## 4 Experiment Analysis  
The FSS is shown in Figure 7, and the rated support load of each support point is 100 N. The weight of the force feedback sensors and connectors installed on each support point will share a part of the load. Therefore, the maximum weight of the FSS that theoretically supports the mirror is 300 kg, which is generally sufficient for the support of an optical mirror with a diameter of 1250 mm. The process of installing the optical mirror in the FSS is as follows: (i) Place the optical mirror on the 36 support points of the FSS and adjust the position to ensure that the center of rotation coincides with the support center of the FSS; (ii) calculate the support stiffness and support pressure that the FSS needs to maintain; (iii) pressurize the three sectors of the FSS to the rated pressure and theoretical height under the current working conditions and maintain them. It can be seen from the above that once the optical mirror and its process are determined, the support parameters of the FSS are determined. In addition, the amount of material removal during the processing of the optical mirror is extremely small compared to the weight of the mirror itself, the change in quality of the optical mirror can basically be ignored, and the rated load of the FSS during the working process does not change. Therefore, the change in the support height, support stiffness, and support pressure of the FSS caused by load changes is not considered during the experiment.  
Figure 6: Support pressure is affected by change in ambient temperature and air content. (**a**) The pressure of upper chamber. (**b**) The pressure of lower chamber. (**c**) The error of upper chamber pressure. (**d**) The error of lower chamber pressure.  
To determine the effect of ambient temperature and air content in hydraulic oil on the FSS in actual work, experimental studies on the influence of different ambient temperatures and air contents on the pressure of upper and lower chambers of the FSS and the support height and stiffness of the support cylinder were carried out. The 36 support cylinders were installed on the support floor, and high-strength tubing was used to connect the upper and lower chambers. The rated working pressure of the connecting tubing selected was 36.0 MPa, and the FSS was 0-1.0 MPa. During the experiment, the measured pressure of the FSS was 0.65 MPa, which was far less than the rated working pressure of the connecting tubing, and the influence of the deformation of the connecting tubing was ignored. Then, the hydraulic oil with unfiltered air and filtered air was tested on the FSS and hydraulic cylinder, respectively. When the hydraulic oil with unfiltered air was tested, the laboratory constant temperature controller was turned off after the hydraulic oil was injected, and the laboratory temperature changed with the ambient temperature. Then, the system pressure was increased to 0.65 MPa, and the FSS pressure and support height under this working pressure were evaluated with the change trend in ambient temperature. When hydraulic oil with filtered air was tested, first the air in the hydraulic oil was filtered through an air filter element. Then, the filtered hydraulic oil was injected into the FSS while ensuring that the hydraulic oil did not re-contact air during the work. Finally, the laboratory constant temperature controller was turned off so that the laboratory temperature changed with the ambient temperature. The main measuring equipment used in experiment is shown in Table 4 and the experimental site is shown in Figure 7.