unknown. The most recent configuration, as described in regulatory filings submitted to the FAA, has a height of 150 m (490 ft). The Starship second stage will feature 9 Raptor engines, while the Super Heavy booster will have up to 35. It is planned to have a payload capacity of at least 200 tons to orbit when reused.

Payloads will be integrated into Starship at a separate facility and then rolled out to the launch site. Super Heavy and Starship are then to be stacked onto their launch mount and loaded with fuel via the ship quick disconnect (SQD) arm and booster quick disconnect (BQD). The SQD and BQD retract, all 33 engines of Super Heavy ignite, and the rocket lifts off.

At approximately 159 seconds after launch at an altitude of roughly 64 km (40 mi), Super Heavy cuts off all but three of its center gimbaling rocket engines. Starship then ignites its engines while still attached to the booster, and separates. During hot-staging, the booster throttles down its engines. The booster then rotates, before igniting ten additional engines for a "boostback burn" which stops all forward velocity. After the boostback burn, the booster's engines shut off with Super Heavy on a trajectory for a controlled descent to the launch site using its grid fins for minor course corrections. Roughly six minutes after launch, shortly before landing, it ignites its inner 13 engines, then shuts off all but the inner 3, to perform a landing burn which slows it sufficiently to be caught by a pair of hydraulic actuating arms attached to the launch tower. The booster landing and catch was successfully demonstrated for the first time on October 13, 2024, with the landing of Booster 12.

Meanwhile, the Starship spacecraft continues accelerating to orbital velocity with its six Raptor engines. Once in orbit, the spacecraft is planned to be able to be refueled by another Starship tanker variant. Musk has estimated that 8 launches would be needed to refuel a Starship in low Earth orbit completely. NASA has estimated that 16 launches in short succession (due to cryogenic propellant boil-off) would be needed to refuel Starship for one lunar landing partially. To land on bodies without an atmosphere, such as the Moon, Starship will fire its engines to slow down. To land on bodies with an atmosphere, such as the Earth and Mars, Starship first slows by entering the atmosphere using a heat shield. The spacecraft would then perform a "belly-flop" maneuver by diving through the atmosphere at a 60° angle to the ground, controlling its fall using four flaps at the front and aft of the spacecraft. Shortly before landing, the Raptor engines fire, using fuel from the header tanks, to perform a "landing flip" maneuver to return to a vertical orientation, with the Raptor engines' gimbaling helping to maneuver the craft. The HLS and depot cannot reenter the atmosphere, as they lack a thermal protection system.

If Starship's second stage lands on a pad, a mobile hydraulic lift will move it to a transporter vehicle. If it lands on a floating platform, it will be transported by a barge to a port and then transported by road. The recovered Starship will either be positioned on the launch mount for another launch or refurbished at a SpaceX facility.

In November 2005, before SpaceX had launched its first rocket the Falcon 1, CEO Elon Musk first mentioned a high-capacity rocket concept able to launch 100 t (220,000 lb) to low Earth orbit, dubbed the BFR. Later in 2012, Elon Musk first publicly announced plans to develop a rocket surpassing the capabilities of Space X's existing Falcon 9. SpaceX called it the Mars Colonial Transporter, as the rocket was to transport humans to Mars and back. In 2016, the descriptor was changed to Interplanetary Transport System, as the rocket was planned to travel beyond Mars as well. The conceptual design called for a carbon fiber structure, a mass in excess of 10,000 t (22,000,000 lb) when fully fueled, a payload of 300 t (660,000 lb) to low Earth orbit while being fully reusable. By 2017, the concept was again re-dubbed the BFR.

In December 2018, the structural material was changed from carbon composites to stainless steel, marking the transition from early design concepts of the Starship. Musk cited numerous reasons for the change of material; low cost and ease of manufacture, increased strength of stainless steel at cryogenic temperatures, as well as its ability to withstand high heat. In 2019, SpaceX began to refer to the entire vehicle as Starship, with the second stage also being called Starship, and the booster Super Heavy. They also announced that Starship would use reusable heat-shield tiles similar to those of the Space Shuttle. The second-stage design had also settled on six Raptor engines by 2019: three optimized for sea-level and three optimized for vacuum. In 2019 SpaceX announced a change to the second stage's design, reducing the number of aft flaps from three to two to reduce weight. In March 2020 SpaceX released a Starship Users Guide, in which they stated the payload of Starship to LEO would be over 100 t (220,000 lb), with a payload to GTO of 21 t (46,000 lb).