Author: Vince Cate
Website: spacetethers.com
This page outlines a proposed first operational space tether mission — not just a demo, but a system that can deliver useful payloads to the Moon, generate revenue, and be reused and expanded.
Moon-1 is a rotating lunar orbital tether, approximately 30 km long, deployed into an elliptical lunar orbit. The system gradually delivers many small payloads (initially ~10 kg each) to the lunar surface using rotational momentum rather than chemical descent propulsion.
The key goal is to demonstrate that tethers can replace large amounts of propellant for repeated lunar cargo delivery — even on the very first mission.
The system relies on high-efficiency electric propulsion rather than chemical rockets. We assume a SpaceX-style argon Hall-effect thruster with approximately:
Multiple thrusters are used for:
After launch to Low Earth Orbit, Moon-1 uses its own solar power and Hall thrusters to spiral outward and insert into lunar orbit.
Assuming 4 thrusters:
This allows transfer from LEO to lunar orbit in approximately 6–8 months, fast enough to allow iteration while keeping propulsion mass low.
The tether rotates such that at perigee the tip velocity nearly cancels the orbital velocity relative to the Moon.
Payloads are released at:
From these heights, impact velocity is modest:
Early payloads use crushable structures or airbags. Lunar regolith is often soft and absorbs some impact energy.
Each delivered payload removes momentum from the system. For a 10 kg payload at ~1600 m/s:
Δp ≈ 16,000 kg·m/s per payload
With 4 thrusters (0.68 N total thrust):
This means momentum replenishment is not a bottleneck, even with conservative assumptions.
Mass at the tether tip is extremely expensive, because tether mass scales with tip mass. A design goal is:
Therefore:
Without a thruster at the tip, rotational energy is built using gravity gradient pumping, as described by Tethers Unlimited, Forward, and Hoyt.
A movable ballast module slides along the tether:
This transfers orbital energy into rotational energy and can spin the tether up to operational speed in roughly 1 day.
Ballast motion also controls rotation phase, ensuring the tip is down at perigee for release.
Because release timing and phase can be adjusted, Moon-1 can place small payloads at many different lunar locations over time.
Early payloads include:
Robotic backhoes assemble a simple catapult using delivered parts. The catapult throws standardized payloads (~10 kg) upward 100–200 meters to rendezvous with the tether tip.
Backhoes fill bags with regolith to make return payloads mass-standardized.
Once payloads flow both ways, Moon-1 becomes a true momentum exchange tether, dramatically reducing thrust needs.
Capture is the hardest problem and is approached incrementally.
Payloads have flexible hooks that pass through the mesh and snag.
Practice includes:
Failure of capture does not end the mission — surface delivery alone is already a success.
A robotic mobile module can traverse the tether:
| Component | Estimated Mass (kg) |
|---|---|
| Tether (30 km) | 300 |
| Tip hardware + net | 20 |
| Ballast / mobile module | 80 |
| Solar arrays (~20 kW) | 120 |
| Thrusters (4) | 9 |
| Power electronics & comms | 60 |
| Initial payloads (80 × 10 kg) | 800 |
| Total | ~1,400 kg |
| Launcher | Cost per kg to LEO | Total Launch Cost |
|---|---|---|
| Falcon 9 | $1,000/kg | $1.4M |
| Starship | $200/kg | $280k |
This does not include development costs, but shows that the launch itself is no longer the dominant expense.
Some early payloads are tiny satellites tossed from lunar orbit toward Earth-Moon L5. Small onboard thrusters provide course correction.
This demonstrates:
The tether orbit is inertially fixed. The Moon rotates beneath it once every ~28 days.
To keep surface assets near the perigee point and in sunlight:
This keeps operations continuous and avoids lunar night.
Moon-1 is unusual in that it can generate revenue on its first flight.
20 customers at $400k each yields $8 million, covering a substantial fraction of development.
The mission’s uniqueness and long-term vision make it especially well suited to crowd funding and early adopter participation.
Moon-1 is not just a demonstration — it is a working transportation system that can grow into a lunar-space infrastructure.
Last updated: 2026
© Vince Cate