In March of 2015, astronaut Scott Kelly headed to the International Space Station (ISS) for 340 days in space, the longest space mission so far, nearly double the average 4-6 month mission. Along with him was Mikhail Kornieko from Russia. While Scott was on the ISS, he saw 13 astronauts come and go and had three spacewalks (two planned, one emergency). He also gathered lots of data about his health, like blood samples and ultrasounds for scientists to compare to his twin brother, and fellow astronaut, Mark Kelly.
One key point of comparison was the effect of zero gravity on Scott’s body. Because the ISS orbits around Earth, astronauts do not experience gravity. This lack of gravity weakened Scott and Mikhail’s cardiovascular systems, which could cause symptoms of low blood pressure upon returning to Earth. To counter this, they drank combinations of salt and water to help increase their plasma levels and keep themselves hydrated for re-entry. For example, they drank chicken broth and Astro-Ade, a drink made especially for astronauts. Their muscles were weakened too, but they couldn’t do very much about that.
At the end of their 340-day mission, Scott, Mikhail, and another astronaut, Sergey Volkov, entered their Russian Soyuz capsule to return to Earth. To do this, they had to pass through Earth’s atmosphere, which is resistant to objects coming from space. This resistance usually works to our advantage, since it protects Earth from meteorites by burning objects that enter the atmosphere. The space capsule’s heat shield protects the astronauts from temperatures that can reach up to 3000 degrees Fahrenheit, caused by friction between the capsule and the atmosphere.
Re-entering the atmosphere is dangerous in many ways since the angle of approach must fall within a narrow range. An overly steep approach will cause the capsule to fall too quickly and collide with the Earth without being able to decelerate. If the approach is too shallow, the capsule will bounce off the atmosphere like a rock skipping on water, causing the capsule to re-enter the atmosphere at an even steeper angle. Even if the capsule survives the heat and the approach, the astronauts will still suffer during deceleration, which can create forces up to four times stronger than gravity.
When they approached the atmosphere, Mikhail and Sergey fired the braking engine for four and a half minutes. Then, they entered the atmosphere at the perfect angle and experienced 25 minutes of free fall. The three modules of the Soyuz separated. This is a particularly dangerous part of reentry. In 1971, three cosmonauts lost their lives when a valve opened during separation and depressurized the cabin. So Scott, Mikhail, and Sergey wore pressurized suits during reentry as a precaution.
Soon, the gravity in the capsule started to increase, and the wind outside could be heard, signs that the capsule was getting closer to the ground. A few miles above Earth’s surface, the capsule’s parachute opened to slow down the capsule for its landing in Kazakhstan. Then, just one meter off the ground, the soft-landing jets fired, and the crew landed. When the capsule was opened, the rescue team helped Scott and the others out, and he was placed in a chair for examination by doctors and nurses.
Once Scott was back home, it took his body time to readjust to life on Earth. As he got used to gravity, he would often stumble. His legs swelled up since they hadn’t been subject to weight or pressure in nearly a year. For the first few weeks, Scott had frequent medical tests, such as CAT scans, ultrasounds and blood drawings to compare to his twin Mark.
What scientists are finding out from comparing Scott and Mark may be important in getting humans to Mars.