Disruptive technologies for space Power and Propulsion

Final Report Summary - DIPOP (Disruptive technologies for space Power and Propulsion)

Space is a very harsh environment: temperatures are extreme on both sides, distances are measured in terms of millions of kilometers, and vacuum make things even worse. To successfully guarantee the sustainable life on Earth by mitigation of collision risk with near Earth objects and asteroids (NEO deflection) or for operation of sustainable industry in space (asteroid mining) or for sciences to explore space with manned spacecrafts, there are some basic 'building blocks' that are needed as a minimum:

1. an effective, reliable and cost-effective way to access Space from Earth (which means a launch system);
2. a robust spacecraft;
3. a shielding system from cosmic rays and solar flares;
4. a power generation system;
5. an efficient and reliable propulsion system.

DIPOP project was aimed to build roadmaps for the introduction of disruptive technologies related to power systems and propulsion systems which are the points 4 and 5 above and the prerequisite for the design of robust spacecrafts as in point 3.

Nuclear fission power sources have been investigated for space power provision since the dawn of the nuclear age. Most studies have been conducted in the United States (US) and Russia. The technology is still disruptive for Europeans.

Such availability of power on board of a spacecraft has been analysed deeply within DIPOP and several classes of missions have been pointed out. For sure propulsion is one of the applications, but also radar observation (useful to discover mining sites on asteroids) is of prime importance.

DIPOP also was aimed to analyse every disruptive and advanced concept of power and propulsion technologies that are slightly known even for most of the experts in those domains.

The main accent provided by DIPOP was to focus on the applications in detail as far as possible.

Although NEO deflection (to lower the risk of collision with the Earth) and space science and exploration will be the main driving force behind the technological development of space power and propulsion, novel techniques and methodologies will equally benefit commercial and industrial space missions (asteroid mining), thus generating a very significant impact on Europe's capabilities to access and develop space. Roadmaps have been proposed for technologies regarding microparticle propulsion, nuclear thermal propulsion, primary electric propulsion and fission nuclear power generation.

DIPOP not only addressed technologies, but also attempted to consider major technological efforts in the framework of social and political scenarios, both internal to Europe and with respect to non-European partners. For example, the general public acceptance for the introduction of new technologies in space have been analysed and directives have been stated in order to achieve successful program involving such technologies. In this respect, there have been discussions and meetings with French, US-American and Russian representative in a dedicated advisory board, in order to add value to the DIPOP results and roadmaps. As a start of international cooperation on those disruptive power and propulsion, the DIPOP team was officially requested to further report to the European Commission (EC) the invitation from the Keyldish General Director to participate in the Russian program Megawatt nuclear power propulsion system (NPPS) programme.

Project context and objectives:

The DIPOP project was aimed to build roadmaps for the introduction of disruptive technologies related to power systems and propulsion systems. Nuclear fission power sources have been investigated for space power provision since the dawn of the nuclear age. Most studies have been conducted in the US and Russia. The technology is still disruptive for Europeans. The availability of such power levels on board of a spacecraft has been analysed deeply within DIPOP and several classes of missions have been pointed out.

For sure propulsion is one of the applications, but also radar observation (useful to discover mining sites on asteroids) is of prime importance.

DIPOP also was aimed to analyse every disruptive power and propulsion technologies that are slightly known even for most of the experts in those domains. No restriction in the scales of the disruptive technologies analysed within DIPOP have been made in order to enable the largest possible items to be considered as for example the short following list:

- high temperature superconductors;
- thinned multi junction cells and panel fission nuclear power generation and stirling cycle thermoelectric radioisotope generator;
- quantum-dot solar cell;
- unitised regenerative fuel cell (URFC) and SABRE engine;
- alternative solid propellants: CL-20;
- micro electric space propulsion (MEP) / microparticle propulsion;
- pulsed inductive thruster;
- ambient plasma wave propulsion.

To achieve the goal, an interdisciplinary team of six partners (three small and medium-sized enterprises (SMEs), two universities, one research centres / government bodies), from four European Union (EU) countries, has been formed, grouping experts and specialists in power and propulsion for space applications.

The whole DIPOP project has been divided into three main technical work packages (WP), each of them fully dedicated to a different topic. The technical WP20 was devoted to disruptive non-nuclear power and propulsion. The WP30 was devoted to disruptive nuclear power and applications. As a synthesis, the WP40 was focusing on missions and applications.

The main final accent provided by DIPOP was to focus on the applications in detail as far as possible. Although NEO deflection and space science and exploration will be the main driving force behind the technological development of space power and propulsion, novel techniques and methodologies will equally benefit commercial and industrial space missions (asteroid mining), thus generating a very significant impact on Europe's capabilities to access and develop space up to building an industrial framework or a space industry. Here, follows a brief summary of each WP, describing the target activities and the main objectives.

In WP20 and WP30 , it was recognised to be very important to give recommendations to the EC for further investment in research and development (R&D) respectively Horizon 2020 not only from scientific and technological point of view. Therefore, in the course of the project, consortium members DLR and CAU (Christian-Albrechts-Universität zu Kiel) have setup a large list of disruptive space power and propulsion technologies. Those technologies were analysed and sorted according to standard hierarchy's techniques with DLR experts. The reports released exhibit the top ten disruptive technologies for space power and propulsion (excluding fission power that is presented next) that have been found by DLR.

In addition, in a sub-WP, an assessment of mission and nuclear electric propulsion system options and power management and distribution and electric propulsion power processing issues has been undertaken by SEP. The analysis identifies also the constraints on design options from external factors such as mission requirements and launch capability. Although most electric propulsion (EP) technologies can probably be adapted for the full range of missions it is not possible given the extent of current knowledge to identify one which achieves this better than any other. Consequently the preferred way ahead at this stage is for a nuclear electric propulsion generator (NEP) to be compatible with all the available EP technologies. Overviews of the technologies available and of the specific needs induced by Nuclear power generator have been reviewed. Among them mission and NEP system options are found, as well as EP technologies, options for thermal to electrical energy conversion, and power management and distribution (PMAD). The main conclusion (summarised with a basic evaluation matrix) is that there are many factors to take into consideration, many of which are mission dependent. Fission nuclear power generation therefore needs to be developed to enable a family of missions not just a single application.

Further in a second sub-WP, an analysis lead by USTUTT (IRS Stuttgart) focuses on nuclear thermal propulsion (NTP) which has principally better overall efficiencies and better system mass specific power for the same energy source due to the omission of one stage of conversion systematically proper to EP. Both disruptive and advanced systems have been summarized. The distinction consists in the readiness of the base technology (TRL). Systems like NERVA which have undergone extensive investigation and even ground testing, and merely lack in-flight experimentation can be considered as disruptive. In contrast, fusion propulsion which relies on nuclear thermal fusion not yet fully technically available is considered as an advanced concept. For the latter, a decisive breakthrough can be expected in the next two decades and thus fusion propulsion has been reviewed too.

In WP30, the analyses lead by the consortium members SEP and ISIS have been focused on the selection of space applications that can most benefit from a 30 or a 200 kWe fission nuclear power generator, taking into account the resources Europe requires to develop the capability. It takes account also of technical progress in Europe and relevant resources and capabilities in Russia and the US. The power of 30 kWe was selected because this was considered to be the lowest sensible size of fission nuclear power generator and a power of 200 kWe was selected as the largest fission nuclear power generator capable of launch by 'Ariane 5 ECA'. The missions analysed include: missions to the outer planets removing 'dead spacecraft'/debris: if safety issues can be satisfactorily addressed NEO management (as part of space situational awareness (SSA)), NEO mining and ground-penetrating radar, NEO asteroids or comets Earth collision avoidance. This last application constitutes a precedent circumventing usual public acceptance issues since the consequences of sufficiently large impacts pose a terminal global threat, a planetary emergency, significantly surpassing undesireable aspects of fission nuclear reactors technologies. It should however also be noted these aspects are of distinct importance to the public under normal conditions. The social support for less contingent operations would depend on a setup of confidence, transparency and best safety and environmental practices.

It is also worth noting that the trend is for the known number of NEO asteroids of diameter lower than 100 m, which can impact the Earth with possible major disastrous consequences, will double in the next 10 years: this was seen very recently with the siberian shower of unknown objects for example, hopefully without any noticable consequences. The conclusions of this analysis can be summarised as the fact that a first step is to define the different activities in sufficient detail to be able to cost them realistically. This can then provide an input to the consideration of space nuclear fission power research in the 'EC Horizon 2020 programme'. Consideration should also be given to developing an industrial business case for a space nuclear fission generator program. Without 100 % R&D funding, the very long station time precludes commercially viable returns on investment unless 'spin-off' to shorter term applications can be identified. Also industry needs to be confident that investment in personnel and infrastructure will have a long term, sustainable future. The final recommendations are provided as well.

In addition, in a WP30 sub-WP, the work on public acceptance, safety and sustainability was developed in support of the assessment of Europe's ability to develop and maintain a space nuclear fission program. Some of the principles may also be adapted to the introduction of other disruptive technologies as well. Analysis of the aspects of nuclear power (particularly in space) associated to public acceptance and safety issues have been led by the consortium member USTUTT (IRS University of Stuttgart).

It was discerned that public acceptance is the social emergence of a supportive attitude of larger parts of the general public which evolves in a dialectic of social implementation of technologies and their public understanding. For example, project responsible should communicate in such a way with the general public as to avoid an eventual alienation and without asymmetry in their communication with the public.

For new disruptive technologies, there will always be concerns about the safety of a technology, or its ecological effect. The analysis summarizes the rules the communication should achieve for enabling the general public's acceptance of a project.

In WP40, the work has been based on the summary of space power and propulsion technologies (fission and non-fission) studied within the DIPOP project as described above. Besides the recommendations of previous WP, the propulsion technologies (high power electric propulsion) in line with 30 kWe and 200 kWe NEP applications shall be developed in parallel with EP energy sources. In addition the analysis lead by DLR concludes with two major ideas:

1. The public acceptance. Achieving public acceptance for realizing and using disruptive space power and propulsion technologies studied in DIPOP can be achieved - with full success - through a rational / emotional balance treatment. For this reason, such disruptive space power and propulsion technologies and applications studied in DIPOP are an interdisciplinary project, which demands long term effort.
2. The international achievements of the independent European leadership in space power and propulsion technologies applications in future space missions. Achieving international enforcement, especially under a European leadership or in minimum with a true, equal balanced partnership of Europe with other space nations is a goal. For reaching that status, EC could push a manned space flight to an asteroid because that is a public as well as a political attractive goal (for preparing a protection of population in case of hazard or for SSA). Manned asteroid flight demands future technology level achievements, which could bring European space industry in much higher levels while restructuring activities and business (raw material mining in asteroids) of European space organisations and industry.

DIPOP not only addressed technologies, but also attempted to consider major technological efforts in the framework of social and political scenarios, both internal to Europe and with respect to non-European partners. For example, the general public acceptance for the introduction of new technologies in space have been analysed and directives have been stated in order to achieve successful program involving such technologies. In this respect, there have been discussions and meetings with French, US and Russian representative in a dedicated advisory board, in order to add value to the DIPOP results and roadmaps. As a start of international cooperation on those disruptive power and propulsion, the DIPOP team was officially requested to further report to the EC the invitation from the Keyldish General Director to participate in the Russian programme Megawatt NPPS programme.

A lively dissemination activity has been carried out in parallel to technical activities, participating at international conferences and producing several high quality papers dealing with the diverse topics investigated along the full year within the DIPOP framework and extended to further years.

Project results:
Scientific and technological results is presented grouped by relevant work package

In WP20 and sub-WP, the main objective was to study the disruptive power and propulsion technologies.

According to the study carried out within DIPOP, a disruptive space technology is an emerging technology, which disrupts the status quo of the space sector by radically improving on the performance along an alternate attribute mix. Several technology databases, desk research in popular and scientific literature and expert surveys were evaluated by usage of the analytic hierarchy process (AHP). AHP, as a multi-criteria decision analysis, which weighted the results by means of matrix, which contains technical, political, economic and social factors, allows to distinguish between many disruptive space power and propulsion technologies.

According to AHP, the following top ten space power technologies, together with fission nuclear power, are ranked within the spacecraft electrical power domain for future EC space power research:

- high temperature superconductors (AHP 7.21);
- thinned multi junction cells and panel (AHP 7.10);
- stirling cycle thermoelectric radioisotope generator (AHP 7.05);
- quantum-dot solar cell (AHP 6.89);
- unitized regenerative fuel cell (URFC) (AHP 6.83);
- holographic planar concentrator photovoltaic (PV) module (AHP 6.78);
- metallic foams for Li-ion batteries (AHP 6.74);
- aneutronic fusion (AHP 6.71);
- silicon nanowire Li-ion battery (AHP 6.66);
- power MEMS (AHP 6.60).

Summarised space propulsion recommendations

Several disruptive space propulsion technologies were also studied by means of the AHP method for DIPOP. The advanced propulsions like continuous detonation wave engine and microparticle propulsion were studied and ranked too by the DIPOP consortium members DLR and CAU (University of Kiel).

For continuous detonation wave engine (CDWE) the physics, technology and related developments in Europe, Russia, US, China and Japan were studied in detail as well. In France, studies on propulsion systems based on detonations are successfully ongoing. MBDA in cooperation with the CNRS and Roxel France is studying the possibility to use such propulsion for space applications. The studies are financially and technically supported by CNES. In Poland, such propulsion is also studied and a patent was even granted in 2009 in collaboration with Japanese researchers. The main focus in Poland is the use of such propulsion for jet engine. Tests for rocket engine applications have been done, because it is the simplest utilisation of continuously rotating detonations. In Germany, work on such propulsion has started in the late 2011 and will continue in 2013 at DLR. No experiment has been done yet in Germany and the focus in currently on the theoretical aspects of such propulsion. After slowed down research on such propulsion in the US, for example currently (in 2010) the initiation of the detonation wave in a chosen direction and sufficient propellant injection are rather in a good development: by means of swirled injection detonation waves were stabilised. Therefore, intensive research is planned in the coming years. Studies on the use of detonation for propulsion applications are also ongoing in China and Japan.

For EC research, DLR proposal is to study the impact of CDWE at system level on a launch vehicle. It will help to determine the real gain that such a rocket engine concept would bring in the next decade.

Microparticle propulsion have the following four advantages:

1) higher thrust levels due to a reduced space-charge limitation of the ion or particle beam;
2) enhanced mission performance due to the possibility of variable specific impulses by using a range of mass-to-charge ratios;
3) possibility of spacecraft refueling with dust from asteroids, comets, or the lunar surface;
4) less relative energy expenditure per mass in ionization or particle charging.

As a result of the DIPOP study, the following concepts of microparticle propulsion have the potential to become a 'disruptive' technology in future, and DLR propose that it should be funded: the droplet or colloid thruster plays an important role because of two reasons:

1) Colloid thrusters are already under development for a longer time, but have to have flight experiences in future.
2) FEEP thruster operates in a special mode.

Therefore, it is recommended, that different charging mechanisms for micro particles propulsion and in addition dust accelerators research for high ejection rates have to be carried out and should be funded by the EC. Also studies and experiments for a thruster, which uses miniaturised fine electrode array instead of a single needle electrode are considered to be necessary with the aim to develop a prototype microparticle propulsion system.

Moreover, the following top ten disruptive space propulsion technologies are the result of AHP performed by DLR for DIPOP:

- SABRE engine (AHP 7.54);
- Alternative solid propellants: CL-20 (AHP 6.79);
- Micro electric space propulsion (MEP) / NanoFET (AHP 6.72);
- Pulsed inductive thrusters (AHP 6.67);
- Ambient plasma wave propulsion (AHP 6.57);
- Fission fragment rocket engine (AHP 6.55);
- Magneto-plasmadynamic thruster (MPDT) (AHP 6.51);
- Magnetic sails (AHP 6.49);
- Variable specific impulse magnetoplasmarocket (VASIMR) (AHP 6.46);
- Electrodynamic tether (AHP 6.44).

Advanced propulsion systems and PPU (WP23)

The subject of WP23 consists in an assessment of potentially disruptive propulsion technology. For this aim, four objectives had to be achieved: First, a system engineering approach had to be established and candidate systems and concepts had to be researched with respect to potential disruptiveness. Second, evaluation matrices to enable a comparison had to be established. Next, the performance of the respective systems had to be estimated and rated quantitatively. Finally, disruptive propulsion systems were to be identified according to the data and information obtained in the process.

To achieve these objectives, a literature research was conducted to summarise existing work and known information about both engineering approaches and propulsion concepts. Concerning the engineering approach, necessary theoretic prerequisites on propulsion were recapitulated and generic system architectures established. First suggestions for an evaluation matrix were made. Further, attractive mission scenarios were collected and briefly described. An enquiry after tools for mission analysis was conducted in order to enable a sustained system performance assessment. Also, a rationale for their selection was formulated. Note, however, that the results of the instrument selection were not applicable due to a lack of licenses detected at a later stage. The results of these activities are concentrated in a report. More detailed evaluation matrices have been generated in the frame of an extensive literature research on propulsion devices. The package focussed on systems for interplanetary transfer of large payloads and an eventual inhabited spacecraft. At the current state, electric and thermal approaches appear to be the most viable and least advanced concepts (as opposed to e.g. interplanetary solar sails). Consequently, the literature research focussed on EP suitable for NEP setups are concentrated in report and concepts of NTP have been are summarised.

Based upon this preparative work, it was possible to conduct the comparative mission analyses. They were conducted with preliminary estimative tools developed for the task and focussed on generic missions to Mars. For NEP and NTP, inhabited and/or cargo mission objectives were considered. For NEP, also robotic missions were considered. The results of these activities are documented in report. The report also includes tables of technological readiness levels (TRL), criteria, parameters and - of course - the results of the mission analyses. From the obtained information, it was learnt that EP devices are well capable if it comes to cargo tugging and robotic missions. The technology should be further pushed to better mass specific power. A tradeoff between thrust level and exhaust velocity was identified demanding more detailed engineering and optimisation for the respective missions. The technology's advantage may consist in being viable with small to mid size nuclear space reactors and the relative modularity of a spacecraft: The same reactor can feed different thruster types among which the one best responding to a mission requirement and transfer optimisation can be equipped.

As for NTP, University of Stuttgart finding is that the approach appears to be extremely attractive for rapid transfers cutting the voyage time from Earth to Mars from currently five to nine month down significantly lower duration and significantly larger dry mass transport in an order of magnitude from several tens of tons to several hundreds of tons. NTP tend to appear as devices enabling high acceleration and consequently enabling a gravity field free consideration. Among NTP, solid core fission reactor based propulsion as conceived in the US American ROVER project (NERVA), appear not only sufficiently enabling, but also sufficiently researched to be qualified as one of the disruptive technologies of choice.

The principal impact consists in the identification of NTP based on solid core fission technology being the system for rapid high mass transfers and of NEP as a versatile cargo tugging concept. Hence, it is recommended to push the development of NEP ahead and start to consider the establishment of European testing facilities. Further, as a transfer from Earth to Mars is similar to a mission to a near Earth asteroid in both its range within the Solar System and distance from the human home planet, especially from the gravity field free point of view of high acceleration systems that NTP proved to be. It should thus be recommended to conduct detailed mission studies concerning NTP contingency missions to asteroids.

Report also contains concentrating road maps proposing a strategy to achieve NEP and NTP capacities in two decades. Augmented attention might accelerate the process. It is also noteworthy, that social aspects play a major role, as noted above and described in detail in the reports of WP33.

In WP30 and sub-WP, the work was dealing with nuclear fission power generation.

A nuclear fission power generator roadmap was developed in WP30. It is based on an assessment the impact on future European space activities of fission nuclear electric power generation at 30 kWe and 200 kWe taking account of:

- the advice of a nuclear power sources (NPS) advisory board;
- the range of potential applications;
- the findings of recent European, US and Russian relevant studies and activities;
- an assessment of a possible future international collaboration based on:

i) applications and technical progress to date and required;
ii) the infrastructure required and existing capabilities which might contribute;
iii) the rationale for investment;

- an assessment of the particular requirements of launch and public acceptance of the technology.

Ground work for WP30 was developed in WP31, based on a 30 kWe generator and WP32, based on a 200 kWe generator. WP31 and WP32 investigated the impact of nuclear power generators for space in terms of:

- applications, collective interests and investment policies for space transportation / solar system exploitation considering European, US and Russian:

i) current programs and long term investment strategies;
ii) relevant infrastructure and potential infrastructure development;
iii) national policies for nuclear energy and space.

- European, US and Russian activities and studies with particular attention to differences in:

i) mass efficiency, operating temperatures, lifetime;
ii) design resilience;
iii) other design drivers (eg launch constraints);
iv) safety;
v) critical technical developments required.

WP31 included a state of the art review and implications such as radiation hazards. The roadmap developed within WP30 also took account of public acceptance, safety and sustainability, investigated in WP33 and reported separately below. It was noted that 'the power level of both the 30 kWe and the 200 kWe nuclear reactor find no parallel in the commercial and military world of nuclear reactors. Compactness, flyweight and reliability over lifetimes of order many years pose special problems. Some, especially life and reliability, have already been solved in submarines by means that are in part completely different and partly similar, but where the information is proprietary or classified.'

It was recognised that Europe has no practical experience of nuclear space projects. An advisory board of European (nuclear), Russian and US experts to review progress and compare the results of the study investigations with their own experience was included in WP30. They were also able to advise on past, current and potential future activities in European terrestrial and Russian and US space nuclear power.

30 and 200kWe nuclear power generator levels were initially selected because it was anticipated that there could be differences in applications and implementation. 30kWe was thought to be the smallest sensible size for a nuclear fission generator and 200kWe the largest that could be launched on an 'Ariane 5 ECA' using next generation technology within foreseen safety constraints. Although some divergence in the range of applications was detected technical, infrastructure, resource, safety, sustainability and public acceptance was found to be similar for both power levels.

30 kWe fission nuclear power generator (WP31)

Applications

The applications identified for a 30 kWe nuclear fission generator were:

- NEO rendezvous and survey;
- small robotic science and exploration missions to the outer solar system;
- power generation for planetary outposts (although the higher power levels might be needed in the longer term);
- high power radar, laser and high data rate / long distance communications.

Radiation

A review of radiation hazards for both humans and electronic components was made. The main conclusions were that the mass of shielding required for human protection from the space radiation environment alone was likely to be prohibitively heavy and one viable solution to be considered is a fast 'trip times' (so a 30 kWe power generator was not powerful enough to give the necessary velocities). It was noted that the electronic component hardening criteria for the US SP100 project prevented failures in test but component degradation suggested further testing to be advisable.

State of the art

A review of past and current projects and studies concluded that: 'Past experience indicates that fission nuclear power generation is technically feasible. Subsequent studies however indicate the need for significant technical development in Europe to realise the performance identified in the range of proposed applications. Current Russian plans for the Megawatt Class NPPS programme development are understood to be based on existing lower temperature nuclear fission reactor and power conversion technologies. This is made possible through the development of the droplet radiator.'

200 kWe fission nuclear power generator (WP32)

Applications

Although it was considered that a 200 kWe nuclear fission generator could perform the same applications as 30 kWe, higher power would be needed for:

- NEO deflection;
- larger robotic (e.g. sample return) missions to the outer planets or beyond;
- support for manned missions such as to transport the infrastructure for landing and ascent on Mars in an acceptable timescale;
- removing 'dead spacecraft' / debris: if safety can be satisfactorily addressed.

Electrical power components

Although 30 kWe is within the range of current space electrical power devices 200 kWe requires the space qualification of a new generation of components. Special consideration is also needed for protection against large load fluctuations (e.g. unplanned large electric propulsion system shut down) and the energy required to commission a reactor from a cold start. Long conventional high power harnesses are heavy and can benefit from research into high temperature super-conductors.

Nuclear electric power generation (WP30)

Structure

The common findings from WP31 and WP32 are brought together in the fission nuclear power generator roadmap. Detailed information is in five appendices, namely:

- Appendix A: Past and current projects and studies
- Appendix B1: Applications (descriptions of all potential applications)
- Appendix B2: Applications review (applications prioritisation)
- Appendix C: European organisations with capabilities to support a space fission nuclear power generator programme
- Appendix D: Principles of public acceptance.

Technical

A review of technical options indicated a preference for closed cycle Brayton power conversion with either an indirect liquid metal cooled or direct gas cooled fast reactor for both power levels. Stirling cycle power conversion is efficient and well researched in the US and subject of European Space Agency (ESA) radio-isotope based projects in Europe. At 30kWe it was considered that Brayton technology is marginally more resilient and is scalable up to MWe power levels. Materials research into the high temperature operation needed to achieve optimal mass efficiency for space reactors (including coolant and control systems), Brayton turbo-alternators and radiators is necessary to determine the trade-off between liquid metal and gas cooled. Research is also needed into very high power electrical equipment (especially at high temperatures). The second advisory board also advised against totally rejecting thermo-electric and thermionic power conversion although Europe has no space expertise in these areas.

European capabilities and capability development

A representative (rather than comprehensive) review of the capabilities of European government organisations, research centres, industry and universities indicated potential expertise and infrastructure for all aspects of a European space nuclear fission programme. 'Generation IV civil terrestrial reactor' research includes high temperature liquid metal and gas cooled projects. These are designed to operate at up to several hundred degrees below optimal temperatures for space systems and are rather larger. However, there are many useful synergies, particularly in associated materials research, which suggest opportunities for mutual benefit.

The survey included nuclear and non-nuclear space industry whose capabilities included power conversion, structures (eg radiators), power management and distribution and project and mission management. Europe also has the facility to launch and operate conventional major space programmes and is active in developing a safety framework to include nuclear mission in the future. Potential interest in a European space nuclear fission programme was expressed by many of the organisations contacted in the survey and covered all aspects. Evidence of programme sustainability is seen as a pre-requisite by government and industry.

European capabilities will have to be developed in terms of technical advances, infrastructure and practical experience. The technical advances are initially mainly in the field of materials research and in due course a prototype research reactor. There is the possibility of some joint use of 'Generation IV' research facilities and renovating and using redundant, relevant infrastructure from civil and submarine projects. Practical experience is essential for success in such a programme.

At the second advisory board, the Director General of the Keldysh Research Centre invited Europe to participate in the Heavy spaceship and NPPS project. He suggested European support for the project would be very helpful and there was scope for European participation in space turbo-alternator development and research into materials for high temperature reactor, shield and turbo-alternator technology. This is the only current opportunity for Europe to gain practical space nuclear fission experience and investigating collaboration is strongly recommended.

Resources

No significant differences were detected in assessments of cost and schedule for 30 kWe and 200 kWe power levels. The cost and schedule for a European nuclear fission programme is difficult to determine. Comparison with the US Prometheus and Russian NPPS programmes suggested significant differences: for example, Prometheus inception to JIMO launch approximately 14 years and programme costs US 7-9 billion; NPPS inception to launch approximately 8 years and development cost US 0.56 billion.

This is partly because of the different range of expertise and infrastructure in Europe, Russia and the US and partly because the different projects have very different starting points. Prometheus was essentially a new development of a relatively high temperature reactor incorporating the quality control in the US nuclear submarine programme. It included an expensive fuel development project and a full mission (JIMO). The MEGAWATT Class NPPS is based largely on current technology and is able to draw on other Russian development programmes.

Advisory board

A view of the advisory board is that it would take a decade to make the technical advances to realise the next generation of space fission nuclear power. Based on Russian and US experience (and taking account of former EC project HIPER and other European studies) this indicates that Europe's first nuclear fission spacecraft could be launched in the 2030 - 35 timeframe. It also assumes that critical research starts in the Horizon 2020 programme in 2015 and that initial results are able to support mission analysis during the same period and both support first mission project phases A and B.

Fission nuclear power generation roadmap

A roadmap schematic (see the slides in the attached final report presentation) illustrates the links between mission selection and definition, technical and expertise development and creating the required infrastructure. The iterative process optimises mission performance specification with technical progress, expertise and infrastructure. Feed-through' to follow-on missions creates a sustainable programme. Recommendations focus on near term enabling research and development, mission analysis and gaining practical experience.

European fission nuclear power generator main achievements:

- First advisory board of European (nuclear), Russian and US (space nuclear) experts
- First survey of European capabilities to support as space nuclear programme
- First funding and resource requirements assessment from Russian and US experience
- First roadmap for both organisational and technical programme requirements
- First strategy for a workshop to develop Horizon 2020 research activities.

Public acceptance (WP33)

The primary objective consisted in understanding why the public opposes some technical or scientific projects and supports others and applying a strategy to ensure the social support for follow-up projects based on the results of DIPOP. The question is traditionally linked to the notion of the so called 'public acceptance' which is a social emergence. Thus, the package has a unique character in the frame of DIPOP, dealing with social, cultural and communicative issues. Initially, it was assumed, that merely safety and sustainability concerns were a driver for the social dynamic towards acceptance or refusal which is partly true. Consequently, a brief safety and sustainability study was conducted and has been released as report. Yet, a first literature research in the topic and a critical rethink documented in report based upon present day examples revealed a more complex situation, affirmed in the continued study. To begin with, the terminology 'public acceptance' proved to be flawed for insinuating the premise that the project in question was in a bad shape. Obviously, respecting normal ethics and normal business practices, this should not be the case. In the understanding obtained through the activities performed, the objective consists in comprehending how project responsible can at best receive public support or public adoption or just classically solidarity of their project, and at least avoid public resistance against it. Further, a theoretical model to understand the matter was evolved in a manner in which findings from the continued literature survey were compared to observations from a contemporary local and concise case, the Stuttgart-21 railroad and main station project. Instances of public support and resistance happened in or very near to the city of Stuttgart where DIPOP consortium member USTUTT is located in the time frame of a couple of years, accompanied by the involved researchers.

The terminology public support is quite self explaining. It describes a social state in which a significant part of a society has a positive or at least neutral stance towards a given project which may be among others of a scientific or a technical nature. Its opposite is a public refusal or resistance. For an individual, the decision among these positions depends on the result of a rational / emotional balance and the related facets of project relevant questions. For example, one may rationally ask 'Does it pay?' but also question emotionally 'Is it worth it?' or, in another example 'What can they prove?' yet 'Can we trust them?' Consequently, merely a fact oriented approach to favour public support, which can be identified as public understanding strategies, may risk failing. However, also a mere social approach, such as the social implementation concept focussing on mutual communication, participation and integration will not work well without the transmission of any rational information. This makes a case for an interdisciplinary approach encompassing natural and social sciences as well as economic sciences; especially as risks are concerned. Risks may cause the public to withdraw support from a project. Typically, technical risks are calculated and minimised by various means. Yet, it was developed, that there are two additional interdisciplinary risks: social risks, i.e. for example project responsible who disrespect the public interest; cost risks, i.e. socialised external costs from accidents, pollution and other undesirable emergences. The first encompasses social and technical aspects. The risk can be resolved through communication / participation and the definition of roles of responsibility. The latter is situated in the domains of economy and technology. Analogously to the former, cost risks can be reduced by definitions of liabilities.

According to this theoretical model, a practical strategy how to obtain a better public support for DIPOP as detailed in report was devised from abstract recommendations of behaviour such as personal social maintenance. One of the key elements in the practice is to realise a good social implementation by participation in public events such as science fairs and in social media. Another one is to strengthen modern means of communication for public understanding. It is recommendable to start a public dissemination of relevant findings of the project in for example Wikipedia. A third cornerstone is the practice of transparency, which nowadays is a must.

As far as the study in this work allowed understanding, the acquisitions of this work appear novel and unique. Despite many other larger projects which already encountered issues of resistance, and despite the intuitively appearing interdisciplinary approach, such has seemingly never been a subject of studies. The similar absence of scientific literature on the topic of the case example of Stuttgart-21 can however be explained with its recent status. Thus, it appears recommendable to encourage researchers in engaging in well funded projects to analyse the respective public support / resistance. Stuttgart-21 is a unique chance to understand underlying process and to create reliable data bases. Another interesting recommendation is to further and improve the theory which is currently sufficiently abstract to be applied to a space technology support project of the EU and EO IPSO to the Stuttgart-21 project. This condition allows to expect further application in other projects.

In WP40 and sub-WP, the main objective was the study of applications.

It was studied the situations related to disruptive space power applications in the fields of space exploration and space situational awareness for space nations like Europe / ESA, US, Russia and Ukraine, China and India. Power in space is a key factor in all space exploration missions from the early, small robotic missions, to a later foreseeable large-scale human presence on Moon, Mars or asteroids and the outer solar system and beyond. The main challenges for power generation are to cope with the harsh environment and provide as much power as needed at a minimum mass particularly where energy from the sun is weak. To receive a leading and strong European position in future applications in space exploration and exploitation like in space science, space situational awareness and habitation new strategic developments for EC space policy, European launcher and spacecraft industry are necessary. Insofar, it is proposed by DIPOP study team to concentrate for further EC space power funding in the four branches:

1) space habitation
2) space exploration
3) space situational awareness and
4) long lasting human space missions to asteroids, Mars and the Moon.

In detail, it is recommended that EC activities should be concentrated on the following three targets and related space power research and technology activities:

1) Low Earth orbit (LEO): Here the space power systems are typically laid out for operational times of about 5 to 15 years, thus long period power supply technologies are needed.
2) Moon: Lunar Missions typically last several days to weeks excluding longer lunar surface expeditions, thus the power requirements differ from the LEO application. On surface there are 14 days intervals with sunlight and without sunlight. Technological including financial support for power in lunar habitats should be also under consideration of EC.
3) Mars / asteroid: Missions towards Mars or asteroids last between 180 days and two years with a greater distance to the Sun. Here, the power requirements are a mixture of LEO and Moon scenarios with additional more restricted constraints regarding energy, mass and life support. Fission nuclear power alone can give the high energy levels for rapid response to deflect earth threatening NEO or more controlled orbital correction over longer periods using NTP in the first case and nuclear electric propulsion (NEP) in the second. These high energy levels are also needed for large robotic missions to the outer solar system, large infrastructure transfer to Mars and potentially for human missions.

Related to the three above mentioned three targets categories, under consideration of economic situation and public attraction Europe must focus on one target in close discussions with the three space fairing nations like the US, Russia and Japan. Having in mind recent meteoroid falls in Russia and related security aspects, NEO encounter between Earth and Moon and several European / Japanese exploration and sample return mission to comets / from asteroids under consideration of future capabilities of potential space body / asteroid mining Europe should find its place in manned, nuclear asteroid rendezvous or even landing.

Especially EC should focus for further EC R&D Horizon 2020 activities related to space exploration technologies and SSA applications (also NEO focus). The preferred disruptive power technologies have different rankings for the transfer, robotic, life support systems and tugs. Especially the ultraflex solar panels, Li-ion batteries, unitised regenerative fuel cell, advanced Stirling isotope generators and high temperature superconductors are ranked on the top together with fission nuclear power. More general: a mixture of tailored space qualified batteries, solar panels, fuel cells and radioactive power systems should be in the focus of Horizon 2020 disruptive space power research and technology developments. Applications of the studied disruptive power technologies for SSA satellites have the restriction of long lasting operations respectively safety and in addition security issues. Therefore, batteries, panels, cells and radioactive devices are in principle applicable for European SSA satellites, but it has to be mind, that EC can play only a role in SSA applications by means of independent European based and owned disruptive space power technology development.

Summarised space propulsion recommendations

In conclusion from the application working packages of DIPOP, the view of DLR in charge of the study is that CDWE shows a strong performance increase (up to 18 % to 19 %) without modifying the current launcher size of Ariane 5. This is very important: it allows the reuse of the existing facilities of Ariane 5 at the European spaceport in Kourou. A further increase of the performances of such propulsion requires a greater launch vehicle. That propulsion is probably not as disruptive as nuclear thermal propulsion or the SABRE engine. However, its development would be less risky and faster as many existing technologies could be reused. Only the combustor would have to be exchanged. Tanks, feed lines, turbo-pumps could be reused from today's launchers. In addition of allowing a reduction of the development time, it would also reduce the development costs. The capability to develop and build such propulsion in Europe would be beneficial in order to keep the leading role of Europe on the commercial future launcher market. It would also broaden the capabilities of Europe by allowing for instance space exploration missions with smaller launch vehicles. For these reasons, DLR suggest that it seems wise to support such propulsion research more actively instead of concentrating only on classic LRE - because LRE will never be able to provide comparable performance increases-.

Because microparticle propulsion, in the sense of solid micro particles, needs still the described research, it is hard to believe about space missions with microparticle propulsion in the next decade. In contrast, colloid thrusters are already considered for contemporary missions like ESA's LISA pathfinder and several satellite formation flying missions. According to DLR, to receive in future microparticle thruster space mission applications the following research - to be funded by EC - is required:

- more activities with respect to real realisation of solid microparticle thruster; and
- increase of investments in the development and maturing of liquid droplet thrusters.

Potential impact:

DIPOP study results in space power and propulsion technologies and their several important ground based infrastructure security related aspects as well demands of space infrastructure protection plus the proposed space power and propulsion application missions must careful consider potential effects on public and political / governmental issues by:

a) public, governmental and international acceptance;
b) economic growth (especially for European space industry in space robotics and other new space fields / contracts);
c) scientific and technological realization in the international context;
d) further leading role / increasing strength of European countries in space;
e) work sharing between governmental and private space business activities, for instance also related to the aspects of laws for space mining and profits; and
f) Europe's potentially, leading role in future space history: the less promoted role of unmanned Titan landing (due to ESA's Huygens probe to this Saturn moon) will be much more highly visible by a manned asteroid landing.

Under consideration of issues a) to f) the exploitation of DIPOP results will be continued by talks and publications of DIPOP consortium members in high level conferences like COSPAR assembly, IAF congresses, tailored space power and propulsion congresses as well as by means of political, organisational and industrial lobbying. A special, nearby dissemination activities is the foreseen contribution by DIPOP talks in the MEGAHIT project workshop. Moreover, there was a first flow of knowledge due to the first DIPOP meeting with potential member of the above mentioned project in 2012 and further promotion is foreseen by participation of DIPOP consortium members at the above mentioned workshop in Belgium for the international political, industrial, organisational and scientific community. In the timeframe of the above mentioned workshop, public EC activities may be strongly promoted towards public release of a European roadmap of disruptive - including low and high energy fission nuclear space power and propulsion systems with a tailored, international space mission under leading European participation.

Project website: http://www.DIPOP.eu

Final Report Summary - DIPOP (Disruptive technologies for space Power and Propulsion)

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