This conceptual design explores a space tug using nuclear fission for electrical power and fusion assistance to enhance exhaust heating, improving efficiency without requiring net positive fusion energy. The system is inspired by concepts like Direct Fusion Drive but relies on fission as the primary power source. Assumptions include a delta-v of approximately 3.9 km/s for the LEO to L5 transfer (based on available data for Lagrange points), ISP of 10,000 seconds, system efficiency of 50%, and an advanced nuclear reactor with a specific mass of 1 kg/kW. Calculations account for spiral trajectories typical of low-thrust propulsion.
The tug consists of a nuclear fission reactor providing megawatt-scale electricity, powering an electric thruster enhanced by fusion reactions to boost exhaust velocity and efficiency. The fusion component adds energy to the propellant exhaust, increasing ISP beyond standard electric propulsion without needing to sustain net fusion gain. Propellant mass is minimal due to high ISP.
| Component | Estimated Mass (kg) | Details |
|---|---|---|
| Nuclear Power Plant | 36,400 | 36.4 MW electric, specific mass 1 kg/kW |
| Fusion-Enhanced Thruster | 10,000 | Includes magnetic nozzles and fusion injection systems |
| Total Tug Dry Mass | 46,400 | Excludes propellant and payload |
For transporting 200,000 kg from LEO to L5 in one month, the required power is approximately 36 MW electric. This scales with payload and transfer time; larger payloads or shorter times demand higher power.
Power plant: 36,400 kg (assuming advanced fission reactor technology with 1 kg/kW specific mass). Fusion-enhanced thruster: 10,000 kg (estimated based on conceptual DFD-like systems, including coils and injectors). Total: 46,400 kg.
10,000 seconds. This high ISP is achieved through fusion assistance, which injects additional energy into the exhaust, potentially starting from 20% enhancement and improving over time as per iterative development.
Approximately 370 N. This low thrust is typical for electric propulsion, enabling efficient but gradual acceleration via spiral trajectories.
30 days, as targeted. This assumes a spiral transfer with continuous low-thrust operation.
Approximately 5.6 days. With no payload, the lower mass allows for faster transfer using the same thrust level.
Approximately 79 days. The increased mass extends the transfer time proportionally, assuming the same power and thrust configuration.
With a high-intensity development effort similar to SpaceX (rapid prototyping, iterative testing, and substantial funding), this could fly in space in 8-12 years (by 2033-2037). Challenges include regulatory approval for nuclear systems, fusion integration (even non-net-positive), and in-space testing. Early prototypes might focus on fission-electric baselines, adding fusion enhancement iteratively.
Note: These estimates are conceptual and based on current research into NEP and DFD systems. Actual development would require detailed engineering and safety assessments.