Faster trips to Mars, or centrifugal force, will be needed to prevent bone and muscle loss for future astronauts.

Humans traveling to Mars may soon be possible. Whether they can survive the trip is another story

Bone mineralization is one of those lack-of-gravity problems. For each month in space, Logan says the human body loses 1 percent of its bone mass. And, once back on Earth, the bones don't grow back. "I'm not trying to throw cold water on the idea of going to Mars.

 From article, (Logan spent 20 years helping diagnose and treat NASA's astronauts. He said the main obstacle to sending humans to Mars is what he calls "the gravity prescription."

He said: "We know what Earth's gravity – one G for 24 hours a day – does. And we know that zero gravity, after four months, begins serious health deterioration."

Bone mineralization is one of those lack-of-gravity problems. For each month in space, Logan says the human body loses 1 percent of its bone mass. And, once back on Earth, the bones don't grow back.

"I'm not trying to throw cold water on the idea of going to Mars. I want to make sure we can survive if we do go," Logan said.

He says, if putting humans on Mars is truly a near-term goal, it means studies today must focus on Martian gravity, or 0.38 Gs.

"We need to start sending more people into space if we're actually going to get somewhere, with even problems we know like the gravity prescription," he added.

The scientist also said that it is critical to use the words "outpost" and "settlement" distinctly when talking about space exploration.

"Let's stop playing fast and loose with this idea that the ISS [International Space Station] is our first settlement in space. We have a permanent presence, but with rotating crews," Logan added. "Settlement is men, women, children, over multiple generations.")

Me, "We can build spacecrafts that can go faster between Mars and Earth so lack of gravity is less of a problem on the human body. We can institute some kind of artificial gravity (Centrifugal Force) spinning a part of the space craft to simulate gravity where astronauts can spend a lot of their time. And, once we get to Mars, we weigh down our clothing, with weights so as to produce, simulated, Earth like gravity, to keep astronaut bones strong. We need to come up with ideas like this to keep the human body, that was built for Earth, to continue to function in other lower gravity, or lack of, locations."

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