Dream's extensive use of the ideal matrix; sandwich core


As you can see above, when the distance between skins is increased to 4t, the stiffness increases by 37 times and the strength increases by 9.2 times, yet weight is only increased by 6%. Dream routinely produces sandwich cored composites with 8-15+ t.

One of the driving factors for the performance of opto-mechanical systems is stiffness. Without enough stiffness and thermal stability in the structures, optical components (mirrors and/or lenses) will not stay in alignment (tip/tilt, de-space, de-center), initially causing off-axis optical performance to degrade and eventually hurting even on-axis performance. A lack of stiffness can obviously affect whole-field pointing and tracking as well, blurring the image. In 2003 Dream realized Carbon Fiber skinned Sandwich Core (CFSC) was an ideal choice for opto-mechanical systems. This technology requires the proper choices for; sandwich core(s), resin system, fabrication techniques, vacuum bagging, baking, etc. It is the full combination of all choices, materials and fabrication methods used that will determine the final performance of the part.
Dream specializes in the use of sandwich core (both honeycomb & foam), using specific carbon fibers & a high performance, high temperature epoxy. Dream has been directly and indirectly supporting precision optics with carbon fiber structures since Dream's inception in 2003. Dream's advanced composite structures have been used to support numerous mirror substrate types and materials, from solid to engineered lightweight mirrors, from ULE to borosilicates.
The other two main benefits of Dream's in-house composite parts are that their CTE (Coefficient of Thermal Expansion) is extremely low and it is more impervious to corrosion and chemical attack.


When compared to metal or even solid laminate (no core) carbon fiber parts of the same stiffness, Dream's Carbon Fiber skinned Sandwich Core (CFSC) parts will be exceptionally light. The right image shows ~1000 pounds of "live" weight on a 16.0 pound CFSC Dream board (2' wide, 6' long and 1.1" thick).

There is an abundance of strength in Dream's parts. Watch these dramatic videos to see how rugged Dream's CFSC parts are.

There are parts where solid laminate CF is a better choice, like small parts. But not for large, main structures; telescope/instrument tubes, backplates, larger parts of the primary mirror mount, etc. For those parts CFSC outperforms solid laminate hands down.
Solid laminate composites are easier for the average composite shop to fabricate but they do not come remotely close to the stiffness and therefore performance that is achieved using sandwich core. This is why Dream specializes in CFSC use.

Dream's CF/CFSC mirror mounts are achieving AND maintaining the surface of the mirror, as it moves during real-world use, to a fraction of a wavelength of light. This is an extreme mechanical requirement.
Dream's thick-walled sandwich core tubes truly have no rivals, which is why we developed them in the first place. They did not and still do not exist anywhere else because of Dream's experience and expertise with this technology. Most applications desire lower moments of inertia in order to accelerate, slew and decelerate faster, allowing demanding project goals to be met. A stiffer structure also yields better pointing, tracking and final performance because the entire system is more rigid. When temperature is dynamic high stiffness is not the only parameter that matters. Thermal stability matters. Focus shifts are one thing but a mirror mount with a much more athermal relationship to the mirror and/or lens will distort that optical surface less than traditional material choices.

Dream produces all of the inserts that we use inside the tubes, mirror supports, etc., in-house. These threaded inserts are stainless steel and have outstanding performance, as tested indepenently by a lab.