> ## 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.

# Power Budgeting

> Plan power generation and consumption across orbit

# Power Budgeting

Model power generation, storage, and consumption for orbital compute systems across the full orbital cycle.

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

## Overview

Power in orbit is fundamentally different from Earth:

* **Solar only** — Primary power source is photovoltaic
* **Eclipse periods** — No generation during Earth shadow
* **Battery cycling** — Must store enough for eclipse
* **Degradation** — Solar cells degrade over mission life

## Quick Start

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

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

  power = client.planning.power(
      orbit="LEO-550",
      compute_load_w=500,
      duty_cycle=0.8,
      mission_life_years=5
  )

  print(f"Solar array: {power.solar_array_m2} m2")
  print(f"Battery: {power.battery_kwh} kWh")
  print(f"Available during eclipse: {power.eclipse_power_w}W")
  print(f"EOL margin: {power.eol_margin_percent}%")
  ```

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

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

  const power = await client.planning.power({
    orbit: 'LEO-550',
    computeLoadW: 500,
    dutyCycle: 0.8,
    missionLifeYears: 5
  });

  console.log(`Solar array: ${power.solarArrayM2} m2`);
  console.log(`Battery: ${power.batteryKwh} kWh`);
  ```

  ```bash cURL theme={null}
  curl https://api.rotastellar.com/v1/planning/power \
    -H "Authorization: Bearer rs_your_api_key" \
    -H "Content-Type: application/json" \
    -d '{
      "orbit": "LEO-550",
      "compute_load_w": 500,
      "duty_cycle": 0.8,
      "mission_life_years": 5
    }'
  ```
</CodeGroup>

## Parameters

<ParamField body="orbit" type="string" required>
  Orbit specification (e.g., `LEO-550`, `GEO`)
</ParamField>

<ParamField body="compute_load_w" type="number" required>
  Peak compute power consumption in watts
</ParamField>

<ParamField body="duty_cycle" type="number" default="1.0">
  Fraction of time compute is active (0-1)
</ParamField>

<ParamField body="mission_life_years" type="number" default="5">
  Mission duration for degradation calculations
</ParamField>

<ParamField body="housekeeping_w" type="number" default="50">
  Non-compute power (thermal, comms, ADCS)
</ParamField>

<ParamField body="battery_dod" type="number" default="0.3">
  Maximum battery depth of discharge (0-1)
</ParamField>

## Response

```json theme={null}
{
  "solar_array": {
    "area_m2": 3.2,
    "power_bol_w": 960,
    "power_eol_w": 768,
    "degradation_percent_per_year": 2.5
  },
  "battery": {
    "capacity_kwh": 0.85,
    "cycles_per_day": 15.5,
    "eol_capacity_percent": 80
  },
  "power_profile": {
    "sunlit_available_w": 680,
    "eclipse_available_w": 420,
    "average_available_w": 580
  },
  "margins": {
    "bol_margin_percent": 25,
    "eol_margin_percent": 12
  },
  "recommendations": [
    "Consider 10% larger array for operational margin",
    "Battery supports 5-year mission with 80% EOL capacity"
  ],
  "orbit_profile": [
    {"phase": "sunlit", "duration_min": 57, "power_w": 680},
    {"phase": "eclipse", "duration_min": 35, "power_w": 420}
  ]
}
```

## Power Budget Breakdown

### Typical LEO Power Budget

| Subsystem      | Power (W) | Notes                  |
| -------------- | --------- | ---------------------- |
| Compute (peak) | 500       | GPU/TPU workloads      |
| Compute (idle) | 50        | Standby mode           |
| Thermal        | 30-100    | Heaters during eclipse |
| Communications | 20-50     | Varies with data rate  |
| ADCS           | 10-20     | Attitude control       |
| Housekeeping   | 20-30     | Avionics, sensors      |

### Power Modes

```python theme={null}
# Model different operating modes
power = client.planning.power(
    orbit="LEO-550",
    modes=[
        {"name": "full_compute", "power_w": 500, "duration_percent": 60},
        {"name": "reduced", "power_w": 200, "duration_percent": 30},
        {"name": "idle", "power_w": 50, "duration_percent": 10}
    ],
    mission_life_years=5
)
```

## Eclipse Operations

During eclipse, power is limited to battery capacity:

```python theme={null}
power = client.planning.power(
    orbit="LEO-550",
    compute_load_w=500,
    eclipse_strategy="reduced"  # or "full", "suspend"
)

# Check eclipse power availability
if power.eclipse_available_w < 500:
    print(f"Must reduce to {power.eclipse_available_w}W during eclipse")
```

### Eclipse Strategies

| Strategy  | Description                        | Use Case                     |
| --------- | ---------------------------------- | ---------------------------- |
| `full`    | Maintain full power                | Large battery, short eclipse |
| `reduced` | Reduce compute during eclipse      | Balanced approach            |
| `suspend` | Suspend compute, housekeeping only | Minimal battery              |

## Degradation Over Mission Life

Solar arrays and batteries degrade over time:

```python theme={null}
# Compare BOL vs EOL power
power = client.planning.power(
    orbit="LEO-550",
    compute_load_w=500,
    mission_life_years=7
)

print(f"Year 1 available: {power.solar_array.power_bol_w}W")
print(f"Year 7 available: {power.solar_array.power_eol_w}W")
print(f"Degradation: {power.solar_array.degradation_percent_per_year}%/year")
```

## Design Recommendations

<AccordionGroup>
  <Accordion title="Solar array sizing">
    Size for end-of-life (EOL) power needs plus 10-20% margin.
    Account for degradation: \~2.5%/year in LEO due to radiation.
  </Accordion>

  <Accordion title="Battery sizing">
    Size for eclipse duration + margin. Limit depth of discharge
    to 30-40% for long cycle life.
  </Accordion>

  <Accordion title="Operational flexibility">
    Design for multiple power modes. Ability to reduce compute
    load extends operational flexibility.
  </Accordion>
</AccordionGroup>

## Next Steps

<CardGroup cols={2}>
  <Card title="Thermal Simulation" icon="temperature-high" href="/planning/thermal">
    Ensure thermal design matches power budget
  </Card>

  <Card title="Feasibility Analysis" icon="calculator" href="/planning/feasibility">
    Complete system feasibility check
  </Card>
</CardGroup>