Gaining a competitive edge with fast-turnaround satellite testing

Major headaches can arise when a satellite must be shipped to an off-site lab for extensive testing, potentially eating away precious time in the program schedule. Expensive satellite parts can be easily damaged in transit or by test cycles that are not carefully controlled. These hazards are being mitigated at a new state-of-the-art “Factory of the Future”. Becoming fully operational in February 2004, the Factory of the Future was conceived by Spectrum Astro Inc. of Gilbert, Arizona. Spectrum Astro is a leading prime contractor in the design and manufacturing of satellites and was recently acquired by General Dynamics C4 Systems, a business unit of General Dynamics.

The factory encompasses more than 135,000 square feet of assembly and test space, including a leading-edge acoustic and vibration chamber that can test up to space shuttle class satellites. A 62-foot high bay supports final assembly and testing of large satellites weighing up to 11,000 pounds. Current projects include NASA’s 10,000-pound Gamma-ray Large Area Space Telescope (GLAST). In the same facility, the testing of these complex and delicate satellite systems is performed using LMS Test.Lab
and a 176-channel LMS SCADAS III system. The LMS system controls the test profile, triggers automatic safeguards when prescribed limits are exceeded, analyzes data in real-time and displays results almost immediately. Testing is key to ensuring that satellites are properly designed and built, and that they literally get off the ground without a hitch. This is how the engineers verify that sensitive payloads can actually withstand extreme g-forces, shock and vibration during liftoff, flight, and deployment.

During acoustic testing, satellites are blasted with up to 160 dB sound pressure from high-intensity acoustic horns that simulate the powerful launch acoustic environment. Third-octave band control is used to achieve the required amplitude and frequency distribution curve in a spectrum from 25 to 1,600 Hz with carry-over to 10,000 Hz. The profile matches the sound output of particular launch vehicles such as Delta, Titan, Pegasus, Taurus, or Atlas rockets, for example. Likewise, vibration tests are performed using profiles matching the type of launch vehicle. Typically, profiles consist of a range of random vibrations and a sine sweep. For these tests, satellites are placed on a 65,000-pound shaker table that can deliver up to a two-inch stroke.

Modal tests are performed mostly during satellite development to verify mode shapes and resonant frequencies previously computed through Finite-Element (FE) analysis on the overall structure as well as individual subsystems and assemblies. In this test, an array of  “stingers” (small solenoids that deliver precise input loads at specified locations) excite the structure mounted on an 800,000-pound modal seismic mass that isolates it from ambient noise and vibration. Also performed during development are static loading tests where the satellite structure and its subsystems are subjected to a compressive “push” or a tensile “pull” force with a hydraulic actuator to simulate the steady-state g-forces experienced during launch and ascent. Sensors on the structure measure stress, strain and deflection, which are then compared with previous calculations done with FEA.

Unfortunately for satellite companies, subjecting satellites to these tests often introduces troublesome delays and may put complex, one-of-a-kind equipment at risk. Advanced satellites can be as large as a house. Yet delicate structural components for deploying solar arrays and antennas, for example, can be as fragile as an eggshell. On-board instrumentation typically contains some of the most sophisticated - and touchy - optical, infrared, and magnetic instrumentation systems known to man. And the sensitive electronics providing the power and embedded intelligence to bring satellites to life in space are complex networks of interconnected components and subsystems that can be jarred loose.

Conventional testing systems often represent a bottleneck in the overall development process. Sometimes hours are required for the system to process the huge amounts of data and print out right up until final vibration and acoustic acceptance tests are being run.

Too much is riding on these tests for satellite manufacturers to trust a system that makes them wait for results and does not have the tight controls needed for advanced levels of environmental testing. To assist in overcoming these limitations of traditional systems, the General Dynamics Factory of the Future is equipped with an LMS SCADAS III data acquisition front-end and LMS Test.Lab software that precisely controls the test profile, triggers automatic safeguards when prescribed limits are exceeded, analyzes data in real-time and displays results almost immediately.

Advanced data acquisition and control

With LMS Test.Lab, real-time control is maintained so that every set of processed data samples on every channel is compared with prescribed limits defined by the user. When safety limits are approached or exceeded, the system may automatically abort the test via a control loop that triggers an end-test command. Fast turnaround of results is phenomenally important in satellite testing. So one of the greatest values of the LMS system here is that it acquires and analyzes test data in near real-time instead of waiting hours as with other systems. On-screen results are displayed almost instantly, and batch plotting provides hardcopy at the end of a run with a single click. Plots are generated at three pages per second. Results are also available on-line through a desktop capability used to quickly view results, analyze specific areas of interest, and generate reports. Real-time data acquisition and analysis is a part of each level of testing, from developmental component-level tests to verification, qualification, and final acceptance testing.

During developmental testing, engineers are given immediate feedback on modal and static loading tests to verify their FE analysis calculations and associated designs and dynamic models. This keeps design engineering moving forward to meet release-to-manufacturing deadlines and spot potential problems earlier and more quickly than would otherwise be possible. Real-time capabilities also keep qualification and acceptance tests moving, with no delays when ramping up from lower excitation levels for acoustic and vibration tests. To protect expensive hardware, testing is started at lower levels and gradually increased. This might require a series of five or ten successive steps. Waiting hours for results between each step could drag out testing to weeks or more. With the near-real-time capabilities of LMS, the same work gets done safely in just a few days. Such efficiency saves time and lowers expenses by freeing up test facilities for additional jobs and by avoiding the high cost and inconvenience of sending test operators, program managers and other personnel to off-site testing facilities for months. Another significant benefit of having a fast-turnaround test system on site is the additional business generated from other companies now subcontracting testing projects to General Dynamics.