D. Horizon Simulation and THD Payload Calibration and Test

In order to calibrate the THD payload a test apparatus was designed and built to simulate the on-orbit payload operation. As illustrated in the Figure below, this apparatus consisted of a temperature controlled hot plate, a chopper wheel, a mechanical slit aperture, and a Tunneling Horizon Detector payload. Tunneling Horizon Detector output data was sampled, stored, analyzed, and verified using an oscilloscope, a spectrum analyzer, and a 486 IBM compatible computer with an A/D data sampling system.

Utilizing this test apparatus, many experiments were performed to determine the THD payload sensitivity and effects of changes in several parameters; the detailed results are contained in the thesis. Based on these preliminary Earth horizon simulation tests, the THD system has a sensitivity of approximately 1,500 V/W, which meets the performance requirements of Earth horizon detection providing a 30-40 mV output signal variation at horizon crossings.

THD Payload Environmental Testing

System environmental testing consists of testing a system in the modes of operation and the environmental conditions it is exposed to. Environmental testing is especially important for spacecraft since they are complex systems that must function reliably, and semi-autonomously under a set of very harsh and different environments. Specifically, the environments spacecraft are exposed to can be categorized into three phases: pre-launch, launch, and space.

The environmental tests performed on the THD included: thermal extremes and thermal cycling, mechanical acceleration, shock, and vibration, and vacuum testing. To simulate the conditions the THD will be exposed to during launch, a systematic procedure was used to test and verify acceptable payload performance. The order the stress testing was performed was designed to correspond with the environments the SAPPHIRE spacecraft will be exposed to during launch through the space environment. Note, before and after each test a baseline functional test was performed to verify continued operation of the payload.

THD Payload to SAPPHIRE Spacecraft Integration

Since the THD Payload is a subsystem of the overall SAPPHIRE microsatellite system, horizon detector payload to SAPPHIRE integration and test was required to ensure the payload performed appropriately when integrated into the spacecraft system. Specifically, this integration consisted of testing and verifying the mechanical, electrical and mission software module interfaces. The overall spacecraft integration process for the THD payload and all the subsystems of the spacecraft was performed utilizing a 3 steps (platforms): Wood 1, Al Wood, and SAPPHIRE. The integration process for the horizon detector and the other subsystems through these 3 steps is briefly described in the following sections. A more comprehensive and detailed description of the actual spacecraft integration and test procedure is documented in the SAPPHIRE Integration and Testing Document. This document includes the integration schedule, as well as the details and scheduling of the overall SAPPHIRE system testing procedure.

To verify complete mechanical, electrical, and software interfaces and overall system operation, all of the testing plans and procedures developed for the Al Wood structure will be performed on the SAPPHIRE spacecraft. The detailed integration and testing plan is contained in the SAPPHIRE Integration and Testing Document.19

SAPPHIRE Integrated Spacecraft Environmental Testing

After completing all the system environmental tests the THD payload, as well as, the other SAPPHIRE components and subsystems will be integrated into the overall SAPPHIRE system. The integrated spacecraft will be subjected to the full battery of typical spacecraft electrical and environmental testing including complete component function test, launch vehicle testing (vibration, mechanical shock,...) and space environment testing (thermal vacuum). However, due to lack of facility resources at Stanford, it is planned that many of these spacecraft system level tests will be performed at SSDL industry and government affiliates (such as Lockheed, Loral, or NASA Ames). The detailed integration and testing plan for the SAPPHIRE integrated spacecraft is contained in the SAPPHIRE Integration and Testing Document .

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