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The Sun–Earth Libration Points (SEL) are an attractive location for many astronomy missions. The transfer towards a libration point orbit requires in many cases an immediate injection, meaning the launch system accelerates the spacecraft into its desired transfer orbit. The limited number of available launcher programs and the launcher dispersion then require a time-critical correction manoeuvre in order to deliver the spacecraft to its intended orbit. This manoeuvre can only be performed after the state of the spacecraft has been determined in a tracking campaign and usually takes place one to two days into the mission. The drawbacks of this strategy are on the one hand the increased Δ V requirement, since a tangential perigee velocity error has by then been amplified by a factor of approximately eight, and on the other hand, the risk of not being able to perform the manoeuvre at day two, further increasing the Δ V requirements or even losing the mission due to the limited thrust capability. This study investigates a strategy to mitigate the criticality of the first correction manoeuvre: the utilization of an intermediate highly elliptical parking orbit (HEO). The goal of this strategy is to increase the robustness of the mission design and to ease the spacecraft operation after launch. While the risk mitigation of the first mission critical manoeuvre is the primary motivation for this study there is also potential for increasing the payload mass due to the staging effect. The paper will first discuss general requirements for the transfer and two examples for missions going to a small amplitude Lissajous and a large Quasi-Halo orbit will be used to demonstrate the indirect transfer option. more...

The Astronautics and Space Station Department of the Universitaet Stuttgart has developed a design environment for the conceptual design of manned space missions. With the assistance of the ESA European Space Operations Center this design environment has been extended to cover exploration missions involving the areas of the collinear Earth–Moon and Sun–Earth libration points, which are of interest as an alternative staging location to the low lunar orbit approach for lunar exploration and for satellite servicing missions, respectively. To allow for a reliable mission design, the transfer times, the Δ V and variations in the Δ V for transfers between the different locations in the Sun–Earth–Moon system must be known, especially taking the rendezvous constraints and safety issues for human spaceflight missions into account. The results of the investigations presented in this paper cover transfer trajectories from Earth to different types of orbits about the collinear Earth–Moon libration points 1 and 2 and further on to the Moon. For the Earth to Earth–Moon libration point transfer, direct trajectories, fly-bys at the Moon and trajectories via the weak stability boundary region of the Sun–Earth system are treated. more...

Reflexion von Infrarot-Strahlung an normalleitenden Metallschichten ist immer mit Absorption verbunden. Metallschichten sind daher zum Einsatz in Fabry-Perot-Interferometern fur THz-Strahlung nicht geeignet. Bislang werden stattdessen feinmaschige Metallnetze als Reflektoren verwendet. Diesen erwachst neuerdings Konkurrenz durch Resonatoren auf der Basis von dunnen Schichten aus Hochtemperatur-Supraleitern. more...

The shape of a horizontal meniscus which is influenced both by capillarity and by an adsorbed thin film is determined. An exact solution is obtained which clearly shows the features of a transition between a curved meniscus and an adsorbed film. The method of matched asymptotic expansions is used to elucidate many of the details of the transition layer, its horizontal thickness, and the question of apparent contact angle. more...

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