> ## Documentation Index
> Fetch the complete documentation index at: https://docs.rotastellar.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Thermal Simulation

> Model heat rejection and thermal cycles in orbit

# Thermal Simulation

Simulate thermal behavior of compute hardware in orbital environments, including eclipse cycles and varying solar flux.

<Info>
  **Status:** Early Access — [Request API key](https://rotastellar.com/developers)
</Info>

## Overview

Space presents unique thermal challenges:

* **No convection** — Heat can only be rejected via radiation
* **Eclipse cycles** — Periodic loss of solar heating
* **Solar flux variation** — Changes with orbit and season
* **Internal heat** — Compute generates significant waste heat

## Quick Start

<CodeGroup>
  ```python Python theme={null}
  from rotastellar import RotaStellarClient

  client = RotaStellarClient(api_key="rs_...")

  thermal = client.planning.thermal(
      orbit="LEO-550",
      power_dissipation_w=500,
      radiator_area_m2=2.0,
      internal_mass_kg=100
  )

  print(f"Steady state: {thermal.steady_state_c}C")
  print(f"Max (sunlit): {thermal.max_temp_c}C")
  print(f"Min (eclipse): {thermal.min_temp_c}C")
  print(f"Thermal margin: {thermal.margin_c}C")
  ```

  ```typescript Node.js theme={null}
  import { RotaStellarClient } from '@rotastellar/sdk';

  const client = new RotaStellarClient({ apiKey: 'rs_...' });

  const thermal = await client.planning.thermal({
    orbit: 'LEO-550',
    powerDissipationW: 500,
    radiatorAreaM2: 2.0,
    internalMassKg: 100
  });

  console.log(`Steady state: ${thermal.steadyStateC}C`);
  console.log(`Max temp: ${thermal.maxTempC}C`);
  ```

  ```bash cURL theme={null}
  curl https://api.rotastellar.com/v1/planning/thermal \
    -H "Authorization: Bearer rs_your_api_key" \
    -H "Content-Type: application/json" \
    -d '{
      "orbit": "LEO-550",
      "power_dissipation_w": 500,
      "radiator_area_m2": 2.0,
      "internal_mass_kg": 100
    }'
  ```
</CodeGroup>

## Parameters

<ParamField body="orbit" type="string" required>
  Orbit specification. Options:

  * `LEO-400` to `LEO-600` — Low Earth Orbit at specified altitude
  * `MEO-2000` to `MEO-20000` — Medium Earth Orbit
  * `GEO` — Geostationary orbit
  * Custom: `{"altitude_km": 550, "inclination_deg": 53}`
</ParamField>

<ParamField body="power_dissipation_w" type="number" required>
  Internal heat generation in watts
</ParamField>

<ParamField body="radiator_area_m2" type="number" required>
  Radiator surface area in square meters
</ParamField>

<ParamField body="internal_mass_kg" type="number">
  Internal thermal mass in kg (affects transient response)
</ParamField>

<ParamField body="radiator_emissivity" type="number" default="0.9">
  Radiator emissivity (0-1)
</ParamField>

<ParamField body="absorptivity" type="number" default="0.3">
  Solar absorptivity (0-1)
</ParamField>

## Response

```json theme={null}
{
  "steady_state_c": 35.2,
  "max_temp_c": 52.8,
  "min_temp_c": 12.4,
  "margin_c": 17.2,
  "eclipse_duration_min": 35.5,
  "sunlit_duration_min": 57.3,
  "cooling_rate_c_per_min": 0.65,
  "heating_rate_c_per_min": 0.48,
  "thermal_profile": [
    {"time_min": 0, "temp_c": 35.2, "phase": "sunlit"},
    {"time_min": 57, "temp_c": 52.8, "phase": "eclipse_start"},
    {"time_min": 92, "temp_c": 12.4, "phase": "eclipse_end"}
  ],
  "recommendations": [
    "Consider active thermal control for tighter bounds",
    "Heaters recommended for eclipse survival"
  ]
}
```

## Thermal Profiles

### LEO Thermal Cycle

```
Temperature (C)
     60 |    ____
        |   /    \
     40 |  /      \____
        | /            \
     20 |/              \
        +-----------------> Time
         Sunlit  Eclipse
```

### Operating Limits

| Component | Min (C) | Max (C) |
| --------- | ------- | ------- |
| GPU/TPU   | 0       | 85      |
| CPU       | -20     | 100     |
| Memory    | -40     | 85      |
| Storage   | -40     | 70      |
| Battery   | 0       | 45      |

## Advanced: Time-Series Simulation

Get detailed thermal behavior over multiple orbits:

```python theme={null}
thermal = client.planning.thermal(
    orbit="LEO-550",
    power_dissipation_w=500,
    radiator_area_m2=2.0,
    simulation={
        "duration_orbits": 10,
        "time_step_sec": 60
    }
)

# Plot thermal profile
for point in thermal.time_series:
    print(f"{point.time_min}: {point.temp_c}C ({point.phase})")
```

## Design Considerations

<AccordionGroup>
  <Accordion title="Radiator sizing">
    Larger radiators = lower steady-state temperature but more mass and cost.
    Rule of thumb: 0.1-0.2 m² per 100W dissipation for LEO.
  </Accordion>

  <Accordion title="Eclipse survival">
    Ensure minimum temperature stays above component limits.
    May require heaters or thermal mass.
  </Accordion>

  <Accordion title="Hot case analysis">
    Consider worst-case solar flux (perihelion + beta angle = 0).
    Add 10-15% margin to maximum temperature.
  </Accordion>
</AccordionGroup>

## Next Steps

<CardGroup cols={2}>
  <Card title="Latency Simulation" icon="clock" href="/planning/latency">
    Model network latency for your orbit
  </Card>

  <Card title="Power Budgeting" icon="bolt" href="/planning/power">
    Plan power generation and storage
  </Card>
</CardGroup>