Version 10 (Starship-March 2019)
The 10th version that was announced in January 2019 made a mockery of Musk’s prior “final iteration” statement. Construction of the carbon fiber Starship had been lagging. The tenth version rectified that by swapping out the prior design’s carbon-fiber structure for 301 stainless steel. The ablative PICA heat shielding featured on all previous designs was replaced by a regenerative heat shield design. In it, liquid methane would be evaporated by heat and allowed to escape the hull via microscopic pores. This would transfer heat away from the Starship, protecting it during atmospheric entry.
In an interview on January 24 with Popular Mechanics Editor in Chief Ryan D’Agostino, Musk noted that a host of factors drove the design change to 301 series stainless steel: it handled structural stress better than carbon fiber, was far more heat tolerant (788 C vs. 250 C), cost $3 a kilogram versus $135 for carbon fiber, does not have carbon fiber’s 35% scrap rate, was easier to work with, remained ductile at cryogenic temperatures unlike most steels, and even had its strength boosted by 50% at those temperatures, limiting the mass difference.
301 stainless steel is a high-tensile strength steel alloy that contains 16-18% chromium, 6-8% nickel, and up to 2% manganese, 1% silicon, 0.15% carbon, 0.045% phosphorous, 0.03% sulfur, and 0.1% nitrogen. At room temperature, it can have a minimum yield strength of 205 MPa (30,000 psi) and resist oxidation up to around 788 Celsius (1450 Fahrenheit).
Its combination of high yield strength, heat tolerance, and good corrosion resistance makes it a common alloy for aircraft structural parts. It is also commonly used in appliances, subway cars, sinks, table wear, and even the cutlery many readers have in their kitchens. 301 stainless steel is also a superb material for cryogenic rocket propellant tanks. It gains about 67% more yield strength (310 to 517 MPa/45,000 to 75,000 psi) when cooled from room temperature to sub-cooled liquid oxygen temperatures of -196 Celsius (-320 Fahrenheit).
Stainless steel unsurprisingly has a long history in rocketry, with one of the earliest orbital launch vehicles built, the SM-65 Atlas intercontinental ballistic missile (ICBM), using stainless steel. To save mass, Atlas rockets used very thin stainless steel balloon propellant tanks. Balloon tanks offer minimal structural support, so to remain upright, they must be pressurized. Similarly, both Starship and Super Heavy will have partial stainless steel balloon tanks. These will likely be strong enough to permit unpressurized ground handling while still saving mass during flight.
Version 11 (Starship-September 2019)
The Starship design started changing again in May 2019, with the Starship upper stage switching to three Raptor vacuum engines and three Raptor sea-level engines.
The Starship Mark 1 presented in September 2019 at Boca Chica was a prototype of this version. At the announcement, Musk announced further changes.
Diagram by NSF member Lamontagne
The Starship upper stage would shrink 5 meters (16.4 ft.) to 50 m (164.0 ft.) in length and ditched the tri-fin layout for two actuated fins for better control in atmospheric maneuvers as well as being lighter in mass. It would also use ceramic tiles in place of a regenerative heat shield and land on six landing legs instead of four.
The Super Heavy added six Raptor engines for a total of 37, gained 5 m (16.4 ft.) in length to 68 m (223.1 ft.), replaced its three fixed landing stubs with six fixed fins, and swapped in welded stainless steel grid fins.
The changes fixed or improved the design in several ways. The use of six landing legs on Starship and six landing fins on Super Heavy reduces risk by not having a single leg or fin failure be a critical failure. The replacement of the rear tri-fin layout with actuated rear wings allows both better balance and more control during atmospheric maneuvers. The addition of six Raptor engines will both substantially increase Starship’s payload capacity and also decrease the delta-v required from the Starship stage due to lower gravity losses.
The switch to ceramic tiles has the advantage of not relying upon a cryogenic liquid, which could potentially clog in the pores of a regenerative heat shield. A disadvantage is that the new heat shield design will likely require inspection and replacement of damaged tiles following each flight. This was made possible by using a longer atmospheric entry, which would help the Starship stage keep heating below critical levels.
Credit: SpaceX
The resulting Starship/Super Heavy would mass 5000 tonnes with payload at liftoff and stand 118 m (387.1 ft.) tall. A Starship holding 1200 tonnes of propellant and 100+ tonnes of cargo and crew would sit on top. Alternative upper stages include the cargo variant, which can hold up to 150 tonnes of cargo, and a tanker with over-sized tanks. The massive Super Heavy Stage sits below and holds 3300 tonnes of propellant. It would lift the vehicle off the pad with 72,569 kN (16,314,200 lbf) of thrust from 37 Raptor engines. It would take 48 A380s taking off at once to equal the Super Heavy’s thrust, and its propellant load alone out masses the entire Saturn V Moon rocket.
Version 12 (Starship-May 2020)
The twelfth version of the design saw yet another Starship variant added: a propellant depot ship. The new version began taking shape after Elon Musk confirmed an array of changes to the design on March 16, 2020, and in later Twitter posts.
Among those changes were a switch to 304L low carbon stainless steel construction, with lengthening of the Super Heavy stage by 2 meters to 70 m (229.7 ft.), the overall stack to 122 m (400.3 ft.), a 300 tonne (661,400 lb) increase in overall propellant mass, the removal of six (later nine) Raptor engines, a new, higher thrust version of the Raptor engine, the addition of new hexagon-shaped, auto-leveling retractable landing legs on Starship, with other potential changes including embedded engines and a more efficient tank curvature.
Improved tanks and more efficient tank curvature would lead to higher propellant mass and lower dry mass in both stages. These changes would increase payload to orbit and potentially lower cost per kilogram and passenger. Improved legs would increase the rocket’s landing stability, likely increasing the number of times the stage could be reused before suffering an accident.
On April 30, 2020, it was announced that SpaceX had won a $135 million NASA Artemis Program contract for a lunar lander version of Starship. It would dwarf the Apollo LM lunar lander, standing over seven times higher at 50 m (164.0 ft.) vs. 7.0 m (22.9 ft.), with fifty times the crew capacity (100 vs. 2) and over 150 times the pressurized volume (1000+ m3 vs. 6.65 m3). The version could potentially land 100 tons of cargo and eight times more astronauts than walked on the Moon during the entire Apollo Program.
SpaceX’s Artemis related plans call for a LEO Starship flight, a follow-up reflight, propellant transfer between a Starship and tanker, a longer duration orbital Starship mission, and a flight beyond LEO. All of this will precede an uncrewed lunar landing demonstration mission in 2022.
Credit: SpaceX
To reduce mass, the lunar lander version of Starship would feature no aerodynamic control surfaces or TPS and uses different final descent engines due to the risk of lunar surface debris kicked up by the Raptor engines. The six rendered thrusters appear higher up on the vehicle’s sides, a design similar to the NASA Langley Hercules concept. It would also feature two fully redundant airlocks. However, it will be the regular Starship and not the lunar lander variant that will carry Japanese billionaire Yusaku Maezawa when he flies around the Moon.
In a September 1, 2020 tweet, Musk noted further changes to the engines. The Super Heavy would now only use 28 Raptor engines, three fewer than before. The regular Raptor engines would see thrust upped by 5% from 200 tf to ~210 tf (2,059 kN/ 463,000 lbf), while a new, fixed thrust version would produce 300 tf (2,942 kN/ 661,400 lbf). Eight centrally mounted, variable thrust gimbaling Raptors would help Super Heavy perform directional changes. Twenty of the more potent non-gimbaling Raptors would provide the majority of the thrust.
Despite the loss of three engines, total thrust would climb 3.8% from 72,569 kN (16,314,200 lbf) to 75,315 kN (16,931,500 lbf). It would take no fewer than 51 A380s to exceed the thrust of Super Heavy.