To Hitch a Ride to Mars, Just Flag Down an Asteroid

By Patrick Morgan | February 11, 2011 11:44 am

Mars missions should probably come with the kind of warning label you’d find on a cigarette pack: “May cause cancer and blindness.”

If you were traveling to Mars solely by spacecraft, your health might take a serious hit during the 18-month or so round-trip journey–and you might not even be able to see your home by the time you got back. Throughout the journey, high-energy particles known as cosmic rays would course through your body, not only damaging your eyesight, but also increasing your risk of cancer by up to 20 percent.

Luckily, one scientist has an answer: Don’t fly a spaceship to Mars, hop on an asteroid instead.

Cosmic rays zing into our solar system from interstellar space; here on Earth our planet’s magnetic field protects us from them, and astronauts aboard the International Space Station are mostly protected by the Earth’s bulk and its magnetic field as well. But astronauts on a long-haul trip to Mars would be in more danger.

As it stands, our current radiation shields are too cumbersome for spacecraft, and light-weight aluminum shields can exacerbate the problem: Cosmic rays can reflect off the metal and create secondary radiation. Hence, the asteroid plan, which Douglas Adams would surely approve of.

In his paper, which is set to be published in Acta Astronautica next month, Gregory Matloff of New York City College of Technology suggests that a Mars-bound spacecraft could settle down on an asteroid for the duration of the trip. By parking in a crater or tunneling into the asteroid’s surface, astronauts would be shielded from cosmic rays by the craggy rock.

Matoff explains that the asteroid should be at least 33 feet wide, and also notes that it would help if it passed by both Earth and Mars. That 33-foot width is based off density measurements of the Ida and Mathilde asteroids, and assumes that spacecraft will be able to bore into a roughly spherical asteroid to escape the cosmic rays, Matloff says. “If our space crew digs in 5 meters [16.4 feet], they have enough shielding from asteroid material,” he adds. “For a spherical asteroid, they will be at the center of a 10-meter or 33-foot sphere.”

That magic number, Matoff says, is a conservative estimate. “We could probably work with a smaller near earth object (NEO).” If the asteroid were porous, the width would have to be larger than 33 feet, and if the asteroid were especially iron-rich, the necessary width would be smaller.

It turns out that there are at least five asteroids passing from Earth to Mars in the next 90 years. But since it would take five years for the space rocks to orbit around Mars on its way back to Earth, the astronauts would be stranded for a bit. Matloff has an answer to this too. As National Geographic reports:

Ideally, astronauts would divert an asteroid so that it cycles permanently between Earth and Mars on a well-timed orbit. Humans could nudge an asteroid into the desired path using a solar sail or gentle propulsion…. Once the asteroid is in a stable orbit, Matloff said, “you’d just jump on it. You could store provisions and spare parts on it and use it for shielding…. “

But other scientists believe this asteroid-riding business is way too complicated. From National Geographic:

Nasser Barghouty, a project scientist at NASA’s Space Radiation Shielding Project, said Matloff’s idea works in theory. But he thinks having so many extra launches and landings would prove too risky…. Like an airline passenger with multiple layovers, “I’d need to hop on so many legs [during the journey],” he said. “That adds to the complexity of the mission, which adds more risk.”

The future, according to Barghouty, lies in plastics, which are light-weight and could shield a spacecraft from radiation–but are also a thoroughly anticlimactic option when compared to latching on to a space rock that’s hurtling through the solar system. Given the choice between plastics and hitching a ride on an asteroid, I think I’ll go with the rock.

Related Content:
80beats: The Real Problem With a Human Trip to Mars: Radiation
80beats: Would A Mission to Mars Drive Astronauts Insane? Six Earth-Bound Volunteers Aim to Find Out.
80beats: Traveling to Mars? You’ll Need This Miniature Magnetic Force-Field
DISCOVER: Russia’s Dark Horse Plan to Get to Mars
DISCOVER: 11 Space Missions That Will Make Headlines in 2011 (photo gallery)

Image: flickr / andrewsrj

  • Kyle

    I like the thinking but, only 33 feet in size? I’d think any craft we would be sending would be a bit larger than that. I’m just saying.

  • Chris Lindsay

    I think Patrick Morgan means the depth of rock has to be at least 33 ft. – or in other words, the thickness of protection would have to be at least 33 feet?

    • Patrick Morgan

      Hi Chris,

      Thanks for the question–I asked Gregory Matloff the same question, and I’ve clarified the article. It turns out he was picturing the asteroid as a sphere, and the spacecraft in the center. So the thickness of protection is roughly 16.4 feet, meaning a 33-foot-wide asteroid would be needed. Here’s his entire response:

      “This is easily clarified. From a standard NASA reference (Space Settlements: A Design Study, NASA SP-413, p. 45), the cosmic-ray shielding by Earth’s atmosphere amounts to the equivalent of 10 tons of material per square meter. This is 20,000 pounds or about 10,000 kilograms per square meter. If we assume that the NEO has a density between that of asteroids Ida and Mathilde, which have been visited by flyby spacecraft, the NEO’s density is 2,000 kilograms per square meter. If our space crew digs in 5 meters, they have enough shielding from asteroid material. For a spherical asteroid, they will be at the center of a 10-meter or 33-foot sphere. As the NASA reference states, these numbers are conservative. We could probably work with a smaller NEO. Also, if it is a porous NEO, it will be larger or if it is an iron NEO it will be smaller to provide the same shielding.”

      Thanks for asking!

  • Me

    I think I saw a movie about this… Asteroid?

  • Brian Too

    I’m having trouble imagining this. What I see as a problem: This is a significant mining operation in a microgravity environment.

    – You are going to generate huge amounts of dust that will be very slow to settle;
    – Mining is an activity that uses heavy tools and lots of them. Heavy is the enemy of spacecraft;
    – This isn’t just a simple 10 cm borehole. You have to hollow out a seriously large cavern because the crew has to live there. You might even want to park the entire spacecraft inside;
    – asteroid composition is highly variable. Hollowing out a rubble pile is basically impossible unless reconceived along different lines;
    – tunnelling an iron asteroid? Really? The energy requirements alone will probably nix that idea;
    – tunnelling an ice asteroid. Now that, it seems to me, might have a chance. Still challenging, but less so than the other possibilities. You could use lasers or other heat sources to carve the asteroid.

  • Jacob

    If we could manipulate asteroids like that we wouldn’t have any problem getting to Mars in the first place, nice try. If anything, that might idea prove feasible long after we’ve been to Mars as a “mars-earth elevator” to save on round-trip fuel costs (similar to the work in trying to get an earth-space elevator) . But even then, I doubt we would be harvesting an asteroid to do it. We’ll already have our earth-space elevator by then so we’ll just make our own “asteroid” (probably more of a hotel at that point).

  • Nullius in Verba

    It wouldn’t be any use as a Mars-Earth elevator – the fuel costs of matching orbit with the asteroid would be the same as required to get onto an Earth-Mars orbit without it. The sophisticated way to save fuel (for the patient) would be to use the Interplanetary Transport Network.

    The idea of using an asteroid (or several, pushed together) for radiation shielding is a sensible one, and not new. And the mass requirements for shielding of various sorts are well known, so I’m not sure why a paper has been written about it. Perhaps to report on those asteroid orbits?

    But it makes a lot more sense to pick it up already in space than try to ship all that mass up from Earth. Getting out of Earth orbit is about 90% of the way to Mars, in fuel terms.

    By the time we get around to building that space-elevator, I expect we’ll solve it by genetically engineering radiation-resistance into the colonists.

  • apeleytheros

    Thats more science fiction than science itself I think… I just think it will be kinda difficult to arrange a launch mission to meet an asteroid in the middle of space. And if its needed to make several missions to change its orbit, to dig deep etc… why not diverting the cost to launch up a shield instead. Heavy yes, but will work for sure (not destroying the entire mission if something goes wrong and we loose the asteroid)

    Couldnt we use a non vital part of the spaceship (i.e. engines etc) looking at the sun all the time as shield; what are the exact requirements for a shield like this;

  • Matt B.

    Matloff’s response in comment #3 implies that NASA hasn’t tested various materials for cosmic-ray penetration depth. Shouldn’t they have done that by now?

    • Greg Kochanski

      No.   We know the shielding characteristics of different kinds of rock and other materials very well.   But we don’t know exactly what each asteroid is made of.   So, we don’t know exactly how good the shielding would be from a particular asteroid.

  • Greg Kochanski

    The idea of riding a rock to Mars isn’t especially new (e.g. see ).  However, Prof. Matloff has actually found a few suitable asteroids.   That’s an important step towards making it all real.


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