Test Now or You Will Test Later

Testing is an essential element of the design process.

"Test what you fly, fly what you test." - Jack Bunting, Lockheed Martin Development and verification testing is at the heart of design.

Testing should be a building block approach, i.e., subscale and full scale, component and systems.

Different types of testing are needed: Development, Qualification, Verification, Certification, Acceptance.

Tests are no better than the assumptions used.

Testing is mandatory for all high performance systems. As the title of the lesson says,

―You can test now or you will test later‖. This makes the point that the initial time a product is operated will be first and foremost a test if adequate testing has not been accomplished already. In addition, no test can fully duplicate all the combined environments of operations, thus for most systems the first few uses are indeed development tests, since this is the first time all the combined environments have been experienced. This is especially true for launch vehicles that must traverse through a varied and complex set of natural and induced

environments. The following discussion emphasizes some of the basic principles of testing and verification with the overarching principle ―Testing is an essential element of the design process.‖

Jack Bunting of Lockheed Martin has said ―Test what you fly and fly what you test.‖

Others have said; ―Development and verification testing is at the heart of design.‖

Developmental testing provides understanding of the system before it is built so that those characteristics can be incorporated into the design, while verification testing determines if the as built design meets the system requirements. Testing is best accomplished using a building block approach so that the elements and the system as well as system interactions are

understood. In today‘s world cost restrictions are eliminating many of the building block tests and/or the final system tests. This places more risks on the first flights and can result in design changes after hardware is built which within itself is as costly. This principle has been demonstrated in most space flight projects. Avionics components and mechanisms have at least six types of tests: development, qualification, verification, certification, assurance, and acceptance. Finally any test is based on a set of assumptions; therefore, no test is better than the assumptions used in the test hardware and the test conditions and environments.

Types of Tests

The following is a list of the types of tests generally used on space systems.

1. Development Tests 2. Qualification Tests 3. Certification Tests

4. Process Assurance Tests 5. Acceptance Tests

6. Systems Integration and Verification Tests 7. Flight Readiness Firing

8. Other Tests (Flight tests, etc.)

Development Tests are tests conducted throughout the design cycle of a project and are used to get basic information about the characteristics of the system, so that the design incorporates these characteristics and can handle the situations induced. Developmental

tests include wind tunnel testing, scale model dynamic testing, thermal testing, materials testing, component vibration testing, acoustical testing, etc. and are fundamental in

understanding systems. Component vibration tests and thermal vacuum tests uncover design flaws that can be corrected before final design is completed.

Qualification Tests are generally of flight type or flight hardware that are tested to at least 3 sigma levels of the environments with the component carrying out certain flight type

functions. Minor changes are easily made after these tests and if changes are required, the tests are generally repeated.

Certification Tests are usually for things like liquid propulsion system engines that can be ground tested under flight conditions using both flight hardware and flight operational procedures. For example certification of the Space Shuttle Main Engines requires that two identical engines be tested under flight profiles and operational procedures for 20,000 seconds. Some of the major problems experienced during certification testing will require hardware changes and a repeat of the certification testing or flying the engines under waivers and operational constraints.

Process Assurance Tests are generally for solid rocket motors and pyrotechnic devices.

Hardware like this is either very costly or is destroyed in the tests so lifecycle testing is not appropriate. The test program usually consists of a few (say 5) motors or devices before flight. During the operational program, a motor or device is periodically pulled from the manufacturing line and tested to ensure that the build process is still meeting requirements.

Acceptance Tests are usually of avionics and mechanisms where each unit is tested when it comes off the production line. The tests are not of full flight duration and are at reduced environments. This testing is to eliminate manufacturing or infant mortality flaws. Flight liquid propulsion engines are tested in this manner using a short duration hot firing of the engine. At various times in space programs the engines attached to flight stages are ground hot fired for short durations to understand the interaction of the engines with the main propulsion

systems.

Systems Integration and Verification Tests are of many types to checkout the integrated system, validate analytical models and induced environments. The following is a partial list of integrated tests for launch vehicles.

 Hardware integration and checkout

 Integrated ground vibration (dynamic) tests to validate dynamic models

 Main propulsion tests to understand the integration of engines with the main propulsion system elements and software.

 Integrated avionics tests using hardware/software components.

 Large scale wind tunnel verification testing for aero and thermal environments.

We can also do Flight Readness Firings on the launch pad, of short duration burn time, of launch systems with liquid propulsion systems. This is done to check out the MPS of any major changes made from prior configurations. One final test program is the Flight Test programs of launch vehicles, where the first two or three flights are test flights that are heavily

instrumented in order to determine combined environments and interactions that are that are not possible to accomplish in the above discussed tests. Flight testing has uncovered many major problems that were not found during the above tests. The following is a discussion of some major tests of previous space systems.

Examples: