SPINLAUNCH — USA

The most wasteful part of any rocket launch is the part close to the ground, where a huge booster needs to expend enormous amounts of fuel while moving at low speed, and the engines are working at reduced efficiency because of the thick atmosphere. So a lot of different ideas have been explored for how to just avoid using a rocket for that part of the job: launching from an airplane, or from a high-altitude balloon, or from some kind of electromagnetic railgun, or from a gigantic miles-high arched bridge supported by the centrifugal force of a spinning chain... or even just from a mountaintop. Some of these ideas have been tried, especially the airplane option. None of the ones that involve using ground-based machinery to fling the craft into the air have been tried yet... but SpinLaunch means to change that.

Instead of gigantic roller-coaster tracks or guns or self-suspending loops, they seem to have found what is probably the cheapest and simplest way to give a spacecraft a hypersonic velocity before it even leaves the ground: put it into a big centrifuge, spin it as fast as possible, and then let it go. The advantages are that the accelerator device needs only a small patch of ground and a reasonable amount of construction material, and doesn’t need to suck in a gigantic amount of electric power in a brief amount of time. Everything is buildable without a Pentagon-sized budget. But there is one big disadvantage: the spacecraft has to survive being accelerated sideways at up to ten thousand gravities for an extended period. This puts very sharp limits on what kinds of payloads it can launch, as most satellite hardware is built flimsy in order to save weight, and would be shattered long before it left the ground if put into this hellish salad-spinner.

The accelerator they envision would be 100 meters in diameter, with a carbon fiber arm inside a big steel vacuum chamber, tilted at an angle around 35 degrees above the horizon. It would spend an hour or so powering up the rotor until the end holding the projectile is going faster than two kilometers per second — they say they might push it to 2.2 km/s, which means that when they release the rocket, it would be going at mach 6.7 through the lower atmosphere.

The release must be timed with great precision to make sure it flies out the exit pipe and not at any other angle. I have no idea what kind of insane mechanism they can use to hold and release something that quickly with that much force involved — it must be an unimaginably difficult piece of mechanical engineering — or how they manage the sudden loss of balance on the rotor when it’s at full speed.

Since the accelerator has no air in it, the rocket has to break through a thin membrane which is keeping the air out. Between the shock of the rupture, the collapse of a ballroom-sized vacuum, and a major sonic boom, his would create a trenendous noise, which is one reason why they’re building it way out in the desert. Punching through a skin that can hold back sea-level air pressure needs a sharp nose, and one that can also withstand the heat and friction of hypersonic flight in thick air. These considerations, plus the need to withstand all the lateral force during spin-up, are incompatible with the light weight that is needed for an orbital rocket, but one solution covers all of these issues: the rocket itself is packed inside a form-fitting shell with protects and supports every part of it. Once the shell (or sabot) drops away, what’s left can be as light and flimsy as you like.

The plan is for the rocket to stay inside the sabot all the way up to an altitude of about 60 kilometers, then emerge and accelerate itself the rest of the way to orbit. This rocket is basically a second stage with no first stage, which would save a lot of money. They haven’t stated any specifics about its size or weight, but they hope for a payload capacity of 200 kilograms, so the rocket stage probably weighs several tons.

Besides the limitations on what kind of payload could survive the launch, there’s another limitation: their concept art shows the accelerator leaning at an angle against a hillside, with no apparent means of being rotated to aim at a different part of the sky. This would limit their launches to just one orbital inclination. Maybe some future upgraded version will be able to offer such options, and/or maybe lower G-forces by using a larger diameter.

All of this is nothing but computer-animated artists’ conceptions, of course. But they do have a smaller version that actually launches stuff: it’s one third scale (33 meters in diameter) and has flung stuff up to an altitude of nine kilometers. That may increase as they push it to greater speeds. Unlike the big version, its exit tube is aimed straight up. It’s been flinging test payloads since 2021, though the early ones were done at fairly low speeds.

Should this be taken seriously? I won’t rule the idea out, but I think there are going to be a lot of obstacles to overcome, and if they do make it work, their impact on the launch market will have to be quite niche, no matter how good their prices are.

(No meaningful stats exist yet for the projectile rocket. They may expect that to be supplied by other companies, for all I can tell.)