Improved shaping approach to the preliminary design of low-thrust trajectories

This paper presents a general framework for the development of shape-based approaches to low-thrust trajectory design. A novel shaping method, based on a three-dimensional description of the trajectory in spherical coordinates, is developed within this general framework. Both the exponential sinusoid and the inverse polynomial shaping are demonstrated to be particular two-dimensional cases of the spherical one. The pseudoequinoctial shaping is revisited within the new framework, and the nonosculating nature of the pseudoequinoctial elements is analyzed. A two step approach is introduced to solve the time of flight constraint, related to the design of low-thrust arcs with boundary constraints for both spherical and pseudoequinoctial shaping. The solution derived from the shaping approach is improved with a feedback linear-quadratic controller and compared against a direct collocation method based on finite elements in time. The new shaping approach and the combination of shaping and linear-quadratic controller are tested on three case studies: a mission to Mars, a mission to asteroid 1989ML, a mission to comet Tempel-1, and a mission to Neptune

Can the EU presidency make its mark on interstate bargains? The Italian and Irish presidencies of the 2003-2004 IGC

According to liberal intergovernmentalism the outcome of EU negotiations is determined by the constellation of member state interests without needing any formal leadership. This article reviews this 'self-clearing thesis' in the context of the 2003-04 IGC. It further examines what impact the European Convention, which prepared a comprehensive draft Constitutional Treaty, has had on these negotiations. Three roles of the Italian and the Irish Presidency leading the 2003-04 IGC are analysed: managing the scope of the negotiations' agenda, brokering efficient deals and promoting specific interests. Little evidence is found that the Presidencies really made a substantial difference in brokering the eventual deals or in promoting their own interests. However, the presence of the Convention's draft allowed the Presidencies to adopt an agenda management strategy that changed the nature of the negotiations and the power configuration of interests and thus radically departed from those normally applying at IGCs