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To find an optimal compromise, a thermal matched aluminum-silicon alloy (silicon contents ≈ 40 wt%) plated with NiP (AlSi40/NiP ) was investigated in a joined project of the Max Planck Institute for Astronomy MPIA and the Fraunhofer Institute for Applied Optics and Precision Engineering IOF. The main tasks of the project were the minimization of the bimetallic bending, the development of reliable stabilizing and aging procedures, and the establishment of a proven fabrication method.
This paper describes fundamental results regarding the optimization of the athermal material combination. Furthermore, the developed production chain for high quality freeform mirrors made of AlSi40/NiP is pointed out.
The project received the green light in October 2010 and in February 2013 passed a Final Design Review. Six months later, the MPG and CSIC, the observatory’s owners, made an independent evaluation concluding that CARMENES had to be ready for operations at the end of 2015. Since then, fulfilling the calendar was the driver of all project decisions. Moreover, the observatory’s survival was linked to the instrument’s success: should the instrument fail, the observatory would be closed. On the contrary, the instrument’s success would give unique capabilities to the Observatory for Big Science. Such a challenge became to be our private Olympic Games: we had to be on time. This decision definitively impacted on the project dynamics, there was no room for a delay. The deadline, December 31st, 2015, was controlled by a strict tracking of the critical path; calendar deviations were corrected with risky decisions while fast tracking or even crashing methods were applied.
The management scenario was far from optimum: most key people in the project shared their time with other duties; the observatory funding cuts; the budget was tight and distributed among the 11 partner centers with their own different rules, etc. Despite these difficulties, the close coordination among the project manager, the system engineer and the work package managers, the hard work of the whole team, and the support from the observatory were our best bets.
Two frenetic years after the calendar decision, we had manufactured, integrated and tested the two spectrographs and we were commissioning the instrument. The instrument first light took place on November, 9th, 2015 and CARMENES entered in operation at the end of December 2015. This paper describes the keys to success.
One of the most challenging systems in this cryogenic channel involves the Cooling System. Due to the highly demanding requirements applicable in terms of stability, this system arises as one of the core systems to provide outstanding stability to the channel. Really at the edge of the state-of-the-art, the Cooling System is able to provide to the cold mass (~1 Ton) better thermal stability than few hundredths of degree within 24 hours (goal: 0.01K/day).
The present paper describes the Assembly, Integration and Verification phase (AIV) of the CARMENES-NIR channel Cooling System implemented at IAA-CSIC and later installation at CAHA 3.5m Telescope, thus the most relevant highlights being shown in terms of thermal performance.
The CARMENES NIR-channel Cooling System has been implemented by the IAA-CSIC through very fruitful collaboration and involvement of the ESO (European Southern Observatory) cryo-vacuum department with Jean-Louis Lizon as its head and main collaborator. The present work sets an important trend in terms of cryogenic systems for future E-ELT (European Extremely Large Telescope) large-dimensioned instrumentation in astrophysics.
The contouring conditions have led CARMENES-NIR to be a schedule-driven project with a extremely tight plan. The operation start-up was mandatory to be before the end of 2015. This plays in contradiction to the very complex, calm-requiring tasks and development phases faced during the AIV, which has been fully designed and implemented at IAA through a very ambitious, zero-contingency plan. As a large cryogenic instrument, this plan includes necessarily a certain number cryo-vacuum cycles, this factor being the most important for the overall AIV duration. Indeed, each cryo-vacuum cycle of the NIR channel runs during 3 weeks. This plan has therefore been driven to minimize the amount of cryo-vacuum cycles.
Such huge effort has led the AIV at system level at IAA lab to be executed in 9 months from start to end -an astonishingly short duration for a large cryogenic, complex instrument like CARMENES NIR- which has been fully compliant with the final deadline of the installation of the NIR channel at CAHA 3.5m telescope. The detailed description of this planning, as well as the way how it was actually performed, is the main aim of the present paper.
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