The International Space Station (ISS) has maintained continuous human presence in space since November 2000, serving as a critical microgravity laboratory for international collaboration, scientific discovery, and the advancement of human exploration.
Over its operational life, the station has hosted more than 290 individuals from 26 countries and facilitated over 4,000 research investigations and technology demonstrations involving more than 5,000 researchers from 110 countries. The ISS also supports the development of a commercial market in low Earth orbit for research, technology development, and transportation services, and is a key platform for preparing for future missions to the Moon and Mars.
The ISS stands as a critical microgravity laboratory, fostering international collaboration, scientific discovery, and advancements crucial for human exploration beyond Earth.
Enduring Role and Milestones
Supported by NASA and its international partners, the ISS reached 25 years of continuous human presence on November 2, 2025. In that year alone, the station completed over 5,800 orbits around Earth and was the site of more than 750 experiments.
Its unique environment enables research and discoveries not possible on Earth or with uncrewed platforms, driving innovation in medical research, fundamental science, and the commercial space economy.
Advancing Human Health in Space and on Earth
The microgravity environment of the ISS allows for extensive research into the physiological changes experienced by astronauts during long-duration spaceflight. NASA's Human Research Program (HRP) investigates these changes and develops countermeasures to maintain crew health.
Astronauts typically engage in approximately two hours of daily exercise to mitigate bone density loss, muscle weakening, and cardiovascular system changes. Readaptation to Earth's gravity can be challenging for returning astronauts, with some reporting altered perceptions and requiring days for recovery.
HRP-led studies monitor these changes and evaluate solutions, including improved exercise regimens, medical monitoring, and nutritional strategies. These findings contribute to new medical technologies and provide data on human adaptation crucial for extended deep space missions. Examples include NASA astronaut Jessica Meir exercising on the Combined Operational Load Bearing External Resistance Treadmill (COLBERT) and astronaut Jasmin Moghbeli retrieving media bags for Emory University's Project EAGLE investigation in the Kibo laboratory module.
Recent and Upcoming Human Health Studies
Recent and upcoming human health studies on the ISS include:
- Venous Flow Study: This investigation, led by Dr. Jason Lytle, examines whether time in space increases the risk of blood clots due to fluid shifts. It involves pre-flight and post-flight MRIs, ultrasound scans, blood draws, and blood pressure checks, with astronauts conducting in-mission jugular vein ultrasounds and collecting samples.
- Manual Piloting Study: Led by Dr. Scott Wood, this study assesses disorientation during gravitational transitions and evaluates astronauts' piloting and decision-making skills. Crew members perform simulated Moon landings before, during, and after their mission, piloting a virtual spacecraft. The research aims to understand an astronaut's ability to operate a spacecraft after adapting to different gravity environments and to inform training strategies for future Artemis missions.
- Spaceflight Associated Neuro-ocular Syndrome (SANS) Study: Researchers are investigating potential treatments for SANS, which causes vision and eye changes, including the effectiveness of a daily B vitamin supplement.
- Landing Injury Study: This research documents injuries sustained during landing to improve spacecraft design for enhanced crew protection.
Terrestrial Medical Breakthroughs
Research conducted aboard the ISS has also contributed to advancements with direct applications on Earth:
Cancer Treatment
Protein crystal growth experiments on the ISS provided insights into the structure and size of particles for a newly FDA-approved injectable medication designed for several types of early-stage cancers. This new delivery method aims to lower costs and reduce treatment time while maintaining efficacy. Microgravity research can produce higher-quality, medically relevant crystals compared to Earth-based laboratories.
3D Printed Medical Implants
Eight medical implants designed for peripheral nerve repair were successfully 3D printed aboard the ISS for preclinical trials on Earth. These implants are intended to improve blood flow and enable targeted drug delivery. Printing in microgravity prevents particle settling, resulting in more uniform and stable structures. This capability also allows astronauts to print devices and tools on demand for future missions.
Preparation for Deep Space Missions
The ISS serves as a testbed for developing skills, technologies, and understanding essential for NASA's Artemis campaign to return to the Moon and for subsequent journeys to Mars. Its unique physical environment allows for research and preparations not feasible on Earth.
Key Contributions to Deep Space Exploration
- Fundamental Task Development: Techniques for essential tasks such as water consumption, sleep, exercise, and material handling in microgravity are developed and refined.
- Technology Testing: The station tests technologies and self-sustaining systems required for deep space travel, including life support, in-orbit agriculture, and 3D printing capabilities.
- Orion Spacecraft Systems: Research aboard the ISS has contributed to establishing life support and safety systems for the Orion spacecraft, which will transport four astronauts around the Moon during the Artemis II mission. These systems encompass radiation sensing, carbon dioxide removal, portable fire extinguishers, emergency fire masks, the toilet, a heat exchanger, and a backup emergency navigation system.
- Artemis II Science Objectives: Several science objectives for Artemis II are rooted in ISS research methodologies:
- Spaceflight Standard Measures: This experiment tracks psychological and physiological data, with plans to expand collection beyond low Earth orbit to understand human adaptation to deep space.
- Organ-chip Experiments: Small devices modeling tissue and organ responses to space stressors and treatments have been used on the ISS. This research will continue in the lunar environment using cells from Artemis II astronauts to study deep space effects on human health.
- Crew Lunar Observations: Methods from Crew Earth Observations on the ISS inform Crew Lunar Observations for Artemis II, supporting handheld imaging and analysis of geologic features on the lunar far side.
- CubeSat Deployments: Small, cost-effective CubeSats, previously deployed from the ISS for technology testing in low Earth orbit, will be deployed during Artemis II for technology demonstrations and studies in high Earth orbit.
The ISS continues to function as a vital laboratory for optimizing critical technologies for lunar and Martian missions, including communications and robotics, and enhancing plant growth to support astronaut wellbeing, preparing humans to venture beyond Earth's orbit.