Vince Cate — spacetethers.com
This page describes a proposed first space-tether mission designed to:
This is not a pure technology demonstration. It is intended as a Minimum Viable Product (MVP) that can do useful work even if later, more ambitious phases are not immediately successful.
Moon-1 is a rotating lunar-orbit tether, approximately 30 km long, that gradually delivers small payloads (≈10 kg each) to the Moon’s surface.
The tether is launched to Low Earth Orbit (LEO), spirals to lunar orbit using high-ISP electric propulsion, then begins a long-duration campaign of payload drops.
At perigee, the tether’s rotation cancels orbital velocity at the tip, allowing payload release at near-zero velocity relative to the Moon, from heights initially around 1000 meters and later as low as 100 meters.
From these heights, impact velocities range from roughly:
Payloads are designed to tolerate this impact using crushable structures, airbags, or sacrificial materials, with lunar regolith absorbing some energy.
The initial mission carries between 50 and 100 payloads of approximately 10 kg each.
Payload cadence is intentionally slow — one payload every few days — allowing:
Early payloads include:
The system uses one or more Turion TIE-20 GEN2 electric thrusters:
These thrusters are mounted on a movable ballast module that usually sits at the non-payload (“ballast”) end of the tether.
Each 10 kg payload requires a momentum change of approximately:
Δp = m × Δv = 10 kg × 1600 m/s = 16,000 kg·m/s
A single TIE-20 provides 0.079 N of thrust:
Time = Δp / F ≈ 16,000 / 0.079 ≈ 203,000 s ≈ 2.35 days
With 4 thrusters, this drops to ~14 hours per payload, easily fitting between drops.
To reach lunar orbit in under 8 months, the baseline design uses:
This provides ~0.32 N total thrust. For a ~2000 kg spacecraft:
This allows a spiral trajectory from LEO to lunar orbit without chemical stages.
The tether length is ~30 km. The tether mass is assumed to be approximately 10× the combined mass of the tip assembly plus one payload.
Minimizing tip mass is therefore critical.
Estimated tip assembly mass: ~20 kg
No thruster is placed at the tip.
Instead, rotational energy is built using gravity gradient pumping, as described by Forward, Hoyt, and Tethers Unlimited.
The movable ballast module:
This transfers orbital energy into rotation, spinning up the tether tip over approximately one day.
By moving the ballast along the tether, we also control rotation phase so the tip reaches minimum altitude exactly at perigee.
Because the release point can be phased precisely, tiny payloads can be dropped at many different lunar locations.
This enables:
After surface infrastructure is established, the system transitions into a true momentum-exchange tether.
Robotic backhoes assemble a simple catapult that tosses standardized payload bags upward ~100+ meters.
The tether tip deploys a 10 m diameter net with ~5 cm holes. Payloads have flexible “hooks” that pass through and then snag.
Relative speed at catch is ~30 m/s, slow enough to manage with a compliant net.
Extensive dry-run testing is done:
The first mission is considered a success even if no catch is ever achieved.
The movable ballast module can traverse the tether:
Future missions reuse the tether, thrusters, and solar arrays, adding only:
| Component | Mass (kg) | Cost ($M) |
|---|---|---|
| Tether (30 km) | 400 | 2.0 |
| Tip assembly | 20 | 1.0 |
| Ballast module & structure | 300 | 3.0 |
| 4× TIE-20 thrusters | 80 | 0.6 |
| Solar arrays (8 kW) | 120 | 1.2 |
| Payloads (100 × 10 kg) | 1000 | — (customer) |
| Total (excluding payloads) | 920 | 7.8 |
| Launcher | Cost / kg | Total Launch Cost |
|---|---|---|
| Falcon 9 | $1,000 | $920,000 |
| Starship | $200 | $184,000 |
Assuming:
Break-even cost:
≈ $9,000 / kg
This is competitive with chemical landers — and future missions are far cheaper.
Some payloads are small satellites tossed toward Earth-Moon L5.
Tip speed is adjusted via ballast position and pumping. Small onboard thrusters perform course correction.
This demonstrates future cargo movement between the Moon and L5.
The tether orbit is inertially fixed; the Moon rotates beneath it in ~28 days.
To keep surface infrastructure sunlit and near the perigee point, the backhoe must traverse ~10–15 km/day — easily achievable.
The tether’s orbital ellipse is slowly rotated using low thrust, completing one full rotation per year.
Eventually, lunar water can be processed and used as reaction mass for electric thrusters, dramatically reducing Earth-supplied propellant.
Proposed pricing:
Just 20 customers at 10 kg raises $8 million.
This project is compelling enough for crowd funding, potentially exceeding initial goals.
Moon-1 is a realistic, scalable first step toward reusable space tethers.
It delivers real payloads, creates real value, and lays the groundwork for a lunar transportation network far cheaper than chemical rockets.
If it works even partially, it is a historic success.