Showing papers by "European Space Operations Centre published in 2015"

The landing(s) of Philae and inferences about comet surface mechanical properties

Abstract: The Philae lander, part of the Rosetta mission to investigate comet 67P/Churyumov-Gerasimenko, was delivered to the cometary surface in November 2014. Here we report the precise circumstances of the multiple landings of Philae, including the bouncing trajectory and rebound parameters, based on engineering data in conjunction with operational instrument data. These data also provide information on the mechanical properties (strength and layering) of the comet surface. The first touchdown site, Agilkia, appears to have a granular soft surface (with a compressive strength of 1 kilopascal) at least ~20 cm thick, possibly on top of a more rigid layer. The final landing site, Abydos, has a hard surface.

SEPEM: A tool for statistical modeling the solar energetic particle environment

Abstract: Solar energetic particle (SEP) events are a serious radiation hazard for spacecraft as well as a severe health risk to humans traveling in space. Indeed, accurate modeling of the SEP environment constitutes a priority requirement for astrophysics and solar system missions and for human exploration in space. The European Space Agency's Solar Energetic Particle Environment Modelling (SEPEM) application server is a World Wide Web interface to a complete set of cross-calibrated data ranging from 1973 to 2013 as well as new SEP engineering models and tools. Both statistical and physical modeling techniques have been included, in order to cover the environment not only at 1 AU but also in the inner heliosphere ranging from 0.2 AU to 1.6 AU using a newly developed physics-based shock-and-particle model to simulate particle flux profiles of gradual SEP events. With SEPEM, SEP peak flux and integrated fluence statistics can be studied, as well as durations of high SEP flux periods. Furthermore, effects tools are also included to allow calculation of single event upset rate and radiation doses for a variety of engineering scenarios.

Free-Flight Experiments in LISA Pathfinder

Abstract: The LISA Pathfinder mission will demonstrate the technology of drag-free test masses for use as inertial references in future space-based gravitational wave detectors. To accomplish this, the Pathfinder spacecraft will perform drag-free flight about a test mass while measuring the acceleration of this primary test mass relative to a second reference test mass. Because the reference test mass is contained within the same spacecraft, it is necessary to apply forces on it to maintain its position and attitude relative to the spacecraft. These forces are a potential source of acceleration noise in the LISA Pathfinder system that are not present in the full LISA configuration. While LISA Pathfinder has been designed to meet it's primary mission requirements in the presence of this noise, recent estimates suggest that the on-orbit performance may be limited by this 'suspension noise'. The drift-mode or free-flight experiments provide an opportunity to mitigate this noise source and further characterize the underlying disturbances that are of interest to the designers of LISA-like instruments. This article provides a high-level overview of these experiments and the methods under development to analyze the resulting data.

In-flight thermal experiments for LISA pathfinder: simulating temperature noise at the inertial sensors

Abstract: Thermal Diagnostics experiments to be carried out on board LISA Pathfinder (LPF) will yield a detailed characterisation of how temperature fluctuations affect the LTP (LISA Technology Package) instrument performance, a crucial information for future space based gravitational wave detectors as the proposed eLISA. Amongst them, the study of temperature gradient fluctuations around the test masses of the Inertial Sensors will provide as well information regarding the contribution of the Brownian noise, which is expected to limit the LTP sensitivity at frequencies close to 1 mHz during some LTP experiments. In this paper we report on how these kind of Thermal Diagnostics experiments were simulated in the last LPF Simulation Campaign (November, 2013) involving all the LPF Data Analysis team and using an end-to-end simulator of the whole spacecraft. Such simulation campaign was conducted under the framework of the preparation for LPF operations.

Disentangling the magnetic force noise contribution in LISA Pathfinder

Abstract: Magnetically-induced forces on the inertial masses on-board LISA Pathfinder are expected to be one of the dominant contributions to the mission noise budget, accounting for up to 40%. The origin of this disturbance is the coupling of the residual magnetization and susceptibility of the test masses with the environmental magnetic field. In order to fully understand this important part of the noise model, a set of coils and magnetometers are integrated as a part of the diagnostics subsystem. During operations a sequence of magnetic excitations will be applied to precisely determine the coupling of the magnetic environment to the test mass displacement using the on-board magnetometers. Since no direct measurement of the magnetic field in the test mass position will be available, an extrapolation of the magnetic measurements to the test mass position will be carried out as a part of the data analysis activities. In this paper we show the first results on the magnetic experiments during an end- to-end LISA Pathfinder simulation, and we describe the methods under development to map the magnetic field on-board.

A Game-changing Radio Communication Architecture for Cube/nano Satellites

Abstract: Technological improvements achieved since 15 years allowed nanosatellites to emerge. 3U and bigger Cubesats permit functions and reliability once specific to microsatellites. The RF gamechanging is related to higher frequencies and data rates. Following the in-orbit X-band High Data Rate TeleMetry success on board the ESA Proba-V microsatellite, Syrlinks has finalized with CNES and ESA the development of a new solution to download payload telemetry in X-Band at high data rate for smaller platforms, such as Nanosatellites and CubeSats. This equipment is able to modulate data up to 100 Mbps using fully CCSDS compatible filtered OQPSK modulation and Convolutional Coding [7,1/2]. It delivers up to 2 Watts RF with no more than up to 10W DC/DC consumption, and fits inside a 0.25 Unit of a standard cubesat. . This miniature X band HDR-TM transmitter is planned to be used on board OPS-SAT, an ESA triple Cubesat dedicated to test new space operation control concepts, currently planned for launch in 2017. It is also planed to be used on board EYESAT, a Student/CNES triplecubsat, also in 2017. More rescently, a decision was taken to test this equipement on board the GOMX-3 triple cubesat in the frame of an ESA project, as soon as till the autumn 2015. In parallel, answering customer requirements, Syrlinks is also developing with CNES a new S -

A strategy to characterize the LISA-Pathfinder cold gas thruster system

Abstract: The cold gas micro-propulsion system that will be used during the LISA-Pathfinder mission will be one of the most important component used to ensure the "free-fall" of the enclosed test masses. In this paper we present a possible strategy to characterize the effective direction and amplitude gain of each of the 6 thrusters of this system.

Decentralized space-data dissemination for low-cost, dense satellite networks

Abstract: Recent trends in scientific low Earth orbit satellite missions involve small, low-cost satellites communicating with multiple low-cost ground stations. We propose a peer-to-peer multicast ground distribution scheme accompanied by a best-effort broadcasting mechanism with randomized retransmissions that is tailored for such satellite missions. Through our simulation tools, we assess the performance of the new, low-cost model; evaluate the benefits of decentralized ground distribution; and quantify the trade-off between data reliability and data return volume.

Bayesian statistics for the calibration of the LISA Pathfinder experiment

Abstract: The main goal of LISA Pathfinder (LPF) mission is to estimate the acceleration noise models of the overall LISA Technology Package (LTP) experiment on-board. This will be of crucial importance for the future space-based Gravitational-Wave (GW) detectors, like eLISA. Here, we present the Bayesian analysis framework to process the planned system identification experiments designed for that purpose. In particular, we focus on the analysis strategies to predict the accuracy of the parameters that describe the system in all degrees of freedom. The data sets were generated during the latest operational simulations organised by the data analysis team and this work is part of the LTPDA Matlab toolbox.

Towards Adaptive Fault Tolerance: From a Component-Based Approach to ROS

Abstract: A system that remains dependable when facing changes (new threats, failures, updates) is resilient. In this paper, we report on an approach taking advantage of Component Based Software Engineering technologies for tackling a crucial aspect of resilient computing, namely the on-line adaptation of fault tolerance mechanisms. The second part of this paper shows how this approach can be implemented on ROS that is presently used for implementing automotive applications, e.g. ADAS. We illustrate the mapping of ideal components to ROS components and give implementation details of a fault tolerance design pattern that is adaptive at runtime. We finally draw the lessons learnt from our first experiments.

A noise simulator for eLISA: Migrating LISA Pathfinder knowledge to the eLISA mission

Abstract: We present a new technical simulator for the eLISA mission, based on state space modeling techniques and developed in MATLAB. This simulator computes the coordinate and velocity over time of each body involved in the constellation, i.e. the spacecraft and its test masses, taking into account the different disturbances and actuations. This allows studying the contribution of instrumental noises and system imperfections on the residual acceleration applied on the TMs, the latter reflecting the performance of the achieved free-fall along the sensitive axis. A preliminary version of the results is presented.