Space doctors outline astronaut's dangers and precautions

Heat, light and gravity, all necessary forlife on Earth, pose serious problemsfor astronauts, a report in the Canadian Medical Association Journal says.

So does the rapid swing between day and night, radiation, vacuums, noise and dangers particular to the environment, such as space debris and buildup of electrical charges.

The potential issues, and precautions, are outlined in an article byRobert Thirsk of the Canadian Space Agency, Andre Kuipers of the European Space Agency Astronaut Corps,Chiaki Mukai of the Japan Aerospace Exploration Agency and David Williams from the department of surgery at McMaster University inHamilton.

All four authors are doctors who have spent time in space. Thirsk began a six-month stay at the International Space Station last week, where an important goal of the mission is totest the endurance of the human body in orbit.

The report outlines several potential effects of space on the body and highlights microgravity weightlessness as "the most profound aspect of the space environment on human physiology."

All organ systemsare affected by weightlessness,and changes to the bodies of the crew will be monitoredthrough tissuesamples and various testing, the NASA website said.

From freezing to boiling

Heat and cold have to be managed carefully during spacewalks because temperatures swing from100 C to 100 C asthe International Space Stationmoves from being exposed to the sun to the shadow of the Earth, with a change every 45 minutes, the report said.

Spacesuits haveactive cooling while heating is "a passive process resulting from accumulated body heat." But there are also heaters in theastronauts' gloves,and thermal mittens canprovide insulation from high temperatures.

With a transition from light to dark every 45 minutes there are 16 daily sunsets and sunrises astronauts face disruptedcircadian rhythms, leading to poor sleep.Medications can help, butnoise has proved to be a bigger sleep problem, the report said.

Fans, pumps and motors on the station produce noisesimilar to a normal conversation, but "inadvertent alarms have woken astronauts from sleep, an issue of particular concern if it occurs before a critical task on the mission."

Moreover, noise canaffect communication between astronauts and might reduceconcentration. To counter noise, the crew has hearing protection, and noisy equipment is muffled.

Radiation, which poseslong-term risks of cataracts and cancer, is many times higher at the space station's orbit 350 kilometres above the Earththan at the surface of the planet.

Astronauts, exposed to galactic cosmic rays (particles from outside our solar system), particles trapped in the Earths Van Allen belts and solar flares, "are regarded as radiation workers and follow the 'as low as reasonably achievable' principles and guidelines, with radiation monitoring to document exposure," the report said.

Low and moderate doses ofionizing radiation can damage DNA,with therisk of damage beinglowerfor older astronauts than for younger ones.

Spacewalking astronauts are also atrisk of decompression sickness as they move fromEarth-like pressureinside the station to the vacuum of space.To offset this, astronautsreduce the level of nitrogen in their systemby breathing oxygen before a spacewalk.They're also trained torecognize the symptoms of decompression.

Physical dangers

The concern that micrometeoroidsor orbital junk could hit the station or an astronaut on a spacewalk is countered by planning, armour and maneuvers.

Hittingeven a small piece of material could be catastrophic.

"The impact of a collision of a one kilogram piece of space debris with the International Space Station has the same energy as a collision involving a 35,000-kg tractor-trailer travelling at 190 km/h," the report said.

But spacecraft are shielded, and the crewtakes steps to avoid potential collisions. Also, spacewalks are scheduled to avoid known meteor showers, and space suits have a micrometeoroid shield.

The station can build up an electrical charge, whichcould arc to aspacewalking astronaut, but there is special equipment onthe space station structure that is used to neutralize thecharge.