RX23 – ARES II (Axial Retention Experiment for PMD Sponges II)
University of Applied Sciences and Arts (HES – SO), SWITZERLAND
Launch Date: March 2018
The experiment revolves around propellant management device, also called “sponge”, composed of a series of radial panels, tapering towards their center to collect liquid at a desired position. These devices are used in the space propulsion community to guarantee the delivery of bubble-free propellant to the liquid propulsion engines when high reliability is needed. This component is based on surface tension forces to control and deliver fluid to a particular location in microgravity environments. Surface tension is produced by asymmetry of molecules at surface of liquids. The resulting force is small in comparison to gravity on Earth. However, the opposite happens in space: surface tension dominates gravity. From the beginning of the 1980s sponges were known and used in space vehicle. Though, no general public documentation is available at the moment about liquid behaviour under axial acceleration. The purpose of this experiment is to partially fill this void by putting sponges in microgravity environment and acquire images of the fluid distribution around it under controlled axial acceleration. Experimental setup is designed to carry four experiments cells varying geometrical parameters. During the flight the sponges will be subject to axial accelerations and the liquid behaviour will be recorded. The experimental results will be compared with ground based tests and numerical analysis in order to characterise the geometrical influence of sponges on liquid behaviour.
RX14 – CAESAR (CApillarity-based Experiment for Spatial Advanced Research)
HES-SO Geneva, Switzerland
Launch Date: 7 May 2013
The CAESAR experiment aims to validate theoretical and numerical data concerning the behaviour of liquids in a panel-shaped propellant management device (PMD), under reduced gravity conditions. PMD’s are often used for managing liquids in microgravity, when high reliability, bubble free liquid delivery is required. In particular the CAESAR team is interested in identifying experimentally the behaviour of the liquid under relatively high Bond (Bo) numbers, so that limited accelerations will have to be imposed on the tests samples. The investigations will be made using three PMD samples, with varying radial acceleration and fluids with different Bond numbers, which will be clearly defined in order to provide comparisons with past experimental results.
RX09 – SPONGE (Sounding rocket Propellant OrieNtation microGravity Experiment)
University of Padova & University of Padua, Italy
Launch Date: 22 February 2011
The SPONGE experiment focused on validating a numerical code to be used for simulating a Propellant Management Device (PMD) known as a Sponge, which makes use of surface tension characteristics to control and/or deliver liquid propellants in rocket fuel tanks. Sponges are open control devices consisting of perforated, close proximity metal panels, which are generally located over the fuel tank outlet. The panels form tapered gaps in which propellant accumulates. The tapered geometry of the sponge forces bubbles outward thereby ensuring that, as the propellant is consumed; it flows in the right direction. The numerical code was derived from OpenFOAM; an open source fluid volume tool that can be updated and modified directly by the user. This was verified against observed results obtained from the experiment, concerning the sponge directional retention capabilities under varying accelerations, which were imposed by a horizontal-plate centrifuge. Specific and appropriate diagnostics were used to monitor the system characteristics during the various phases of the experiment. The results obtained from this experiment can be expanded, by applying the fluid dynamic similitude theory, to sponges of larger dimensions; making production of PMD’s easier for industry.
RX09 – EXPLORE (EXPeriment for Liquid On-orbit REfueling)
University of Stuttgart, Germany
Launch Date: 22 February 2011
The EXPLORE team aimed to investigate the technologies and processes required for future in-orbit refuelling activities; a technology that could greatly enhance the payload capability of human and large-cargo spacecraft. Historically, cryogenic fuel tanks are pressurised by a gas, which then remains in the tank after the fuel is depleted. Refuelling activities would then have to take place, without mixing the liquid and gaseous phases, whilst also maintaining optimum pressure to avoid propellant boil-off. This process represents the greatest challenge of in-orbit refuelling and was reproduced in the EXPLORE experiment, using six scaled transparent test chambers, with interconnected gas reservoirs. Each reservoir was filled by two additional centralised liquid reservoirs. The fuel transfer process is governed by several parameters – including gravity level, surface tension, tank geometry, local temperature and in-flow velocity – and was observed visually by camera, and through temperature and pressure measurements. The flow velocity profiles were also varied for each test chamber to identify optimal conditions for maximum test chamber filling.
BX10 – SCRAT (Spherical Compact Rechargeable Air Thruster)
University of Padova, Italy
Launch Date: 9 October 2010
The SCRAT experiment aimed to develop and flight-test a rechargeable, low-thrust cold gas actuator for use on Lighter Than Air (LTA) vehicles. The SCRAT propulsion system used compressed air collected directly from the surrounding atmosphere as propellant, thereby eliminating the need to store fuel on-board. The increasing use of LTA vehicles for scientific and civil applications; such as atmospheric research, communication systems, the exploration of hazardous zones and potentially even interplanetary exploration, requires a new generation of airships and balloons that are subjected to continuous miniaturisation. Use of such systems creates a need for compact, low-thrust and accurate actuators (in the range of 10-100 mN). SCRAT operated by collecting air through two micro-compressors, which was then fed into a two-stage tank separated by automatic valves. The compressed air was then expelled from the second stage, through a nozzle, finally delivering thrust. Careful design of the two-stage operating cycle made it possible to maximise the peak thrust or the total impulse, according to the application requirements. A complete evaluation of the thruster’s performance at varying altitudes and atmospheric conditions was performed, from which peak thrust and total impulse profiles were derived. SCRAT also doubled as an atmospheric sounding device; measuring temperature and pressure profiles along the BEXUS flight path, in a bid to contribute data to the polar atmospheric model.