To achieve this limited goal, teams of 4 people are brought up to the Plateau by helicopter for a nominal duration of 7 days each Thursday, but these periods are extended as necessary if the meteorological conditions do not meet certain, very restrictive criteria which have been agreed jointly between IRAM and the S.A.F. (Services Aériens Français). In a few cases people have also been brought by ground transport and on foot by a mountain guide, but these are exceptions, and equally restrictive weather conditions are applied as for the helicopter flights.
All technical interventions have so far been limited to diagnosing the state of the cable car installations and doing the necessary repairs, with the particular aim of avoiding any follow-on damages to the system that has been weakened by the helicopter accident. This work which is carried out under the direction of the Technical Division of CNRS-INSU, is still ongoing. In parallel, CNRS-INSU has delegated to an engineering company the preparations which are necessary to bring back a certain functionality to the system, exclusively for the transport of materials, the aim being to reduce again the number of helicopter flights. Any change in the current level of activity on the Plateau de Bure will be preceded by an analysis of the risks associated with that activity, and such analyses are in progress. We have received the support from a team of experts belonging to the Safety Division at CERN, Geneva, which will make a safety audit for the station. They visited the Plateau de Bure during the period May 9-11, 2000.
In parallel, CNRS-INSU has prepared and issued a call for tender for an access study that will look at the technical feasibility and risks, the schedule and the costs of all means of access to the Plateau de Bure that one can realistically envisage. A similar study has been made in 1978/1979, and led to the recommendation of the cable car solution. Modern construction techniques may offer alternatives that did not exist at that time.
Within IRAM, we are looking in detail at the steps that are required to establish the actual technical state of the telescopes and the various subsystems which have not been operated since December, and to study the conditions under which observations could be restarted, at least in a limited way. As we want to keep the number of staff on the Plateau as small as possible, we will have to prioritise the activities, amongst which the necessary maintenance work on the antennas for the next winter season will inevitably be ranked very highly. Another priority task is the installation of the new correlator system which should normally take place in September this year and commissioned in the weeks to follow. Any remaining capacity will go to antenna 6, but it is clear that this antenna will not be completed this year.
All efforts mentioned above are based on the assumption that the problem of access to the Plateau de Bure can be solved and that the observatory will continue to deliver high quality scientific data for many years to come. This determination has not only been confirmed by all IRAM partners at the last Council meeting, but it has most recently been re-confirmed during a top level meeting between the CNRS and the Max-Planck-Society on May 2nd, 2000, and IRAM is grateful for this strong support.