Abstract
<title>Abstract</title> <p>The high-frequency (HF) shortwave band, approximately 3–30 MHz, together with adjacent upper-medium-frequency extension down to about 0.3 MHz form one of the least explored radio windows in near-Earth space. From the ground, this band is both a resource and a barrier: the ionosphere enables long-distance shortwave communication by refraction, but the same dispersive and magnetized plasma blocks, bends, absorbs, scintillates and depolarizes extraterrestrial radio waves. Above the main ionospheric layers, shortwave signals from the Sun, planetary magnetospheres, lightning, terrestrial transmitters, and the Galactic radio background can be measured directly under conditions unavailable to ground-based instruments. A spaceborne HF mission can therefore serve three communities at once: heliophysics and space weather, low-frequency radio astronomy and planetary science, and ionospheric radio-propagation and spectrum-environment monitoring. We propose the Spaceborne High Frequency Mission (SHFM) as a staged constellation mission for receiving, classifying and locating shortwave radio signals above the ionosphere. The present concept deliberately adopts a conventional and technically mature payload architecture: deployable electrically short HF antennas, high-impedance low-noise preamplifiers, broadband high-dynamic-range receivers, multi-channel synchronized digitizers, onboard intelligent signal processing, precision timing, and calibrated ground-space experiments. The baseline constellation consists of multiple small satellites in controlled relative orbits, forming a spaceborne HF receiving array. By combining signals coherently or non-coherently, the array will improve sensitivity, enable direction finding and source separation, suppress interference through spatial filtering, and establish the measurement basis for future low-frequency radio imaging missions. The mission has four primary scientific objectives: (1) characterize the orbital shortwave radio environment and its dependence on local time, geomagnetic latitude and space weather; (2) observe solar, heliospheric, planetary and Galactic radio sources in a band severely distorted or inaccessible from the ground; (3) determine upward trans-ionospheric HF propagation using calibrated ground beacons and natural impulsive sources; and (4) demonstrate multi-satellite HF array reception above the ionosphere. In addition, SHFM has clear application value: it can monitor the global HF spectrum environment, identify and locate strong shortwave radiation sources, support interference diagnosis and radio-environment awareness, and provide data products useful for HF communication resilience during disturbed space-weather conditions. This paper defines the scientific rationale, mission objectives, measurement requirements, key technologies and staged mission profile for SHFM.</p>