Particle Sampling in Space: A New FrontierPost by: Gary S. Casuccio
Why are we sampling particles in space?
Our understanding of the living conditions astronauts experience in the International Space Station (ISS) may be colored by our exposure to science fiction. Based on this experience, you might assume that an unknown airborne substance in a spacecraft was of alien origin, seeping in by accident or on purpose.
In reality, particulate in the air of the ISS is generated mostly by the activities of humans and mechanical devices. The cabin air quality is obviously critical to the health and well-being of the crew and the equipment, and thus understanding the quantity and nature of particulate matter is paramount not only for ISS crew members, but also for future long-term missions such as the Journey to Mars. In spite of high-efficiency filtration systems on the ISS, the astronauts have reported itchy eyes and other allergy-type symptoms, and NASA experts suspect the issues are caused by particulate in the air.
How are we sampling particles in space?
Enter the TPS100 Nanoparticle Sampler. The TPS100 is a compact, microcontroller-based sampling device that uses thermophoresis to deposit nanoparticles directly on an electron microscope (EM) grid. Thermophoresis is particle movement induced by a thermal gradient. The TPS100 uses a temperature gradient across a narrow sampling channel to capture airborne particles on the grid. The technology is especially effective for capturing nanoparticles – a thousand such particles laid side-by-side would roughly equal the width of a human hair. By virtue of the sampling process, nanoparticles collected by the TPS100 are highly visible compared to other sampling approaches such as filter based methods in which the nanoparticles can be masked by larger particles or by the sampling media itself. The TPS100 attracted the attention of NASA, who will now be using the sampler in slightly modified form – dubbed Active Aerosol Sampler (AAS) – to help quantify airborne particles in the ISS.
Background on the TPS100
The commercially available TPS100 is based on a proof-of-concept prototype conceived by Dr. John Volckens, Professor of Mechanical Engineering at Colorado State University (CSU) and a researcher with the CSU Energy Institute. Funded by the National Institute for Occupational Safety and Health (NIOSH), the prototype demonstrated the validity of using thermophoresis for collection of nanoparticles. Following a meeting at a conference, Dr. Volckens and RJ Lee Group Vice President and Senior Scientist Gary Casuccio formed a collaboration with the goal of creating a commercially viable device.
RJ Lee Group sought and was awarded funding from the Pennsylvania Nano Commercialization Center, and added Senior Electronics/Firmware Engineer Hank Lentz to the team along with CSU Mechanical Engineer Dan Miller-Lionberg. Together, the designers re-imagined and miniaturized the sampling core, provided fully-automated electronic control, and with guidance and feedback from RJ Lee Group scientists added ergonomic touches such as cartridge keys that make sample exchange simpler than changing a light bulb.
‘It was definitely a challenge to develop a precision sampler with the small physical envelope, ergonomics, and long battery life that’s required for a commercially viable instrument’ said Mr. Lentz. ‘There’s a lot of technology in a very small space and the RJ Lee Group/CSU team was really uniquely qualified to define the design parameters from the perspective of the scientist in the field. John Volckens of CSU gave us a great head start with his group’s original proof-of-concept work, and we were very fortunate to work with a gifted mechanical engineer in Dan Miller-Lionberg to create a polished product and one that was deemed worthy of selection for the ISS mission.’
In addition to the size and compactness of the TPS100, the sample collection process is very unique.
RJ Lee Group Senior Scientist Dr. Kristin Bunker states, “Samples collected with the TPS100 are well suited for electron microscopy analysis because they are collected directly onto a carbon film grid and no sample preparation is needed. We can then directly place the grid into a high resolution electron microscope to study the size, morphology and chemistry of the nanoparticles. Collection of particles onto a carbon film grid provides an ideal substrate for nanoparticle examination.”
Dr. Marit Meyer, researcher at NASA Glenn Research Center, saw the potential of the TPS100 through meeting Mr. Casuccio at an aerosol conference and then gained experience with the TPS100 by using it to perform some terrestrial experiments with 3D printers. Dr. Meyer was attracted by the compact, self-contained form-factor, as well as the fact that thermophoresis is not sensitive to orientation and therefore ideal for experiments to be performed in the microgravity environment of the ISS.
Meeting NASA Requirements
As RJ Lee Group looked to this new frontier, the TPS100 would need to undergo a stringent vetting process to gain NASA approval for flight. While passing muster successfully for a variety of electrical, electromagnetic, and mechanical requirements, the TPS100 required modifications to meet the ISS touch-temperature requirements. To generate thermophoresis, the TPS100 must dissipate heat through natural convection – not a problem on Earth, where warm air rises and carries heat away from the unit. In the microgravity environment on the ISS, however, there is very little natural convection. So the team went back to the drawing board and added a special forced-air cooling plate. Lab testing at RJ Lee Group with the TPS100 packed in insulating material – to simulate the worst-case thermal conditions in microgravity – proved the modifications were successful, and the AAS was born.
Following approval by NASA, RJ Lee Group supplied two AAS units to NASA for launch to the ISS. While on the ISS, eight to ten separate multi-hour sampling sessions will be performed in different ISS locations to collect nanoparticulate during activities such as cleaning and use of exercise equipment, as well as opening the hatch after a cargo vehicle docks.
Enter the Passive Aerosol Sampler
Since the AAS focuses almost exclusively on nanoparticles, the RJ Lee Group team worked with Mr. Miller-Lionberg again to meet Dr. Meyer’s need to collect larger particles as well. This is important because, per Dr. Meyer, “We take it for granted, but on Earth, gravity cleans our air quite nicely. In space, cookie crumbs don’t fall down, they float around and move with the air flow in the spacecraft cabin.” The result was the modified passive aerosol sampler (PAS), a device based on the University of North Carolina passive sampling technology developed by Jeff Wagner and David Leith. The PAS was designed with five small, drawer-like sampling chambers that will be used to collect particulate on ISS air vents for durations of 2, 4, 8, 16, and 32 days. Seven PAS and two AAS units will be utilized in this this space experiment, to provide a profile of particles across a wide range of size, time, and locale.
To watch the NASA videos regarding the samplers, please click below.
Aerosol Sampler Overview and Passive Sampler Deployment
Active Sampler Activation and Deployment
Active Sampler Retrieval and Stow
Upon return to Earth, the AAS cartridge keys along with the PAS samples will be analyzed using a variety of light, laser and electron microscopy techniques. Collecting particulate on the ISS using the AAS and PAS will provide a wealth of information on particle characteristics on the ISS. In the words of Dr. Meyer, “The goal of this experiment is data collection. If we know the characteristics of the airborne particles on ISS, it will help us choose or design an appropriate particulate matter monitor for use on ISS and future space missions.”
From the data generated, NASA will learn about the true nature of airborne particulate in the ISS – and thus begin to separate science facts from science fiction.
UPDATED 11/30/2016 – TPS Samplers are Installed
Quoted from Marit Meyer, Ph.D. from NASA: “Yesterday astronaut Peggy Whitson deployed the seven Passive Samplers on vents/air inlets where they are exposed to incoming particle-laden air (see attached 1 minute video). They will remain in place for 32 days and the five exposed ‘drawers’ (collection surfaces) will be closed on days 2, 4, 8, 16 and 32. The two Active Samplers were charged and deployed for 6-hour collection sessions and sample cartridges were removed today. There will be additional active sampling sessions in the next 30 days near each Passive Sampler. ” Read more here and watch the video below.
UPDATED 10/24/2016 – Arrival at ISS
The Orbital ATK successfully reached the ISS on 10/23/2017. Watch the video below!
UPDATED 10/17/2016 – The Launch
The Orbital ATK launched successfully on Monday, October 17 at 7:45 pm! To read the post-launch press release, click here. To watch the launch, please click the video below.
For more information, please contact RJ Lee Group at 1-800-860-1775, press Option 4, then Option 4 again, or click the button below.