The International Space Station (ISS) has maintained a continuous human presence in low Earth orbit since November 2000. Supported by NASA and international partners, the station serves as a microgravity laboratory, facilitating over 4,000 experiments and hosting more than 290 individuals from 26 countries. Its research contributes to advancements in human health, medical technology, and the development of capabilities for future deep space missions, including the Artemis campaign to the Moon and subsequent journeys to Mars.
Operational History and Scope
The ISS reached 25 years of continuous human presence on November 2, 2025, having begun hosting crews on November 2, 2000. It has hosted over 290 individuals from 26 countries and a variety of international and commercial spacecraft. The station supports a commercial market in low Earth orbit for research, technology development, and transportation services.
Within its microgravity laboratory, more than 4,000 experiments have been conducted by over 5,000 researchers from 110 countries. In 2025, the ISS completed over 5,800 orbits and saw over 750 experiments conducted, contributing to exploration missions and fostering commercial opportunities.
Human Health and Medical Research
The microgravity environment of the space station enables research with applications for Earth and prepares humans for extended deep space missions. NASA's Human Research Program (HRP) investigates physiological changes astronauts experience in orbit and develops countermeasures to maintain crew health before, during, and after spaceflight.
Astronauts on the station engage in approximately two hours of daily exercise to mitigate bone density loss, muscle weakening, and cardiovascular system changes. Prolonged exposure to microgravity can affect readaptation to Earth's gravity, with some returning astronauts reporting altered perceptions of Earth's environment. HRP-led studies monitor these physiological changes and evaluate solutions, including improved exercise regimens, medical monitoring, and nutritional strategies. NASA astronaut Jessica Meir was observed exercising on the Combined Operational Load Bearing External Resistance Treadmill (COLBERT) in the Tranquility node. Astronaut Jasmin Moghbeli recently retrieved media bags for Emory University's Project EAGLE investigation in the Kibo laboratory module.
Research conducted aboard the ISS has contributed to insights for a newly FDA-approved injectable medication for several types of early-stage cancers. Protein crystal growth experiments in microgravity provided information into the necessary structure and size of particles for the medication, aiming to lower costs and reduce treatment time. Additionally, eight medical implants designed for peripheral nerve repair were 3D printed aboard the ISS for preclinical trials on Earth. These implants are intended to improve blood flow and enable targeted drug delivery in cases of nerve damage, with microgravity printing contributing to more uniform and stable structures by preventing particle settling.
Deep Space Exploration and Technology Development
The space station serves as a platform for developing skills, technologies, and understanding essential for NASA's Artemis campaign to return to the Moon and subsequent journeys to Mars. The orbital laboratory supports research and preparations not feasible on Earth due to its unique physical environment. This includes:
- Developing techniques for fundamental tasks such as water consumption, sleep, exercise, and material handling in microgravity.
- Creating solutions for challenges and changes in the human body induced by microgravity.
- Testing technologies and self-sustaining systems required for deep space travel, such as life support, in-orbit agriculture, and 3D printing.
- Refining methods and procedures for data and imagery collection and analysis.