Qualification Testing

The purpose of a qualification test program is risk mitigation. Unlike terrestrial power supply applications, environmental testing is performed in conjunction with analysis, not as an either/or situation. Testing alone may not reveal design margins or weak spots. Analysis alone may be flawed. Therefore, a balanced combination of analysis and testing is generally favored. The most significant tests are usually shock, vibration, thermal vacuum, EMI and radiation.

Most applications for space power supplies have a relatively benign shock and vibration environment on orbit, but a severe requirement during transportation and launch. Pyrotechnic shocks are normally the most challenging requirement for low mass units. Thermal vacuum testing is another important area that cannot be confirmed without testing. Every heat dissipating component must have a reliable path of conductive heat removal. Many power supplies designed for non-space use neglect this necessity, and so fail when exposed to the hard vacuum environment of space.

EMI is another important area that varies widely from application to application. Because of the small capacity of most space electrical bus systems, there has been little standardization of bus specifications. This translates to a wide diversity of EMI requirements. Test plans, always important, assume an even greater importance in light of this diversity.

Successful testing programs characterize the equipment with minimal cost and schedule impact. One of the best ways found to facilitate this is to precede a formal qualification test program with an informal pre-qual program.

A pre-qual program is designed to hit the hot spots, or technical high risk areas of the development task, at an early stage in the program and at a modest cost. An assessment is made of the highest technical risk areas, and only those areas are tested. Test plans, procedures and reports are kept informal, which holds down costs. Source inspection is not invoked, streamlining the schedule. A pre-qual program can be performed with a brassboard, prototype or pre-production unit, and does not require flight level hardware.

A pre-qual program has two benefits. If it precedes a formal qual program, it gives early assurance of a satisfactory design. If testing shows that changes are necessary, changes can be made on non flight hardware, avoiding the high costs and long lead times of flight hardware.

The second benefit of pre-qual testing exists when the next higher assembly beyond the power supply will be subjected to formal qualification tests. In that event, the pre-qual program will give reasonable justification for combining the formal qualification test of the power supply with the testing of the next higher assembly.

Test plans are an important part of any test program. It is not correct to assume that specifications covering environmental or EMI testing are in themselves sufficient for conducting tests. What is missing is the mechanical configurations, electrical connections, ambient conditions and pass/fail criteria. These elements must be reviewed by the test activity, as well as the customer, prior to conducting the tests. The test plan is the vehicle that describes the missing information prior to test execution.

When the test plan is approved by the customer, a test procedure is generated, covering the actual testing. This embodies the elements of the test plan. The test procedure describes the testing in greater detail, listing the equipment or facilities to be used as well as the sequence of testing.

Following the actual testing, test reports are generated. They describe the test results, and are often accompanied by photographs. If any anomalies have occurred during testing, they are noted in the report.