Comment by weinzierl | Hacker News Reader

Comment by weinzierl | Hacker News Reader

My first job was finite element analysis for mirrors at an antenna test site. The larger mirror was about 10 m by 12 m, if I remember correctly, the other one not much smaller.

The mirrors where placed in huge RF test chamber. Being inside of it was mighty impressive. The cones must have been made of a conductive material, but I think they were also some kind of foam, which made the whole thing act like an anechoic chamber as well. Very eery experience and the complete opposite of what I experienced in the other building at the same site I had the pleasure to visit.

The environmental lab (with environmental meaning the harsh conditions space vehicles encounter). It was were the shaker equipment was operated. Basically gigantic magnetic speakers, large enough to bolt satellite parts on and subject them to the vibrations they were to encounter during the rocket launch. Solid metal parts wobbling like pudding at a noise level that'd make AC/DC blush. Not eery, but the other kind of frightening.

EDIT:

Found an image of the chamber where I worked. The reflectors we were designing were for a different, a bit bigger but otherwise similar site I unfortunately never visited.

https://www.alamy.de/aggregator-api/download/?url=https%3A%2...

Here's some info on how the absorbing cones in these chambers are constructed:

https://en.wikipedia.org/wiki/Radiation-absorbent_material

"To be sufficiently lossy, RAM can be neither a good electrical conductor nor a good electrical insulator as neither type actually absorbs any power. Typically pyramidal RAM will comprise a rubberized foam material impregnated with controlled mixtures of carbon and iron. The length from base to tip of the pyramid structure is chosen based on the lowest expected frequency and the amount of absorption required."

Bit of advice: If you are ever moving RAM, wear gloves. Looks just like anechoic foam, but has the capacity to carry very sharp bits and cut you up.

At first glance at the pic, my impression was it wasn't that impressive compared to other shots I had seen on the interwebs. Then, I saw the person for scale, and the meh went right out the window =)

I haven't been inside an RF protected room, but the eerie feeling reminds me of being in a professional sound proof recording booth. Once the door closes, you can't hear anything while hearing everything at the same time. It is surreal the first few times, and then it just becomes one of those things of going to work and you no longer notice it until you stop to think about it again.

> Solid metal parts wobbling like pudding at a noise level that'd make AC/DC blush. Not eery, but the other kind of frightening.

Reminds me of something my dad snarked on decades after happened. He was on a team doing FEA to verifying satellite structures. They told one team that a cross member on their design was going to break when subjected to launch vibrations. Other team had a big hissy fit and told them to buzz off. And it broke on the shake table.

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