Quote:
Originally Posted by brian nordstrom
 I hear you but if you are worried about those values , you would not have a mirror/lense made out of glass? would you not  .
Sorry its not a perfect world we live in , in more ways than one , CF is still sexy , and a good tube material .
Brian. |
Hi Brian, That is exactly my point... the mirror has 40x the heat capacity of the CF tube and 1/10th the surface area, so it takes several orders of magnitude more time to equilibrate... It also follows that the contribution to OTA tube currents due to heat shedding is proportional to the ratio of thermal masses... ie) the disturbance to the wavefront from the OTA cooling would not be perceptible over the contribution from the main mirror.
Also, the tube will quickly pass through ambient temperature as a result of radiative cooling to the sky and will generally sit a degree or so below ambient. At this stage, if the OTA is made with something that has some sort of insulation properties, there is probably some benefit.
fwiw) The specific heat of CF is 0.16 kJ/kg K
The specific heat of steel is 0.5 kJ/kg K ... so if the steel tube is 3 times heavier, it will store 9x the heat energy of CF..
By any measure other than price, it is the absolute best material to build a telescope tube from.... period.
regards,
~c