ESA's XMM-Newton space observatory, the flagship of European X-ray astronomy, is after it's launch in 1999 the most powerful X-ray telescope ever placed in orbit. The mission originally designed for a 10 years lifetime is planned to be operated long into this decade since spacecraft and instruments are operating admirably without major degradation. Therefore recently a system called XMM Early Warning System (XEWS) is developed to perform near-real-time trend analysis of spacecraft parameters in order to detect early degradation of components. This will enable the mission to perform early counter measures in case degradation is detected. During the development of XEWS it has been spotted that one of XMM-Newton's reaction wheels shows since 2008 non-periodic friction increase during stable pointing. We present an analysis of all four reactions wheels since the start of the mission identifying the periods of increased friction and giving some possible causes and cures for this effect that is as well know as "cage instability" and describe the impact on operations. Additionally a comparison with the wheels of ESA's INTEGRAL spacecraft which is using effectively the same Attitude and Orbit Control System will be presented..
ESA's XMM-Newton space observatory launched in 1999, is the flagship of European Xray astronomy and the most powerful X-ray telescope ever placed in orbit. The mission, originally designed for a 10 years lifetime, is planned to be operated long into this decade since spacecraft and instruments are performing admirably without major degradation. The ultimate mission end of life was defined as 2019, limited by the hydrazine reserves on board. Since scientific demand on XMM-Newton is very high and the mission has been ranked top level by the ESA advisory structure, various options to reduce the fuel consumption have been investigated. Some of these have been put in place in the course of the last years, especially we have updated the on-board software of the Attitude Control Computer to allow operating all four reaction wheels in parallel instead of only running three of them as done previously. Simulations and experience from ESA's HERSCHEL mission have shown that this should reduce the fuel consumption by up to a factor of two. In addition, operating with four reaction wheels offers the possibility to apply some measures against increased bearing noise due to aging, which has been detected on two of the XMM-Newton reaction wheels. The usage of all fuel saving methods may extend the potential lifetime to 2030. We present the implementation and results of the applied fuel saving methods and describe the increased bearing noise and its mitigation measures. In addition will report on the outcome of relubrication exercises performed on two of the wheels to cure the increased bearing noise. Furthermore we describe plans that are currently developed to operate the Hydrazine Propulsion System in the so-called near fuel depletion regime at the end of the technical life limit. In addition, ground segment evolution related to hardware, software and automation possibilities facing the new very long term perspective are discribed.
The flagship of European X-ray astronomy, ESA's XMM-Newton space observatory, was launched in 1999 with an expected lifetime of up to ten years. Through an operational change of the AOCS system, we extended its potential lifetime until the late 20ies of this century. Spacecraft and instruments are performing without major degradation. Because of the highly elliptical orbit, the spacecraft is permanently visible from the ground station network. For this and other reasons, the originally chosen on-board autonomy design is very limited. Fifteen years of inflight experience created a deep understanding of the spacecraft behavior including elaborated strategies and procedures to recover from reoccurring non-critical anomalies on board. Based on this experience, an automated ground failure detection system has been developed to provide reliable fault isolation and adapted reaction. We present here the system put in place to conduct automatically some of the nominal XMM-Newton operations and share our experience with the automatic contingency recovery tool after half a year of usage. The on-ground Failure Detection, Isolation and Recovery (FDIR) system is able to read various sorts of anomaly messages, either from the spacecraft (telemetry being out-of-limit), from the ground segment (link loss) or from the mission control software (an application stopped). Upon detection of anomaly, the automation system starts the execution of a procedure to confirm its consistency and persistency to avoid over reaction to minor events. Once the anomaly has been confirmed and identified, the recovery is kicked off under the supervision of the operator or autonomously. The targeted level of automation shall release the operator from activities that were so far manually performed, let him concentrate on other activities running in parallel, reduce the stress in contingency situations and lessen the probability of human error.
During eclipses, the spacecraft cannot rely on solar energy and must exploit the power coming from the on-board batteries. Critical for the payload is to maintain its temperature inside a specific predetermined range to avoid degradation and malfunctioning. For XMM-Newton, this is done through the Temperature Closed Loop (TCL) unit, which automatically turns on and off the heaters when the instruments reach the minimum and maximum temperatures, respectively. A possible scenario is the case when more than a single instrument reaches the minimum temperature simultaneously, thus causing a peak in the demand of power from the batteries and threatening their integrity. Such a circumstance may impact the overall mission and a better battery management is therefore required. Here we propose a solution that uses machine learning to optimize the battery consumption during eclipses. We show that after training the algorithm with past data, we are able to predict the temperature profiles of the instruments with good accuracy. These predictions provide the relevant insight to determine the optimal times at which the heaters should be turned on and off, thus improving and optimizing the current eclipse operations. The approach presented here helps overcome the issue of excessively stressing the batteries and, despite being tailored for XMM-Newton, can be extended and applied to other missions as well.
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