1. History

The Starship engine layout and reentry aerodynamic surface designs have changed noticeably since the initial public unveiling of the 9-meter (30 ft) diameter rocket in September 2017, in order to balance objectives like payload mass, landing capabilities, and reliability.

The initial design at the unveiling showed the ship with six Raptor engines (two sea-level, four vacuum) and a delta wing with split flaps.^[1]

By late 2017, SpaceX added a third sea-level engine to increase engine-out capability and allow landings with greater payload mass, bringing the total number of engines to seven.^[2] Seven engines, three sea-level and four vacuum, remained the design until September 2018, when SpaceX indicated that early flights would happen with exclusively sea-level nozzle engines.

The late-2018 Starship design with seven sea-level Raptor engines and the revised aerodynamic control surface layout. https://handwiki.org/wiki/index.php?curid=1295342

In 2018, a new version of the design was revealed with the announcement of the #dearMoon project. The presentation for this mission (planned to launch in 2023) depicted the Starship with seven identical sea-level rated Raptor engines. These engines were also used in the design of the first-stage of the BFR launch vehicle, Super Heavy.^[3]

In January 2019, Elon Musk announced that the Starship would no longer be made out of carbon fiber, and stainless steel would be used instead to build the Starship. Musk cited several reasons including cost, strength, and ease of production to justify making the switch.^[4]

In May 2019, the Starship design changed back to just six Raptor engines, with three optimized for sea-level and three optimized for vacuum.^[5]

By late May 2019, the first prototype, Starhopper, was preparing for untethered flight tests in early June in South Texas, while two orbital prototypes were under construction, one in South Texas and one on the Florida space coast. The build of the first Super Heavy booster stage was expected to be underway by September.^[6] 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.^[7]

By June 2019, SpaceX publicly announced discussions had begun with three telecom companies for using Starship, rather than Falcon 9, for launching commercial satellites for paying customers as early as 2021. No specific companies or launch contracts were announced at that time.^[8]

2. Description

Starship is a 9-meter (30 ft)-diameter, 55-meter (180 ft)-tall,^[3] fully reusable rocket design with a dry mass of 85,000 kg (187,393 lb),^[9] powered by six methane/oxygen-propellant Raptor engines.^[5] Total Starship thrust is approximately 11,500 kN; 2,600,000 lbf (1,170 tf).

Unusual for previous launch vehicle and spacecraft designs, Starship is to function as both a second stage for the BFR launch vehicle that provides acceleration to orbital velocity on all launches from Earth, and yet will also be used in space as an on-orbit long-duration spacecraft.^[3][9]

The Starship design is intended to be fully reusable even when used as a second stage for orbital ascent from Earth. Starship is being designed so as to be capable of reentering Earth's atmosphere from orbital velocities and landing vertically, with a design goal of rapid reusability.

As announced in May 2019,^[5] 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 first-stage of the BFR launch vehicle, Super Heavy.^[3] Subsequent versions for interplanetary travel are expected to utilize a vacuum-optimized Raptor engine variant to optimize specific impulse (I_sp).

Starship will eventually be built in at least three operational versions:^[10]

• spaceship: a large, long-duration spacecraft capable of carrying passengers^[10] or cargo to interplanetary destinations, to LEO, or between destinations on Earth.
• satellite delivery spacecraft: a vehicle able to transport and place spacecraft into orbit^[8], or handle the in-space recovery of spacecraft and space debris for return to Earth or movement to another orbit. In the 2017 early design concept, this was shown with a with a large cargo bay door that can open in space to facilitate delivery and pickup of cargo.^[10]
• 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.^[11]

Major characteristics of Starship include:^{[9][10][12][13]}

• being designed such that the ship can return from Earth orbit and land near the launch mount using retropropulsive landing and the reusable launch vehicle technologies developed earlier by SpaceX
• landing reliability is projected by SpaceX to ultimately be able to achieve "airline levels" of safety due to engine-out capability.
• rendezvous and docking operations will be automated
• on-orbit propellant transfers from Starship tankers to Starship spaceships or cargo spaceships, but initially from one standard orbital Starship to another.^[11]
• a Starship and its payload will be able to transit to the Moon or fly to Mars after on-orbit propellant loading
• stainless steel structure and tank construction. Its strength-to-mass ratio is 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^[14]
• 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."^[14]
• the thermal protection system against the harsh conditions of atmospheric reentry will utilize a double stainless-steel skin with active coolant flowing in between the two layers. Hexagonal stainless steel tiles will blanket the windward side of Starship, and some areas will additionally contain multiple small pores that will allow for transpiration cooling.^[15][16][17]
• as envisioned in the 2017 design unveiling, the Starship is to have a pressurized volume of approximately 1,000 m³ (35,000 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 plus 12 unpressurized aft cargo containers of 88 m³ (3,100 cu ft) total.^[9]
• flexible design options; for example, a possible design modification to the base Starship—expendable 3-engine Starship with no fairing, canards, rear fins, nor landing legs—to optimize mass ratio for interplanetary exploration with robotic probes.^[18]

When Starship is used for 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.^[10] Some lunar flybys will be possible without orbital refueling as evidenced by the mission profile of the #dearMoon project.^[19]

3. Starship Specifications (Planned)

Data from ^[5]

General characteristics

• Capacity: ≤ 100 people
• Diameter: 9 m (29 ft 6 in) ^[3]
• Height: 55 m (180 ft 5 in) ^[3]
• Volume: 1,000 m³ (35,000 cu ft) ^[9]
• Empty weight: 85,000 kg (187,393 lb) ^[1]
• Gross weight: 1,335,000 kg (2,943,171 lb) ^[1]
• Fuel capacity: 1,100,000 kg (2,400,000 lb)
• Powerplant: 3 × Raptor rocket engine
• Powerplant: 3 × RaptorVac rocket engine

4. Prototypes

Two test articles were being built by March 2019, and three by May.^[20] The low-altitude, low-velocity Starship test flight rocket was used for initial integrated testing of the Raptor rocket engine with a flight-capable propellant structure, and will 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-meter-diameter rocket. SpaceX originally developed their reusable booster technology for the 3-meter-diameter Falcon 9 from 2012 to 2018. It will also be the platform for the first flight tests of the full-flow staged combustion methalox Raptor engines, where the hopper vehicle is expected to be flight tested with up to three engines to facilitate engine-out tolerance testing.^[15]

The high-altitude, high-velocity Starship orbital prototypes will be used to develop and flight test novel thermal protection systems and hypersonic reentry control surfaces.^[15] Each orbital prototype is expected to be outfitted with more than three Raptor engines.

4.1. Starhopper

The construction of the initial test article—the "Starship test flight rocket"^[21] "test hopper,"^[22] "Starship Hopper"^[23] or "Starhopper"^[24][25] —was begun 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 two miles from Boca Chica Beach in South Texas, the external body of the rocket rapidly came together in less than six weeks. Originally thought by watchers of construction 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 meters (30 ft) in diameter and was originally 39 meters (128 ft) tall in January 2019.^[14][22] 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.^[26]

From mid-January to early-March, 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 two miles to the launch pad on 8 March.^[27] Following initial integrated system testing of the Starhopper test vehicle with Raptor engine serial number 2 engine (Raptor S/N 2) in early April, the engine was removed for post-test analysis and several additions were made to the Starhopper. Attitude control system thrusters were added to the rocket, along with shock absorbers for the non-retractable landing legs, and quick-disconnect connections for umbilicals. Raptor S/N 4 was installed in early June for fit checks, but the first test flight that is not tethered was expected to fly with Raptor S/N 5,^[26] until it suffered damage during testing at SpaceX Rocket Development and Test Facility, in McGregor, Texas. Actually, the engine that will be used in Starship Hopper for the first untethered flights will be Raptor S/N 6.^[28]

The test article will be used to flight test a number of subsystems of the Starship and will be used to expand the flight envelope as the Starship design will be finalized.^[22][29][30] Initial tests began in March 2019.^[31] All test flights of the "test hopper"^[22] will be at low altitude, under 5 kilometers (16,000 ft).^[32] 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.^[33] On 21 June 2019, the FAA issued a one-year experimental permit to fly Starhopper at Boca Chica including pre-flight and post-flight ground operations.^[34] See Testing section below for full testing history and details.

4.2. Starship Orbital Prototypes

Two orbital prototype ships—referred to as Mk1 or Mk I,^[35] and Mk2^[6]—are under construction as of May 2019, one in South Texas and one on the space coast of Florida.

Initial construction was underway by December 2018 when subsections of a Starship orbital prototype—also referred to as the "Starship Mk I orbital design" were stated to be under construction in California.^[35] Planned for high-altitude and high-velocity testing,^[36] the orbital prototype will be taller than the suborbital hopper, have thicker skins, and a smoothly curving nose section.^[37] Both prototypes will fly test flights with at least three Raptor engines, and possibly all six.^[6][6][38]

By March 2019, construction of the full external structure and propellant tanks of the first orbital prototype ("Mk 1"^[38]) was well underway at the SpaceX "ad-hoc South Texas 'shipyard'," with an expectation that the vehicle could be complete and ready to begin testing as early as June.^[39] The new build of additional 9-meter diameter stainless steel structures in South Texas in late February was originally misattributed and thought to be a second and more substantial version of the Starhopper's upper section, following the destruction of the first Starhopper upper section, damaged by high winds in January.^[27] The Mk1 prototype will fly with three Raptor engines.^[40]

By May 2019, SpaceX revealed that they were building not one but two orbital prototypes, Mk1 in Texas and a second one, Mk2, in Florida. The two Starship prototypes are being constructed by competing teams, that are required to share progress, insights, and build techniques with the other team, but neither team is required to use the other team's techniques.^[6][20][41]

4.3. Testing

Integrated system testing of the first Starship prototype (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."^[15]

The first static fire test of the Starhopper test vehicle, with a single Raptor engine attached, occurred on 3 April 2019. The firing was a few seconds duration, and was classed as successful by SpaceX.^[15] A second tethered test followed just two days later, on 5 April.^[20][42]

(As of May 2019), SpaceX is planning flight tests both in South Texas and on the Florida space coast.^[41] with the first test flights in Texas—nominally aiming for height of 20 m (66 ft), which is expected from mid-July.^[6][26]

5. Intended Uses

Starship is intended to become the mainline SpaceX orbital vehicle, as SpaceX has announced it intends to fully replace its existing Falcon 9 launch vehicle and Dragon space capsule fleet with Starship/Super Heavy during the early 2020s.^{[1][10][46]:24:50–27:05}

Starship will be utilized for:^[12][46]

• legacy Earth-orbit satellite delivery market. In addition to the standard external launch market that SpaceX has been servicing since 2013, the company intends to use Super Heavy/Starship to most cost-effectively launch the largest portion of its own satellite internet 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.^[47]
• long-duration spaceflights in the cislunar region
• Mars transportation, both as cargo ships as well as passenger-carrying transport
• long-duration flights to the outer planets, for cargo and astronauts^[48]

In 2017, SpaceX mentioned the theoretical ability of using a boosted Starship to carry passengers on suborbital flights between two points on Earth in under one hour, providing commercial long-haul transport on Earth, competing with long-range aircraft.^[49][50] SpaceX however announced no concrete plans to pursue this two stage "Earth-to-Earth" possibility.^[29][51] use of BFR.^[1] Over two years later, in May 2019, Musk floated the idea of using single-stage Starship to travel up to 10,000 kilometers (6,200 mi) on Earth-to-Earth flights at speeds approaching Mach 20 (6.8 km/s; 25,000 km/h; 15,000 mph) with an acceptable payload saying it "dramatically improves cost, complexity & ease of operations."^[52]