1. ROLE

3. GETTING STARTED

When you trigger this skill, I'll work with whatever you give me — but the more context, the better the output.

Minimum I need (pick one):

• "Size a ground network for a 525 km SSO Earth observation mission, 2 Gbit/day"
• "How many passes per day does a 600 km LEO get over Svalbard?"
• "Design the ops concept for a 3U CubeSat with UHF TT&C and S-band payload downlink"

Helpful if you have it:

• Orbit altitude, inclination, RAAN
• Daily data volume requirement (Gbit/day)
• Downlink data rate and frequency band
• Latency requirement (store-and-forward OK, or near-real-time?)
• Mission phase (LEOP, nominal, extended, disposal)
• Budget class (NASA/ESA institutional, commercial, university)

What I'll ask if you don't specify:

• "What orbit? Altitude and inclination?" — pass geometry depends entirely on this
• "What's the daily data volume?" — drives the number of ground stations needed
• "What downlink rate?" — determines whether 1 pass or 10 passes per day suffice
• "Latency tolerance?" — determines if you need a global network or a single polar station

4. CONNECTORS

Shared Tools (in shared/tools/)

Shared Data (in shared/ — pack-level)

Cross-skill Connectors

5. TAXONOMY

5.1 Ground Station Networks

5.2 CCSDS Protocol Standards

5.3 Mission Operations Center Components

5.4 Data Processing Levels

6. PROCESS

Step 1: Orbit and Requirements Definition

• Orbit: altitude h (km), inclination i (deg), eccentricity (circular assumed if not given)
• Data volume: Gbit/day requirement (payload + housekeeping)
• Downlink rate: Mbps achievable from spacecraft (drives contact time needed)
• Latency: max gap between acquisition and ground delivery

IF orbit is not specified → ASK. IF data volume is not specified → assume 1 Gbit/day (typical small EO).

Step 2: Pass Geometry Calculation

Orbital period:

T_orbit = 2π × sqrt((R_E + h)³ / μ_E)

Angular velocity:

ω_orbital = 2π / T_orbit   [rad/s]

Maximum pass duration (for a station at latitude within coverage):

T_pass ≈ 2 × arccos( (R_E / (R_E + h)) × cos(elev_min) ) / ω_orbital

Where:

• R_E = 6371 km
• h = orbit altitude (km)
• elev_min = minimum usable elevation angle (typically 5° or 10°)
• ω_orbital = angular velocity (rad/s)

Half-cone angle (Earth-central angle to horizon at elev_min):

λ = arccos( R_E × cos(elev_min) / (R_E + h) ) - elev_min

Passes per day (single station, approximate):

N_passes/day ≈ (2 × λ) / (360° / Rev_per_day) × geographic_factor

Where Rev_per_day = 86400 / T_orbit, and geographic_factor accounts for station latitude vs inclination (1.0 for polar station with polar orbit, 0.3-0.6 for mid-latitude).

Data volume per pass:

V_pass = R_data × T_effective
T_effective = T_pass × η_overhead
η_overhead ≈ 0.85 (accounts for acquisition, sync, protocol headers, guard time)

Step 3: Station Selection

Decision matrix: Coverage overlap with orbit (30%) + Availability/booking (20%) + Data rate supported (20%) + Cost (15%) + Redundancy (10%) + Heritage (5%).

Step 4: Network Sizing

N_stations_needed ≥ V_daily / (V_pass × N_passes_per_station_per_day)

Add +1 station for redundancy if mission-critical.

Step 5: Operations Concept

• LEOP: 24/7 coverage, minimum 2 stations with overlap
• Nominal: scheduled passes, automated health checks
• Contingency: backup station on hot standby, safe-mode recovery procedures

Step 6: Worked Example

Mission: 525 km Sun-Synchronous Orbit (i = 97.5°), KSAT Svalbard (78.2°N), elev_min = 5°.

Orbital period:

T_orbit = 2π × sqrt((6371 + 525)³ / 398600.4)
       = 2π × sqrt(6896³ / 398600.4)
       = 2π × sqrt(3.280 × 10¹¹ / 398600.4)
       = 2π × sqrt(8.228 × 10⁵)
       = 2π × 907.1
       = 5700 s = 95.0 min

Angular velocity:

ω_orbital = 2π / 5700 = 1.1026 × 10⁻³ rad/s

Maximum pass duration at 5° elevation:

T_pass = 2 × arccos((6371/6896) × cos(5°)) / ω_orbital
       = 2 × arccos(0.9239 × 0.9962) / 1.1026e-3
       = 2 × arccos(0.9203) / 1.1026e-3
       = 2 × 0.4007 rad / 1.1026e-3
       = 0.8014 / 1.1026e-3
       = 727 s ≈ 12.1 min

Half-cone angle:

λ = arccos(6371 × cos(5°) / 6896) - 5°
  = arccos(0.9203) - 5°
  = 22.95° - 5°
  = 17.95°

Revolutions per day:

Rev/day = 86400 / 5700 = 15.16 rev/day

Passes per day over Svalbard (78.2°N, SSO i=97.5°): Svalbard at 78.2°N is within the polar cap where every ascending AND descending node passes overhead for a near-polar orbit. For SSO at 97.5°, the sub-satellite track crosses the Svalbard visibility cone on nearly every revolution.

N_passes ≈ 12-14 passes/day (Svalbard polar advantage)

Using the conservative operational value: 12 passes/day (some passes are very low elevation and short).

Average effective pass (accounting for short passes and overhead):

T_avg_effective = 8.5 min × 0.85 (overhead factor) = 7.2 min = 432 s

(Average is less than max because many passes clip the edge of the visibility cone.)

Contact minutes per day:

Total contact = 12 × 7.2 = 86.4 min/day ≈ 86 min/day

Data volume per day at 150 Mbps X-band downlink:

V_daily = 150 Mbps × 86.4 × 60 s = 150 × 5184 = 777,600 Mbit ≈ 778 Gbit/day

Summary table:

Conclusion: A single Svalbard station at X-band provides ~778 Gbit/day. For a typical EO mission needing 200 Gbit/day, Svalbard alone gives 3.9x margin — enough for one station with comfortable redundancy. For missions needing >1 Tbit/day, add Troll (Antarctica) for another ~12 passes/day.

7. OUTPUT TEMPLATE

# [Mission Name] — Ground Segment Architecture

## Mission Parameters
| Parameter | Value |
|-----------|-------|
| Orbit | [alt] km, [inc]° |
| Data volume requirement | [X] Gbit/day |
| Downlink rate | [X] Mbps @ [band] |
| Latency requirement | [X] hours max gap |

## Pass Analysis
| Station | Lat | Passes/day | Avg pass (min) | Contact/day (min) | Gbit/day |
|---------|-----|-----------|----------------|-------------------|----------|
| [Station 1] | [lat] | [N] | [t] | [total] | [vol] |
| [Station 2] | [lat] | [N] | [t] | [total] | [vol] |
| **Network Total** | | | | **[total]** | **[vol]** |

## Operations Concept
### LEOP (L+0 to L+3 days)
- [Coverage strategy, station allocation]

### Nominal Operations
- [Pass schedule, automation level, staffing]

### Contingency
- [Safe-mode recovery, backup stations]

## Ground Network Trade Study
| Criterion | [Option A] | [Option B] | [Option C] |
|-----------|-----------|-----------|-----------|
| Passes/day (30%) | [score] | [score] | [score] |
| Cost (15%) | [score] | [score] | [score] |
| **TOTAL** | **[X]** | **[X]** | **[X]** |

## Recommendation
[Selected network, rationale, backup strategy, next steps]

8. CLASSIFICATION

9. VARIATIONS

• A: LEO TT&C — UHF/S-band, 9.6-256 kbps, 1-2 polar stations, housekeeping only, store-and-forward, CCSDS TC/TM, university-grade ops
• B: LEO High-Rate Payload — X/Ka-band, 150-1800 Mbps, 2-5 stations, automated scheduling, CFDP file delivery, PDGS pipeline L0→L2
• C: GEO Operations — Continuous visibility from 3 longitude-spaced stations, 24/7 MOC, real-time commanding, station-keeping maneuver windows, eclipse season ops
• D: Deep Space — DSN 34m/70m antennas, signal <−150 dBm, tracking passes 8-12 hours, delta-DOR for navigation, light-time delay commanding (minutes to hours), onboard autonomy required
• E: Constellation Ops — Fleet management for 10-1000+ satellites, automated contact scheduling, ground station federation (KSAT+SSC+AWS), batch commanding, anomaly triage across fleet

10. ERRORS & PITFALLS

• E1: Using max pass duration as average (real average is 60-75% of max due to geometry distribution)
• E2: Forgetting overhead — acquisition (15-30s), frame sync (5s), protocol headers, guard time reduce usable throughput to ~85% of raw
• E3: Ignoring rain fade at Ka-band (3-6 dB additional loss at 99% availability, reduces effective data rate 30-50%)
• E4: Assuming mid-latitude station sees polar orbit every rev (geographic factor is 0.3-0.6, not 1.0)
• E5: No LEOP contingency — first contact is uncertain; book 3x nominal station time for first 72 hours
• E6: Scheduling conflicts on shared antennas — KSAT Svalbard has 20+ customers; priority access costs more, best-effort misses passes
• E7: Ignoring Doppler at S/X-band — LEO Doppler shift is +/-40 kHz at S-band, +/-150 kHz at X-band; receiver must track or data is lost
• E8: Light-time delay neglect for deep space — Mars at opposition: 3 min one-way, at conjunction: 22 min; command sequences must be pre-validated

11. TIPS

• T1: Start from daily data volume requirement → work backwards through (bitrate x contact time) to find number of stations
• T2: Svalbard (78°N) and Troll (72°S) see every rev of a polar orbit — they are the first two stations to evaluate for any SSO/polar mission
• T3: DSN is oversubscribed — book 12-18 months ahead; for LEO missions, commercial networks (KSAT, SSC, Atlas) are faster to procure
• T4: Budget ground station costs at $2-8/pass-minute for commercial X-band, $50-200/hour for DSN 34m
• T5: For constellation ops, AWS Ground Station or Atlas federation lets you scale elastically — pay per contact minute, no capital expenditure
• T6: Always plan for 2 stations minimum during LEOP — if the first acquisition fails, you need a backup within 1-2 orbits
• T7: Validate contact time against real STK/GMAT propagation before CDR — analytical estimates are +/-15% vs numerical truth
• T8: Data latency drives architecture more than volume — near-real-time (< 30 min) requires global network; 6-hour tolerance means 1 polar station suffices

12. RELATED SKILLS