LFSC - “DAEDALUS”: A Low-Flying Spacecraft for the exploration of the Earth’s Upper Atmosphere A Greek Technology Demonstration Initiative
LFSC | A Low Flying Spacecraft Mission
In the framework of the ESA-Greece Task Force Programme, a team lead by the ATHENA-Space Programmes Unit has completed successfully a study demonstrating that an exploratory mission of the MLT region by a Low-Flying Spacecraft (LFSC) is feasible. The proposed Reference Mission Concept involves a highly elliptical dipping-orbit main satellite which releases a number of small sub-satellites with minimal instrumentation at selected perigee passes. The sub-satellites perform an orbit that gradually reduces its perigee altitude due to atmospheric drag. During each sub-satelliteís descent, the co-temporal measurements by the main satellite and the sub-satellite offer a unique and unprecedented synchronized two-point measurement through the whole MLT region.
- Feasibility Study for a Low-Flying Spacecraft:
- Initiated by ATHENA-SPU under the ESA-Greece Task Force initiative
- Based on an innovative mission scenario, the study has demonstrated that it is feasible to conduct a low-cost technology demonstration mission to visit one of the least explored regions in the Earth’s atmosphere: the Lower Thermosphere (hence dubbed the “Ignorosphere”)
- The concept has received excellent reviews by ESA and support by many upper atmosphere experts, about both its technical feasibility and scientific significance.
- Key Features of a Low-Flying Spacecraft mission:
- The main innovation of this mission is that it is able to perform low-altitude, in-situ measurements in the Lower Thermosphere, the least explored region in the Earth’s atmosphere.
- Low-altitude in-situ measurements are performed by a spacecraft that “dips” in the Earth’s atmosphere, performing short excursions by use of propulsion.
- The Low-Flying spacecraft and sub-satellite concept are designed based on existing and well-proven technologies, using innovative orbital manoeuvres and measurement techniques.
Phases (Work-Packages) of the Feasibility Study:
WP-1: Literature Review
- Status of characterization (review of past and current measurement techniques)
- Identification of measurement gaps (review of the the current state of knowledge)
The scope of this Work Package was to review the current state of knowledge in the MLT region and to identify gaps in measurements as well as in MLT processes that can not be positively identified by existing measurements. To that direction, key atmospheric processes in the MLT and the role of the MLT region in global transport and dynamics were outlined. MLT measurement techniques and the current state of knowledge of the MLT were discussed: More analytically, ground-based measurement techniques were discussed (lidars, ionosondes, radars, and optical measurements); satellite missions that have studied the MLT from higher altitudes by remote sensing techniques were discussed. In-situ measurements by Sounding rockets, Satellite/Space Shuttle/ISS orbits re-entry orbits and spacecraft that have performed in-situ MLT measurements were presented. And, finally, the key Science Questions in the MLT were listed, together with the observables that are required for resolving each question and a best approximation of the temporal and spatial variations that each observable undergoes, meant to provide the basis for an estimate of the required resolution to resolve each process. The results of this study are available online at an Upper Atmosphere Wiki that we created based on the results of this study, as well as the Mesospheric Lidar study
WP-2: Mission Science Objectives
- Overview of key science questions
- Overview of Science Objectives
The scope of this Work Package was to further elaborate on the processes of greatest influence on thermosphere dynamics and composition, listing them in order of significance. Emphasis is placed on the most fundamental concepts and processes of the Lower Thermosphere and on phenomena that have global impacts; emphasis is also placed on the dynamics of the region from 100 km to 200 km, the transition region for many processes and features of the upper atmosphere, also termed the “ignorosphere” due to a shortage of measurements. The discussions are aimed to draw conclusions related to the potential science objectives and potential contributions of a low-cost mission, performing measurements at low-altitudes; the combination of these two guidelines points in the direction of a science mission targeting primarily to perform in-situ measurements in the MLT region. The discussion starts with the most significant processes related to the energy balance in the MLT region, such as Solar heating, particle precipitation, Joule heating, and chemical heating; possible heating from Sprites and other Transient Luminous Events is also discussed, due to the particular nature of the phenomenon. Following the discussion on energy balance-related processes, processes related to neutral and ion composition and chemistry are discussed, as well as coupling processes between the two. Due to the involvement of Oxygen in multiple processes as well as in multiple measurement techniques, a dedicated section discusses the Oxygen Cycle in the thermosphere as well as various measurement techniques related to atomic and molecular oxygen. Finally, the outstanding science questions are selected, and the science objectives of a mission to explore the key science questions are outlined.
WP-3: In-situ Instrumentation
- Instrument selection & prioritization
- Instrument resolution & sensitivities
- Source/Mass-power-size budgets/Cost analysis
As part of this Work Package, the instrumentation required to fulfill the science objectives set in WP2 were defined and relevant instrument types were reviewed, focussing on instruments for an in-situ mission. Remote sensing instrumentation that would assist these observations were also discussed: these included UV spectrometers, infrared radiometers/Bolometers, Fabry-Perot interferometers and GPS receivers. Out of the reviewed instruments, a sub-set of instruments was selected and prioritized, taking into account relevance to science objectives, cost, availability and instrument capabilities.
WP-4: Mission Concept & Performance Requirements
The scope of this Work Package was to elaborate on possible Mission Concepts capable to resolve the defined Science Objectives and fulfil the defined Observation and Instrument Requirements, focusing in particular on the advantages or limitations of in-situ measurements, as compared to other spaceborne or ground-based remote sensing techniques. Analytically, critical aspects and operational constraints in the region of interest were discussed; possible mission concepts and their variations were reviewed; and, finally, a reference mission was selected. For the selected mission concept, mission definition trade-offs were listed and discussed; main satellite concept, elements and subsystems were overviewed; sub-satellite concept, main elements and subsystems were identified; launcher considerations were presented; and the ground segment architecture and subsystems were discussed.
- Key Greek Industry and Institution Partners:
- ATHENA Research Center/Space Programmes Unit (Leader)
- Democritus University of Thrace/Space Research Laboratory
- Hellenic Aerospace Industry S.A.
- Johns Hopkins University Applied Physics Laboratory