Locomotion in space

Locomotion in space refers to the methods and actions used to move the body through the outer space environment. In these conditions, humans exist in microgravity, which is a state of very low gravitational pull. Moving in microgravity is fundamentally different from moving within a 1-G environment like Earth. Because humans evolved under Earth's standard atmospheric and gravitational conditions, the transition to space presents significant biological challenges. Understanding these mechanics is vital for researching how humans can survive long-term space travel.

The space environment is extremely harsh and requires specialized equipment for survival. Outside of a spacecraft, astronauts must perform extravehicular activities, or EVAs. During an EVA, they must be protected from the vacuum of space. Without protection, the lack of oxygen, extreme temperature differences, and extreme pressure changes can cause death quickly. High radiation levels also pose a constant threat. Even inside a spacecraft, the lack of gravity affects how every movement is made.

Extended exposure to reduced gravity causes several detrimental effects on the human body. These changes are often similar to the processes seen in aging or certain diseases. One major issue is muscle atrophy, which is the decrease in muscle volume. During a six-month mission, muscle volume can decrease by as much as 20%. Bone density also suffers, decreasing at a rate of approximately 1.4% at the hip in just one month. Additionally, fluids in the body undergo head-ward shifts. This can result in headaches, sinus congestion, and facial swelling.

To fight these effects, scientists use various countermeasure technologies. One method is transcutaneous electrical muscle stimulation, or EMS. This involves using an electric current to stimulate muscle activity. In 1989, a researcher named Duovoisin tested this during a 30-day bed rest study. While it decreased the rate of muscle atrophy in the stimulated limb, it did not necessarily prevent all effects. Later, in 2003, a study by Yoshida et al. showed that EMS helped prevent muscle function deterioration in rats during hind limb suspension.

Another category of technology includes loading suits, which are different from the space suits used for EVAs. Loading suits are garments designed to maintain weight-like pressure on the bones. The Pingvin suit is a lightweight garment that uses elastic bands to create vertical loads. It can load the upper body with up to 88 lb. (40 kg) to prevent back muscle atrophy. A more modern version is the Gravity Loading Countermeasure Skinsuit, or GLCS. The GLCS uses elastic materials to mimic the loads experienced while standing on Earth. It creates a loading gradient that increases toward the feet.

Astronauts also use specialized exercise equipment on the International Space Station (ISS). The Treadmill Vibration Isolation and Stabilization system, or TVIS, is a modified treadmill. It uses a series of bungee straps called subject load devices to hold the user down. These straps provide resistive forces between 40 lb. and 220 lb. to simulate weight. Another tool is the Cycle Ergometer with Vibration Isolation System, or CEVIS. This device provides aerobic exercise while preventing vibrations from traveling into the station.

Some researchers explore the use of artificial gravity (AG) to protect the body. Artificial gravity is the use of forces, such as centripetal force, to create a feeling of weight. A short arm centrifuge can be used to generate these loading conditions. In a 2008 study, Caiozzo and Haddad compared subjects on bed rest to those using a centrifuge for one hour a day. The group using artificial gravity showed less severe loss in muscle fiber cross-sectional area. However, rotating a whole spacecraft is very expensive and complex.

Future designs continue to push the boundaries of space locomotion. The DYNASUIT is a conceptual design that would use many subsystems. It could include an artificial muscle subsystem using electro-active polymers or pneumatics. It might also include a bio-parameter subsystem to monitor heart rate and oxygen saturation. Another concept is ViGAR, or Virtual Gravity Artificial Reality. Proposed in 2005, this device would combine a centrifuge with a bicycle and virtual reality. These technologies aim to ensure humans can move and stay healthy across the stars.