The Frequency Agile Solar Radiotelescope (FASR) is a next generation radio interferometer array dedicated to solar and space weather research. FASR will build upon the technology that enabled the Expanded Owens Valley Solar Array, but with 10 times more antennas, 100 times more baselines, and an order of magnitude wider bandwidth, it will enable radio imaging with unprecedentedly high image dynamic range, fidelity, and sensitivity. Together with greatly enhanced angular resolution, spectral resolution, and time cadence, it will bring the transformative technique of “ultrawide-band radio video camera” to solar and space weather studies.

By virtue of its broad frequency coverage, FASR will image the entire solar atmosphere multiple times per second from the chromosphere through the corona, while retaining the capability to image a selected frequency range with as little as millisecond-level time resolution. FASR is sensitive to temperatures from < 10,000 K to > 30 MK, and nonthermal particle energies from ∼ 20 keV to > 1 MeV. Moreover, FASR’s panoramic view allows the solar atmosphere and the physical phenomena therein, both thermal and nonthermal, to be studied as a coupled system.

Decadal Recommendation

FASR is ranked by the 2024-2033 Solar and Space Physics Decadal Survey, released in December 2024, as one of the highest priority projects for the National Science Foundation’s Mid-Scale Research Infrastructure (MSRI) program. The specific recommendation is to “Develop the project execution plan for the Frequency Agile Solar Radiotelescope (FASR) and proceed to implementation as an MSRI-2 project.” The recommendation is by virtual of FASR’s revolutionary contribution to both basic science:

“Conclusion: There has been a longstanding need to exploit imaging and spectroscopy over a broad range of radio wavelengths. … FASR fulfills this need.” (pp. 168),

and space weather:

“Conclusion: Implementation…will…require collaboration across multiple NSF divisions. New research infrastructure, such as…FASR…would bring significant new contributions to observing the space weather drivers and impacts.” (pp. 107)

Scientific Objectives

The science FASR addresses is as broad as solar physics itself. FASR measures the polarized brightness temperature spectrum along every line of sight to the Sun as a function of time. It would operate from 0.2 to 20 GHz (or 30 GHz if the hardware allows) with two co-located arrays: FASR-A (2-20 GHz or 1.5-30 GHz) and FASR-B (0.2-2 GHz). Radiation over this vast wavelength range probes the solar atmosphere from the middle chromosphere into the middle corona—the dynamic, magnetoactive, plasma environment in which a wealth of astrophysical and space weather processes occurs. The broad science topics addressed by FASR may be loosely grouped into the following themes:

Magnetic Reconnection & Particle Acceleration
Probing the physics of energy release, particle acceleration, and the formation of flare-accelerated populations during solar flares and eruptive events.

Coronal Magnetography
Mapping coronal magnetic fields using advanced radio diagnostics to understand field topology, dynamics, and their role in structuring the solar atmosphere.

Coronal Heating & Solar Wind Acceleration
Investigating the conversion of magnetic energy into thermal and kinetic energy, including mechanisms that heat the corona and drive the solar wind.

Drivers of Space Weather
Characterizing solar activity that perturbs the heliosphere and affects the geospace environment, improving our ability to forecast space-weather conditions.

The working reference design below is evolving with community input—new science use cases help refine these targets and trade-offs.

• Meet the team →