Ground Segment Development Research Articles

11.5.3 Cost‐Benefit Analysis of SysML Modelling for the Atomic Clock Ensemble in Space (ACES) Simulator

AbstractSystems Engineering has successfully supported the space industry since its inception with methodologies and techniques to handle complex projects. However, the conventional design approach, ‘Document‐Based Systems Engineering’ (DBSE), is more and more reaching its limits. This research evaluates the benefits and the cost associated with the paradigm of ‘Model Based Systems Engineering’ (MBSE) instead of DBSE by applying the Systems Modelling Language (SysML) in the frame of the Atomic Clock Ensemble in Space (ACES) project. ACES is indeed deemed to be a suitable project for this study as it includes both a very complex ground segment as well as a challenging space segment on board the International Space Station.Following an introduction to SysML and the ACES mission, we first develop the metrics on which the cost‐benefit analysis is based on. Then, we explain the methodology and models used to perform the analysis which targets to characterise DBSE versus MBSE based on the ACES ground segment development. Then, we use the Analytical Hierarchical Process to determine weighted criteria where attention is also given to the transitional process between DBSE and MBSE.After a critical reflection upon the analysis methodology and its results, we focus on lessons‐learned from the use of SysML for the implementation of MBSE in space projects. We have identified five key areas of lessons‐learned for using MBSE with SysML itself as well as main deficiencies for Enterprise Architect, the tool used to implement SysML. We conclude with seven suggested improvements which are considered valuable to help improving the performance and acceptance of MBSE for the development of (space) projects in the future.

Rosetta Ground Segment and Mission Operations

At the European Space Operations Centre in Darmstadt (Germany) the activities for ground segment development and mission operations preparation for Rosetta started in 1997. Many of the characteristics of this mission were new to ESOC and have therefore required an early effort in identifying all the necessary facilities and functions. The ground segment required entirely new elements to be developed, such as the large deep-space antenna built in New Norcia (Western Australia). The long duration of the journey to the comet, of about 10 years, required an effort in the operations concept definition to reduce the cost of routine monitoring and control. The new approaches adopted for the Rosetta mission include full transfer of on-board software maintenance responsibility to the operations team, and the installation of a fully functioning spacecraft engineering model at ESOC, in support of testing and troubleshooting activities in flight, but also for training of the operations staff. Special measures have also been taken to minimise the ground contact with the spacecraft during cruise, to reduce cost, down to a typical frequency of one contact per week. The problem of maintaining knowledge and expertise in the long flight to comet Churyumov–Gerasimenko is also a major challenge for the Rosetta operations team, which has been tackled early in the mission preparation phase and evolved with the first years of flight experience.

Impact on Sea Surface Salinity Retrieval of Different Auxiliary Data Within the SMOS Mission

Aiming to provide sea surface salinity (SSS) maps with a spatiotemporal averaged accuracy of 0.1 psu (practical salinity units), the Soil Moisture and Ocean Salinity (SMOS) community is increasingly focusing on the determination of a robust inversion scheme to enable SSS retrieval from L-band brightness temperature data. In the framework of the Synergetic Aspects and Auxiliary Data Concepts for Sea Surface Salinity Measurements from Space project, efforts have been oriented toward a quantitative analysis of SSS retrieval using different auxiliary data sets. This paper aims to contribute to the assessment of the SMOS salinity retrieval error budget in view of the upcoming SMOS mission ground segment development. Aiming to do that, different models and auxiliary data to simulate and invert the brightness temperature data have been used. An estimation of the different auxiliary parameters' influence has been performed to quantitatively predict at what extent it is reasonable to expect to retrieve salinity once the brightness temperatures are directly measured by the sensor. Statistical distributions of the spatiotemporal averaged errors are provided

Utilising Rosetta commonality to reduce mission operations cost for Mars Express

The European Space Agency is preparing two major deep-space scientific missions for launch in 2003: Rosetta, a mission to comet P-Wirtanen, and Mars Express, a Mars Orbiter with a lander. In order to remain within the extremely tight budget available for the Mars Express ground segment development and operations, this mission will inherit and re-use as much as possible from what is developed and used for Rosetta. Although the two missions and spacecraft are very different from each other, the key to re-use of ground segment elements is in the identical interfaces to the space segment. This paper describes for the two missions the joint operations concept, the parallel mission preparation activities and the approach to achieve an integrated flight operations team. Cost savings in ground segment development and operations are identified and compared to a traditional solution. The initial implementation experiences are critically presented.