Origins of JWST multi-mirrors technology

[gdelottle]

JWST has brought the use of segmented mirrors to the forefront. In fact, this technology has long been the norm for large telescopes because of the light weight and current ability to accurately control their shape. Keck, Grantecan, GMT, TMT and ELT, by the others but not forgetting all gamma-ray telescopes (from MAGIC to HESS to CTA) do or will make use of segmented mirrors, almost all of them hexagonally shaped as for the JWST.

The question is: who first conceived segmented mirror technology and which was the first telescope actually built to use this technology? Wikipedia and many sources point to Jerry Nelson, LBNL in the '80s. However, there are indications that Guido Horn d'Arturo, an Italian astronomer, conceived the idea of hexagonal multi-mirror telescope as early as 1932. "After a 1 m diameter prototype, in 1952 Horn d’Arturo made a 1.8 m diameter telescope, assembling 61 hexagonal mirrors, each of which was aligned and focused by three underlying screws" (from https://adsabs.harvard.edu/pdf/2018MmSAI..89..448B).

Does anyone have further information regarding the origin of this extremely fruitful idea? Thanks in advance for any hint.

[Blackstar]

JWST has brought the use of segmented mirrors to the forefront. In fact, this technology has long been the norm for large telescopes because of the light weight and current ability to accurately control their shape. Keck, Grantecan, GMT, TMT and ELT, by the others but not forgetting all gamma-ray telescopes (from MAGIC to HESS to CTA) do or will make use of segmented mirrors, almost all of them hexagonally shaped as for the JWST.

The question is: who first conceived segmented mirror technology and which was the first telescope actually built to use this technology? Wikipedia and many sources point to Jerry Nelson, LBNL in the '80s. However, there are indications that Guido Horn d'Arturo, an Italian astronomer, conceived the idea of hexagonal multi-mirror telescope as early as 1932. "After a 1 m diameter prototype, in 1952 Horn d’Arturo made a 1.8 m diameter telescope, assembling 61 hexagonal mirrors, each of which was aligned and focused by three underlying screws" (from https://adsabs.harvard.edu/pdf/2018MmSAI..89..448B).

Does anyone have further information regarding the origin of this extremely fruitful idea? Thanks in advance for any hint.

The MMT was built in 1979, so multiple mirrors in a telescope predates the 1980s.

https://en.wikipedia.org/wiki/MMT_Observatory

[ttle2]

It seems that Horn d’Arturo's segmented telescopes weren't co-phased, so their diffraction limit would have been set by the size of an individual segment. It didn't really matter at that time, though, since without adaptive optics seeing wouldn't allow diffraction-limited imaging anyway.

MMT was co-phased a few years after its construction (1983 or 84 I think), so I believe that's the first "modern" multiple/segmented mirror telescope.

[jg]

The original form of the MMT was 6 light weight conventional mirrors on a single alt-az mount; it also was one of the first big alt-az telescopes.  The mirrors were left over from an Air Force satellite program, IRRC.

It was certainly operating as a single large telescope by sometime in 1979, though initially mirror stacking was a manual affair. I remember having to take each image and stack them in a manual process. Resolution was pretty much atmospheric seeing limited. I remember us dropping a single object down a .7 arc second wide slit in the spectrograph of that era on a good night, with no light spilling over the wings of the slit.

The MMT was also one of the first big telescopes that worked hard to ensure that the "seeing" of the completed telescope matched the site survey, by various measures including a tunnel that pulls air in the slit and exhausts it downwind, ensuring that heat from the building and instrumentation does not have a chance to hurt the air. It is unfortunate that Mt Hopkins only had space on its summit for one major telescope.

Other enhancements occurred over the years, as the MMT history explains; these days it is one of Roger Angel's very large single mirrors that are "spun" in the mirror lab at UofA.

[gdelottle]

My apologies: I forgot to include the... Multiple-Mirrors Telescope in my list. 

p.s. I met Roger Angel long ago. He was interested in a project I was involved in. Pure genius in the field.

[gdelottle]

The original form of the MMT was 6 light weight conventional mirrors on a single alt-az mount; it also was one of the first big alt-az telescopes.  The mirrors were left over from an Air Force satellite program, IRRC.

Several sources point to an abandoned KH-10 DORIAN reconnaissance mission project as the source of the original mirrors for the MMT. Conversely, I haven't found any reference online to an IRRC project. Can you please explain what are you referring to? Maybe that was an older acronym for the same project?

[Jim]

Conversely, I haven't found any reference online to an IRRC project. Can you please explain what are you referring to? Maybe that was an older acronym for the same project?

He meant IIRC.   " if I remember correctly"

[gdelottle]

Thanks for clarifying. I was not familiar with this acronym.