The thermosphere is a band of rarefied air surrounding the Earth’s surface. In this layer of the atmosphere, surfaces which absorb and reflect solar radiation undergo dramatic temperature changes.
Much of the aurora activity occurs within the thermosphere, as elemental gases such as oxygen, nitrogen, and helium at very low density and other molecules are excited by charged particles entering our atmosphere.
Objects deployed to the thermosphere are in what is known as Low Earth Orbit, and are subject to extremes of temperature, radiation, and the shock and vibration of launch and deployment.
These necessarily remote deployments mean that quality assurance levels such as MIL-PRF-38534 Class K are critical when it comes to the design and development of satellites and the components and materials that they contain, which are subject to rigorous testing, even before they are shipped.
Our client provides high-reliability electronic components tested and qualified for high-performance applications in high-temperature and extreme environments such as space.
Another earlier contractor had developed the bulk of an NI LabVIEW / TestStand test harness to verify a CMOS EEPROM memory module in 3.3V and 5V 4Mb and 1Mb device variants. Our client engaged us to complete the test harness.
The production test sequence included tests at different operating temperatures, speed binning to classify individual devices at speeds ranging from 120ns to 250ns, and verification of the AC and DC electrical characteristics.
When we received the test harness, the production test sequence was unoptimized and took about 1½ hours to complete for the 1Mb memory module, and four times that for the 4Mb module – 5 hours – which extended the qualification period significantly. Our client hoped that we could also reduce the test duration without affecting the quality of the testing.
We took over the development of the test harness. We had to understand the work which had already been done, including a large LabVIEW / TestStand system. At a minimum this meant understanding:
- the signal behaviour of the 1Mb and 4Mb modules, and the test instrumentation itself, e.g. the control signals and waveforms necessary to read and write data to the memory modules;
- measurement issues in the test instrumentation, e.g. propagation delays and channel skew;
- the electrical characteristics of the modules and equipment; and
- test limitations, e.g. measurements at or near the limits of test hardware.
We completed any missing or broken LabVIEW VIs (virtual instruments) and reworked some test sequences that might miss certain classes of errors, e.g. some of the bit patterns in the original test system might have masked bit failures.
At this point, we were in a position to optimise the test duration. We analysed the test performance, performed a timing review, removed bottlenecks and found more efficient paths through the test sequences. A simple reordering meant that some tests could take advantage of earlier test setup, and, where this also removed lengthy memory write steps, had the added benefit of reducing device fatigue.
We also tidied up the TestStand test reporting and assisted our client with the qualification of an initial batch of 4Mb modules, before supporting the handover of the completed test harness to their site.
The test harness had two main parts:
- the test instrumentation; and
- the test fixture.
The test instrumentation comprised a 19” rack NI PXI chassis with a number of NI PXI cards including:
- an industrial 96-channel 5V/TTL/CMOS digital I/O module;
- 2 x 100MHz 20-channel high-speed digital waveform generator / analyser;
- digital multi-meter;
- a power source measure unit (SMU);
- 2 x programmable power supply units (PSU); and
- a USB thermocouple
The test fixture contained the relays and buffers for signal routing and conditioning, and a socket adapter for the variants of memory module under test.
The test software was broken into two areas of responsibility:
- monitoring and control; and
- test sequencing and reporting.
A large NI LabVIEW system of 23 VIs was responsible for monitoring and controlling the test fixture via the various cards in the PXI chassis. The software included:
- waveform generation and control of the test instrumentation, e.g. powering the memory module via the test fixture; and
- power and timing measurements, e.g. to check that the read and write waveforms corresponded to the specified timings.
An NI TestStand test framework integrated with the LabVIEW VIs in order to drive the tests from a higher level, including the test sequences and the test reports.
This was a challenging project with considerable complexity at both the hardware and software level. We understood the importance of the test system and the stringent standards required of devices in the extreme environment of space.
We rapidly got up to speed with a large LabVIEW / TestStand system (less than 1 week).
We went beyond the core remit to scrutinise the tests for errors, but still delivered our changes in a timely manner.
At the end of the project, our software optimisations meant that the production test sequence ran in just over 1 hour for the 4Mb module – about a quarter of the original time. This meant that our client could qualify 4 times the number of modules in the same time frame.