What kinds of activities experiment and procedures done on the ISS must be done in nominal-pressure chambers that need to be vented to space?

Question

This answer to the question in 3D Printing SE How is 3D printing done in space? says

The first big space-specific issue is actually air quality. You can't just open a window to air out the molten-ABS smell from the ISS!

FFF printers put out fumes and nanoparticles. In a space station, the same air gets recycled over and over, and the air purification systems have a specific set of contaminants that they are optimized for, as well as a design capacity for air turnover and chemical removal rates that won't be adjusted just because somebody's printing a space-ratchet today. Protecting cabin air quality is a huge design factor for any experiment that goes into space.

The Made in Space printing experiments on the ISS to date were performed in one of the vacuum experiment chambers, so any unfiltered fumes (or fire flare-ups) could be vented directly to space if required. In the long run, this isn't going to work -- other experiments may need the vacuum chamber, or "production" printers may be too large to fit. So the printer needs to have its own internal air purification system.

Question: I am wondering what kinds of activities, experiment and, procedures done on the ISS must be done in vacuum or air-tight, atmospheric isolation chambers that can be vented directly into space?

Exclude anything that actually requires vacuum or a specialized gas environment. The focus here is on things that should be done in a nominal environment, but emit gas, particles, vapors, pathogens, etc. that the humans wouldn't want in their environment.

hint: apparently 3D printing is one.

Answer 1

Note: This is an answer was originally written to answer an earlier version of the question: "What kinds of activities, experiments, and procedures done on the ISS must be done in a vacuum or within atmospheric isolation chambers that can be vented directly into space?" It has since been adapted.

Broadly speaking the reasons for isolating an experiment are: a) To prevent the environment from contaminating the experiment, and b) To protect the experiment from contaminating the environment. Performing procedures either outside of the station or within chambers that can be vented to space can help to prevent either kind of cross-contamination.

Preventing Experiment to Environment Contamination

The ISS supports ExPRESS Racks which support a Vacuum Exhaust System. This feature can be used to simply vent contaminants from the experiment out into space. But it also makes these chambers ideal for experiments that require both microgravity and exposure to vacuum, but where:

• Direct exposure to space radiation is less important,
• Where temperature control is important,
• Where it would be best not to allow any parts of the experiment drift away (3D printing, or crystal growth experiments), or
• Where it is important for astronauts to be able to frequently access the experiment

For example, Mitsubishi is developing an antenna that can be 3D printed in space; however, the plastic they use needs sunlight to cure so their technology might not be a good fit for the ExPRESS Racks.

Reference: Slide 21

There are several experiments (see: Scientific research on the International Space Station) where it would seem advisable to prevent contamination of the crew's air supply or cross-contamination of other experiments. For example, the Fluids and Combustion Facility, The Ryutai Fluids Experiment Rack, and several of the biological experiments.

Preventing Environment to Experiment Contamination

In some cases, the experiment needs to be protected from being contaminated by the environment inside the ISS. Many of these kinds of experiments are quite interesting in their own right.

The broader question of how effective these procedures are is important as well. For example, if return samples from Mars were to be analyzed on the ISS, and evidence of abiogenic life were detected in these samples, researchers would want to be extremely confident that the ISS's stringent procedures for preventing sample contamination rule out any possibility of their being an embarrassing error in their findings.

According to this Sept 2023 NASA article the ISS National Lab sponsors a series of investigations called the Materials International Space Station Experiment (MISSE) to analyze how exposure to space affects specific materials and components. These experiments test coatings, a lunar regolith or dust simulant, and other materials with potential for use in future spacecraft, spacesuits, and other components needed for research and space exploration including imaging sensors, window coatings, 3D printed polymers, and electronic components. Many of the experiments specific goals are to test the durability in space of polymers, composites, thermal protection systems, photovoltaic technologies and radiation shielding materials.

MISSE Sample Carriers (MSCs) are sent out through the station’s JEM airlock and then the robotic arm installs them onto the facility. Afterward, materials are retrieved and returned to Earth for post flight analysis. In some cases, to prevent these samples from becoming contaminated by, for example, moisture in the air, it might be essential for them to be sealed inside an airtight container before they are brought back inside the ISS. This will, of course, depend on the nature of the experiment.

View of samples for MISSE-3 and 4 installed on the exterior of the space station (Credit NASA)

You can learn about the specifics of many of the MISSE missions on NASA's website:

• MISSE-3 and 4
• MISSE-5
• MISSE-7
• MISSE-6A and 6B
• MISSE-9-NASA
• MISSE-12-NASA
• MISSE-13-NASA
• MISSE-18-NASA
• MISSE-18-Commercial

The ESA (European Space Agency) EXPOSE-R2 facility is another platform used to test samples in space. ESA investigations BOSS and BIOMEX used it to determine whether microorganisms could repair DNA damage resulting from space exposure.

JAXA (Japan Aerospace Exploration Agency) exposed microbes and organic compounds to space to test the “panspermia” hypothesis (the theory that the seeds of life could travel among celestial bodies) in a series of experiments called Tampopo (the Japanese word for dandelion).

It is important to keep experiments from fouling the air or infecting the crew, especially as the crew themselves are being studied to learn more about how space affects human physiology. But we can also learn how to improve containment by studying (and publishing) information about experiments that were affected by contamination in the environment to experiment direction.

Answer 2

The Vacuum System on the International Space Station is composed of two separate parts: the VRS (Vacuum Resource System) and the VES (Vacuum Exhaust System).

The VRS is for maintaining a vacuum required for conducting science. Many payloads may be actively using the VRS simultaneously.

The VES is for venting a chamber down to vacuum or exhausting hazardous byproducts to space. Only one payload or system may use the VES at a time in order to avoid cross contamination and prevent any chemical reactions occurring between simultaneously vented byproducts.

One of the only payloads that connects to both VES and VRS is MSRR (Materials Science Research Rack), which vents to vacuum using VES and then uses VRS to maintain the vacuum for insulating its furnace which can reach 1400°C.

Many different ISS payloads (science experiments) use the VES to vent byproducts of their experiments to space. This payload complement often changes with each Expedition, but there are some long-running experiment facilities that use VES:

Among those is CIR (Combustion Integrated Rack - pronounced "sir"), which vents combustion byproducts to the VES.

Another is Amine Swingbed, which is an experiment-turned-facility that scrubs CO2 from the ISS cabin atmosphere.

Any payload developers that plan to use the VES system have to provide detailed information of what they'll be venting:

For each mode of operation: Provide a list of vented gases to include the constituent vented, the total mass vented, initial temperature, initial pressure, concentration of the constituent, mass flow rate, frequency and duration of venting operations, and pressure versus time curve at the payload interface.

Source: NASA ISS Pressurized Payloads Interface Requirements Document

Other payloads that need to use VES but don't have an interface directly to the VES system can use MSG (Microgravity Science Glovebox) to vent. MSG is also used to contain experiments using hazardous substances. Rodent Research specimen handling is performed in MSG, as are many other biological experiments. Some of the experiments listed in NASA's page for MSG use VES through the glovebox's interface.

I believe Made In Space's original 3DP experiment was run in MSG. Their later AMF facility does not use VES - they must have incorporated an air filter in that design. (I was an MSFC POIC Operations Controller responsible for managing real-time payloads resources while AMF was/is an active experiment, but 3DP was before my time at NASA.)