Structural design of an innovative electrical connector for Satellite Test of the Equivalence Principle

Satellite Test of the Equivalence Principle is developing a spacecraft to improve current measurements of the equivalence principle by five orders of magnitude. The primary science instrument is a precision differential accelerometer with a sensitivity of 10-48 g. This level of accuracy is achieved through precision engineering and manufacturing of a quartz accelerometer housing, high-precision superconducting sensors, and a drag-free control system which minimizes experimental disturbances. For the past several years, STEP has been engaged in a technology development effort to create the first flight-like prototype of the accelerometer.; One critical system within the accelerometer is the Electrostatic Positioning System (EPS) that uses an array of 17 electrodes to capacitively detect the test mass position and orientation in five degrees of freedom. A necessary step in developing the accelerometer prototype involved designing an electrical connector that could be used to connect a cable to the thin film gold coatings that form the EPS electrodes. A demanding set of design constraints made this a tightly-constrained design problem requiring an innovative solution. The connector needed to fit within a 2 mm diameter by 1 mm through hole. In addition to this small size, the connector could not outgas, shed particles, or be made of materials that are magnetic at low temperature. The connector needed to be easy to install, easy to remove, and robust even after numerous thermal cycles to 4 K. Because the connector will be onboard a spacecraft, electrical and mechanical reliability was of paramount importance.; After considering many designs that failed to meet all of the requirements, I developed a successful electrical connector that mimicked an internal retaining ring. The beryllium copper electrical connector acts as a spring when it is installed providing a sufficient force to make reliable electrical contact with the gold coating on the surface of the hole. A miniature coaxial cable is soldered to the connector to transmit the electrical signal outside of the accelerometer.; Developing a successful design required extensive technical analysis. Finite element models were developed to determine the spring force the electrical connector would provide. Hand calculations verified the finite element analysis results. A material for the connector was selected and then its magnetic properties were measured at low temperature to verify the connector would not interfere with the performance of the inductive position sensors. The connector was manufactured using a wire EDM process and then metrology was performed to assess the accuracy of the manufacturing method. Once the cable was soldered to the electrical connector, tests were conducted to determine low temperature reliability. Finally, experimental modal analysis was used to validate the finite element model and experimentally determine whether the electrical connector was applying the expected spring force. Formal design methodology was used to validate the success of the connector design.; With a successful connector it was possible to begin testing the EPS. Measurements were performed to determine the amount of electromagnetic interference between the two primary position sensors: the capacitive position sensor (EPS) and the superconducting inductive position sensor (SRS). Test results showed that the EPS couples directly to the SRS pick-up coil as well as indirectly through the test mass. Low temperature testing showed that the coupling decreased dramatically below niobium's superconducting transition temperature of 4 K. An important outcome of the testing was that EPS performed similarly at room temperature and low temperature, indicating the EPS could primarily be tested at room temperature. Future testing will assess whether the EPS affects the SQUID noise in the inductive circuit.