SNIFFLES I: Intended Emission, Unwanted Emission, and Unintended Radiation from Low-Earth Orbiting Satellites Impacting Radio Astronomy from 1–26 GHz

Abstract We present the first results of SNIFFLES, an ongoing observational programme to characterise intended emission, unwanted emission, and unintended radiation from non-geostationary satellite orbit (NGSO) systems across common radio astronomy receiver bands from 1–26 GHz (L, S, C, X, and K bands). Using the Australian 22m Mopra radio telescope near Coonabarabran, New South Wales, with follow-up observations from a single dish of the Australia Telescope Compact Array (ATCA) interferometer and its new BIGCAT backend, we conducted 4629 tracked observations of satellites from four NGSO constellations (Starlink, OneWeb, Amazon LEO, and Guowang), amounting to 375.9 hours of telescope time. Satellite identification was confirmed by correlating detected Doppler shifts with predicted ephemerides. We detected 2345 instances of intended emission, unwanted emission, and unintended radiation at 300+ unique frequencies from three of the four systems. The detections span all three interference classes affecting radio astronomy: (1) intended emission (including Direct-to-Cell), (2) unwanted emission (out-of-band emission, including up to the fourth harmonic of the Starlink DTC signal at approximately 2.6 MHz, with the fourth harmonic detected near 10.5 GHz), and (3) unintended radiation from satellite platform electronics. Several detections fall within primary radio astronomy allocations, including 1613.19 MHz within the protected OH line band, and at 2690.76 MHz and 2700 MHz. At 2700 MHz, unintended radiation was detected in 76.9 per cent of all observations of the relevant satellite version. ATCA follow-up measurements confirm flux densities up to eleven orders of magnitude brighter than typical astronomical sources, well in excess of levels that saturate radio astronomy receivers.