A review of gas-surface interaction models for orbital aerodynamics applications

Renewed interest in Very Low Earth Orbits (VLEO) - i.e. altitudes below 450 km - has led to an increased demand for accurate environment characterisation and aerodynamic force prediction. While the former requires knowledge of the mechanisms that drive density variations in the thermosphere, the latter also depends on the interactions between the gas-particles in the residual atmosphere and the surfaces exposed to the flow. The determination of the aerodynamic coefficients is hindered by the numerous uncertainties that characterise the physical processes occurring at the exposed surfaces. Several models have been produced over the last 60 years with the intent of combining accuracy with relatively simple implementations. In this paper the most popular models have been selected and reviewed using as discriminating factors relevance with regards to orbital aerodynamics applications and theoretical agreement with gas-beam experimental data. More sophisticated models were neglected, since their increased accuracy is generally accompanied by a substantial increase in computation times which is likely to be unsuitable for most space engineering applications. For the sake of clarity, a distinction was introduced between physical and scattering kernel theory based gas-surface interaction models. The physical model category comprises the Hard Cube model, the Soft Cube model and the Washboard model, while the scattering kernel family consists of the Maxwell model, the Nocilla-Hurlbut-Sherman model and the Cercignani-Lampis-Lord model. Limits and assets of each model have been discussed with regards to the context of this paper. Wherever possible, comments have been provided to help the reader to identify possible future challenges for gas-surface interaction science with regards to orbital aerodynamic applications

Early Results from the DISCOVERER Project

The use of very low Earth orbits (VLEO), for communications and remote sensing satellites, offers a number of significant payload and platform benefits. Imaging from these altitudes allows higher resolution or smaller optical payloads, whilst radar also benefits from improved link budgets leading to smaller antennas and lower transmission power. Communications payloads also have improved link budgets, reduced latency, and improved frequency reuse factors. Platform benefits include a more benign radiation environment, lower cost per kilogram to launch satellites, and atmospheric drag makes the environment inherently sustainable, simultaneously removing debris objects and ensuring satellites are quickly removed from orbit at the end of their operational lives. However, the impact of drag on satellite and mission operations must also be addressed. The DISCOVERER project, which commenced in 2017, is addressing the following key questions about technologies that would enable the commercially viable and sustained operation of satellites in VLEO: 1. Are there materials or processes which reduce the induced drag on spacecraft surfaces? 2. Are there propulsion methods which use the residual atmospheric gas as a propellant, providing drag compensation whilst removing the lifetime limits caused by carrying a limited amount of propellant? 3. How can we improve our understanding of, and make best use of, the orbital aerodynamics of a space platform and its ability to perform attitude control manoeuvres? 4. And what are the new opportunities that these technologies may bring to the market? This paper provides highlights from the developments made during the DISCOVERER project to date, demonstrating the potential for a new, commercially attractive, class of aerodynamic satellites operating in VLEO.Article signat per 30 autors: Peter C.E. Roberts, Nicholas H. Crisp, Vitor T.A. Oiko, Steve Edmondson, Francesco Romano, Silvia Rodriguez-Donaire, Daniel Garcia-Almiñana, Sarah J. Haigh, Brandon E.A. Holmes, Sabrina Livadiotti, Alejandro Macario-Rojas, Katharine L. Smith, Luciana A. Sinpetru, Jonathan Becedas, Valeria Sulliotti-Linner, Simon Christensen, Thomas K. Jensen, Jens Nielsen, Morten Bisgaard, Yung-An Chan, Georg H. Herdrich, Stefanos Fasoulas, Constantin Traub, Miquel Sureda, Dhiren Kataria, Badia Belkouchi, Alexis Conte, Simon Seminari, Rachel Villain, Ameli Schwalber.Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraPostprint (published version

Intake design for an Atmosphere-Breathing Electric Propulsion system (ABEP)

Challenging space missions include those at very low altitudes, where the atmosphere is source of aerodynamic drag on the spacecraft. To extend the lifetime of such missions, an efficient propulsion system is required. One solution is Atmosphere-Breathing Electric Propulsion (ABEP) that collects atmospheric particles to be used as propellant for an electric thruster. The system would minimize the requirement of limited propellant availability and can also be applied to any planetary body with atmosphere, enabling new missions at low altitude ranges for longer times. IRS is developing, within the H2020 DISCOVERER project, an intake and a thruster for an ABEP system. The article describes the design and simulation of the intake, optimized to feed the radio frequency (RF) Helicon-based plasma thruster developed at IRS. The article deals in particular with the design of intakes based on diffuse and specular reflecting materials, which are analysed by the PICLas DSMC-PIC tool. Orbital altitudes and the respective species based on the NRLMSISE-00 model (O, , , He, Ar, H, N) are investigated for several concepts based on fully diffuse and specular scattering, including hybrid designs. The major focus has been on the intake efficiency defined as , with the incoming particle flux, and the one collected by the intake. Finally, two concepts are selected and presented providing the best expected performance for the operation with the selected thruster. The first one is based on fully diffuse accommodation yielding to and the second one based on fully specular accommodation yielding to . Finally, also the influence of misalignment with the flow is analysed, highlighting a strong dependence of in the diffuse-based intake while, for the specular-based intake, this is much lower finally leading to a more resilient design while also relaxing requirements of pointing accuracy for the spacecraft.Article signat per 32 autors/es: F. Romano, J. Espinosa-Orozco, M. Pfeiffer, G. Herdrich, N.H. Crisp, P.C.E. Roberts, B.E.A. Holmes, S. Edmondson, S. Haigh, S. Livadiotti, A. Macario-Rojas, V.T.A. Oiko, L.A. Sinpetru, K. Smith, J. Becedas, V. Sulliotti-Linner, M. Bisgaard, S. Christensen, V. Hanessian, T. Kauffman Jensen, J. Nielsen, Y.-A. Chan, S. Fasoulas, C. Traub, D. García-Almiñana, S. Rodríguez-Donaire, M. Sureda, D. Kataria, B. Belkouchi, A. Conte, S. Seminari, R. Villain.Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraPostprint (published version

Launch, Operations, and First Experimental Results of the Satellite for Orbital Aerodynamics Research (SOAR)

The Satellite for Orbital Aerodynamics Research (SOAR) is a 3U CubeSat that has been designed to investigate the aerodynamic performance of different materials at low orbital altitudes. The spacecraft has been developed within the scope of DISCOVERER, a Horizon 2020 project that aims to develop foundational technologies to enable sustainable operations of Earth observation spacecraft in very low Earth orbits (VLEO) i.e., those below 450 km. SOAR features two payloads: i) a set of steerable fins that can expose different materials to the oncoming atmospheric flow developed by The University of Manchester, and ii) a forward-facing ion and neutral mass spectrometer (INMS) that provides in-situ measurements of the atmospheric density, flow composition, and velocity from the Mullard Space Science Laboratory (MSSL) of University College London. These payloads enable characterisation of the aerodynamic performance of different materials at very low altitudes with the aim to advance understanding of the underlying gas-surface interactions in rarefied flow environments. The satellite will also be used to test novel aerodynamic attitude control methods and perform atmospheric characterisation in the VLEO altitude range. SOAR will perform the first in-orbit test of two novel materials that are expected to have atomic oxygen erosion resistance and drag-reducing properties, providing valuable in-orbit validation data for ongoing ground-based experimentation. Such materials hold the promise for extending operations at lower altitudes with benefits particularly for Earth observation and communications satellites that can correspondingly be reduced in size and cost. The platform for SOAR is largely based on GOMX-3 heritage and the spacecraft was assembled, integrated, and tested by GomSpace A/S. The satellite was launched on the SpX-22 commercial resupply service mission to the International Space Station in on 3rd June 2021 was subsequently deployed into orbit on the 14th June 2021. This paper presents the final preparations of SOAR prior to launch and provides an overview of the planned operations of the spacecraft following deployment into orbit.Article signat per 30 autors/res: Nicholas H. Crisp, Alejandro Macario-Rojas, Peter C.E. Roberts, Steve Edmondson, Sarah J. Haigh, Brandon E.A. Holmes, Sabrina Livadiotti, Vitor T.A. Oiko, Katharine L. Smith, Luciana A. Sinpetru, Jonathan Becedas, Valeria Sulliotti-Linner, Simon Christensen, Virginia Hanessian, Thomas K. Jensen, Jens Nielsen, Morten Bisgaard, Yung-An Chan, Georg H. Herdrich, Francesco Romano, Stefanos Fasoulas, Constantin Traub, Daniel Garcia-Almiñana, Silvia Rodriguez-Donaire, Miquel Sureda, Dhiren Kataria, Badia Belkouchi, Alexis Conte, Simon Seminari, Rachel VillainObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraPostprint (published version