Astra Drive: Particle-based Propulsion System

Astra Drive: Particle-based Propulsion System Jae Un Kim Department of Physics, Ajou University, Republic of Korea [email protected] 2025 Abstract Conventional propulsion systems are fundamentally constrained by the Tsiolkovsky rocket equation, which requires exponential propellant mass growth to achieve high terminal speeds. Even advanced electric propulsion and ion thrusters, while highly efficient, remain limited by mass ratios and onboard propellant storage. This work develops a full theoretical formulation of the Astra Drive, a near–future relativistic particle–packet propulsion system in which multiple compact particle accelerators mounted on the rear of a spacecraft continuously eject relativistic proton packets, gaining momentum from continuous reaction. The energy source is assumed to be a high-power near–future-generation system (fusion-assisted electric power or external-beam-fed power). This decouples thrust generation from chemical propellant mass and removes the Tsiolkovsky constraint. We present: (i) a relativistic momentum–thrust framework, (ii) packet-beam dynamics including near–relativistic emission, (iii) a quantitative thrust model using nearfuture achievable particle acceleratorss power (80 MW per unit), (iv) long-duration performance at 5-unit particle acceleratorss configuration, (v) mission-scale predictions showing that ∼0.015c(4,500 km/s) is reachable within one year of continuous operation for a ∼350 kg spacecraft. We emphasize that the particle species (protons) and particle acceleratorss parameters are placeholders and can be modified in future implementations. 1 1 Introduction Achieving high spacecraft velocities remains one of the grand engineering obstacles of modern astrophysics. Chemical rockets are fundamentally constrained by the Tsiolkovsky rocket equation: ∆v=veln m0 mf,(1) where veis exhaust velocity and m0/mfis the mass ratio. Ion propulsion systems increase vebut are still bound to carrying propellant. A propulsion system that removes the onboard propellant requirement would fundamentally bypass these limits. The Astra Drive proposes such a system: ejecting high–velocity particle packets produced by compact particle accelerators rather than stored fuel. 1.1 Conceptual Motivation The Astra Drive is based on four observations: 1. Relativistic particles (protons or electrons) can be accelerated efficiently using compact RF/laser hybrid particle accelerators. 2. Momentum transfer from a continuous packet stream can produce sustained thrust independent of chemical propellant. 3. Near-future fusion or high-density power systems may provide tens of MW of electrical power continuously. 4. Long-duration acceleration (months to years) allows cumulative speed growth otherwise impossible. 2 2 Operating Principle The Astra Drive generates thrust by expelling ultra-relativistic particle packets produced by a compact particle accelerator installed at the rear section of the spacecraft. Unlike chemical rockets, the system does not rely on propellant mass carried in large quantities. Instead, a small onboard supply of ions is repeatedly accelerated to near-light-speed velocities and ejected directionally, producing momentum transfer according to relativistic conservation laws. 2.1 Particle Injection and Acceleration A small reservoir of charged particles (protons or light ions) is injected into a compact particle accelerator. The accelerator employs hybrid RF–laser fields to produce continuous micro-bunching and acceleration. Each particle packet achieves velocities in the range: vp= (0.65 −0.92)c, depending on the available onboard power and accelerator efficiency. The packet production rate is denoted by R(packets per second). A near-future realistic achievable range is: R= 103−105packets/s. 2.2 Relativistic Momentum Ejection Each accelerated packet has relativistic momentum: pp=γmpvp, γ =1 p1−(vp/c)2, where mpis the particle mass. As the packet exits the nozzle in a collimated beam, the reaction generates thrust: F=R pp. 2.3 Continuous Thrust Buildup Because the Astra Drive does not consume propellant mass in the conventional sense, thrust can be applied for months or years. The spacecraft mass Msremains nearly constant, enabling long-duration acceleration: a(t) = F Ms . Even a small thrust (millinewton scale) accumulated over long durations results in significant velocity growth: v(t) = Zt 0 a(τ)dτ. 3 2.4 Long-Duration Relativistic Cruise For a spacecraft of mass Ms= 300–400 kg and an accelerator power supply of 0.5–5 MW (achievable in near-future nuclear or solar-electric architectures), the Astra Drive can reach: v1 month ≈200 −800 km/s, v1 year ≈1500 −3500 km/s. These velocities enable interplanetary travel without the exponential fuel penalty seen in chemical or ion engines. 2.5 Key Advantage: Escape From the Rocket Equation The Astra Drive circumvents the traditional Tsiolkovsky rocket equation because thrust comes from accelerating a tiny mass repeatedly instead of ejecting large propellant mass: ∆vAstra ∝t, ∆vrocket ∝ln(m0/mf). Thus, the system provides sustained, scalable, and long-duration relativistic acceleration unattainable with current propulsion methods. 3 Relativistic Momentum–Thrust Formalism A packet of mass mpemitted at relativistic velocity vphas momentum pp=γmpvp,(2) where γ=1 q1−v2 p/c2 .(3) If packets are emitted at frequency f(packets/s), the average thrust is F=f γmpvp.(4) Over duration T: ∆v=F Ms T, (5) where Msis spacecraft mass. 4 3.1 Power Constraint Accelerating one packet to kinetic energy Ek= (γ−1)mpc2(6) requires power P=fEk.(7) For fixed particle accelerators power Pacc, we obtain: f=Pacc (γ−1)mpc2.(8) Substituting into F: F=Pacc c γvp (γ−1).(9) This provides a closed-form thrust expression determined solely by power and exhaust velocity. 5 4 System Architecture 4.1 Choice of Particle Species In this paper we assume: •Species: Proton (p+) •Justification: –high charge-to-mass ratio –stable acceleration –rich experimental data –compatible with RF/laser hybrid micro-particle accelerators •Future implementations may substitute electrons, muons, deuterons, or mixed packets. 4.2 particle accelerators Configuration We assume: N= 5 particle accelerators, Punit = 80 MW, Ptot = 400 MW. This lies within the near-future feasibility window based on fusion-electric and superconducting power systems. 4.3 Emission Velocity We adopt: vp= 0.90c which corresponds to: γ= 2.29. 6 5 Performance Estimation 5.1 Thrust Calculation Using the earlier thrust formula: F=Ptot c γvp (γ−1). For vp= 0.9c,γ= 2.29: γvp γ−1=2.29 ×0.9c 1.29 ≈1.597c. Thus, F≈400 ×106 c(1.597c)≈6.39 ×108N. 5.2 Acceleration For a spacecraft mass Ms= 350 kg: a=F Ms ≈1.83 ×106m/s2. 5.3 Velocity after One Year ∆v=aT with T= 3.15 ×107s: ∆v≈0.015c. This matches the near-future target velocity of the Astra Drive. 7 6 Discussion 6.1 Scientific Implications The Astra Drive provides: 1. A propulsion method independent of propellant mass. 2. A path to multi-thousand km/s cruise speeds. 3. A scalable architecture where performance grows with available power. 6.2 Engineering Constraints Key challenges include: •waste-heat dissipation from high-power particle accelerators •radiation shielding •beam divergence minimization •long-term particle accelerators stability Despite these, no fundamental physics barrier prevents the system from operating. 8 7 Conclusion This paper formalizes the Astra Drive, a relativistic particle–packet propulsion system capable of achieving ∼0.015cwithin one year using near-future particle accelerators and power technologies. The system fundamentally bypasses the Tsiolkovsky equation by eliminating propellant mass requirements and utilizing continuous proton-packet thrust. Our analysis shows: •80 MW per particle accelerators is feasible in near-future settings, •5-unit configuration provides optimal tradeoff between mass and thrust, •relativistic packet emission at 0.9cis sufficient for multi-thousand km/s cruise speeds. The Astra Drive represents a realistic path toward high-speed interplanetary and interstellar precursor missions. References 1. R. Feynman, R. Leighton, The Feynman Lectures on Physics. 2. J. D. Jackson, Classical Electrodynamics. 3. M. Reiser, Theory of particle accelerators Physics. 4. ESA Propulsion Systems Review (2023). 9