I have wanted to build these for years. I could see them in my mind and they were captivatingly beautiful kinetic structures. I wanted others to be able to enjoy that which only I could, but the materials that would make them possible hadn't been invented. Once they were and this could actually be possible, there were many hurdles to overcome; safety issues to be considered, a new way of blowing the glass to be perfected and a way of accurately balancing the structure to be devised.
A major challenge was a method of determining the length of the spars, without trial and error, so that the glass spheres would never meet each other, or the wall, no matter how the mobile moved. I quickly came to the conclusion that I couldn't keep it all in my head, not to discount the fact that the weight of things kept changing as the design and manufacturing evolved. To solve that, I wrote software to be able to predict the lengths and balance points of all of the spars in a given size mobile; all driven by the measured weight of its components, as we created them, and limited by its maximum rotational diameter.
A low mass redundant safety system was created, so that in the unlikely event that any component should fail, nothing reaches the ground. Even shipping methods were of concern. Transporting the delicate components safely from the studio to where the mobile would be assembled and flown for all to enjoy is the final crucial step to success.
Only the aircraft hardware is off the shelf. Everything else is specially fabricated for each individual mobile. The Sun and planets are blown glass. It's a challenge to have them look like the planet they represent. The density of the glass gives away quite a bit in mass but the unsurpassed beauty of it is worth the effort. Hence, they are suspended from spars of carbon fiber in order to trim back some of the mass and significantly reduce the influence of the very long moment arms that this mobile requires.
We were planning to have Burt Rutan of Scaled Composites build the spars for us but by the time our schedule came to this point Spaceship One had flown and his dance card was full, so we created a carbon fiber lab here at the studio. It was a good thing that we did. Many design changes along the way necessitated revisions and invention in the way that the spars are built.
With the composite spars, 2024-T4 aircraft aluminum, Torlon bearings, Polycarbonate, AN Type II Class 3 drilled head aircraft hardware secured with safety wire; this is as much spacecraft, Formula One or Indy Car as it is a dynamic work of art.
The mobile shown here is 12 feet (3.65 m) from Sun to Pluto/Charon mini-mobile and weighs only 38 lbs. (17 kg).
In the 40 foot (12.2 m) version, there are four mini-mobiles: one representing the Earth/Moon system, one the Asteroid Belt, one for Pluto/Charon and one for the Kuiper Belt out past the orbit of Pluto. It weighs only 49 lbs. (22 kg).