Secondary Systems

The International Space Station (ISS) is a large spacecraft that orbits around the Earth. It is a home away from home for crew members to live during space flight missions. Crew members also use the ISS as a place to do science experiments in reduced gravity.

The ISS is an amazing feat of science and engineering. A set of systems, or connected equipment and software that work together, make up the ISS. Theses systems operate together as one spacecraft to keep the crew healthy, the environment safe, and the ISS a good place for doing research.

Living and working on the ISS is a unique experience. The ISS relies on the core systems working together with secondary systems, or subsystems, to allow the crew members to live and work. The core systems and secondary systems must operate as one unit to make certain the mission is successful.

The secondary systems control the living environment, hygiene needs, exercise equipment, inventory and supplies, task lighting, tools, spacewalks, spacesuits, well-being of the crew, daily schedule, research activities, operation of the robotic arm, and more.

Learn more about the following ISS Secondary Systems:

Crew Support System (CSS)

The crew onboard the ISS need certain equipment in order to live and work. This Flight Crew Equipment (FCE) supports hygiene, habitation, productivity and general well being. FCE includes equipment and consumables (items that get used up). The Crew Support Group (CSG) is responsible for this Flight Crew Equipment.

Some of the Flight Crew equipment includes:

  • Housekeeping/Trash Management - items used for routine space station cleaning and trash collection.
  • Crew Provisioning - items used for personal and entertainment activities.
  • Exercise Equipment - items used for exercising and maintaining strength.
  • Inventory Management - items used to track consumables and loose equipment.
  • Portable Illumination - movable lights used for standard work activities.
  • Restraints and Mobility Aids - items used to keep the crew and equipment in place (such as seat restraints or Velcro) or help the crew move around (such as handholds).
  • Tools and Diagnostic Equipment - items used for routine maintenance.
  • Stowage Equipment - items used to transport cargo to and from ISS in a Multi Purpose Logistics Module (MPLM).
  • Payload Equipment Restraint Systems - items used to help the crew transfer and restrain loose equipment.


Extravehicular Activity System (EVA)

When work is done outside of the ISS by a crew member it is called Extravehicular Activity (EVA), more commonly known as a spacewalk. The Extravehicular Activity System (EVA) is responsible for monitoring and helping the EVA crew complete their tasks. The EVA system is responsible for the systems, tools, and procedures that the crew will use to successfully complete their EVA tasks.

Typical responsibilities of the EVA officer include: planning out the best order for accomplishing the various tasks in a spacewalk, determining the best tools to use, making sure that all the EVA Systems (like the suit and airlock) are properly maintained and ready, developing the procedures to properly size the spacesuits for the crewmembers who will be going EVA, developing contingency plans in case something goes wrong during the EVA, and training the crew, both before launch and through lessons sent to the crew after they are already onboard the space station.

The EVA systems are made up of the following:

  • Extravehicular Mobility Unit (EMU) - This is the spacesuit the crew wear when outside. It consists of several components:
    • Space Suit Life Support System - provides a habitable environment inside the spacesuit, such as oxygen, stable pressure and ventilation.
    • Space Suit Assembly - This is the wearable portion of the suit, including the torso, limbs, and helmet. Many of the pieces come in different sizes, and can be assembled to optimally fit each individual crewmember.
  • Space Suit Ancillary Equipment - consists of the hardware necessary to support the spacesuit before, during and after the spacewalk. This includes helmet mounted lights and video camera.
  • Simplified Aid for EVA Rescue (SAFER) propulsion backpack system - a small jet pack used as a self-rescue device. SAFER allows EVA crew to maneuver themselves if needed.
  • ISS Joint Airlock - module where space suits are serviced, maintained, put-on, taken-off, and stored. The module also provides access to outer space and communications.

EVA Tools Include (among many others):

  • Tethers - Several different kinds are used, among the types: Safety tethers to keep crew from accidentally floating away from ISS, Equipment Tethers to keep tools from floating away from the crewmember and hold things in place, and the Body Restraint Tether (BRT), which holds the crewmember in place while they work with both hands.
  • Pistol Grip Tool (PGT) - essentially a programmable socket driver. It can be set to drive only to a specified torque and then stop.
  • Adjustable Portable Foot Restraint (APFR) - a device which holds the EVA crewmember's feet securely, allowing them do work with both hands without floating away

EVA Procedures include considerations such as:

  • Which Tools to Use - Picking the best tools for the job
  • How to do each Task - Does the Task take one crewmember or two, should they be in a restraint so they can use both hands or can they work with one hand while holding onto a handrail with the other, would using the robotic arm help get the job done quicker?
  • Contingency Plans - What to do if something goes wrong with the task (a bolt won't go in, the crew is unable to connect an electrical line), and what to do if something goes wrong with one of the suits


Crew Health System (CHS)

The Crew Health System (CHS) is responsible for the hardware that provides medical and environmental monitoring capabilities onboard the International Space Station (ISS). This hardware is called the Crew Health Care System/Integrated Medical Systems. This system ensures the health, safety, and performance of the crew.

This system is divided into 3 main subsystems:

  • Countermeasures System (CMS) - Equipment and activities for daily exercise and crew health. These exercises and tasks are needed to reduce the side effects of living in space.
  • Environmental Health System (EHS) - Equipment and activities that monitor the atmosphere for dangerous gases, water quality, noise and radiation levels.
  • Health Maintenance System (HMS) - Equipment and activities that monitor crew health, provide life support and medical care.


Maintenance and Repair System (MRS)

The Maintenance and Repair System (MRS) is responsible for keeping the equipment and components that make up the International Space Station (ISS) working properly. All equipment with mechanical and electrical parts must be maintained in order to function correctly. The equipment must also be repaired when malfunctioning. Maintenance activities fall into three categories:

  • Preventative Maintenance - routine maintenance performed to prevent failure of equipment and components from occurring
    • Sampling (air, water…)
    • Inspections (seals, filters…)
    • Charging (batteries, backup lights…)
    • Cleaning (filters, test beds…)
  • Corrective Maintenance - maintenance performed to correct any failure so that the item can be restored.
    • Repair and replace equipment
    • Recalibrate and reconfigure equipment
  • Contingency Maintenance - planned action devised for a specific situation that might occur.
    • Soldering (wiring)
    • Scavenging (spare parts)
    • Jumpering (around failed equipment)
    • Fabricating (creating new equipment)
    • Banging with hammer (self-explanatory)


ISS Payloads Office (PLG)

The International Space Station is a uniquely capable scientific research and technology platform in microgravity. Research is performed in the areas of biology and biotechnology, physical sciences, human research, technology development and demonstration and earth and space sciences. The ISS Payloads Office is responsible for the payload (research cargo) systems and equipment used. They also make it possible for researchers on earth to link with their experiments and the crew onboard the ISS.

Some of the Payloads systems operations include:

  • Planning and implementation of research requirements across all agencies and nations
  • Planning of research missions
  • Ensuring safe execution of research cargo operations
  • Manage and integrates ISS flight, stage and increment activities
  • Handle research procedures, training, and communications with the crew
  • Manage command and data transmissions of experiment data


Robotics System (RBS)

The Robotics System (RBS) is responsible for the robotics systems and robotic operations onboard the ISS. Robotics systems are used to perform operations that a human could not perform (e.g. assembling the ISS), reduce the dangers to humans, and when tasks requiring great precision are to be performed. Robotics systems also reduce costs since the use of humans in space is expensive. Robotic systems are used for handling research cargo, assistance during spacewalks, and maintaining the ISS. Robotic systems also played an important role in building the ISS.

The ISS Robotics systems include the following:

  • Mobile Servicing System (MSS) - comprised of 3 robots that work independently:
    • Space Station Remote Manipulator System(SSRMS) "Canadarm2" - Robotic arm used to assemble the ISS, move supplies, equipment, and spacewalking crew. Also captures free-flying vehicles and berths them to the ISS.
    • Mobile Base System (MBS) - Moveable work platform and storage facility for crew during spacewalks.
    • Special Purpose Dexterous Manipulator (SPDM) "Dextre" - Small two-armed robot that handles delicate maintenance tasks.
  • European Robotic Arm - Used for maintenance and support for EVA on the Russian segment of the ISS. Also helps with some assembly tasks.
  • Japanese Experiment Module Remote Manipulator System (JEMRMS) - handles research cargo and experiments on the outside of the ISS.
  • Robonaut 2 (R2) - The first humanoid robot in space. Its primary job is teaching engineers how dexterous robots behave in space. It is hoped that someday it could help EVA crew with tasks outside the ISS or perform scientific work.


Transfer Vehicle Group (TVG)

The Transfer Vehicle Group (TVG) oversees preparation and transfer of crew and cargo to and from the ISS. Maintaining the ISS is a difficult task and requires a lot of planning and preparation. Crew and science experiments must be rotated. Provisions must be resupplied. Waste must be removed. All these activities are important to keep the ISS operating.

Transfer operations are made up of the following:

  • Preflight Operations
    • Making sure the correct items are loaded onto the resupply vehicle.
    • Developing the products and instructions the crew need for the transfer. This includes items such as transfer bags, transfer list, and timelines.
    • Develop and conduct training sessions for the crew.
  • Real-time Operations
    • Answering crew's questions, working changes to the transfer lists, tracking all transfers.
  • Post-flight Operations
    • Organizing the post-flight crew debrief.