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Improving Low Earth Orbit Security With Enhanced Electric Propulsion

Final Report Summary - LEOSWEEP (Improving Low Earth Orbit Security With Enhanced Electric Propulsion)

Executive Summary:
The total mass of space debris in the low Earth orbit region is estimated to be close to 2,500 tons. About half of this mass is composed by rocket upper stages clustered in high inclination orbital regions. Because they are grouped in a relatively small number of families, acquiring the capability to deorbit just a few upper stage types would lead the way towards the elimination of hundreds of tons of debris material in the future. The goal of the LEOSWEEP project (improving Low Earth Orbit Security With Enhanced Electric Propulsion) is to demonstrate the technological feasibility of a first active removal mission of a Ukrainian rocket upper stage, prove its economic viability, and propose a convincing legal and policy implementation to “kick-start” large-scale active debris removal activities in Ukraine, Europe and other space faring nations in the future.
Project Context and Objectives:
The total mass of space debris in the low Earth orbit region is estimated to be close to 2,500 tons. About half of this mass is composed by rocket upper stages clustered in high inclination orbital regions. Because they are grouped in a relatively small number of families, acquiring the capability to deorbit just a few upper stage types would lead the way towards the elimination of hundreds of tons of debris material in the future.

The goal of the LEOSWEEP project (improving Low Earth Orbit Security With Enhanced Electric Propulsion) is to demonstrate the technological feasibility of a first active removal mission of a Ukrainian rocket upper stage, prove its economic viability, and propose a convincing legal and policy implementation to “kick-start” large-scale active debris removal activities in Ukraine, Europe and other space faring nations in the future.

The Ion Beam Shepherd (IBS) concept is employed as the key removal technology where the use of ion beams provide an efficient and contactless manipulation of the debris to be deorbited. The IBS is essentially a “contactless” actuator, which allows modifying the orbit and/or the attitude of a generic object (the “target”) using the momentum transfer of one or more ion beams produced by Electric Propulsion (EP) thrusters on-board a nearby spacecraft (the “shepherd”), and properly pointed towards the target by means of the shepherd’s attitude control that includes Chemical Propulsion (CP) thrusters. A schematic view of IBS operation scheme is presented in Figure 1 1.

In order to prove the feasibility of the proposed solution and prepare for its future implementation a series of key milestones will be achieved:

1. A detailed understanding of the physics underlining the concept.
2. The identification of key technological challenges and concrete solutions.
3. The assessment of the concept capability in dealing with large-scale removal operations.
4. The development of ground-based laboratory experiments.
5. The definition of a clear technology and policy development roadmap.
6. The pre-phase A design of a small technology demonstration mission.
7. The exploitation and dissemination of the proposal outcomes.

A world-class international team of universities and industrial partners from Europe and Ukraine was formed in order to perform this study with a high level of theoretical and technical expertise in all relevant fields.
Project Results:
The overall strategy of the work plan is developed in four main phases (Figure 1-2).

During this third report period, work has been focused on phases 3 and 4, resulting in the whole Project completion. The results were presented in November 2016 during the Final Presentation at European Commission Research Executive Agency premises in Brussels.

The second period concluded with the IBS Mission and Platform Design Review and the ITT Acceptance Review. Departing from those, this third period has been focused on consolidating the proposed IBS demonstration mission design, its GNC, the DSF tool as well as the ITT thruster core testing activities development, execution and analysis. The overall Acceptance Review took place in summer 2016, proceeding to the final LEOSWEEP phase, were the Project’s results have been assessed and analysed as a whole.


Phase 1: Requirements specifications

In this phase the mission was preliminary designed. The main issues, technical challenges and key points characterising the Ion Beam Shepherd were identified.

In addition to this a list of priority targets of Ukrainian upper stages for removal from Low Earth Orbit was produced, analysing the close approaches probability and identifying most critical targets requiring Active Debris Removal (ADR). Information about the Ukrainian launchers upper stages that could serve both as launch vehicles for IBS and as targets for the LEOSWEEP mission, was also compiled.

All these activities served as inputs to the Mission Review (MR), where the baseline was defined for LEOSWEEP mission future studies, setting the foundations for coming more detailed design activities. The baseline under study in LEOSWEEP was agreed to be a deorbiting mission for a Cyclone-3 upper stage removal from an initial 639km orbit to a 300km orbit.

Once the mission was preliminary defined, the project requirements were flown down and distributed to the team, iterated and consolidated: mission requirements, IBS platform requirements, Impulse Transfer Thruster (ITT) requirements, etc...

Phase 1 ended with the Requirement Review (RR).


Phase 2: Design & Analysis activities

Departing from the requirements specification for the mission, the team started to work on the design and analysis activities defined in Project phase 2.
These activities have been split into two different blocks, progressed in parallel.

On one hand, the Platform and GNC technologies are analysed and designed. In this sense, the Platform design first iteration has been concluded, developing the design and components selection for all the subsystems comprising the platform (Propulsion, Power, Structure, Thermal, Command & Data handling, mechanism, Telemetry, Tracking & Command subsystems). This design has been concluded with the preliminary calculation of system budgets, both mass and power.

The Design Simulation Facility (DSF) related tasks have also progressed. During the first report period, the DSF requirements were consolidated. Furthermore the DSF constituting blocks were clearly defined and the interfaces among them were established. During this second report period the different DSF constituting blocks (sensors, actuators, DKE, GNC) have been designed, coded and integrated into the simulation facility, as well as validated for the Shepherding Phase.

On the other hand, the ITT design, construction, manufacturing and assembly tasks have been finished. During the first period, the thruster requirements were consolidated after being iterated among mission, system and thruster responsible. In addition to this, the ion beam modelling activities were also started. During this second period, ITT design was consolidated, and the manufacturing and assembly have also been finished taking into account the design restrictions.

Interactions between the two development branches have been necessary and have occurred during their progress.

Phase 2 was concluded with the Design Review (DR) for both the mission, platform and ITT and with the dedicated ITT Acceptance Review (IAR).


Phase 3: Testing and Design Consolidation

The phase 2 concluded with an assembled ITT thruster ready for tests, as well as a preliminary IBS Mission and System design.

During phase 3, the Impulse Transfer Thruster has been extensively tested in order to characterise its performances and to check them against the requirements established in phase 1. In addition to this, two specific test campaigns have been developed to study and analyse, on one hand, the impulse transfer efficiency from the thruster to a target located 7m away from its exit and, on the other hand, the sputtering effects of a high energy ion beam that impinges a representative upper stage surface target probe. These results have served to confirm the suitability of the designed and developed ITT for ion beam shepherding, as well as to predict how the proposed specific operation of the thruster-target system may impact the IBS platform lifetime and performances.

The electric propulsion test campaign execution have been supported by key facilities at three different sites: U. Southampton, DLR Göttingen and ITM premises in Dnepropetrovsk). These facilities have been equipped and customised to host the LEOSWEEP electric propulsion tests, providing very valuable results for the Project.

Along with these activities focused on the ITT thruster testing, the Team has also worked on the evolution of the preliminary design of IBS mission and platform.

On one hand, the Design Simulation facility, concluded in phase 2 for the shepherding phase modelling, was validated also for the rendezvous phase of the mission. In this way, the tool was available for the extensive test campaigns that were carried out in phase 3, simulating different IBS operation scenarios. The DSF has resulted a very important tool for designing, analysing and validating the Guidance, Navigation and Control methods, sensors, actuators and algorithms proposed in previous Project phases. The results obtained from the different simulations and tests run have been of high importance to analyse the best control practises that could help in reducing the propellant consumption during the shepherding phase, nowadays one of the main drivers of the IBS mission design.

On the other hand, this phase has also contributed to the Project with an important input: the legal and policy implementation framework analysis and definition for the IBS demonstration mission. With focus on the mission baseline defined in previous phases, the collaboration scenario between Ukraine and Europe for Ukrainian upper stages active removal has been analysed, different solutions have been proposed, and draft documents for the contractual relations among the parties involved have been formulated.

LEOSWEEP’s Phase 3 concluded in summer 2016 with the overall technical activities Acceptance Review (AR).


Phase 4: Project Results Assessment

The Acceptance Review meeting made available more than 100 documents for review and assessment. This review process served as a basis for further iteration and refinement of some of the IBS spacecraft design options. For instance, the results related to propellant consumption for the shepherding phase were considered to update the Platform System budgets. In addition to this, some subsystems were subject to a new design iteration. In this way, the IBS mission was consolidated and a valid design solution was proposed, discussing, when applicable, how to overcome the non-compliance towards some of the requirements specified in Project’s phase 1.

Apart from the IBS Platform design consolidation, the LEOSWEEP assessment was developed by comparing the original Project’s goals to the outcomes achieved from the different tasks and activities carried out so far. In this way, the Project’s results were presented and discussed as a whole.

The critical technologies and future tasks towards a first IBS demonstration mission were identified, the phase 4 concluding with an analysis of the development needs for the IBS to be proven in Space in a 5 years horizon. Results dissemination, Intellectual Property protection strategy as well as exploitation of the LEOSWEEP results beyond Project’s duration were also analysed in this phase 4, summarising the main findings in the corresponding concluding reports and plans.
Potential Impact:
LEOSWEEP intends to pave the way for large-scale active debris removal activities in the near future by using IBS as a key enabling technology. The proposed design, development and test activities have not only improved technical knowledge on IBS, but also set precedence that the Consortium hopes will help to stimulate the international debate and promote international cooperation in the definition of launcher upper stages removal demonstration missions.

The Project has succeeded in generating progress beyond the state-of-the-art in different fields by introducing new developments such as: in-orbit contactless actuation (usually, grabbing techniques are employed), low divergence (50% less than current technologies) ion thrusters, proximity formation flying operations and associated Guidance, Navigation and Control techniques as well as specific ion beam and ion beams-solid interaction characterisation.

In addition to these technical achievements, a legal framework for the first IBS demonstration mission has been proposed, as well as a roadmap for regulating future orbital debris removal activities.
List of Websites:
https://leosweep.upm.es/en/