A new and patented polishing tool called Orthogonal Velocity field Tool (OVT) was built and its material removal characteristics from Chemical Vapor Deposition Silicon Carbide (CVD SiC) mirror surfaces were investigated in this study. The velocity field of OVT is produced by rotating the bicycle type tool in the two orthogonal axes, and this concept is capable of producing a material removal foot print of pseudo Gaussian shapes. First for the OVT characterization, we derived a theoretical material removal model using distributions of pressure exerted onto the workpiece surface, relative speed between the tool and workpiece surface, and dwell time inside the tool- workpiece contact area. Second, using two flat CVD SiC mirrors that are 150 mm in diameter, we ran material removal experiments over machine run parameter ranging from 12.901 to 25.867 psi in pressure, from 0.086 m/sec to 0.147 m/sec tool in the relative speed, and 5 to 15 sec in dwell time. Material removal coefficients are obtained by using the in-house developed data analysis program. The resulting material removal coefficient varies from 3.35 to 9.46 um/psi hour m/sec with a mean value of 5.90 ± 1.26(standard deviation). We describe the technical details of the new OVT machine, the data analysis program, the experiments, and the results together with the implications to the future development of the machine.
In this study, we propose a thermal design for an on-board blackbody (BB) for spaceborne infrared (IR) sensor calibration. The main function of the on-board BB is to provide highly uniform and precise radiation temperature reference sources from 0 °C to 40 °C during the calibration of the IR sensor. To meet the functional requirements of BB, a BB thermal design using a heater to heat the BB during sensor calibration and heat pipes to transfer residual heat to the radiator after calibration is proposed and investigated both numerically and experimentally. The main features of the proposed thermal design are a symmetric temperature gradient on the BB surface with less than 1 K temperature uniformity, ease of temperature sensor implementation to estimate the representative surface temperature of the BB, a stable thermal interface between the heat pipes and BB, and a fail-safe function under one heat pipe failure. The thermal control performance of the BB is investigated via in-orbit thermal analysis, and its effectiveness is verified via a heat-up test of the BB under ambient conditions. These results indicate that the temperature gradient on the BB surface was obtained at less than 1 K, and the representative surface temperature could be estimated with an accuracy of 0.005 °C via the temperature sensor.
A carbon composite was synthesized by mechanical mixing of ball-milled graphite and PVC powders, followed by pyrolysis reaction of PVC. Natural graphite ball milled under atmosphere of argon or air leads to a disordered structure. It appears that the electrochemical lithium intercalation reaction is dependent on the atmosphere in which the graphite is ball milled. The carbon composite obtained using air-milled graphite shows a high reversible capacity and high initial coulombic efficiency compared to argon-milled graphite. This is attributed to the enhanced thermal stability of a disordered structure in the air milled sample. For the one with air-milled graphite, the disordered structure is maintained during heat treatment, while argon-milled graphite is partially crystallized.
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