The Regenerative Thermal Core (RTC) is the high-temperature heat engine at the heart of the Spacecraft Layered Propulsion Architecture (SLPA). It stores, distributes, and regenerates heat for propulsion, logistics, and survival, using technologies that are conceptually familiar from terrestrial thermal systems but adapted to the space environment.
Modern terrestrial heating systems use a central hot reservoir, a distribution manifold, and multiple independent radiator loops. The RTC applies these principles at spacecraft scale. Instead of warm water, SLPA circulates superheated working gases at 600–1200 °C. Instead of domestic radiators, it uses STIP thruster assemblies that can operate as both propulsion units and radiators. Instead of copper plumbing, it uses high-temperature hot-bus manifolds.
These hot-bus manifolds are conceptually similar to under-floor heating distribution manifolds: a central header that feeds multiple independent loops. Each hot-bus loop serves one propulsion/radiator face and can be isolated, depressurised, and shut down for maintenance without disabling the rest of the system.
As with terrestrial boilers, required capacity depends on how much area you intend to heat and how quickly. A small boiler can heat a small house slowly; a larger building needs a larger unit. In SLPA, the same scaling applies: the more propulsion faces you want to operate simultaneously at high output, the larger the RTC must be. Total thrust capability scales with thermal power; endurance scales with core volume.
In the inner solar system, “burn → recharge → burn” cycles are practical. The ship draws heavily from the RTC during thrust phases, then uses solar input or depot heat transfer to restore the core temperature during coast phases. Further out, larger RTCs and orbital thermal depots become more important.
A key design goal is maintainability. Unlike nuclear or cryogenic propulsion systems that demand specialised crews, RTC-based ships can be operated and serviced by existing industrial trades:
The architecture is deliberately aligned with skills that already exist on Earth, so spacecraft can be treated more like extreme-temperature industrial plants than experimental nuclear platforms.
The RTC underpins all heat-driven subsystems in SLPA. Its main roles are:
The RTC absorbs solar or electrical energy and stores it in a refractory thermal mass. This stored heat can be delivered at controlled rates for propulsion, thermal management, and power conversion.
Because energy is stored in the core, the ship can deliver high thermal power even when solar input is low or intermittent. This allows:
In SLPA, STIP thrusters draw their primary heat from the RTC. In purely thermal modes, gas is heated by contact with hot RTC-linked structures. In chemical-augmented modes, the RTC preheats the gas before combustion. In plasma modes, the RTC can reduce the electrical power required to reach target temperatures.
A charged RTC can maintain internal habitat temperatures and protect critical systems during power anomalies, offering a long-duration thermal safety buffer that conventional spacecraft typically lack.
Terrestrial thermal stores and space-based RTCs share the basic idea of storing energy as heat in a solid mass, but their operating environments and roles are very different:
| Property | Terrestrial Thermal Store | Space-Based RTC |
|---|---|---|
| Environment | Convection and conduction dominate losses. | Losses are almost entirely radiative. |
| Insulation | Bulk insulation, masonry, soil. | Vacuum gaps, MLI, and optional aerogel panels. |
| Regeneration | Heated intermittently, tends to cool down. | Can be kept at temperature or recharged continuously. |
| Mobility | Stationary, fixed to infrastructure. | Integrated into a mobile spacecraft structure. |
| Function | Space heating and buffering. | Propulsion, heating, and logistics energy reservoir. |
| Typical Range | 200–600 °C. | 600–1200 °C depending on material and mission. |
In SLPA, the RTC is not just a passive store; it is an active spacecraft subsystem, designed for multi-year operation and tightly coupled to propulsion and logistics.
Multiple geometries are possible, but a two-level structure is particularly effective: a cylindrical inner core housed within a cube-like or tetrahedral outer module.
The inner thermal mass is typically a right circular cylinder, offering:
The outer module provides flat faces for mounting propulsion, radiators, and interfaces. A cube offers six faces, five of which may serve as propulsion/radiation/energy collection surfaces, with the remaining face dedicated to minimising heat input via energy reflection. It also acts as the centralised docking point when recharging the RTC when docked with an Orbital RTC or for gas refueling for the ship.
A tetrahedral configuration is also feasible, with the cylindrical core aligned along the altitude of the tetrahedron and faces dedicated to sun-facing, anti-sun, and lateral propulsion roles.
High-temperature gas transfer between the RTC and propulsion faces is handled by a hot-bus network:
This arrangement closely resembles an industrial heating manifold or under-floor heating distributor, but designed for much higher temperatures and for use in vacuum.
The RTC thermal mass can be built from different materials depending on mission requirements:
Over time, more advanced refractory composites may extend operating temperatures further, enabling even higher performance propulsion regimes.
To make regeneration practical, the RTC must lose heat very slowly relative to its storage capacity. The insulation stack typically combines:
With appropriate design, radiative losses can be brought down to levels where slow “trickle charge” from solar concentrators or steady resistive heating is sufficient to maintain or increment core temperature, even in the Mars–Jupiter region.
When the RTC is at or near its target upper temperature, surplus heat must be rejected. SLPA leverages the existing STIP propulsion faces as controllable radiators:
This reduces or eliminates the need for separate large radiator farms and simplifies spacecraft layout: one set of faces provides both propulsion and controlled heat rejection.
A further operational benefit is positional heat management. When the spacecraft moves behind a planetary body—crossing the terminator line into shadow—the absence of direct solar input naturally reduces thermal load. In these conditions, the ship can conserve propellant otherwise spent on active cooling and allow STIP radiator-faces to reject heat more efficiently. This makes orbital night-side passes, moon-shadow arcs, or deep-space alignments valuable operational tools for managing RTC temperature without consuming working gas.
RTC sizing is driven by mission profile, available solar flux, and depot support. Key drivers are:
Typical strategies by region:
| Region | RTC Strategy | Implication |
|---|---|---|
| Inner System (0.7–1.5 AU) | Small to medium cores with frequent direct solar recharge. | Compact tugs; high thrust duty cycle. |
| Mars–Jupiter Transition | Medium to large cores, supplemented by depots. | Multi-RTC ships or chained modules; mixed recharge sources. |
| Outer System (> 5 AU) | Large cores plus regular depot recharging. | Heavier vessels, longer ranges; depots become primary energy nodes. |
SLPA favours a modular approach, with standardised RTC modules that can be chained or clustered as mission demands grow.
The RTC and hot-bus network are designed for industrial-style maintainability:
This allows SLPA operations to draw on existing industrial skill sets rather than niche aerospace specialties, reducing both training overhead and operational risk.
The Regenerative Thermal Core is the central enabling subsystem for SLPA. By combining high-temperature thermal storage, regenerative operation, modular integration, and industrial maintainability, it provides a practical path to scalable, multi-planetary logistics without relying on large nuclear reactors or vast electric propulsion farms.
The RTC:
No existing propulsion architecture combines this level of safety, flexibility, scalability, and manufacturability in a single, coherent thermal design.