Understanding the Risks: Radiation Exposure During Interplanetary Travel (Issue #26)

Guest blog by Kathryn Sharp

RadiationRecent years have seen an exciting uptick in the number of humans-to-Mars mission plans, from manned fly-bys to permanent settlements. Each lays out its own priorities and objectives, suggesting creative solutions to challenges common to all of them. One important challenge each mission will face is the danger of space radiation exposure over the course of lengthy interplanetary travel.

There are two major types of radiation: ionizing and non-ionizing. Many forms of nonionizing radiation will sound familiar: your car radio, cell phone, microwave, all of which operate at frequencies low enough that their energy isn’t sufficient to damage human DNA. These are therefore not considered to be carcinogenic, or cancer-causing. On the other hand, ionizing radiation carries energy high enough to break chemical bonds and damage DNA, which in turn increases the risk of developing cancer. Some examples include medical X-rays and CT scans, which, when used infrequently, do not significantly increase cancer risk, and radioactivity remaining from the era of atmospheric nuclear testing.

Insp mars shipOf course, these are only man-made sources of radiation. The sun showers the Earth every moment with both ionizing and non-ionizing radiation. Thankfully, our protective atmosphere and magnetosphere shield us from a majority of the harmful radiation, with only some UV rays reaching the surface. Beyond our atmosphere however, solar energetic particles (SEPs), ejected from the sun by solar flares and coronal mass ejections, as well as galactic cosmic rays (GCRs) from interstellar space blast through our solar system unmitigated.

In space, astronauts face much higher radiation exposure from these sources than we do down here on the surface. On average, an astronaut on the International Space Station (ISS) will receive as much radiation in one six-month stay as they would in twenty years back home on Earth. As humans venture beyond low-Earth orbit and the sheltering bands of Earth’s magnetic field, their lives will depend on proper shielding in their spacecraft.

ss-121109-mars-curiosity-tease.photoblog900In 2011, when the Mars Science Laboratory (MSL) Curiosity Rover launched from Cape Canaveral it carried with it a small instrument for measuring space radiation in a shielded environment similar to that of a manned mission. Based on the measurements of the unit called the Radiation Assessment Detector (RAD), Marsonauts would receive a dose equivalent of roughly 0.6 Sieverts (Sv) in 360 days of travel to-and-from Mars, not counting any radiation received while operating on the surface of Mars itself. This dose is akin to receiving 1 to 2 abdominal CT scans each week over the course of a year.

Currently, NASA limits the cumulative lifetime dose for its astronauts at 1 Sievert. This dose is associated with a roughly 5% increase in lifetime cancer risk. For reference, the current lifetime risk of dying of cancer for someone in the US is around 20%, so a dose of 1 Sv would raise this risk from 20 to 25%. While 0.6 Sieverts is a large dose of radiation in a relatively short period, clearly it is within established limits and should not halt further development of manned missions to Mars.

Although this dose falls within NASA’s established limit, developers of any future crewed Mars mission shoulder the responsibility of sheltering its astronauts and reducing their exposure to the lowest levels possible. How can we limit the radiation dose to Marsonauts in an efficient and cost-effective way?

victoria2_opportunityThree major factors limit a person’s exposure to radiation: time, distance, and shielding. Limiting the time astronauts are exposed to space radiation is a surefire way to reduce their dose. However, the only way to reduce the time of exposure is to speed up the spacecraft: no easy feat. Existing spacecraft rely on heavy fuels, which in turn lead to heavier payloads, resulting in slower speeds and higher costs. Conceptual space vehicles that rely on other sources of energy, such as nuclear power, are on the drawing board, but waiting through the long development period for such technologies will only further delay a crewed mission.

Because the source of solar energetic particles, the sun, is a fixed source, and because galactic cosmic rays are pervasive throughout the solar system, we cannot significantly increase the distance between the astronauts and the source of the radiation. At this time, the most convincing method of reducing exposure is effective shielding. Unfortunately, different materials are necessary to shield against different types of radiation. For example, high-energy gamma rays require very dense, thick materials, such as lead, to shield, whereas neutrons are best-shielded by hydrogen-rich materials such as concrete. These are both heavy materials that will add significant mass to the payload, requiring more fuel and incidentally, more money.

Current radiation shielding plans minimize the amount of these materials by allowing for a narrow shelter in the center of the spacecraft to be used during large SEP-producing events such as solar flares or coronal mass ejections. The measurements taken by the RAD aboard Curiosity confirmed that this type of arrangement would be sufficient to shield the majority of SEPs, but astronauts would still be vulnerable to, and receive the majority of their dose from, galactic cosmic rays. This constant stream of heavy, high energy particles presents the biggest shielding challenge.

Several mitigation strategies are being considered to reduce the dose from GCRs. We could utilize existing resources aboard the ship, such as the crew’s water or fuel supply, as shielding agents. Water is an excellent shield for GCRs, but it is heavy. A water shield around the crew’s living quarters would need to be several meters thick, and could add hundreds of tons to the payload. This is an insurmountable weight for current mission designs, and would send launch costs skyrocketing.

Alternatively, we could construct the spacecraft from light, hydrogen-rich plastics such as polyethylene rather than the aluminum shell that the ISS employs. This could reduce both the payload weight and cost, but further research is necessary in order to improve the strength and heat tolerance of these materials.  Another theoretical strategy would be to generate a small magnetic field to deflect incoming radiation much the same way Earth’s magnetic field functions. Generating a magnetic field requires energy however, and generating one large enough to shield an entire spacecraft would require considerable energy: a precious commodity when you are 35 million miles from home.

a Mission to Mars Pic 06While all possible ways of limiting radiation exposure ought to be explored, it is important to keep these risks in context. In his book, The Case for Mars, Mars Society President Dr. Robert Zubrin puts these concerns in perspective: “While such doses are not to be recommended to the general public, they represent a small fraction of the total risk of not only space travel, but such common recreations such as mountain climbing or sailboarding. Radiation hazards are not a showstopper for a piloted Mars mission.”

As Zubrin’s statement suggests, we must bear in mind that a manned Mars mission is not a routine endeavor, it is an extraordinary one. Every extraordinary mission in the history of mankind has involved significant risk, and with it, the potential for remarkable reward. We can and should do our best to limit these risks, but must understand that we cannot eliminate them.

 

[Images: publicdomainpictures.net, Inspiration Mars, NASA]

Why Could We Be Descendants of Martians? (Issue #22)

By: Dr. Steven Benner and Nicole Willett

For many years, scientists have considered the model that life originated on Mars and was transported to Earth, rather than originating on Earth.  This model turns on answers to the question: What molecular structures are necessary for biology to “switch on”, moving from an inanimate state to a living state, where reproduction and adaptation (key parts of Darwinian evolution) are able to allow life to manage challenges to its blog 22 dnaexistence. For many, this switch requires the emergence, from a “prebiotic soup”, genetic molecules such as DNA and RNA. And, if this is true, the model then turns on the questions: Could genetic molecules have emerged on Earth? Could they have emerged on Mars? And given what we think about the environments on early Earth and Mars, which were more suited for the kinds of prebiotic chemistry that might give genetic molecules?

Dr. Steven Benner, of the Foundation for Applied Molecular Evolution in Florida, presented findings at the Goldschmidt Conference in Florence, Italy last week that suggest that Mars was more suited. His research increases the chance that life originated on Mars and was transported to Earth via meteorites.  Some people say this is an outlandish claim, while others are becoming more intrigued by the facts that support this model.

To understand this subject, let’s start with some background information about chemistry and biology.  Chemistry is the study of the elements (atoms) on the periodic table and how they connect and interact to make up everything in the universe, including you.  Prebiotic chemistry is the study of how complex molecules that might allow the “switch” to biology might have emerged without life. Models in prebiotic chemistry describe how these non-biological molecules might, under defined conditions, somehow become biological.  The missing link is the “somehow become biological”.  Many studies and journal articles have been published on this subject.  Some have been found to be incorrect and others linger with unanswered questions.

blog 22 single cell fsu eduThe first form of life was, we presume, a single celled organism.  Even so, the cells were complex compared to the prebiotic molecules that preceded them.  The most important elements to early cells are, we presume, also those important to modern biology: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. These were almost certainly combined on early Earth and Mars, first into small molecules (hydrogen cyanide, for example, HCN, or water HOH, or formaldehyde, HCHO). Processes are known where they can be further assembled (without life) to give components of genetic molecules, including the nucleic acid bases adenine, thymine, uracil, guanine, and cytosine. These bases are the individual letter codes commonly seen in articles and television shows where people check DNA tests.

But here the chemistry becomes more difficult. To further assemble these units into genetic molecules like RNA (believed to be a precursor of DNA), several things must happen. First, the organic molecules present on early Earth and early Mars, must avoid decomposition. As anyone knows who has left the stove on too long in the kitchen, organic molecules given energy tend to devolve into tar. For RNA to have a chance of emerging prebiotically, the devolution of its building blocks must be prevented.

In Florence, Benner presented evidence that minerals (like borax) containing the element boron (in the form of borate) are able to prevent this devolution. Borate captures carbohydrates that are formed in the prebiotic soup before they devolve to a tarry fate.

blog 22 meteor maryland weatherSecond, the atoms in the borate-captured carbohydrates must be rearranged to give ribose, the “R” in RNA. Dr. Benner presented the results of experiments that showed that minerals containing the element molybdenum (in its oxidized form, molybdate) can do this rearrangement.

Third, the ribose must be attached to adenine, uracil, cytosine, and guanine, each by forming bonds that are not easily formed in water. Then, phosphate must be added, also by forming bonds that are not stable in water. To do this, the amount of water available must be controlled; from time to time, the mixture must dry out.

This is all simple enough in the laboratory today. However, Dr. Benner pointed to models from geologists who hold that water was so abundant on early Earth that no dry land was available. Further, these models suggest that borate could not have been presented in useful concentrations. They also suggest that early Earth was insufficiently oxidizing to give molybdenum in its oxidized molybdate form. In short, geologists were suggesting that RNA could not have emerged on early Earth, at least not by way of the prebiotic chemistry that Dr. Benner has proposed.

blog 22 MarsAsteroidImpactHowever, conditions on Mars appear to have been more favorable for Benner’s prebiotic chemistry. First, Mars has always had less water; it was easier to dry out on Mars. This should have allowed borate to be concentrated. Mars may have also had a more oxidizing environment, allowing for molybdate. Finally, phosphate may have been more accessible on early Mars.

We know of this thanks to the orbiters, landers, and rovers that have been studying Mars for nearly 40 years.  We have also collected a large number of meteorites that have come from Mars.  These meteorites contain, among other things, borate minerals and other species that Benner’s prebiotic chemistry requires for the formation of RNA, which is believed to be a predecessor to DNA.

But even if Mars was a more suited planet for life to form, that life must have come to Earth. The idea that life is delivered to one planet from another is called panspermia.  This is certainly possible. About one kilogram of Mars comes to Earth every day, after it is flung from Mars into the Solar System by a meteorite impacting on Mars. The low surface gravity of Mars makes escape from the Red Planet easier than from Earth. Reentry is sufficiently fast that microbes that originated on Mars would survive, arriving on Earth without damage. Here, they would find a planet that was habitable, able to sustain life, even Earth was not suited for life to originate in the first place.

blog 22 icebreaker model nasaTo further this analysis, we must fund and support missions to Mars that include new technology, such as the Icebreaker Mission.  This mission has a six foot drill that will drill beneath the surface of Mars in order to get samples that are far enough below the surface to be shielded from harmful UV radiation.  We must also fund and support missions that will send humans to Mars.  We need humans on Mars in order to respond imaginatively to uncertain conditions on the planet, required to do the appropriate science with the proper laboratory equipment in order to get the answers that have eluded us for decades, possibly centuries.  We need to find life on Mars in order to compare the DNA of the Martians to the DNA of the Earthlings.  Could we all be Martians?

“The emergence of life on Earth might have been an inevitable consequence of the laws of physics, and if that is true, then a living cosmos might be the only way our cosmos can be”   [Professor Brian Cox]

[Images: Benner, FSU, Md Weather, Spaceports, NASA]

Space Exploration Alliance Blitz (Issue #11)

Guest Blog by Kerri Beauchesne
A Call to Action!  Join the 2013 SEA Legislative Blitz
Sunday, February 24 – Tuesday, February 26, 2013
Capitol Hill, Washington, D.C.
blog 11 capitol parabolic arc comThe United States and the former Soviet Union began sending spacecraft to Mars in the 1960s. Although both nations experienced failures in the early days, success rates since have improved dramatically, resulting in a large store of information about Mars’ atmosphere, gravity, surface, chemical composition, and, most importantly, water. Today, Mars is a busy planet, hosting three active orbiters (Mars OdysseyMars Express and Mars Reconnaissance) and two operational rovers (Opportunity and Curiosity).  Future NASA and joint missions include MAVENExoMars and InSight.

Unfortunately, despite these successes, we have begun losing important ground. For example, in the 2009 Mars Exploration Joint Initiative, NASA was to collaborate with the European Space Agency on astro-biological research, delivering an orbiter, two landers, and a rover to Mars between 2016 and 2018. When the Obama administration announced its 2013 budget, however, the program was canceled and the funding redirected to bolster the dramatically over-budget James Webb Space Telescope. Since the U.S. withdrew from the joint initiative, the ESA has reorganized and is now working with the Russian Federal Space Agency on the project.blog 11 explore mars org

Although MAVEN is close enough to launch to be considered a done deal, funding for InSight could be in danger if NASA’s budget is cut too deeply this year. And with such shaky funding prospects for unmanned missions, the outlook for manned missions is bleak indeed.

The future of America’s space program depends largely on funding from Congress. But with concerns over the pending U.S. budget crisis, many members of Congress are reticent to allocate money for programs they deem frivolous or unlikely to produce a substantial return on investment. Also, the idea of manned missions to Mars doesn’t enjoy the same widespread public enthusiasm at this stage as the Moon race in the 1960s.

So what can we do to persuade members of Congress to support policies and funding favorable to space exploration? Here are a few things to keep in mind:

  • Decision-makers on Capitol Hill need to know that their constituents do support a strong and sustainable space program. But they receive letters, emails, and online petitions by the thousands, on every imaginable topic. In-person, pre-scheduled meetings hold the greatest potential for making an impact on individual members of Congress.
  • Not every member of Congress is well-informed about the benefits of a robust space program. Go in armed with clear talking points that a layman can understand.
  • They need compelling reasons for supporting specific missions in space, beyond generalizations about America’s primacy and the future of the human race. Presenting them with ready-made, goal-driven, financially viable plans gives them something they can support immediately, with a minimum of staff-hours spent on research.
blog 11 uni graz at

 “I’m no expert. I strongly support space exploration, but I wouldn’t know what to say.”

Great news – you don’t have to! That’s the idea behind the SEA Legislative Blitz, an annual grassroots campaign in which members of thirteen 

space advocacy groups, including the Mars Society, meet with members of Congress to educate them about space exploration and to advocate for specific endeavors. On Day One, organizers will spend time training participants. They will brief you on the members of Congress that you and your small group will meet, giving you talking points customized for that person and his or her constituents’ interests.[For more information, read this excellent article by Kelly Thomas, a then 17-year-old participant in the 2012 Legislative Blitz.]

“What if I want to go but can’t?”

Great news again – the SEA does this every year, so if you can’t participate next month, you can start making plans now for 2014. Butthis year is crucial, given the cuts that NASA has already endured. If you can’t make it to Capitol Hill this year, try something local: do a little research and make an appointment with your own member of Congress (or his or her aide) at the local office.  Also, consider joining an advocacy group, like the Mars Society, and get involved with a local chapter.

It is our destiny to explore and settle space.  We have made great strides since the 1960s, but our collective momentum and resolve have faltered.  Please get involved today. Send a message to America’s leaders that we want to continue our great tradition of human exploration and discovery.

Kerri Beauchesne is a high school English teacher, a Ph.D. student (English) at the University of Texas (Arlington) and a newly appointed staff writer for the Mars Society.

[Images: Parabolicarc.com, Exploremars.org, Unigraz.at]