The natural history of bugs: using formal methods to analyse software related failures in space missions

Space missions force engineers to make complex trade-offs between many different constraints including cost, mass, power, functionality and reliability. These constraints create a continual need to innovate. Many advances rely upon software, for instance to control and monitor the next generation ‘electron cyclotron resonance’ ion-drives for deep space missions.Programmers face numerous challenges. It is extremely difficult to conduct valid ground-based tests for the code used in space missions. Abstract models and simulations of satellites can be misleading. These issues are compounded by the use of ‘band-aid’ software to fix design mistakes and compromises in other aspects of space systems engineering. Programmers must often re-code missions in flight. This introduces considerable risks. It should, therefore, not be a surprise that so many space missions fail to achieve their objectives. The costs of failure are considerable. Small launch vehicles, such as the U.S. Pegasus system, cost around $18 million. Payloads range from$4 million up to $1 billion for security related satellites. These costs do not include consequent business losses. In 2005, Intelsat wrote off$73 million from the failure of a single uninsured satellite. It is clearly important that we learn as much as possible from those failures that do occur. The following pages examine the roles that formal methods might play in the analysis of software failures in space missions

Design and fabrication of high quality-factor 1-d photonic crystal/photonic wire extended microcavities

We have successfully demonstrated experimentally the fabrication and measurement of high quality-factor one-dimensional photonic crystal/photonic wire extended cavities based on silicon-on-insulator. The cavities that we have investigated ranged from 3 to 8 m in length. A quality-factor of nearly 74 000 was measured at a cavity length of 5 m through the use of tapering both within and outside the cavity, showing good agreement with the finite-difference time-domain simulation approach use

Coupling strength control in photonic crystal/photonic wire multiple cavity devices

Resonance splitting has been demonstrated for two coupled micro-cavities with control of the free spectral range between the resonance peaks, together with a normalised transmission level of approximately 60%. Coupled micro-cavity-based structures that were separated by two closely spaced in-line coupler sections between the two micro-cavities have also been successfully fabricated and measured. The coupling strength of the two cavities was controlled via the use of hole tapering in the middle section between the two cavities. 2D finite-difference time-domain simulation shows close agreement with the results of measurements

La nidification des flamants de Camargue en 1970 et 1971

En 1970 et 1971, malgré le faible nombre de couples nicheurs, les Flamants ont connu un bon succès de reproduction : 280 jeunes élevés en 1970 et 1 500 environ en 1971. En 1970, il est fort probable qu’une autre colonie plus importante, probablement en Afrique du Nord, ait abouti à une réussite d’élevage puisque un certain nombre de jeunes de l’année ont été observés en Camargue avant le départ de nos jeunes. L’îlot de nidification choisi durant ces deux années n’a pas été utilisé par les Flamants depuis trente à quarante ans. Nous proposons que cette localité reste anonyme et l’appelons ic,i l’Etang A. Les flamants y ont cohabité avec plusieurs espèces de laro-limicoles, y compris les Goélands. A l’écart des intrusions humaines les colonies ont pu jouir de la tranquillité qui leur est nécessaire et les deux saisons de reproduction se sont déroulées d’une façon régulière. Aucun baguage n’a été effectué..

Les Flamants en 1964 et 1965

Johnson Alan. Les flamants en 1964 et 1965. In: La Terre et La Vie, Revue d'Histoire naturelle, tome 20, n°3, 1966. pp. 255-257