C&T — Communications & Trackin

📡 On the Screen: “Active Antennas”

The main image is a 3D side view of the ISS.

Highlighted in magenta are the antennas that are currently active—these are part of the S-band and Ku-band antenna systems located on the Z1 truss and P6/S6 truss segments.

Here’s what you’re seeing:

💡 What “Active” Means Here

The highlighted magenta antennas are:

• Powered on

• Transmitting or receiving signals

• Linked to active data paths through the TDRS network (Tracking and Data Relay Satellites) in geostationary orbit

Inactive antennas appear in gray — they’re part of redundant systems that can be switched on if another fails.

🧠 Communication Path Summary

1. Crew and onboard systems → send voice, video, and telemetry.

2. ISS Antennas (S-band or Ku-band) → transmit to TDRS satellites orbiting Earth.

3. TDRS satellites → relay signals down to Mission Control Centers (Houston, Huntsville, Moscow, etc.).

4. The same path works in reverse for commands and software uploads.

⚙️ C&T Subsystem Breakdown

🧭 In Simple Terms

This screen shows which of the ISS’s antennas are actively talking to Earth.

It’s the “Wi-Fi map” of the station — letting mission controllers verify that communication pathways are open and data is flowing through the correct hardware.

🧩 Hardware Overview

The SASA (S-Band Antenna Subassembly) contains:

• Reflector dish and electronics that transmit and receive S-band signals.

• It’s part of two antenna sets on the truss structure:
  
  

  • RFG1 (Radio Frequency Group 1) — mounted on the S1 truss (starboard side).

  • RFG2 (Radio Frequency Group 2) — mounted on the P1 truss (port side).

These two antennas work redundantly, meaning one can automatically take over if the other fails or if the station’s orientation makes one temporarily blocked from satellite view.

📊 Telemetry (Right Side of Display)

Green text means nominal (healthy and active).

⚙️ System Operation Summary

1. The S-band antennas transmit and receive radio signals through NASA’s TDRSS (Tracking and Data Relay Satellite System) network.

2. These satellites relay data between the ISS and Mission Control in real time.

3. The azimuth and elevation values are constantly adjusted by onboard systems to maintain a perfect line of sight with the relay satellite.

4. The redundant RFG1 and RFG2 ensure continuous communication, even if one is obstructed by the station’s solar arrays or structure.

💡 In Simple Terms

This screen shows the directional pointing and operational status of the two main S-band antennas on the ISS.

They are the “voice and telemetry antennas” that keep the ISS connected to Earth 24/7 — transmitting everything from astronaut conversations to system data used in the ISS Mimic simulation you’re displaying.

🛰️  “Space-to-Ground Antenna”

This display focuses on the Ku-Band SGANT, which is a high-gain dish antenna mounted on the Z1 truss of the ISS.

It’s responsible for broadband data transmission — essentially, it’s the “high-speed Wi-Fi dish” of the ISS.

It connects the station to geostationary TDRS satellites, which then relay data back to Earth at White Sands, New Mexico, and on to Mission Control.

⚙️ Purpose of the Ku-Band System

The Ku-Band antenna provides:

• High-speed data transfer (for experiments, telemetry, and video)

• Live video streams to Mission Control and NASA TV

• Internet and file exchange for crew and onboard systems

• Payload data downlinks (e.g., science from modules like Destiny, Kibo, Columbus)

It connects to NASA’s TDRSS (Tracking and Data Relay Satellite System) — a constellation of geostationary satellites that maintain continuous contact with the ISS even as it orbits Earth every 90 minutes.

🔧 Parameters Displayed

If the link were lost, it might read “SEARCH”, “STOWED”, or “ERROR” depending on mode.

⚙️ How It Works

1. Ku-Band SGANT on the ISS transmits a narrow-beam signal toward a TDRS satellite positioned in geostationary orbit (~35,800 km above Earth).

2. The TDRS satellite relays that signal to NASA’s ground stations in White Sands.

3. Data is then routed to Mission Control Center-Houston (MCC-H) and distributed worldwide.

4. Uplink data (commands, internet packets, etc.) follow the reverse path.

The antenna automatically adjusts its azimuth (side-to-side) and elevation (up-down) angles to maintain a continuous link as the ISS moves at 7.7 km/s.

🧠 In Simple Terms

This is the ISS’s main “video and data antenna.”

It provides the live video feeds, experiment downloads, and communication bandwidth that make the station’s daily operations and public outreach possible.

If the S-Band is like a radio walkie-talkie, the Ku-Band SGANT is like a satellite broadband dish — both critical, but the Ku-Band handles the heavy data.

📡 UHF System Overview

UHF (Ultra-High Frequency) operates in the 400 MHz range — much lower than the S-band (2–4 GHz) or Ku-band (12–15 GHz) systems used for long-distance links.

It provides:

• Two-way voice communication with astronauts performing EVAs (spacewalks).

• Voice and telemetry to and from visiting spacecraft during proximity operations.

• A backup communication method for direct Earth contact (through amateur radio or S-band audio routing).

 🧩 Display Sections Explained

🔹 Left Side Text

Explains the function of the UHF system:

“Provides two-way voice communication with spacewalking astronauts and the ISS. Spacesuit data is also transmitted via UHF.”

That means each EMU spacesuit (Extravehicular Mobility Unit) has a UHF radio transceiver that connects to the ISS via the UHF antennas.

The note “It can also be used to talk to the ground when the audio is connected to the S-Band system” means the UHF audio can be routed internally so Mission Control can hear the astronauts during a spacewalk.

🔹 Frequencies

At the bottom left you see:

• Uplink: 145.99 MHz → From Earth to ISS

• Downlink: 437.8 MHz → From ISS to Earth

These are the same frequencies used by the ARISS (Amateur Radio on the International Space Station) program — allowing licensed amateur radio operators to communicate with ISS crew when permitted.

🔹 Right Side Telemetry

Green color = Nominal (working correctly).

When astronauts are performing an EVA, both UHF 1 and/or UHF 2 would switch to On-Active, and you’d see continuous frame sync lock for live voice and biometric telemetry.

⚙️ System Function During a Spacewalk

1. Astronauts’ EMU radios transmit voice and telemetry on UHF.

2. The UHF antennas on the station receive the signal.

3. That signal is routed through the S-Band system for relay to Mission Control.

4. Ground control’s voice goes back through the same path in reverse.

This ensures real-time communication even if other high-bandwidth systems are busy or temporarily blocked.

🧠 In Simple Terms

The UHF system is the ISS’s walkie-talkie network — simple, reliable, and crucial during spacewalks and docking events.

It’s low-power and short-range but provides clear, constant communication when astronauts are outside the station or when  spacecraft are approaching.