One of the critical activities in the systems engineering scope of work is managing requirements. In line with this, E-ELT devotes a significant effort to this activity, which follows a well-established process. This involves optimally deriving requirements from the user (Top-Level Requirements) through the system Level 1 Requirements and from here down to subsystems procurement specifications.<p> </p> This paper describes the process, which is illustrated with some practical examples, including in particular the role of technical budgets to derive requirements on subsystems. Also, the provisions taken for the requirements verification are discussed.
After having completed the phase B (front-end design) of the several subsystems, the E-ELT project is entering into the
construction phase. The subsystems specifications, interface control documents and accompanying technical
documentation resulting from the said design activities are being drafted along with the statements of work needed for
the tendering processes.
This paper presents an overview of the Systems Engineering Plan for the construction phase focusing on the specific
systems engineering processes. The goal is to ensure that this phase is developed following an efficient systems
engineering approach based on the lessons learned during phase B. The ultimate objective is that the E-ELT meets the
science requirements defined by the users while the risk of overruns in cost or schedule, which might otherwise originate
from the lack of a system perspective, is minimized.
The E-ELT is an active and adaptive 39-m telescope, with an anastigmat optical solution (5 mirrors including two flats), currently being developed by the European Southern Observatory (ESO). The convex 4-metre-class secondary mirror (M2) is a thin Zerodur meniscus passively supported by an 18 point axial whiffletree. A warping harness system allows to correct low order deformations of the M2 Mirror. Laterally the mirror is supported on 12 points along the periphery by pneumatic jacks. Due to its high optical sensitivity and the telescope gravity deflections, the M2 unit needs to allow repositioning the mirror during observation. Considering its exposed position 30m above the primary, the M2 unit has to provide good wind rejection. The M2 concept is described and major performance characteristics are presented.
The Atacama Large Millimeter/submillimeter Array (ALMA) will be composed of 66 high precision antennae located at
5000 meters altitude in northern Chile. This paper will present the methodology, tools and processes adopted to system
engineer a project of high technical complexity, by system engineering teams that are remotely located and from
different cultures, and in accordance with a demanding schedule and within tight financial constraints. The technical and
organizational complexity of ALMA requires a disciplined approach to the definition, implementation and verification of
the ALMA requirements. During the development phase, System Engineering chairs all technical reviews and facilitates
the resolution of technical conflicts. We have developed analysis tools to analyze the system performance, incorporating
key parameters that contribute to the ultimate performance, and are modeled using best estimates and/or measured values
obtained during test campaigns. Strict tracking and control of the technical budgets ensures that the different parts of the
system can operate together as a whole within ALMA boundary conditions. System Engineering is responsible for
acceptances of the thousands of hardware items delivered to Chile, and also supports the software acceptance process. In
addition, System Engineering leads the troubleshooting efforts during testing phases of the construction project. Finally,
the team is conducting System level verification and diagnostics activities to assess the overall performance of the
observatory. This paper will also share lessons learned from these system engineering and verification approaches.
FriOWL is a site selection tool for large or extremely large telescope projects. It consists of a graphical user interface
and a large global climatic and geophysical database, and is directly accessible on the world wide web. A new version
(version 3.1) of the software has recently been developed by scientists at the University of Bern (Switzerland) and
European Southern Observatory (Germany).
The main feature of the new FriOWL database is the inclusion of ERA40 re-analysis data, giving access to over 40 years
of long-term climate data. New software tools, programmed in the style of a Geographical Information System, include
the capability of resampling layers and time series extraction. A new global seismic hazard layer has been introduced, as
well as very high resolution (1km) topographic tiles. Reclassification and overlaying of layers is also possible.
Although FriOWL is primarily designed for site selection projects, it can equally be used in other climate studies. It is
especially important in the determination of the climatic stability of a potential site, and in the analysis of climatic
anomalies and trends. The long-term astroclimatological seeing and photometric statistics for the Paranal and La Silla
observatories can be used to validate FriOWL. A case study of ESO Paranal using FriOWL reveals that the deterioration
in seeing conditions since 1998 is co-incident with a strong increase in 1000 hPa geopotential height to the south-east of
the observatory; there may be a link with the Interdecadal Pacific Oscillation.
Remotely sensed data can be of great interest for the site selection of astronomical observatories. In particular, candidate
sites of the future European Extremely Large Telescope (E-ELT) of
30-60 m diameter from ESO need to be assessed and
analytically compared in their observing characteristics. Parameters such as cloud cover and precipitable water vapor
which are important for optical and infrared astronomical observations have been assessed with the MEdium Resolution
Imaging Spectrometer (MERIS) instrument on the Envisat satellite with a resolution of 1km pixel. A validation of the
data was made by comparing MERIS data and in situ measurement available from ESO observatories in Chile, La Silla
and Paranal, combined with lower resolution values from the GOES weather satellite. A detailed analysis of daytime
cloud cover from 2002 to 2006 at four sites under study both in the northern and in the southern hemisphere for the E-ELT