PLATO Telescope Optical Units

Meeting in BernMarch 12th 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 22nd 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 12th 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/2009.081 (Nov. 12 2009):

• “…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 60%@500nm and 82%@650nm in 3 years)

• Outside lens: dramatic deterioration to, 8%@500nm and 75%@700nm...!!!

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 2nd 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