What Is Network Loading?

Network Loading & Modeling is the capacity planning discipline that determines whether a ground antenna network can serve all its space missions. It answers the fundamental question: "Do we have enough ground infrastructure to support every spacecraft that needs it?"

This is distinct from scheduling, which handles real-time decisions about which antenna talks to which satellite right now. Loading is done beforehand — during annual budget planning, when a new mission joins the network, or when a ground asset changes. It is the planning that ensures the schedule can succeed.

Think of it like cellular network planning: scheduling decides which tower handles your phone call now, while loading analysis determines whether your city has enough towers for all its subscribers.

Live Satellite Data

This application uses real orbital data for every satellite shown on the globe. Here is how it works:

• TLE (Two-Line Element) Data — Each satellite's orbit is defined by a standardized TLE set maintained by the U.S. Space Force 18th Space Defense Squadron and published via CelesTrak (celestrak.org). TLEs encode the satellite's orbital parameters: inclination, eccentricity, mean motion, argument of perigee, and epoch.
• SGP4 Propagation — The application uses the satellite.js library (SGP4/SDP4 algorithms) to propagate each satellite's position forward and backward in time from its TLE epoch. This is the same mathematical model used by NASA and the U.S. military for tracking objects in Earth orbit.
• Live TLE Refresh — When the timeline is within 24 hours of the present, the application automatically fetches fresh TLE data from CelesTrak every 2 hours. This keeps orbital positions accurate to within a few kilometers for LEO satellites.
• Embedded Fallback — Each mission includes embedded TLE data so the application works fully offline. When online, live data takes priority over the embedded fallback.

Satellite Catalog

Click the Catalog button to browse the global satellite catalog — over 10,000 active objects tracked by CelesTrak. You can:

• Search by name (e.g., "ISS", "GOES", "Starlink")
• Browse by group (Weather, GPS, Military, Science, etc.)
• Add any satellite to the 3D globe with live orbit visualization
• Promote a catalog satellite to a full analysis mission (assigns priority and SLA requirements)

Catalog data is fetched from celestrak.org/NORAD/elements/gp.php in OMM (Orbit Mean-Elements Message) JSON format. The application converts OMM records to TLE strings for SGP4 propagation.

How the Analysis Works

When the analysis runs, it performs these steps:

1. Sort missions by priority — Tier 1 (Emergency) through Tier 10 (Maintenance). Lower tier number = higher priority. Tiers 1–4 cannot be bumped under any circumstances.
2. Compute contact windows — For every mission-antenna pair, calculate all time periods when the satellite is above the antenna's minimum elevation angle (typically 5 degrees). This uses SGP4 propagation with position checks every 30 seconds, running in a Web Worker thread to keep the UI responsive.
3. Allocate by priority — Starting with the highest-priority mission, assign it to its preferred antenna during available contact windows. Move down the priority list, allocating each mission in turn.
4. Detect conflicts — When two missions need the same antenna at the same time, a conflict is recorded.
5. Resolve conflicts — The engine applies four strategies in order:
   • Bump Lower Priority — If the conflicting mission can be bumped (Tiers 5–10), remove its allocation and give the window to the higher-priority mission.
   • Move to Alternate — Find a compatible contact window on a different antenna within 2 hours.
   • Accept Reduced — Use a shorter portion of the contact window (minimum 30% of the original pass duration).
   • Wait for Next Pass — Defer to the next orbital pass (typically ~90–108 minutes for LEO).
6. Calculate SLA fulfillment — Compare allocated contact minutes against each mission's Service Level Agreement commitment (e.g., "420 minutes per year for ACE"). Displayed as percentage bars in the Loading Matrix.
7. Calculate antenna utilization — Determine what percentage of each antenna's available hours (max 18 hrs/day) are allocated. Shown in the matrix footer row.

Priority System

The 10-tier priority system mirrors real NASA and Space Force operations:

Key rule: If ISS needs time on an antenna, every lower-priority mission gets bumped — even a $10 billion telescope like JWST. Tiers 1–4 are absolute and non-negotiable.

The 3D Globe

The interactive globe is powered by CesiumJS, a WebGL-based 3D geospatial engine. It displays:

• Ground stations — Colored markers at each antenna's geographic location with translucent coverage circles showing the area where satellites can be contacted (based on minimum elevation angle and effective radius).
• Satellite orbits — Animated paths showing each mission's trajectory. Satellites move in real time along their computed orbital track. The trail shows one full orbit ahead and behind.
• Contact lines — Glowing lines that appear between a satellite and a ground station whenever the satellite is within the station's coverage. These update every clock tick, creating a live visualization of which satellites are communicating with which antennas.
• TDRSS relay satellites — Gold diamond icons at geostationary orbit (35,786 km altitude) showing the Tracking and Data Relay Satellite System. When a LEO satellite relays data through TDRSS, two-hop lines are drawn: satellite-to-TDRSS and TDRSS-to-ground terminal.
• Coverage gaps — Red zones highlighting regions where no ground station can provide contact, used in the Guam Coverage Gap Demo.

Use the timeline scrubber at the bottom of the globe to move forward/backward in time. All orbits, contact lines, and visualizations update as you scrub.

Weather Overlays

The application includes 18 real-time and historical weather/Earth observation layers sourced from:

• NASA GIBS (Global Imagery Browse Services) — Global satellite imagery including VIIRS true color, MODIS, cloud top temperature, water vapor, aerosol, wildfires, sea surface temperature, snow cover, sea ice, land surface temperature, and night lights.
• Iowa Environmental Mesonet — US real-time GOES-16 infrared, visible, water vapor imagery, and NEXRAD radar.

Weather directly impacts ground station operations: Ka-band links suffer 4–14 dB rain fade attenuation, while optical links are completely blocked by cloud cover. The analysis applies weather degradation factors to contact window quality calculations.

Network Modes

Three pre-configured network datasets are available via the Network dropdown:

• Demo (4+2) — 4 missions (ISS, Hubble, Jason-3, TSIS-1) and 2 antennas (Goldstone DSN 34m, White Sands Optical). Ideal for learning and presentations.
• NASA Full (53+35) — All 53 active NASA missions across 35 ground stations including the Deep Space Network (Goldstone, Canberra, Madrid), Near Earth Network (Wallops, Alaska, Svalbard, McMurdo, etc.), Space Network (TDRSS ground terminals), and optical terminals.
• Space Force (60+90) — Military satellite operations across the Air Force Satellite Control Network (AFSCN), GPS ground segment, GEODSS optical sites, WGS/AEHF terminals, SBIRS warning stations, and allied partner stations. Uses a separate priority system (NC3, Missile Warning, GPS, etc.).

The Loading Matrix

The bottom panel displays the Loading Matrix — an interactive heat-map table showing the allocation of antenna time across all missions:

• Rows = Missions (sorted by priority tier, highest first)
• Columns = Ground antennas
• Cells = Allocated contact minutes, color-coded by intensity (blue = low, green = moderate, yellow = high, red = overloaded)
• SLA column = Progress bar showing what percentage of each mission's Service Level Agreement is fulfilled
• Utilization row = Per-antenna utilization percentage (green < 70%, yellow 70–90%, red > 90%)
• Conflict icons = Red pulsing warning icons on cells where scheduling conflicts exist

Click any cell to fly the globe to that antenna and highlight that mission's orbit. Click a mission name to select it across all views.

What-If Analysis

The right panel provides What-If controls for scenario testing:

• Toggle antennas on/off — Simulate an antenna failure or addition. Disable Goldstone and watch the entire matrix recalculate, SLA bars collapse, and the globe dim that station.
• Toggle missions on/off — Remove a mission from the network or add a new one. See how it impacts loading on every antenna.
• Re-Run Analysis — After making changes, click to recompute all contact windows, conflict resolution, and SLA fulfillment.

This is the core value of the tool: instantly see the impact of any network change, without waiting for a 5-month scheduling cycle.

Budget Projection

The budget projection models network capacity across fiscal years (FY2026–FY2029). It applies growth factors to mission data demands and identifies when the network reaches saturation — the point where no antenna configuration can meet all SLA commitments. This supports the annual budget planning process where agencies request funding for new antenna construction 2–4 years in advance.

Coverage Gap Demo (Guam Story)

Click Coverage Gap Demo for a narrated experience that explains why loading analysis matters. It tells the true story of how, in the 1960s, loading analysis for the first human spaceflights revealed a critical coverage gap over the Indian Ocean. Any launch emergency in that zone meant astronauts would be completely unreachable. This discovery led directly to building the Guam Ground Station — one antenna that closed the gap and saved lives.

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