What engineering challenges will NASA's most ambitious mission face?
Cosmologists have been debating for years over the so-called Hubble tension: different methods yield different estimates of the expansion rate of the Universe. Data from the cosmic microwave background yields a value of about 67.4 kilometers per second per megaparsec, while observations of Cepheids and supernovae yield a value closer to 73. A new report from NASA's Innovative Advanced Concepts program proposes an unusual approach to the problem from a different angle: extending a radio interferometer to almost the entire Solar System and measuring cosmic distances geometrically, without the traditional distance ladder. A preprint describing the concept has appeared on arXiv.
The project is called the Cosmic Positioning System, or CPS. The authors propose assembling a network of five spacecraft, spreading them across the Solar System at bases of tens of astronomical units. The report suggests distances of approximately 20-100 AU. This range should help capture the curvature of electromagnetic wave fronts from distant sources and directly estimate their distances. If the scheme is successful, several repeating fast radio bursts could yield a constraint on the Hubble constant with an accuracy of better than 1%. The authors expect there to be between 10 and 100 suitable sources.
The idea is based on a principle similar to GPS navigation, but extended to cosmological scales. Instead of satellite geolocation, the scientists want to use precise measurements of the arrival times of signals from repeating fast radio bursts. According to the team's plan, antennas distributed throughout the outer solar system will be able to reconstruct the source's position and distance using trilateration based on signal delays. This method is important primarily because it provides a direct geometric measurement rather than relying on a chain of calibrations between different types of objects.
Behind the beautiful concept lies a heavy engineering component. Each spacecraft, according to the nominal design, must carry a deployable antenna approximately eight meters in diameter, operate in the 3-6 GHz range, and have a receiving system with a temperature below 30 Kelvin. At greater distances from the Sun, the cold helps, but it doesn't completely solve the problem, so the project may require active cooling. Another critical component is related to the clock: the concept requires an onboard atomic clock of the GPS or Deep Space Atomic Clock class, and one that is compact and energy-efficient, as energy becomes scarce at the outskirts of the Solar System.
Power supply is also a challenge. Solar panels alone may not be sufficient at such distances, so the authors are considering radioisotope power sources. Without a stable power supply, it will be impossible to maintain precise time, digitize a wide radio frequency range, or transmit massive amounts of data to Earth. The team also points to the need for a ground-based network for range calibration and prompt alerts about fast radio bursts. The authors cite the properties of repeating FRBs themselves at frequencies of several gigahertz as the main risk factor in their current form: the concept requires additional observations to demonstrate how well such sources are suited for the task.
Even if successful, the mission won't be limited to cosmology alone. The same configuration could help search for microhertz gravitational waves, filling the gap between pulsar timing arrays and LISA, clarify the small-scale structure of dark matter, and measure the mass distribution in the outer Solar System. This set of tasks even includes indirectly testing Kuiper Belt models and searching for traces of the hypothetical Planet Nine through weak gravitational perturbations in the trajectories of the spacecraft themselves.
So far, this is only the early research phase of NIAC, where NASA typically tests the most daring ideas for feasibility. The program's status doesn't mean an imminent launch, and CPS has not yet received additional funding beyond Phase I. Nevertheless, the report itself is already important: the team demonstrates that what was once a near-fictional proposal now has a working architecture, a clear set of technologies, and a scientific objective that warrants serious discussion of a satellite system the size of an interplanetary navigation network.
Cosmologists have been debating for years over the so-called Hubble tension: different methods yield different estimates of the expansion rate of the Universe. Data from the cosmic microwave background yields a value of about 67.4 kilometers per second per megaparsec, while observations of Cepheids and supernovae yield a value closer to 73. A new report from NASA's Innovative Advanced Concepts program proposes an unusual approach to the problem from a different angle: extending a radio interferometer to almost the entire Solar System and measuring cosmic distances geometrically, without the traditional distance ladder. A preprint describing the concept has appeared on arXiv.
The project is called the Cosmic Positioning System, or CPS. The authors propose assembling a network of five spacecraft, spreading them across the Solar System at bases of tens of astronomical units. The report suggests distances of approximately 20-100 AU. This range should help capture the curvature of electromagnetic wave fronts from distant sources and directly estimate their distances. If the scheme is successful, several repeating fast radio bursts could yield a constraint on the Hubble constant with an accuracy of better than 1%. The authors expect there to be between 10 and 100 suitable sources.
The idea is based on a principle similar to GPS navigation, but extended to cosmological scales. Instead of satellite geolocation, the scientists want to use precise measurements of the arrival times of signals from repeating fast radio bursts. According to the team's plan, antennas distributed throughout the outer solar system will be able to reconstruct the source's position and distance using trilateration based on signal delays. This method is important primarily because it provides a direct geometric measurement rather than relying on a chain of calibrations between different types of objects.
Behind the beautiful concept lies a heavy engineering component. Each spacecraft, according to the nominal design, must carry a deployable antenna approximately eight meters in diameter, operate in the 3-6 GHz range, and have a receiving system with a temperature below 30 Kelvin. At greater distances from the Sun, the cold helps, but it doesn't completely solve the problem, so the project may require active cooling. Another critical component is related to the clock: the concept requires an onboard atomic clock of the GPS or Deep Space Atomic Clock class, and one that is compact and energy-efficient, as energy becomes scarce at the outskirts of the Solar System.
Power supply is also a challenge. Solar panels alone may not be sufficient at such distances, so the authors are considering radioisotope power sources. Without a stable power supply, it will be impossible to maintain precise time, digitize a wide radio frequency range, or transmit massive amounts of data to Earth. The team also points to the need for a ground-based network for range calibration and prompt alerts about fast radio bursts. The authors cite the properties of repeating FRBs themselves at frequencies of several gigahertz as the main risk factor in their current form: the concept requires additional observations to demonstrate how well such sources are suited for the task.
Even if successful, the mission won't be limited to cosmology alone. The same configuration could help search for microhertz gravitational waves, filling the gap between pulsar timing arrays and LISA, clarify the small-scale structure of dark matter, and measure the mass distribution in the outer Solar System. This set of tasks even includes indirectly testing Kuiper Belt models and searching for traces of the hypothetical Planet Nine through weak gravitational perturbations in the trajectories of the spacecraft themselves.
So far, this is only the early research phase of NIAC, where NASA typically tests the most daring ideas for feasibility. The program's status doesn't mean an imminent launch, and CPS has not yet received additional funding beyond Phase I. Nevertheless, the report itself is already important: the team demonstrates that what was once a near-fictional proposal now has a working architecture, a clear set of technologies, and a scientific objective that warrants serious discussion of a satellite system the size of an interplanetary navigation network.
