Going weightless might look easy, but in reality it takes a heavy toll on the human body.
"While you may float in space, there are actually some very harmful things that can be happening to you," explains Linda Loerch, manager of the Exercise Countermeasures Project at NASA.
"Good Morning America" anchor Chris Cuomo tested it out for himself today in a gravity-enhancing centrifuge at the National Aerospace Training and Research Center.
In zero-gravity, muscles shrink, which means our most important muscle, the heart, also shrinks.
The flow of blood throughout the body is also compromised. On earth, hearts are constantly fighting gravity to pump blood upwards, but in zero-gravity blood rushes unhindered to the top of the body, creating puffy faces and eyes that sometimes bulge.
A lack of gravity even affects the spine: vertebrae stretch, sometimes painfully, making the human body about two and a half inches taller in orbit.
The immune system also weakens in zero "Gs"
Astronauts have been known to experience recurrences of childhood bouts of the chicken pox on missions.
"We carry some medicine to help with the itching," said Jeff Jones, NASA Flight Surgeon.
Treating any orbital illnesses can be difficult. Studies indicate some drugs, including antibiotics and birth control pills, lose their potency in a weightless environment.
Muscle atrophy is especially accelerated in a low-gravity environment.
"In terms of the strength of their muscles, they're down about 30, maybe 40 percent. Those don't come back for several weeks and the mass of their bones, the mineral in their bone, doesn't come back sometimes for a year, even longer than that," said Jones.
So imagine the toll a lengthy trip to Mars — a mission that could last a couple of years— could take on the body.
Ironically, the best way scientists have found to study the effects of space on earth is bed rest. Remaining motionless for months on end has the same effect on the body as living in zero-gravity.
One of the early solutions is "space-er-cizing" on a vertical treadmill. It looks odd, but has been effective in maintaining bone and muscle, moreso than traditional treadmills. The key: it works with zero gravity, not against it.
A centrifuge, which many may remember from the famous scene in the James Bond film "Moonraker" when one was used to try to kill 007, may be another means of counteracting the negative effects of zero-gravity.
In real life, NASA is looking at including one of these rotating devices aboard any ship that would go to Mars. Scientists believe that time spent in a centrifuge, which creates gravity, may counteract the negative effects of weightlessness.