Magnetic Ballooning through the Solar System

1
Magnetic Ballooning through the Solar System

• Robert Sheldon
• UAH Physics Colloquium
• September 5, 2000

2
Credits

• Dennis Gallagher -- MSFC/SD50 Space Plasma
  Physics Branch (and Vic, Paul, Mark etc.)
• Tim Gautier ALL the MSFC Test Area 300
  personnel!
• Les Johnson - MSFC Propulsion Directorate
• Robert Winglee -The University of Washington (and
  Tim, Ben, etc.)
• Wes Swift - UAH CSPAR
• Clark Hawk - UAH/PRC

3
The Rocket Equation

• Vexhaust Isp g d/dt(MV) 0
• dV Vexhaust log( final mass / initial mass)
• Material Isp Limitation
• solid fuel 200-250 mass-starved
• LH2/LOX 350-450 mass-starved
• Nuclear Thermal 825-925 mass-starved
• MHD 2000-5000 energy-starved
• ION 3500-10000 energy-starved
• Matter-Antimatter 1,000,000 mass-starved
• Photons 30,000,000- both-starved

4
Ad Astra?

• To do interstellar flight, we need to approach
  relativistic speeds, say, 12 c (which doesnt do
  much to our clocks)
• Isp Mass_rocket/Mass_payload
• 2,000,000 6
• 1,000,000 50
• 500,000 2670
• 150,000 264,000,000,000
• Conclusion we arent going to do Interstellar
  travel any time soon

5
Okay, how about Pluto

• Voyager16 years to Pluto. A 1.6 year trip would
  take dV 5.8e12m/5e7 s 100 km/s
• Isp M_rocket/M_payload
• 100,000 1.1
• 10,000 2.7
• 1,000 22,000
• 400 72,000,000,000
• We arent going to use chemical rockets if we
  want a fast Pluto flyby larger than a pencil
  eraser.

6
How do solar sails work?

• Momentum of photon E/c, if we reflect the
  photon, then dp 2 E/c. At 1 AU, E_sunlight
  1.4 kW/m2 gt 9mN/m29mPa
• Then to get to Pluto in 1.6 years, we need 0.004
  m/s2 of acceleration. To get this acceleration
  with sunlight we need a mass loading of lt2gm/m2
  !
• Mylar materials 6 gm/m2
• Carbon fiber mesh lt 5 gm/m2 ( 3/2/2000)
• We are getting close!

7
Solar Sails and Space Tethers

• Robert Sheldon
• University of Alabama in Huntsville
• Advanced Propulsion Workshop
• April 9, 1999

8
Sea Sailing

• Tacking into the wind requires 2 forces acting
  together wind water.
• The boats keel acts to convert momentum gained by
  wind, into a force from the water.
• The Keel force also produces a torque.

9
Tacking Torques

• Since the Keel is below the water, and the wind
  above the water, the forces not only add as a
  resultant, but generate a torque, twisting the
  sailboat.

10
The Americas Cup

• The keel force generates a torque which must be
  compensated.
• Sailors hang off the edge.
• Or Australias invention keel winglets.
• After 133 years Aussies took it.
• Moral the more forces you control, the more
  maneuverable you are.

11
Solar Sail Forces Sunlight

• Sunlight reflected at an angle exerts a cos2
  force.
• Depending on symmetry, it is also a torque force.
• Maintaining the tack angle may require
  trimming

12
Pole Sitter Auroral Observer

• By placing an inclined sail behind and above the
  Earth, gravity and lift cancel resulting in a
  stationary orbit which can observe the Northern
  hemisphere and aurora continuously.
• A Russian or Canadian GEO!

13
Trimmers

• Trimmers are usually shown as moveable elements
  arranged near the edges of the sail.
• Changing their angle adjusts the torques on the
  sail.
• These trimmers function as gyros on satellites,
  e.g., HST, Rosat, SPOT...

14
Solar Sails Magnetic Torque

• The magnetic torque force attempts to anti-align
  the B-field magnetic dipole. t m x B
  NiA x B
• Plugging in for standard
• 10nT IMF B-field, 10kA, 0.9Mm2 90N-m
• .at/I 0.16mdeg/s2
• 12 min/45deg adjustment

D
B
i
1 loop 1 degree of freedom. 2-axes may be
required. Spin may do it.
15
Torquers Are Not Propulsion!

• If we have gone to all the effort of including
  magnetic torquers on our sail, then can we use
  the same equipment for propulsion?
• Yes!
• (In fact we can use the same equipment for many
  other tasks radio receivers, magnetic field
  sensors, sail actuators that can turn the sail
  into a rubber mirror)

16
Propulsive Forces

• Static FxB force
• Linear B current carrying wire in B-field
• Quadratic B dipole-dipole interaction
• Dynamic Plasma forces (from a long list)
• Solar wind sailing
• Interaction size is determined by the standoff
  distance between the solar wind mag field
  sail.
• Tethers w/e- w/ions
• A solar wind ion engine
• The MHD solar wind engine

17
Scooped Twice_at_APW!

• Robert Forward and mag sail
• Dani Eders 1994 Collection of Propulsion
  Concepts. (takes a superconductor).
• Robert Winglees M2P2 or mini-magnetospheric
  plasma propulsion
• Use plasma to greatly inflate the magnetic field
  in the mag sail concept and couple to the solar
  wind with 10X or 1000X the diameter.
• A better terminology might be magnetic balloon,
  though Winglee liked his name better.

18
Principle of Mag Balloons

• Solar wind density 3/cc H at 350-800 km/s
• H Flux thru 1m2/s 1m2400km3e6/m31.2e12
• Pressure 2e-27kg1.2e12400km/s 1nPa
• Thats 1/10,000 the pressure of light!
• Why would anyone ever bother with Solar Wind?
• Because it isnt pressure, its acceleration we
  are after. If we can make a mag balloon lighter
  than a solar sail, we may still achieve higher
  acceleration.
• Magnetic fields dont weigh very much for their
  size.
• Trapped plasma can make an even larger mag field.

19
What it doesnt look like.
Supersonic Solar Wind (350-800 km/s)
Magnetic Wall 15-30 km radius Electromagnetic-
plasma interaction Not mechanical Constant
Force Surface
Streamlines Density color contours
20
Winglees M2P2
Interplanetary Magnetic Field
Bow Shock
Plasma Injection
Current Sheet B R-1
Dipole B R-3
21
M2P2 Capabilities

• Inflation is electromagnetic--no mechanical
  struts
• Balloon size depends on ambient pressure, so it
  expands as it moves away from Sun. gt Constant
  force surface
• 10-30km diameter 1-3 N of Solar Wind Force
• which is 0.6 MW of Solar Wind Energy
• If payload weight were 20-100 kg, it would attain
  50-80 km/s over a 3-month acceleration period.
• Limiting speed is, of course, solar wind speed.
  However the balloon expands to some maximum size
  which limits its force as well.

22
The Plasma Inflator
23
Some Lab shots
Nitrogen Plasma Helium Plasma 0.5
mTorr, 350G, 500W 4.0mTorr,350G, 500W
24
What sort of things can go wrong?

• Scaling The nemesis of plasma physics has been
  scaling up something that works at small scales.
  The reason is that plasmas have long-range
  forces. They are not local.
• Plasma loss rate If the plasma is lost too
  quickly, we end up losing the inflation, and we
  revert to a magnetic sail or dipole field.
• Waves If the SW plasma can slip by without
  transferring momentum, we lose our thrust.

25
(No Transcript)
26
Tim, Dennis Pump
27
Scaling from 3 to 30
Helium Plasma
28
roll footage
29
Some Firsts (to my knowledge)

• First artificial magnetosphere constructed in the
  laboratory and filled with plasma.
• Largest space-physics laboratory experiment.
• We will soon be blasting it with a Hall
  thruster--the first full blown solar-wind/magsphe
  re experiment ever performed. (Date - middle
  September, 2000.)
• First test-bed for global MHD models.

30
Can balloons compete w/sails?

• Lets be honest. Sails work 10,000 times better
  than SW balloons. If 30 km is the biggest balloon
  we can make, then a 300m sail will have equal
  thrust. At 5gm/m2, that is a mass of 354 kg.
  With some incremental improvements to sail
  materials, Winglees COTS advantage will be
  gone. Should we invest in mag balloons when sails
  are nearly there?
• YES! Because there are ways to make balloons even
  more efficient, and therefore better than sails.
• If plasma is opaque to light, even at 0.1 its a
  10-fold increase in thrust over SW.

31
Black Plasma

• Charged dust, when combined with a plasma,
  scatters light. At proper conditions, it even
  forms a Coulomb crystal

32
What sort of mass loading?

• The dust grains are micron-sized, which is about
  1e-15 kg apiece. At 36/mm3, that gives a density
  of about 36 mg/m3.
• Since the volume (and mass) go as r3, while area
  goes as r2, the mass loading is r dependent 25
  mg r. A 200 meter radius dusty plasma sail
  would then have the mass-loading of a carbon
  fiber sail.
• Can we make the dust lighter and more reflective?
  Perhaps buckeyballs with chelated sodium atoms.
  Or even reflective ions - e.g., transition metal
  ions.

33
A Mars Mission Scenario
34
Mars Express
35
Hypothetical Balloon

• Lets suppose that we find an opaque plasma
  material for our balloon that weighs the same as
  the propellant 100 kg. Then let satellite
  propellant payload 300kg
• 30 km diameter with 1 opacity 91nPa
• 64 N / 300 kg 0.21 m/s2 2 of g!
• 36 days to Mars
• 72 days to Jupiter
• 7.4 months to Pluto

36
Conclusions

• Magnetic balloons may be the fastest way through
  the solar system. They offer COTS technology for
  very fast transport.
• The technology may not scale, however we are
  confident that it works from 1m gt 10m
• If opaque plasma were used, balloons may stay
  competitive with sails up to the many kilometer
  scale size.
• One could imagine hybrid balloon/sail systems
  that combine both methods of travel.