future launchers future →
→ A TOUCHSTONE for SUCCESS
Core technology activity for future launchers
Guy Ramusat Future Launchers Preparatory Programme (FLPP), Directorate of Launchers, ESA HQ, Paris, France
Whether you’re going into Earth orbit, exploring expendable launchers have reached a ‘plateau’ in terms of distant worlds, or coming back home, the first and technical implementation and cost per flight. last few hundred kilometres of the journey are Novel technological solutions, which cope with the ever- always the toughest part. The Core Technology changing environmental loading conditions from launch project of ESA’s Future Launcher Preparatory until to payload delivery in orbit, are required to improve Programme is helping to prepare future access to performance and reduce the cost of access to space, while space, and make it cheaper, safer and more flexible still keeping high reliability. than today. Since the beginning of the 1990s, and backed up by a long-term vision, ESA has performed several trade studies Large numbers of spacecraft manufacturers worldwide to identify and assess new and innovative approaches or rely on the healthy and competitive European expendable concepts for advanced as well as reusable launch vehicle launcher vehicle fleet – namely Ariane-5 and soon Soyuz and systems. However, these attempts have never yielded Vega – to successfully transport their various payloads into development programmes, due to the changing market space. requirements and funding issues.
However, in general, these commercial launch vehicles are In 2004, together with several ESA Member States and based mainly on ‘conventional’ rocket technology. Today’s European industry, ESA agreed to forge ahead with projects
European Space Agency | Bulletin 137 | February 2009 41 lauchers to assess next-generation launcher concepts, to look at 180 European current situation and to foster future prospects 160 in this field. The Future Launchers Preparatory Programme 140 (FLPP) currently evaluates the development provisions 120 required to design and build these future launchers for 100 the most critical technologies in relation with the system studies. 80 60 Over the past 50 years, large budgets were spent worldwide 40 on technology development programmes to dramatically
increase the launch vehicle performances, to reduce costs of programmes growth cost Percent 20 and to provide safer and more reliable access to space. 0 New system studies and associated technology capabilities 0 5 10 15 20 25 are essential elements to support future Earth-to-orbit Phase A/B investment % of programme total transportation developments, allowing the reduction of both development risk and associated costs. ↑
Statistics based on 30 years of NASA civil space programmes Prior investment invariably teads to lower cost overruns, argue in favour of the fact that investment spent in as found in US Space programmes (W. E. Hammond - technology and the definition phases had actually reduced Space Transportation, A System Approach to Analysis and cost overruns. During those 30 years, ‘no project enjoyed Design - AIAA series, 1999) less than a 40% cost overrun unless it was preceded by an investment in studies and technology of at least 5 to 10% of the actual project budget’, and a strong prior investment elements as well programmatic ones to make an informed in such areas invariably tended to lower the cost overrun. decision in the future on the best operational launch vehicle Such results have also been confirmed by US military system to respond to the future institutional needs, while programmes. maintaining competitiveness on the commercial market at that time. At ESA agency level, the establishment of plans for advancing the development of critical technologies are This innovative and flexible programme has been investing considered as well as the introduction of technology in the development of industrial launcher technology readiness reviews for projects, in connection with System capabilities in some main transatmospheric and space cargo Requirement Reviews (SRRs), allowing a better identification transportation areas since 2004. How well ESA does this will and mitigation of technology risks. This reflects the be a major determining factor in Europe’s effectiveness in importance of the technologies in the preparatory activities. providing for this assured access to space in the future.
Representing a sizeable European investment, the general Past and current European programmes developed the objective of the FLP Programme is to prepare these technical Ariane, Vega and Soyuz at CSG launch vehicle assets, as
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The FLP Programme is an ESA optional their subcontractors, for the NGL the related High-thrust Engine programme, where 13 Member system activities, the management integrated demonstrator. States are participating, with a of several technologies and balanced subscription between the is responsible for the overall More than 60 companies, institutes three major contributors (France, Technology Development and or universities are involved in Germany and Italy). The industrial Verification Plan. these activities. The programme organisation, where new industrial benefits from this large industrial schemes are implemented, reflects The Joint Propulsion Team, a effort, where subcontractors can be this configuration. consortium of EADS Astrium Space involved early in system studies for Transportation GmbH, Avio SpA trade-offs, and organisations not NGL Prime SpA, a joint venture of and SNECMA, is responsible, with currently working on ESA-developed EADS SPACE (70%) and Finmeccanica their subcontractors, for main launchers can promote their know- (30%), has the responsibility, with stage propulsion technologies and how for future involvement.
42 www.esa.int lauchers well as the required systems and industrial competencies Through technology, the FLPP is also an opening for new in this field. However, to maintain these competencies, entrants to the launchers sector. As such, the whole FLPP and a competitive European position, more-challenging programme will contribute to unleashing the true potential programmes have to be put in place. of space to the long-term benefit of the European citizens and the industry of ESA Member States. The technological know-how in all launch vehicle fields cannot be considered as something ‘once gained and never Snapshot of FLPP activities lost’, especially because Europe must respond to the future The preparation of these technical and programmatic institutional launch vehicle requirements and be able to elements is based on the maturation of enabling compete in the strong commercial market. technologies that will mitigate risks in any future space transportation system development. The Period-1 of FLPP, On the other hand, it not wise to depend on as-yet- which was decided in 2003 and is covering the years unavailable technology to reach a fixed schedule and cost 2004-6, was focused on system studies and technology in a future launch vehicle development programme. The developments for the preparation of the Reusable Launch FLPP Core Technology project, with its various subsystem Vehicles (RLV) for the Next Generation Launcher (NGL). demonstrators, will demonstrate feasibility and answer the The second period of FLPP was adopted in 2005 and is now under way. The contents of this second period have been oriented towards Expendable Launch Vehicles (ELV). A first step was adopted in 2005 and Step 2 was approved at the ESA Ministerial Council in November 2008, with the objectives to continue for the preparation of the NGL for the distant future, and to contribute to the preparation of short/ medium-term decisions.
The programme implements a system-driven approach, largely addressing integrated demonstrators, as the most efficient way to increase the technology readiness level and address at the same time system-level capabilities, motivating and federating industry teams and capabilities behind concrete technological end-products, from their initial definition to their manufacturing, ground/flight testing and exploitation of results. Various launch vehicle system concepts (NGL or other advanced concepts) target an initial operating capability between 2025 and 2035, depending on the type of vehicle eventually selected for development. Aside from launch vehicle system concepts ↑
System studies on various Expendable Launch Vehicle concepts, baselines for technology activities (NGL Prime)
question for each concept: “Does the technology for a Next Generation Launcher exist, or is it within reach?”
The technology activities already carried out over FLPP Period 1 show that the technology assumptions are achievable. Whether the current FLP Programme is a success or not will depend on the follow-up applications. For instance, the technology improvement of the ceramic shield elements will support future re-entry vehicles and the FLPP Expander Engine Demonstrator activity led yet to a building block application in the post-Ariane ECA programme. ← With the technical support of the ESA’s European Space Technology and Research Centre (Noordwijk), as well Cross-section view inside as European national space agencies and research a typical future launcher. organisations, the FLPP Core Technology project enables ESA Several key technologies to capitalise on launcher technology as one of the steps to are required to develop prepare for future cheaper, safer and more flexible access to such a high-performance space. launcher (NGL Prime)
44 www.esa.int and configurations, the areas of liquid propulsion for main the programme framework assures that the technologies stages and upper stages, cryogenic issues for upper stages have maximum application owing to synergy with the other future launchers future
and atmospheric reentry are also being investigated in the activities of FLPP. To close the loop, the concepts studied by → frame of FLPP (see Bulletin 123, August 2005), at the levels the system rely to varying degrees on the development of of either technology or integrated demonstrators (e.g. the technologies that are needed to mitigate architecture risk. IXV for reentry technologies and the High-thrust Engine Demonstrator for main stage propulsion technologies, see The FLPP Core Technology portfolio includes major Bulletin 128, November 2006). challenges in the numerous technical areas relevant to launch fabrication to mastering materials, processes, design Technology constituents of FLPP and structures, avionics, pyrotechnics, aerodynamics and Current FLPP technology demonstration activities focus on aerothermodynamics issues, health monitoring, ground various technologies and integration methods to improve test facilities, etc. Part of these activities is also dealing reliability and reduce design cycle time, to refine analytical with investigations in promising technologies at early techniques, to increase robustness, to provide assessments stage of maturation that might lead to potential technical which will yield high-fidelity information early in the design breakthroughs. process, and all in order to derive cost-effective technologies for launchers. Some of the technologies developed in this The improvements of individual technologies, as well as activity may find application in the short and medium terms sub-system integrated technologies, are assessed according on evolutions of the current ESA-developed launchers. to the Technology Readiness Level (TRL) scale. The TRL (from 1 to 9) index ranking is set up for each product/subsystem Chemical rocket propulsion technology activities represent based on various parameters, such as materials/components a large part of these technology activities (see Bulletin 134, characterisation and availability, processes maturity, type May 2008). Beside the propulsion activities, the FLPP Core of element, element analysis, and element verification Technology theme is structured to cover subsystems for the environment. NGL ELVs and to a lesser extent, as part of Period 1 activities, RLVs future developments. This area of the FLPP programme The accomplishments is the result of a multidisciplinary approach, based on a Structures, materials and processes technology technology logic and ‘roadmap’ (TDVP), and research as well Due to the unique requirements of launch vehicles, the as development and testing of technology demonstrations overall structural architecture – including tanks, structures which are carried out to achieve a ‘minds on’ (system-driven) and thermal protection – must achieve, as a design goal, and ‘hands on’ (integrated demonstrator) maturation the lowest mass possible compatible with the combined approach of the various enabling technologies. In addition, mechanical, thermal and fatigue loads and cost objectives. Major challenges include reducing overall structural mass, manage structural margins for robustness, containment of cryogenic hydrogen and oxygen propellants, reusable thermal protection system for RLV, etc.
Future launch vehicle requirements, for instance in upper- stage structures, will require higher structural efficiency which in turn will need investigations into new materials and new processing technologies. Emerging technologies that can significantly reduce the dry mass are studied in the programme. The leap in technology is the development of low specific mass materials and stiff structures that can withstand high stresses. This development of these advanced materials and processes must be carried out well ahead of the design phase.
Optimisation of design, using non-conventional structural concepts and investigation of characteristics associated with future in-orbit manoeuvres, will introduce improvements that can initially verified on representative vehicle structural models. These structural demonstrations will have to follow concepts and system requirements defined during the system phase of the programme. ↑ Carbon-fibre reinforced polymer (CFRP) structures The latest conceptual designs for reusable space Automatic isogrid CFPR panel construction (EADS CASA transportation systems require unprecedented and very Espacio) large lightweight metal and composite airframe structures.
European Space Agency | Bulletin 137 | February 2009 45 lauchers An investigation and characterisation of a reusable bismaleimide (BMI) resin-based CFRP structure was performed in high-temperature and harsh environment conditions, using an isogrid stiffened intertank panel does the technology demonstrator manufactured with an automated facility, and a wing box type structure. Optical fibre sensors were for a Next Generation integrated in the test demonstrators to monitor potential damage during cyclic testing. This represents a step forward Launcher exist, or is it towards large unpressurised lightweight CFRP structures. within reach? The heat transfer from hot spots to the surrounding composite structure was investigated with CFRP panel combining heavy load and high temperature resistant properties.
Thermal Protection Systems (TPS) and hot structures Based on a European heritage, three main families of The reusable NGL system concepts studies and IXV ‘passive’ TPS are generally considered to achieve the required development have spurred technology activities related to goals of future operational lift/drag efficient orbit-to-Earth structures used in harsh environment. These activities were reusable hypersonic vehicles, namely: metallic panels, rigid carried out in order to validate dedicated critical ceramic CMC shingles and flexible ceramic blankets. and metallic TPS architectures as well as ceramic matrix composites (CMC) hot structures. Vehicle trajectory peak Reusable launch vehicles also require highly loaded heat flux and dynamic pressure dictate the TPS shingle outer structural components, exposed to medium to high heat surface material. Heat loading decides the thickness of the fluxes. Examples of these components are nose caps, leading insulation material stack. Before being applied to future edges of wings, body-flaps, ailerons, flaps and rudders. operational developments, these subsystems were defined through computational fluid dynamics (CFD) methods, Cryogenic upper-stage activities plasma wind-tunnel tests and in-flight experimentations. The activity concerning the cryogenic upper-stage The demonstrator structural integrity verifications are technologies is part of the system-driven technology benefiting from the existing European high-temperature development approach implemented within the FLPP. mechanical testing chambers and plasma flow facilities. This approach ensures consistency at launcher system level between: (i) launcher system concept definition A variety of reusable TPS concepts are being developed and and selection activities and (ii) several lines of launcher verified in this programme, addressing the requirements of technology developments in propulsion, materials and future hypersonic vehicles. Selection of the optimum TPS for structures, and upper-stage cryotechnologies carried out a particular vehicle is a complex and challenging task that under separate activities and performed in parallel by requires consideration of not only mass, but also operability, different industrial teams. aerodynamic shape preservation, maintenance with rapid turnaround capabilities, durability, initial cost, life-cycle The activity identifies and develops critical technologies, cost, and integration with the vehicle structures, including enabling versatile missions and improving the performances cryogenic propellant tanks. of a reignitable cryogenic upper stage. The cryotechnology
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One of the main roles of ESA is and distributing work approved at In applying this scheme, the FLPP to consolidate space activities in Programme Board level. Core Technology project also relies Europe, drawing on all expertise on the support, for example, of of the Member States to realise ESA strengthens the levels Italian space agency’s technical a common vision. This is done by of technical competences by centre CIRA, the French centres at coordinating the technical activities avoiding duplication, by managing CNES Evry and Toulouse and German of Member States’ national agencies, investments in a cooperative way DLR centres. technical centres and research and at the same time bearing down institutions, and by optimising on industrial activity cost.
46 www.esa.int future launchers future →
European Space Agency | Bulletin 137 | February 2009 47 lauchers
←
FLPP covers the whole range of advanced technologies involved in launcher design: structures, pyrotechnics, propellant, reentry aerodynamics, for example.
project is organised in three parts: (i) activity dedicated Pyrotechnics to critical technologies selection, (ii) activity targeting the This FLPP technology activity initiates investigations to technology development to reach TRL5/6, and (iii) in-flight develop innovative techniques using pyrotechnic subsystems demonstration of gravity-dependent technologies. in term of concepts, manufacturing and integration of key functions (such as engines and large rocket motor ignition, On the other hand, the inert mass of an upper stage has a ground-to-launcher, stage-to-stage and launcher-to- direct impact on launch vehicle performance. To maximise payload separation systems, release functions and launcher the payload mass, the upper stage must use lightweight neutralisation and safety), as well as a momentum and structural concepts to improve the mass fraction of the maturation of these techniques for applications outside the stage. Therefore, it is critical that tailored and appropriate space industry (in cars or aircraft, for example). criteria and margins are used. For that reason, this technology activity is designed to demonstrate, through The innovative pyrotechnics subsystems for future launchers analysis and ground demonstrations, that system level and will be based on two types: ‘electro-pyrotechnics’ and ‘opto- technology improvements of an advanced material tank pyrotechnics’. Improvements of conventional pyrotechnics wall system and innovative upper-stage primary structure based on electro-pyrotechnics draw on the accomplishments and mechanisms can lead to mass decrease, cost efficiency and wide experience gained so far in Europe; these devices and robustness, improved margins and operational have been used on European launchers since Ariane 1 and flexibility of a reignitable expendable upper stage. have been proved reliable and safe with use through to Ariane 5. Such pyrotechnics have been taken up for the Vega Avionics/health monitoring launcher. However, to be competitive, electro-pyrotechnic Advanced avionics architecture will be required for all future subsystems and devices must be upgraded to meet future launcher applications, providing the processing capability needs in terms of size, cost and environmental regulations. for the mission and launch vehicle management, health management, guidance, navigation, and control functions. Opto-pyrotechnics is a technology currently being evaluated worldwide as one of the key subsystems for the evolution of Ariane 5 has a well-known avionics system. But new current launchers and future developments. These devices requirements or obsolescence will lead to the definition have the following advantages: reduced mass, recurring of new computer/avionics architectures, and to the cost reduction (at both system and pyro-subsystem levels), development of new flight application software. The main improvements at Reliability, Availability, Maintainability, critical avionics technologies are the digital architecture Safety level by the removal of primary explosives from the for on-board computers with their associated software, system, simplification of operations prior to launch, increase and data buses (including optical fibre support) to provide of safety, and immunity to electromagnetic interference and high data rates, as well as health monitoring. To take into electrostatic discharge. account all these needs and cover all missions envisaged today (especially reentries), these new architectures should Densified propellants be as modular and scalable as possible, in particular for Furthering European knowledge in slush hydrogen redundancy. technologies, there is activity in assessing the feasibility and advantages of this type of propellant into the NGL concepts. The activity consists in consolidating a technology roadmap, preparing associated means and defining further The advantages are due to the higher density and heat development work necessary to bring these technologies to capacity that can be achieved by adding a solid fraction to an operational qualification level. liquid hydrogen. However this mixture presents a number
48 www.esa.int of issues that still need to be resolved to make it a practical and analysis of the launcher itself. Aerodynamic analysis potential propellant for future space transportation. of any trans-atmospheric vehicle requires a database with future launchers future
both static and dynamic derivatives. However, conventional → The activity performed under FLPP is based on a promising wind tunnel facilities cannot duplicate flight conditions ‘snow-gun’ preparation method, demonstrated at for: (i) the hypersonic regime as the state of the flow field laboratory scale. The proposed work will be dedicated to upstream of the model is not representative, the gas is the topics dealing with improvement of slush hydrogen partially dissociated when reaching the test section, or (ii) production facilities measurement devices development, lower Mach numbers, where the aerodynamic coefficients characterisation of stored slush (i.e. particles size over time, are affected by the structure of the flow field in the wake. particle settling velocity), slush transfer (i.e. expulsion from tanks, flow through pipes and valves), long-term storage The presence of a string holding the model disturbs the issues. The Critical Design Review of the pilot plant took duplication of wake flow phenomena, which govern the place recently. stability behaviour. An advanced method to generate these coefficients is being investigated, based on an experimental Parallel system studies were conducted to assess launch method of free-flight stability assessment of vehicles where vehicle concepts based on combinations of densified the model is moving into ambient gas at rest. The model propellants. Based on concurrent engineering activities, can move freely around all axes, under correct influence of these preliminary investigations provided positive results; forces and damping. In addition, information on the detailed the use of densified propellants in existing launchers flow structure can be obtained (e.g. shock impingement and may give a payload mass increase between 2% and 10%, control surfaces). depending on the densification level, the application stage and the target orbit. Application to upper stages is easier Up to now this test method has been used for ballistic (less propellant mass, less launcher modifications) and bodies, providing direct contributions to the aerodynamic more effective (the structural mass fraction role is more database and also valuable data for code calibration. Of important). The advantages and drawbacks related to particular relevance are the studies of unsteady base the use of slush into propulsion systems have still to be flows as well as buffeting phenomena for the aft sections evaluated further. of launchers, the studies of separation events and of deployments. Aerodynamics Preparation of future technologies is not only limited to on-board systems, but also covers methods for the design ↘
Test for IXV heatshield element in the Scirocco facility
→ Plasma wind tunnels for reentry simulation
One of the most critical aspects of a space mission is the ‘reentry’, the return of a vehicle from orbit into Earth’s atmosphere. This hypersonic flight regime can be simulated with a wide range of ground-test facilities that duplicate aspects of atmospheric entry, such as total enthalpy and stagnation pressure for high altitudes.
● Inductive Plasma Wind Tunnel, or ‘Plasmatron’ (VKI, ● Scirocco Plasma Wind Tunnel Facility (CIRA, Italy) Belgium) This facility consists of an arc-heated gas generator and Unpolluted plasma flows of any gas can be produced an expansion nozzle exhausting in a vacuum chamber. by inductive heating. This facility uses a high-frequency Air is injected from an upstream reservoir in the gas generator and torch to generate a plasma flow, and generator and heated as it flows through a constricted is mainly devoted to the testing of specimens of TPS section by the electric arc established between the materials to be used in the manufacture of shingles of cylindrical cathode and the annular anode before the FLPP CMC TPS demonstrator. expanding in the nozzle. The FLPP CMC TPS demonstrator was tested in this facility.
European Space Agency | Bulletin 137 | February 2009 49