Article: International Space Station
Section: Scientific research

Question: Why can't humans stay in spaceflight for longer?

The ISS provides a platform to conduct scientific research that cannot be performed in any other way.
While small unmanned spacecraft can provide platforms for zero gravity and exposure to space, space stations offer a long term environment where studies can be performed potentially for decades, combined with ready access by human researchers over periods that exceed the capabilities of manned spacecraft.
The Station simplifies individual experiments by eliminating the need for separate rocket launches and research staff.
The wide variety of research fields include astrobiology, astronomy, human research including space medicine and life sciences, physical sciences, materials science, space weather, and weather on Earth (meteorology).
Scientists on Earth have access to the crew's data and can modify experiments or launch new ones, benefits generally unavailable on unmanned spacecraft.
Crews fly expeditions of several months duration, providing approximately 160-man-hours a week of labour with a crew of 6.
Kibō is intended to accelerate Japan's progress in science and technology, gain new knowledge and apply it to such fields as industry and medicine.
To detect dark matter and answer other fundamental questions about our universe, engineers and scientists from all over the world built the Alpha Magnetic Spectrometer (AMS), which NASA compares to the Hubble telescope, and says could not be accommodated on a free flying satellite platform due in part to its power requirements and data bandwidth needs.
On 3 April 2013, NASA scientists reported that hints of dark matter may have been detected by the "Alpha Magnetic Spectrometer".
According to the scientists, "The first results from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays.
"The space environment is hostile to life.
Unprotected presence in space is characterised by an intense radiation field (consisting primarily of protons and other subatomic charged particles from the solar wind, in addition to cosmic rays), high vacuum, extreme temperatures, and microgravity.
Some simple forms of life called extremophiles, including small invertebrates called tardigrades can survive in this environment in an extremely dry state called desiccation.
Medical research improves knowledge about the effects of long-term space exposure on the human body, including muscle atrophy, bone loss, and fluid shift.
This data will be used to determine whether lengthy human spaceflight and space colonisation are feasible.
As of 2006, data on bone loss and muscular atrophy suggest that there would be a significant risk of fractures and movement problems if astronauts landed on a planet after a lengthy interplanetary cruise, such as the six-month interval required to travel to Mars.
Medical studies are conducted aboard the ISS on behalf of the National Space Biomedical Research Institute (NSBRI).
Prominent among these is the Advanced Diagnostic Ultrasound in Microgravity study in which astronauts perform ultrasound scans under the guidance of remote experts.
The study considers the diagnosis and treatment of medical conditions in space.
Usually, there is no physician on board the ISS and diagnosis of medical conditions is a challenge.
It is anticipated that remotely guided ultrasound scans will have application on Earth in emergency and rural care situations where access to a trained physician is difficult.