Paul Bernhardt, University of Alaska; Sam McKay, University of Alaska; Bengt Eliasson, University of Strathclyde; W.A. Scales, Virginia Tech; Andrew Howarth, University of Calgary; Victoria Foss, University of Calgary; Robert Scott, Defence R&D, Canada
Keywords: Plasma Waves, Space Debris
Abstract:
One objective of the High-Altitude Aurora Research Program (HAARP) at the University of Alaska is to demonstrate both excitation and amplification of plasma waves from space objects flying through the artificially modified ionosphere. New techniques are being developed to track small objects in space using plasma waves produced by orbital debris as they pass through the ionosphere [1, 2, 5]. This process has been studied with computer simulations and laboratory measurements. In situ observations confirming the presence of these plasma waves have been made during space sensor conjunctions with known space objects. Small space objects, when they pass through a structured environment, can also be detected with ground sensors and remote satellite instruments. The HAARP HF facility in Alaska is being used to generate field aligned irregularities (FAI) to form an artificially structured environment. HAARP, with an effective radiated power of 2.9 GW in the 2.6 to 10 MHz frequency range, generates large regions of irregularities in the ionosphere with scales sizes of centimeters over spatial regions of tens of kilometers. Space debris and satellites moving through these irregularities and can excite plasma emissions such as whistler, compressional Alfven, or lower hybrid waves. A whistler wave disturbance is generated by conversion of orbital kinetic energy into an electromagnetic plasma oscillation when a charged space object encounters a field aligned irregularity (FAI)[3]. Whistlers propagate undamped at around 9000 km/s from the source regions and can be detected at ranges of several earth-radii.
In addition to the HAARP HF system producing whistler waves on FAI striations, it is used amplify the satellite generated waves [1]. Waves excited by the motion of charged space objects though a plasma have small amplitudes and are often confined to magnetic field lines. A new process called Ionospheric Amplification (IA) has provided a 30 dB increase in whistler waves in space. The HAARP HF facility converts the ionosphere into a nonlinear medium capable of intensifying whistlers, and other signals generated by space objects. There are over 160 space objects that have the correct perigee (< 350 km altitude) and inclination (> 62 degrees) to pass though the HAARP HF beam in the ionosphere. During HAARP campaigns, with over twenty opportunities per day, space objects have the proper orbit geometry to be detected by the HAARP operations.
Measurements of satellites passing over the HAARP site in Gakona, Alaska can show signatures of plasma waves generated by charged space objects. These measurements use the 3.0 MW transmitter at HAARP to both excite and amplify whistler mode waves from overhead satellites and space debris. The high latitude geometry of Alaska is optimal because whistler wave generation requires that orbits cross nearly orthogonal to the magnetic field lines. Ground receivers at ranges up to 150 km from the HAARP transmitter record both VLF and HF signals that are produced by nonlinear scattering from the charged space objects. Similar receivers on satellites are can be tasked to detect these signals in space at ranges from 500 to 40000 km.
This approach to space debris observation uses scattered electromagnetic waves from the plasma oscillations that accompany the target object. The stimulated scatter technique could use any high-power ground HF transmitter, such HAARP in Alaska or EISCAT in Norway, to illuminate the bottomside F-region with high power electromagnetic radiation that could mix with satellite generated waves and scatter an electromagnetic wave back to a ground receiver. This process is related to stimulated electromagnetic emissions (SEE) including stimulated Brillouin scatter of magnetized ion-acoustic and ion-cyclotron waves and of injected probe waves [4]. In this application of Brillouin scatter, the satellite would provide the injected wave that yields a frequency shift in the scattered signal. Data from an array of ground-based receiver antennas may yield an image of a charged space object passing through the HF beam. The stimulated electromagnetic scatter (SES) could provide a signal from a small (i.e., 1 cm) object because the plasma wave spread traveling with the object could be much larger (i.e., 50 km) in size. The Rayleigh scatter of an HF (i.e., 5 MHz) wave is not detectable because radar cross section vanishes for radio wavelengths (i.e., 60 meters) much larger than the object. The SES process can be highly efficient if the satellite waves seed parametric amplification of propagating waves.
References
1. P.A. Bernhardt, R.L Scott, A Howarth, G. J. Morales (2023) Observations of Plasma Waves Generated by Charged Space Objects, Phys. Plasmas 30, 092106, https://doi.org/10.1063/5.0155454
2. P.A. Bernhardt, R.L. Scott, A. Howarth, Victoria Foss, George. J. Morales, (2023) Modeling of Plasma Wave Generation by Orbiting Space Objects for Proximity Detection, 2023 AMOS Proceedings, Maui, Hawaii.
3. E., B., and K. Papadopoulos (2008), Numerical study of mode conversion between lower hybrid and whistler waves on short-scale density striations, J. Geophys. Res.,113, A09315, doi:10.1029/2008JA013261
4. B. Eliasson, A. Senior, M. Rietveld, A. D. R. Phelps, R. A. Cairns, K. Ronald, D. C. Speirs, R. M. G. M. Trines, I. McCrea, R. Bamford, J. T. Mendonça, and R. Bingham (2021), “Controlled beat-wave Brillouin scattering in the ionosphere”, Nat Commun. 12, 6209.
5. R.L. Scott, P.A. Bernhardt, A. Howarth, (2023) Space-based observations of plasma waves during conjunctions between host sensors and space objects, 2023 AMOS Proceedings, Maui, Hawaii.
Date of Conference: September 17-20, 2024
Track: Atmospherics/Space Weather