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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - HiperLoc-EP (High performance low cost electric propulsion system development)

Teaser

Summary

1.1 Summary & Context
The HiperLoc-EP project will develop a disruptive electric propulsion technology that provides a High performance Low cost Electric Propulsion system. HiperLoc-EP will provide critical propulsion functionality for micro satellite and satellite constellations typified by Samsungâ€™s Earth-wide internet proposal requiring 4600 micro-satellites. The HiperLoc-EP technology is an Electrospray Colloid Electric Propulsion System (ECEPS). In this type of propulsion system, the propellant is stored as an un-pressurized liquid and this is ionized directly in an intense electric field, with this field also being used to accelerate the ionized species. From this system the thrust scales directly with thrust head active area, which is anticipated to be ~0.2mN/cm2. Significantly this means that there are no physical processes which limit the thrust obtained to maintain a particular efficiency. The system produces a neutral plasma and hence there is no requirement for a neutralizer.
The use of a liquid propellant also benefits efficiency: it requires lower power inputs than some other micro propulsion systems. The principal competitor technologies for high specific impulse micro-propulsion are pulsed plasma thrusters (PPT) and field emission electric propulsion (FEEP). In the former the fundamental process of propellant ablation has low efficiency, limiting systems to ~10% at best. FEEP requires additional power to phase change a solid propellant and to provide a neutralizer, factors again which reduce overall efficiency. Also in contrast to FEEP the propellant used in the ECEPS is benign: it is an organic ionic liquid which does not have any of the chemically aggressive features associated with FEEP liquid metal propellants.
The potential applications for our technology are very broad however, during the project we are focusing the development towards micro propulsion consistent with satellites having mass spanning the range from a multi-unit CubeSat to small satellites less than 100kg. The performance target is a thruster whose efficiency is ~50%, some 6 times that possible with typical current PPT designs, but comparable to conventional EP such as GIE and HET. The ECEPS can be designed to operate over a broad range of Isp from ~1000s to ~4000s; herein and consistent with resources of micro-satellites we will demonstrate an Isp greater than 1000s. This new electric propulsion system will have low volume and low power demands and is ideally suited to micro satellite constraints. The summary performance target that we are working towards are:
Propulsion system wet mass: <550 g
Total propulsion system size: < 9.5 cmx9.5 cmx5 cm
Total Impulse: 2000Ns
Î”V: > 500 m/s
Isp: > 1000 s
Thrust: > 0.5 mN
Thrust accuracy: < Â±5%
Power consumption: <10W
This emerging technology will clearly disrupt the status quo of the space sector by providing a radical improvement in performance and cost, critical to customers hoping to operate in the dawning market for micro-satellite based systems.

Work performed

The project addressed the markets that may be disrupted by the HiperLoc technology being available and the system requirements for a suitable HiperLoc configuration. Fundamental proof of concept tests were also been carried out to verify the approach proposed in the three subsystems: Colloid Thrust Head subsystem (CTH), Propellant Storage and Feed subsystem (PSFS) and the Power Processing subsystem (PPU).
From the analysis performed, the possible missions can be divided in 3 broad categories of requirements:
1. Nano/Microsatellite market:
This rapidly growing market represents one of the main users of a low cost EP system. Particularly these applications will require low level of thrust, and accept a low specific impulse, prioritizing extremely low cost and compactness over performance.
2. Small satellites mega-constellations:
This market is shifting the paradigm of the use of space with unprecedented volumes of production, that require easy to manufacture and cheap systems. These applications will have requirements somewhat similar to the nanosatellitesâ€™ market, prioritizing cost over performance (no need for low noise or high thrust resolution/throttling). But the required thrust will be in the tens of mN range and the Isp will probably be higher to save on the propellant mass consumed.
3. Science Missions:
Finally, science missions encompass both flagship missions like LISA and LEO science missions like NGGM. While the requirement will be clearly slightly different between the systems, the emphasis will be on performance. The required activities of formation flying and/or precise pointing will require sub-mN thrusts, with very high thrust resolutions (~0.5 Î¼N) and the ability to continually throttle the thrust.
Of these the dominant market in the near future for the ECEPS will be the constellations and mega-constellations of CubeSats, especially in the 3U format. Therefore, this was selected as the baseline for the HiperLoc development and the requirements were derived accordingly.
Broadly, the ECEPS is required to be able to provide the required propulsion functionality for a 3U CubeSat platform to perform:
â€¢ Constellation deployment
â€¢ Station keeping in LEO for 5 years
â€¢ Deorbiting at EOL
Critical component testing was undertaken for each of the principal subsystems that comprise the ECEPS, namely: CTH, PSFS and the PPU. These tests allowed for detailed design to take place for each of the subsystems and a Bread Board Model (BBM) for the entire propulsion system was then manufactured to this design. This BBM can be seen in figure 1.
The results of the BBM tests have been used to identify modifications required to the system in order to take forward a further development of the system. These lessons learnt have been then included in a development plan. The development plan has identified a target opportunity for In-orbit Demonstration of the technology within the next two years.

Final results

The design approach in HiperLoc-EP is a radical innovation within the context of colloid systems that have been considered by other researchers. Thus the element of the EP system that develops thrust is completely integrated with the Power Processing Unit; the thrust head itself is a multilayer PCB. Core to our methodology is a novel route to manufacturing the EP system. Thus the thrust head manufacture process is inspired by a system we have successfully used in another technology domain in terrestrial applications. The propellant storage system can be achieved using 3D printing techniques. Fabrication, integration and propellant costs are, as a result, anticipated to be several orders of magnitude below conventional EP procurement.
The PPU and the PSFS have been validated at TRL 4. Manufacture delays in the CTH has limited this subsystem to be at TRL 3 for this innovative thruster.