Showing papers by "European Space Operations Centre published in 2000"

Representing Requirements on Generic Software in an Application Family Model

Abstract: Generic software is built in order to deal with the variability of a set of similar software systems and to make their construction cheaper and more efficient. A typical approach to representing requirements variability in generic software is through the use of parameters, i.e. quantitative variability. Qualitative variability, however, is often dealt with in an implicit and ad hoc manner. In previous work, we used discriminants for representing qualitative variability in a model of application family requirements. In this paper we extend this approach by combining discriminants and parameters for modelling qualitative and quantitative variability. Using this approach, we present a case study in the domain of spacecraft control operating systems and focus on building an application family model. The experience suggests that our approach provides a clean and well-defined way of representing the variability of generic software.

Autonomous Procedure Execution: A Means Of Reducing Rosetta Operations Cost

Abstract: The International Rosetta Mission is a scientific mission of the European Space Agency. It will be launched in January 2003 and it will reach, after a journey of about 9 years, the nucleus of comet P/Wirtanen, to orbit around it for almost two years. The characteristics of the mission, in particular its long duration and the fact that the most critical and intense operations phases occur many years after launch, induced ESA to define an operations concept that could take advantage of the low activity level required during the cruise phases. The aim was to minimise human intervention during non-critical mission phases by means of automated ground systems operations, in order to reduce the size of the flight control team.

Rosetta Common Check-Out and Control System: A Challenge and a Way to Reduce Cost

Abstract: The International Rosetta mission will be launched in 2003. After a flight of about 9 years the spacecraft will approach comet P-Wirtanen and orbit it for almost two years, performing scientific investigations of the comet nucleus environment, at distances of the order of a few kilometers from the nucleus surface. Rosetta will also release a probe that will land on the surface of the nucleus to perform in-situ investigations.

Slew Calibration for Spin-Stabilized Satellites

Abstract: The slewing of the rotation axis of a spin-stabilized satellite along a rhumb line by means of thrust pulses is addressed.Itisshown thatonecan calibratethemean thrustleveland themean pulsecentroiddelay independently from attitude knowledge before and beyond the slew. To achieve this one has to consider two successive slews or a slew broken down into two legs with different rhumb angles. The basic condition is that the thruster behavior is approximately equal in both legs. The required data are the solar aspect angles each time just before and just beyond the reorientation maneuvers. For the special case where the breakdown is made in two equal legs, called doglegs,ithasbeeninvestigatedwhichpathincreasehastobeexpectedandtowhichextenttheprobabilityincreases to end with a larger off-target error than with a single direct slew. Also the extrapolation of the initial attitude by using the planned maneuver data with corrrected calibration has been inspected by means of covariance analyses. In all of these aspects, the results of analyses are favorable. Finally, the calibration technique has been applied in three very large maneuvers on three similar spacecraft and the corresponding operational results are discussed. Nomenclature k = pulse strength calibration factor N = spin axis direction unit vector S = sun direction unit vector D att = angular difference between attitude estimates, deg d = declination in a sun coordinate system, rad ≤ = rhumb angle correction term, rad g = selected rhumb angle offset, rad h = sun angle, rad k = right ascension in a sun coordinate system, rad q = rhumb angle of a maneuver on the Mercator projection, rad r i = standard deviation of parameter i u = maneuver pathlength, rad {}0/e = parameter for initial/e nal attitude of a maneuver