European Student Moon Orbiter solar electric propulsion subsystem architecture: An all-electric spacecraft

Abstract

This paper presents the Phase A study of the Solar Electric Propulsion subsystem selected for the ESA European Student Moon Orbiter enhanced microsatellite, performed at QinetiQ under ESA funding. To minimise mass, a so-called "all electric" approach is adopted based around the re-use of the GOCE T5 gridded ion engine and the introduction of Hollow Cathode Thrusters (HCTs) for attitude control functions. Three different subsystem architectures are considered and analyzed with reference to the mass, cost, risk and level of integration between the HCTs and the T5. The favoured system architecture that best meets the various requirements adopts a shared tank and gas flow controller between the HCTs and the T5, with power being supplied from two dedicated power processing units. The possibility of reducing the propellant requirement by using an engine gimbal mechanism is also presented. The study also demonstrates how an increase in the T5 specific impulse to higher values than used on GOCE does not offer substantial system-level mass savings in this particular case. Nomenclature FCU= flow control unit GIT = gridded ion thruster HCT = hollow cathode thruster PPU = power processing unit

A T5 Hollow Cathode Thruster: Experimental Results and Modelling

“…The use of HCTs as attitude control thrusters will be particularly beneficial on board of satellites that already use electric propulsion (like GIEs or HETs) as main propulsion, since HCTs would highly integrate with the primary propulsion system leading to what is known as 'allelectric spacecraft'. Past missions studies such as SIMONE [3] and ESMO [4] showed different levels of integration between HCTs and ion engines. Recently an ESA ITT study kicked off, aiming to investigate the thrust production mechanism of a hollow cathode thruster, in order to design and test an optimized HCT.…”

Assessment of the T5 and T6 Hollow Cathodes as Reaction Control Thrusters

“…The scaling of gridded ion thrusters (GITs) and Hall effect thrusters for the low-power (less than 100 W) RCS role while maintaining total efficiency is challenging, largely due to the increasing fraction of wall losses with surface area-to-volume ratio and reduction in primary electron containment length in electrostatic thrusters [6][7][8][9][10]. However, the high molecular mass of xenon restricts the performance of conventional electrothermal resistojets to a 50-60 s specific impulse (ISP) [7,8].…”

“…The space heritage of some cathodes may also present reduced requalification requirements. Concurrent design studies as part of this work have outlined a mission design for an all-electric lunar transfer orbiter using the T5 gridded ion thruster with eight T5 hollow-cathode (HC) RCS thrusters at less than a 150 kg wet mass [9]. The propulsion system wet mass was 31 kg, which is only 2 kg heavier than the Small Missions for Advanced Research in Technology-1 (SMART-1) electric propulsion system (29 kg), which did not include the hydrazine system dry mass at a further 12.5 kg [10].…”

A thrust balance for low power hollow cathode thrusters

“…The possibility of using EP to replace CP to perform EWSK and wheel momentum management is under investigation by many consortiums. In particular, Hollow Cathodes (HCs) have been investigated in [1] to give birth to an all-electric spacecraft since they can be highly integrated with the existing EP systems used for NSSK (hall thruster and gridded ion engines) reusing the existing tanks, fluid lines, flow control units and power supplies providing large dry mass savings. In the last decade HCs as standalone thrusters (Hollow Cathode Thrusters, HCTs) have been investigated at the University of Southampton (UoS), where the performances of QinetiQ T5 and T6 HCs for various discharge currents, mass flow rates and anode geometries [2,3] have been measured with indirect thrust balances [4][5][6][7].…”