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the use of sandwich core
(10/6/06) DuPont granted Dream usage rights of the chart near the middle of this page. It illustrates the substantial gain that can be obtained through the use of sandwich core. Dream is the only company in the world with this type of in-house ability and expertise, specifically for highly demanding thermal and mechanical performance required for opto-mechanical systems.
Dream specializes in the use of sandwich core, using specific carbon fibers & a high performance, high temperature epoxy. We have been supporting optics with carbon fiber structures since Dream's inception in 2003. Dream's advanced composite structures have been used to support numerous substrate types and materials, from solid to engineered lightweight mirrors, from ULE to borosilicates.
The other two main benefits of Dream's specific advanced composite parts are that their CTE (Coefficient of Thermal Expansion) is extremely low and it is more impervious to corrosion and chemical attack.

As you can see below, 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.

   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) part will be exceptionally light. If a solid laminate tube is the same mass as Dream's CFSC tube, then it will be substantially lower in stiffness. Remember the "I" beam above & in real-life. Also remember that stiffness in opto-mechanical systems is far, far more important than strength. These are two distinct properties of a material, not one.

There is an abundance of strength in Dream's parts. Watch these dramatic videos to see for yourself.

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.
If the solid laminate part is close to the mass of Dream's CFSC tube, then the solid laminate tube is substantially lower in stiffness. No amount of marketing will have an affect on this physical fact. Remember, it is stiffness NOT strength that we need in high-performance opto-mechanical systems. Otherwise the optics will not hold their alignment and the focal plane quality will be hurt.

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. When someone tries to sell you on the benefits of low stiffness, simplified mirror mounts and a lack of engineering & advanced composite product experience, run...
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 on the market.

Most applications desire lower moments of inertia in order to accelerate, slew and decelerate faster. A stiffer structure also yields better pointing, tracking and final performance because the entire system is more rigid.

We have been seeing more and more companies advertise that they are using "sandwich" carbon fiber tubes. Yet these "sandwich" tubes are nothing more than solid laminate carbon fiber, with no sandwich core at all.

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.