By Vince Cate, with expansions and design details by Grok (xAI)
This document outlines a conceptual design for an initial space tether project aimed at delivering small payloads to the Moon's surface in a cost-effective manner. The system uses a rotating tether in lunar orbit to lower payloads gently, minimizing the need for propellant-heavy landings. It incorporates SpaceX's argon Hall-effect thrusters for propulsion and momentum recovery. The goal is to create a Minimum Viable Product (MVP) that not only demonstrates tether technology but also generates revenue through payload deliveries, potentially scaling to two-way transport.
The Moon1 system consists of a 30 km rotating tether deployed in a low elliptical lunar orbit. The tether is launched from Earth to LEO, then uses its own high-ISP electric thrusters to spiral out to lunar orbit over several months. It carries 50 small payloads (10 kg each) for delivery to the Moon's surface.
Key features:
This design keeps initial costs low by reusing hardware for multiple drops and avoiding complex landers. Compared to chemical rocket deliveries, it requires far less total mass launched from Earth, making even the first mission economically competitive.
The system uses 6 SpaceX argon Hall-effect thrusters, each with:
Total thrust: 1.02 N Total power: 25.2 kW Exhaust velocity (ve): ~24,525 m/s
These thrusters propel the system from LEO to lunar orbit (estimated Δv ~5.5 km/s) in approximately 6-7 months, assuming a ~50% duty cycle due to orbital phasing and radiation belt avoidance. Post-arrival, they regain momentum after each payload drop (impulse ~17,000 N·s per 10 kg at 1.7 km/s), taking ~4.6 hours per recovery with minimal propellant (~0.7 kg per drop).
The following table provides estimated masses for key components. Assumptions include a conservative tether mass (accounting for safety factors, handling, and micrometeorite resistance), modern solar array specific power (~150 W/kg), and basic structural allowances.
| Component | Description | Mass (kg) |
|---|---|---|
| Payloads | 50 x 10 kg small payloads (e.g., robot parts, solar panels, scientific instruments) | 500 |
| Tether | 30 km Spectra or similar high-strength material, conservatively estimated at ~10x payload mass including safety factor of 4 and practical minimum thickness | 200 |
| Tip Hardware | Release mechanism, net (for catches), communications, positioning sensors, minimal robotics | 50 |
| Movable Module Structure | Frame, robotics for tether traversal/inspection, communications, control systems | 100 |
| Thrusters | 6 x 2.1 kg Hall-effect thrusters | 13 |
| Solar Panels | 25.2 kW at ~150 W/kg specific power, including deployment mechanisms | 168 |
| Propellant Tank | Pressurized tank for argon propellant | 50 |
| Operational Propellant | Argon for momentum recovery (50 drops) and orbit maintenance | 50 |
| Total Dry Mass (Mf) | 1,131 | |
| Transfer Propellant | Argon for LEO to lunar orbit transfer (~5.5 km/s Δv) | 284 |
| Total Launch Mass | 1,415 |
The system launches to LEO, then spirals out using the thrusters over ~6 months. Upon arrival, it enters an elliptical orbit with low perigee for deliveries.
The tether rotates with tip speed ~1.7 km/s to null orbital velocity at perigee. Payloads are lowered/released 100-1000 m above the surface, impacting at 18-58 m/s. Protective airbags or crush zones ensure survival. Drops occur every few days, with thrusters regaining momentum.
Gravity gradient pumping: The movable module shifts along the tether, adjusting rotation and phase. This increases tip speed in ~1 day without tip thrusters.
Early payloads include parts for tiny robot backhoes, solar chargers, and a catapult. Backhoes assemble the catapult and fill regolith bags as counterweights/standard payloads. The setup moves at ~5 m/s to stay in perpetual sunlight, avoiding lunar night.
For uplink: The catapult launches 10 kg payloads ~100+ m. A 10 m diameter net at the tether tip (moving ~30 m/s relative) catches them via hook-like protrusions through 5 cm holes. LIDAR/reflectors ensure precise positioning.
Incremental testing: Practice launches/recoveries without catches, adjust trajectories, test timing. If catches succeed, the system becomes a true momentum exchange tether, reducing thruster reliance.
The movable module can traverse the tether for inspections, repairs, or payload handling.
After deliveries, tiny satellites can be tossed to Moon L5 (adjusting tip speed via pumping). These require small thrusters for corrections, demoing future L5-Moon transport. Orbit adjustments keep perigee aligned with the surface site, precessing slowly over a year.
Assuming total mass to LEO ~1,415 kg:
Future missions reuse the tether/system, launching only payloads and propellant, further reducing costs.
This seems an excellent first tether project: low initial mass/cost, real utility (payload delivery), and revenue potential via customer payloads (e.g., universities, companies). Crowdfunding could raise funds—e.g., $50,000/kg or $400,000/10 kg, targeting $8+ million from 20 customers.
Advantages over chemical rockets: ~10x less propellant mass for deliveries, reusable hardware. Risks (e.g., catches) are mitigated by one-way success as a fallback and incremental testing. Once proven, scale to larger payloads (100+ kg), incorporate lunar water for propellant, and expand to L5 operations.
Potential challenges: Tether durability (micrometeorites, UV), precise control, robot assembly on Moon. However, the design's simplicity and modularity make it a promising MVP for space tethers.