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In the 1990s, Dr. John Hunter led what was known as Super HARP, which was a methane-and-hydrogen powered ballistic launch system that achieved exit velocities of 6,700 mph (10,800 kph). Rival startup Green Launch asserts that laboratory-based hydrogen systems have achieved exit velocities of 25,000 mph (39,600 kph) and that a full-scale projectile speed of 9,000 mph (14,400 kph) is accessible. In fact, a December 2021 test achieved exit velocities of 4,400 mph (7,200 kph): nearly matching SpinLaunch’s desired full-scale goals. While SpinLaunch will require at least two extra stages to reach space, Green Launch aims to reach the Kármán line that defines the start of space, 100 kilometers (62 miles) up, from the projectile launch alone.

There’s no doubt that there’s a lot of truth to the old saying that “fortune favors the bold,” and SpinLaunch is certainly a bold idea. However, the laws of physics pose numerous obstacles for those who would build high-powered, rapidly moving large-scale apparatuses with moving parts. In the 1990s, the Department of Energy attempted to build enormous centrifuges for accelerating large objects, but they always began to break down at speeds of ~3,100 mph (5,000 kph): about 60% of the speeds that SpinLaunch aims to achieve. The challenges before the team aiming to reach their stated goals are enormous.

That isn’t to say that SpinLaunch is impossible or that its concepts violate the laws of physics; they do not. However, there’s a very big distinction between what’s physically possible and what’s physically practical. It’s not clear that, with three times the diameter of the current prototype, the desired launch parameters can be met. Even if they are, it remains to be seen if the later-stages required to take the launched payloads to orbit can operate after experiencing the extreme SpinLaunch spin-up and launch and drag conditions. It’s important to explore a variety of options in the quest to reach space, but scaling up a prototype is rarely as easy as one might initially think.