Challenging space missions include those at very low altitudes, where the atmosphere is source of aerodynamic drag on the spacecraft. To extend such missions lifetime, an efficient propulsion system is required. One solution is Atmosphere-Breathing Electric Propulsion (ABEP). It 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 planet with atmosphere, enabling new mission at low altitude ranges for longer times. Challenging is also the presence of reactive chemical species, such as atomic oxygen in Earth orbit. Such species cause erosion of (not only) propulsion system components, i.e. acceleration grids, electrodes, and discharge channels of conventional EP systems. IRS is developing within the DISCOVERER project, an intake and a thruster for an ABEP system. The paper describes the design and implementation of the RF helicon-based inductive plasma thruster (IPT). This
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.
The most difficult problem for High Test Peroxide (HTP), which is used in monopropellant thruster for satellite, is the catalyst bed design. According to literature, silver has the best catalytic performance for HTP, but its low melting point usually sinters the silver catalyst bed during decomposition processes. A superior catalyst bed design has to deal with the balance of the highest specific impulse produced and life-span of the active catalyst bed performance. The sintering effect always accompanies with the incomplete decomposition in cold start and oscillation in chamber pressure. Even more, it will induce flow instability in the supplying system. In this paper, we add some ceramic materials to increase the thermal resistance ability of catalyst bed, which names as composite silver catalyst. We design a HTP monopropellant thruster model for the test of the proposed catalyst; and discuss the factors influencing the decomposition processes and the deterioration of the catalyst bed. By anticipate packing, we can find an excellent result for the test of catalyst. No matter in cold start or hot fire, the C * efficiency in the catalyst is almost 100%. The I sp from cold start is 104.9 s; and I sp from hot fire is 114.9. The start transient is about 100ms and 50ms, which include the operation time of solenoid valve, from cold and hot fire. It is a successful development for H 2 O 2 monopropellant thruster.
Challenging space missions include those at very low altitudes, where the atmosphere is the source of aerodynamic drag on the spacecraft, that finally defines the mission's lifetime, unless a way to compensate for it is provided. This environment is named Very Low Earth Orbit (VLEO) and it is defined for h < 450 km. In addition to the spacecraft's aerodynamic design, to extend the lifetime of such missions, an efficient propulsion system is required.One solution is Atmosphere-Breathing Electric Propulsion (ABEP), in which the propulsion system collects the atmospheric particles to be used as propellant for an electric thruster. The system could remove the requirement of carrying propellant on-board, and could also be applied to any planetary body with atmosphere, enabling new missions at low altitude ranges for longer missions' duration. One of the objectives of the H2020 DISCOVERER project, is the development of an intake and an electrode-less plasma thruster for an ABEP system.This article describes the characteristics of intake design and the respective final designs based on simulations, providing collection efficiencies up to 94%. Furthermore, the radio frequency (RF) Helicon-based plasma thruster (IPT) is hereby presented as well, while its performances are being evaluated, the
After decades of traditional space businesses, the space paradigm is changing. New approaches to more efficient missions in terms of costs, design, and manufacturing processes are fostered. For instance, placing big constellations of micro-and nano-satellites in Low Earth Orbit and Very Low Earth Orbit (LEO and VLEO) enables the space community to obtain a huge amount of data in near real-time with an unprecedented temporal resolution. Beyond technology innovations, other drivers promote innovation in the space sector like the increasing demand for Earth Observation (EO) data by the commercial sector. Perez et al. stated that the EO industry is the second market in terms of operative satellites (661 units), micro-and nano-satellites being the higher share of them (61%). Technological and market drivers encourage the emergence of new start-ups in the space environment like Skybox, OneWeb, Telesat, Planet, and OpenCosmos, among others, with novel business models that change the accessibility, affordability, ownership, and commercialization of space products and services. This chapter shows some results of the H2020 DISCOVERER (DISruptive teChnOlogies for VERy low Earth oRbit platforms) Project and focuses on understanding how micro-and nano-satellites have been disrupting the EO market in front of traditional platforms. Satellites Missions and Technologies for Geosciences 2 Figure 1. Micro-and nano-satellites launched between 1997 and 2017, classified by sectors (own elaboration).
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