The "Spacecraft Speedometer" is a novel and cutting-edge method for monitoring satellite movement.

The Spacecraft Speedometer was tested on the Space Test Program-Houston 5 platform on the International Space Station. Credit to: NASA

Researchers from Los Alamos National Laboratory and the United States Air Force Academy have created an innovative device known as the Spacecraft Speedometer—a compact and efficient tool designed to measure a satellite’s velocity while in orbit around Earth or other planets. This sensor uses a distinctive setup of forward- and rear-facing plasma spectrometers to take on-board velocity measurements.

“The Spacecraft Speedometer is a small instrument with the potential to deliver vital, real-time velocity data directly from the spacecraft,” said Carlos Maldonado, principal investigator of the project and a member of Los Alamos’ Space Science and Applications group. “These measurements are essential for enhancing our ability to precisely track satellite positions, enabling timely maneuvers to avoid collisions with other satellites and space debris.”

Dodging space debris

In recent years, the dramatic rise in the number of satellites and orbital debris has posed a serious threat to the continued safe use of low Earth orbit (LEO) for both commercial and national security operations. The population of active satellites has surged from 2,287 in 2019 to over 10,000 by 2024. With increasing launch activity and the emergence of large satellite constellations, managing space traffic and ensuring orbital sustainability has become a pressing challenge.

At present, a satellite's position and speed are typically determined using ground-based methods such as active radar, narrow field-of-view sensors, or global navigation systems like GPS—provided the satellite carries a GPS receiver. These measurements feed into models that forecast the satellite’s future trajectory. However, ground stations can only observe satellites intermittently, often just once every several hours or days, depending on the satellite’s orbit. Moreover, GPS accuracy can be degraded during solar storms—precisely when reliable tracking is most critical for space traffic control.

This groundbreaking technology offers essential velocity data during situations when traditional tracking methods fail, such as during intense space weather events or in regions where GPS access is unavailable. The Spacecraft Speedometer can also deliver velocity information during spacecraft entry into planetary atmospheres beyond Earth, where GPS coverage does not exist. In addition, the sensor tracks the surrounding space environment and spacecraft charging conditions, providing operators with valuable data to help prevent potentially damaging situations.

How Spacecraft Speedometer works

The Spacecraft Speedometer features a unique design that incorporates two laminated plasma spectrometers—one oriented forward in the direction of the satellite's movement and the other facing backward. This setup is similar to a car driving through a rainstorm: as the vehicle moves forward, more raindrops strike the front windshield with greater force, while fewer hit the rear. In the satellite’s case, it travels through a stream of charged particles—ions and electrons—in Earth’s upper atmosphere.

The front-facing spectrometer captures a higher number of atmospheric ions, a process known as the "ram" measurement, where particles are effectively slammed into the sensor. Meanwhile, the rear-facing spectrometer detects fewer ions, referred to as the "wake" measurement. By analyzing the difference in both the quantity and impact energy of ions recorded by the front and rear sensors, the Spacecraft Speedometer is able to accurately determine the satellite's velocity in real time while in orbit.