This claim asserts that the screw flights along the entire length of the acceleration and deceleration sections can safely operate with a tangential (tip) speed of 525 m/s. This refers to the local surface speed at the flight tip radius, not the vehicle speed. The vehicle's speed at any given position is computed by multiplying the tip velocity by the screw's pitch at that position.

Comparable Technologies

The tips of the fan blades in modern airliners jet engines move at speeds on the order of 500 m/s. High-speed steel rotors in centrifuges and turbomachinery routinely operate with peripheral speeds in the ~300–500 m/s range, and composite flywheels exceed that. VPSL’s 525 m/s target is of the same order as established high-speed rotating systems. The screws operate in vacuum on magnetic bearings and thus avoid aero loads at speed.

Engineering Specifics

A screw segment from a high-pitch position was is described in the section entitled "F. Linear Active Magnetic Bearings (AMBs)" of this paper. Figure 13 shows the results of a simple stress simulation for a muzzle-end screw segment with eight starts (sets of flights). The simulation estimates the maximum tip speed given a set of input parameters. In this case an engineering factor of 1.5 was applied. The inner radius is 0.15 m and the radius to the tips of the screw flights is 0.5 m. The theoretical maximum tip speed is estimated to be 530 m/s. The material used for this simulation was A514 steel (T-1 high-strength) with a yield strength of 690 MPa, which is a high-strength, quenched and tempered alloy steel known for its excellent toughness and weldability. It is commonly used in heavy-duty structural applications like bridge construction, buildings, and machinery.

With higher-strength steels (e.g., maraging), feasible limits approach ~1000 m/s (with cost/complexity trade-offs). Even higher speeds might be possible with other metals or composites, but then the challenge of bonding a ferromagnetic material would increase leading to higher manufacturing costs.

The investigation also confirmed that the additional lateral loads fall well within the stress limits of the design. Figure 15 shows the lateral load-induced stresses only, and reveals that these stresses (up to 161 MPa) are small compared to the stresses caused by centrifugal forces (~1500 MPa).

Back-of-the-Envelope Check

A thin-ring estimate applies to the shaft and gives intuition for plausibility. For density ρ and allowable tangential stress σ_allow, the peripheral speed scales roughly as:

• v_max ≈ sqrt(σ_allow / ρ)

For A514 steel with σ_allow ≈ 690 MPa/1.5, ρ ≈ 7850 kg/m³, and an engineering factor of 1.5:

• v_max ≈ sqrt(690e6 / 1.5 / 7850) ≈ 242 m/s

The screw flight tip radius is roughly 2.25 times the shaft outer radius, so the tip speed is 242*2.25 = 544 m/s.

Other considerations

The screws operate within a temperature-controlled, evacuated environment, where they are not exposed to significant thermal cycling, oxidation, or high-cycle fatigue. In most terrestrial applications, metal alloys are formulated to balance competing properties such as strength, ductility, toughness, and corrosion resistance. In the controlled environment of the launch system, however, these trade-offs shift substantially. Because corrosion and large temperature swings are largely eliminated, the alloy composition and heat treatment can be optimized primarily for static and fatigue strength, even if this entails reduced ductility or corrosion resistance relative to conventional structural alloys. The analysis above assumes that commercially available metals are used in the screw's construction, and does not account for the additional gains that could be made with custom-engineered alloys.

See Also This video on YouTube claims to have spun a 3" diameter aluminum skateboard wheel up to 100,000 RPM with a waterjet, which is equivalent to a rim speed of 400 m/s (but not 8829 mph, or 3947 m/s as was claimed in the video).