Starship development history

The SpaceX Starship is a fully-reusable launch vehicle and spacecraft that is being privately developed by SpaceX.[1] It is designed to be a long-duration cargo and passenger-carrying spacecraft.[2] The development of the Starship began around 2012.

While the Starship program had only a small development team during the early years, and a larger development and build team since late 2018, Musk made Starship the top SpaceX development priority following the first human spaceflight launch of Crew Dragon in May 2020, except for anything related to reduction of crew return risk.[3]

Background

The launch vehicle was initially mentioned in public discussions by SpaceX CEO Elon Musk in 2012 as part of a description of the company's overall Mars system architecture, then known as Mars Colonial Transporter (MCT).[4] It was proposed as a privately-funded development project to design and build a spaceflight system[5] of reusable rocket engines, launch vehicles and space capsules to eventually transport humans to Mars and return them to Earth.

As early as 2007 however, Musk had stated a personal goal of eventually enabling human exploration and settlement of Mars.[6][7] Bits of additional information about the mission architecture were released in 2011–2015, including a 2014 statement that initial colonists would arrive at Mars no earlier than the middle of the 2020s,[4] and SpaceX began development of the large Raptor rocket engine for the MCT before 2014.

Musk stated in a 2011 interview that he hoped to send humans to Mars' surface within 10–20 years,[7] and in late 2012 that he envisioned the first colonists arriving no earlier than the middle of the 2020s.[4][8][9]

In October 2012, Musk first publicly articulated a high-level plan to build a second reusable rocket system with capabilities substantially beyond the SpaceX launch vehicles on which SpaceX had by then spent several billion US dollars.[10] This new vehicle was to be "an evolution of SpaceX's Falcon 9 booster ... much bigger [than Falcon 9]." But Musk indicated that SpaceX would not be speaking publicly about it until 2013.[4][11] In June 2013, Musk stated that he intended to hold off any potential IPO of SpaceX shares on the stock market until after the "Mars Colonial Transporter is flying regularly."[12][13]

In February 2014, the principal payload for the MCT was announced to be a large interplanetary spacecraft, capable of carrying up to 100 tonnes (220,000 lb) of passengers and cargo.[14] Musk stated that MCT will be "100 times the size of an SUV".[15] According to SpaceX engine development head Tom Mueller, concept designs at the time indicated SpaceX could use nine Raptor engines on a single rocket, similar to the use of nine Merlin engines on each Falcon 9 booster core, in order "to put over 100 tons of cargo on Mars."[15] At that time, it appeared that the large rocket core that would be used for the booster to be used with MCT would be at least 10 meters (33 ft) in diameter—nearly three times the diameter and over seven times the cross-sectional area of the Falcon 9 booster cores—and was expected to have up to three rocket cores with a total of at least 27 engines.[5]

By August 2014, media sources speculated that the initial flight test of the Raptor-driven super-heavy launch vehicle could occur as early as 2020, in order to fully test the engines under orbital spaceflight conditions; however, any colonization effort was then reported to continue to be "deep into the future".[16][17]

Interplanetary Transport System
Interplanetary Spaceship design concept, 2016 (with nine Raptor engines)

In January 2015, Musk said that he hoped to release details of the "completely new architecture" for the Mars transport system in late 2015 but those plans changed and, by the end of the year, the plan to publicly release additional specifics had moved to 2016.[14][18] Musk stated in June 2016 that the first uncrewed MCT Mars flight could happen as early as 2022, to be followed by the first crewed MCT Mars flight departing as early as 2024.[19][20] By mid-2016 the company continued to call for the arrival of the first humans on Mars no earlier than 2025.[19] By 2016, the rocket had not yet been given a formal name by SpaceX, although Musk commented on a proposal on Twitter to name it "Millennium".[21] In his September 2016 announcement, Musk referred to the vehicle versions as the "ITS booster", the "Interplanetary Spaceship", and the "ITS tanker".

In mid-September 2016, Musk noted that the Mars Colonial Transporter name would not continue, as the system would be able to "go well beyond Mars", and that a new name would be needed. The name selected was Interplanetary Transport System (ITS), although in an AMA on Reddit on Oct 23, 2016, Musk stated, "I think we need a new name. ITS just isn't working. I'm using BFR and BFS for the rocket and spaceship, which is fine internally, but...", without stating what the new name might be.[22]

Musk unveiled details of the space mission architecture, launch vehicle, spacecraft, and Raptor engines that power the vehicles at the 67th International Astronautical Congress on September 27, 2016. The first firing of a Raptor engine occurred on a test stand in September 2016 as well.[23][24]

In October 2016, Musk indicated that the initial prepreg carbon-fiber tank test article, built with no sealing liner, had performed well in initial cryogenic fluid testing, and that a pressure test of the tank at approximately 2/3 of the design burst pressure was slated for later in 2016, with the very large tank placed on an ocean barge for the test.[25] This test was successfully completed in November 2016.[26]

In July 2017, Musk indicated that the architecture had "evolved quite a bit" since the 2016 articulation of the Mars architecture. A key driver of the updated architecture was to be making the system useful for substantial Earth-orbit and cislunar launches so that the system might pay for itself, in part, through economic spaceflight activities in the near-Earth space zone.[27] In September 2018, a less drastic redesign was announced, stretching the second stage slightly and adding radially-steerable forward canards and aft fins, used for pitch control in a new reentry profile resembling a descending skydiver. The aft fins act as landing legs, with a third leg on the top that looks identical but serves no aerodynamic purpose.[28]

Design

The ITS stack was composed of two stages. The first stage was always to be an "ITS booster" while the second stage would have been either an "Interplanetary Spaceship" (for beyond-Earth-orbit missions) or an "ITS tanker" (for on-orbit propellant transfer operations).

Both stages of the ITS were to be powered by Raptor bipropellant liquid rocket engines utilizing the full flow staged combustion cycle with liquid methane fuel and liquid oxygen oxidizer.[29] Both propellants would be fully in the gas phase before entering the Raptor combustion chamber.[5] Both stages were intended to utilize a bleed-off of the high-pressure gas for autogenous pressurization of the propellant tanks, eliminating the problematic high-pressure helium pressurization system used in the Falcon 9 launch vehicle.[30][31] The self-pressurization gas system is a critical part of SpaceX strategy to reduce launch vehicle fluids from five in their legacy Falcon 9 vehicle family to just two, eliminating not only the helium tank pressurant but all hypergolic propellants as well as nitrogen for cold-gas reaction-control thrusters.[23]

The overall launch vehicle height, first stage and the integrated second-stage/spacecraft, was 122 m (400 ft).[32] Both stages of the ITS were to have been constructed of lightweight-yet-strong carbon fiber, even the deep-cryogenic propellant tanks, a major change from the aluminum-lithium alloy tank and structure material used in SpaceX Falcon 9 family of launch vehicles. Both stages are fully reusable and will land vertically, technology initially developed on the Falcon 9 launch vehicle first stages in 2012–2016.[30][31] Gross liftoff mass is 10,500 tonnes (23,100,000 lb) at a lift-off thrust of 128 meganewtons (29,000,000 lbf). ITS would be able to carry a payload to low-Earth orbit of 550 tonnes (1,210,000 lb) in expendable-mode and 300 tonnes (660,000 lb) in reusable mode.[33]

ITS booster

The ITS booster was a 12 m-diameter (39 ft), 77.5 m-high (254 ft), reusable first stage, to be powered by 42 sea-level rated Raptor engines producing some 3,024 kilonewtons (680,000 lbf) of thrust in each engine. Total booster thrust would have been approximately 130 MN (29,000,000 lbf), several times the 36 MN (8,000,000 lbf) thrust of the Saturn V Moon mission launch vehicle.[30]

The design engine configuration included 21 engines in an outer ring and 14 in an inner ring, with these 35 engines fixed in place. The center cluster of seven engines were to be gimbaled for directional control, although some directional control to the rocket was to be performed by utilizing differential thrust on the fixed engines. Design thrust on each engine was aiming to be variable between 20 and 100 percent of rated thrust.[31]

Methane/oxygen would also be used to power the control thrusters, as gas thrusters rather than the subcooled liquid used to power the main engines. The methalox control thrusters were to be used to control booster orientation in space, as well as to help provide additional accuracy in landing once the velocity of the descending booster has slowed.[31]

The design was intended to use about 7% of the total propellant load at launch in order to support the reusable aspect and bring the booster back to the launch pad for a vertical landing, assessment, and relaunch,[31] assuming a separation velocity of approximately 8,650 km/h (5,370 mph).[34] The design called for grid fins to be used during atmospheric reentry, once the atmosphere is sufficiently dense, to control the attitude of the rocket and fine tune the landing location.[31] The booster return flights were expected to encounter loads lower than those experienced on the Falcon 9 reentries, principally because the ITS would have both a lower mass ratio and a lower density than Falcon 9.[25] The booster was to be designed for 20 g nominal loads, and possibly as high as 30–40 gs without breaking up.[25]

In contrast to the landing approach used on SpaceX's mid-2010s reusable rocket first stages—either a large, flat concrete pad or downrange floating landing platform used with Falcon 9 and Falcon Heavy—the ITS booster was to be designed to land on the launch mount itself, where it may then be refilled with propellant and checked out for follow-on flights.[31]

Spacecraft that operate briefly as upper stages during launch

The ITS did not have a dedicated and single-function second stage in the way most launch vehicles have had. Instead, the upper stage function of gaining sufficient velocity to place a payload into Earth orbit is provided as a relatively short term role by a spacecraft that has all the requisite systems for long-duration spaceflight.[31] This is not a role that most upper stages have had in launch vehicle designs through the 2010s, as typical upper stage on-orbit life is measured in hours. Previous exceptions to this norm exist, for example the Space Shuttle orbiter provided part of the boost energy and all of the second stage energy for lofting itself into low-Earth orbit. Differences also exist: the Space Shuttle expended its propellant tank and primary launch vehicle structure on ascent, whereas the ITS first- and second-stage options are designed to be fully reusable.

In the 2016 design, SpaceX had identified two spacecraft that would also play the upper stage role on each Earth-away launch: the "Interplanetary Spaceship" and the "ITS tanker". Both spacecraft are the same physical external dimensions: 49.5 m (162 ft)-long and 12 m (39 ft)-diameter 17 m (56 ft) across at the widest point. Both designs were powered by six vacuum-optimized Raptor engines, each producing 3.5 MN (790,000 lbf) thrust, and were to have had three lower-expansion-ratio Raptor engines for in-space maneuvering as well as during descent and landing to allow for reuse on future launches.[30][33]

Interplanetary Spaceship

The Interplanetary Spaceship was a large passenger-carrying spacecraft design proposed by SpaceX as part of their ITS launch vehicle in September 2016. The ship would operate as a second-stage of the orbital launch vehicle on Earth-ascents—and would also be the interplanetary transport vehicle for both cargo and passengers—capable of transporting up to 450 tonnes (990,000 lb) of cargo per trip to Mars following propellant-refill in Earth orbit.[30]

In addition to use during maneuvering, descent and landing, the three lower-expansion-ratio Raptor engines were also to have been used for initial ascent from the surface of Mars.[30] In 2016, the first test launch of a spaceship was not expected until 2020 or later, and the first flight of the ITS booster was expected to follow a year or more later.[35]

Early Mars flights—in the mid-2020s or later—were expected to carry mostly equipment and few people.[4]

ITS tanker

The ITS tanker is a propellant tanker variant of the ITS second stage. This spacecraft design was to be used exclusively for launch and short-term holding of propellants to be transported to low-Earth orbit. Once on orbit, a rendezvous operation was to have been effected with one of the Interplanetary Spaceships, plumbing connections made, while a maximum of 380 tonnes (840,000 lb) of liquid methane and liquid oxygen propellants would be transferred in one load to the spaceship. To fully fuel an Interplanetary Spaceship for a long-duration interplanetary flight, it was expected that up to five tankers would be required to launch from Earth, carrying and transferring a total of nearly 1,900 tonnes (4,200,000 lb) of propellant to fully load the spaceship for the journey.[33][31]

Following completion of the on-orbit propellant offloading, the reusable tanker was to reenter the Earth's atmosphere, land, and be prepared for another tanker flight.[33]

Reusability
2016 artist's concept of ITS booster returning to the launch pad

Both stages were to be designed by SpaceX to be fully reusable and were to land vertically, using a set of technologies previously developed by SpaceX and tested in 2013–2016 on a variety of Falcon 9 test vehicles as well as actual Falcon 9 launch vehicles.[30]

Importantly, the "fully and rapidly reusable" aspect of the ITS design was the largest factor in the SpaceX analysis for bringing down the currently huge cost of transporting mass to space, in general, and to interplanetary destinations, in particular. While the transport system under development in 2016-2017 relied on a combination of several elements to make long-duration beyond Earth orbit (BEO) spaceflights possible by reducing the cost per ton delivered to Mars, the reusability aspect of the launch and spacecraft vehicles alone was expected by SpaceX to reduce that cost by approximately 2 1/2 orders of magnitude over what NASA had previously achieved on similar missions. Musk stated that this is over half of the total 4 1/2 orders of magnitude reduction that he believes is needed to enable a sustainable settlement off Earth to emerge.[36][33]

Operations concept

The concept of operations for ITS launches envisioned the fully loaded second-stage reaching orbit with only minimal propellant remaining in the Interplanetary Spaceship's tanks. Then, while the spaceship remained in Earth orbit, three to five ITS tankers would be launched from Earth carrying additional methane fuel and liquid oxygen oxidizer to rendezvous with, and transfer propellant to, the outgoing spaceship. Once refueled, the spaceship was to perform a trans-Mars injection burn, departing Earth orbit for the interplanetary portion of the journey.[30]

Big Falcon Rocket
2017 artist's concept of BFS cargo

In September 2017, at the 68th annual meeting of the International Astronautical Congress, SpaceX unveiled the updated vehicle design. Musk said, "we are searching for the right name, but the code name, at least, is BFR."[37]

The Big Falcon Rocket (BFR), also known as Big Fucking Rocket, was a 9-meter (30 ft) diameter carbon-composite launch vehicle, using methalox-fueled Raptor rocket engine technology directed initially at the Earth-orbit and cislunar environment, later, for flights to Mars.[38][39]

The BFR was cylindrical and included a small delta wing at the rear end which included a split flap for pitch and roll control. The delta wing and split flaps were said to be needed to expand the flight envelope to allow the ship to land in a variety of atmospheric densities (none, thin, or heavy atmosphere) with a wide range of payloads (small, heavy, or none) in the nose of the ship.[38][37]:18:05–19:25 Three versions of the ship were described: BFS cargo, BFS tanker, and BFS crew. The cargo version would be used to launch satellites to low Earth orbit—delivering "significantly more satellites at a time than anything that has been done before"[38]—as well as for cargo transport to the Moon and Mars. After retanking in a high-elliptic Earth orbit the spaceship was being designed to be able to land on the Moon and return to Earth without further refueling.[38][37]:31:50

The engine layout, reentry aerodynamic surface designs, and even the basic material of construction have each changed markedly since the initial public unveiling of the BFR in 2017, in order to balance objectives such as payload mass, landing capabilities, and reliability. The initial design at the unveiling showed the ship with six Raptor engines (two sea-level, four vacuum), aerodynamic control surfaces of a delta wing with split flaps, and a plan to build both stages of the launch vehicle out of carbon composite materials.[37]

By late 2017, SpaceX added a third sea-level engine to the conceptual design to increase engine-out capability and allow landings with greater payload mass, bringing the total number of engines to seven.[40]

Additionally, the BFR was shown to theoretically have the capability to carry passengers and/or cargo in rapid Earth-to-Earth transport, delivering its payload anywhere on Earth within 90 minutes.[38]

By September 2017, Raptor engines had been tested for a combined total of 1,200 seconds of test firing time over 42 main engine tests. The longest test was 100 seconds, which was limited by the size of the propellant tanks at the SpaceX ground test facility. The test engine operates at 20 MPa (200 bar; 2,900 psi) pressure. The flight engine is aimed for 25 MPa (250 bar; 3,600 psi), and SpaceX expects to achieve 30 MPa (300 bar; 4,400 psi) in later iterations.[37] In November 2017, SpaceX president and COO Gwynne Shotwell indicated that approximately half of all development work on BFR was then focused on the Raptor engine.[41]

The aspirational goal in 2017 was to send the first two cargo missions to Mars in 2022,[38] with the goal to "confirm water resources and identify hazards" while deploying "power, mining, and life support infrastructure" in place for future flights, followed by four ships in 2024, two crewed BFR spaceships plus two cargo-only ships bringing additional equipment and supplies with the goal of setting up the propellant production plant.[37]

By early 2018, the first ship using carbon composite structure was under construction, and SpaceX had begun building a new permanent production facility to build the 9-meter vehicles at the Port of Los Angeles. Manufacture of the first ship was underway by March 2018 in a temporary facility at the port,[42] with first suborbital test flights planned for no earlier than 2019.[42][43] The company continued to state publicly its aspirational goal for initial Mars-bound cargo flights of BFR launching as early as 2022, followed by the first crewed flight to Mars one synodic period later, in 2024,[42][39] consistent with the no-earlier-than dates mentioned in late-2017.

Back in 2015, SpaceX had been scouting for manufacturing facility locations to build the large rocket, with locations being investigated in California, Texas, Louisiana,[44] and Florida.[45] By September 2017, SpaceX had already started building launch vehicle components: "The tooling for the main tanks has been ordered, the facility is being built, we will start construction of the first ship [in the second quarter of 2018.]"[37]

In March 2018, SpaceX announced that it would manufacture its next-generation, 9-meter-diameter (30 ft) launch vehicle and spaceship at a new facility the company is constructing in 2018–2019 on Seaside Drive at the Port of Los Angeles. The company had leased an 18-acre (7.3 ha) site for 10 years, with multiple renewals possible, and will use the site for manufacturing, recovery from shipborne landings, and refurbishment of both the booster and the spaceship.[46][47][48] Final regulatory approval of the new manufacturing facility came from the Board of Harbor Commissioners in April 2018,[44] and the Los Angeles City Council in May.[49] By that time, approximately 40 SpaceX employees were working on the design and construction of BFR.[44] Over time, the project was expected to have 700 technical jobs.[45] The permanent Port of Los Angeles facility was projected to be a 203,500-square-foot (18,910 m2) building that would be 105 feet (32 m) tall.[50] The fully assembled launch vehicle was expected at that time to be transported by barge, through the Panama Canal, to Cape Canaveral in Florida for launch.[44]

In August 2018, for the first time, the US military publicly discussed interest in using the BFR. The head of USAF Air Mobility Command was specifically interested in BFRs ability to move up to 150 t (330,000 lb) of cargo to anywhere in the world using the projected Earth-to-Earth capability in under 30 minutes, for "less than the cost of a C-5". They projected the large transport capability "could happen within the next five to 10 years."[51][52]

Starship and Super Heavy
2018 artist's concept of the Starship's former design following stage separation

In a September 2018 announcement of a planned 2023 lunar circumnavigation mission, a private flight called #dearMoon project,[53] Musk showed a redesigned concept for the BFR second stage and spaceship with three rear fins and two front canard fins added for atmospheric entry, replacing the previous delta wing and split flaps shown a year earlier. The revised BFR design was to use seven identically-sized Raptor engines in the second stage; the same engine model as would be used on the first stage. The second stage design had two small actuating canard fins near the nose of the ship, and three large fins at the base, two of which would actuate, with all three serving as landing legs.[54] Additionally, SpaceX also stated later that September that they were "no longer planning to upgrade Falcon 9 second stage for reusability."[55] The two major parts of the re-designed BFR were given descriptive names in November: "Starship" for the upper stage and "Super Heavy" for the booster stage, which Musk pointed out was "needed to escape Earth's deep gravity well (not needed for other planets or moons)."[56]

In May 2019, the final Starship design changed back to six Raptor engines, with three optimized for sea-level and three optimized for vacuum.[57]

Prototypes and testing
Name Start of construction Decommissioned Construction site Status Flights Notes
Starhopper December 2018 August 2019 Boca Chica, Texas Retired 3
Mk1 December 2018 November 2019 Boca Chica, Texas Destroyed 0
Mk2 c. December 2018 – c. May 2019 November 2019[58] Cocoa, Florida Suspended 0 Was never completed, described as dead before arrival on November 2019.[58]
Mk4 October 2019[59] November 2019 Cocoa, Florida Suspended 0 Unknown stage of completion, presumed not assembled at all (only some components made); perhaps to be scrapped. Described as dead before arrival.[58]
SN1[lower-alpha 1] c. October 2019 February 2020 Boca Chica, Texas Destroyed 0 Destroyed during a pressure test on 28 February 2020.[61]
SN2 February 2020 March 2020 Boca Chica, Texas Retired N/A Designated SN2 but was only a small scale test tank used to test welding quality on the thrust puck on 8 March 2020, found on the bottom of the vehicle where three sea-level Raptor engines would be mounted, after the failure of SN1 thrust puck during a cryogenic tank pressure test.[62]
SN3 March 2020 April 2020 Boca Chica, Texas Destroyed 0 On 3 April 2020, it was destroyed during tank testing due to a test configuration error.[63] Had been slated for a Raptor static fire and short-duration low-altitude test flights.[64]
SN4 March 2020 May 2020 Boca Chica, Texas Destroyed 0 Completed five Raptor static fire tests and planned for short duration low altitude test flights with one mounted Raptor engine. First full Starship tank to pass cryogenic pressure test and Raptor static fire. It was destroyed on 29 May 2020 after a static fire test of its single Raptor engine due to a failure with the Ground Support Equipment's quick disconnect function.[65][66][67] SN4 was planned to make a short hop test flight once regulator suborbital launch license would have been received.[68]
SN5 April 2020 N/A Boca Chica, Texas Undergoing testing 0 Currently planned to have three Raptor engines attached. As of mid-May, it was expected to be the first test vehicle to attempt a high-altitude (20 km) test flight.[68] SN5 is currently on the test pad waiting for first tests.
SN6 May 2020 N/A Boca Chica, Texas Under construction[68][69] 0
SN7 May 2020 June 2020 Boca Chica, Texas Destroyed N/A Designated SN7 but was only a small scale test tank. On 15 June 2020, the tank did not burst, but began to leak at a pressure of 7.6 bar. [70][69] After repairs, the tank was tested to destruction on 23 June 2020.[71]

Starhopper
Starhopper
Starhopper configuration as flown in August 2019

On December 2018, nine months after starting construction of some parts of the first test article carbon composite Starship low-altitude test vehicle, Musk announced a "counterintuitive new design approach" would be taken by the company: the primary construction material for the rocket's structure and propellant tanks would be "fairly heavy...but extremely strong" metal,[72][73][74] subsequently revealed to be stainless steel.[75] Musk revealed on 23 December 2018 that the initial test article—the Starship Hopper,[76] Hopper, or Starhopper[77][78]— had been under construction there for several weeks, out in the open on SpaceX property. The Starhopper was being built from a 300-series stainless steel. According to Musk, the reason for using this material is that "it's [stainless steel] obviously cheap, it’s obviously fast—but it's not obviously the lightest. But it is actually the lightest. If you look at the properties of a high-quality stainless steel, the thing that isn’t obvious is that at cryogenic temperatures, the strength is boosted by 50 percent."[79] The high melting point of 300-series still would mean the leeward side of Starship would need no insulation during reentry, while the much hotter windward side would be cooled by allowing fuel or water to bleed through micropores in a double-wall stainless steel skin, removing heat by evaporation. The Starhopper had a single engine and was used for a test flight to develop the landing and low-altitude/low-velocity control algorithms.

By late May 2019, while the Starhopper was preparing for untethered flight tests in South Texas, they were building two high-altitude prototypes simultaneously, Mk1 in Texas and Mk2 in Florida. The two ships were constructed by competing teams—that were required to share progress, insights, and build techniques with the other team, but neither team is required to use the other team's techniques.[80][81][82] The larger Mk1 and Mk2 test vehicles featured three Raptor methalox engines meant to reach an altitude of no more than 5 km (3.1 mi), and the initial flight was expected no earlier than the first half of 2019.[83][84] Construction of a Mk3 prototype began in late-2019. A first orbital flight was not expected until Mk4 or Mk5 in mid 2020.[85] The build of the first Super Heavy booster stage was projected to be able to start by September.[81] At the time, neither of the two orbital prototypes yet had aerodynamic control surfaces nor landing legs added to the under construction tank structures, and Musk indicated that the design for both would be changing once again.[86] On 21 September 2019, the externally-visible "moving fins"[87] began to be added to the Mk1 prototype, giving a view into the promised mid-2019 redesign of the aerodynamic control surfaces for the test vehicles.[88][89]

In July 2019, the Starhopper made its initial flight test, a "hop" of approximately 20 m (66 ft) altitude,[90] and a second and final "hop" in August, reaching an altitude of approximately 150 m (490 ft)[91] and landing approximately 100 m (110 yd) from the launchpad, demonstrating the first use of the Raptor engine in real flight.

Mk1, Mk2, Mk3, Mk4
Starship Mk1

SpaceX completed the external structure of the Starship Mk1 in time for Musk's public update in September 2019. Watching the construction in progress before the event, observers circulated photos online and speculated about the most visible changes, including a move to two tail fins from the earlier three. During the event, Musk added that landing would now be accomplished on six dedicated landing legs, following a re-entry protected by ceramic heat tiles.[92] Updated specifications were provided: when optimized, Starship was expected to mass at 120,000 kg (260,000 lb) empty and be able to initially transport a payload of 100,000 kg (220,000 lb) with an objective of growing that to 150,000 kg (330,000 lb) over time. Musk suggested that an orbital flight might be achieved by the fourth or fifth test prototype in 2020, using a Super Heavy booster in a two-stage-to-orbit launch vehicle configuration,[93][94] and emphasis was placed on possible future lunar missions.[95]

In September 2019, Elon Musk unveiled Starship Mk1,[96][97] and in 20 November 2019, the Mk1 test article came apart in a tank pressure test in Texas.[98] The same day, SpaceX stated they would stop developing Mk1 and Mk2 and move on to work on the Mk3 and Mk4 articles.[99][98][100] Construction began on the Starship Mk4 in Florida by mid-October 2019.[101] A few weeks later, the work on the vehicles in Florida paused, with apparent cancellation of Mk4. Some assemblies that had been built in Florida were transported to the Texas assembly location in Boca Chica; there was reportedly an 80% reduction in the workforce at the Florida assembly location as SpaceX paused activities there.[102] SpaceX's Starship development work was now focused on the Texas site.

Characteristics

Data from: [88]

  • Size: 9 m (30 ft) diameter by approximately 50 m (160 ft) tall[85]
  • Mk1 empty mass: 200,000 kg (440,000 lb); Gross mass with propellant loaded: 1,400,000 kg (3,100,000 lb)[103]
  • Principal use: prototype test articles for engineering extension of the rocket's powered flight and atmospheric reentry flight envelope, to higher altitudes (>200 meters) and velocities than the two test flights of the Starhopper in summer 2019.
  • Test methodology: vertical-takeoff and vertical-landing suborbital spaceflight. One of many engineering objectives of the early test flights is to recover the test vehicle so that the vehicle can continue to be used on subsequent test flights to further extend the flight envelope. This is a test regime frequently seen with new aircraft, but has rarely been done with orbital spacecraft (the Space Shuttle is an exception), and has never been done on a launch vehicle second stage on powered test flights into the upper atmosphere.
  • Propulsion: (initially) three Raptor methalox engines; may test with up to six engines later in the flight test program[89]
  • Attitude control:
  • Nose cone equipment: header tanks for landing, batteries, mounting and reaction control for the front movable fins[89][105]
  • Starship prototype flight test locations:[81][80][109]
    • Texas
    • Florida

Starship SN1 (Mk3) and SN2

In December 2019, Musk announced that the Starship Mk3 would be redesignated "Starship SN1" and there would be at least minor design improvements at least through Starship SN20.[110] Musk also explained that there was a change in the production of Starship. Some parts are now stamped and TIP TIG welded vs bump-formed and flux core welded. The new production process guarantees stronger joints and a mass reduction of 20%.[111]

In January 2020, SpaceX performed pressurization tests on two test article tanks in Boca Chica[112]. One such test took place on 10 January 2020, when a test tank was intentionally destroyed by over-pressurizing it; the tank achieved pressure of 7.1 bar (710 kPa).[113] Later, another test tank underwent at least two pressurization tests; in the first experiment, on Monday 27 January 2020, the test tank withstand a pressure of 7.5 bar (750 kPa) before springing a leak. The leak was welded and the tank subjected to cryogenic pressure test on 28 January 2020, when the tank was intentionally pressurized until it ruptured and was destroyed at the pressure of 8.5 bar (850 kPa). The test was however considered a success despite the destruction of the tank, as the pressure reached, 8.5 bar (850 kPa), the pressure the tank needed to hold to be considered safe for human spaceflight; that is, the tank demonstrated a safety factor of 1.4 (1.4 times the operational pressure).[114]

Starship SN1 (originally known as Starship Mk3) was stated to be "designed for orbit" according to SpaceX. Later on, it was unclear whether this was the case (that SN1 would fly to orbit), and whether Starship SN1 would be used only for static fire testing (with one or more Raptor engines installed) and perhaps for one or more suborbital flights taking the vehicle to a 20 kilometer altitude with a soft landing back to Boca Chica.[115]

SpaceX began construction of internal components for the vehicle in December 2019, and started stacking SN1 at Boca Chica two months later.[115][116]

SpaceX began stacking SN1 in February 2020 after a series of pressurization tests on propellant tank prototypes. The weld quality of the rings had been improved[115] but SN1 failed a cryogenic pressurization test on 28 February 2020 due to a design failure in the lower tank thrust structure[117] and the test article was destroyed. The structure ruptured from the bottom up, with most of the top part sent flying in the air and crashing into ground. At the time of the rupture, the SN1 vehicle had no nose cone, flight control structures, or Raptor engines installed, and was positioned on a test stand. The loss of SN1 was similar to the loss of Starship Mk1 in November 2019, leaving little of the vehicle intact. There were no injuries.[118]

After the incident, SpaceX announced they were focusing their efforts on the next test article, Starship SN2.[118] SpaceX adjusted their Starship SN2 testing plans to verify that the failure had been corrected, and conducted a successful test using much shorter SN2 tank structure on 8 March 2020.[117]

Starship SN3 and SN4
Static fire of SN4.

In March 2020, Musk discussed SpaceX's future plans for Starship prototype tests. Starship SN3 was planned to be used for static fire tests and short hops, while SN4 will be used for longer flights.[117]

Starship SN3 was destroyed during testing on 3 April 2020.[119][120]. The cause of the failure was a testing configuration error.[121] The liquid oxygen tanks housed in the lower part of the prototype were pressurised with nitrogen in order to keep them pressurised and structurally capable of withstanding the weight of the full methane tanks undergoing testing. A valve was inadvertently commanded to open resulting in pressure loss and structural failure as the lower portion of the prototype crumbled under the weight of the heavy methane tanks.[121] While Starship SN3 was originally planned to be used for static fire tests and short hops, this setback delayed the testing timeline by a few weeks. SN4 was built reusing parts of SN3 not damaged during the mishap.[122]

Starship SN4 passed cryogenic pressure testing on 26 April 2020, making it the first prototype since the smaller SN2 test tank to do so. On the 5th[123] and 6th of May 2020, SN4 passed two static fires: One using the main tanks, while the other used the fuel header tank. Three nights later after uninstalling the engine, a new cryogenic pressure test was conducted. The prototype achieved 7.5 bar of pressure. On 19 May 2020 during the third test firing of the engine, vibrations shook loose the methane fuel piping in the engine causing a leak which ignited and spread to flammable insulation, the fire caused significant damage to the base of the rocket and destroyed the control wiring leaving SpaceX unable to command the depressurization of the fuel tanks for two days.[124] SN4 was destroyed on 29 May 2020 after a successful static fire test of its single Raptor engine, due to a failure with the Ground Support Equipment's quick disconnect function.[66]

Starship SN5 and SN6

Later in the spring 2020, SpaceX planned to conduct a 20 km test flight of Starship. The first orbital test flight of Starship is aspirationally planned to occur before the end of 2020, possibly using SN5 or SN6.[125][117]

Starship SN7

Testing of a new material, 304L steel, was conducted with SN7. [70] Destructive cryogenic strength test was performed on 15 June 2020. The test article achieved pressure of 7.6 bar before it started leaking. The leak caused only a limited damage relatively to a burst, which is a more typical result of this type of test. After repairs, the tank was tested to destruction on 23 June 2020.[126]

Suborbital test flights
Flight No. Date and time (UTC) Vehicle Launch site Suborbital apogee Outcome Duration
1 5 April 2019 Starhopper Boca Chica, Texas ~ 1 m (3 ft) Success
—
Tethered hop which hit tethered limits. With a single Raptor SN2 engine.[109]
2 25 July 2019[127] Starhopper Boca Chica, Texas 20 m (66 ft)[128] Success ~ 22 seconds
First free flight test. Single Raptor engine, S/N 6. Was previously scheduled for the day before but was aborted.[128] A test flight attempt on 24 July was scrubbed.[129]
3 27 August 2019[130]
22:00[131]		 Starhopper Boca Chica, Texas 150 m (490 ft)[130] Success ~ 57 seconds[132]
Single Raptor SN6 engine. SpaceX called this the "150 meter Starhopper Test" on their livestream. Starhopper was retired after this launch, with some parts being reused for other tests.[130][133] The test flight attempt on 26 August was scrubbed due to a problem with the Raptor engine igniters.[129]
4 TBD[134] SN5[134] Boca Chica, Texas 150 m (490 ft)[134] Planned

See also

Notes
  1. Originally designated Mk3 before naming scheme was reset after the failure of Mk1.[60]

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