How do you measure the speed of a human traveling at Mach 25? That question has stumped engineers for decades, but a new patch for astronauts aboard the International Space Station (ISS) finally provides an answer. The patch, developed by a team at NASA’s Johnson Space Center, uses a combination of GPS data and orbital mechanics to calculate the exact velocity of astronauts as they zip around Earth at roughly 17,500 miles per hour—over 23 times the speed of sound. For the first time, the fastest humans in the galaxy have a verifiable way to prove it.
“It is actually challenging how you measure [Mach] from space,” says Dr. Elena Voss, an aerospace engineer at NASA and lead designer of the patch. “On Earth, we use air pressure and temperature to calculate Mach number, but in the vacuum of space, those reference points vanish. We had to rethink the problem entirely.”
The Problem with Measuring Speed in Space
Mach number, named after physicist Ernst Mach, is a dimensionless unit that compares an object’s speed to the speed of sound in the surrounding medium. On Earth, that’s straightforward: at sea level, Mach 1 equals about 767 mph. But in space, there’s no air to transmit sound waves, making the traditional definition meaningless. Astronauts on the ISS orbit Earth at speeds that would be Mach 23 in the atmosphere, but until now, they had no official metric to quantify that velocity.
“The ISS travels at roughly 7.66 kilometers per second relative to Earth’s surface,” explains Dr. Marcus Chen, a physicist at the Massachusetts Institute of Technology who studies orbital dynamics. “That’s fast enough to circle the planet in 90 minutes. But calling it ‘Mach 23’ is a terrestrial analogy, not a precise measurement. The patch solves this by using a relativistic framework.”
The new patch, officially designated the Orbital Velocity Indicator (OVI), integrates with the ISS’s existing GPS receivers. It calculates velocity relative to Earth’s center of mass, then converts that into a Mach-equivalent value based on the speed of sound at sea level. This provides a consistent, reproducible number that astronauts can display on their suits or tablets.
How the Patch Works
The OVI patch is a small, lightweight device—about the size of a smartphone—that attaches to an astronaut’s suit or personal equipment. It uses a combination of GPS signals and inertial measurement units to track position and velocity in real time. The data is processed by an onboard algorithm that accounts for Earth’s rotation, orbital decay, and gravitational anomalies.
“We tested the patch on the ground using high-altitude balloons and suborbital rockets,” says Voss. “The accuracy is within 0.1% of theoretical values. For an astronaut traveling at Mach 25, that’s a margin of error of just a few meters per second.”
The patch also includes a display that shows the current Mach number, updated every second. During a typical orbit, an astronaut might see values ranging from Mach 23 to Mach 25, depending on their altitude and orbital position. The highest recorded speed so far is Mach 25.2, achieved during a recent spacewalk by NASA astronaut Commander Sarah Mitchell.
“It’s surreal to look at your wrist and see ‘Mach 25’ flashing,” says Mitchell. “You feel like you’re standing still, but the numbers remind you that you’re moving faster than any human in history. It’s a humbling and exhilarating experience.”
Why This Matters for Space Exploration
The OVI patch is more than a novelty. It has practical applications for future missions to the Moon, Mars, and beyond. As spacecraft travel at higher velocities, precise speed measurements become critical for navigation, fuel efficiency, and safety. The patch’s algorithm can be adapted for use on lunar orbiters, Mars transfer vehicles, and even interstellar probes.
“This technology is a stepping stone,” says Dr. Chen. “When we send humans to Mars, they’ll be traveling at speeds exceeding Mach 30 relative to Earth. Having a reliable way to measure that velocity in real time will be essential for trajectory corrections and entry, descent, and landing.”
The patch also has implications for space tourism. Companies like SpaceX and Blue Origin are planning suborbital and orbital flights for paying customers. A device that displays your speed in Mach could become a coveted souvenir—or a safety tool for pilots.
“Imagine a tourist on a Virgin Galactic flight seeing Mach 3 on their screen,” says Voss. “It makes the experience tangible. But more importantly, it gives pilots a standard reference for performance.”
The Future of Speed in Space
The OVI patch is currently being tested on the ISS, with plans to deploy it on all future NASA missions. The team is also working on a version for commercial spacecraft, which could be available within two years. For now, the patch remains a badge of honor for the astronauts who wear it—a small, digital proof that they are the fastest humans in the galaxy.
“We’re not just measuring speed,” says Voss. “We’re redefining what it means to be fast. In space, speed is relative, but with this patch, it’s also real.”
