A postcard or post card is a rectangular piece of thick paper or thin cardboard intended for writing and mailing without an envelope. There are novelty exceptions, such as wood postcards, made of thin wood, and copper postcards sold in the Copper Country of the U.S. state of Michigan, and coconut "postcards" from tropical islands.
In some places, it is possible to send them for a lower fee than for a letter. Stamp collectors distinguish between postcards (which require a stamp) and postal cards (which have the postage pre-printed on them). While a postcard is usually printed by a private company, individual or organization, a postal card is issued by the relevant postal authority.
Thanks, Dave, for all that info on potential dangers of composites, as well as the info about the lack of dangers in some cases. I agree, the unintended consequences of a new technology must be carefully considered before its implementation.
@3drob: You're right about carbon fibers causing a skin rash. It's not particularly serious from a medical perspective, but apparently it can cause a world of discomfort.
You're also absolutely right that it's important to consider all kinds of possibilities when evaluating a new technology.
Believe it or not, NASA actually did a study regarding the possibility of damage to electrical and electronic equipment resulting from the crashing of commercial airliners with carbon-fiber reinforced parts. Carbon fibers are electrically conductive, so presumably if they are released in the atmosphere after a crash, they could get into ground-based electronics and cause shorts. NASA did a fairly detailed analysis and concluded that this was very unlikely.
A lot of work has also been done on how carbon-fiber reinforced composites break up during atmospheric re-entry. This is actually something that's fairly well understood, since one use for carbon-fiber reinforced composites is as ablative barriers (where the break-up of the composite protects a capsule on re-entry).
Dave Palmer answered my question about inhalation dangers. I've heard from people that work with it that while fiberglass fibers work their way out of your skin, carbon fibers tend to work back into the skin (so the disintigration in atmosphere could be a source of polution).
My other question was centered on the idea that objects constructed of carbon fiber are fundamentally more durable than those constructed of standard materials. The assumption with a booster is that it will disintigrate on use (unlike prior applications like planes, well, at least hopefully planes). If so, they may not disintigrate as assumed and could become a hazard to earth bound objects (myself included). Even if they disintigrate, they may not become small enough pieces to be harmless. How durable are carbon fiber materials?
It wouldn't be the first time some game changing technology was introduced by Engineers who didn't re-examine long held prior assumptions.
@3drob: Inhalation of carbon fibers is not really all that dangerous, at least as far as inhalation of foreign substances goes. (When it comes to carbon nanotubes, it may be a different story). At any rate, the airborne concentration of carbon fibers produced by re-entry of a launch vehicle is likely to be extremely small -- the earth's atmosphere is really big, and fibers are likely to be widely dispersed by the time they reach ground level. Inhalation hazards are more of a concern for people working in composites manufacturing, where it is important to have adequate personal protective equipment.
Chuck, composites have been used in launchers before, but not for the entire shell. The reasons for their use are basically the same ones as in other aerospace apps: light weight and toughness. CFR composites just keep getting stronger. Here's some info from Hexcel:
What makes this movie stand out from the typical high school sports story is that the teenagers are undocumented immigrants, and the big game is a NASA-sponsored marine robotics competition. Like many other Hollywood movies, however, Spare Parts only tells part of the story. What the film shows -- and doesn’t show -- raises important issues affecting STEM education in the US.
Instead of sifting through huge amounts of technical data looking for answers to assembly problems, engineers can now benefit from 3M's new initiative -- 3M Assembly Solutions. The company has organized its wealth of adhesive and tape solutions into six typical application areas, making it easier to find the best products to solve their real-world assembly and bonding problems.
Load dump occurs when a discharged battery is disconnected while the alternator is generating current and other loads remain on the alternator circuit. If left alone, the electrical spikes and transients will be transmitted along the power line, leading to malfunctions in individual electronics/sensors or permanent damage to the vehicle’s electronic system. Bottom line: An uncontrolled load dump threatens the overall safety and reliability of the vehicle.
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