Building the Terrestrial Abyss

Subsurface Realities

As seen in the Team Umbrella mission proposal (ISU MSS 2026), lava tubes are the "holy grail" of Martian exploration. They offer protection from radiation and meteorites, but they present a navigation nightmare.

Inside a lava tube, an agent is effectively isolated from the rest of the solar system. The thick basaltic ceilings act as a Faraday cage, creating a zone of near-total radio silence. Traditional positioning systems (like GPS on Earth or orbital relay tracking on Mars) are non-existent. Without line-of-sight to satellites, drones cannot rely on external corrections for their position.

This same challenge applies to Earth. Search and Rescue (SAR) drones inside collapsed buildings or deep cave systems cannot rely on GPS. They must navigate using pure Ego-Motion and tactile/range-based sensors like Lidar.

Protocol 1: Project Initialization

Protocol 2: The Environment (Cave Design)

We need a tunnel, not just a plane. We will use ProBuilder to model it quickly.

Step 2.1: Initial Cave Segment

1. Go to Tools > ProBuilder > ProBuilder Window.
2. Click New Shape.
3. Select Pipe shape.
4. Set Radius: 5m, Thickness: 0.5m, Height: 10m.
5. In the Hierarchy, rename it to Cave_Segment_01.
6. Rotate it 90 degrees on X-axis so it lays flat as a tunnel.

Step 2.2: Physics & Materials

Go to your Project window (bottom).

1. Right-click > Create > Physic Material. Name it RoughRock.
2. Set Dynamic Friction: 0.8, Static Friction: 0.8.
3. Drag this material onto your cave segment in the Scene view.
4. Why? If the drone crashes, we want it to snag and tumble, not slide infinitely like ice.

Protocol 3: The Agent (Drone)

Step 3.2: The "Eyes" (Ray Perception)

This is the critical sensor for dark environments.

1. On DroneAgent, add component Ray Perception Sensor 3D.
2. Rays Per Direction: 12 (Total rays = 25).
3. Max Ray Degrees: 60 (Wide field of view).
4. Sphere Cast Radius: 0.1 (Thick rays).
5. Detectable Tags: Add a tag "Wall" and apply it to your Cave Segment object.
6. Stacked Raycasts: 1 (No history needed yet).

Protocol 4: The Brain (Scripting)

Create a new C# script named CaveExplorerAgent.cs and paste this code.

using UnityEngine;
using Unity.MLAgents;
using Unity.MLAgents.Actuators;
using Unity.MLAgents.Sensors;

public class CaveExplorerAgent : Agent
{
    Rigidbody rBody;
    public float flySpeed = 10f;

    public override void Initialize()
    {
        rBody = GetComponent();
    }

    public override void OnEpisodeBegin()
    {
        // Reset velocity
        rBody.velocity = Vector3.zero;
        rBody.angularVelocity = Vector3.zero;
        
        // Reset position to start of tube
        transform.localPosition = new Vector3(0, 0.5f, 0); 
        transform.localRotation = Quaternion.identity;
    }

    public override void OnActionReceived(ActionBuffers actions)
    {
        // Inputs from Neural Network
        float moveForward = actions.ContinuousActions[0];
        float yaw = actions.ContinuousActions[1];

        // Apply Forces
        Vector3 force = transform.forward * moveForward * flySpeed;
        rBody.AddForce(force);
        
        Vector3 rotation = transform.up * yaw * 100f;
        rBody.AddTorque(rotation);

        // Energy Penalty (existential cost)
        AddReward(-0.001f);
    }

    // Manual Control for Testing
    public override void Heuristic(in ActionBuffers actionsOut)
    {
        var continuousActionsOut = actionsOut.ContinuousActions;
        continuousActionsOut[0] = Input.GetAxis("Vertical"); // W/S
        continuousActionsOut[1] = Input.GetAxis("Horizontal"); // A/D
    }
    
    // Collision Logic
    void OnCollisionEnter(Collision collision)
    {
        if (collision.gameObject.CompareTag("Wall"))
        {
            SetReward(-1.0f); // Big Penalty for crashing
            EndEpisode();
            Debug.Log("Crashed into Wall!");
        }
    }
}