How can astronauts withstand high g-forces? --- Sudhir, Hyderabad, India
Marshall Brain Answers:
There are two types of people who experience high G forces on a regular basis: Astronauts during takeoff and landing, and pilots who fly high-performance airplanes.
An astronaut experiences G forces during takeoff because, for example, the space shuttle accelerates from zero to 17,000 miles per hour in 8.5 minutes. That means the G forces on the astronauts top out at around 3 times the force of gravity, or 3 Gs. The astronauts handle these G forces by lying on their backs.
Re-entry G forces can be even higher, especially if something goes wrong. This article discusses G forces as high as 10 Gs during a problematic re-entry of a Soyuz capsule. But even in the normal case, the Soyuz capsule experiences high Gs as the atmosphere slows the lightweight craft down very quickly. Astronauts therefore wear G suits and learn muscle contraction techniques as discussed on this page. The shuttle again tops out at about 3 Gs during re-entry, but astronauts are weaker after being weightless for more than a week. So astronauts also wear G suits during re-entry.
G suits were developed in the 1940s to help fighter pilots cope with high G forces during turns. The basic idea is to help keep blood from pooling in the legs by putting pressure on the legs with air bladders. Essentially the suit is squeezing the blood out of the legs sort of like a person uses pressure to squeeze toothpaste out of a tube. Pilots also learn to tighten certain muscles in the abdomen to aid the process.
Red Bull sponsors a series of airplane races where pilots are subjected to high Gs in the turns. The pilots wear passive G suits, where shifting water sewn into the suit in bladders keeps pressure on the legs. You can learn more about these suits in this post:
This video offers a nice overview of the suits:
See also: How do you calculate G-forces?
and All about G forces.