# Test Verification Guide

Quick reference for testing orbital mechanics using `configs/test_simple.txt`.

## Test Command

```bash
make
./orbit_sim configs/test_simple.txt --headless --readable --days 365
```

## Test Bodies

- **Sun**: Origin (0, 0, 0)
- **Earth**: 1.0 AU, circular orbit (e=0), period ~365 days
- **Mars**: 1.5 AU, circular orbit (e=0), period ~687 days
- **Comet**: 2.5 AU semi-major axis, eccentric orbit (e=0.7), period ~1444 days
  - Starts at perihelion (0.75 AU)
  - Aphelion at 4.25 AU

All orbit counter-clockwise (viewed from +Z).

## Expected Behavior

**Circular orbits (Earth, Mars):**
- Distance from Sun remains constant
- Velocity magnitude remains constant
  - Earth: ~29.8 km/s
  - Mars: ~24.3 km/s
- Return to starting position after full period

**Eccentric orbit (Comet):**
- Distance varies: 0.75 AU (perihelion) to 4.25 AU (aphelion)
- Velocity varies: faster at perihelion, slower at aphelion
- Period ~1444 days

## Quick Tests

```bash
# Earth full orbit
./orbit_sim configs/test_simple.txt --headless --readable --days 365

# Mars full orbit
./orbit_sim configs/test_simple.txt --headless --readable --days 687

# Comet full orbit (eccentric)
./orbit_sim configs/test_simple.txt --headless --readable --days 1444
```

## Acceptable Tolerances

Due to Euler integration with dt=60s:
- Distance variation: ±0.001 AU
- Velocity variation: ±0.1 km/s
- Position after full orbit: Within 0.01 AU of start

## Output Flags

- `--headless`: Terminal output only (no GUI)
- `--readable`: Human-friendly units (AU, km/s) instead of SI (m, m/s)
- `--days N`: Simulation duration in days