The term "Unobtanium" originated in the 1950s as a humorous engineering term for a hypothetical, perfect material that was impossible to obtain or did not exist. Some infrastructure concepts popularized in science fiction rely on breakthroughs in materials science that we haven't achieved yet, either in discovering a new material with advanced properties, a way to manufacture a material developed in the lab at enormous scales, the ability to achieve incredibly low defect rates when manufacturing at scale, or the ability to massively reduce the cost of manufacturing the material. Therefore, it is reasonable to wonder if perhaps the Variable Pitch Screw Launcher is relying on some overly optimistic assumptions in the field of materials science. This claim asserts that the baseline architecture of VPSL and its cost estimates rely entirely on materials for which there is already an established industrial base, where there are already lots of data on how these materials perform in other applications, and where the cost of purchasing and forming the materials into useful parts is well understood by fabricators.

This does not preclude the possibility of engineers proposing improvements to the baseline architecture by taking advantage of new breakthroughs in materials science - such proposals could be evaluated against the baseline architecture to perhaps demonstrate ways that the baseline architecture could be further improved upon.

We will examine the various sub-components of the VPSL baseline architecture and discuss how the likely candidate materials have a heritage of being used in other, similar, applications.

The Evacuated Tube used in the Horizontal Acceleration and Ramp Sections

The horizontal acceleration section is assumed to use a steel-reinforced concrete outer structure and a vacuum-tight steel or stainless-steel inner liner. These are not exotic materials. Reinforced concrete is one of the most widely used civil engineering materials in the world. Steel pressure vessels, steel pipelines, immersed tunnels, and large-diameter welded steel structures are also mature industrial products. The proposed system is unusually long, but the materials themselves are conventional.

The use of a vacuum-tight tube is also not a speculative materials problem. LIGO provides a particularly useful precedent because its long beam tubes are made from stainless steel and have maintained ultra-high vacuum conditions over kilometer-scale distances for decades. The VPSL tube would be much longer, but it would operate at a far less demanding pressure than LIGO. The relevant lesson is not that VPSL is a direct copy of LIGO, but that long, welded, stainless-steel vacuum tubes are already a demonstrated industrial technology. The VPSL paper referenced in the VPSL concept description also notes that similar spiral-welding techniques are used in large cylindrical structures such as wind turbine towers, indicating that the manufacturing approach does not depend on a novel material or laboratory-only process.

Thermal expansion and structural loading are also handled using ordinary civil and mechanical engineering methods. Submerged and tunneled sections operate in relatively stable thermal environments, while expansion joints, reinforcement ribs, and conventional structural supports can be used where needed. These details may require careful engineering, but they do not require a new class of material.

This sub-component is described in more detail in the claims entitled "The Required Geometric Straightness of the Submerged Acceleration Section is Achievable" and "A long tube equipped with a vacuum pumping system can be built to achieve the required vacuum level cost-effectively".

The Elevated Evacuated Tube

The Elevated Evacuated Tube (EET) is discussed in more detail in the related claims on vacuum-system feasibility, exit altitude, endoatmospheric transit, and environmental impact. This section focuses only on the materials question: whether the EET requires any material that is unavailable, speculative, or outside normal industrial practice.

The EET is positioned around the spacecraft’s ballistic flight path after the launch sled and vehicle have already been accelerated. It is not part of the primary acceleration system, and it does not need to support, push, steer, or redirect the spacecraft at high speed. Its main structural role is to provide a low-pressure corridor through the denser part of the atmosphere so that the vehicle can continue along its intended trajectory while avoiding most of the aerodynamic drag and heating that would otherwise occur.

From a materials standpoint, the EET can therefore be treated primarily as a long, lightweight vacuum shell. Its wall must support the pressure difference between the evacuated interior, estimated at approximately 5 Pa, and the ambient pressure at the altitude where is is stowed in its hanger when not deployed. At the exit altitude, the uploaded vacuum-system draft uses an ambient pressure of approximately 12,000 Pa, which is far below sea-level atmospheric pressure. The pressure load is therefore meaningful, but it is not an unprecedented pressure-vessel requirement.

Aircraft provide a useful comparison. Airliner fuselages are also designed to support a pressure difference across a lightweight cylindrical shell. In the VPSL paper, the EET is compared to aircraft fuselage manufacturing, with the important caveat that aircraft fuselages include many additional requirements that a bare evacuated tube would not have. The paper estimates EET tube cost by comparison with Spirit AeroSystems fuselage production and uses a cost-per-meter figure of roughly $115,000/m as an upper-bound budgeting reference.

This comparison is useful because it anchors the EET in an existing aerospace manufacturing base. The likely material family is conventional aerospace aluminum alloy or a comparable lightweight structural material, formed into a stiffened shell with ordinary aerospace joining, inspection, and corrosion-control methods. The EET may be long, roughly 100 km in the current architecture, but its material requirement is not for a new material. It is for a lightweight, inspectable, manufacturable shell structure whose pressure loads are within the range of known engineering practice.

The open questions are therefore design and cost questions, not unobtainium questions: wall thickness, stiffener spacing, buckling margin, fatigue life, joining method, seal design, inspection intervals, and repair procedures. Those questions should be addressed in the more detailed EET and vacuum-system claims rather than rehashed here. For this claim, the relevant point is that the EET does not depend on a breakthrough material. It depends on applying known aerospace shell-structure materials and manufacturing methods to an unusually long, low-pressure tube.

The Screws

The screws and internal flywheels are covered in far more detail in "The Targeted Screw Flight Tip Velocity of 525 m/s is Attainable", "Momentum Transfer from the Flywheels, through the Screws, to the Adaptive Nut is Feasible", and "Heat Can Be Transferred Out of the Screws".

For this claim, the relevant point is that the screws and flywheels are not assumed to be made from an exotic material. The baseline analysis treats them as steel rotating components. In the screw flight tip velocity claim, the simulated screw segment uses A514 steel, also known as T-1 high-strength steel, with a yield strength of 690 MPa. The claim describes A514 as a high-strength, quenched and tempered alloy steel used in heavy-duty structural applications such as bridges, buildings, and machinery. The same analysis estimates that a screw flight tip velocity near the 525 m/s target is attainable using this material, with higher-strength steels such as maraging steel available as a more expensive margin-improving option rather than a required breakthrough material.

The internal flywheels are likewise analyzed as steel components. The momentum-transfer claim assumes steel with a density of 7850 kg/m³ and evaluates a cylindrical flywheel geometry. It also estimates a maximum flywheel rotation rate using steel with a 690 MPa yield stress and an engineering factor of 1.5. This matters because the flywheel is not being treated as a carbon-nanotube rotor, laboratory composite, or other speculative energy-storage material. It is being analyzed using ordinary steel properties and conservative rotating-machinery assumptions.

The material comparison to commercial aircraft is useful because modern aircraft engines already use high-speed rotating components whose blade tips move at roughly the same order of speed. The screw-tip claim notes that fan blade tips in modern airliner jet engines move on the order of 500 m/s, while high-speed steel rotors in centrifuges and turbomachinery routinely operate in the roughly 300 to 500 m/s range. VPSL’s target screw flight tip speed of 525 m/s is therefore not outside current engineering practice for rotating machinery. The VPSL screws also operate in vacuum on magnetic bearings, so they avoid the aerodynamic loading that aircraft engine fan blades must tolerate at similar tip speeds.

The heat-transfer claim reinforces the same materials point. Heat generated in the screw and flywheel system is modeled using ordinary steel density and heat capacity values, and the claim concludes that the heat generated per launch can be absorbed by the bulk mass of the screw and flywheel and radiated away between launches. The cooling argument does not depend on a superconductor, exotic heat pipe material, or unknown thermal medium. It depends on steel thermal mass, radiative heat transfer from coated surfaces, and conventional bracket-mounted cooling paths for the motor stators.

The only notable material refinement is that the screw flight tips may need to balance mechanical strength with magnetic performance. That could lead to the use of a high-strength steel body with magnetically favorable steel, laminations, coatings, inserts, or bonded regions near the flight tips. This is a normal engineering trade rather than an unobtainium assumption. Many mature machines use different materials in different regions to balance strength, fatigue life, magnetic behavior, heat flow, manufacturability, and cost.

Therefore, the screws should be understood as challenging high-speed rotating steel components, not speculative materials. Their design will require stress analysis, fatigue testing, spin testing, magnetic-loss testing, heat-treatment optimization, nondestructive inspection, and supplier engagement. But the material families under consideration are already used in heavy machinery, turbines, centrifuges, aircraft engines, flywheels, motors, and magnetic machinery. The baseline architecture does not require a new material to be discovered before the screw system can be evaluated.

Magnetic Coupling

Magnetic coupling is used between the moving components (specifically, the adaptive nut and the launch sled) and the "stationary" components (specifically the guideway and the spinning screws). Examples of other technologies that make use of magnetic levitation or magnetic confinement include high-speed maglev trains, magnetic bearings, and particle accelerators such as CERN's large hadron collider.

Particle accelerators are relevant because they demonstrate that magnetic systems can guide moving bodies with very large stored kinetic energy, tight positional tolerances, and very low fractional energy loss. When operating near its design limits, each circulating proton beam in the Large Hadron Collider stores approximately 362 MJ of kinetic energy, comparable to a 1,000 metric ton freight train moving at about 60 mph. Each 7 TeV proton loses only about 7 keV per turn to synchrotron radiation, or roughly one billionth of its energy per circuit. While a particle beam is very different from a train or a launch sled, the accelerator’s magnets must continuously bend and confine that high-energy beam around the ring while preserving the beam energy well enough for multi-hour operation. This makes the LHC a useful example of precise, low-loss magnetic guidance. Since the protons are ultra-relativistic, the approximate transverse force required to bend one stored beam around the ring is:

$F \approx \frac{E}{r}$

Using $E = 362 \text{ MJ}$ and an LHC bending radius of roughly $r = 2800 \text{ m}$:

$F \approx \frac{362 \times 10^6}{2800} \approx 1.3 \times 10^5 \text{ N}$

So the magnets are collectively providing on the order of 130 kN of transverse guidance force to each beam, while maintaining extremely precise confinement. That is not directly the same kind of load path as VPSL, but it is a strong precedent for using engineered magnetic fields to guide and control high-energy moving systems without mechanical contact.

Magnetic bearings are a particularly relevant precedent because they are already used to support high-speed rotating machinery without mechanical contact. The Global Active Magnetic Bearing Market was valued at USD 320 million in 2024 and is anticipated to reach USD 521.7 million by 2032, making it an established industrial product category.

Common applications include turbocompressors, turbines, pumps, motors, generators, chillers, flywheel energy storage systems, and vacuum equipment. Magnetic bearings are typically chosen over ball or roller bearings when non-contact operation provides a practical advantage: reduced wear, low friction, no lubricant requirement, reduced contamination risk, lower maintenance, and better suitability for vacuum or high-speed operation.

The most common type is the active magnetic bearing, or AMB. In an AMB, electromagnets are arranged around a ferromagnetic rotor. Position sensors measure the rotor’s location, a controller compares that location to the desired position, and power electronics adjust current in the electromagnets to keep the rotor centered. In simple terms, the bearing replaces physical contact with a continuously controlled magnetic field. This is directly relevant to VPSL because the baseline architecture also depends on maintaining controlled gaps between moving and stationary components without relying on rolling or sliding contact.

Maglev trains provide another useful precedent because they show that magnetic suspension can be scaled from rotating machinery to full vehicle systems. In practice, the two main approaches are electromagnetic suspension and electrodynamic suspension. Electromagnetic suspension, or EMS, uses controlled electromagnets on the vehicle to attract it toward a ferromagnetic guideway. Because magnetic attraction becomes stronger as the gap closes, EMS is inherently unstable and requires active feedback control to maintain the air gap. This is the approach associated with systems such as the German Transrapid and the Shanghai Maglev.

Electrodynamic suspension, or EDS, works differently. It uses relative motion between magnets on the vehicle and conductors in the guideway to induce currents. Those induced currents create magnetic fields that oppose the changing field and generate lift and guidance forces. EDS can be implemented using superconducting magnets, as in Japan’s SCMaglev, or using permanent magnets arranged in Halbach arrays, as in Inductrack-type concepts. EDS systems generally require some forward speed before levitation becomes effective, but they can be passively stable once operating.

Maglev technology is not limited to passenger trains. The U.S. Air Force’s 846th Test Squadron at Holloman Air Force Base in New Mexico has also tested magnetically levitated rocket sleds, including a 2016 run that reached 633 mph on a 2,100-foot track. The system used electrodynamic suspension, with cryogenically cooled superconducting magnets on the sled interacting with passive copper rails in the guideway. This provides a useful precedent for applying magnetic suspension to high-speed, high-acceleration test hardware.

Superconductors have been used in some maglev approaches, but they are not universal to maglev, and they are not room-temperature superconductors. Japan’s SCMaglev uses superconducting onboard magnets cooled cryogenically, with public descriptions citing liquid helium cooling near minus 269 °C. Other systems, such as EMS maglev trains, use conventional electromagnets rather than superconductors, while Inductrack-type systems use permanent magnets and passive conductive tracks.

This distinction is important for the unobtainium claim. VPSL does not require room-temperature superconductors or any other futuristic magnetic material. Superconductors, including low-temperature and high-temperature superconductors, may be useful in some future design variants if they provide a favorable trade between field strength, cooling cost, mass, reliability, and maintenance. But they are not required by the baseline architecture. The baseline magnetic-coupling argument can be made using conventional electromagnets, ferromagnetic steels, permanent magnets where useful, copper or aluminum conductors, sensors, and active control systems, all of which are established industrial technologies.

The Spacecraft's Thermal Protection System

The spacecraft’s thermal protection system is discussed in more detail in the claim entitled "An Exit Altitude of 15 km Enables Safe Endoatmospheric Transit". For this claim, the relevant materials question is whether the thermal protection system requires a new or unavailable material. It does not.

The thermal loads encountered after exiting the Elevated Evacuated Tube are expected to be intense but brief. The spacecraft exits the tube at approximately 15 km altitude (a placeholder value in the current architecture), where atmospheric density is much lower than at sea level. It then rapidly gains altitude along its outbound trajectory, so the most severe heating occurs over a short portion of the flight rather than throughout a long atmospheric climb. The purpose of the EET is to move the start of endoatmospheric transit high enough that this brief heating pulse can be handled by known thermal protection technologies. The VPSL paper referenced in the concept's description describes the architecture as accelerating vehicles to 11,123 m/s and having them exit the elevated evacuated tube into rarefied atmosphere at 15 km altitude.

Thermal protection materials can be divided into two broad categories: ablative and non-ablative. Ablative heat shields protect the vehicle by intentionally consuming material. As the surface heats, it chars, melts, pyrolyzes, or vaporizes, carrying heat away from the vehicle and creating a protective boundary layer. Common examples include phenolic-impregnated carbon ablator, Avcoat, cork-phenolic materials, carbon-phenolic composites, silicone-based ablators, and other resin-impregnated or fiber-reinforced ablative systems. Their main advantage is that they can tolerate very high heat fluxes with relatively simple passive behavior. Their disadvantages are that they are consumed during use, may require refurbishment or replacement, can shed material, and may be difficult to reuse without inspection or repair.

Non-ablative heat shields protect the vehicle primarily by surviving the heating environment without being intentionally consumed. They may insulate the underlying structure, radiate heat away, or conduct heat into a larger thermal mass. Common examples include reinforced carbon-carbon, carbon-carbon composites, ceramic matrix composites, silicon carbide-based materials, ultra-high-temperature ceramics such as hafnium carbide or zirconium diboride, reusable ceramic tiles, high-temperature metallic panels, and actively cooled metallic or ceramic structures. Their main advantage is potential reusability. Their disadvantages are that they may require more careful structural design, may be sensitive to cracking or oxidation, and may need more complex attachment, coating, inspection, or cooling systems. Both categories are already part of the aerospace materials base. Ablators have extensive heritage in capsules, planetary probes, and high-energy reentry systems. Non-ablative systems have heritage in reusable spacecraft, hypersonic test articles, rocket nozzles, leading edges, and high-temperature propulsion components.

The design goal is to select a thermal protection system from the best available heat shield technologies, evaluate its performance in the expected flight environment, and then determine the lowest altitude from which the spacecraft can safely exit the Elevated Evacuated Tube and begin endoatmospheric transit. Framed this way, the question is not whether a new material must be invented, but which existing thermal protection approach provides the best combination of heat tolerance, mass efficiency, reusability, inspectability, and cost for this specific trajectory. In the current architecture, 15 km is used as a nominal placeholder for that altitude. Once refined aerothermal analysis and material trade studies are completed, this exit altitude will define the highest altitude that the EET must be able to reach and operate at.

Summary

Materials used in the VPSL architecture:

• Aerospace aluminum alloys
• Stainless steel or corrosion-resistant steel in selected fittings, seals, ducts, or interfaces
• High strength steels
• Conventional coatings for corrosion protection, thermal control, and environmental durability

Materials not used in the VPSL architecture:

• Room-temperature superconductors
• Giant superconducting levitation cables
• Carbon nanotube structural cables
• Perfect or near-perfect graphene sheets
• Bulk diamond, exotic monocrystals, or defect-free megastructure materials
• Any material requiring a breakthrough in strength-to-weight ratio before the architecture can be evaluated
• Any material that currently exists only at laboratory scale and cannot be procured through an industrial supply chain