The ‘Spacecraft Speedometer’ is a new, innovative way to track satellites

Researchers at Los Alamos National Laboratory and the United States Air Force Academy have developed a novel instrument called the Spacecraft Speedometer — a compact, resource-efficient device — capable of determining the velocity of a satellite in while it is in orbit around Earth or even other planets. The sensor can perform on-board measurements of spacecraft velocity using a unique configuration of forward and rear facing plasma spectrometers.

“The Spacecraft Speedometer is small instrument that has the potential to provide critical on-board and real time spacecraft velocity measurements,” said Carlos Maldonado, of Los Alamos’ Space Science and Applications group and principal investigator of the Spacecraft Speedometer project. “These measurements are necessary for improving our ability to accurately predict satellite locations so that we can perform maneuvers to avoid other active satellites and debris.”

Dodging space debris

In recent years, the number of satellites and orbital debris objects has increased so much that they threaten the usability of low Earth orbit (LEO) for commercial and national security purposes. The number of active satellites in space has grown exponentially — from 2,287 satellites 2019 to more than 10,000 in 2024. Space traffic management and orbit sustainability is a critical issue as LEO has become more congested due to increased launches and the dawn of mega satellite constellations.

Currently, satellite location and velocity can only be determined by measurements from the ground by active radar or narrow field-of-view sensors, or via a global navigation satellite system such as GPS, if a satellite is equipped with a GPS receiver. The location and velocity data are used in models that precisely predict the future orbit. However, ground stations can only track satellites as they pass overhead, which can be once every few hours to once every few days, depending on the orbit. GPS location tracking accuracy may be compromised during solar storms, the exact moment when it is most needed for space traffic management.

This novel technology provides critical velocity data for operations during times when GPS or ground station tracking fails, such as during severe space weather events or in GPS-denied environments. Additionally, the Spacecraft Speedometer has the potential to provide velocity data during spacecraft insertions into other planetary atmospheres, where GPS is not available. The sensor also monitors the local space environment and spacecraft charging levels, which provides a tool for spacecraft operators to potentially mitigate hazardous conditions on their spacecraft.

How Spacecraft Speedometer works

The Spacecraft Speedometer design utilizes twin laminated plasma spectrometers: one facing forward along the satellite trajectory and another identical unit facing backward. Like a car driving through a heavy rain, the satellite passes through the charged particles, ions and electrons, that comprise the Earth’s upper atmosphere. In the case of the car, many raindrops will hit the car’s front windshield while fewer raindrops will hit the rear windshield. In addition to the difference in number of raindrops on the front and back of the car, the raindrops on the front hit the windshield harder.

Many atmospheric ions will hit the front-facing sensor head of the Spacecraft Speedometer; this is called the ram measurement — ions are literally being rammed into the sensor head of the spacecraft. Fewer ions are measured by the rear-facing sensor; this is called the wake measurement. The Spacecraft Speedometer uses the difference in the number and impact energy of measured ions collected with the ram and wake sensor heads to provide an on-orbit and real time spacecraft velocity measurement.

The Spacecraft Speedometer is a patent-pending technology.

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