 SpaceX Starship SN8 prototype during a flight test at Boca Chica, Texas, December 2020 | |
| Function | |
|---|---|
| Manufacturer | SpaceX |
| Country of origin | United States |
| Cost per launch | US$2 million (aspirational) |
| Size | |
| Height | 120 m (390 ft) (not including landing legs) |
| Diameter | 9 m (30 ft) |
| Mass | 5,000 t (11,000,000 lb) (with maximum payload)(estimated) |
| Stages | 2 |
| Capacity | |
| Payload to LEO | |
| Mass | +100 t (220,000 lb) |
| Volume | 1,100 m3 (39,000 cu ft) |
| Associated rockets | |
| Family | SpaceX launch vehicles |
| Comparable | |
| Launch history | |
| Status | In development |
| Launch sites | |
| First stage – Super Heavy | |
| Length | 72 m (236 ft) (including landing legs) |
| Diameter | 9 m (30 ft) |
| Propellant mass | 3,400 t (7,500,000 lb) |
| Engines | ~28 Raptors |
| Thrust | c. 76,000 kN (17,000,000 lbf) |
| Specific impulse | 330 s (3.2 km/s) |
| Fuel | Subcooled CH 4 / LOX |
| Second stage – Starship | |
| Length | 50 m (160 ft) |
| Diameter | 9 m (30 ft) |
| Empty mass | (goal) 120 t (260,000 lb) |
| Gross mass | 1,320 t (2,910,000 lb) |
| Propellant mass | 1,200 t (2,600,000 lb) |
| Engines | 6 Raptor |
| Thrust | c. 12,000 kN (2,700,000 lbf) |
| Specific impulse | 380 s (3.7 km/s) (vacuum) |
| Fuel | Subcooled CH 4 / LOX |
The SpaceX Starship system is a proposed 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".The second stage is being designed as a long-duration cargo, and eventually, passenger-carrying spacecraft. The spacecraft will serve as both the second stage and the in-space long-duration orbital spaceship.
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. The first prototypes made low-altitude, low-velocity flight testing of vertical launches and landings in 2019-2020. 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. More prototype Starships have been built and more are under construction as the iterative design progresses. 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. 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. As of March 2021, SpaceX is conducting atmospheric flights to 10 km altitude with Starship prototypes.
Nomenclature
The name of the vehicle changed many times after its first announcement and during the first several years of development. 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", 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. 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". SpaceX President Gwynne Shotwell subsequently stated that BFR stands for "Big Falcon Rocket". 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. The BFR had also occasionally been referred to informally by the media and internally at SpaceX as "Big Fucking Rocket". At the time, the second stage/spacecraft was referred to as "BFS" (Big Falcon Ship or Big Fucking Ship). The booster first stage was also at times referred to as the "BFR" (Big Falcon Rocket or Big Fucking Rocket).
In November 2018, the spaceship was renamed Starship, and the first stage booster was named Super Heavy. The whole system, with the booster stage and spaceship, is also referred to as "Starship". The combination of Starship spacecraft and Super Heavy booster is called the "Starship system" by SpaceX in their payload users guide. 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.
History
Early concepts
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). 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".
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). In September 2017, at the 68th annual meeting of the International Astronautical Congress, SpaceX unveiled an updated vehicle design.
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. He also announced a planned 2023 lunar circumnavigation mission, a private spaceflight called dearMoon project. 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)".
Shift to steel and early testing
In January 2019, Musk announced that 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. Later in May, the Starship design changed back to just six Raptor engines, with three optimized for sea-level and three optimized for vacuum. 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.
Starhopper made its initial flight test in July 2019, a "hop" of around 20 m (66 ft) altitude, and a second and final "hop" in August 2019, reached an altitude of ~150 m (490 ft) and landing around 100 m (330 ft) from the launchpad. In September 2019 Musk unveiled Starship Mk1, a more advanced test article. 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.
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. 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; SN2 ended up being basically a test tank. This time the pressure test was successful and SpaceX began work on SN3. However, in April 2020, SN3 was also destroyed during testing due to a test configuration error. At that time, construction of SN4 was underway.
Prototypes testing
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. 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. 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.
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, and remained so in September 2020. In September 2020, Musk clarified that SpaceX intends to exclusively fly cargo transport missions initially, and that passenger flights would come only much later.
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. 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.
On 9 December 2020, SN8 flew a largely successful 12.5 km (41,000 ft) flight test, which included the first 3-engine flight test, the first test of the body flaps during its novel "bellyflop" descent, and the first test of the "flip maneuver" landing burn at the end of the free-fall phase. However the fuel header tank pressure was low during the landing burn, and SN8 landed at a higher speed than intended and exploded. On 2 February 2021, SN9 attempted a 10 km (33,000 ft) flight, but once again exploded on landing after one of the Raptor engines failed to ignite.
On 3 March 2021, SN10 successfully completed the first landing of Starship after a 10km ascent. However, the landing was harder than expected due to unexpected low thrust. Immediately after the landing, there was a fire visible near the vehicle's skirt, prompting the deployment of the landing site's fire suppression system. Approximately eight minutes after the landing, the vehicle's liquid oxygen and methane tanks ruptured catastrophically, resulting in the fiery explosion of SN10 on the landing pad before it could be made safe and recovered.
Starship upper stage
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.
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. Some lunar flybys will be possible without orbital refueling as evidenced by the mission profile of the dearMoon project.
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. For example, it is planned for the spacecraft to eventually incorporate life support systems, but as of September 2019, Musk has stated that it is yet to be developed, as the early flights will all be cargo only.
General characteristics
As of September 2019, 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, 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.
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, where "body flaps" are used to control attitude during descent and optimize both trajectory and energy dissipation during descent.
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.
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 (Isp) to approximately 380 s (8,300 mph; 3.7 km/s). Total Starship thrust will be approximately 11,500 kN (2,600,000 lbf).
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). 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.
Variants
Starship is planned to eventually be built in at least these operational variants:
- Spaceship: a large, long-duration spacecraft capable of carrying passengers or cargo to interplanetary destinations, to LEO, or Earth-to-Earth spaceflight.
- Satellite delivery spacecraft: a vehicle able to transport and place spacecraft into orbit, 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.
- 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.
- 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 an interplanetary exploration with robotic probes.
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 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."
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. 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.
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, 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. 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.
SpaceX is one of three organizations developing their lunar lander designs for the Artemis program over a 10-month period in 2020–2021, starting in May 2020. 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). At the end of the ten-month program on 28 February 2021, NASA had planned to evaluate which contractors would be offered contracts for initial demonstration missions and select firms for development and maturation of their lunar lander system designs. However, on 27 January 2021, NASA informed each of the HLS contractors that the original ten-month program would be extended two months to end on or before 30 April 2021.
Prototypes and testing
The SpaceX testing philosophy, referred to as "test, fly, fail, fix, repeat", is evident in the Starship development and testing program. SpaceX is willing to regularly test prototypes to destruction, counting the data gathered as a successful part of the overall process. This allowance for failures, willingness to build flight articles in view of the public, and fast cadence of prototype construction makes the Starship design process unique in the spaceflight industry.
In the first two years of development, from December 2018 to December 2020, SpaceX built and tested 13 (12 if the unfinished MK4 is not counted) prototypes. These include MK4 whose development was suspended mid-construction; MK1, SN1, SN3, SN4, SN7 (test tank), SN7.1 (test tank) and SN8 which were tested to destruction; MK2 and SN2 (test tank) which were retired before flight; Starhopper, SN5 and SN6 which were flight tested and retired. In 2021 SpaceX has continued building and testing prototypes including SN7.2 (test tank) and SN9 with SN10.
Starhopper
The construction of the initial test article—the Starship Hopper or Starhopper—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. 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. 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 an 18 m (59 ft) tall test vehicle.
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. 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. Only one engine was installed but Starhopper could have been fitted with up to three engines to facilitate engine-out tolerance testing. Starhopper was also used to flight test a number of subsystems of Starship to begin to expand the flight envelope of the Starship design. Starhopper testing ran from March to August 2019 with all Starhopper test flights at low altitude.
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). This was not a full-duration burn but a 22-second test. 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. 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).
Low-altitude prototypes
Construction of the Mark 1 (Mk1) in Boca Chica, Texas and Mark 2 (Mk2) in Cocoa, Florida began in December 2018. Planned for high-altitude and high-velocity testing, the prototypes were described to be taller than the Starhopper, have thinner skins, and a smoothly curving nose section. Like Starhopper, the vehicles measured 9 m (30 ft) in diameter but were full-height at approximately 50 m (160 ft), making them the first full-size Starship prototypes. 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. After the incident, SpaceX decided not to repair and retest Mk1. Both Mk1 and Mk2 were retired and focus turned to the Mk3 and Mk4 builds which were designed for orbit.
The prototype in Texas (Mk3) was renamed to SN1 (serial number 1). It was destroyed in February 2020 during a pressure test when the tank ruptured near the thrust puck. The thrust puck serves as both the lower dome of the fuel tank and the mount for the raptor engines. After this incident, SpaceX built SN2 as a scaled down test tank to focus testing on the structure of the thrust puck. SN2 successfully passed the pressure and cryogenic tests proving the design changes. SpaceX returned to full size prototype testing with SN3 which failed the cryogenic proof test. During testing the LOX (Liquid Oxygen) Tank experienced a loss of pressure and collapsed due to bad commanding in the test sequence. SN4 successfully completed a cryogenic pressure test on 26 April 2020. but exploded a few weeks later after a successful engine test when SpaceX tested a new "quick disconnect" design as part of ground support equipment testing. After passing all pad tests, SN5 completed a 150 m hop on 4 August 2020, descending to a nearby landing pad. This marked the first successful launch and landing of a prototype with full-height propellant tanks. SN6 performed the same flight test plan just one month later.
High-altitude prototypes
High-altitude prototypes include installation of the nose cone and aerodynamic surfaces allowing testing of ascent, controlled engine cutoff, vehicle reorientation, controlled descent, the flip maneuver and landing. SN8 was the first high-altitude prototype to perform a test flight. On 9 December 2020, SN8 launched and ascended to an altitude of 12.5 km (41,000 ft). During ascent, the three raptor engines were cut one by one allowing the rocket to performed a successful and novel skydiver-like horizontal descent. As the vehicle neared the ground, it used a combination of aerodynamic surfaces and engine gimbaling to rotate back to a vertical position for a propulsive landing attempt. Lower than expected pressure in the methane header tank following the rapid rotation caused inadequate final deceleration and a hard landing resulted in an explosion on the landing pad and total destruction of the test vehicle. SN9 and SN10 both followed the same general test flight plan. SN9's flight took it to 10 km (33,000 ft), on 2 February 2021. The flight went well up until the landing, where one of the raptor engines did not relight causing a failure to counteract the momentum of the landing flip maneuver. This failure caused SN9 to slam into the ground diagonally and explode. SN10 performed the same test profile, but used all three engines for the final flip maneuver successfully decelerating enough to land intact. Several minutes after the landing the Starship exploded and was tossed in the air, before slamming down on its side on the landing pad. SpaceX CEO Elon Musk later revealed that the single Raptor engine that was used for the final landing burn couldn't reach high thrust despite being commanded to do so, thus SN10's landing was harder than intended.
Testing program
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. 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. SN9 was the first prototype to arrive at the test stand with engines already installed. For previous test articles with thrust structures, 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. 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.
Since 2019, prototypes of the upper stage of Starship have been flown 7 times. Prototypes of Starship that performed suborbital flights include Starhopper, SN5, SN6, SN8, SN9, and SN10. All test flights launched from the Boca Chica launch site in Texas.
Super Heavy booster
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 t (8,110,000 lb).
It is to be constructed of stainless steel tanks and structure, holding subcooled liquid methane and liquid oxygen (CH
4/LOX) propellants, powered by ~28 Raptor rocket engines that will provide 72,000 kN (16,000,000 lbf) total liftoff thrust.
The specification propellant capacity of Super Heavy was shown as 3,400 t (7,500,000 lb) in May 2020, 3% more than estimated in September 2019.
The initial prototype Super Heavy will be full size. It is expected however, to initially fly with less than the full complement of 28 engines, perhaps approximately 20.
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 as fairings to cover the six landing legs, and four diamond-shaped welded steel grid fins to provide aerodynamic control on descent, was discussed. In August 2020, as the first build of "booster prototype 1" was to get underway, Musk noted that the leg design had been modified to just four landing legs and fins, to improve supersonic engine plume re-circulation margins.
Landing
In September 2016, Elon Musk described the possibility of landing the ITS booster on the launch mount. He re-described this concept in September 2017 with the Big Falcon Booster (BFB). In 2019, Musk announced that the booster would initially have landing legs to support the early VTVL development testing of Super Heavy. More recently, Musk had again expressed the long term goal of landing on the launch mount. 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.
Prototypes
In late 2020, the segments of the first booster, codenamed BN1 were observed at Boca Chica. In March 2021, Elon Musk indicated that the goal for the first orbital flight is in July 2021. The two segments of BN1 were stacked together in the High Bay for the first time on 18 March 2021. The first booster is a production pathfinder and will also help develop transport processes from the Boca Chica build area to the launch/landing area.
Intended uses
Orbital launches
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. 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.
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. 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.
Other space missions
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. Specifically, in addition to orbital launches, Starship is designed to be used for:
- Long-duration spaceflights to outer space, beyond the earth-moon system.
- Sending crew such as space tourists to the International Space Station, the Lunar Gateway, and other orbital installations.
- 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.
- 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); 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.
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. SpaceX however announced no concrete plans to pursue the two stage "Earth-to-Earth" use case.
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". 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".
Funding
SpaceX has been developing the Starship partially with private funding, including the Raptor rocket engine used on both stages of the vehicle, since 2012. Some of the funding came from public grants. In January 2016 the US Airforce awarded SpaceX a US$33.7m grant to optimise the Raptor engine for use in the upper atmosphere with a further US$61.4m available for stretch goals.
Beginning in 2019, SpaceX began to offer specific services to potential future customers using Starship/Super Heavy/Raptor technology, and such product offerings have resulted in revenue to the company from this line of technologies. In June 2019, SpaceX indicated they could potentially launch commercial payloads using Starship as early as 2021, which often results in the recognition of revenue before a flight is launched. 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".
In April 2020, NASA announced they would pay SpaceX US$135 million for initial design work of a variation of the Starship second-stage vehicle and spaceship—a "Starship Human Landing System", or Starship HLS—as one of three potential Lunar human landing systems for the NASA Artemis program 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 the tanks of two Starship vehicles.
Criticism
The Starship vehicle design has been criticized for not adequately protecting astronauts from ionizing radiation on Mars missions; 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". 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.
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