Starship

SpaceX Starship SN8 prototype during a flight test, December 2020
Function	Reusable launch system Space tourism Earth-lunar transport Mars colonization[1] Multiplanetary transport Intercontinental transport
Manufacturer	SpaceX
Country of origin	United States
Cost per launch	US$2 million (aspirational)[2]
Size
Height	122 m (400 ft)[3][4]
Diameter	9 m (30 ft)[5]
Mass	5,000,000 kg (11,000,000 lb) (with payload)[6][4]
Stages	2
Capacity
Payload to LEO
Mass	+100,000 kg (220,000 lb)[7]
Volume	1,100 m3 (39,000 cu ft)[7]
Associated rockets
Family	SpaceX launch vehicles
Comparable	Saturn V N1 Space Launch System Long March 9 Falcon Heavy Energia Space Shuttle
Launch history
Status	In development
Launch sites	Boca Chica Floating launch platform
First stage - Super Heavy
Length	72 m (236 ft)[4][7]
Diameter	9 m (30 ft)[7]
Empty mass	180,000 kg (400,000 lb) (estimated)[6]
Gross mass	3,580,000 kg (7,890,000 lb) [6][7][8]
Propellant mass	3,400,000 kg (7,500,000 lb)[7]
Engines	~28 Raptor[9]
Thrust	65,000 kN (15,000,000 lbf)[10]
Specific impulse	330 s (3.2 km/s)[11]
Fuel	Subcooled  / LOX[5]
Second stage - Starship
Length	50 m (160 ft)[7]
Diameter	9 m (30 ft)[7]
Empty mass	120,000 kg (260,000 lb)[6]
Gross mass	1,320,000 kg (2,910,000 lb)[6][7][8]
Propellant mass	1,200,000 kg (2,600,000 lb)[7]
Engines	6 Raptor[5]
Thrust	c. 12,000 kN (2,700,000 lbf)[5]
Specific impulse	380 s (3.7 km/s) (vacuum)[12]
Fuel	Subcooled  / LOX[5]

The SpaceX Starship system is a fully reusable, two-stage-to-orbit, super heavy-lift launch vehicle under development by SpaceX. The system is composed of a booster stage, named Super Heavy, and a second stage, also referred to as "Starship".^{[13]:16:20-16:48} The second stage is being designed as a long-duration cargo, and eventually,^[1] passenger-carrying spacecraft. The spacecraft will serve as both the second stage and the in-space long-duration orbital spaceship.^[14]

Engine development started in 2012, and Starship development began in 2016 as a self-funded private spaceflight project. Testing of the second stage Starship began in 2019 as part of an extensive development program to prove out launch-and-landing and iterate on a variety of design details, particularly with respect to the vehicle's atmospheric reentry.^[15][16] Integrated system testing of a proof of concept for the second stage began in March 2019 with a prototype nicknamed Starhopper, which made low-altitude, low-velocity flight testing of vertical launches and landings.^[17] This was followed by two additional full-size tank prototype versions (SN5 and SN6), which also made low-altitude test flights in August and September 2020.^[18] On 9 December 2020, Starship prototype SN8 performed the first high-altitude test flight, demonstrating most of the atmospheric re-entry maneuvers. The test was deemed a success, although a hard landing caused the explosion of the prototype.^[19][18] More prototype Starships have been built and more are under construction as the iterative design goes through several iterations.^[18][20] All test articles have a 9 m (30 ft)-diameter stainless steel hull.

In June 2019, SpaceX indicated they could potentially launch commercial payloads using Starship as early as 2021.^[21] In April 2020, NASA selected a modified crew-rated Starship system as one of three potential lunar landing system design concepts to receive funding for a 10-month-long initial design phase for the NASA Artemis program.^[22]

Nomenclature

The name of the vehicle changed many times after its first announcement and during the first several years of development.^[23] In its final iteration, the combination of Starship spacecraft and Super Heavy booster is called the "Starship system" by SpaceX in their payload users guide.^[24] Sometimes, as on the SpaceX website, the term "Starship" is used as a collective term for both the Starship spacecraft and the Super Heavy booster.^[5]

At least as early as 2005, SpaceX used the codename, "BFR", for a conceptual heavy-lift vehicle, "far larger than the Falcon family of vehicles",^[25][26] with a goal of 100 t (110 tons) to orbit. Beginning in mid-2013, SpaceX referred to both the mission architecture and the vehicle as the Mars Colonial Transporter.^[27] By the time a large 12-meter diameter design concept was unveiled in September 2016, SpaceX had begun referring to the overall system as the Interplanetary Transport System.

With the announcement of a new 9-meter design in September 2017, SpaceX resumed referring to the vehicle as "BFR".^[28][29][30] Musk said in the announcement, "we are searching for the right name, but the code name, at least, is BFR".^[11] SpaceX President Gwynne Shotwell subsequently stated that BFR stands for, "Big Falcon Rocket".^[31] However, Elon Musk had explained in the past that although BFR is the official name, he drew inspiration from the BFG weapon in the Doom video games.^[32] The BFR had also occasionally been referred to informally by the media and internally at SpaceX as "Big Fucking Rocket".^[33][34][35] At the time, the second stage/spacecraft was referred to as "BFS".^[36][37][38] The booster first stage was also at times referred to as the "BFR".^[39][40][41] In November 2018, the spaceship was renamed Starship, and the first stage booster was named Super Heavy.^[14][42]

The term "Super Heavy" had also been previously used by SpaceX in a different context. In February 2018, at about the time of the first Falcon Heavy launch, Musk had suggested the possibility of a Falcon Super Heavy--a Falcon Heavy with extra boosters. "We could really dial it up to as much performance as anyone could ever want. If we wanted to we could actually add two more side boosters and make it Falcon Super Heavy".^[43]

History

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).^[44] 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".^[45]

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).^[46] In September 2017, at the 68th annual meeting of the International Astronautical Congress, SpaceX unveiled an updated vehicle design.^[11]

In September 2018 Musk showed another redesigned concept for the 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.^[47] He also announced a planned 2023 lunar circumnavigation mission, a private spaceflight called dearMoon project.^[48] The two major parts of the launch vehicle were given descriptive names in November 2018: "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)".^[14]

In January 2019, Musk announced that the Starship would no longer be constructed out of carbon fiber, and that stainless steel would be used instead, citing several reasons including cost, strength, and ease of production.^[49] Later in May, the Starship design changed back to just six Raptor engines, with three optimized for sea-level and three optimized for vacuum.^[50] Later that month, an initial test article, Starhopper, was being finished for untethered flight tests at the SpaceX South Texas launch site, while two "orbital prototypes" without aerodynamic control surfaces were under construction, one in South Texas and one on the Florida Space Coast. The following month, SpaceX publicly announced that discussions had begun with three telecommunications companies for using Starship, rather than Falcon 9, for launching commercial satellites for paying customers in 2021. No specific companies or launch contracts were announced at that time.^[21]

Starhopper made its initial flight test in July 2019, a "hop" of around 20 m (66 ft) altitude,^[51] and a second and final "hop" in August 2019, reached an altitude of ~150 m (490 ft)^[52] and landing around 100 m (330 ft) from the launchpad.

In September 2019 Musk unveiled Starship Mk1, a more advanced test article.^[53][54] The Mk1 was destroyed in a tank pressure test in November, and SpaceX ceased construction on the Mk2 prototype in Florida and moved on to work on the Mk3 article.^[55] Adopting a new "serial number" nomenclature, the Mk3 article was renamed Starship SN1 by SpaceX to signify the major evolution in building techniques: the rings were now taller and each was made of one single sheet of steel, drastically reducing the welding lines (thus failure points). The worksite in Texas was also significantly expanded.

In February 2020, SN1 was also destroyed during pressurization.^[56] The company then focused on resolving the problem that led to SN1's failure by assembling a stripped-down version of their next planned prototype, SN2.^[57][58] This time the test was successful and SpaceX began work on SN3.^[59][58] However, in April 2020, SN3 was also destroyed during testing due to a test configuration error.^[58][60] At that time, construction of SN4 was underway.^[60]

On 26 April 2020, Starship SN4 became the first full-scale prototype to pass a cryogenic proof test. On 5 May 2020, SN4 completed a single engine static fire with one mounted Raptor engine and became the first full Starship tank to pass a Raptor static fire.^[61] SN4 would complete a total of 4 short static fires (2 to 5 seconds long) before being destroyed in a massive explosion due to a propellant leak from the quick disconnect mechanism.^[62]

On 4 August 2020 Starship SN5 completed a 150 meter flight test, landing at an adjacent landing site, thus becoming the first full-scale prototype to perform a successful flight test.^[63] SN9 was the first prototype to be built entirely of the type 304L stainless steel.^[64]

While the Starship program had a small development team for several years, and a larger development and build team since late 2018, Musk declared in June 2020 that Starship was by then the top SpaceX priority, except for anything related to reduction of Crew Dragon return risk for the upcoming Crew Dragon Demo-2 flight to the ISS,^[65] and remained so in September 2020.^[1]

In July 2020, SpaceX procured two deepwater oil rigs from Valaris plc for $3.5 million each. These semi-submersible platforms, renamed Deimos and Phobos after the two moons of Mars, will be modified into two floating launch platforms for Super Heavy/Starship orbital launches. As of January 2021, refit is underway on Deimos at the Port of Brownsville, and Phobos at the Port of Galveston.^[66][67] Current plans are for both the first stage (Super Heavy) booster and the second stage (Starship) to be landed on land, unlike the many sea landings seen with their Falcon 9 boosters.^[68]

In September 2020, Musk clarified that SpaceX intends to exclusively fly cargo transport missions initially, and that passenger flights would come only much later.^[9][1]

On 9 December 2020, SN8 flew a largely successful 12.5 km flight test, which included the first 3-engine flight test, the first test of the body flaps during its novel "bellyflop"^[69] descent, and the first test of the "flip maneuver"^[70] landing burn at the end of the free-fall phase.^{[69][full ]} However the fuel header tank pressure was low during the landing burn, this precipitated to a high touchdown velocity which destroyed SN8.^[71]

Super Heavy booster

Comparison of full stack Starship with other super heavy launch vehicles

The booster stage Super Heavy is expected to be 72 m (236 ft) long and 9 m (30 ft) in diameter with a gross liftoff mass of 3,680,000 kg (8,110,000 lb).^[6][8] It is to be constructed of stainless steel tanks and structure, holding subcooled liquid methane and liquid oxygen (/LOX) propellants, powered by ~28 Raptor rocket engines^[72] that will provide 72,000 kN (16,000,000 lb_f) total liftoff thrust.^[73][5] The specification propellant capacity of Super Heavy was shown as 3,400,000 kg (7,500,000 lb) in May 2020,^[7] 3% more than estimated in September 2019.^[5]

The initial prototype Super Heavy will be full size.^[74] It is expected however, to initially fly with less than the full complement of 28^[75] engines, perhaps approximately 20.^[76]

The Super Heavy external design changed throughout 2019/2020 as the detailed design was iterated and the Raptor engines were tested and achieved higher power levels. In September 2019, a design change for the booster stage to have six fins that serve exclusively^{[77]:26:25-28:35} as fairings to cover the six landing legs, and four diamond-shaped welded steel grid fins^[78] to provide aerodynamic control on descent, was discussed.^[79] In August 2020, as the first build of "booster prototype 1" was to get underway,^[9] Musk noted that the leg design had been modified to just four landing legs and fins, to improve supersonic engine plume re-circulation margins.^[80]

Landing

In September 2016, Elon Musk described the possibility of landing the ITS booster on the launch mount.^[81] He re-described this concept in September 2017 with the Big Falcon Booster (BFB).^{[82][83][84][37]} In 2019, Musk announced that the booster would initially have landing legs to support the early VTVL development testing of Super Heavy.^[85][86][87] More recently, Musk had again expressed the long term goal of landing on the launch mount.^[88] In December 2020, Musk added the possibility of catching the booster by the grid fins using the launch tower arm, eliminating the need for landing legs entirely and simplifying recovery processes.^[89][88][90]

Starship upper stage

Artist's concept of an earlier version of Starship upper stage following stage separation

The upper stage of Starship is intended to function both as a second stage to reach orbital velocity on launches from Earth, and also be used in outer space as an on-orbit long-duration spacecraft. This is in contrast to most previous launch vehicle and spacecraft designs. Starship is being designed to be capable of reentering Earth's atmosphere from orbital velocities and landing vertically, with a design goal of rapid re-usability without the need for extensive refurbishment.^[77]

According to Musk, when Starship is used for beyond Earth orbit (BEO) launches to Mars, the functioning of the overall expedition system will necessarily include propellant production on the Mars surface. This is necessary for the return trip and to reuse the spaceship to keep costs as low as possible. Lunar destinations (circumlunar flybys, orbits and landings) will be possible without lunar-propellant depots, so long as the spaceship is refueled in a high-elliptical orbit before the lunar transit begins.^[83] Some lunar flybys will be possible without orbital refueling as evidenced by the mission profile of the dearMoon project.^[12]

The SpaceX approach is to tackle the hardest problems first, and Musk sees the hardest problem for getting to sustainable human civilization on Mars to be building a fully-reusable orbital Starship, so that is the major focus of SpaceX resources as of 2020.^[91] For example, it is planned for the spacecraft to eventually incorporate life support systems, but as of September 2019^[update], Musk has stated that it is yet to be developed, as the early flights will all be cargo only.^{[1][92][93][94]}

General characteristics

As of September 2019^[update], the Starship upper stage is expected to be a 9 m (30 ft) diameter, 50 m (160 ft) tall, fully reusable spacecraft with a dry mass of 120 t (120 long tons; 130 short tons) or less,^[77] powered by six Raptor engines.

Starship is designed with the ability to re-enter Earth's atmosphere and retropropulsively land on a designated landing pad. Landing reliability is projected by SpaceX to ultimately be able to achieve "airline levels" of safety due to engine-out capability. The spacecraft is also designed to be able to perform automatic rendezvous and docking operations, and perform on-orbit propellant transfers between Starships.^[95]

Starship is also designed with the goal to reach other planets and moons in the solar system after on-orbit propellant loading. While retropropulsion is intended to be used for the final landing maneuver on the Earth, Moon, or Mars, 99.9% of the energy dissipation on Earth reentry is to be removed aerodynamically, and on Mars, 99% aerodynamically even using the much thinner Martian atmosphere,^[96] where "body flaps"^[69][97] are used to control attitude during descent and optimize both trajectory and energy dissipation during descent.^[98]

As envisioned in the 2017 design unveiling, the Starship is to have a pressurized volume of approximately 825 m³ (29,100 cu ft), which could be configured for up to 40 cabins, large common areas, central storage, a galley, and a solar flare shelter for Mars missions.^[37]

Propulsion

The methane/oxygen-propellant Raptor engines will be the main propulsion system on Starship. Starship will use three sea-level optimized Raptor engines and three vacuum-optimized Raptor engines. The sea-level engines are identical to the engines on the Super Heavy booster. Transport use in space is expected to use a vacuum-optimized Raptor engine variant to optimize specific impulse (I_sp) to approximately 380 s (8,300 mph; 3.7 km/s).^[77] Total Starship thrust will be approximately 11,500 kN (2,600,000 lbf).^[99]

Starship will use pressure fed hot gas reaction control system (RCS) thrusters using methane gas for attitude control, including the final pre-landing pitch-up maneuver from belly flop to tail down, and stability during high-wind landings up to 60 km/h (37 mph).^[100][101] Initial prototypes are using nitrogen cold gas thrusters, which are substantially less mass efficient, but are expedient for quick building to support early prototype flight testing.^[77]

Variants

Starship is planned to eventually be built in at least these operational variants:^[83][102]

• Spaceship: a large, long-duration spacecraft capable of carrying passengers or cargo to interplanetary destinations, to LEO, or Earth-to-Earth spaceflight.^[83]
• Satellite delivery spacecraft: a vehicle able to transport and place spacecraft into orbit,^[21] or handle the in-space recovery of spacecraft and space debris for return to Earth or movement to another orbit. In the March 2020 users guide, this was shown with a large cargo bay door that can open in space to facilitate delivery and pickup of cargo.^[83]
• Tanker: a cargo-only propellant tanker to support the refilling of propellants in Earth orbit. The tanker will enable launching a heavy spacecraft to interplanetary space as the spacecraft being refueled can use its tanks twice, first to reach LEO and afterwards to leave Earth orbit. The tanker variant, also required for high-payload lunar flights, is expected to come only later; initial in-space propellant transfer will be from one standard Starship to another.^[95]
• Lunar-surface-to-orbit transport: a variant of Starship without airbrakes or heat shielding that is required for in-atmosphere-operations. Additionally, the ship will be equipped with a docking port on the nose, additional landing engines (installed much higher up to reduce dust clouds during landing) and have white paint (as opposed to the bare steel planned for regular Starships). On 30 April 2020, NASA selected SpaceX to develop a human-rated lunar lander for the Artemis program, therefore requiring SpaceX to develop an approach for a direct lunar landing.

The spaceship design is expected to be flexible. For example, a possible design modification to the base Starship - expendable three-engine Starship with no fairing, rear fins, nor landing legs in order to optimize its mass ratio for a interplanetary exploration with robotic probes.^[103]

Materials and construction

Starship has a stainless steel structure and tank construction. Its strength-to-mass ratio should be comparable to or better than the earlier SpaceX design alternative of carbon fiber composites across the anticipated temperature ranges, from the low temperatures of cryogenic propellants to the high temperatures of atmospheric reentry^[104] Some parts of the craft will be built with a stainless steel alloy that "has undergone [a type of] cryogenic treatment, in which metals are ... cold-formed/worked [to produce a] cryo-treated steel ... dramatically lighter and more wear-resistant than traditional hot-rolled steel."^[104]

The spacecraft will also have a thermal protection system against the harsh conditions of atmospheric reentry. This will include hexagonal ceramic tiles that will be used on the windward side of Starship.^{[105][106][107]} Earlier designs included a double stainless-steel skin with active coolant flowing in between the two layers, or with some areas additionally containing multiple small pores that would allow for transpiration cooling.^{[106][108][109][110]}

Starship Human Landing System

A modified version known as the Starship Human Landing System (Starship HLS) was selected by NASA in April 2020 for potential use for long-duration crewed lunar landings as part of NASA's Artemis program. The Starship HLS variant is being designed to stay on and around the Moon and as such both the heat shield and air-brakes--integral parts of the main Starship design--are not included in the Starship HLS design. The variant will use high-thrust methox RCS thrusters located mid-body on Starship HLS during the final "tens of meters" of the terminal lunar descent and landing,^[111][112] and will also include a smaller crew area and a much larger cargo bay, be powered by a solar array located on its nose below the docking port. SpaceX intends to use the same high-thrust RCS thrusters for liftoff from the lunar surface.^[111]:50:30 If built, the HLS variant would be launched to Earth orbit via the Super Heavy booster and would use orbital refueling to reload propellants into Starship HLS for the lunar transit and lunar landing operations. In the 2020 mission concept, a NASA Orion spacecraft would carry a NASA crew to the lander where they would depart and descend to the surface in Starship HLS. After Lunar surface operations, it would ascend using the same Starship HLS vehicle and return the crew to the Orion. Although not confirmed yet, the vehicle in theory could be refueled in orbit to carry more crews and cargo to the surface.^[113][114]

SpaceX is one of three organizations developing their lunar lander designs for the Artemis program over a 10-month period in 2020-2021. If SpaceX completes the milestone-based requirements of the design contract, then NASA will pay SpaceX US$135 million in design development funding. The other teams selected were the 'National Team'--led by Blue Origin but including Lockheed Martin, Northrop Grumman, and Draper (with US$579 million in NASA design funding) and Dynetics, including SNC and other unspecified companies (with US$253 million in NASA funding).^[114][113] At the end of the ten-month program, NASA will evaluate which contractors will be offered contracts for initial demonstration missions and select firms for development and maturation of lunar lander systems.^[114][115]

Prototypes and testing

Two test articles (Starhopper, Mk1) were being built by March 2019, and three (Starhopper, Mk1, Mk2) by May 2019.^[116] The low-altitude, low-velocity Starhopper was used for initial integrated testing of the Raptor rocket engine with a flight-capable propellant structure, and was slated to also test the newly designed autogenous pressurization system that is replacing traditional helium tank pressurization as well as initial launch and landing algorithms for the much larger 9-metre (30 ft) diameter rocket.^[108] SpaceX originally developed their reusable booster technology for the 3-meter-diameter Falcon 9 from 2012 to 2018. The Starhopper prototype was also the platform for the first flight tests of the full-flow staged combustion methalox Raptor engine, where the hopper vehicle was flight tested with a single engine in July/August 2019,^[117] but could be fitted with up to three engines to facilitate engine-out tolerance testing.^[108]

The high-altitude, high-velocity "Starship orbital prototypes" (everything after Starhopper) are planned to be used to develop and flight test thermal protection systems and hypersonic reentry control surfaces.^[108] Each orbital prototype is expected to be outfitted with more than three Raptor engines.^[17][118]

Starhopper

Picture of Starhopper before flight

The construction of the initial test article--the Starship Hopper^[119] or Starhopper^[120][121]--began in early December 2018 and the external frame and skin was complete by 10 January 2019. Constructed outside in the open on a SpaceX property just 3.2 km (2.0 mi) from Boca Chica Beach in South Texas, the external body of the rocket rapidly came together in less than six weeks from half-inch (12.5 mm) steel.^[122] Originally thought by onlookers at the SpaceX South Texas Launch Site to be the initial construction of a large water tower, the stainless steel vehicle was built by welders and construction workers in more of a shipyard form of construction than traditional aerospace manufacturing. The full Starhopper vehicle is 9 m (30 ft) in diameter and was originally 39 m (128 ft) tall in January 2019.^[104][123] Subsequent wind damage to the nose cone of the vehicle resulted in a SpaceX decision to scrap the nose section, and fly the low-velocity hopper tests with no nose cone, resulting in a much shorter test vehicle.^[124]

From mid-January to early-March 2019, a major focus of the manufacture of the test article was to complete the pressure vessel construction for the liquid methane and liquid oxygen tanks, including plumbing up the system, and moving the lower tank section of the vehicle 3.2 km (2.0 mi) to the launch pad on 8 March 2019.^[125] Integrated system testing of the Starhopper--with the newly built ground support equipment (GSE) at the SpaceX South Texas facilities--began in March 2019. "These tests involved fueling Starhopper with LOX and liquid methane and testing the pressurization systems, observed via icing of propellant lines leading to the vehicle and the venting of cryogenic boil off at the launch/test site. During a period of over a week, StarHopper underwent almost daily tanking tests, wet dress rehearsals and a few pre-burner tests."^[108]

Following initial integrated system testing of the Starhopper test vehicle with Raptor engine serial number 2 (Raptor SN2) in early April 2019, the engine was removed for post-test analysis and several additions were made to the Starhopper. Attitude control system thrusters were added to the vehicle, along with shock absorbers for the non-retractable landing legs, and quick-disconnect connections for umbilicals. Raptor SN4 was installed in early June for fit checks, but the first test flight that is not tethered was expected to fly with Raptor SN5,^[124] until it suffered damage during testing at SpaceX Rocket Development and Test Facility, in McGregor, Texas. Subsequently, Raptor SN6 was the engine used by Starhopper for its untethered flights.^[126]

Low-altitude prototypes

By December 2018, initial construction of two low-altitude prototype ships had begun, referred to as Mk1 at Boca Chica, Texas,^[127] and Mk2 at the space coast of Florida in Cocoa.^[17][127] Planned for high-altitude and high-velocity testing,^[128] the prototypes were described to be taller than the Starhopper, have thicker skins, and a smoothly curving nose section.^{[17][118][129]} Both prototypes measured 9 m (30 ft) in diameter by approximately 50 m (160 ft) in height.^[130]

On 20 November 2019, the Starship Mk1 was partially destroyed during max pressure tank testing, when the forward LOX tank ruptured along a weld line of the craft's steel structure, propelling the bulkhead several meters upwards. The upper bulkhead went airborne and landed some distance away from the craft. No injuries were reported.^[131] In a statement concerning the test anomaly, SpaceX said they will retire the Mk1 and Mk2 prototypes after the incident, and focus on Mk3 and Mk4 designs, which are closer to the flight specifications.^[132][133]

Construction had begun on the Mk2 Starship in Florida by mid-October 2019,^[134] but work then ceased in Florida (with apparent cancellation of Mk2^[135]) and focused on the Texas site.^[136] The prototype in Texas (Mk3) was renamed to SN1 (serial number 1). It was destroyed during a pressure test on 28 February 2020.^[137] After this incident, SpaceX announced they would focus on the next prototype, the Starship SN2.^[56] SN2 successfully went through a pressure and cryo test, but was not used for a static fire or hop. Instead, SpaceX moved on to SN3, the next prototype. SN3's cryo test then failed, the result being the LOX (Liquid Oxygen) Tank collapsing due to underpressurisation.^[138] On 26 April 2020, SN4 successfully completed a cryogenic pressure test.^[139] On 20 May 2020, SN4 exploded after a successful engine test when SpaceX tested a new "quick disconnect" design as part of ground support equipment testing. On 4 August 2020, SN5 completed a 150 m hop, its first successful launch and landing,^[3] with SN6 performing the same feat just one month later.^[140]

High-altitude prototypes

Several high-altitude prototypes (SN9-SN18) were undergoing testing (SN9) or were under construction (SN10-SN18) by January 2021. SN8 had passed cryogenic tests, preburner and static fire tests.^[141] A flight of SN8 to an altitude of 12.5 km took place on 9 December 2020. After successful ascent, various test maneuvers--followed by a successful and novel skydiver-like horizontal descent and vehicle rotation back to vertical for a propulsive landing attempt--lower than expected pressure in the methane header tank following the rapid rotation resulted in inadequate final deceleration and a hard landing, resulting in an explosion on the landing pad and total destruction of the test vehicle.^[19]

Testing

SN5 being moved by a crane onto a stand before test flight.

Starhopper was used to flight test a number of subsystems of Starship to begin to expand the flight envelope of the Starship design.^{[123][142][143]}Starhopper testing ran from March to August 2019 with all Starhopper test flights at low altitude.^[144][145] On 3 April 2019, SpaceX conducted a successful static fire test in Texas of its Starhopper vehicle, which ignited the engine while the vehicle remained tethered to the ground.^[146]

The first static fire test of the Starhopper, with a single Raptor engine attached, occurred on 3 April 2019. The firing was a few seconds in duration, and was classed as successful by SpaceX.^[108] A second tethered test followed just two days later, on 5 April 2019.^[116][147]

By May 2019, SpaceX was planning to conduct flight tests both in South Texas and on the Florida space coast.^{[16][17][124]} The FAA issued a one-year experimental permit in June 2019 to fly Starhopper at Boca Chica, including pre-flight and post-flight ground operations.^[148]

The maiden flight test of the Starhopper test vehicle, and also the maiden flight test of any full-flow staged combustion rocket engine, was on 25 July 2019, and attained a height of 18 m (59 ft).^[117][149] This was not a full-duration burn but a 22-second test. It accidentally ignited nearby vegetation.^[150] SpaceX is developing their next-generation rocket to be reusable from the beginning, just like an aircraft, and thus needs to start with narrow flight test objectives, while still aiming to land the rocket successfully to be used subsequently in further tests to expand the flight envelope.^[117] The second and final untethered test flight of the Starhopper test article was carried out on 27 August 2019, to a VTVL altitude of 150 m (490 ft).^[126]

On 4 August 2020, Starship prototype SN5 with full-height propellant tanks and a single Raptor engine, conducted a test flight to a height of about 150 m (490 ft), descending to a nearby landing pad.^[20]

On 9 December 2020, Starship prototype SN8, with the full body of the rocket and three Raptor engines, conducted a test flight to a height of 12.5 km (7.8 miles), and tested the bellyflop maneuver that will be used when landing Starship from orbit and any other high altitude flights.^[19]

On 13 January 2021, the SN9 Starship prototype performed static-fire tests. After some issues detected, it was decided to postpone its test flight for swapping out two of its Raptor engines, engines 44 and 46.^[151]

Pad testing

Starship prototypes are subjected to several tests on the launch stand before flight testing. These include the ambient pressure test, cryogenic proof test, and static fire of the engines. During the ambient pressure test the test article's propellant tanks are filled with benign air-temperature nitrogen gas. This test checks for leaks, verifies basic vehicle valve and plumbing performance, and ensure a basic level of structural integrity.^[152] The ambient pressure test is followed by the cryogenic proof test where the vehicle's oxygen and methane tanks are loaded with liquid nitrogen. This also tests structural integrity but adds the challenge of thermal stresses to ensure that Starship can safely load, hold, and offload supercool liquids.^[152] SN9 was the first prototype to arrive at the test stand with engines already installed. Before that a hydraulic ram was attached to the thrust puck to simulate the thrust of one, two, or three Raptor engines. SN4 was the first full scale prototype to pass the cryogenic proof test.^[153] Finally a static fire test is performed by loading liquid oxygen and liquid methane and firing the raptor engines briefly while Starship is held down on the test stand.

Suborbital flight testing

Since 2019, prototypes of the upper stage of Starship have been flown 6 times. Prototypes of Starship that performed suborbital flights include Starhopper, SN5, SN6, and SN8. All test flights launched from the Boca Chica launch site in Texas.^[154]

Intended uses

Starship is intended to become the primary SpaceX orbital vehicle. SpaceX intends to eventually replace its existing Falcon 9 and SpaceX Dragon 2 fleet with Starship, which is expected to take cargo to orbit at far lower cost than any other existing launch vehicle.^{[194][83][11]:24:50-27:05} In November 2019, Elon Musk estimated that fuel will cost US$900,000 per launch and total launch costs could drop as low as US$2 million.^[195]

Starship is an architecture designed to do many diverse spaceflight missions, principally due to the very low marginal cost per mission that the fully-reusable spaceflight vehicles bring to spaceflight technology that were absent in the first six decades after humans put technology into space.^{[13]:30:10-31:30} Specifically, Starship is designed to be used for:^[194][82]

• Earth-orbit satellite delivery market. In addition to the commercial launch market that SpaceX has been servicing since 2013, the company intends to use Starship to launch the largest portion of its own internet satellite constellation, Starlink, with more than 12,000 satellites intended to be launched by 2026, more than six times the total number of active satellites on orbit in 2018.^[196] An orbital launch of Starship could place ~400 Starlink satellites into orbit with a single launch, whereas the Falcon 9 flights in 2019-2020 can launch only ~60.^[1]
• Long-duration spaceflights to outer space, beyond the earth-moon system.
• Sending crew such as space tourists to the International Space Station and to the lunar gateway spacestation.^[197]
• Mars transportation, both as cargo ships as well as passenger-carrying transport.
• Long-duration flights to the outer planets of the Solar System, for cargo and astronauts.^[198]
• Reusable lunar lander, for use transporting astronauts and cargo to and from the Moon's surface and Gateway in lunar orbit via Starship Human Landing System (Starship HLS);^[113] as well as more advanced heavy cargo lunar use cases that are envisioned by SpaceX but are not any part of the HLS variant that NASA has contracted with SpaceX for early design work.^{[13]:13:34-20:10}

Long-haul Earth transport

In 2017, SpaceX mentioned the theoretical possibility of using Starship to carry passengers on suborbital flights between two points on Earth. Any two points on Earth could be connected in under one hour, providing commercial long-haul transport competing with long-range aircraft.^[199][200] SpaceX however announced no concrete plans to pursue the two stage "Earth-to-Earth" use case.^{[11][142][201]}

Over two years later, in May 2019, Musk floated the idea of using single-stage Starship to travel up to 10,000 km (6,200 mi) on Earth-to-Earth flights at speeds approaching Mach 20 (25,000 km/h; 15,000 mph) with an acceptable payload saying it "dramatically improves cost, complexity and ease of operations".^[202] In June 2020, Musk estimated that Earth-to-Earth test flights could begin in "2 or 3 years", i.e. 2022 or 2023, and that planning was underway for "floating superheavy-class spaceports for Mars, Moon and hypersonic travel around Earth".^[203]

Funding

SpaceX has been developing the Starship with private funding, including the Raptor rocket engine used on both stages of the vehicle, since 2012.^[15] In 2020, SpaceX has contracted with NASA to do limited early design work for 10 months on a human lunar lander variant Starship--Starship HLS--that might be used to land astronauts on the lunar surface as part of the NASA Artemis program after 2024.

The development work on the new two-stage launch vehicle design is privately funded by SpaceX. The entire project is possible only as a result of SpaceX's multi-faceted approach focusing on the reduction of launch costs.^[204]

The full build-out of the Mars colonization plans was envisioned by Musk in 2016 to be funded by both private and public funds. The speed of commercially available Mars transport for both cargo and humans will be driven, in large part, by market demand as well as constrained by the technology development and development funding.

Elon Musk said that there is no expectation of receiving NASA contracts for any of the ITS system work SpaceX was doing. He also indicated that such contracts, if received, would be good.^[205]

In 2017, the company settled on a 9-meter diameter design and commenced procuring equipment for vehicle manufacturing operations. In late 2018, they switched the design from carbon composite materials for the main structures to stainless steel, further lowering build costs.^[48] By late 2019, SpaceX projected that, with company private investment funding, including contractual funds from Yusaku Maezawa who had recently contracted for a private lunar mission in 2023, they have sufficient funds to advance the Earth-orbit and lunar-orbit extent of flight operations, although they may raise additional funds in order "to go to the Moon or landing on Mars".^[15]

In April 2020, NASA announced they would pay SpaceX US$135 million for design and initial development over a 10-month design period for a variation of the Starship second-stage vehicle and spaceship--a "Starship Human Landing System", or Starship HLS--as a Lunar human landing system for the NASA Artemis program; NASA is paying US$579 million and US$253 million to other contractors developing competing lunar landing designs.^[114][115]

In October 2020, NASA awarded SpaceX US$53.2 million to conduct a large scale flight demonstration to transfer 10 metric tons of cryogenic propellant between tanks on the Starship vehicle.^[206]

Criticism

The Starship vehicle design has been criticized for not adequately protecting astronauts from ionizing radiation on Mars missions;^{[207][208][209][210]} Musk has stated that he thinks the transit time to Mars will be too brief to lead to an increased risk of cancer, saying "it's not too big of a deal".^{[207][211][212]} The lifetime cancer risk increase caused by the dose incurred on a multi-year Mars mission has been estimated to amount to a 5% increase in total cancer risk, a number which can be greatly reduced through simple shielding measures.^[213]

See also

• List of Starship flights
• List of crewed spacecraft
• Mars to Stay – Mars colonization architecture proposing no return vehicles
• Space colonization – Concept of permanent human habitation outside of Earth
• Space exploration – Discovery and exploration of outer space

References

External links

• Official website