How ISS Telemetry Works: From Sensors to Your Screen

Every system on the International Space Station - from life support to power generation - is monitored by sensors that constantly measure temperature, pressure, voltage, flow rates, and hundreds of other parameters. This stream of measurements is called telemetry, and it is one of the most critical parts of keeping the station running safely.

Sensors everywhere

The ISS has thousands of sensors spread across its modules. The ones most relevant to daily life on board include:

• USLAB000058 - Cabin pressure in the US Lab, measured in millitorr (converted to mmHg)
• USLAB000059 - Cabin temperature in the US Lab, in degrees Celsius
• USLAB000039 - Total station mass in kilograms
• NODE3000005 - Urine tank level in Node 3, as a percentage
• NODE3000008 - Waste water level
• NODE3000009 - Clean water level

These are not arbitrary identifiers. Each one maps to a specific Lightstreamer item name in the ISSLIVE adapter that NASA uses to stream live data from the station.

The data pipeline

Sensor data follows a specific path from the station to the ground:

1. On-board computers collect raw sensor readings and package them into telemetry frames.
2. TDRS satellites (Tracking and Data Relay Satellite System) relay the data to ground stations. The ISS communicates with Earth through a constellation of these satellites in geostationary orbit, giving near-continuous coverage.
3. Mission Control at Johnson Space Center receives the data and makes it available internally.
4. Lightstreamer (push.lightstreamer.com, adapter ISSLIVE) provides a public real-time feed of selected telemetry items. This is what external applications - including ISS Monitor - use to access live data.

How ISS Monitor collects data

ISS Monitor connects to the Lightstreamer feed every minute and records the latest values for each telemetry item. Altitude data comes from a separate source (wheretheiss.at), which calculates the station's position based on its orbital elements (TLE data published by NORAD).

The collected data is stored in a database with timestamps, which allows us to build the history charts you see on the dashboard. Each data point represents a snapshot of the station's state at that moment.

The entire pipeline - from a sensor on the station to a number on your screen - typically takes just a few seconds. That is what makes it possible to track the ISS in near real-time from anywhere in the world.