Abstract
Abstract. The Daedalus mission has been proposed to the European Space Agency (ESA) in response to the call for ideas for the Earth Observation program's 10th Earth Explorer. It was selected in 2018 as one of three candidates for a phase-0 feasibility study. The goal of the mission is to quantify the key electrodynamic processes that determine the structure and composition of the upper atmosphere, the gateway between the Earth's atmosphere and space. An innovative preliminary mission design allows Daedalus to access electrodynamics processes down to altitudes of 150 km and below. Daedalus will perform in situ measurements of plasma density and temperature, ion drift, neutral density and wind, ion and neutral composition, electric and magnetic fields, and precipitating particles. These measurements will unambiguously quantify the amount of energy deposited in the upper atmosphere during active and quiet geomagnetic times via Joule heating and energetic particle precipitation, estimates of which currently vary by orders of magnitude between models and observation methods. An innovation of the Daedalus preliminary mission concept is that it includes the release of subsatellites at low altitudes: combined with the main spacecraft, these subsatellites will provide multipoint measurements throughout the lower thermosphere–ionosphere (LTI) region, down to altitudes below 120 km, in the heart of the most under-explored region in the Earth's atmosphere. This paper describes Daedalus as originally proposed to the ESA.
Highlights
1.1 Science contextThe Earth’s upper atmosphere, which includes the lower thermosphere and ionosphere (LTI), is a complex dynamical system, responsive to forcing from above and below: from above, solar radiation, solar wind and solar disturbances such as flares, solar energetic particles and coronal mass ejections cause strong forcing through many complex processes and produce ionization enhancements, electric fields, current systems, heating and ion-neutral chemical changes, which are not well-quantified
An overview of the energy and transport processes in the LTI resulting from the interaction with near-Earth space can be seen in Fig. 1, showing the complexity of simultaneous processes such as the following: incoming energy from solar and magnetospheric processes; the lower atmosphere driving the low-latitude ionosphere; Joule heating at higher latitudes; energetic particle precipitation (EPP) along field lines at high latitudes; the auroral electrojet – the large (∼ 1 × 106 A) horizontal currents that flow in the E-region (90–150 km) in the www.geosci-instrum-method-data-syst.net/9/153/2020/
We provide further details of the observational and measurement requirements placed on the Daedalus mission concept in terms of the observation geometry and placement of the instruments, the observing scheme of the main satellite combined with the subsatellites, spatial and temporal coverage and resolution, and a preliminary assessment of accuracy requirements; these will be further consolidated during the first phases of the Daedalus mission definition
Summary
The Earth’s upper atmosphere, which includes the lower thermosphere and ionosphere (LTI), is a complex dynamical system, responsive to forcing from above and below: from above, solar radiation, solar wind and solar disturbances such as flares, solar energetic particles and coronal mass ejections cause strong forcing through many complex processes and produce ionization enhancements, electric fields, current systems, heating and ion-neutral chemical changes, which are not well-quantified. During geomagnetic storms and substorms, currents with increased amplitudes close through the LTI, producing enhanced Joule heating (Palmroth et al, 2005; Aikio et al, 2012) and leading to significant enhancements in neutral density at high altitudes, which results in enhanced satellite drag. The LTI is the least measured and understood of all atmospheric regions; in particular, the altitude range from ∼ 100 to 200 km, where the magnetospheric current systems close and where Joule heating maximizes, is too high for balloon experiments and too low for existing LEO satellites due to significant atmospheric drag. The ever-increasing presence of mankind in space and the importance of the behavior of this region for multiple issues related to aerospace technology, such as orbital calculations, vehicle reentry and space debris lifetime, together with its importance in global energy balance processes and in the production of GICs and GNSS scintillation, make its study a pressing need
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