Generating requirements for complex embedded systems using State Analysis

It has become clear that spacecraft system complexity is reaching a threshold where customary methods of control are no longer affordable or sufficiently reliable. At the heart of this problem are the conventional approaches to systems and software engineering based on subsystem-level functional decomposition, which fail to scale in the tangled web of interactions typically encountered in complex spacecraft designs. Furthermore, there is a fundamental gap between the requirements on software specified by systems engineers and the implementation of these requirements by software engineers. Software engineers must perform the translation of requirements into software code, hoping to accurately capture the systems engineer's understanding of the system behavior, which is not always explicitly specified. This gap opens up the possibility for misinterpretation of the systems engineer's intent, potentially leading to software errors. This problem is addressed by a systems engineering methodology called State Analysis, which provides a process for capturing system and software requirements in the form of explicit models. This paper describes how requirements for complex aerospace systems can be developed using State Analysis, using representative spacecraft examples.     

Development of plant protoplasts during the IML-1 mission.

During the 8 day IML-1 mission, regeneration of cell walls and cell divisions in rapeseed protoplasts were studied using the Biorack microscope onboard the Space Shuttle "Discovery". Samples from microgravity and 1g protoplast cultures were loaded on microscope slides. Visual microscopic observations were reported by the payload specialist Roberta Bondar, by down-link video transmission and by use of a microscope camera. Protoplasts grown under microgravity conditions do regenerate cell walls but to a lesser extent than under 1g. Cell divisions are delayed under microgravity. Few cell aggregates with maximum 4-6 cells per aggregate are formed under microgravity conditions, indicating that microgravity may have a profound influence on plant cell differentiation.     

Identification and origin of plant pathogenic microorganisms in recirculating nutrient solutions.

Avoidance of root-infecting microorganisms was originally considered one of the advantages of cultivation of crops in a soilless, recirculating nutrient solution. However, to date, four viral, three bacterial and 21 fungal pathogens have been identified as causal agents of root disease in hydroponically-grown crops. Root-infecting fungi, particularly those which produce a motile stage known as a zoospore, have been the primary pathogens associated with extensive crop losses. Documented sources of these root pathogens in hydroponic systems include peat, surface water such as rivers and streams, and insects. The severity of disease caused by these introduced root pathogens is primarily governed by the genetic susceptibility of each crop and the temperature of the recirculating nutrient solution.     

Experimentally tracing the key steps in the origin of life: The aromatic world

Life is generally believed to emerge on Earth, to be at least functionally similar to life as we know it today, and to be much simpler than modern life. Although minimal life is notoriously difficult to define, a molecular system can be considered alive if it turns resources into building blocks, replicates, and evolves. Primitive life may have consisted of a compartmentalized genetic system coupled with an energy-harvesting mechanism. How prebiotic building blocks self-assemble and transform themselves into a minimal living system can be broken into two questions: (1) How can prebiotic building blocks form containers, metabolic networks, and informational polymers? (2) How can these three components cooperatively organize to form a protocell that satisfies the minimal requirements for a living system? The functional integration of these components is a difficult puzzle that requires cooperation among all the aspects of protocell assembly: starting material, reaction mechanisms, thermodynamics, and the integration of the inheritance, metabolism, and container functionalities. Protocells may have been self-assembled from components different from those used in modern biochemistry. We propose that assemblies based on aromatic hydrocarbons may have been the most abundant flexible and stable organic materials on the primitive Earth and discuss their possible integration into a minimal life form. In this paper we attempt to combine current knowledge of the composition of prebiotic organic material of extraterrestrial and terrestrial origin, and put these in the context of possible prebiotic scenarios. We also describe laboratory experiments that might help clarify the transition from nonliving to living matter using aromatic material. This paper presents an interdisciplinary approach to interface state of the art knowledge in astrochemistry, prebiotic chemistry, and artificial life research.     

A geomagnetic activity forecast for improving the efficiency of aeromagnetic surveys in Greenland

In recent years several aeromagnetic surveys were carried out in Greenland and more will be carried out in the future. We describe some of the characteristics pertinent to surveys in Greenland and the problems faced and experiences made by the survey teams working there, with special emphasis on the west coast where most surveys were conducted. Both unfavorable terrestrial weather and space weather appear to complicate survey planning. We discuss possible options available to the survey teams for mitigating the adverse effect of part of the problems, namely survey data contamination by intense geomagnetic activity. The implementation of a prototype geomagnetic activity forecast service as an aid to planning survey flights is discussed in more detail. The forecast service was tested by an independent observer, and the performance of the scheme is evaluated by a subsequent comparison between forecast and actual measurements. The comparison rendered largely acceptable results, but their validity is limited by the fact that the two-month test interval was characterized by a mostly relatively quiet magnetic field.     

FGGE operations and data management

This paper summarizes the international operational monitoring and coordination of the field phase of the First GARP Global Experiment. Some preliminary assessments of the operational experience for each component of the composite observing system and data management programme are given.     

Initial experimental results from the Laboratory Biosphere closed ecological system facility.

An initial experiment in the Laboratory Biosphere facility, Santa Fe, New Mexico, was conducted May-August 2002 using a soil-based system with light levels (at 12 h per day) of 58-mol m-2 d-1. The crop tested was soybean, cultivar Hoyt, which produced an aboveground biomass of 2510 grams. Dynamics of a number of trace gases showed that methane, nitrous oxide, carbon monoxide, and hydrogen gas had initial increases that were substantially reduced in concentration by the end of the experiment. Methane was reduced from 209 ppm to 11 ppm, and nitrous oxide from 5 ppm to 1.4 ppm in the last 40 days of the closure experiment. Ethylene was at elevated levels compared to ambient during the flowering/fruiting phase of the crop. Soil respiration from the 5.37 m2 (1.46 m3) soil component was estimated at 23.4 ppm h-1 or 1.28 g CO2 h-1 or 5.7 g CO2 m-2 d-1. Phytorespiration peaked near the time of fruiting at about 160 ppm h-1. At the height of plant growth, photosynthesis CO2 draw down was as high as 3950 ppm d-1, and averaged 265 ppm h-1 (whole day averages) during lighted hours with a range of 156-390 ppm h-1. During this period, the chamber required injections of CO2 to continue plant growth. Oxygen levels rose along with the injections of carbon dioxide. Upon several occasions, CO2 was allowed to be drawn down to severely limiting levels, bottoming at around 150 ppm. A strong positive correlation (about 0.05 ppm h-1 ppm-1 with r2 about 0.9 for the range 1000-5000 ppm) was observed between atmospheric CO2 concentration and the rate of fixation up to concentrations of around 8800 ppm CO2.     

Structural and functional organisation of regenerated plant protoplasts exposed to microgravity on Biokosmos 9.

Preparatory experiments for the IML-1 mission using plant protoplasts, were flown on a 14-day flight on Biokosmos 9 in September 1989. Thirty-six hours before launch of the biosatellite, protoplasts were isolated from hypocotyl cells of rapeseed (Brassica napus) and suspension cultures of carrot (Daucus carota). Ultrastructural and fluorescence analysis of cell aggregates from these protoplasts, cultured under microgravity conditions, have been performed. In the flight samples as well as in the ground controls, a portion of the total number of protoplasts regenerated cell walls. The processes of cell differentiation and proliferation under micro-g did not differ significantly from those under normal gravity conditions. However, in micro-g differences were observed in the ultrastructure of some organelles such as plastids and mitochondria. There was also an increase in the frequency of the occurrence of folds formed by the plasmalemma together with an increase in the degree of complexity of these folds. In cell cultures developed under micro-g conditions, the calcium content tends to decrease, compared to the ground control. Different aspects of using isolated protoplasts for clarifying the mechanisms of biological effects of microgravity are discussed.