(Columbia FAQ - PLASMA: What is it?)
http://www.space.com/missionlaunches/co ... tml#plasma
(Emphases mine, mostly)[IMPORTANT NOTE: Officials now say that the hot gas that surrounded Columbia and appeared to breach the craft had probably not yet reached the plasma state.]
Plasma is sometimes called a fourth state of matter (in addition to solid, liquid, gas). It's created when gas is superheated and electrons are stripped out, leaving electrically charged particles.
Plasma occurs naturally in interstellar space and in the atmospheres of our Sun and other stars. Scientists also create plasma in labs in order to study emissions from the violent regions around black holes. A fluorescent lamp is an example of a highly contained plasma.
Plasma reaching as much as 3,000 degrees surrounds the shuttle during re-entry as the craft plows through Earth's atmosphere. Plasma can also be created by impacts from meteoroids or space debris. NASA has not said how Columbia's problem-causing plasma was allowed under the craft's skin, though they know there must have been some sort of hole or gash.
Satellite operators worry about impact-generated plasma. Even a relatively small meteoroid would vaporize upon impact, generating a cloud of plasma. (IMPORTANT: Small meteoroids hit shuttles frequently without causing problems other than minor pits in heat tiles.)How plasma can damage a satellite. NASA says hot gas, but probably not plasma, breached Columbia.
On a satellite, however, electrical parts are exposed. Because the plasma is electrically charged, short circuits can result. An electrical current flows from one electrical part of the satellite to another location, through the cloud, and damages an instrument. It is similar to the damage a lightning strike might cause.
In 1993, during the August Perseid meteor shower, a meteor hit an Olympus communications satellite. The impact formed a plasma cloud, and the craft's attitude control system was zapped. By the time operators could stabilize it, they had depleted all of its attitude-control propellant and the satellite was lost.
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So, let's take their contradictory statements one at a time (approximately in order):
Appears to affirm that something gaseous+ breached the craft. Noncommittal about whether it was "plasma" or just "hot gas."IMPORTANT NOTE: Officials now say that the hot gas that surrounded Columbia and appeared to breach the craft had probably not yet reached the plasma state.
Appears to indicate that, as the shuttle descends through the atmosphere, a plasma forms around the shuttle. One would assume that means around the wings as well as the body?Plasma reaching as much as 3,000 degrees surrounds the shuttle during re-entry as the craft plows through Earth's atmosphere.
Appears to affirms that something penetrated under the craft's skin and indicates that it was plasma. Adds that there must have been some kind of hole or gash through which the plasma entered. One might surmise that the portion of the wing where there was suspected existing damage would be a likely weak point through which something might inevitably enter.NASA has not said how Columbia's problem-causing plasma was allowed under the craft's skin, though they know there must have been some sort of hole or gash.
The explanation then reverts back to the noncommittal statement that it may or may not have been a plasma or a "hot gas."NASA says hot gas, but probably not plasma, breached Columbia.
It seems there are still questions that need answering.
Was the "hot gas" around the shuttle actually a plasma? Keeping in mind that even "gases" with extremely low ionization can still behave like a plasma, even dusty plasmas where charged dust grains behave in a manner similar to plasma.
Was it the "hot gas" / plasma that did Columbia in? If so, through what mechanism: simple mechanics / thermal stresses (heat melting away everything) or an induced electrical malfunction or electrical damage (Electrical Discharge Machining [EDM]) to the structure due to the conductivity of plasma?
One (such as myself) is immediately reminded of the space tether experiment that ended prematurely.
In any event, it should make for some interesting discussion...It took a considerable amount of detective work to figure out what had happened. Back on Earth the frayed end of the tether aboard the space shuttle was examined, and pieces of the cable were tested in a vacuum chamber. The nature of the break suggested it was not caused by excessive tension, but rather that an electric current had melted the tether.
The electric conductor of the tether was a copper braid wound around a nylon string. It was encased in teflon-like insulation, with an outer cover of kevlar, a tough plastic also used in bullet-proof vests, all this inside a nylon sheath. The culprit turned out to be the innermost core, made of a porous material which, during its manufacture, trapped many bubbles of air, at atmospheric pressure.
Later vacuum-chamber experiments suggested that the unwinding of the reel uncovered pinholes in the insulation. That in itself would not have caused a major problem, because the ionosphere around the tether, under normal circumstance, was too rarefied to divert much of the current. However, the air trapped in the insulation changed that. As it bubbled out of the pinholes, the high voltage ("electric pressure") of the nearby tether, about 3500 volts, converted it into a plasma (in a way similar to the ignition of a fluorescent tube), a relatively dense one and therefore a much better conductor of electricity.
The instruments aboard the tether satellite showed that this plasma diverted through the pinhole about 1 ampere, a current comparable to that of a 100-watt bulb (but at 3500 volts!), to the metal of the shuttle and from there to the ionospheric return circuit. That current was enough to melt the cable.
As the broken end whipped away from the shuttle, the plasma established electric contact with the ionosphere directly. The satellite on the distant end monitored the current: after about half a minute it stopped, then it reignited and flowed again for about another half minute, stopping for good when (presumably) all the trapped air was gone.