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The far-infrared (FIR) regime is one of the few wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist yet. Neither of the medium-term satellite projects like SPICA, Millimetron or OST will resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, from highly excited carbon monoxide (CO) and especially from water lines would open the door for transformative science. These demands call for interferometric concepts. We present here first results of our feasibility study IRASSI (Infrared Astronomy Satellite Swarm Interferometry) for an FIR space interferometer. Extending on the principal concept of the previous study ESPRIT, it features heterodyne interferometry within a swarm of five satellite elements. The satellites can drift in and out within a range of several hundred meters, thereby achieving spatial resolutions of <0.1 arcsec over the whole wavelength range of 1-6 THz. Precise knowledge on the baselines will be ensured by metrology methods employing laser-based optical frequency combs, for which preliminary ground-based tests have been designed by members of our study team. We first give a motivation on how the science requirements translate into operational and design parameters for IRASSI. Our consortium has put much emphasis on the navigational aspects of such a free-flying swarm of satellites operating in relatively close vicinity. We hence present work on the formation geometry, the relative dynamics of the swarm, and aspects of our investigation towards attitude estimation. Furthermore, we discuss issues regarding the real-time capability of the autonomous relative positioning system, which is an important aspect for IRASSI where, due to the large raw data rates expected, the interferometric correlation has to be done onboard, in quasi-real-time. We also address questions regarding the spacecraft architecture and how a first thermomechanical model is used to study the effect of thermal perturbations on the spacecraft. This will have implications for the necessary internal calibration of the local tie between the laser metrology and the phase centres of the science signals and will ultimately affect the accuracy of the baseline estimations.

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Today's airport capacity is severely limited by separation of approaching and to a lesser extent departing aircraft to ensure that following aircraft do not encounter the wake vortex generated by the preceding one. The encounter of wake vortices, especially during take-off and landing, can cause critical or even catastrophic flight situations for the succeeding plane. Historically, the wake vortex separation standards are based on a 'worst-casescenario' assuming calm and still air conditions responsible for a relatively long wake vortex lifetime. They have proven sufficiently safe but are unnecessarily limiting capacity in favourable, even in average weather conditions. Thus a capacity increase brought about by any change in separation rules has at least to preserve (or, given the expected traffic growth, even improve) the current level of safety. Accordingly, wake vortex warning systems have been devised to increase airside capacity and are nearing experimental implementation. The current systems contain a forecasting component based on meteorological conditions and on propagating the vortex evolution. Secondly a sensing system is ensuring the required level of safety. Both the model predictions and the sensing systems each have their advantages but also individual drawbacks. This paper presents a novel approach on collaboration of the wake vortex prediction and the sensing part. A general overview on the wake vortex phenomenon is given and an approach of fusing the wake vortex prediction with wake vortex measurement is shown. By means of examples the major advantages of the collaboration approach are presented. A discussion on implementation constraints of the proposed system closes the paper.