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Higher power cathodes are increasingly utilizing LaB6 emitters due to their increased emission cu... more Higher power cathodes are increasingly utilizing LaB6 emitters due to their increased emission current density capabilities over barium oxide emitters, however, these emitters require higher operating temperatures which poses a significant challenge to maintain heater reliability. Hence, there is ongoing development of heaterless hollow cathodes that allow for potentially higher reliability through design simplicity of removing the heater component, and in addition, there is potential savings in mass, volume, ignition time and power. In this study a LaB6 heaterless hollow cathode with imbedded high temperature thermocouple instrumentation demonstrated reliably operation in diode mode from 5-8 A at xenon flow rates of 0.2-1.75 sccm. Thet emperature profile of the emitter is characterized through ignition, which lasts up to 50 seconds. In addition, pyrometer measurements in an open keeper configuration have shown the emitter surface temperature to be significantly lower than that pred...

Despite the interest in formation ﬂying and cubesats over something like the last decadeor so, cl... more Despite the interest in formation ﬂying and cubesats over something like the last decadeor so, close controlled formation ﬂying of two cubesat size spacecraft has not been achieved.Similarly, despite the growing interest in propulsion systems for cubesats, there are very fewcommercially available and ﬂight ready systems. If these are coupled with the realizationthat formation ﬂying could be an enabling technology for cubesats [1] enhancing capabilitiesand opening up possibilities for new types of missions, it seemed timely to revisit theproblem of rendezvous and docking for cubesats to examine what might be possible witha pulsed propulsion system based on a pulsed plasma thruster(PPT) that is close to ﬂightqualiﬁcation [2].The approach taken was to build on previous work [3,4] which developed a universaladaptive control system for formation ﬂying by adding constraints on the actuators interms of their pulsed nature and also actual performance characteristics. The formalismand theory...

A novel high-current heaterless hollow cathode (HHC) has been designed, constructed, and tested, ... more A novel high-current heaterless hollow cathode (HHC) has been designed, constructed, and tested, with the developed system successfully demonstrating operation up to 30 A. This system overcomes the need for excessive ignition voltages or propellant pulsing, by utilising a reduced keeper orifice that enables ignition with <350 V, and nominal flow rates (<15 sccm). The system has also demonstrated full ignition in 50 seconds compared with conventional ignition, which can require more than 10 minutes; additionally, the system requires as little as 1/6th of the ignition energy compared to that of conventional designs. The HHC’s performance was characterised with operation tested in Xe, Kr and Ar. Optical pyrometry has allowed measurements of the emitter tip temperature of a HHC for the first time. Furthermore, the internal cathode-keeper plasma has been investigated using optical emission spectroscopy to determine the plasma electron density.

PPTCUP is an ablative pulsed plasma thruster designed to provide translational control for Cubesa... more PPTCUP is an ablative pulsed plasma thruster designed to provide translational control for Cubesat platforms. The engineering model presented in this paper has been developed by Mars Space Ltd, Clyde Space Ltd and the University of Southampton to optimize the performances whilst keeping lifetime long enough to fulfill the mission requirements. A lifetime test campaign has been carried out to prove the thruster and the conditioning electronics lifetime. The experimental campaign achieved more than 1,800,000 shots. The results gathered will be presented, showing that overall performances are not influenced by the thruster aging.

Solid-fed Pulsed Plasma Thrusters (PPTs) are the only mission employed devices to-date, although ... more Solid-fed Pulsed Plasma Thrusters (PPTs) are the only mission employed devices to-date, although they suffer from low-efficiency and lifetime limiting post-ablation effects; oppositely, gas-fed PPTs offer high efficiency (~15 – 50 %) and no contamination; however, they are subject to propellant leakage issues, difficult ignition synchronisation and higher implementation costs. Liquid-fed PPTs require the sub-systems to be revisited to adapt the device to the intrinsic benefits of fluid propellants; it is suggested to use electrowetting to initiate Perfluoropolyether (PFPE) motion under the influence of electric fields. Employing a combination of dielectric materials, locally enhanced electric fields may be manipulated to decrease the ignition voltage and consequently increase efficiency. Preliminary measurements of PFPE bulk breakdown and the electrowetting-tip ignition at the liquid surface leading to reliable ignition voltages of 8.98 ± 0.86 kV are reported. The significance of PF...

The performance of an indirect pendulum thrust balance suitable for micro-Newton level thrusters ... more The performance of an indirect pendulum thrust balance suitable for micro-Newton level thrusters is presented. A design based on a frictionless pendulum with a laser optical lever and detection system makes it possible for thrusters to be mounted independently of the thrust measurement system. This simplifies the process of calibration without having to compensate for electrical connections, flow lines and other equipment. Measurements are not limited by thruster mass and offer thrust measurements down to 80?N. The balance was demonstrated by measuring the performance of two micro propulsion devices; the T5 and T6 hollow cathode thrusters. The T5 generating thrusts from 0.1mN to 1.4mN and the T6 showed thrusts from 0.2mN to 1.9mN.

This paper describes the design and testing of a direct torsional impulsive thrust balance. The d... more This paper describes the design and testing of a direct torsional impulsive thrust balance. The design philosophy allows the balance to measure impulse bits (Ibit) in the range of 20 – 120 Ns typical of Pulsed Plasma Thrusters (PPTs) for pico and nano-satellite. The uncertainty in the Ibit measurement is quantified to be about 8.8 %, smaller than the typical values of this kind of balances (between 12 and 15%). This has been possible due to an in-depth analysis of all the possible sources of disturbance, which allows the choice of the most suitable measurement and estimation methods to minimize the errors. The balance has successfully been used for testing two PPTs with different propellant feeding system, nominal energy, mass and delivered impulse bits.

Higher power in-space propulsion systems are increasingly been developed and utilised due to payl... more Higher power in-space propulsion systems are increasingly been developed and utilised due to payload increases and mission demands. This requires higher current cathodes to match this demand, as such cathodes are increasingly adopting lanthanum hexaboride (LaB6) emitters due to the higher current density operation capabilities. However, LaB6 cathodes operate at higher temperatures compared with traditional barium oxide cathodes, due to the material’s relatively higher work function. Hence, this poses higher challenges to the heater technologies, which raise convention HCs to thermionic temperature. Here we present the development of a heaterless hollow cathode (HHC) system, which self-heats within only tens of seconds before nominal operation, and enables currents up to 30 A. Such that the system effectively removes the burden of the heater subcomponent. Within this work, the breakdown, cold (heating) discharge and nominal performance of the HHC have been characterised. In addition,...

Cubesats are one of the fastest growing sectors in the space industry, allowing for cheap access ... more Cubesats are one of the fastest growing sectors in the space industry, allowing for cheap access to space. ESA has funded a project involving Clyde Space Ltd, Mars Space Ltd and the University of Southampton to develop an adaptation of a Two-Stage PPT to perform drag compensation for a Cubesat platform, with the aim of doubling the time needed for the Cubesat to naturally de-orbit (hence doubling its lifetime). In this paper the mission requirements and the design process of this Two-Stage PPT will be presented.

Hollow Cathodes have good flight heritage being used in GIEs and HETs since late ‘60s. The possib... more Hollow Cathodes have good flight heritage being used in GIEs and HETs since late ‘60s. The possibility of using them as standalone thruster (Hollow Cathode Thrusters, HCTs) has been investigated at the University of Southampton for the last ten years. In order to use HCTs to replace chemical thrusters on commercial communication satellites with HCTs to perform EWSK and wheel offloading performance requirements in terms of thrust (>0.6 mN) and specific impulse (>300 s) were obtained. In this paper the results obtained from the test of an optimized HCT based on a QinetiQ T6 neutralizer are presented. The T6 HCT was tested at UoS and AER with two different direct thrust balances in cold gas and discharge mode at 10, 15, 20 and 24 A. The thrust was measured in the discharge mode also with an applied magnetic field. The thruster was found to fulfill the requirements showing thrust up to 2.6 mN with an Isp of 260s and a maximum specific impulse of 323 s with a thrust of 1.5 mN.

A model for the insert chemistry developed by the authors and based on the knowledge of the BaO –... more A model for the insert chemistry developed by the authors and based on the knowledge of the BaO – CaO – Al2O3 ternary system the ELT discharge cathode insert from the Deep Space 1 life test has been simulated. The computed data show a good agreement with the experimental one; the agreement increase with the imposition of boundary conditions closer to the experimental evidence. Tungsten deposition effect have been introduced into the model using experimental data and further improving the agreement between computed and measured data. The deposition trend found suggests the possibility of a link between barium depletion and tungsten deposition.