Project description:
The Navy Prototype Optical Interferometer (NPOI) is located near Flagstaff, Arizona. The NPOI facility is working in collaboration with the US Naval Observatory, Naval Research Laboratory and Lowell Observatory. The NPOI station uses a series of mirrors placed in vacuum tubes and reflects the light along the tubes to ultimately generate a picture of the sky without losing resolution while generating the same view of an equivalent diameter solid satellite dish. For example by having three strategically placed arms each of a length of 218.5 meters the three arms are capable of producing the same results as a solid dish with a diameter of 437 meters. Because these three arms are collecting starlight and then sending the starlight along the vacuum tubes using a series of mirrors the starlight must be compressed into a dense beam of photons using a beam compressor. The beam compressor takes the incoming starlight from one primary mirror and reflects it down the length of the beam compressor to a secondary mirror much smaller in diameter and then sends the new beam along a continuing series of vacuum tubes. This allows the observatory to capture more light from each siderostat station placed along the array and for a database to be made of the stars at a higher resolution leading to more stars to be categorized for the Navy. Issues with the existing beam compressor are at night it must be exposed to the elements and surrounding vibrations traveling through the bedrock. These vibrations currently have the beam compressor vibrating at a measured 15 Hz and Finite Element Analysis indicates a frequency of 17.4 Hz. These frequencies are causing the beam compressor to vibrate and distort the compressed light so the categorization of stars is not maximized. To maximize results we plan to implement Dr. Ernesto Penado’s Finite Element Analysis bracing plan found in the report “Stiffening an off-axis beam compressor mount for improved performance”. This will hopefully increase the fundamental frequency of the beam compressor causing it to vibrate much faster at a frequency of 127.6 Hz which is 7.3 times the current frequency allowing for the starlight to properly be compressed and a higher resolution image of fainter stars to be rendered from the collected data. The materials proposed to be used are aluminum tubing with an outer diameter of one inch and a wall thickness of .087 inches or less to keep close to the projected weight increase of the beam compressor. Our approach is to identify three designs for mounting the tubing to the railing of the beam compressor while constructing and testing each case proposed in the report through the use of Isotron accelerometers.
Project Requirements:
1) All added members must be exposed to the elements.
2) Weight of the added members must stay within 10% of the initial 235.9 lbs.
3) Light path must be unobstructed.
4) Distance between mirrors must remain unchanged.
5) A metal to metal contact must happen for all added members attached to the beam compressor.
6) The top part of the mount shall remain open to allow space for access.