Port 1426: SAS-1 — The port that received signals from the first black hole hunter

Registered Port | TCP/UDP | Satellite-data Acquisition System 1

Port 1426 is registered to SAS-1 (Satellite-data Acquisition System 1), the ground station protocol used to receive telemetry and X-ray data from Uhuru—the first satellite ever launched specifically for X-ray astronomy.¹²

The Satellite That Changed Astronomy

On December 12, 1970, NASA launched a satellite from an Italian platform off the coast of Kenya. They named it Uhuru—Swahili for "freedom"—in recognition of their Kenyan hosts.³ It was also called SAS-A, Explorer 42, and Small Astronomy Satellite 1.

Uhuru's mission: perform the first comprehensive survey of the entire sky for X-ray sources. Before Uhuru, X-ray astronomy was done with brief rocket flights and balloons. Uhuru stayed up there, watching continuously.

What it found changed everything.

What Uhuru Discovered

Uhuru discovered and studied pulsing X-ray binary sources: Centaurus X-3, Vela X-1, Hercules X-1. These were neutron stars pulling matter from companion stars, the material heating to millions of degrees as it spiraled inward.⁴

But the most significant discovery was Cygnus X-1—the first strong candidate for a black hole. Uhuru detected intense X-rays from an invisible object pulling matter from a blue supergiant star. The object was too massive to be a neutron star. It had to be something else. A black hole.⁵

This was 1971. Most people had never heard of black holes. Stephen Hawking famously bet against Cygnus X-1 being a black hole (he lost the bet in 1990).⁶

All of this data—the pulses, the X-rays, the evidence for black holes—flowed down from orbit through ground station receivers using the SAS-1 protocol on port 1426.

The SAS Family

Port 1426 is part of a family of satellite data acquisition ports registered by NASA:

• Port 1426 — SAS-1 (Satellite-data Acquisition System 1) for Uhuru
• Port 1436 — SAS-2 (Satellite-data Acquisition System 2) for the second Small Astronomy Satellite
• Port 1501 — SAS-3 (Satellite-data Acquisition System 3) for the third mission⁷

Each port corresponded to ground stations receiving telemetry from these early space observatories.

The Port Today

Uhuru's mission ended in March 1973.⁸ The satellite reentered the atmosphere and burned up in 1979. But port 1426 remains registered in the IANA database—a digital monument to a mission that discovered black holes before most people knew what they were.

The port is rarely used today. Modern satellite ground systems use different protocols and port ranges. But if you scan port 1426 on a network and find something listening, you're either looking at legacy scientific equipment or someone using an obscure registered port for their own purposes.

How to Check What's Listening

On Linux or macOS:

sudo lsof -i :1426

On Windows:

netstat -ano | findstr :1426

If nothing returns, the port is closed. If you see a process, something is using the port that once carried signals from humanity's first dedicated X-ray observatory.

Why This Port Matters

Port 1426 represents a moment when the Internet and space exploration were both young. NASA needed a way for ground stations to receive satellite data. They registered ports. They built protocols. They pointed antennas at the sky and waited for signals.

What came down through those signals—through ports like 1426—was evidence of black holes, neutron stars, the violent high-energy universe invisible to optical telescopes.

The port is a reminder: every port number has a story. Some carry email. Some carry web pages. Some carried the first evidence that black holes are real.

Port 1426 carried that.