Science and Technology

The CHARA Project, Part 1

By Marv Collins
Chief Engineer, KFI/KOST/KACE/KRTO Los Angeles

Yesterday I made my usual trip to Mt. Wilson. After finishing my business at the KOST transmitter I decided to drive over to the Mt. Wilson Observatory and check the progress of the CHARA project. I had the good fortune to meet an astronomer by the name of Nils. I thought I was going to get a quick view of the inside of the CHARA building. Instead I spent two and a half hours with Nils seeing the CHARA project and the old (1917) Mt. Wilson Hooker telescope, which is adjacent to the new CHARA building. It was an incredible tour, just the two of us. I wish I could remember and understand all that he told me. I had the chance to visit parts of the old observatory that I had never seen before. I found the original box used to haul the 100-inch mirror up the front side of the mountain. I also learned that the mirror has to be re-mirrored every three years. The re-mirroring work is done on site inside the observatory building.

I have attached a photo of the inside of the long CHARA interferometry building where the light from the six one-meter CHARA telescopes are adjusted for path length and then combined. You can see the long tracks that the mirror sleds travel on. The mirror sleds are automatically operated by a computer system. Each sled has a motor drive, two voice coil positioners and one piezo electric motor positioner. The latter is the fine adjust. Each of the three positioners has the job of keeping the succeeding positioner in the center of its range. I did not fully understand the operation of the detector tube on the sled, but its function is to cause the sled to be positioned just right so the mirror on the sled will be in the correct position. As the six telescopes are aimed from one object to another the sleds must move to bring the light beams back into synchronization. I hope to learn more on subsequent visits.

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Edited by Gary Stigall. Posted 30-Apr-99.