According to tweets published by CEO Elon Musk on July 21st, SpaceX’s combined Starship and Super Heavy launch vehicle (BFR) could have as many as 41 Raptor engines at liftoff.
As with all other aspects of SpaceX’s next-generation rocket, this is a sign that things remain in flux as the company nears the point at which a specific design will need to be settled on for the first flight-ready prototype(s). With 6 Raptors on the upper stage (Starship) and 35 Raptors on the first stage/booster (Super Heavy), the rocket will – without a doubt – be the most powerful launch vehicle ever developed when it attempts its inaugural launch.
Now expected to feature 35 Raptors in its final iteration, SpaceX’s Super Heavy booster can now be expected to produce a minimum of ~70,000 kN (15.7M lbf) of thrust at full throttle, assuming that all 35 Raptors are the throttleable ~2000 kN variant. According to Musk, SpaceX may also develop a simplified Raptor with minimal throttling that would produce upwards of ~2500 kN (550,000 lbf) of thrust.
If, say, 5 throttleable Raptors were kept as the center cluster of engines used for landing and critical recovery-related burns, a Super Heavy booster with 30 uprated Raptors could produce upwards of 85,000 kN (19.1M lbf) of thrust at launch. In no uncertain terms, a Super Heavy booster anywhere inside those rough bounds (70 MN to 85 MN) would be packing double the thrust of NASA’s Saturn V rocket and double the thrust of NASA’s in-development SLS rocket in its higher-thrust variants.
Put simply, this is a spectacular amount of thrust and energy, so much so that launching a c. 2019 BFR might very well destroy any launch pad in existence today, including SpaceX’s own Pad 39A. Rated and built – in some sense – for Nova, a 10 to 20 million pound-thrust rocket meant to follow Saturn V, it’s likely that Pad 39A would/will need some significant modifications to support a full-stack Starship/Super Heavy launch, especially with a full complement of Raptor engines installed. According to Musk, work has already begun on a Starship launch structure, while the vehicle’s ‘pad’ will be situated on the opposite side of Pad 39A as its Fixed Service Structure (FSS), the tower holding SpaceX’s Crew Access Arm (CAA).
If all goes well, Musk – likely telegraphing his old, wildly optimistic, “Musk-time” self – believes that the first Starship prototypes (one in Texas, one in Florida) will be ready for inaugural flight tests as early as September/October 2019.