Component Level Testing Research Articles

Proton‐induced degradation in interferometric fiber optic gyroscopes

Recent advances in Interferometric Fiber Optic Gyroscope (IFOG) technology have enabled these devices to equal, and in some respects exceed, the performance of the floated, spinning wheel rate integrating gyroscope. However, their ability to perform in a space radiation environment has been a significant concern. Test results are presented addressing the effects of space radiation on the performance of a high precision pointing grade IFOG. Proton-induced degradation of the optical components of an IFOG is evaluated based on testing performed at the Harvard Cyclotron Laboratory (HCL). Rationale is provided for using the HCL proton accelerator as a reasonable simulation of the space environment. An analysis is presented which prioritizes the component-level dose tests based on expected radiation sensitivities. The evaluation addresses both total dose (to about 12 krad) and dose rate effects. Testing was performed at the component level as well as the system level with an expanded version of a closed-loop operational IFOG. Primary concerns include permanent attenuation and spectral transmission (wavelength) sensitivity to total dose, and angle random walk and bias stability degradation as a function of dose rate. Component level results are presented for a superfluorescent light source, integrated optics chip (IOC), coupler, and polarization maintaining fiber coils. Closed-loop transient noise results are evaluated based on dose rate testing of the IOC, coupler, and fiber coil.

Technical and programmatic constraints in dynamic verification of satellite mechanical systems

The development and verification of satellite systems covers various programmatic options. In the mechanical systems area, spacecraft test verification options include static, shaker vibration, modal survey, thermoelastic, acoustic, impact and other environmental tests. Development and verification tests influence the provision of satellite hardware, e.g. the structural model, engineering model, flight model, postflight etc., which need to be adopted by projects. In particular, adequate understanding of the satellite dynamic characteristics is essential for flight acceptance by launcher authorities. In general, a satellite shaker vibration test is requested by launcher authorities for expendable launchers. For the latter the launcher/satellite interface is well defined at the launcher clampband/separation device, and the interface is considered conveniently as a single point at the centre of the clampband. Recently the need has been identified to refine the interface idealization in launcher/satellite coupled loads dynamic analysis, particularly in cases where concentrated satellite loads are introduced at the interface, e.g. platform support struts. In the case of shuttle payloads, which are attached directly to the shuttle, shaker vibration at a single interface is not meaningful. Shuttle launcher authorities require identification of the satellite dynamic characteristics, e.g. by modal survey, and structural verification can be demonstrated by analysis, testing or a combination of analysis and testing. In the case of large satellite systems, which cannot be tested due to the limitation of the vibration shaker test facilities, a similar approach can be adapted for expendable launchers. In such an approach the dynamic characteristics of the satellite system will be identified by the modal survey test, and detailed satellite verification/qualification will be accomplished by analysis supported by subsystem and component level tests. Mechanical strength verification is usually accomplished by the static/centrifuge test. Shaker vibration tests cover dynamic response and support subsequent functional tests, e.g. deployment of appendages. As a result, the unavailability of the shaker vibration tests will have distinct implications on the functional and satellite alignment tests, particularly in cases where such tests cannot be easily performed at component and subsystem level. Consequently, alternative test verification of the satellite system to the classical shaker vibration test will vary significantly from project to project. The feasibility and constraints of an alternative satellite shaker vibration test to classical satellite system shaker vibration will be considered for the verification/qualification of satellite systems. This paper will present the utilization of emerging technologies to enhance space systems while striving for a competitive edge in satellite applications by reducing the effort for the end-to-end system. The limitations in adequately representing vibroacoustic excitation of large payload units with random shaker excitation will be presented. The employment of shaker vibration advancements to cover modal survey tests will be presented. The considerations will be amplified with realistic application examples for satellites under development. The application details will cover a wide spectrum of underlying technical and programmatic requirements.

Validation Approach for the Modular Attitude Determination Control Subsystem Implemented on Topex/Poseidon (T/P)

Abstract The Modular Attitude Control Subsystem (MACS) was developed as part of the Multimission Modular Spacecraft for NASA Goddard Space Flight Center in the late 1970s. This subsystem has demonstrated performance on multiple low earth orbit scientific missions. Application on T/P is derived from the flight proven LANDSAT-5 design and represents the first Fairchild development of the MACS. Design and development are complete with final ground verification underway to support a July 1992 T/P launch. The philosophy of the ground verification process is described in detail. The discussion will provide the approach of subsystem verification from component level testing through ever increasing levels of subsystem and satellite integration. The role of analyses will be described and some on-orbit subsystem performance issues are presented. This work was performed for the Jet Propulsion Laboratory, California Institute of Technology, sponsored by the National Aeronautics and Space Administration.

Thermal design verification of a large deployable antenna for a communications satellite

A large deployable antenna for a communication satellite requires sophisticated thermal control to satisfy the temperature requirements for electrical characteristics, and its performance must be confirmed by a thermal balance test. The results of a tradeoff study of the thermal control method for an antenna conducted in an effort to meet temperature requirement demands indicate that the thermal design of an antenna system can be accomplished by using passive thermal control techniques and heaters in spite of the large and complicated structure. Antenna system thermal balance tests are limited by the volume of the space simulation chamber. To overcome this problem, we introduce a two-step thermal design verification method consisting of component level tests and a whole antenna system level test. This paper describes the thermal control method, the thermal design verification method, and the predicted antenna temperatures in a geostationary orbit obtained from the verified thermal analytical model.