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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>
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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>)
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WIDTH="280" HEIGHT="209" ALIGN="RIGHT" BORDER="1" NATURALSIZEFLAG="3"
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
away."</P>
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
space."</P>
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>
<CENTER><A HREF="http://science.nasa.gov/programs/mail/sendfriend.asp"><FONT
FACE="Arial,Helvetica,san-serif">SEND THIS STORY TO A FRIEND</FONT></A></CENTER></P>
"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"
WIDTH="200" HEIGHT="227" ALIGN="LEFT" BORDER="2" NATURALSIZEFLAG="3"
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>
<TABLE WIDTH="250" BORDER="1" CELLSPACING="0" CELLPADDING="5"
ALIGN="RIGHT">
<TR>
<TD WIDTH="100%" BGCOLOR="#fffff0">
<CENTER><FONT SIZE="+1" FACE="Arial">Magnetospheres around
the Solar System</FONT></CENTER></P>
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>
</TR>
</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.</TD>
</TR>
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<FONT SIZE="-1" FACE="Arial"><A HREF="../../newhome/headlines/prop19aug99_1.htm">Dashing
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SIZE="-1" FACE="Arial"> -- 1999 Science@NASA story about M2P2</FONT></P>
<A HREF="http://science.nasa.gov/ssl/pad/sppb/edu/"><FONT
SIZE="-1" FACE="Arial">What is a Magnetosphere?</FONT></A><FONT
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<TITLE>Hitching a Ride on a Magnetic Bubble</TITLE>
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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>
</TD>
</TR>
</TABLE></CENTER></P>
<CENTER><TABLE BORDER="0" CELLPADDING="5" WIDTH="600" CELLSPACING="2">
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<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"
WIDTH="280" HEIGHT="209" ALIGN="RIGHT" BORDER="1" NATURALSIZEFLAG="3"
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
away."</P>
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
space."</P>
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>
<CENTER><A HREF="http://science.nasa.gov/programs/mail/sendfriend.asp"><FONT
FACE="Arial,Helvetica,san-serif">SEND THIS STORY TO A FRIEND</FONT></A></CENTER></P>
"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"
WIDTH="200" HEIGHT="227" ALIGN="LEFT" BORDER="2" NATURALSIZEFLAG="3"
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>
<TABLE WIDTH="250" BORDER="1" CELLSPACING="0" CELLPADDING="5"
ALIGN="RIGHT">
<TR>
<TD WIDTH="100%" BGCOLOR="#fffff0">
<CENTER><FONT SIZE="+1" FACE="Arial">Magnetospheres around
the Solar System</FONT></CENTER></P>
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>
</TR>
</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.</TD>
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<FONT SIZE="-1" FACE="Arial"><A HREF="../../newhome/headlines/prop19aug99_1.htm">Dashing
and Coasting to the Interstellar Finish Line</A></FONT><FONT
SIZE="-1" FACE="Arial"> -- 1999 Science@NASA story about M2P2</FONT></P>
<A HREF="http://science.nasa.gov/ssl/pad/sppb/edu/"><FONT
SIZE="-1" FACE="Arial">What is a Magnetosphere?</FONT></A><FONT
SIZE="-1" FACE="Arial"> -- from the NASA/Marshall Space Flight
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<A HREF="http://space.rice.edu/hmns/dlt/Jupmag.html"><FONT
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-- from Rice University</FONT></P>
<A HREF="http://www.windows.ucar.edu/cgi-bin/tour_def/jupiter/upper_atmosphere.html"><FONT
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SIZE="-1" FACE="Arial"> -- from "Windows to the Universe"</FONT></TD>
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<FONT SIZE="-1">Author: <A HREF="maimailto
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[This message has been edited by Time/02112 (edited November 07, 2000).]