Two related concepts, the Electromagnetic Defense Field and the Electrostatic Defense Field, will be discussed in their own articles. Magnetic Sails, a form of deep space propulsion, also uses similar technology. Plasma shields may turn out to be the closest 'realistic' technology can come to mimicking the nigh-magical force fields of science fiction.
Plasma shields postulate using cold plasmas in conjunction with powerful electromagnetic fields to protect spaceships from hazards. This type of shield is thought to be most useful against space-born radiation, but they could also offer decent protection against micrometeoroids, shrapnel, beam weapons, and other types of physical damage if made sufficiently potent.
Cold plasmas are just what they sound like. Normal plasmas, such as those used in fusion and rocket research, can usually only be produced at very high temperatures. Cold plasmas are produced at room temperature or lower, making them ideal for a number of practical applications. Ionized hydrogen is usually cited for space applications, as a strong electrical current can easily strip the element into raw nuclei and electrons.
Cold plasmas are much easier to generate in a vacuum environment such as space, so its likely their first large-scale applications will be found there in the form of a protective shield for spacecraft.
|A laboratory magnetic field holding cold plasma.|
The ship generates an electromagnetic field about itself, much as in the case of electromagnetic defense shields. In this case, however, cold plasmas are ejected around the ship and held in place by the magnetic fields. As the plasma is itself electrically charged, it adds to the field's strength, allowing it to obtain much greater resilience at lower power levels than magnetic fields alone.
The powerful magnetic field will turn away the charged particle that make up space-borne radiation hazards such as the solar wind. Physical objects such as micrometeoroids or shrapnel will become ionized on encountering the outer edges of the field and can be deflected by the like-charged but much stronger inner portions of the field, assuming the field is made strong enough to overcome their kinetic energy. The ionized plasma particles of the field will greatly aid this effect, by knocking off surface electrons via impacts on incoming objects and by setting up swirling electrical eddies throughout the field.
The denser the plasma in the field, the better the field will be at deflection. Dense plasma shields also offer protection against beam weapons such as lasers by creating an obscuring cloud that can dissipate the beam's energy. The plasma cloud can also help stymie the neutral particle beams used in space combat.
In order to generate the field, meshes or loops of superconductors would have to be affixed to the outer hull of a spacecraft. There are two modes of thought on the actual design: one, an 'open' shield design, would rely on the magnetic fields generated directly from the hull. These would work similarly to the Van Allen radiation belts that naturally trap ionized particles in Earth's magnetic field. The second option, a 'closed' shield, would use the electromagnetic field of a wire mesh suspended some distance from the spacecraft.
Both options have their advantages and disadvantages. An open shield design would be slowly but constantly bleeding away plasma just from normal entropy, and any hit on the shield would deplete it that much more. Thus, open plasma shields would require constant replenishing of the plasma, which would require a greater supply of fuel, which in turn can add to the weight, bulk, and expense of the spacecraft. However, open shields can be deployed and dissipated rather quickly.
A closed shield would prevent most plasma loss by literally forming an enclosed magnetic bottle around the vessel, and allow the ship to carry much less fuel for the shield. However, the shield would take more time and effort to deploy and take down each time than an open version, and would be much more vulnerable to physical damage. Closed shields would also tend to be more complicated in their construction and use.
Thus, closed shields will probably be used in situations where spaceship mass and fuel needs to be conserved, such as on near-term interplanetary missions. Open shields, because they are relatively simpler and can be deployed faster, will more likely be used farther in the future on ships designed for combat.
It should be noted that even though cold plasmas are used to initiate these shields, there is no guarantee that the plasma will remain cold for long. If used as a radiation shield, it will pick up heat from the rays its absorbing and deflecting. If used as a weapons shield, this problem becomes even more exacerbated. In fact, if hit by a sufficiently powerful beam weapon or explosion, the shield may be successful in deflecting the attack, but it may heat up so much that it could bake the crew inside.
Certain types of propulsion, such as plasma rockets and ion drives, generate plasma exhausts. Its certainly possible that some of this exhaust could be diverted into the shields to give the spaceship an alternate source of fuel for the shields.
Additional problems may arise with communications and sensors while the plasma shield is in operation, but this can be circumvented by telescoping an antenna past the field or towing a sensor/communication package behind the main spacecraft.
Plasma shields can be employed by vehicles and bases within an atmosphere, but at reduced efficiency. The magnetic field would be constantly losing more energy than it would in a vacuum from ionizing the air molecules around it. The interaction with the atmospheric gasses would bleed away the plasma more quickly and could even lead to lightning-like electrical discharges, making them hazardous to be around for friend and foe alike.
Plasma Shieldshttp://www.space.com/businesstechnology/technology/cold_plasma_000724.html http://space.newscientist.com/article/dn9567-plasma-bubble-could-protect-astronauts-on-mars-trip.html http://space.newscientist.com/article.ns?id=dn11623
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