EMA SERE ESD Chamber
The space environment is dynamic, complex, and harsh. The primary cause of risk for components and spacecraft in this environment is due to the energetic charged particles emitted by the sun resulting in charging. If proper consideration is not taken, catastrophic effects can lead to component or even mission failure. Thus, it is important to design, build, and test spacecraft and spacecraft components with charging effects in mind. In order to analyze the test materials and components, EMA has developed both simulation and testing tools. Space environment testing is a vital part of the spacecraft building process, however, due to the time and cost requirements, it is often neglected, or shortcuts are taken. Simulation tools can help alleviate the time and cost requirements; however, it is not a substitute to proper testing. Because of this, EMA supports a combination of testing and simulation to provide a complete spacecraft charging solution. By recreating the test setup in the simulation tool, a validated model can be created which can then be used to iterate through designs, materials, and environments. A final complete test can then be performed on the final design to ensure reliability.
To this end, the Space Environment and Radiation Effects (SERE) lab at EMA is designed to study and test spacecraft, components, and materials destined for the space environment or other similar harsh environments. By combing the results from the SERE lab with the simulation tools developed by EMA, such as EMA3D® Charge, a more complete understanding of the problem can be developed. For instance, using the materials properties measured in the lab for a bulk material, a simulation of a charging component undergoing radiation can be created to compare to testing results done in the SERE Electrostatic Discharge (SERE ESD) chamber.
Once the simulation has been validated against the testing in the lab, the environment can then be changed to see how the component would behave in a more complex or dynamic environment. This allows efficient and extensive analysis that is otherwise not possible with simulation or testing alone. In order to validate a simulation, however, the testing must be able to recreate an environment where the physical processes are identical to those found in the target environments. This requires complex equipment and instrumentation, most of which has to be custom made.
The main environmental characteristics that the SERE ESD chamber must reproduce include:
- High vacuum with pressures less than 1E-7 torr. This is accomplished using a custom designed and built vacuum chamber that was designed by EMA and acquired through Kurt J. Lesker and Leybold MAG Integra Turbomolecular Pump.
- Temperature controlled with temperatures ranging from -300 °C to +100 °C. This is accomplished using a two-part sample plate where the outside sample plate has the ability to internally flow liquid nitrogen and the inside sample plate is connected to DE110 ARS Cryo cooler.
- Electron radiation with energies comparable to the space environment. While future energy ranges are planned, our current capabilities include the Staib EHF-100, an electron source with electron energies ≤100keV and current densities ≤5 nA/cm2.
- Electromagnetic radiation with a spectrum with wavelengths that extend to ultraviolet light seen above the earth’s atmosphere. This can be achieved using a Krypton light source such as the Resonance KrLM-LHP. An LED full spectrum UV solar simulator is also being developed to create a tunable light source to recreate the solar spectrum for wavelengths greater than ~350nm.
In order to quantify the results of the testing, several measurements can be made. The measurements include:
- Video monitoring to detect visible ESD to determine occurrence and spatial location. This is done using an ImagingSource USB3.1 video camera using a 1.1″ Sony PREGIUS IMX253 monochrome sensor with a global shutter combined with a 25mm F/1.8 lens.
- Current and voltage measurements to measure beam current and ESD waveforms. Measurements are made using either electrometers (2X Keithley DMM6500 and 1X 6517B) or oscilloscopes (2X Keysight InfiniiVision 2000 X-Series).
- Surface Voltage measurements using a high voltage electrostatic voltmeter (Trek 341B). This is attached to the linear translation stage which allows the instrument to be swept across the sample.
- Surface Electric fields using an Electrostatic Field probe.
- Plasma Measurements using Langmuir probe (To be determined).
- High frequency measurements using a custom wideband monopole antenna to measure the emitted electromagnetic spectrum from ESD events and captured using an oscilloscope (Keysight InfiniiVision 2000 X-Series).
In order to demonstrate the ESD measurement capabilities of the chamber, EMA’s logo was etched into a piece of glass and then the etched regions were filled with a conductive phosphor epoxy. This was then mounted inside the chamber with the outer border of the logo grounded to the sample plate. The chamber was then pumped down and the sample irritated with a high energy electron beam with energies ranging from 30 keV to 100 keV. To detect arcing, both the video and the wideband antenna instrumentation were used.
The video instrumentation employs custom software that uses real-time processing of the video stream in order to detect arcing. This is done via three different trigger detection schemes that all run simultaneously. The first method uses the absolute difference between pixels of subsequent frames. If this difference exceeds a user defined trigger value, then the frames before, during, and after the trigger are saved.
The second and third schemes both rely on a three-frame moving average of the average intensity. The second method uses the full frame to calculate the average intensity of the frame by summing the intensity of each pixel and then dividing by the total number of pixels. The third method uses a user defined mask where only the pixels within the mask are used in the average intensity calculation. When this moving average exceeds a user defined trigger value, the software also saves the frames before, during, and after the trigger.
These averaged intensity values, for both the full frame and for any number of masks, are written out to a data file that can be analyzed and compared to other instrumentation data. The triggers and trigger type are also written to this file and all images are saved with a timestamp to make direct correlation between the data and images possible.
The wideband antenna measurements were made using a Keysight 2000 X-Series oscilloscope interfaced with Labview. The oscilloscope waveforms are timestamped according to the run start time so that they can be correlated to the video data but the original waveform data is still captured in order to extract the necessary information from waveforms.
The resulting images saved from the video triggers can then be composited into a single image and overlaid onto a bright image of the sample plate. The resulting image gives a total time overview of all ESD’s detected by the video detection system.
EMA is investing and continues to invest in capabilities and technology that will allow the testing, simulation, and analysis of the next generation of spacecraft hardware. Whether it be new materials, external hardware, or solar panels, EMA has the tools and expertise to identify and mitigate risk from the design stage to deployment.
Contact EMA’s team of experts to learn more about we can help you with your spacecraft hardware, here.