Australian Science

Author: Sharon

  • The Risk of Human Space Flight to Mars

    The Risk of Human Space Flight to Mars

    This past week NASA announced that in 2015 they would be sending two astronauts to the International Space Station (ISS) for a year-long mission. This is an expected, and necessary step in the preparation for human spaceflight to Mars. If we are to have human explorers on the surface of Mars, we need to understand the effects on humans of long-term space travel. At the moment trips to the ISS last on average 5-6 months. A mission to Mars may take 6-8 months, plus an extended time on the planet, and a 6-8 month return trip. In reality astronauts could be sent on missions of 2 years or longer.

    The ISS as it orbits Earth. Photo credit NASA.
    The ISS as it orbits Earth. Photo credit NASA.

    Astronauts are exposed to a number of conditions in space that can pose serious health risks, especially if exposure takes place over a long period of time. There are lots of hazards and risks for humans in space, including: ascent and descent accidents; space sickness; debris collisions; micrometeorites; hazardous and toxic gas leaks on the spacecraft; EVA (Extra Vehicular Activity) accidents; sudden unexpected illness and the list goes on. Today I’m talking about the specific issues that affect astronauts during long distance flights. (By the way I use the term ‘astronaut’ as a general term, which includes astronauts from various nations, including cosmonauts from Russia, and teikonauts from China.)

    Some of the major issues for astronauts during long duration space flights include:

    Exposure to radiation – Astronauts live and work well above the protective atmosphere of earth, so they are subject to the full force of the sun’s radioactive output as well as high energy cosmic rays that originate outside of our solar system. Long distance missions do not have the benefit of Earth’s protective atmosphere and magnetic field. Material shielding is effective against low energy radiation, but may create damaging secondary radiation for higher energy particles. The ISS uses aluminium to protect the spacecraft and crew. As the thickness of the shielding material increases, the probability that the particle will survive with enough energy to damage human issue is decreased. Low levels of radiation generally do not pose a significant health risk to astronauts, however the effects of radiation are cumulative, so long term exposure increases the lifetime risk to astronauts. Crews of future long duration interplanetary missions will have to travel through the Van Allen radiation belts, and be exposed to more galactic cosmic rays, and as a result will be exposed to higher levels of radiation than those remaining in Earth’s orbit. Increased and prolonged exposure to radiation has serious health consequences for astronauts, including cancer, leukaemia, heart disease, and damage to the central nervous system.

    Muscle atrophy – Our muscles, bones and organs have adapted to work in the environment we inhabit, which is exposed to the effects of gravity. When exposed to an environment where there is little or no gravity, our muscles, bones and organs begin to lose condition – becoming more problematic the longer the astronaut is in space. On Earth, our muscles are constantly working against gravity. In space there is no force of gravity for muscles to work against, so astronauts will lose muscle tone. Loss of muscle tone starts to occur shortly after launch, and continues whilst the astronaut is in a reduced-gravity environment. During longer missions, muscles may atrophy, and astronauts may experience uncontrolled muscle twitching, and a loss of fine motor control. The loss of muscle tone, strength and control can be mitigated with regular exercise during the mission.

    Astronaut Robert Thirsk, asleep in his sleeping quarters in the ISS. Photo credit NASA.
    Astronaut Robert Thirsk, asleep in his sleeping quarters in the ISS. Photo credit NASA.

    Cardiovascular damage – When in space, the body no longer needs to maintain the powerful heart muscles needed on Earth, so heart tissue begins to shrink. In space, astronauts experience a redistribution of body fluids, which results in changes to cardiovascular physiology. The heart doesn’t have to work as hard pumping blood in a microgravity environment as it does on earth so crew members are encouraged to undertake aerobic exercise as part of their daily routine, in addition to exercises designed specifically to maintain as much muscle tone as possible. Whist exercise is beneficial, it appears that it cannot reverse the process, but can help slow it down.

    Bone density – In microgravity, the lack of impacts in weight bearing exercise means that newly created bone tissue is not incorporated into bones as normal, so as bone tissue is created it is absorbed into the system, not used as it would be on Earth. This results in high calcium levels elsewhere in the body, which can lead to significant health issues. Studies have revealed a significant loss of calcium from weight bearing bones of astronauts. This is a concern for astronauts as it suggests a risk of renal stone formation on long duration missions. Density in such bones as the pelvis and legs decreases by approximately 1 to 2 percent a month on average, which presents concerns for astronauts during long haul missions. Unfortunately exercise does not seem to reduce the level of bone loss, but is beneficial for many other issues as discussed previously.

    Sunita Williams exercising on the ISS. Photo credit NASA.
    Sunita Williams exercising on the ISS. Photo credit NASA.

    Hyperarousal – Don’t worry – it’s not what you think! Astronauts may experience hyperarousal, their reaction to a changed schedule, working under pressure, sleep deprivation, and the excitement of being in space. Hyperarousal can cause insomnia, disrupt the appetite, result in impaired concentration, cognitive dysfunction, and decreased co-ordination. Fatigue is often a side effect of hyperarousal, as is anorexia and sudden weight loss. Over time space agencies have developed strategies to deal with hyperarousal, including giving crews adequate rest time, control over some of their tasks, adequate leisure time, and regular contact with family and friends.

    Sleep deprivation – The amount and quality of sleep experienced in space is poor for a number of reasons including: variable cycles of ‘day’ and ‘night’; poor illumination during daytime hours in the space craft; environment outside the windows at the ‘wrong’ time of day; hectic work schedule; noise of the spacecraft; altered diet; and the physical challenge of sleeping in space. Sleep deprivation may compromise the immune system, which whilst not a significant issue during short term missions, is a potentially debilitating condition during long-term missions. Sustained physical stress over a long term period may result in an immune system that is so compromised that the body is unable to fight serious infections. Precautions include wearing sleeping masks and earplugs, anchoring themselves down to sleep, maintaining a steady routine of work and sleep, and using shades and other devices to block out the windows.

    Psychological Issues – Working away from friends and family, and working with people from other cultures presents a number of psychological and social challenges. The psychological welfare of a crew of astronauts is critical to the success of a space mission. Interpersonal relationships during a mission may be a significant source of psychological stress. Crews do many things in space to try to maintain a sense of ‘normalcy’ during long stays in space. When crews aren’t required to work, they are encouraged to undertake other activities, which include reading, listening to music, writing e-mails and letters to family and friends, and exercising. In 2007 American astronaut Sunita Williams ran the Boston Marathon on the treadmill in the ISS, completing the race in just over 4 hours. During low earth orbit missions crews receive periodic care packages from their family with CDs, DVDs, books, magazines, photos, and letters. In addition to the packages, the ISS also has library lockers that contain music, books, and videos.

    Over the last 40 years humanity has overcome enormous social, technical and physical challenges to put humans into space. When Yuri Gagarin became the first human in space by orbiting the Earth for 108 minutes on the 12th of April 1961, very little was known about the space environment and how it would affect humans. Just over 40 years later we now have a permanent presence in space with the introduction of the ISS into low Earth orbit. We know a lot about the physiology and psychology of humans in space, and have made space a relatively comfortable existence for astronauts. The future of space exploration may include human missions to other planets within our solar system, such as Mars. Before any long-term exploration of Mars could be contemplated, further research is needed in a number of areas to ensure the safety, and longevity of all crew members during the mission and beyond.

  • The Case for Neptune

    The Case for Neptune

    Take a moment to consider Neptune. The eighth planet in our solar system, the planet farthest from the Sun, and the third most massive planet in our solar system.  Also one of the least visited, and consequently one of the least understood planets in our solar system. Neptune was discovered in 1846.  Forty years later, in 1886, astronomer Sir Robert Ball wrote ‘Besides this brief sketch of the discovery of Neptune, we have little to tell with regard to this distant planet.  With a good telescope and a suitable magnifying power we can indeed see that Neptune has a disc, but no features on that disc can be identified’.

    Unfortunately in the last 126 years not much has changed. Due to its enormous distance from Earth (~ 30 Astronomical Units) Neptune remains little more than a blurry disk in the eyepiece of the most powerful ground based telescopes.  In the past astronomers  studied Neptune by examining the planet as it occulted, or passed in front of the light of another object, usually a star, allowing scientists to calculate its diameter, chemical composition, and temperature.  The opportunity to study the gas giant only improved when Voyager flew by Neptune in 1989, and the Hubble Space Telescope was launched in 1990.

    Voyager 2 launched in 1977, and reached Neptune on the 25th of August 1989 (click here for an impressive animation of the Voyager 2 flyby of Neptune). Although Voyager 2 began imaging the planet from about 35,000,000 million miles out, most of the data we have today is from a 24 hour period, during which Voyager 2 passed 4,500 kilometres above Neptune’s north pole at an eye watering 67,000 km per hour.  During the trip to Neptune Voyager gathered about 5 trillion bits of information or about .5 of a Terabyte of data. That doesn’t sound much now, but back in 1977 the 3 computers on the Voyager spacecraft had a combined memory of 68Kb, so Voyager sent back almost 15 million times more data that could be stored in it’s memory!!

    Scientists were thrilled by the data from Voyager 2 and set to work learning as much as they could about the distant blue planet.  We learnt that Neptune is mostly composed of gas, is likely to have a rocky or metallic core, and that the majority of Netpune’s mass is hydrogen and helium, with traces of water, methane, ammonia, and other compounds.  Thanks to Voyager 2 we learnt an enormous amount about Neptune’s atmosphere, weather systems, magnetic field, moons, and ring system.  But that was over 30 years ago – and we now have more questions than answers.

    Images from Voyager 2 showed that the most obvious feature of Neptune is its stunning blue colour, the result of methane in the atmosphere.  Voyager 2 also revealed a more dynamic and turbulent atmosphere than anyone expected.  Neptune’s atmosphere consists of layers of clouds, banded features, and unexpected structures, including what was termed the Great Dark Spot (GDS). Neptune generates the strongest jet streams anywhere in the solar system, reaching speeds of up to 2,400 kms per hour. Voyager detected weak auroras, similar to those on Earth, but because of Neptune’s complex magnetic field, the auroras appear over wide regions of the planet, not just near the planet’s poles.  Despite what we do know, the structure and composition of Neptune’s atmosphere remains poorly understood. What accounts for the relatively high percentage of methane and lack of hydrogen and helium? What is the energy source responsible for powering the incredibly high speed winds and variable storm systems? What happened to the Great Dark Spot (observed by Voyager in 1989, but no where to be seen when Hubble observed the planet in 1994). Why is the temperature of Neptune’s thermosphere, a staggeringly high 750K (4760 degrees celsius)?  How can Neptune be so cold and distant from the Sun, and yet radiate so much energy?

    Thanks to Voyager 2 we know that Neptune’s magnetic field is approximately 25 times stronger than Earths, and that it’s lopsided (like Uranus), at 47o to the rotation axis and offset from the planet’s centre.  Although we suspect that Neptune’s magnetic field is generated by currents within Neptune’s icy mantle – we do not fully understand why Neptune’s magnetic field is oriented the way it is, or what processes could generate such an off-kilter magnetic field.

    Voyager 2 image of Triton (Credit Nasa)
    Voyager 2 image of Triton (Credit NASA)

    Before Voyager 2, Neptune was thought to have 2 moons, Triton and Nereid. Voyager 2 discovered 6 new moons, and since Voyager’s visit, astronomers have discovered a further 5 moons.  Most of what we know of Triton, Neptune’s largest satellite, was acquired in a single encounter by the Voyager 2 spacecraft, which imaged about 40% of its surface.  If scientists were surprised by the images from Neptune, they were stunned by the images of Triton.  Triton, is an icy moon with a surface temperature of -235o, the coldest place known in the solar system.  Voyager’s images revealed a geologically active planet, geysers spewing nitrogen gas and dust particles high into the atmosphere, rocky outcrops, canyons, and plains of frozen methane.  Triton has a very thin nitrogen atmosphere with small amounts of methane, above a scarred and cracked surface.  Triton showed no fresh impact craters, an indication of an active planet experiencing periodic resurfacing.  But there’s still a lot to learn. Perhaps the most tantalising questions are about Neptune’s largest moon.  Was Triton formed near Neptune, or is it a captured object from the Kuiper belt?  What is the composition of Triton, and what causes the geologic activity, and has the distribution of the ice geysers changed dramatically since the Voyager flyby?  Will further analysis of Triton tell us more about the solar system, and our place in it?  Is there a sub surface ocean? Could Triton harbour life?

    Earth-based observations during the 1980s suggested that there were a number of partial rings surrounding Neptune, and Voyager 2 discovered a system of equatorial, circular rings.  Although Voyager 2 gave us a good look at Neptune’s rings, the details of their composition is still uncertain, we don’t know how long they’ve been there, or even if they are stable.

    Despite the valuable insights bought to us by the Voyager mission, the Hubble Space Telescope and other studies, clearly there are still a number of questions about Neptune that still need to be answered. Technology has advanced enormously since 1977 and any new mission would be well equipped to examine Neptune, its rings and a number of its moons.  A mission to Neptune would enable us to learn more about our outer solar system, and exploration of Triton may provide our best opportunity to examine the surface and atmosphere of a Kuiper Belt Object in orbit around a planet in our solar system.  In 2003 NASA proposed a Neptune Orbiter/Triton Explorer, however, that mission appears defunct.  Neither NASA nor ESA have any current or future plans for the exploration of Neptune.

    I think that needs to change.