Showing papers by "European Space Operations Centre published in 2017"

Charge-induced force-noise on free-falling test masses: results from LISA Pathfinder

Abstract: We report on electrostatic measurements made on board the European Space Agency mission LISA Pathfinder. Detailed measurements of the charge-induced electrostatic forces exerted on free-falling test masses (TMs) inside the capacitive gravitational reference sensor are the first made in a relevant environment for a space-based gravitational wave detector. Employing a combination of charge control and electric-field compensation, we show that the level of charge-induced acceleration noise on a single TM can be maintained at a level close to 1.0 fm s-2 Hz-1/2 across the 0.1–100 mHz frequency band that is crucial to an observatory such as the Laser Interferometer Space Antenna (LISA). Using dedicated measurements that detect these effects in the differential acceleration between the two test masses, we resolve the stochastic nature of the TM charge buildup due to interplanetary cosmic rays and the TM charge-to-force coupling through stray electric fields in the sensor. All our measurements are in good agreement with predictions based on a relatively simple electrostatic model of the LISA Pathfinder instrument.

REAPER: Reprocessing 12 Years of ERS-1 and ERS-2 Altimeters and Microwave Radiometer Data

Abstract: Twelve years (1991–2003) of ERS-1 and ERS-2 altimetry data have been reprocessed within the European Space Agency (ESA) reprocessing altimeter products for ERS (REAPER) project using an updated, modern set of algorithms and auxiliary models. The reprocessed data set (identified as RP01) has been cross-calibrated against the reprocessed ENVISAT V2.1 data. The format of this reprocessed data set is network common data form (version 3). The new data set shows a clear improvement in data quality beyond that of previous releases. The product validation shows reduction of the mean standard deviation of the sea-surface height differences from 8.1 (previously available product) to 6.7 cm (RP01). This paper presents the details of how the reprocessing was conducted and shows selected results from the validation and quality-assurance processes. The major improvements of the REAPER RP01 data set with respect to the previous ESA ERS radar altimetry (RA) products are due to the use of four ENVISAT RA-2 retrackers, RA calibration improvements, new reprocessed precise orbit solutions, ECMWF ERA-interim model for meteorological corrections, new ionospheric corrections, and new sea state. The intent of this paper is to aid the reader in understanding the benefits of the new data set for their particular use-case.

An autonomous medical monitoring system: Validation on arrhythmia detection

Abstract: In this paper, we present a generic platform for autonomous medical monitoring and diagnostics. We validated the platform in the context of arrhythmia detection with publicly available databases. The big advantage of this platform is its capacity to deal with various types of physiological signals. Many pre-processing steps are performed to bring the input information into a uniform state that will be explored by a machine learning algorithm. Since this block plays a crucial role in the entire processing pipeline, three different methods were evaluated for detection and classification of anomalies. The results presented in this work are validated on cardiac beats, where the highest accuracy was obtained on the classification of normal beats (94%). On the other hand, atrial fibrillation and premature ventricular contraction beats were classified with an accuracy of 78%.

Relay communications support to the ExoMars Schiaparelli lander

Abstract: The European Space Agency's ExoMars Trace Gas Orbiter (TGO) arrived at Mars on October 19, 2016, three days after releasing the Schiaparelli Lander on a ballistic trajectory to Meridiani Planum. During the separation event, and subsequently during Schiaparelli's Entry, Descent, and Landing (EDL), the NASA-provided Electra Ultra-High Frequency (UHF) payload onboard TGO was used to record signals from the Schiaparelli Lander for post-processing on the ground to recover both tracking of the lander's carrier signal and reconstruction of the lander's 8 kb/s telemetry. In addition, ESA's Mars Express orbiter recorded the Schiaparelli signal, with ground post-processing providing independent tracking of the lander carrier signal, and the Giant Metrewave Radio Telescope near Pune, India was configured to provide real-time detection of the lander carrier signal. While an anomaly in the latter stages of EDL led to loss of the lander, these critical event data sets, and in particular the telemetry reconstruction enabled by the TGO Electra recording, proved essential in enabling detailed diagnosis of the anomaly. While the loss of the lander during EDL precluded the planned surface relay operations, the preparations for that activity provide important lessons learned for future Mars relay support scenarios.

Uncertainty treatment in the GOCE re-entry

Abstract: This paper presents the work to characterize and propagate the uncertainties on the atmospheric re-entry time of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite done with the framework of an ESA ITT project. Non-intrusive techniques based on Chebyshev polynomial approximation, and the Adaptive High Dimensional Model Representation multi-surrogate adaptive sampling have been used to perform uncertainty propagation and multivariate sensitivity analyses when both 3 and 6 degrees-of-freedom models where considered, considering uncertain-ties on initial conditions, and atmospheric and shape parameters. Two different uncertainty quantification/characterization approaches have been also proposed during the project. The same interpolation techniques used for non-expensive non-intrusive methods for uncertainty propagation, allowed the development of two methods based on direct optimization approaches, the Boundary Set Approach and the Inverse Uncertainty Quantification. Moreover, an innovative approach to treat the empirical accelerations has been proposed, based on polynomial expansions in the state variables. The method has been tested and further developed to consider uncertainties in the initial conditions, leading to a statistical characterization of the coefficients and representation of the possible trajectories. Finally, the investigation on the use of meta-modeling techniques to directly map a range of initial conditions and model uncertainties, as well as characteristics of the considered object, into the parameters of the skew-normal distribution that usually characterizes the re-entry time windows, bringing to a very fast characterization of the output PDF not requiring any further propagation at all, is also briefly described.

Vertical land motion and sea level change in Macaronesia

Abstract: S U M M A R Y This study addresses long-term sea level variability in Macaronesia from a holistic perspective using all available instrumental records in the region, including a dense network of GPS continuous stations, tide gauges and satellite observations. A detailed assessment of vertical movement from GPS time series underlines the influence of the complex volcano-tectonic setting of the Macaronesian islands in local uplift/subsidence. Relative sea level for the region is spatially highly variable, ranging from −1.1 to 5.1 mm yr−1. Absolute sea level from satellite altimetry exhibits consistent trends in the Macaronesia, with a mean value of 3.0 ± 0.5 mm yr−1. Typically, sea level trends from tide gauge records corrected for vertical movement using the estimates from GPS time series are lower than uncorrected estimates. The agreement between satellite altimetry and tide gauge trends corrected for vertical land varies substantially from island to island. Trends derived from the combination of GPS and tide gauge observations differ by less than 1 mm yr−1 with respect to absolute sea level trends from satellite altimetry for 56 per cent of the stations, despite the heterogeneity in length of both GPS and tide gauge series, and the influence of volcanic-tectonic processes affecting the position of some GPS stations.

Benchmarking the future of RF in space missions: From low earth orbit to deep space

Abstract: This paper reports on an internal study carried out at the European Space Agency (ESA) for assessing the reference performance of Payload Data Transmitters achieved in the mid-term. This assessment is meant to provide input to the ESA roadmaps for the 2023 time frame. The assessment is carried out for various space missions, from low Earth to deep space orbits. Taking advantage of technology evolution combined with innovative architectures and advanced digital signal processing, the paper shows how the data return in several space missions can be dramatically increased by reasonably extrapolating existing RF technology.

CNES and ESOC Flight Dynamics Operational Experience on First Nominal FOC Launch and Fine Positioning Activities of GALILEO

Abstract: The involvement of the French Space Agency in GALILEO Launch and Early in Orbit Phase (LEOP) operations dates from 2006. This involvement has required the development of an organization that is able to answer to the mission requirements taking into account operations recurrence and taking full advantage of the partnership between the French Space Agency (CNES) and the European Space Operations Center Teams (ESOC). The implementation of this organization at flight dynamics level has been set up for the first GALILEO launch in 2011 and, then, improved launch after launch. The objective of this chapter is to give an overview of the way CNES Flight Dynamics operations are organized after 9 years and four launch campaigns taking as illustration the fourth launch. After a general description of GALILEO LEOP concepts, the CNES Flight Dynamics team organization will be detailed and then illustrated in the light of the Flight Dynamics operations performed for the 4th launch, from preparation to the end of execution.

Laser Interferometer Space Antenna (LISA) Pathfinder: New Methods for Acquisition of Signal After Large Apogee-Raising Maneuvers

Abstract: LISA Pathfinder (LPF) tests the concept of low-frequency gravitational wave detection in flight: it puts two test masses into a near-perfect gravitational free fall, controlling and measuring their motion with unprecedented accuracy. LPF’s operational orbit is a 500,000 km by 800,000 km free-insertion orbit around the Lagrange point L1, also called the Sun-Earth libration point 1, which is located about 1.5 million kilometers toward the Sun. This orbit fulfills the disturbance requirements of the LPF technology demonstration package, while providing also an acceptable communication distance of less than 1.8 × 106 km.