The Lunar Solar-Train Challenge
A proposal for a University-led distributed robotics mission to the Moon, utilizing space tether deployment and sun-synchronous traversal strategies.
The Core Vision: A swarm of small, modular rovers dropped sequentially by a rotating space tether. Once on the surface, they assemble into a "Solar Train"—a fault-tolerant, distributed vehicle designed to race the sunset and remain permanently powered.
1. The Deployment: Rotating Tether Drop
Traditional rocket landings are expensive. This mission utilizes a momentum-exchange tether system to gently lower payloads to the lunar surface. By utilizing a "bucket brigade" approach, we lower the cost per kilogram significantly.
- Payload Size: Small, 10 kg units (CubeSat class).
- Drop Sequence: Sequential drops reduce the structural load on the tether tip.
- Landing Dispersion: Drops occur approximately every 2 hours. Due to the Moon's rotation, this creates a natural spacing between rovers that the "swarm" must bridge.
2. The Objective: Sun-Synchronous Traversal
Batteries are heavy. The most efficient way to survive the Moon is to never let the sun go down. By moving westward at the same speed the Moon rotates, the rovers remain in eternal dawn/dusk, ensuring constant solar power availability.
10.5 MPH
Speed required at Equator (4.67 m/s)
0.8 MPH
Speed required at 85° Latitude (0.37 m/s)
Note: While the equatorial speed is a high bar for small rovers, the high-latitude target (85°) is highly achievable, even allowing for time to navigate obstacles and charge.
3. The "Solar Train" Architecture
Rather than one large, failure-prone rover, we propose a swarm of 10 units (10 kg each) that link physically to form a distributed locomotive.
Mechanical Symbiosis
The rovers feature a smart-docking system. When connected:
- Reduced Rolling Resistance: The lead rover acts as a compactor, flattening the loose regolith. Following rovers expend less energy rolling on the compacted track.
- Active Articulation: The hitch lifts the front steering wheels of the following rover. This creates a snake-like "multi-articulated" vehicle where followers trail the leader perfectly without active steering input.
- Resource Sharing: A common power bus allows the train to share solar energy. If one rover passes through a shadow, the others keep it alive. computing power and radio bandwidth are similarly pooled.
Fault Tolerance & Redundancy
The train is designed to fail gracefully.
| Failure Scenario |
System Response |
| Lead Rover Steering Failure |
The train halts. The lead rover disconnects and moves to the back (or is discarded). The second rover takes command as the new Lead. |
| Drive Motor Failure (Middle Rover) |
The rover shifts to "neutral/freewheel" mode and is pushed/pulled by the healthy rovers, still contributing solar power and computing. |
| Catastrophic Jam |
The train uncouples. Individual rovers attempt to navigate around the obstacle independently before re-assembling on the other side. |
4. The University Challenge
To drive innovation, this mission is structured as a global competition.
- Participants: 10 Universities selected globally.
- The Allocation: Each university is allotted 100 kg of payload mass, divided into ten 10 kg independent units.
- Design Freedom: Universities can design their swarm however they choose.
- Strategy A: 10 identical "Train Cars."
- Strategy B: 2 dedicated "Tractors" (heavy motors) and 8 "Cargo/Solar" trailers.
- Strategy C: 5 Rolling Rovers and 5 Walking/Humanoid scouts for rough terrain.
- Cooperation Bonus: Universities can form alliances. If University A's train loses battery power, University B's train can physically dock and transfer charge.
5. Concept Evaluation & Feasibility
Strengths
- Cost Efficiency: Tether delivery of small payloads is orders of magnitude cheaper than soft-landing large rovers.
- Reliability: Distributed systems eliminate single points of failure. A 10% failure rate is fatal for a mono-rover; for a swarm, it is merely a degradation of performance.
- Thermal Management: Staying in the sun eliminates the need for heavy radioactive heaters (RHUs) required to survive the 14-day lunar night.
Challenges to Overcome
- Assembly Navigation: The first rover dropped must wait for the second (2 hours later). It must navigate accurately to the drop zone of the second rover without GPS (which does not exist on the Moon).
- Regolith Dust: While compacting helps rolling resistance, the lead rover will kick up significant dust. The joints and solar panels of the following rovers must be aggressively sealed and dust-proof.
- Speed at Equator: 10.5 MPH is extremely fast for off-road autonomous driving with light-speed lag time. The 85° latitude target is the realistic starting point for this technology.