Artificial ionospheric modification: The Metal Oxide Space Cloud experiment

Abstract

Clouds of vaporized samarium (Sm) were released during sounding rocket flights from the Reagan Test Site, Kwajalein Atoll in May 2013 as part of the Metal Oxide Space Cloud (MOSC) experiment. A network of ground‐based sensors observed the resulting clouds from five locations in the Republic of the Marshall Islands. Of primary interest was an examination of the extent to which a tailored radio frequency (RF) propagation environment could be generated through artificial ionospheric modification. The MOSC experiment consisted of launches near dusk on two separate evenings each releasing ~6 kg of Sm vapor at altitudes near 170 km and 180 km. Localized plasma clouds were generated through a combination of photoionization and chemi‐ionization (Sm + O → SmO+ + e–) processes producing signatures visible in optical sensors, incoherent scatter radar, and in high‐frequency (HF) diagnostics. Here we present an overview of the experiment payloads, document the flight characteristics, and describe the experimental measurements conducted throughout the 2 week launch window. Multi‐instrument analysis including incoherent scatter observations, HF soundings, RF beacon measurements, and optical data provided the opportunity for a comprehensive characterization of the physical, spectral, and plasma density composition of the artificial plasma clouds as a function of space and time. A series of companion papers submitted along with this experimental overview provide more detail on the individual elements for interested readers.

A physics‐based model for the ionization of samarium by the MOSC chemical releases in the upper atmosphere

“…A striking image of the ion/neutral cloud has been given in the MOSC overview paper by Caton et al . [].…”

“…Previously studied materials such as barium, strontium, xenon, lithium, or cesium have required solar photons or particle collisions for ionization [ Bernhardt , ]. The plasma clouds are used to study plasma instabilities, produce reflection layers for communications or short‐out ambient electric fields that affect the motion of ionospheric plasma [ Caton et al ., ]. The plasma‐producing efficiency of these materials is often measured remotely with HF sounders, UHF radars, or in situ with plasma probes and radio propagation beacons.…”

A combined spectroscopic and plasma chemical kinetic analysis of ionospheric samarium releases

“…Many other rocket experiments followed in subsequent decades as investigations of both the neutral and ionized atmospheric regions at a range of altitudes [ Davis , ]. A review of past experiments using sounding rocket and satellite platforms, with specific intent to modify both the plasma characteristics of the ionosphere and the RF propagation environment, is detailed in another paper in this Special Section by Caton et al [ and references therein].…”

“…Igniters in the canisters were triggered by timed electric signals to ignite the fuel, vaporize the samarium, and exit the vehicle a second later through burst disks. The MOSC experiment overview [ Caton et al ., ] describes the particulars of both the sounding rockets and diagnostic instruments in significantly greater detail.…”

“…Considerable time and effort were spent by AFRL in previous decades to identify chemical release candidate materials that would produce ions by an exothermic chemi‐ionization process involving atomic oxygen: M + O → MO + + e − . Samarium was chosen for the MOSC experiment owing to an exothermic chemi‐ionization reaction with atomic oxygen and its low vaporization energy compared to other chemi‐ionizing metals, permitting ease of vaporization when heated by a high‐temperature reaction [ Caton et al ., , and references therein]. While other sounding rocket experiments have previously used Sm [ Larsen et al , ; Stokes and Murphy , ], none to date included diagnostic measurements capable of quantifying the plasma enhancement generated by the release.…”