Image credit: NASA

Manned missions to Mars have captured the public imagination since the first sci-fi novels in the late 1800s allowed people to imagine what it might be like to explore the Red planet. But it is only in the past few years that such an endeavor has been seriously discussed by NASA and by private sector organizations. Just this year, two separate private space groups announced their plans to send humans to Mars within the next 10 years. The Inspiration Mars Foundation [1], a non-profit organization founded by Dennis Tito, plans to send two humans on a mission to orbit Mars with a target launch date of January 5th, 2018. Mars One [2], a non-profit Dutch foundation, hopes to send astronauts on one-way trips to establish a permanent human settlement on Mars by 2023. While neither group has declared specific scientific goals, manned missions to Mars are widely considered to be the next frontier in human space travel.

Two weeks ago, I had the opportunity to talk with NASA astronaut John David Bartoe at a public event in Heidelberg, Germany. Bartoe said while he thinks manned missions to Mars are feasible, the costs will be enormous and private businesses are likely underestimating the cost of the projects. Mars One is certainly the most ambitious of these projects. Its team estimates that the total cost of the project will be $6 billion USD [2]. This projection includes the cost of the one-way trip from Earth to Mars, plus that of building a permanent habitat on Mars and equipping it with lifetime supplies for the astronauts who make the trip. NASA expects the costs will be more on the order of $100 billion USD (for a return mission) and that the soonest humans could set foot on Mars is in the 2030s. The question then arises, why is there such a large discrepancy in the estimated cost?

Certainly a large part of the cost discrepancy is the increased cost of a return versus one-way journey, especially since a return mission will require the development of new technologies. While the private sector is known for being innovative and finding cheaper solutions to big projects than the government, both Inspiration Mars and Mars One are currently planning to use existing NASA technologies, whereas NASA is taking a more cautious approach and mandating new technology development, including new shielding materials and faster propulsion systems to protect the astronauts from radiation on what will be a very long journey.

Radiation Concerns

A recent report has caused some concern about the levels of radiation astronauts will face en route to Mars. On Earth, we are protected from most radiation by our ozone layer and Earth’s magnetic field. In the vacuum of space, radiation travels unimpeded, approaching dangerous levels for complex life forms such as humans. Radiation is measured in units called Sieverts with 1 Sievert (1,000 millisieverts) of exposure over a lifetime equaling about a 5% increased risk of developing a fatal cancer. NASA sets a maximum lifetime radiation dose to which astronauts can be exposed at a level that would increase an astronaut’s lifetime risk of developing a fatal cancer by 3%. Other space agencies, like the Russian and European space agencies, tolerate up to a 5% increase in risk [3].

NASA sent a radiation assessment detector (RAD) on the Mars Rover Curiosity and published the findings last month [4]. RAD, unlike previous radiation detectors, was situated in a similar place to where human passengers would be on a spacecraft, and therefore was protected from radiation at the same level as future potential astronauts. En route to Mars, the device measured radiation levels close to 1.84 millisieverts per day, over 100 times what the average American receives on a daily basis[5]! Once on the planet, Mars has a small atmosphere and magnetic field that will deflect some, but not all, of the radiation. At the surface of Mars, unshielded, an astronaut would receive around 0.7 millisieverts of radiation per day.

Figure 1. NASA’s Radiation Assessment Detector sent on the Curiosity rover in a location comparable to where humans would be on such a journey. NASA/JPL-Caltech/SwRI

Ultimately, this means that in either an orbiting return mission or a one-way permanent settlement mission, astronauts may quickly rack up a lifetime dose exceeding NASA’s 3% safety limit depending on how much time the journey takes and how much time outside a well-protected Mars habitat the colonists would have to spend. Mars One hopes astronauts will make a 210-day journey to Mars and spend minimal amounts of time outside on the surface once they get there. To reduce radiation risks, they plan to bury the habitat under several meters of soil. No red sunsets!

Is Mars the Future for Humanity?

In order to ensure the long-term survival of our species, sending human colonists to Mars will eventually need to be a priority for humanity [6]. After all, one major planetary disaster, such as a megavolcano or large asteroid, could easily cause a planet-wide mass extinction as it has done in the past. Even if we eventually have the technology to avert these disasters, ultimately, as our Sun ages, Earth will be come uninhabitable for humans. Sending humans to Mars, either in a return or one-way mission, represents our first real step off this planet and into the Cosmos. However, we need to carefully consider the risks before sending even the keenest individual on what could potentially become a suicide mission.

NASA is currently researching two approaches to reduce radiation risks for future astronauts. One is by creating better shielding materials to protect astronauts from solar flares, periods of intense radiation from our Sun, as well as from galactic cosmic rays, high-energy particles originating outside our solar system. Galactic cosmic rays are more difficult to shield against, and with current materials, would require meters-thick shielding, which is impractical for space flight. Another possibility is to reduce space flight duration by creating better propulsion systems. One such system in development is a nuclear thermal propulsion system, which would use a similar power source as in nuclear power plants to fuel the journey. Nuclear thermal rockets would also be faster, and reducing the total trip time would have the added benefit of relieving some of the psychological considerations of travel to Mars in addition to the radiation concerns.

Psychological considerations

Spending five hundred days in a tin can hurtling through space will require extreme mental fortitude. Several experiments, such as Biosphere 1 & 2 [7] and Mars-500 [8], have been done on Earth to assess the psychological impacts of isolating people for this length of time. Inspiration Mars Foundation’s orbiter mission is slated to take 501 days and the one-way journey to Mars on Mars One is expected to take 210 days. Boredom, monotony and isolation will be serious factors for astronauts to contend with. In the simulation Biosphere 2, the crew divided into two enemy factions that would not speak beyond the absolute essentials. Imagine the implications of a similar situation developing on the one-way Mars One venture, where crew members would not have the luxury of returning to Earth or of choosing their friends.

Sleep deprivation or sleep cycle abnormalities may also be a major factor in the success of a crew [9], and certainly the isolation would be beyond anything experienced before in any trial mission or on any other space mission. Astronauts on the International Space Station (ISS) can be in real-time communication with their family and send emails, videos and pictures easily. Additionally, in an extreme medical emergency, an ISS crew member can be in a hospital back on Earth in 24 hours. Astronauts on a mission to Mars will be too far away to have real-time communication with Earth due to the time radio and light signals take to travel, and any medical or engineering problems will have to be solved solely by the crew.

Man’s first trip to another planet may not be as easy as science fiction stories would have us believe. New information from NASA’s RAD instrument aboard the Curiosity Rover has raised ethical questions surrounding safety measures and allowable risks in our pursuit of putting men and women on the Red Planet. Now that the radiation risks are better understood, Mars One and Inspiration Mars Foundation will have to decide whether their missions are worth the risks involved and how best to combat these risks with new technologies.

Would you take a one-way trip to Mars?

Sarah Rugheimer is a PhD candidate in the Astronomy Department at Harvard.


[1] Inspriation Mars Foundation:

[2] Mars One Foundation:

[3] Astronaut Radiation Limits:

[4] C. Zeitlin, D. M. Hassler, F. A. Cucinotta, B. Ehresmann, R. F. Wimmer-Schweingruber, D. E. Brinza, S. Kang, G. Weigle, S. Böttcher, E. Böhm, S. Burmeister, J. Guo, J. Köhler, C. Martin, A. Posner, S. Rafkin, G. Reitz. (2013) Measurements of Energetic Particle Radiation in Transit to Mars on the Mars Science Laboratory Science 340, 1080. DOI: 10.1126/science.1235989

[5] United States Nuclear Regulatory Commission. Fact Sheet on Biological Effects of Radiation.

[6] Mankind must abandon earth or face extinction: Hawking.

[7] Biosphere 2:

[8] Mars-500: (original page is in Russian, wikipedia has nice summary)

[9] The main problem for a manned Mars mission? Sleep deprivation
Research reveals physical and psychological challenges of sending astronauts to Red Planet.

Further reading and additional resources:

TEDx talk from Jane Poynter on Living in Biosphere 2

More on propulsion systems:

Recent news articles about the findings on radiation doses from the Curiosity Rover.

Psychology and spaceflight:

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