AT THE beginning of the Apollo program no one knew how spaceflight would affect the human body.
In fact illness in space caused the first astronaut rebellion.
Apollo 7 commander Wally Schirra was the first person to suffer from a head cold in space and when Mission Control asked him to flip a switch, he refused.
"[W]e have not eaten at this point, I still have a cold, I refuse to foul up our timelines this way," he snapped.
Some experts now think Schirra had not just a cold but also space sickness - nausea and disorientation astronauts feel until they adjust to weightlessness.
The Apollo 7 command module was the first spacecraft big enough to let astronauts float around freely, and that makes space sickness worse.
A few other Apollo astronauts also reported being ill, some speaking about it only years after they'd flown because none wanted to give NASA a reason to ground them.
During Apollo 15, NASA learned that weightlessness was also causing the astronauts to lose excessive amounts of potassium.
Low potassium can cause weakness, tiredness and disturbed heart rhythm, so on Apollo 16 NASA made the astronauts take supplements in their orange juice, which they disliked.
"I haven't eaten this much citrus fruit in 20 years ... And if they offer to serve me potassium with my breakfast, I'm going to throw up," Apollo 16 commander John Young complained.
Astronauts' sleep schedules were carefully managed but sometimes conditions were difficult.
For example, the Apollo 11 astronauts rested in their lunar module after their historic moonwalk, Aldrin on the module's floor and Armstrong on top of the engine cover.
Neither slept because the cabin was brightly lit, cold and noisy (from the sound of a pump) and their spacesuits were awkward to sleep in.
But the spacesuits - multilayered and water-cooled - did a great job of keeping them comfortable outside on the Moon, where temperatures can swing from below -170°C at night to well over 100°C at noon.
Apollo astronauts avoided those extremes, but the Apollo 15 crew was still able to work outside when the temperature hit 69°C.
Space dust
Spacesuits were also designed to protect against micrometeoroids - tiny, fast-moving rocks and dust, debris from comets and asteroids.
The Moon has no atmosphere to burn them up and receives a continual pelting.
Micrometeoroids wear away the Moon's rocks, churn up its surface and will make the Apollo astronauts' footprints vanish after thousands of years.
When they hit Moon the micrometeoroids create shock waves in the soil, some of which melts and then freezes into tiny razor-sharp shards - lunar dust, another big hazard.
Exposed to the sun, this dust becomes electrically charged and clings to all it touches. Its sharp edges make it very abrasive; it destroys seals and erodes spacesuits and the fine particles work their way through zippers.
Dust carried into a lunar module smelled like gunpowder and made astronauts sneeze, but breathing it in is actually a health risk - it's like the silica dust that gives stoneworkers the deadly disease silicosis.
Radiation risks
NASA has worked on ways to handle the dust but the risk that perhaps worried NASA most was radiation, especially high-energy particles from the Sun.
Earth's magnetic field protects us from most of these particles, which pile up in doughnut-shaped regions around the planet called the Van Allen belts after their discoverer.
Astronauts have to travel through the belts to get to the Moon.
In 1962 Van Allen himself suggested that a controlled nuclear explosion might clear particles out of the inner belt, reducing the radiation. But this was never tried.
By 1964 NASA had decided that the astronauts would travel through the belts so fast that their spacecraft would give them enough protection.
The Apollo flight trajectories were also plotted to miss the inner belt and go through the thinnest part of the outer belt.
Once beyond the Earth's magnetic field astronauts were vulnerable to any sudden eruptions of particles from the Sun.
NASA had contingency plans for such events. But the Apollo crews were lucky - the Sun was fairly quiet during their flights.
A massive solar storm took place in August 1972, between Apollo 16 and 17. It unleashed so much radiation that if any astronauts had been on the Moon then they would have fallen ill or even died.
The Apollo astronauts wore radiation monitors that showed the cumulative dose they'd received.
Other monitoring devices were worn in specific garments and collected information on the different types of radiation the astronauts were exposed to.
For keeping tabs on their general health, the astronauts also had electrodes stuck to their bodies that let Mission Control watch their blood pressure, body temperature, heart rhythms and breathing.
The Apollo missions lasted for days rather than months, but still told us a lot about how spaceflight affects the body and what is needed to live and work on the Moon.
NASA plans to send astronauts to the Moon again in the 2020s and in the 2030s there may also be crewed missions to Mars.
Space biomedicine is a key area for NASA and other space agencies, and for high-profile companies such as Boeing.
In Australia, CSIRO is looking at how its research could contribute to life-support and biomedical systems for space.
- One Giant Leap is a joint initiative with CSIRO, Australia's national science agency, to celebrate the 50th anniversary of the moon landing.
Read more: New moon mission 'stepping stone to Mars'
