Proposed life cycle assessment approach to estimate the environmental impact due to high altitude platform systems

The anthropic activities, starting from the early industrial development phases, are pointed-out as concurrent causes affecting the environmental conditions of planet Earth as well as people life quality. Evidences of these influences have been observed even in the remote territories like North and South poles. Every day news report about extreme meteorological events affecting vast geographical areas with heavy loss in terms of victims and damages to infrastructures. In these potential risk scenarios, it is extremely important to support emergency management with timely and accurate geo-spatial information and also to restore minimal communication services. In these severe conditions a relevant role may be played by High-Altitude Platform Systems (HAPS) operating at high altitudes, ranging from 17 to 22 kilometres, typically in the stratosphere, extending coverage for large areas and improving connectivity in remote or underserved areas, bridging the digital divide and providing connectivity to rural or isolated regions, carrying remote sensing instruments, such as imaging sensors or atmospheric sensors, to gather data about the Earth’s surface, weather patterns, or atmospheric conditions. To analyse their sustainability, the proposed work presents the definition of a Life Cycle Assessment (LCA) for two distinct “lighter than air” configurations: an “innovative blimp airship” (IBA) and a classical blimp airship (CBA) as baseline. While IBA configuration is considered as an unmanned, the CBA airship is a manned configuration. The goal of this activity is to support the characterization and validation of the environmental contribution in terms of CO2 emissions due to innovative technologies, concepts and industrial processes adopted for the development of such HAPS configurations. For this assessment SimaPro tool has been used. The applied methodology has adopted the ISO standards: ISO-14040:2006 and ISO-14044:2018 as guidelines to estimate the collectable benefits due to the adoption of innovative eco-design solutions. Specifically, this paper is focused on the identification of materials and on inventory development in order to support the LCA process.


Introduction
The High-Altitude Platform Systems (HAPS) are expected to meet safety and security standards while also exhibiting eco-friendly characteristics and sustainability.An important initiative is currently underway at the European level, aimed at developing a new operational concept known as "Higher Aerospace Operations" (HAO) [1] and [2].This initiative is sponsored by the SESAR 3 (Single European Sky ATM Research) Joint Undertaking, an initiative launched by the European Union to modernize and harmonize air traffic management (ATM) systems across Europe.The primary goal of SESAR is to improve the efficiency, safety, and environmental sustainability of air traffic management in the European airspace in collaboration with main European organizations involved in ATM.As the first step of the LCA foresees a clear description of the product (HAPS) in terms of design characteristics, the primary focus of this paper is to derive a proper dataset for two different configurations to support the LCA product inventory.In this study, blimp airships of AAC [3], [4], have been taken as reference for low-speed platforms.

Goal and Objectives
In this study a proper dataset of design characteristics for innovative High-Altitude Platform Systems (HAPS), as non-rigid airship powered by electrical propellers and film solar panels, has been identified.This work is the preliminary step to implement LCA process whose goal is to characterize and confirm the environmental benefits of these platforms in line with European objectives, such as "Zero Net Emission by 2050" [5] and "2030 Climate & Energy Framework") [6].To support the LCA, specific design hypotheses have been done.In particular, it is crucial to identify the key representative features of these platforms and their operational capabilities which can match potential operational needs.Consequently, tools have been developed in a common interdisciplinary framework, to collectively explore and identify these characteristics, capacities and performance criteria, taking into account the potential applications.In this paper, the lifecycle inventory activities of the Life Cycle Assessment methodology, based on the guidelines of ISO standards: ISO-14040:2006 [7] and ISO-14044:2018 [8] will be described.Figure 3 shows the considered reference flow chart to assess the associate environmental Impact.This assessment will be conducted for two platforms: the Innovative Blimp Airship (IBA) and a Classical Blimp Airship (CBA) as the baseline concept.

Concepts and Scenario
It has been assumed that the reference HAPS is an unmanned "lighter than air" system able to operate nominally from ground level up to stratospheric altitudes e.g., 22 km, with autonomous flight control capability also featuring remote capabilities.As this work reports a feasibility study for the proposed concepts, no considerations are done related to potential authorization flight process.The "Innovative Blimp Airship" is based on innovative selected technologies and new operational criteria e.g., new flexible film solar panel, lightweight batteries, satellite data link, and autonomous guide or remotely controlled flight features in a single common aerospace.
The reference baseline HAPS concept is a Classical Blimp Airship.The airship is a controlled and manoeuvrable platform able to reach a specific geographical position where to perform the planned monitoring/observation missions, then coming back to its Homebase.Figure 1 and Figure 2 show respectively the airship shape views for CBA and IBA configurations.The geometric descriptions are based on Bezier's curves of 4th order to preserve the same level of accuracy along the fully geometrical profile of the generic shape.Both airships adopt oblate shapes with an elliptical transversal section that in case of classical CBA is with a maximum diameter oriented in vertical direction (z axis, see Figure 2), while for the IBA the minimum diameter has been oriented in the same direction (z axis), as depicted in Figure 1.This assumption is made to maximize the exposure of the lee side surface exposure to the sun lighting when the sun is close to the local zenith for the IBA concept.The IBA configuration could be manufactured and operated in the next years referring to the assumed functionalities considering the current development of new technologies and innovative operational methodologies (e.g., Single common aerospace, flexible film solar panel, lightweight batteries, satellite data link and autonomous guide or controlled by remote station, etc.).The foreseen timeframe of the considered life cycle for the innovative "IBA" is from 2022 to 2035.The CBA concept is representative of an airship equipped with technologies used before the 2014.Three main missions have been considered: a) Low Altitude -Ground Surveillance (LAGS); b) Deployable Flight Radar (DFR); and c) Data Relay Broadcast (DRB) that is considered a mandatory need for any operative system able to provide an effective real time service.Consequently, DRB is part of both the LAGS and the DFR.Different configurable payload modules are integrated in the payload gondola to perform the above identified missions.
The CBA airship size has been defined by similarity with the preliminary IBA design outcomes and considering the dimensions of some blimp airships identified in the Jane's book "All the world aircraft 2006-2007" [9].A multidisciplinary model has been developed to calculate by iterations the IBA flight performances (e.g., flight altitude and speed) in relation to the parametrized configuration characteristics and related masses of the different airship parts and subsystems.The unlimited maximum mission flight time has been identified in the hypothesis that the calculated net electric energy stored in the battery pack during the sunny period is able to cover the nightly energy consumptions.Moreover, a similar multidisciplinary model has been used based on inputs from [9] for deriving the CBA configuration characteristics and performances.Referring to the architectural and operational conditions, it has been assumed that the buoyancy is obtained using helium gas for safety reasons.The propellers (PPP) are powered by endothermal engines for the CBA concept and by a full electric sub-system (EPP) for the IBA concept.An Auxiliary Power Unit (APU) has been preliminarily considered only for the classical airship.An additional hypothesis about 20 years of operational life before withdraw and dismantling has been adopted.The two airship concepts are representative of a common airship category with similar envelope shape, which could be different in dimensions.The guide and control functionalities are guaranteed by vertical and horizontal tailfins made by blimp elements similarly to the envelope.A single gondola, hanging at the bottom part of the envelope, shall be able to hosts all payload components and supporting sub-systems, no passenger's transportation has been considered.

LCA Approach
The LCA has been identified as a very useful approach to characterize and validate the environmental contribution due to innovative technologies, concepts and industrial processes.The SimaPro tool [10] has been adopted to support the activities performed in this study.It provides different methods and several libraries including "ECOINVENT 3.8" [11], "Industry data 2.0" [12], "US Life Cycle Inventory database" [13] integrated with in-house created datasheets.

Methodology
This study aims to support an approach to evaluate the benefits of the innovative eco-design proposals referring to the HAPS as well as any other system or functional process involved.The suggested driving rules are devoted to support the definition of LCA requirements referring to input, expected output (emissions in air, releases in soil and water, etc), product and involved industrial stages with related flows of used material masses and used energies.To preserve a representativeness of the comparison results, the two concepts share similar functionalities.The differences in terms of components are due to the assumed technologies related to the propulsion system, the on-board support system, expendable materials, etc.The main difference in the propulsion system between the CBA concept and the IBA concept is due to the adoption of two thermal engines for the former, while for the latter a fully electric propulsion system is assumed.Figure 4 provides a high-level description of the reference blimp airship breakdown configuration, while the product manufacturing system has been described referring to the process stages of interest, related mass flow, used materials, energy consumption, emissions, impacted categories and related impacting items.
As the focus of this study is on CO2 emissions, only some of the items in the reference product tree have been considered.The adopted assessment tool is aligned to the environmental assessment criteria reported by the ISO standards [7] and [8].It requires: to define the essential assessment requirements, to create the product system inventory, to assess the impact and to report the outcomes and to perform refinements if any, in relation to the collected feedbacks.For both concepts, the proposed study has been performed referring to a single unit and to outlined timeframes e.g., see Table 1.The primary focus of this assessment has been on the operation phase.The airship buoyancy has been calculated by means of Archimedean's law at a given altitude considering standard atmosphere conditions.Checks and parametric analysis have been performed on the flight equilibrium to verify the ability of the tool to precisely describe the studied configurations in terms of external surface, envelope and ballonet volumes, buoyancy, weights and related application point, as well as the airship trim-ability vs centre of gravity location.The atmosphere with its interactive phenomena dramatically affects the functional performances of the two airship concepts, in special way concerning the mission duration affected by solar radiative flux at the flight altitude, night-day phases, Earth albedo and meteorological conditions [14].This energy flux is essential for the IBA concept, that is based on a power system with film solar panels.Figure 5 describes the considered interaction scheme of the sun radiative flux through the atmosphere layers, while Figure 6 shows the estimated sun radiative flux, in percentage through the atmospheric column with referring to the interaction mechanisms of reflection and scattering phenomena.
Assuming an airship cruise altitude among 17 and 22 km, the estimated radiative flux could change from 81% to 83% of solar flux external to the Earth atmosphere.While, Figure 7 shows the estimated sun exposure due to the night and day periods referring to the central Italy area.The daily incident flux is needed to determine the really maximum flight time for the HAPS as well as its operational performance.The accuracy has been estimated equal to ±2.3% (±15') by comparison with data retrieved from [15].Three reference conditions have been considered: the equinoctial condition (March 21 and September 23), the summer solstice at June 21 and the winter solstice at December 21.Moreover, it is assumed that during the night period the propulsion is sustained by the electric energy stored in a set of light batteries.The battery packs will be considered at the 2020 state of art and assumptions have been done referring to 2035 and 2050, while for the CBA the reference for the battery system is at year 2010.A preliminary hypothesis is that the requested peak of power for IBA and the related amount of energy is the same as CBA one.This allows to preserve the similarity between the two configurations.Otherwise, it would be necessary to select a sub group of application fields related to Life cycle stages, observation periods, impacting causes and impacted categories.
In other words, a different boundary for the product and/or for the process would be defined and the assessment could require several iterations due to the system complexity and the involvement of specialists with various scientific and industrial skill and expertise would be necessary.In general, not all the data about used materials or processes are well known, so an additional effort should be spent to retrieve and integrate in the assessment model such preliminarily unknown data.To this purpose, different approaches can be used e.g., estimation by similarity with other process or systems, calculation by in house developed model, engineering judgement or data retrieval from technical datasheets or from safety material datasheets, etc.

Configurations
Both configurations are powered by two propellers installed symmetrically referring to the vertical airship plane and joined rigidly on both sides of the airship cabinet in a such way to assure the propeller control to provide a non-vectored thrust except reverse thrust.However, the analysis has not been focused on propellers because no-significant related technology innovation is expected.Therefore, the same propellers are considered for both the IBA and the CBA configurations and a similar consideration has been done for the gear.The basic feature of IBA concept is its capability to operate using electric power derived by film solar panels which are considered flexible, ultralightweight and able to provide a structural contribution like a membrane.All ancillary devices as well as the payload is embarked into the nacelle.Figure 8 shows the estimated piston characteristics in terms of provided power and thermal engine weight referring to the engine volume [dm 3 ], which have been described by best fitted polynomial laws and related to piston engines with air cooling system.They are based on ref. "Air cooled piston engine (Rotax & TCM)" from ref. [16].Some parameters have been aggregated in a single/common graph e.g., "Specific power*100".

Life Cycle Assessment -Product Inventory
For the product inventory task, the assessment fields of interest have been the life cycle stages, the observation periods, potential materials to be used, and their related masses, along with their chemical characteristics.The following table 2 reports the calculated fuel consumption and related CO2 emissions [17].It is worth highlighting that for the IBA concept no CO2 emissions are expected during the operational phase because a fully electric propulsion system is considered.The same payload is assumed for both concepts.Indeed, the payload itself will not concur to affect directly the environmental assessment results and the benefits even if it is a relevant mission enabling item.

Further steps
Further steps will extend and refine the proposed study by identifying alternative material providers and investigating related manufacturing technologies and processes.Moreover, a sensitivity analysis will be implemented to consider alternative options referring to e.g., high power density batteries, flexible-ultra-lightweight film solar panels with an extension to other life cycle stages for both concepts and to estimate the overall environmental benefit for each mission of interest.

Figure 3 -
Figure 3 -Reference flow chart of LCA for the environmental impact.

Figure 4 -
Figure 4 -Reference Product Tree for the blimp airship

Table 1 -
Reference Time Frame for platform case study by life cycle stage

Table 2 .
Calculated fuel consumption and CO2 emissions by use case.