How much radiation is there in space, and how will it affect space travel?

Off the top of my head, I believe there is 1322 W/m^2 incident on the earth from our sun.

In space, this energy can be converted to propulsion, life support, etc... and is limited by the thermodynamic laws.

Three Kinds of Space Radiation
While on Earth, there are ways for humans to protect themselves against radiation's effects. But as the human gaze shifts more and more towards the heavens, scientists must find ways to combat the radiation traveling unhindered through space. Sunscreen might block UVA and UVB rays but is ineffective against gamma rays. The Earth's atmosphere shields humans from much of the energetic radiation. However, the atmosphere is not as thick 250 miles above the ground. The astronauts on the International Space Station are sitting ducks for radiation.

Ionizing radiation in space comes in three main types. The first is Galactic Cosmic Rays. Astronomers believe that these rays originate mainly in supernovae, although they also appear to come from quasars and solar flares from stars outside the Solar System. Every star reaches a point in its lifetime when the hydrogen in its core has all been converted to helium. This starts a series of reactions which forces the core to collapse in on itself. When a star with a mass 10 times that of the Sun collapses, a vast amount of energy is released in an explosion. A shock wave travels from the core and blows apart the star. Positively charged nuclei of atoms are spewed into space. These highly energetic nuclei travel through space almost as quickly as light!

(See http://www.rog.nmm.ac.uk/leaflets/supernovae/supernovae.html and http://www.chapman.edu/oca/benet/mrgalaxy.htm for more information on supernovae.)

The second type of radiation that astronauts must be concerned with is solar protons. The protons originate in the sun. For reasons not fully understood by scientists, the sun sometimes ejects magnetic energy in the form of solar flares. Solar flare activity is linked with sunspots and the Sun's eleven year cycle. During a flare, temperatures range from 10 to 20 million degrees Kelvin. The high temperatures accelerate particles in the solar atmosphere. One of the most astounding things about solar flares is the amount of energy released in a single eruption. A flare usually releases 10^27 ergs/sec! During the course of the entire flare, the released energy would be the same as that given off by the simultaneous explosion of several million, 100-megaton hydrogen bombs! This energy takes the shape of many things, including solar protons. The protons travel through space in the solar wind (http://csep10.phys.utk.edu/astr162/lect/sun/wind.html) which has a velocity of approximately 400 km/sec.

(See http://spacescience.spaceref.com/ssl/pad/solar/flares.htm and http://hesperia.gsfc.nasa.gov/~benedict/flare.htm for more information on solar flares. An incredible video at http://spacescience.spaceref.com/ssl/pad/solar/images/limb_flare.mpg shows the sheer power of a solar flare.)

The third type of radiation is high energy electrons and protons trapped by the Earth's magnetic field. The areas of trapped radiation are called Van Allen belts. Protons surrounded by an inner and outer belt of electrons form a belt which circles the Earth like a doughnut. NASA discovered these belts in 1958 during the Explorer I mission. The particles in Van Allen belts come from solar flares, magnetic storms, and collisions of cosmic rays with particles in the Earth's atmosphere. Due to the placement of the Earth's dipolar field, the trapped electrons and protons attain their lowest altitude in a region called the South American Anomaly. The particles increase in density in this area off the coast of Brazil. All three forms of radiation can be extremely dangerous to astronauts, especially when they are performing extravehicular activities (EVAs). The risk of radiation sickness will also increase on longer voyages to places like Mars. Radiation can cause immeasurable damage by penetrating the skin and destroying cells. Many possible problems can ensue, depending upon the severity of the damage. Temporary sterility in men and women, bone-marrow damage, radiation burns, cancer, chromosome breakage (http://www.ratical.com/radiation/CNR/RICIP.html ), and damage to the central nervous system are all possibilities. Although these run the gamut from mild to serious for those of us on Earth, they all spell trouble in space. If an astronaut on the International Space Station becomes ill, he may not be able to complete all necessary tasks and may have impaired judgment.

(See http://see.msfc.nasa.gov/see/ire/iretech.html and http://wwwssl.msfc.nasa.gov/headlines/y2001/ast04may_1.htm for more information.)


Dangers to Astronauts
In the past, several monitoring devices onboard Mir and the space shuttle have measured radiation levels. Scientists have used everything from passive dosimeters (radiation detectors) to a radiation environment monitor. The data they received was helpful, but only told them about the doses of radiation absorbed by the external skin of an astronaut. The scientists knew that in order to find a way to protect the astronauts, they had to know what levels of radiation were penetrating the inner organs where cancer could form. Thus, Fred was born. Fred is NASA's Phantom Torso traveling in the International Space Station. This replica of a human torso, see picture, is composed of 35 one-inch layers, each carrying passive dosimeters to measure the total radiation that travels through the torso. Real-time radiation levels will also be measured in the Phantom's brain, stomach, heart, colon, and thyroid. Fred's "skin" is made of Nomex, a non-flammable material used in the suits worn by NASCAR drivers. Two more passive dosimeters in the "skin" measure external radiation doses. The data from the internal detectors can then be compared with data from the external detectors. NASA hopes that this experiment will provide information on how to better protect the astronauts.

(See http://www1.msfc.nasa.gov/NEWSROOM/background/facts/phantom.html for more information.)

Two other experiments measuring radiation are also onboard the International Space Station (ISS). The German Space Agency sent up a Dosimetric Mapping System. The system is designed to measure the different types of radiation that are penetrating the outside of the ISS. Dosimeters specific to various types of radiation are placed in the ISS. For three months these dosimeters will record radiation levels. High energy particles entering the ISS will be measured by the tracks they leave behind in the Nuclear Tracking Detector Packages. Two Dosimetry Telescopes were placed in the U.S Laboratory where they will measure ions streaming into the ISS. The final piece of the German system is 12 thermoluminescence dosimeters which measure the neutron dose. The entire system is scheduled to return to Earth on STS 105. Once scientists go through all of the data, they should know how much radiation astronauts are being exposed to in the ISS.

(See http://www.spaceref.com/iss/payloads/dosimetric.mapping.html for more information on the Dosimetric Mapping System.)

The third experiment comes from the Japanese Space Agency, NASDA. Unlike the prior two experiments, the Bonner Ball Neutron Detector has flown on previous missions. Its primary function is to measure neutron radiation. Because neutrons pass through an astronaut's skin and may damage the bone marrow, NASDA and the German Space Agency are dedicating experiments to recording data on neutrons. The Bonner Ball consists of 6 spheres filled with Helium 3 and connected to the control unit by a wire. Each sphere is covered with polyethylene, the material used to protect sailors in nuclear submarines. Neutrons enter each sphere where they react with the Helium to form electrons. These electrons travel in a current down the wire into the control unit where this current's strength is recorded. Scientists are hoping to collect information which will allow them to assess the risk astronauts experience while traveling in the ISS.

(See http://www.spaceref.com/iss/payloads/bonner.ball.neutron.det.html and http://www.nsbri.org/Radiation/BonnerBallWorkings.html for more information on Bonner Balls.)

All three experiments have precise and individual short term goals. Yet, they share one long term goal as well. By discovering all that we can about radiation now, we may someday find a way to protect our astronauts from this radiation. Only then will long voyages to distant planets be possible. Who knows? Perhaps the solution will be space sunscreen! With every experiment that takes place in space, we are one step closer to finding the answer.

(For more information on the three experiments go to http://www.nsbri.org/Radiation/ISS-EXP.html.)