1. Introduction

Access to space remains fundamentally constrained by the high-energy demands of overcoming Earth's gravity and atmosphere, a challenge historically met by the chemical rocket. Conventional rockets achieve this by carrying their entire energy supply as propellant, a paradigm that is efficient for heavy payloads but scales poorly for smaller, distributed systems due to the cube-square law, where tankage and engine mass become disproportionately large for smaller vehicles. Nature, however, offers alternative solutions. Fungal spores and spiders, for example, achieve remarkable atmospheric dispersal not by brute force, but by subtly manipulating local aerodynamic and electrostatic fields. They are masters of "environment-coupled" propulsion. This paper outlines an integrated launch architecture that translates these low-energy, high-efficiency strategies into an engineered system for launching kilogram-class payloads, moving from a reliance on onboard energy to a system that harvests and reacts against its environment.

2. The Myco-Architecture Stack

The proposed architecture is a five-stage process where the vehicle transitions between dominant physical regimes as it ascends. Each stage is designed to operate where its underlying physics is most effective, handing off to the next as atmospheric conditions change.

Stage A — Myco-convection (Ground → Boundary Layer)

• Biological Inspiration: Fungal caps generate a localized updraft by evaporatively cooling the surrounding air. The release of water vapor cools the air immediately adjacent to the cap, making it denser. This denser air sinks, creating a toroidal vortex that gently draws air from below the cap and pushes it upward in a sustained, self-generated updraft that carries spores away, even in still air ^[1][2].

• Engineering Analogue: This mechanism is not for primary lift but for pre-conditioning airflow during the critical initial launch phase. A ground installation or launch shroud equipped with evaporative coolers could generate a stable, controlled vortex. This managed airflow would reduce parasitic drag on the ultralight ascent vehicle and ensure a clean, predictable flow of air into the Stage C EHD propulsion system, preventing ingestion of turbulent or debris-laden ground-level air.

• Governing Physics: The buoyant plume's velocity scale, $w$, over a characteristic length $L$ is driven by the density deficit, $\Delta \rho$. For an ideal gas where the coefficient of thermal expansion $\beta \approx 1/T$: $$ \frac{\Delta\rho}{\rho} \approx -\beta,\Delta T $$ $$ w \sim \sqrt{2 g \beta,\Delta T,L} $$ For mushrooms, with ΔT∼1−2∘ C and $L\sim 0.1$ m, this yields velocities of cm/s, consistent with observations ^[1]. For an engineered system, a larger $L$ and controlled $\Delta T$ could create a significantly more powerful and stable effect.

Stage B — Electro-ballooning (Boundary Layer → Lower Troposphere)

• Biological Inspiration: Spiders achieve flight ("ballooning") by extruding charged silk that interacts with the Earth’s ambient atmospheric electric field. This field, part of the global atmospheric electrical circuit, averages ~100 V/m in fair weather, providing sufficient electrostatic force for liftoff and dispersal across vast distances ^[3][4].

• Engineering Analogue: During ascent through the turbulent troposphere, a deployable, ultralight charged ribbon array provides passive stability. The electrostatic force, $F=qE$, acts as a virtual guidewire, constantly pulling the vehicle upward and damping oscillations. This provides a small but persistent upward force to reduce sink rate and smooth the vehicle's trajectory through gusts, reducing the control authority required from the primary EHD system. The challenge lies in maintaining a high net charge on the ribbons against atmospheric discharge.

• Governing Physics: While the electrostatic force is insufficient for primary lift of a kg-class payload, its utility as a stabilizing and assisting force is well-documented ^[5]. It is a force that comes "for free" from the environment, requiring only a system to maintain vehicle charge.

Stage C — Electroaerodynamic (EHD) Thrust (Lower Stratosphere)

• Biological Inspiration: Fungal spores naturally acquire charge, allowing them to be influenced by electric fields. EHD thrust is the macro-scale analogue, where a strong electric field at a sharp emitter electrode creates a corona discharge, ionizing the surrounding air. These ions are then accelerated by the field toward a collector electrode, colliding with and transferring momentum to neutral air molecules, resulting in a net thrust—an "ionic wind" ^[6][7][8].

• Engineering Analogue: As demonstrated by the first solid-state aircraft ^[6], EHD thrusters can provide silent, moving-parts-free propulsion. In the MYCOSAIL architecture, an array of EHD thrusters provides the primary propulsive force for the climb through the dense lower atmosphere up into the stratosphere. This stage requires a significant power source, but the thrusters themselves are simple, lightweight, and robust.

• Governing Physics: The condition for climb is when thrust ($T$) exceeds the sum of gravity ($mg$) and drag ($D$). EHD thrust-to-power ratios are typically on the order of 1–3 N/kW ^[6]. EHD is most effective in the lower stratosphere, where air density is still high enough for efficient momentum transfer but lower than at sea level, reducing overall drag. $$ T > mg + D $$

Stage D — Photophoretic Lift (Stratosphere → Mesosphere, ~20–60 km)

• Biological Inspiration: Dark, microscopic spores absorb sunlight and, in a rarefied atmosphere, experience a net force from thermal transpiration. Gas molecules on the warmer, illuminated side of the spore rebound with greater kinetic energy than those on the cooler side, resulting in a net momentum transfer that pushes the spore away from the light source. This is photophoresis ^[9][10][11].

• Engineering Analogue: We propose an ultralight vehicle structure composed of "nanocardboard"—a metamaterial with microscopic channels. When illuminated from below by a ground-based laser or a high-altitude carrier, a temperature differential drives a sustained gas flow through the channels from the cool side to the warm side. This creates a significant pressure difference across the structure, yielding a strong photophoretic lift force, orders of magnitude greater than pure radiation pressure.

• Governing Physics: Levitation occurs when the photophoretic force per unit area (Fph​/A) exceeds the vehicle's areal density ($\sigma$) times gravity. This effect is maximized in the low-pressure environment of the mesosphere (roughly 50-80 km), where the mean free path of air molecules is comparable to the scale of the microchannels ^[9][12]. $$ \frac{F_{\text{ph}}}{A} \gtrsim \sigma g $$

Stage E — Beamed Energy (Exo-atmospheric)

• Biological Inspiration: Biology offers no analogue for achieving orbital velocities. At this stage, the architecture transitions to a conventional physics-based approach where propulsive energy is supplied externally from the ground.

• Engineering Analogue: Once atmospheric drag is negligible ($\gtrsim 100$ km), the vehicle requires a significant delta-v ($\Delta v$) of ~9.4 km/s for LEO. Two primary options are viable:

  1. Laser/Microwave Thermal Propulsion: A ground-based beam heats an onboard propellant (e.g., water), which is then expelled through a nozzle. This "Lightcraft" concept decouples the specific impulse from the propellant's chemical energy, allowing for extremely high efficiency with a simple, inert propellant ^[13][14][15].

  2. Laser-Pushed Lightsail: For gram-scale payloads, pure photon pressure from a powerful ground-based laser can be used. The vehicle unfurls a highly reflective sail. The thrust is given by $T\approx 2P/c$ for a perfect reflector, where $P$ is the laser power and $c$ is the speed of light. This is the principle behind initiatives like Breakthrough Starshot ^[16][17].

3. Integrated Vehicle Concept & Flight Profile

The MYCOSAIL vehicle is envisioned as an ultralight, transformable plate-sail. Its core is the photophoretic structure, with perimeter EHD bars and retractable electro-ballooning ribbons.

• Takeoff & Climb (Stages A-C): The flight begins within a ground-based myco-convective shroud (Stage A) that stabilizes the initial ascent. The vehicle lifts off using its EHD thrusters (Stage C). As it ascends, electro-ballooning ribbons (Stage B) deploy to provide passive stability through the turbulent troposphere, reaching an altitude of ~15–20 km.
• Stratosphere→Mesosphere (Stage D): As the air thins, the EHD system becomes less effective and is powered down. The vehicle's primary plate structure begins to generate photophoretic lift as it is illuminated from a carrier aircraft or ground array. This becomes the dominant lift mechanism for a slow, efficient ascent from ~20 km to 60 km.
• Orbit/Escape (Stage E): In the exo-atmosphere, the vehicle configures for final propulsion. For kg-class payloads, it would orient itself to capture a ground-based beam in a "pusher plate" cavity for thermal propulsion. For gram-scale payloads, the entire structure would unfurl and function as a lightsail.

4. Key Performance Parameters & Feasibility

• EHD Segment: A target thrust-to-power ratio of $T/P\approx 2$ N/kW is a reasonable goal ^[6]. A 10 kg vehicle would require $T\gtrsim 120$ N (including drag margin), demanding a power system in the tens of kilowatts. This could be supplied by next-generation batteries or short-term power beaming.

• Photophoretic Segment: Success hinges on achieving an ultra-low areal density of $\sigma \le 5$ g/m². This is a significant material science challenge, requiring advanced composites or aerogels. Published demonstrations have achieved stable lift of cm-scale plates, indicating that scaling via tiling and microchannel optimization is a viable research path ^[9].

• Laser Sail: The physics is straightforward: a 1 MW laser yields 6.7 mN of thrust. This can accelerate a 1-gram probe at a brisk 6.7 m/s² but a 1-kg craft at only a sluggish 0.0067 m/s². This approach is immediately feasible for ultra-light probes and scales with the significant investment in ground-based laser power ^[16].

5. Conclusion & Near-Term R&D Path

The MYCOSAIL concept synthesizes multiple bio-inspired propulsion and lift mechanisms into a single, cohesive launch architecture. Its core novelty lies in systematically exploiting ambient atmospheric properties and external energy sources to overcome gravity without carrying propellant for the atmospheric ascent phase. Each stage is based on demonstrated, peer-reviewed physics. The critical challenge is the engineering integration: developing a vehicle that can physically transform and a control system that can manage the transitions between fundamentally different propulsion modes.

A near-term (6–18 month) R&D path should focus on:

• Benchtop Validation: Characterize photophoretic lift on 30–60 cm plates under representative pressure (1–100 Pa) and illumination (~1–10 kW/m²) to determine optimal microchannel geometries. Validate EHD thruster arrays to confirm T/P ratios and longevity.

• Subscale Flight Test: Conduct high-altitude balloon drops (20–30 km) to test the deployment and control of a combined photophoretic plate and EHD system. The key goal is to demonstrate stable, controlled descent and loiter, validating the vehicle's aerodynamics and control authority in a relevant environment.

• High-Altitude Demonstrator: Air-launch a demonstrator to 35–45 km to achieve minutes of powered photophoretic flight, using EHD for attitude control. This would be a crucial "Wright brothers" moment for this architecture, proving that sustained, propellantless flight in the upper atmosphere is possible.