Ultimate Rocket

For more than a year, I have been iterating on rocket designs. It is easy to write that a rocket will use LOX as the oxidizer, methane or propane as fuel, and feature aerospike nozzles. However, designing and manufacturing these vehicles is not easy. For countries with advanced infrastructure, such designs may look acceptable. However, I wanted to find an alternative to overcome the logistical and structural bottlenecks of cryogenic propellants. To attain maximum thrust efficiencies, conventional propellant choices are pushed to their metallurgical limits, as are the engine designs. By selecting less aggressive chemicals and less demanding engines, the architecture can be altered to overcome baseline inefficiencies. As I keep saying: "Systems need to be optimized as a whole, including their supporting processes. A system optimized section-by-section may not be the best performer." Here is the rocket design I developed that can be implemented without pushing the limits of materials science and precision engineering. A successful rocket should be easy to develop, manufacture, and launch. Space exploration requires momentum, and over-complex systems cannot achieve that.

I started by looking at non-cryogenic oxidizers. There are few viable options, and High-Test Peroxide (HTP)—which refers to high-purity (98%), rocket-grade hydrogen peroxide (H₂O₂)—is the best among them. It does not generate hazardous gases and is relatively easy to handle compared to other alternatives, especially LOX. On the other hand, LPG was the ideal fuel choice. Its density, storage complexity, cost, and Iₛₚ value offered the optimum balance compared to other hydrocarbons. For the structural layout, I opted for my latest vehicle architecture, the Naked Rocket. By pairing High-Test Peroxide with Liquefied Petroleum Gas, this architecture effectively bridges the gap between traditional propulsion extremes, creating a 'best of both worlds' hybrid. It delivers the instant, reliable restart capabilities and long-term storable convenience of highly toxic military hypergolic propellants, yet utilizes completely non-hazardous, sustainable, and cheap civilian commodities without a single cryogenic complication.

Inside the engine, the liquid HTP decomposes into oxygen gas and superheated steam (950°C) via a silver catalyst bed. To decompose the oxidizer rapidly and reliably, I opted for a radial flow splitter design. Fine silver particles are encapsulated inside an Inconel mesh. This keeps the catalyst matrix intact even when the silver softens and sinters at high operating temperatures, allowing a large volume of oxygen to be produced within a compact, lightweight space. The fuel, LPG, can be safely stored as a liquid without intensive cryogenic cooling or ultra-high tank pressures.

One of the primary bottlenecks of cryogenic propellants is their highly complex turbopumps. HTP also requires delicate mechanical handling. For that reason, my design utilizes small-diameter, multi-stage radial pumps connected in series that operate at a low, stable RPM (3,600). This gentle mechanical operation prevents fluid shear heat and allows safe pressurization of the HTP up to 100 bar. Only the first stage of the Naked Rocket utilizes these pump stacks; the upper stages do not. Because both propellants are fully gasified prior to the injector face, injector pressure losses are drastically minimized. This allows a 100 bar pump discharge to easily drive a 90 bar combustion chamber.

The liquid LPG is fully gasified via regenerative cooling channels running through the lost-wax cast aerospike nozzle. Because of its direct-ascent trajectory, the first stage requires altitude-compensating aerospike nozzles. We rarely see operational rockets utilizing aerospikes due to conventional propellant choices. LOX/RP-1 and LOX/Methane engines produce extreme core flame temperatures (~ 3,400°C), causing even the most advanced aerospike tips to melt. However, due to its high steam content, my engine operates at a considerably lower exhaust temperature (~ 2,400°C), which allows efficient cooling via the LPG. Due to the low molecular weight of the resulting steam exhaust, the total net thrust generated is highly comparable to conventional alternatives.

As the rocket ascends and consumes its propellant mass, a constant thrust profile would generate immense, structurally damaging G-forces. Therefore, the booster must be throttled down progressively. To achieve this without choking valves or inducing pump stalls, I opted for multiple small, isolated engines clustered at the base of each structural stud. The rocket features a total of 4 studs with 4 engines each, totaling 16 independent aerospike units. Each active engine always runs at its peak design pressure (90 bar). Throttling is achieved by cleanly shutting down individual engine and pump units one by one. This completely eliminates high-pressure manifold valves and fluid hammer risks.

The direct-ascent trajectory requires the first stage to burn for 3 minutes, reaching a burnout altitude of approximately 50 km. The vehicle then climbs to a 100 km apogee utilizing its residual kinetic energy. At the exact moment of stage separation, the booster’s forward velocity drops to almost zero. This eliminates high-speed staging risks and drastically simplifies the separation mechanics.

The physical layout of the Naked Rocket allows for passive aerodynamic stability, which reduces the active thrust-vectoring steering requirements. Furthermore, a direct-ascent trajectory requires minimal steering corrections. Because rigid aerospike nozzles eliminate heavy, complex hydraulic gimbals, the vehicle utilizes warm-gas attitude control thrusters instead. A small fraction of the decomposed HTP steam is diverted to power these lateral thrusters, providing a compact, lightweight control system without requiring secondary propellants.

The rocket's two upper stages operate exclusively in the vacuum of space, which drastically simplifies their structural design. Their combustion chambers operate at a modest pressure of only 5 to 6 bar, completely removing the need for heavy turbopumps. This lean, pressure-fed layout maximizes mass efficiency by delivering an exceptionally low dry-mass ratio while improving overall ignition reliability.

This architecture becomes a massive differentiator for high-energy deep space missions that require parking in Low Earth Orbit (LEO) before executing a Trans-Lunar Injection (TLI) or interplanetary escape burn. Classical cryogenic rockets suffer from a severe "boil-off" problem, where liquid oxygen and liquid methane continuously vaporize and vent into space during orbital coast phases, rapidly draining the mission's fuel reserves. Because my HTP and LPG propellant matrix remains completely stable as liquids at ambient temperatures, the upper stages experience zero boil-off losses, allowing the vehicle to coast in orbit for days or weeks without losing delta-V capacity.

Furthermore, multiple precise refirings of these pressure-fed engines are incredibly simple and viable. Without complex cryogenic turbopumps to chill down before ignition, or delicate electric spark systems to fail, restarting the engine simply requires reopening the main propellant valves. The HTP instantly decomposes upon contacting the silver catalyst beds, providing immediate, highly reliable ignition on demand. Consequently, these upper stages are expended to maximize payload capacity per deep space launch at minimal cost. The upper stages utilize the same warm-gas HTP thruster design as the booster for orbital maneuvering and precise attitude adjustments during long-duration transit phases.

Only the first-stage booster is recovered after a launch. Due to the zero-velocity direct-ascent staging profile, recovery operations are safe and straightforward. The reduced thermal stress on the engine components, the clean gas-gas combustion (the high steam content prevents LPG soot formation inside the injectors), and the rapid refueling process (with no cryogenic boil-off or pumping delays) enable rapid turnaround and deployment of the booster fleet.

While High-Test Peroxide is often perceived as difficult to handle, its operational complexity is significantly lower than that of cryogenic systems. Even though the baseline chemical Iₛₚ is lower, an overall system-optimized vehicle can easily compete with complex, high-cost rocket architectures. Additionally, the Naked Rocket’s wide-diameter, quad-strapped hull architecture accommodates large-diameter payloads and enables the deployment of four separate satellites into distinct orbits in a single launch. The full structural breakdown of this multi-manifest capability can be found in my accompanying Naked Rocket article.