Hitching a Ride on a Magnetic Bubble!

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    <H1><CENTER>Hitching a Ride on a

    Magnetic Bubble</CENTER></H1>

    <H4><CENTER>Scientists from the University of Washington and
    NASA are experimenting with miniature magnetospheres as an innovative
    form of space transportation.</CENTER></H4>


    <A HREF="http://science.nasa.gov/headlines/images/m2p2/audio/story.ram"><IMG
    SRC="../images/cometlinearx/audio/Speaker.gif" WIDTH="21" HEIGHT="22"
    ALIGN="LEFT" BORDER="0" NATURALSIZEFLAG="3" ALT="Link to story audio"><FONT
    SIZE="-1" FACE="Arial">Listen to this story</FONT></A><FONT
    SIZE="-1" FACE="Arial"> (requires <A HREF="http://science.nasa.gov/newhome/browsers.htm#disclaimer">RealPlayer</A>)
    <A HREF="../images/m2p2/m2p2_big.jpg"><IMG SRC="../images/m2p2/m2p2.jpg"
    ALT="see caption"></A></FONT>October 4, 2000 -- "Mom!
    I'm going shopping on Ganymede today. Can I have the keys to
    the saucer?"</P>

    "Yes dear, but be home in time for supper. And I heard
    there's going to be an awful solar flare today, so be careful!</P>

    Space-age moms have more to worry about than ever.... But
    if a group of NASA-funded researchers have their way, parents
    in the next century can breath a little easier. Every family
    saucer will come equipped with a fuel-efficient magnetic bubble
    that speeds its occupants from planet to planet and wards off
    the very worst solar flares.</P>

    <FONT SIZE="-1" FACE="Arial">Above</FONT><FONT SIZE="-1"
    FACE="Arial">: An artist's concept of a space probe riding a
    solar-wind driven magnetic bubble past Jupiter.</FONT></P>

    Most planets in the solar system already have such bubbles
    -- they're called magnetospheres. Earth's magnetosphere is an
    extension into space of the familiar magnetic field that causes
    compass needles to point North. Our planet sits at the heart
    of the bubble, which occupies a volume at least <FONT COLOR="#000000">1000</FONT>
    times greater than Earth itself. The magnetosphere protects us
    from solar wind gusts and from potentially deadly solar flares.
    Without it, Earth might be as barren as Mars or the Moon, two
    worlds without magnetospheres.</P>

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    </TABLE>"The magnetosphere not only shields us from solar
    radiation but it also acts something like a solar sail,"
    says Dennis Gallagher, a space physicist at the Marshall Space
    Flight Center. "The solar wind pushes on the magnetosphere
    constantly, but fortunately Earth is just too massive to blow

    What might happen, though, if we created a magnetic bubble
    around something much smaller than the Earth -- like a spacecraft?
    Could it ride the solar wind from planet to planet? Gallagher
    and his colleagues think so.</P>

    "A 15 km-wide miniature magnetosphere one astronomical
    unit from the Sun would feel 1 to 3 Newtons of force from the
    solar wind," says Gallagher, "That's enough to accelerate
    a 200 kg spacecraft from a dead stop to 80 km/s (180,000 mph)
    in only 3 months.</P>

    "If we launched a space probe now equipped with such
    a bubble it would easily overtake Voyager and become the first
    spacecraft from Earth to cross the boundary into interstellar

    The ingenious notion to use miniature magnetospheres as a
    form of advanced propulsion was first suggested by Robert Winglee
    at the University of Washington. The NASA Institute for Advanced
    Concepts awarded Winglee a Phase I Revolutionary Advanced Concepts
    grant two years ago followed by a Phase II contract, and already
    the idea has leapt off the drawing board and into the lab.</P>

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    "We've just finished our first round of tests in a 20
    by 30 foot vacuum chamber here at the Marshall Space Flight Center,"
    says Gallagher, the experiment's principal investigator at Marshall.
    "We're conducting the tests as a cooperative effort between
    NASA and the University of Washington, with support from the
    University of Alabama."</P>

    "The magnetic field for our magnetosphere comes from
    a 1-ft diameter coil of 16 gauge enameled wire. We run 5 to 30
    amp currents through the coil; that creates a 300 gauss field
    at the mouth of the solenoid" -- about 3 times stronger
    than a typical refrigerator magnet.</P>

    Normally, the intensity of such a magnetic field diminishes
    rapidly with increasing distance from the coil. "It's similar
    to a dipole field that falls off as the cube of the distance,"
    explains Gallagher. "Dipolar magnetic bubbles are a problem,
    though, because they don't present the cross section we need
    to intercept plenty of solar wind power."</P>

    <A HREF="../images/m2p2/marshall_plume.jpg"><IMG SRC="../images/m2p2/marshall_plume_med.jpg"
    ALT="see caption"></A>To make the bubble bigger, Gallagher and
    his colleagues blew up the magnetic field -- much like inflating
    a balloon -- by injecting ionized gas near the coil. The innovative
    use of ionized gas (called plasma) to blow up the magnetic bubble
    is what gives the project its name: Mini-Magnetospheric Plasma
    Propulsion or M2P2 for short.</P>

    <FONT SIZE="-1" FACE="Arial">Left</FONT><FONT SIZE="-1"
    FACE="Arial">: A luminous plasma plume inflates an invisible
    magnetic bubble inside the vacuum chamber at NASA's Marshall
    Space Flight Center.</FONT></P>

    "The thing that makes M2P2 special is that we inflate
    the field from the inside with low-energy plasma," says
    Gallagher. "Earth's magnetosphere is inflated with plasma,
    too, but it's not as dense as the plasma inside the M2P2 bubble.
    Jupiter's magnetosphere comes closer -- the sources of plasma
    there are active volcanoes on Io."</P>

    The Marshall scientists use a more down-to-Earth plasma source
    for their M2P2 experiments -- a <A HREF="http://www.anutech.com.au/asi/helicon.htm">helicon
    plasma generator</A>, which ionizes gaseous argon and helium
    with high-power radio waves. "Helicons are fairly common,"
    noted Gallagher. They are routinely used for fundamental plasma
    research and to etch commercial semiconductors.</P>

    "Last week's test was a success. We were able to completely
    fill the vacuum chamber with a magnetic bubble. The only thing
    that stopped the expansion was the presence of the chamber walls.
    In space this same experiment might create a mini-magnetosphere
    15 km across."</P>

    Maintaining such a bubble in space would require about 1 kW
    of power and less than 1 kg per day of helium propellant for
    the plasma source. In return, the bubble would intercept about
    600 kW of solar wind power.</P>

    "One of the advantages of M2P2 is that it requires no
    new technology," says Gallagher. "The plasma sources
    and solenoids at the heart of the bubble are off-the-shelf devices."</P>

    "M2P2 is a 'constant-force' device," he added. "And
    that's another big advantage. If you sail the spacecraft far
    from the Sun, you won't lose thrust."</P>

    How can that be?</P>

    <TD WIDTH="100%" BGCOLOR="#fffff0">

    <CENTER><FONT SIZE="+1" FACE="Arial">Magnetospheres around
    the Solar System</FONT>

    Most planets are <A HREF="http://science.nasa.gov/ssl/pad/sppb/edu/magnetosphere/">huge
    magnets</A> with magnetic fields that extend far into space.
    The exceptions are Venus, Mars, and probably Pluto (although
    we have not yet visited Pluto and don't know for sure). When
    the solar wind runs into a planetary magnetic field, the electrons
    and ions are deflected around it. The cavity that the planetary
    magnet carves out is called a magnetosphere. It's shaped something
    like a comet with a long tail that points away from the Sun.</P>

    <CENTER><A HREF="http://science.nasa.gov/ssl/pad/sppb/edu/magnetosphere/"><IMG
    SRC="../images/m2p2/mag_small.gif" WIDTH="180" HEIGHT="100"
    ALIGN="BOTTOM" BORDER="1" NATURALSIZEFLAG="3" ALT="Earth's Magnetosphere"></A></CENTER></P>

    <A HREF="http://www.windows.ucar.edu/cgi-bin/tour_def/jupiter/upper_atmosphere.html">Jupiter's
    magnetosphere</A> is the biggest thing in the entire solar system.
    Not only is it large enough to hold all of Jupiter's moons, but
    the Sun itself could fit inside many times over. If you could
    see Jupiter's magnetosphere at night, it would appear to be nearly
    twice as wide as the Full Moon.</TD>
    </TABLE>The force exerted on a magnetic bubble depends on how
    big it is. Big bubbles intercept more solar wind than little
    ones do and thus lend greater thrust to the spacecraft inside.
    Bubbles that travel away from the Sun naturally expand as the
    solar wind pressure plummets. They grow for the same reason that
    a child's balloon inflated at sea level will expand in rarefied
    air at high-altitudes.</P>

    "The sizes of balloons and of magnetic bubbles are set
    by the same thing -- a balance of internal and external pressures,"
    says Gallagher. "For M2P2, the internal pressure comes from
    the plasma and the solenoidal magnetic field. The external pressure
    is the solar wind."</P>

    The solar wind's force per unit area decreases as the square
    of the distance from the Sun. Doubling the distance, for instance,
    decreases the solar wind pressure by a factor of four. "The
    solar wind is weaker far from the Sun, but the bubble is bigger,
    too (precisely because the solar wind pressure is lower),"
    he continued. "It so happens that the cross section of the
    bubble increases by the same factor that the solar wind
    pressure declines. The two effects completely cancel." It
    seems amazing, but the propulsive thrust of an M2P2-powered craft
    remains the same whether the spacecraft is near the Sun or in
    the outer reaches of the solar system.</P>

    For human travelers the greatest advantage of M2P2 might not
    be steady acceleration or fuel efficiency, but rather its impressive
    safety features. Just as the Earth's magnetosphere protects us
    from solar radiation, an M2P2 bubble could shield spacefarers
    from cosmic rays and solar flares.</P>

    "The magnetic shielding idea needs to be investigated
    more carefully," noted Gallagher, "but it looks promising.
    By chaining multiple M2P2 units together on the same spacecraft,
    we should be able to minimize plasma losses and end up with a
    better cosmic ray shield as a bonus."</P>

    "I like to think of M2P2 as the first externally-powered
    fusion engine," he concluded. "The engine is the Sun
    itself -- M2P2 bubbles just ride along on the exhaust."</P>

    The next round of M2P2 tests is slated for 2001. Buoyed the
    success of the ongoing lab experiments (and, of course, by the
    solar wind) magnetic bubbles could well become the space carriage
    of choice for the next century.</P>

    Mini-Magnetosphere Plasma Propulsion studies at the Marshall
    Space Flight Center are a cooperative effort between NASA and
    the University of Washington, with support from the University
    of Alabama.

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    [This message has been edited by Time/02112 (edited November 07, 2000).]
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  3. Tony H2o Registered Senior Member

    Way cool TicToc,

    I don't always get time to reply but a lot of your posts are interesting, some a little far fetched but interesting non the less.

    Thanks and Allcare

    Tony H2o
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