Project Moon1: The Tether Bootstrap

The Vision

This is a design for a Minimum Viable Product (MVP) tether system that pays for itself. Instead of a massive multi-billion dollar infrastructure project, we propose a "bootstrap" mission: a light, rotating tether capable of soft-landing payloads on the Moon using momentum exchange, and eventually catching return payloads.

By utilizing high-efficiency electric propulsion (SpaceX Argon Hall thrusters) and solar power, the system transports itself from Low Earth Orbit (LEO) to Lunar Orbit, then acts as a reusable skyhook. The goal is not just a demo, but a revenue-generating transport service.

System Architecture

1. The Propulsion: Argon Hall Thrusters

We will utilize the specs of the SpaceX Argon Hall thruster. These are mass-producible, highly efficient, and utilize cheap propellant (Argon).

Thrust: 170 mN
ISP: 2,500 seconds
Power: 4.2 kW
Mass: 2.1 kg

Design Choice: To meet the transit time requirement (< 8 months LEO to Moon), the system requires 3 active thrusters plus 1 spare. This provides ~0.5 N of thrust, allowing the spiral transfer to complete in approximately 6.5 months.

2. The Tether

A 30 km rotating tether composed of high-strength Zylon or Spectra.

Tip Speed: ~1,600 m/s (matching Lunar orbital velocity).
G-Force at Tip: ~9g (Payloads must be ruggedized, e.g., regolith bags, solid-state electronics).
Structure: Tapered design. The mass is primarily in the tether itself, which is ~10x the mass of the tip hardware.

3. The "Crawler" (Mobile Module)

The bulk of the mass (solar panels, thrusters, avionics, and argon tanks) resides at the "ballast end." This module can crawl along the tether.

Function 1 (Center of Mass): Adjusts the center of mass as payloads are released or caught.
Function 2 (Pumping): By moving up and down the tether in phase with the orbit, we utilize Gravity Gradient Pumping to spin the tether up or down without using propellant.

Concept of Operations

Phase 1: Transit (LEO to Moon)

The system launches compact. It unfolds solar arrays (approx 15 kW) and uses its own thrusters to spiral out from LEO.
Estimated Transit Time: 200 days (6.5 months) using 3 thrusters firing continuously.

Phase 2: The Drop

Once in a specific elliptical lunar orbit, the tether spins up. We time the rotation so the tip is vertical at perigee.

Relative Velocity: The tip is moving backward at 1,600 m/s, canceling the orbital speed. The payload is released 100m - 1,000m above the surface with near-zero horizontal velocity.
Momentum Debt: Dropping a 10 kg payload slows the tether's rotation slightly (momentum transfer of ~16,000 kg-m/s).
Recharging: Using the high-ISP Argon thrusters, we restore this momentum. With 3 thrusters (0.51 N total), it takes approx 9 hours of thrusting to recover the energy from one drop. This allows for a daily drop cadence.

Phase 3: Surface Ops & The Catch

Early payloads include micro-excavators (robot backhoes) and parts for a mechanical catapult.

Bootstrap: The robots assemble the catapult and fill "dummy payloads" (bags of regolith) to verify mass.
Practice: The catapult tosses payloads 100m up. The tether performs "virtual catches" with Lidar to refine targeting.
The Loop: Once perfected, the tether catches a payload. If we drop 10kg and catch 10kg simultaneously, the momentum balances out—we become a self-sustaining momentum exchange system requiring almost no fuel.

Mass & Budget Estimates

The following table assumes a bootstrap mission carrying 100 payloads (10kg each) to start.

Component	Mass Estimate (kg)	Notes
Payloads (100 units)	1,000 kg	Robots, Solar, Catapult parts, Regolith bags
Tether (30 km)	250 kg	High-strength Spectra/Zylon (Safety factor included)
Tip Hardware	25 kg	Release mechanism, Net, Lidar/Comms
Mobile Module (Bus)	300 kg	Structure, Winches, Avionics, Robotics
Power System (15 kW)	100 kg	Thin-film solar arrays (150 W/kg)
Propulsion System	25 kg	4x Argon Thrusters + PPU + Plumbing
Propellant (Argon)	500 kg	Enough for LEO->Moon transit + 1 year station keeping
TOTAL LAUNCH MASS	2,200 kg	Fits easily on Falcon 9 or Rideshare

Launch Economics

Total Project Mass is ~2,200 kg.

Scenario A (Falcon 9 Rideshare @ $1,000/kg): Launch cost = $2.2 Million.
Scenario B (Starship @ $200/kg): Launch cost = $440,000.

Revenue Potential

Crowdfunding/University Payloads:
Selling slots for early access to the lunar surface.
20 slots @ $400,000 (10kg) = $8,000,000.
Result: The mission can be profitable on the first launch.

Future Expansions: Moon to L5

Once surface operations are reliable, we can adjust the tether pumping to increase tip velocity slightly. This allows us to toss payloads not just to the surface, but into a trajectory toward the Earth-Moon L5 point. Small thrusters on these payloads can circularize them at L5, creating a supply line for a future station.

Eventually, the backhoes on the surface will load water ice into the catapult. This water becomes the reaction mass for our thrusters, closing the loop entirely and making the system independent of Earth-launched fuel.