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Small debris removal by laser illumination and complementary technologie

Final Report Summary - CLEANSPACE (Small debris removal by laser illumination and complementary technologie)

Executive Summary:
The number of pieces of debris in Low Earth Orbit is rapidly increasing with, in the short term, potential collisions between debris and space assets. This is why research and technology activity in this field is becoming one of the corner stone of European Space policy in order to protect European satellites and launchers as well as securing long term commercial use of space. This initiative also intends to protect the environment from the possible chain reaction of debris production.

The CLEANSPACE study is an answer to FP7 Security research call SPA-2010-2.3.02 “need to protect space assets from on orbit collision” by defining the necessary requirements for the safe and routine removal of small space debris between 1 and 10 centimetres in Low Earth Orbit with ground-based high energy laser stations in order to protect valuable space assets from destructive on orbit collisions.

A system of ground-based laser stations would create a very small thrust on space debris by ablating its surface. Ultimately, the impact of such lasers would modify the velocity of the space debris, which would lead it into a lower orbit. Hence, the concept would allow both for changing the course of a piece of debris, thereby avoiding a predicted collision with valuable space infrastructure, and ultimately the removal of the waste as its new course takes on a course to atmospheric re-entry.
Figure 1: Laser Debris Removal

Project Context and Objectives:
CLEANSPACE is a three year project which began the first of June 2011.
The overall CLEANSPACE objective is to define a global architecture (including surveillance, identification and tracking) for an innovative ground-based laser solution which can remove hazardous medium debris (from 1 cm to 10 cm) around selected space assets. This approach is divided into three steps:
• To propose an efficient and affordable global system architecture by taking up survey, tracking, identification and debris treatment by laser system in a way that is complement with the ESA Space

Situational Awareness (SSA) program,
• To tackle safety regulation aspects, political implications and future collaboration,
• To develop affordable technological bricks and to establish a roadmap for the development and the future implementation of a fully functional laser protection system.
A system of ground-based laser stations would create a very small thrust on space debris by ablating its surface. Ultimately, the impact of such lasers would modify the velocity of the debris, which would lead it into a lower orbit. Hence, the concept would allow both for changing the course of a piece of debris, thereby avoiding a predicted collision with valuable space infrastructure, and ultimately the removal of the debris as its new course takes it on a course to atmospheric re-entry

Project Results:
Thanks to research and technology developments regarding laser, technology reviews for accompanying technologies, laser debris removal architecture study, elaboration of system requirements, trajectory simulations and evaluation of “policy, ethical and societal” implications, the CLEANSPACE study dealt with an innovative ground-based laser station network, which allows protecting space assets from orbit collision regarding small size debris.
The CLEANSPACE exploitation phase allowed to synthesis and to highlight all the major outcomes and outputs of the project which are reviewed below:

3.1 The system requirements
The system requirements were elaborated leading to 51 requirements, of which 5 business type, 29 product type and 17 process type. The review was based on the current situation concerning space debris regulations, the actual and predicted debris population, the hazard potential of space debris and the actual monitoring techniques and networks.

3.2 The main functions of the Operational concept
Survey, identification and trajectography of debris, de-orbitation strategy, characterization and highly precise tracking of debris, laser pushing system with adaptive optics, evaluation of orbital modification and re-entry predictions were identified.
The monitoring of space debris with high accuracy is a prerequisite for laser debris removal. Active optical observation systems will provide unprecedented precision, even for cm-class debris, by combining highly accurate determination of angular coordinates with precise distance information from time-of-flight measurements with laser pulses (laser ranging)

Figure 2: The role of active-optical monitoring in LDR strategy

Figure 3: Debris tracking mock-up from CLEANSPACE Demo-Day
The pushing phase is the other main function of the debris removal concept. Irradiation of the debris particle with high laser fluence induces an ablation process at the particle surface, creating a plasma jet of ablated material, and generating a laser-induced force on the debris particle due to the recoil of the jet.

Figure 4: Laser-induced ablation of material causes a recoil momentum
This pushing phase create a deceleration of the debris particle, a trajectory transition to lower orbit and then a burn-up in the atmosphere.
This phase has been studied inside the project by a demonstration in vacuum illustrated in the figure below and demonstrated during the demonstration day.

Figure 5: A “laser wheel” driven by laser ablative thrust demonstrates the process of laser ablation propulsion

3.3 International Space Debris Removal Organization concept
To ensure lasting international support and a smooth debris removal process on the whole, an international organization has been proposed. This International Space Debris Removal Organization (ISDRO) would have an international legal status and would coordinate and supervise the global laser debris removal process, managing data catalogues and providing information to all authorized organizations.

Figure 6: ISDRO concept
3.4 Laser safety
Regarding Laser safety some guidelines have been identified as for the Laser Debris Removal (LDR) station to be located far away from airports and air routes, located from populated areas at a minimum distance of around 7.5 Km. For the operational concept, the permanent and temporal limitation of the solid angles used for LDR during operations have been studied (mainly arcs oriented in North-South direction covering the typical SSO orbits of the debris). The results are synthesized in the figure below:

Figure 7: Laser safety areas to protect

3.5 Laser station location
Location of stations has been studied, especially with respect to identification of the criteria for the selection of possible sites. Core criteria are geographical latitude, altitude, cloud cover and preliminary laser safety considerations. Applying these criteria to a selection of astronomical sites and satellite laser ranging sites, 15 possible locations have been identified.

Figure 8: Access to objects on sun-synchronous orbits from Kourou (green), Grasse (pink), Kiruna (white)
3.6 Laser architecture
The scalable laser architecture is one of the main output of the study. Merged from the two initial laser concepts (one from CILAS and one from DLR) and from an external work done at CILAS, the third architecture is using the best concepts and especially the actively coupled Nd:Yag thick disks amplifiers.

Figure 9: Suggested active beam control setup for coherent beam combining

For this topics two other important progress are to mention: the first one is the laser architecture moved from passively couple coherently high energy pulse laser beams to a new phase locking approach of a beam array in an active way. For the second one, the ceramic topic is to underlined with the possibility achieving quite large laser matrixes including cladding around a central area within a monolithic piece which is highly suitable for high energy lasers. This potentiality have been demonstrated on a Y3Al5O12 (YAG) matrix, which is the final matrix selected by the project.

The heart of a laser debris removal system is the laser source. The investigation of suitable laser technologies for future high energy laser sources is a key objective of the CLEANSPACE project.

Figure 10: A demonstration setup based on thin-disk laser technology

Figure 11: “Thin” and “thick” disk for high energy
Debris removal through laser matter interaction requires extremely high pulse energy with relatively high repetition rate and very good beam quality. This last point is very important in order to ensure a high laser energy fluence on the debris to produce the “pushing” effect. All these specifications lead to a very challenging laser design. To overcome material limitations, a demonstration setup has been installed allowing the coherent coupling of nine laser beams of moderate energy. This coherent beam coupling is able to generate a “super-mode” with the combined energies and a beam quality close to that of a single beam.

Figure 12: A demonstration setup based on active coherent coupling of nine pulsed laser beams presented during Demonstration Day

On the contrary to single-crystal growth technique, the ceramic technology allows elaborating large size samples with complex shape and luminescent dopant repartition. During the project it has been demonstrated the feasibility of large active media for high power laser operations.

Figure 13 : Ceramics in the form of Nd:Lu2O3 disc (a), Nd:YAG disc (b), Nd:YAG disc with YAG cladding (c), Nd:YAG slab (d).

3.7 Laser matter interaction
Laser matter interaction topics has confirmed that irradiation of the debris particle with high laser fluence induces an ablation process at the particle surface yielding a plasma jet of ablated material and laser-induced force acting on the debris particle due to the recoil of the jet. The parameters which influence the laser/matter interaction are the material properties, the laser pulse fluence, laser wavelength, pulse length and temporal shape, polarization and incidence angle.

Figure 14: Regimes of laser- matter interaction: Generation of plume and momentum.

Figure 15: Experimental data on momentum coupling for space debris relevant materials.
3.8 Trajectory prediction for single pass operation
Orbital tools and simulations of laser effects have, thanks to precise predictions with the different geopotential models (with all perturbation factors on the highest accuracy level) confirmed the feasibility and evaluated the potential gain in term of reducing the lifetime of a representative small debris for one pass to 6 months.

Figure 16: Debris deorbiting by pulsed laser illumination within one pass.

Figure 17: Simulated altitude change and remaining lifetimes for debris object TLE # 4877 after illumination in one pass mode for various repetition rates.

3.9 State of the art and market review
Main components (hardware and software) have been evaluated and the TRL level has been determined for:
• Telescope, adaptive optics and Satellite Laser Ranging technologies are close to the required level of performances (TRL ~ 5-6),
• High precision tracking technologies requires some developments, according to the high accuracy and the high velocity that are required to aim at the target with a large structure (TRL ~ 4),
• Imaging technologies require very high resolution performances to characterize 10cm class objects. A 10 cm resolution is within the actual state of the art for LEO objects (TRL 9).


Starting from the actual state of the art, the realization of a LDR system can be separated in two phases. Phase one will deal with
• necessary technology steps, chiefly concerning the laser development
• the integration of several technologies into a demonstrator
• the implementation of a first debris monitoring and cataloguing network
• the political implementation
The total time span required for phase one is 5 years. The different tasks are only weakly interdepending: parts of the developed laser technology must be ready in time to be integrated into the demonstrator; the successful demonstration is the base for a funding decision for the next phase, finalizing the political implementation.
The second phase can be started only after a commitment of the European Union and some additional major space faring nations to ground based Laser Debris Removal and a funding decision for the realization of the LDR system. In this phase, the LDR station will be constructed and the high energy LDR laser, the telescope and some additional optical components will be fabricated and integrated into the LDR station. It seems feasible to realize an operational LDR system with 5 years time span for the second phase.

From the time schedule for the different tasks, several technical milestones were identified. The core milestones in phase one are:
• the successful coupling of a high number of pulsed amplifiers as evidence for the feasibility of the intended laser concept
• the successful high power illumination of a space object as demonstration of the successful integration of the different technologies
• the creation of a first catalogue of medium space debris objects as prerequisite for engagement planning and debris removal

In phase two, the core milestone is the completion of the LDR station construction as this is the prerequisite for the installation of the high energy LDR laser and the telescope on site.
Besides the technology steps concerning the high energy LDR laser, also for the telescope architecture, the fast tracking mount, the adaptive optics and the identification of debris, the necessity of further technology steps was recognized.
For a successful implementation of a LDR system, some additional political and legislative actions are required, dealing with an adaption of laser safety regulations and the implementation of an international organization for the coordination of debris removal activities.

As a conclusion, once can retain that such an innovative ground-based laser station to deal with small debris is feasible:
• feasibility determination has been confirmed with scalable technologies,
• after a 10 years program effort, a first LDR station may exist.

Potential Impact:
The expected final results and their potential impact:
CLEANSPACE will significantly contribute to the development of European capacity to protect space assets from space debris by tackling the issue of medium size debris with a ground based laser solution. CLEANSPACE proposes a solution that could protect the surroundings of European space assets but also space assets manufactured by European industries.
CLEANSPACE will mainly contribute to the architecture elaboration of the future laser protection system and to the most critical technologies development. CLEANSPACE will help EU and ESA to elaborate a roadmap for the development of such a system.
Most of the technologies developed or implemented in the frame of the Space Situational Awareness (SSA) program will be reused, improved if necessary and implemented in the CLEANSPACE system to reach the necessary precision for safe and efficient laser operations. Moreover, the core of the project is well focused on topics which are not taken up in SSA. So CLEANSPACE is fully complementary to the SSA program and should provide an improvement of the European capacity in terms of precision for the tracking and the forecast of orbits of small and medium debris.

Societal impact:
For a society which is relying on spacecraft for various purposes (communication, navigation, environmental monitoring, surveillance, fundamental research …) and with an increasing economic impact, space debris is an important issue. If nothing is done, on the short-term scale, it will increase the costs and consumption of natural resources for of space application, on the long-term scale it might lead to a cumulative effect, making space missions nearly impossible.
A laser debris removal system will be an effective and cost efficient way to mitigate these problems. Additionally, space debris can also be a threat for humans or infrastructure on ground. Depending on the characteristics of the objects and their trajectories, space debris objects can hit the ground, and have the potential to cause damage. In the case of uncontrolled de-orbiting, the location of the impact cannot be precisely predicted and typical advance warning times would be less than a few hours.
A laser debris removal system would enable the controlled de-orbiting of smaller space debris objects, choosing a suitable location for the impact which reduces the threat for humans, infrastructure or ecology.

Economic impact
Due to political issue linked to the use of a high power laser to protect space assets from on orbit collision by debris, future international collaborations are the only way to assure that this concept will become an operational system to protect space assets. CLEANSPACE is the first step to this future international collaboration. To propose CLEANSPACE at European level instead of national or local levels will help Europe to acquire key competences, to be considered as a credible actor at international level and in the near future to be able to participate at international level in discussions involving the main space actors: the USA, Russia, and China …
At a European level, the main impacts of CLEANSPACE are:
• To position Europe as a key and credible actor in space assets protection. Thus Europe won’t have a solution and regulation imposed by others and could conversely propose to them innovative solution.
In the long term, it will help secure the European access to space which is indispensable for our economy,
• To orient international thinking , regulations and certifications by advisory groups, and at the UN level about protection issues,
• To elaborate doctrines to avoid irradiating satellite both by an intentional misuse or when debris and satellite are too close,
• To propose new possibilities to ESA in this field,
• To support space missions mainly those to the ISS by providing effective protection.

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