PLATO Telescope Optical Units Meeting in Bern March 12 th 2010

(proposed) Agenda 9:15 Welcome & scope of the meeting (Ragazzoni) 9:25 Optical design status (Magrin) 9:55 Radhard glass affaire (Ragazzoni) 10:15 Mechanical design status (Piazza) 10:45 Coffee break (careful in Swiss you get 2 coffes..) 11:00 AIV and prototype activity (Farinato) 11:30 Discussion on prototyping (All) 12:15 Setting up of next steps (Catala +All)

Scope of the meeting By 22 nd of March we are supposed to deliver to ESA a nominal design and a plan for prototyping Consolidating (or defining policy to achieve such a goal) the nominal design Protoyping activity is “to be assessed if necessary” accordingly to the ESA document (Nov 12 th 2009) Furthermore in view of talks with industry we should start to establish how TOUs will be splitted among the Alps…

Rad Hard glasses business From beginning we setup an internal catalog of radhard glasses BaF2 was among them and was selected as front lens BaF2 was (properly) criticized and dropped after the Yellow Book released Instead S-FPL-51 by Ohara was choosen for front lesn Other lenses assumed being shielded by 3mm Alluminum

Rad Hard glasses business Thaless design used the same glass as front lens Prophetical words extracted from ESA doc. SRE-PA/ (Nov ): “…radiation hardness.. may generate surprise in the detailed design phase.” Analysis of the L2 environment with a simplified model of the tubes commenced several weeks ago…

Rad Hard glasses business …but (detailed) outcome only yesterday (sigh…). Radation dose in L2 is 3.5 krad/yr inside the tube and 55 krad/yr for the front lens Inside lenses: only one lens significantly affected (dropping transparency to and in 3 years) Outside lens: dramatic deterioration to, and

Rad Hard glasses business The inside lens can be easily substitude by its rad-hard counterpart The front lens glass is to be replaced but this requires careful re-optimization We are confident this can be done in a week time span, but this requires here we define policy on how to choose rather than taking a final decision.

Other issues raised by the ESA document…??? Main concern is on CCD (optomechanics is 2 nd place) and assumes prototyping is being done in the coming year. Criticism of taking Thaless as starting ref. already largely discussed in ESA Pointing stability (but this is to be taken into account by the bus industrial studies) Suggestion of the aspheric being a pure conical is a good one but unfortunatley unfeasible (but we take as action to consider designing a null-lens in our study)

Other issues raised by the ESA document…??? Further to rad hardness “thermal performances and stability at low temperature not properly taken into account” so we take the action to discuss this item with our Milan collegues. “Studying optical methods of assembling optics in barrel segments” is already in place It is missing a “full verification at P/L system level” criticism that we have to take seriously in the coming time