Materials, mechanics, and vibration control behind our giant portable telescope
In the first article of this series, I explained how the size of our telescope was ultimately determined by a very practical constraint: it had to fit inside a van and inside our garage.
That limitation led to the final design of a 32-inch telescope. But defining the size of the mirror was only the beginning.
The real challenge was designing a structure capable of supporting such a large optical system while remaining portable, rigid, precise, and reasonably lightweight.
For a telescope that operates outdoors every night on the slopes of Mount Teide, these requirements are absolutely critical.
Stability, Rigidity, and Weight: The Core Design Problem
Any portable telescope that is not permanently installed in an observatory dome must satisfy three fundamental requirements:
- Structural rigidity
- Mechanical stability
- Pointing precision
But portability introduces an additional constraint: weight.
Large fixed observatory telescopes can rely on extremely massive structures, while many commercial amateur telescopes are designed primarily for cost efficiency and ease of manufacturing.
Our telescope required something different.
To achieve a structure with no major compromises, I had to combine very different materials and manufacturing technologies throughout the design.
Some components would be built from marine plywood, a material that is lightweight, extremely strong, and easy to machine. Other components would be manufactured from solid metal parts with tight tolerances, typical of precision mechanical engineering.
This hybrid approach also offered an unexpected advantage.
Controlling Vibrations in a Giant Telescope
When designing a large telescope, one often underestimated problem is vibration.
Many commercial telescopes are built mostly from aluminum, which is strong and lightweight but can also resonate at relatively low frequencies.
A good way to imagine this effect is to think about striking a metal bell. The sound continues for a long time because the material vibrates and slowly dissipates the energy.
Now imagine that such a structure holds a telescope magnifying an object 500 times. Even a small vibration could translate into a visible movement of the image in the eyepiece, making the view blurry until the vibration finally stops.
Wood behaves very differently.
If you strike a wooden structure, the vibration is short and quickly damped. Instead of ringing like a bell, the energy dissipates almost immediately.
By combining marine plywood, carbon fiber components, and high-strength nylon parts, it was possible to create a structure with:
- very high resonance frequency
- extremely fast vibration damping
- excellent rigidity
This combination makes the telescope far more stable during observation than structures built from a single material.
Designing the Primary Mirror Support
The most critical mechanical component of any reflecting telescope is the primary mirror cell.
Because this telescope had to be portable, the primary mirror would be significantly thinner than those typically used in fixed observatories.
Thinner mirrors are lighter and less expensive, but they require much more sophisticated support systems to avoid flexure. Even tiny deformations can introduce astigmatism or optical distortion at the focal plane.
A typical 32-inch mirror designed for a permanent observatory might be:
- 8–10 cm thick
- supported by a 18-point mirror cell
For our telescope, the mirror thickness would be only 52 mm.
That meant the mirror needed a much more advanced support structure: a 27-point floating mirror cell, designed to distribute the load perfectly and eliminate even the smallest deformation.
The advantage of this design is remarkable.
While the mirror cell itself weighs only slightly more than a standard 18-point cell, the thinner mirror reduces the overall mass dramatically. The combined weight of the mirror and its support structure is almost half of what a comparable system designed for a fixed installation would weigh.
For a portable telescope, this weight reduction is essential.
The mirror cell itself was designed in stainless steel, partially machined from solid blocks and partially laser-cut for maximum rigidity. The mirror and cell assembly—once optimized—would weigh around 150 kg.
To house this system, I designed a strong mirror box made from 22 mm marine plywood, providing both structural rigidity and vibration damping.
A Lightweight Secondary Mirror Structure
The secondary mirror is much smaller than the primary, but its support structure must be designed very carefully.
In our case, the secondary mirror measures 7 inches in diameter and weighs only 3.2 kg. The goal was therefore to create a structure that was:
- extremely lightweight
- very rigid
- capable of producing minimal diffraction
Because light passes across this structure before reaching the eyepiece, the support must obstruct the beam as little as possible.
The design centered around a laser-cut plywood honeycomb ring, permanently glued and assembled to create a very stiff yet lightweight structure.
The internal secondary holder was built using a combination of machined aluminum parts and 3D-printed components made from nylon reinforced with 25% carbon fiber.
The inner structure was then connected to the outer ring using tensioned steel cables, minimizing diffraction spikes while maintaining excellent rigidity.
The final weight of the entire secondary assembly—including the mirror—was about 10 kg.
This extremely low mass also allowed the telescope to be perfectly balanced without additional counterweights, which again improves portability.
The Carbon Fiber Truss Structure
The primary and secondary assemblies are connected by a truss structure, the classic solution used in large Dobsonian telescopes.
For our design, the truss tubes were made from carbon fiber, offering an ideal combination of:
- high stiffness
- very low weight
- excellent thermal stability
Two different tube diameters were used so that the structure could be designed as a telescopic system, allowing the telescope to occupy less space during transport.
This solution improved both portability and structural rigidity, while also giving the telescope a distinctive and elegant appearance.
Mount, GOTO System, and Motion Control
Once the optical tube assembly was defined, the next challenge was the mount and motion system.
The complete optical tube weighed roughly 200 kg, so the mount had to move this large mass with precision and repeatability.
To achieve this, I designed the main axes using large needle roller bearings. This allowed a very large contact surface while keeping the overall dimensions relatively compact.
For the transmission system, I chose a classic but extremely precise solution: worm gears driving large gear wheels.
This type of mechanism is more complex to design and manufacture than many commercial alternatives, but it offers significantly better precision and tracking stability.
Most of these mechanical components were designed specifically for this telescope to optimize the performance-to-weight ratio, even though this approach increased the manufacturing cost.
The electronics, however, could rely on a commercial GOTO control system, chosen for its reliability, ease of use, and continuous firmware updates.
Designing the Transport and Lifting System
At this stage, the CAD model estimated a total telescope weight of around 300 kg.
This meant the telescope also needed a dedicated mobility system capable of moving and lifting the entire structure.
The solution was a tilting support frame capable of lifting the telescope approximately 25 cm using a powerful electric motor and two heavy-duty gear reducers.
This system serves two purposes:
- It allows the telescope to be transported over uneven ground without damaging the base.
- It keeps the eyepiece height lower during observations.
In Newtonian telescopes the eyepiece sits near the top of the optical tube, so reducing the overall height helps visitors reach the eyepiece more comfortably without climbing too high on the observing ladder.
Below the tilting frame, two pairs of motorized wheels driven by powerful electric motors allow the entire structure to move easily. The system was also designed so the telescope could be loaded into the van using a small ramp.
Completing the Design
At this point, about 95% of the telescope design was complete.
Only smaller optimizations remained, such as:
- accessory mounts
- finder scope supports
- electrical system routing
- cable management
In roughly two months, the full telescope design was completed in CAD.
The next step was finally possible: ordering the custom optics and all commercial components such as motors, bearings, bolts, and hardware.
In total, the project included around 700 individual parts, many of which would have to be manufactured individually—either in our garage workshop or by specialized machining companies.
And that is where the real adventure began.
Because designing a telescope is one thing.
Actually building it is another story entirely.
In the next article, I will describe the construction of the 32-inch telescope, the challenges of machining hundreds of components, and the process of assembling one of the largest portable telescopes used for public astronomy experiences.