Project Description

While touring the NPOI facility grounds and being shown the physical locations of the project's environment, it became obvious to our group that the driving force for our project was the safety of the employees who interact with the current system. Although the automation of these mirror covers will eliminate unnecessary man hours; more importantly, the current system involves an unacceptable level of danger for the operators. Coupled with the possibility of damage to highly sensitive equipment that is put at risk with the current procedure, our needs statement is as follows:

Potential for injury to employees of the Navel Prototype Optical Interferometer is unacceptable.
A solution for removing and replacing essential mirror dust covers must be found while maintaining functionality of existing equipment, adding a minimum amount of mass to the system while incorporating autonomous/ semi-autonomous operation during power loss situations.

The new cover must operate remotely, from outside of the equipment housing, keeping observers out of potential danger and protecting the equipment from accidental impacts. The mirror must be kept in a nitrogen environment in order to displace moisture. In order to do this, an orifice, 4 thousands of an inch in diameter must allow 10 psi of nitrogen to be injected through the mirror cover, purging atmospheric air. The nitrogen flow needs to automatically shut off when the cover is open. In addition, the equipment must maintain balance so that motor components are not exposed to excess stress during rotation. The new equipment should enhance the performance of the equipment that is in place and should in no way hinder the operations of the equipment.

The cover must not block any light from the mirror’s lens. The full range of motion of the siderostat must be maintained after installation of the automated cover. This includes a vertical tilt from -10 to 60 degrees and a horizontal pan of -60 to 60 degrees. The cover must be able to close in the event of a power failure.

Testing new designs at NPOI might jeopardize the equipment which is expensive and precise therefore a scale model of the housing will be constructed to provide a more appropriate test environment. The model will need to replicate the -10° to 60° range of motion of the siderostat to assure that our design does not hinder the movement of the mirror. The scale model will also assure that the mirror cover does not interfere with light collection while in the open position. The design is also required to operate between a temperature range of -20°F to 100°F. Critical components will be tested in an environment cooled by dry ice in order to replicate operational requirements. Large components will be tested during sufficiently cold nights. A comprehensive thermal analysis will supplement findings if negative 20 degrees is not reached. The design will be tested with the nitrogen purge operating to assure the design does not restrict the flow of the inert gas protecting the siderostat. NPOI will provide the compressed nitrogen for this test.