Sun Explorer: Reliability Testing for The Solar Orbiter Instrumentation

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"The NI platform and the expertise provided by Metis Automation has proven the reliability of the SPICE instrument, ensuring it is can deliver ground-breaking insight into the physics of the Sun."

- Grant Munro, ESR Technology Ltd

The Challenge:
Proving the reliability of key hardware on board the Solar Orbiter, which is a European Space Agency (ESA) spacecraft that will find out more about our nearest star.

The Solution:
Using CompactDAQ hardware to perform thorough and extensive testing of the scan-focus mechanism on the SPICE instrument on board Solar Orbiter, and using LabVIEW software to develop an automated test framework called Metest to aid in creating a software solution.

Author(s):
Grant Munro - ESR Technology Ltd
Martin Griffiths - Metis Automation

Figure 1. Artist Impression of Solar Orbiter Device, Launching in 2018 (Credit: ESA)

Solar Orbiter—Next Generation Sun Explorer

The Sun is by far Earth’s most important energy source. It is a giant ball of plasma, 109 times wider than Earth, and it accounts for 99.86 percent of the total mass of the entire solar system. It has been burning for over 4.6 billion years and constantly produces energy through nuclear fusion. History is rife with solar worship as a part of mythology for many different cultures. Humankind has always been fascinated by the Sun. Modern technology can help us get ever closer to it to learn more of its secrets.

Solar Orbiter will launch from Earth to hurtle hundreds of millions of kilometres through space to examine how the Sun creates the heliosphere, the vast bubble of charged particles blown by the solar wind into the interstellar medium. Ten science instruments on board the spacecraft will perform a range of measurements and imaging of the Sun to gain new information about the solar wind, the heliospheric magnetic field, energetic particles, transient interplanetary disturbances, the Sun’s magnetic field, and its dynamic atmosphere.

Figure 2. The Sun’s High Energy Atmosphere (Credit: NASA/Solar Dynamics Observatory)

Scheduled for launch in October 2018, the mission will provide high-latitude observations of the Sun from 40 million kilometres, inside the orbit of the closest planet Mercury and closer than any man-made object in history.

Space mechanism manufacturer ESR Technology is testing the Spectral Imaging of the Coronal Environment (SPICE) instrument, which performs extreme ultraviolet imaging spectroscopy to remotely characterize plasma properties of the Sun’s on-disk corona. This may teach us more about the causes of solar flares, the structure of the heliosphere, solar wind, and how the Sun creates its magnetic field.

Test System

Space is one of the harshest environments we ever expect our technology to function in. Temperatures can vary wildly. Cosmic radiation can cause problems in circuitry. Lubricants that work well on Earth can be entirely ineffective in the vacuum of space. Because of these issues, the key to a successful space exploration mission is reliable and proven components and instruments, since problems are virtually impossible to correct after launch.

ESR Technology has been involved in many of the most challenging space missions of the last four decades, specialising in problems related to friction and wear of moving parts. Our work includes consultancy, R&D, testing, and developing mechanical hardware for the space industry.

We chose NI products because we felt that CompactDAQ hardware and LabVIEW software could provide a complete automated test, control, and data-logging solution for a rigorous series of validation tests spanning nine months. We also felt the versatility of NI products would cover a diverse range of uses because the variety of C Series modules can cope with many different signal types. As our requirements and projects evolve, we may also look to modify the system or the test process, which makes the flexibility of the NI platform a real advantage to us.

Metis Automation’s solution to the problem relies on this flexibility to acquire signals from multiple devices simultaneously. It presents the test operator with a simple interface that requires no knowledge of the instrumentation detail behind the scenes, making it quicker and easier to run the tests.

 

Figure 3. Overview of the Test System

Test Automation

Tests of SPICE require a combination of manual interaction and automated control. The solution Metis developed allows the creation of automated test scripts so one engineer can run a test unattended and only return occasionally (usually once per day to monitor thermal control baths). This is a massive improvement over manual testing that previously would have required a test operator to attend to the test rig full time and make frequent manual adjustments to the system. Another key benefit of the automated test system was the repeatability of tests. Once we create an automated test script, we can re-run it. We can now easily repeat complex tests that give unexpected results to help identify any issues with the unit under test or determine whether environmental factors affected the result, which is extremely beneficial to us.

Figure 4. SPICE Scan Focus Mechanism Test Rig (Credit: ESR Technology)

Flexible Data Logging

We needed high-speed data logging for high-resolution data of important events, but constant high-speed logging leaves you with the challenge of unmanageable volumes of data over long test periods. The Metis software solution includes the option to automatically schedule or trigger data logging at fast rates, which means the operator can configure a test in advance and schedule when high-speed logging should occur. Only the relevant data is acquired at high rates, which saves terabytes of disk space and simplifies data analysis.

A Flexible, Maintainable System

CompactDAQ modules have many types of signal conditioning built in, so we can directly wire all our sensors (RTDs, transducers, and analogue voltages) into our modules to simplify our wiring. We can also adapt the test hardware for new signals by simply changing C Series signal conditioning modules, which makes this test system flexible and extensible for future tests. The NI-DAQmx driver set even lets users acquire from multiple different signal types within the same measurement task, making software development easy.

Figure 5. CompactDAQ has a Wide Variety of Modules with Built-in Signal Conditioning

High Speed, Synchronised Data Acquisition

ESR Technology needed to combine measurements from some generic analogue sensors with Micro Epsilon capacitive sensors, which have very high resolution and micron-accuracy distance measurements. All sensor readings had to be synchronised to be useful.

Figure 6. MICRO-EPSILON capaNCDT Sensors

Micro Epsilon provides LabVIEW drivers for reading values through an Ethernet connection at high rates. Metis Automation has several experienced Certified LabVIEW Developers and Certified LabVIEW Architects. We used a little known, but immensely useful, LabVIEW feature—the ability to synchronise the start of timed loops—to deliver code that can synchronise measurements across sensors from different vendors. Our code can acquire synchronised data from the CompactDAQ and the Micro Epsilon sensors with the flexibility to handle errors for each device, whilst remaining modular.

Figure 7. Named ‘Timed Loop’ Synchronisation

 

Before using this feature, engineers reported data samples that were out of sync by hundreds of milliseconds, adding significant post-processing effort. With the Metis solution, we synchronised samples to within a single millisecond.

Simplifying Code with LabVIEW Object-Oriented Techniques

The LabVIEW software was developed using object-oriented techniques. Object-oriented programming (OOP) simplifies hardware dependencies and test steps for more flexible software development that can accommodate changes to the test requirements without affecting code already written. Using OOP saved us a lot of time during the extensive test and debugging phase of the project.

 

Figure 8. Object Oriented Programming Approach

Summary

Developing hardware for space relies on the ability to verify demanding performance characteristics under a variety of environmental extremes. ESR Technology and Metis Automation have developed a flexible and reliable testing solution using LabVIEW and CompactDAQ. The NI platform and the expertise provided by Metis Automation has proven the reliability of the SPICE instrument, ensuring it is can deliver ground-breaking insight into the physics of the Sun. The modularity and scalability of the system will allow us to extend this architecture into future test rigs.

Author Information:
Grant Munro
ESR Technology Ltd
grant.munro@esrtechnology.com

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