# Analysis on the Isostatic Bipod Mounts for the HERA Mission LIDAR
## 3 Design  
The design was iterated several times, with the focus being on the initial design and a final design. The first design of the isostatic bipod mounts was presented in HELENA [6; 7], which was the starting point of the isostatic bipod mount for PALT. This first design is depicted in Figure 2.  
This design followed the one implemented on HELENA LIDAR [6; 7] (see Figure 3).  
The primary mirror of HELENA had a 100 mm diameter and 11 mm thickness.  
For PALT, a 70 mm diameter mirror was required. A first approach on the isostatic bipods mount design was based on the HELENA's optomechanics. The simulations of this design are presented in Section 4, and it was concluded that further optimization was desirable.  
In a second version, the mirror's thickness was decreased to 8 mm and the three extrude bosses were equally distributed with an 8 mm length (where isostatic bipod mounts are assembled). Both isostatic bipod mounts combine tangential and radial blades in each support leg, arranged in a triangle. The proposed design includes two blade radial flexures and a tangential blade between the radial blades, whose purpose is to compensate for radial and tangential deformations, respectively. The material chosen for this isostatic mount is Titanium Grade 5 (Ti-6 Al-4V) (see Table 1).  
Figure 3: Isostatic bipod mount assembled on HELENA.  
Figure 2: First design of isostatic bipod mount, which are positioned symmetrically around the mirror, and the representation of the adhesive pads area (highlighted in green).  
The bipod isostatic mount presented in this article is shown in Figure 4, and it has dimensions of 33 mm height and a maximum length of 8 mm. Since the optimized implementation is a key element to achieve the required performance, the optimization of the design of the isostatic bipod mount was divided into four elements: a base flexure, two columns, and a top fitting. The separation of the bipod eases the bonding process between the mounts and the mirror extrude bosses.  
The extruded areas presented in the inner upper structure of the isostatic bipod mount are adhesive areas where the mirror is to be attached. The adhesive is presented as a thin pa  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Material** & **Physical Property** & **Value** \\ \hline  & Density & 2530 kg/m\({}^{3}\) \\  & Coefficient of Thermal & \(1\times 10^{-7}\)/K \\  & Expansion & 84.7 GPa \\ Zerodur & Elastic modulus & 84.7 GPa \\  & Poisson’s ratio & 0.25 \\  & Thermal conductivity & 1.46 W/m.K \\  & Ultimate strength & 30 MPa \\ \hline  & Density & 2800 kg/m\({}^{3}\) \\  & Coefficient of Thermal & \(2.36\times 10^{-5}\)/K \\  & Expansion & 72 GPa \\ Aluminium 7075-T7351 & Elastic modulus & 0.33 \\  & Poisson’s ratio & 0.33 \\  & Thermal conductivity & 155 W/m.K \\  & Yield strength & 435 MPa \\ \hline  & Density & 4430 kg/m\({}^{3}\) \\  & Coefficient of Thermal & \(8.6\times 10^{-6}\)/K \\  & Expansion & 113.8 GPa \\ Titanium Grade 5 (Ti-6 Al-4V) & Elastic modulus & 113.8 GPa \\  & Poisson’s ratio & 0.33 \\  & Thermal conductivity & 6.7 W/m.K \\  & Yield strength & 1100 MPa \\ \hline  & Density & 1300 kg/m\({}^{3}\) \\ Epoxy 2216B/A Gray & Coefficient of Thermal & \(102\times 10^{-6}\)/K \\  & Thermal conductivity & 0.394 W/m.K \\  & Ultimate strength & 10.2 MPa \\ \hline \hline \end{tabular}
\end{table}
Table 1: Properties of the materials.  
Figure 4: Isostatic bipod mount that will be assembled in PALT. They are positioned symmetrically around the mirror, and the adhesive pads area are displayed (highlighted in blue).