This document expands on Vince Cate's ideas for a minimum viable product (MVP) space tether system designed to deliver small payloads to the lunar surface at low cost. The system uses a rotating tether in lunar orbit to lower payloads gently, minimizing the need for propellant-heavy landings. It incorporates high-ISP ion thrusters like the Turion TIE-20 GEN2 for orbit transfers and momentum restoration. The design aims for initial deployment from LEO to lunar orbit in under 8 months, with potential for revenue generation through payload deliveries.
The core is a 30 km rotating tether made of high-strength material (e.g., Spectra or carbon fiber composite) deployed in a low lunar elliptical orbit. The tether rotates to match the orbital velocity at perigee, allowing payloads to be released with near-zero relative velocity to the Moon's surface from 100-1000 meters altitude. Initial drops use airbags or crush zones for soft landings at 18-58 m/s impact speeds.
The system launches from Earth with 50 payloads of 10 kg each, attached along the tether or in a dispenser. It uses ion thrusters to spiral from LEO to lunar orbit. Once in place, it drops one payload every few days, restoring momentum via thrusters after each drop.
A movable module at the ballast end houses thrusters, solar panels, and robotics. It slides along the tether for gravity gradient pumping to adjust rotation speed and phase, enabling precise perigee alignments over different lunar sites.
Advanced features include a net at the tip for catching payloads launched from the surface via a small catapult assembled from early drops. This enables bidirectional transport, turning it into a true momentum exchange tether with minimal propellant use.
Additional capabilities: Toss small satellites to Lunar L5 from orbit as a demo, with minor course corrections needed.
The design minimizes tip mass to reduce tether requirements. Gravity gradient pumping transfers orbital to rotational energy without tip thrusters. If catches work, propellant needs drop dramatically for future missions (reuse tether/hardware, just add payloads/propellant).
This seems a promising first tether use: Low initial mass/cost, revenue from deliveries, scalable. Challenges include precise control, tether dynamics, surface ops in regolith. Incremental testing (drops from higher altitudes, practice catches) mitigates risks. Compared to chemical landers (e.g., $1.2M/kg), this could deliver at ~$8,000/kg breakeven (direct costs). Reusability boosts future economics.
Moon's slow rotation means perigee shifts ~13°/day; backhoe needs ~400 km/day speed? No: Moon circumference ~10,900 km, rotation 28 days, surface speed at equator ~0.46 m/s (slow walk). Backhoe can relocate slowly (~1-2 km/day) to stay near target sites. Orbital precession can be managed via minor thrusts.
| Component | Mass (kg) | Cost ($) |
|---|---|---|
| Tether (30 km) | 300 | 500,000 |
| Tip End Assembly | 20 | 100,000 |
| Movable Module | 50 | 200,000 |
| Thrusters (3x TIE-20) | 30 | 450,000 |
| Solar Panels (6000W) | 60 | 1,200,000 ($200/W) |
| Payloads (50x10kg) | 500 | Customer-funded |
| Propellant (Xenon) | 146 | 15,000 ($100/kg) |
| Total Hardware Mass (excl. payloads/prop) | 460 | 2,450,000 |
| Total Launch Mass | 1,156 | N/A |
Direct mission costs (hardware + launch + prop, excl. development): ~$3.6M (Falcon-9) or ~$2.7M (Starship). Delivers 500 kg. Breakeven: $7,200/kg (Falcon-9) or $5,400/kg (Starship). With crowdfunding ($400k/10kg = $40k/kg), could cover costs easily (20 customers = $8M revenue).
Once proven, scale to larger payloads (100+ kg), reuse hardware, add water from Moon for propellant. Enables low-cost lunar infrastructure, L5 transfers, and bidirectional ops without constant thrusting.
Updated: January 03, 2026. Contact: Vince Cate