[mental4astro (Alexander)]

The heat retention method only applies to a closed tube situation, like an SCT or Mak & even a refractor, not an open tube.

Open tube OTA's, be it a solid tube Newt or a truss structure need movement of air to avoid heat plumes by distrupting their formation.

Lining an open tube with cork will not give any benefit. Only complicate things.
* in an unventilated OTA it will still trap heat plumes
* adds an organic component that will only deompose over time, bringing the complications associated with this process

If flocking is your purpose, there are easier and less detrimental ways of achieving this.

Please do not confuse the insulation method for Maks, SCT's and fracs as applicable to open tube systems, like Newts, classical cassegrains, DK's, RC'S and the such. These need ventilation to distrupt potential heat plumes. In a closed OTA system, you are able to control the temperature differential between the fast cooling tube and the slow cooling optics and baffle tube because the air inside the OTA is trapped. In any open tube system (solid tube or truss) there is no trapped air.

If you want to control heat plume formation in an open tube, ventilation is the option available. This needs to be applied in a careful and considered way or you will introduce heat differentials inside the optics, inducing strain on the glass and distort the shape of the precious figure.

All the clues are given by professional observatories. Thing is prof obs are not designed by the astronomers. The astronomers say what they want to achieve, teams of engineers, opticians and technicians design and build the scope & surrounding structures and systems as they have the thermodynamics & material science knowledge. We should be looking more at how they do things rather than ignore them.

Alex.

Edit - I've just seen Hamish's post. How he has used the space blanket is a different application in a truss scope and there are other factors at play. It is not the same as heat retention/insulation of a closed tube OTA. Very clever , but a different application. I like it.