Aluminium mirror..possible???

[xelasnave]

I notice Alex is looking for a 20 inch mirror and wondered if making a large mirror from aluminum would be possible...the cry will be that temperature fluctuation will make such a venture unviable however these days we have computers and ability to control temperature rather precisely.
So why not a large alluminium mirror with insulation and computer controls to keep it at a specific temperature.
Or are there other issues to consider?
Alex

[Wavytone]

Done, but not trivial - the machinery is well beyond DIY efforts... many examples http://lmgtfy.com/?q=optical+mirror+machined+aluminiu m
See for example
https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10566/105660P/Directly-polished-lightweight-aluminum-mirror/10.1117/12.2308200.full?SSO=1

What makes glass special is that its so stiff, yet easily abraded with abrasives to produce accurate spherical surfaces, in a process that is incredibly simple.

[xelasnave]

Hi Nick
I loved the first link☺
And the second.
So what can I now do with this 3 foot dia alluminium cylinder☺
Alex

[Wavytone]

Alex what dimensions ? You mean 90 cm diameter solid disk ? How thick ?

[leon]

Aluminum, although light and very useful for lots of projects, is very prone to oxidation, one would have to polish it every couple of months IMHO.

Leon

[Sunfish]

I think you saw the link to the Japanese SUBARU TELESCOPE video where half way through they explain the ten year development of the computer control actuators to keep the thin mirror flat by the only company who can do this.

Different application but just as complex for any thin mirror I would imagine.

Unless you only point straight up.

http://www.iceinspace.com.au/forum/showthread.php?t=175762

[Sunfish]

Aluminium oxide on the other hand, ie anodising, is extremely durable as long as you keep it away from alkaline liquids.

[xelasnave]

I was trying to be funny as I have no such disk.
Alex

[skysurfer]

The segments of the JWST (https://en.wikipedia.org/wiki/James_Webb_Space_Telescope) are made of beryllium which is a metal like aluminum, but is floating 1.5 million km 'behind' Earth as seen from the Sun, it is the largest telescope in space to date. To enhance reflectivity, the mirror is gold coated.

[alan meehan]

Well we have a mirror maker in our club ,those who know him George Lavarnos has been making telescopes and aluminium mirrors up to 30"for years grinds them all by hand,and they work i have personally looked looked through them

[Sunfish]

Are these aluminium mirrors or aliminium coated glass mirrors, or nickel coated aluminium mirrors?

[Sunfish]

I notice they mention this one can not be fixed later. The sun/ earth Lagrange point. That is remarkable.

[billdan]

The James Webb Telescope hasn't left Earth yet, the launch has now been delayed until 2021. Once its deployed there will nobody going to fix it, if it fails, just too far away.

Because its an Infrared only telescope, it needs to hide in the Earths shadow so the heat from the Sun doesn't corrupt the images.

[alan meehan]

Hi Ray these are aluminium mirrors ,of coarse not all the mirrors he makes are aluminium he grinds glass as well he sits and grinds for days or used to he is in his 70s now and does not do as many

[xelasnave]

Back when I started I would come up with ways to make a mirror rather than buy one..wild ideas..even gathing crystal from the nearby rain forest and melting it ... or making a porcelain blank with a thin sheet of glass melted onto that and a thin sheet of alluminium melted on top of that☺. The porcelain approach would allow honey comb structure...fortunately I never go ahead on any of these ideas☺ ... so ok can we build such a mirror..one meter f1.8 with a curved sensor ..heck the rods forming the the strutts could be porcelain. .bake them like cakes...or single unit carbon fibre ..nil flex..what about an array of 10 inch mirrors all bought to focus in a single curved sensor in a porcelain and carbon fibre frame...something simple you can build in your garage...seven ten inch would be doable maybe...mmm but the mount..☺☺☺☺☺

[xelasnave]

Just about finished the mount design if anyone thinks the first bit could work...
Alex

[xelasnave]

What about an array of sensors that can only pick up light paths parrallel to each other...so with an array ten meters wild would only pick up a ten meter image...like a photo copier I guess...and so you can observer ten mtr objects on Mars say☺
Alex

[Sunfish]

Very interesting. I have read about amateur mirror makers grinding aluminium and the difficulties of using the material. I did not know it was a widely ground and used mirror material without other coatings.

[astro_nutt]

What about a lens focusing light onto an optic fibre, then combining the light gathered into one image, via imaging software?...just a wild theory.