Rosetta Lander Philae Research Articles

On-Board Telemetry Monitoring via Support Vector Machine with Application to Philae Solar Generator

Recent developments in machine learning for anomaly detection make it possible to use spacecraft status telemetry to produce sophisticated system health monitoring applications, that can run autonomously on-board. Both archived and simulated data are used to train intelligent algorithms to automatically detect and classify anomalous time series of the produced telemetry. The focus of this work is the application of a Support Vector Machine (SVM) based classifier to monitor the status of an interplanetary probe photovoltaic system with a minimum set of available measurements. SVM is a popular machine learning method for classification and regression and it has outstanding generalization performance. The Rosetta lander Philae is considered as test case. A complete model of power production subsystem has been developed to simulate the real telemetry. Training data, generated for nominal and faulty cases, are used to train the SVM model, with the goal of classifying permanent and temporary power loss conditions. The simulated telemetry is then used to test its performance and to identify the minimum number of measurements that is necessary for a successful classification of the failures of interest.

Structure and elastic parameters of the near surface of Abydos site on comet 67P/Churyumov–Gerasimenko, as obtained by SESAME/CASSE listening to the MUPUS insertion phase

The accelerometers of the SESAME/CASSE instrument aboard Rosetta's lander Philae recorded surface waves produced during the MUPUS hammering phase. After presenting evidence that all feet of Philae were in contact with the ground, we analyze group arrival time differences between the three feet of Philae and obtain a Rayleigh wave velocity between 79ms−1 and 400ms−1, which translate into a shear modulus μ of 3.6 MPa ≤ μ ≤ 346 MPa, and a Young's modulus E of 7.2 MPa ≤ E ≤ 980 MPa (with the lower bounds being better constrained than the upper bounds). Mixture models of snow and regolith suggest a porosity below 0.74. From the frequency-dependent dispersion of the average signal we conclude that the above values are valid for a surface layer of 10 cm to 50 cm thickness, while rigidity is significantly reduced underneath this layer. Our findings are consistent with the concept of a thin consolidated shell around a less rigid interior.

Reconstruction of the flight and attitude of Rosetta's lander Philae

Since Rosetta's lander Philae touched down on comet 67P/Churyumov-Gerasimenko on November 12, 2014, many tools have been applied to reconstruct Philae's flight path and attitude between separation, the touchdowns, collision and the final landing at Abydos. In addition to images from the cameras onboard both orbiter and lander (“OSIRIS”, “CIVA” and “ROLIS”), radio tracking results, solar array and radio data link housekeeping data, one of the major sources for timing and attitude information were two point magnetic field measurements by the magnetometers “ROMAP” and “RPC-MAG” aboard Philae and Rosetta. In this study all the different results are combined to determine in further detail what happened to Philae during its travel above the surface of 67P/Churyumov-Gerasimenko. In addition to a description of the descent dynamics and the attitude during rebound, the approximate coordinates for the collision at 16:20 UTC with the rim of the Hatmehit crater and the second touchdown are estimated. It is also shown, that Philae did not change attitude between the end of the first-science sequence and September 2, 2016.

Rosetta lander Philae: Flight Dynamics analyses for landing site selection and post-landing operations

On the 12th of November 2014, The Rosetta Lander Philae became the first spacecraft to softly land on a comet nucleus. Due to the double failure of the cold gas hold-down thruster and the anchoring harpoons that should have fixed Philae to the surface, it spent approximately two hours bouncing over the comet surface to finally come at rest one km away from its target site. Nevertheless it was operated during the 57h of its First Science Sequence. The FSS, performed with the two batteries, should have been followed by the Long Term Science Sequence but Philae was in a place not well illuminated and fell into hibernation. Yet, thanks to reducing distance to the Sun and to seasonal effect, it woke up at end of April and on 13th of June it contacted Rosetta again. To achieve this successful landing, an intense preparation work had been carried out mainly between August and November 2014 to select the targeted landing site and define the final landing trajectory. After the landing, the data collected during on-comet operations have been used to assess the final position and orientation of Philae, and to prepare the wake-up. This paper addresses the Flight Dynamics studies done in the scope of this landing preparation from Lander side, in close cooperation with the team at ESA, responsible for Rosetta, as well as for the reconstruction of the bouncing trajectory and orientation of the Lander after touchdown.

Rosetta lander Philae – Landing performance and touchdown safety assessment

This paper describes the simulation and analysis work on Rosetta lander Philae׳s touchdown dynamics which was done to support its Landing Site Selection Process. The simulation part consists of a numerical multi-body simulation to describe Philae׳s touchdown dynamics. Suitable performance metrics in conjunction with Monte Carlo trajectory data from the flight dynamics analysis yields landing area specific landing gear performance and safety figures. These were then incorporated into the site selection process with regard to landing system performance margins and touchdown safety. While Philae finally made a nearly successful landing the actual flight data were used to review and discuss the applicability of the presented simulation and analysis scheme.

COMETARY SCIENCE. 67P/Churyumov-Gerasimenko surface properties as derived from CIVA panoramic images.

The structure and composition of cometary constituents, down to their microscopic scale, are critical witnesses of the processes and ingredients that drove the formation and evolution of planetary bodies toward their present diversity. On board Rosetta's lander Philae, the Comet Infrared and Visible Analyser (CIVA) experiment took a series of images to characterize the surface materials surrounding the lander on comet 67P/Churyumov-Gerasimenko. Images were collected twice: just after touchdown, and after Philae finally came to rest, where it acquired a full panorama. These images reveal a fractured surface with complex structure and a variety of grain scales and albedos, possibly constituting pristine cometary material.

Philae Attitude Determination through Nonlinear Optimal Identification of Solar Arrays Telemetry

In Rosetta lander Philae, the ability to increase the on-comet power production gives the chance to maintain the system alive, as well as the opportunity to accomplish scientific experiments during the Long Term Science (LTS) phase. This can be accomplished if the lander operates at solar incidence angles that maximize the total power produced by the solar arrays. However, due to strict mass limitations, the lander lacks of systems for attitude determination. In this work, a method based on system identification and parameter estimation has been developed to reconstruct the Sun orbit relative to Philae in on-comet conditions. The objective is to find the azimuth and elevation angles of the Sun as a function of time, which is done by post-processing the telemetry data acquired few hours after landing. This allows us to design the optimal rotation of Philae to maximize the power produced, and thus the scientific return.

Simulation of Low-Intensity, Low-Temperature Solar Arrays with Software and Hardware Tools

In this work we discuss issues related to the simulation of low power systems with hardware means. Simulating low power systems is a challenging task as the possible low-intensity, low-temperature environment, together with possible dust deposition and ice condensation, worsen not only the production of power but also make it difficult to predict it. To overcome these problems, we have developed solutions in terms of software and hardware tools for power estimation and simulation. The developed low power, hardware solar array simulator system is briefly discussed in this paper. Although this solution is reported for the case of Rosetta lander Philae, it applies also to possible low power future missions aimed to perform in-situ operations on comets and asteroids.

The Rosetta Mission: Flying Towards the Origin of the Solar System

The ROSETTA Mission, the Planetary Cornerstone Mission in the European Space Agency’s long-term programme Horizon 2000, will rendezvous in 2014 with comet 67P/Churyumov-Gerasimenko close to its aphelion and will study the physical and chemical properties of the nucleus, the evolution of the coma during the comet’s approach to the Sun, and the development of the interaction region of the solar wind and the comet, for more than one year until it reaches perihelion. In addition to the investigations performed by the scientific instruments on board the orbiter, the ROSETTA lander PHILAE will be deployed onto the surface of the nucleus. On its way to comet 67P/Churyumov-Gerasimenko, ROSETTA will fly by and study the two asteroids 2867 Steins and 21 Lutetia.