SAMP, the Simple Application Messaging Protocol: Letting applications talk to each other

SAMP, the Simple Application Messaging Protocol, is a hub-based communication standard for the exchange of data and control between participating client applications. It has been developed within the context of the Virtual Observatory with the aim of enabling specialised data analysis tools to cooperate as a loosely integrated suite, and is now in use by many and varied desktop and web-based applications dealing with astronomical data. This paper reviews the requirements and design principles that led to SAMP's specification, provides a high-level description of the protocol, and discusses some of its common and possible future usage patterns, with particular attention to those factors that have aided its success in practice.Comment: 12 pages, 3 figures. Accepted for Virtual Observatory special issue of Astronomy and Computin

Representation and intervention: The symbiotic relationship of conservation and value

Physical and intellectual access to heritage is shaped by conservation through a longterm, cyclic and symbiotic relationship of representation and intervention (or lack of it). This informs future use and representation. Value (which may be assigned for different reasons) makes heritage. All heritage is valued for varied reasons. Some argue that heritage has inherent value; this is not covered in this paper. Some values are preferred over others in decisions on what to use or conserve. The process below describes a number of different recurring phases in this relationship, which differs with different kinds of heritage: 1. Various agents change heritage; 2. Change affects valued elements of heritage; 3. Valued elements affect how change is perceived; 4. What is perceived as damage affects decisions about conservation interventions; 5. Conservation affects which valued elements are most likely to be preserved; 6. Preserved elements influence how heritage is represented; 7. New forms of representation will affect future conservation decisions. Historically, how heritage has been represented has affected how an object is preserved. This affects later representation and use, making the relationship symbiotic

The SAS-D nutation control system

A control law is developed for the SAS-D nutation control system. Nutation is removed in a sub-optimal manner with respect to fuel consumed, but attitude errors are minimized. The research performed consist of an investigation of nutation theory and nutation due to energy dissipation, nutation detection analysis, nutation control analysis, and error analysis. The resulting nutation control system uses an accelerometer or rate gyro to sense the nutation angle theta which varies sinusoidally at the nutation frequency omega. The sensed nutation angle is compared with a threshold theta sub tau. If the sensed nutation is greater, a thrust pulse of duration equal to the period of one spin cycle is initiated. Since the threshold theta sub tau is set equal to the amount of nutation that can be removed by one thrust pulse of duration equal to one spin cycle, the spacecraft nutation is reduced to near zero. Error analysis indicates that the nutation sensed, the threshold, the amount of nutation that can be removed during one thrust pulse, and the time duration of one thrust pulse are all sensitive to the spacecraft spin frequency imparted by the Delta rocket. Thus, the nutation control system was designed to be adaptive to the possible variations in imparted spin frequency