System modelling of very low Earth orbit satellites for Earth observation

The operation of satellites in very low Earth orbit (VLEO) has been linked to a variety of benefits to both the spacecraft platform and mission design. Critically, for Earth observation (EO) missions a reduction in altitude can enable smaller and less powerful payloads to achieve the same performance as larger instruments or sensors at higher altitude, with significant benefits to the spacecraft design. As a result, renewed interest in the exploitation of these orbits has spurred the development of new technologies that have the potential to enable sustainable operations in this lower altitude range. In this paper, system models are developed for (i) novel materials that improve aerodynamic performance enabling reduced drag or increased lift production and resistance to atomic oxygen erosion and (ii) atmosphere-breathing electric propulsion (ABEP) for sustained drag compensation or mitigation in VLEO. Attitude and orbit control methods that can take advantage of the aerodynamic forces and torques in VLEO are also discussed. These system models are integrated into a framework for concept-level satellite design and this approach is used to explore the system-level trade-offs for future EO spacecraft enabled by these new technologies. A case-study presented for an optical very-high resolution spacecraft demonstrates the significant potential of reducing orbital altitude using these technologies and indicates possible savings of up to 75% in system mass and over 50% in development and manufacturing costs in comparison to current state-of-the-art missions. For a synthetic aperture radar (SAR) satellite, the reduction in mass and cost with altitude were shown to be smaller, though it was noted that currently available cost models do not capture recent commercial advancements in this segment. These results account for the additional propulsive and power requirements needed to sustain operations in VLEO and indicate that future EO missions could benefit significantly by operating in this altitude range. Furthermore, it is shown that only modest advancements in technologies already under development may begin to enable exploitation of this lower altitude range. In addition to the upstream benefits of reduced capital expense and a faster return on investment, lower costs and increased access to high quality observational data may also be passed to the downstream EO industry, with impact across a wide range of commercial, societal, and environmental application areas

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 $h=150-250$ km and the respective species based on the NRLMSISE-00 model (O, $N_2$, $O_2$, 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 $\eta_c=\dot{N}_{out}/\dot{N}_{in}$, with $\dot{N}_{in}$ the incoming particle flux, and $\dot{N}_{out}$ 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 $\eta_c<0.46$ and the second one based un fully specular accommodation yielding to $\eta_c<0.94$. Finally, also the influence of misalignment with the flow is analysed, highlighting a strong dependence of $\eta_c$ in the diffuse-based intake while, ...Comment: Accepted Versio

RF Helicon-based Inductive Plasma Thruster (IPT) 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 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 paper deals in particular with the design and implementation of a novel antenna called the birdcage antenna, a device well known in magnetic resonance imaging (MRI), and also lately employed for helicon-wave based plasma sources in fusion research. This is aided by the numerical tool XFdtd®. The IPT is based on RF electrodeless operation aided by an externally applied static magnetic field. The IPT is composed by an antenna, a discharge channel, a movable injector, and a solenoid. By changing the operational parameters along with the novel antenna design, the aim is to minimize losses in the RF circuit, and accelerate a quasi-neutral plasma plume. This is also to be aided by the formation of helicon waves within the plasma that are to improve the overall efficiency and achieve higher exhaust velocities. Finally, the designed IPT with a particular focus on the birdcage antenna design procedure is presented

New test of modulated electron capture decay of hydrogen-like 142Pm ions: Precision measurement of purely exponential decay

An experiment addressing electron capture (EC) decay of hydrogen-like 142Pm60+ions has been conducted at the experimental storage ring (ESR) at GSI. The decay appears to be purely exponential and no modulations were observed. Decay times for about 9000 individual EC decays have been measured by applying the single-ion decay spectroscopy method. Both visually and automatically analysed data can be described by a single exponential decay with decay constants of 0.0126(7)s−1for automatic analysis and 0.0141(7)s−1for manual analysis. If a modulation superimposed on the exponential decay curve is assumed, the best fit gives a modulation amplitude of merely 0.019(15), which is compatible with zero and by 4.9 standard deviations smaller than in the original observation which had an amplitude of 0.23(4)

Towards a fast calculator for the radiation characteristics of radiative recombination and radiative electron capture

Abstract The radiative capture of free electrons (radiative recombination) and bound electrons (radiative electron capture) are among the most important charge changing processes for fast, highly-charged ions. While total cross sections can be obtained by an approximate formula with reasonable accuracy, the estimation of angular distributions and polarization properties of the emitted radiation requires a fully relativistic treatment that is numerical expensive. Therefore we recently started the development of a fast calculator for these radiation characteristics. The program is based on a grid of rigorously calculated data points for free- electron capture into bare ions, between which interpolation is performed to obtain radiation characteristics for specific collision systems. Also capture into few-electron systems is taken into account in an approximate way. We present first results from this development

Airborne re-entry observation experiment SLIT: UV spectroscopy during STARDUST and ATV1 re-entry

Emission spectra during re-entry have been measured in 2006 for the STARDUST capsule and in 2008 for the ATV1 Jules Verne re-entry. This paper summarizes the approach to design the airborne UV spectroscopic setup and its modifications with respect to the missions. For the STARDUST mission, results of data analysis of data presented in 2008 are given while for the ATV1 observation first spectra of the main disruption are exemplary presented. The surface radiation during the STARDUST re-entry is used to estimate convective and radiative heat flux using different analytical models. A first look at the spectroscopic footprint of ATV1 shows that during the first explosive event, a severe break-up of the main ATV1 structure occurs. However, a correlation with an explosion of fuel could not be observed

A ground calibration facility for ion and electron spectrometers on the bepicolombo and juice missions

The Max Planck Institute for Solar System Research (MPS) is contributing among other instruments to the plasma packages of the up-coming missions JUICE to Jupiter and BepiColombo to Mercury. JUICE will carry the Particle Environment Package (PEP) of six different sensors with the MPS contribution JEI (Jovian Electron and Ion Sensor). Upon its arrival at Jupiter in 2030, JEI is designed to characterize the plasma parameters of the Jovian magnetosphere and the plasma interaction with the Galilean moons. It is an electrostatic analyzer and covers an energy range of 1eV to 40keV for electrons and ions respectively at 10% resolution. The field of view is almost one hemisphere at 22.5° resolution. The measurements will allow determining temporally and spatially resolved distributions of charged particles. BepiColombo consists of two spacecraft (Mercury Planetary Orbiter MPO and the Mercury Magnetospheric Orbiter MMO, now called MIO), targeted to launch in October 2018. MPO will carry the particle instrument suite SERENA (Search for Exospheric Refilling and Emitted Natural Abundances) consisting of four sensors where MPS contributed hardware to the Planetary Ion Camera PICAM. This sensor is an ion imager with 2Ï€ field of view. It has an energy range of 1eV to 3keV at an energy resolution of up to 10% and a time-of-flight analyzer with a m/δm ratio of about 100. PICAM will contribute to the analysis of the magnetic field configuration of Mercury and its interaction with the solar wind. In addition, MPS is also involved in the Mass Spectrum Analyzer MSA, one out of six sensors of the particle instrument MPPE (Mercury Plasma Particle Experiment) onboard MIO. In this paper we concentrate on JEI and PICAM only. For the ongoing calibration of the instruments JEI and PICAM, the existing ion and electron source at MPS has been upgraded. An increased beam quality and automatized measurement procedure allows a detailed characterization for both polar angles, accelerator voltages and instrument operation modes. In course of the measurement, cross talk, angular and energy resolution as well as the ion grid optics have been mapped. © 2018 International Astronautical Federation, IAF. All rights reserved