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The record for the fastest thing ever created by humans is a tie between the Helios 2 probe… and a manhole cover.

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As with so many records, this one was made to be broken. But for now, the fastest thing ever created by humans is probably a tie between the Helios 2 solar probe and a flying manhole cover.

Let's rewind to August 27th, 1956. The United States Nuclear program was in full swing and a lab in Nevada was developing bombs for a series of tests called "Operation Plumb-bob". The Pascal experiments were part of this series, the first American nuclear test conducted in underground shafts.

The idea was to create a concrete chute for the bomb to explode in, cover it with a nearly 2 ton concrete plug, and top that all off with a ten centimeter thick steel plate, like a manhole cover. The scientists also set up a high speed camera to record what happened. But the explosion turned out to be a lot more than they bargained for. The Pascal-B test was supposed to be what's called a One-Point Safe, a safety feature where only one part of the bomb detonates. It was supposed to explode with no more than the force of 1 kilogram of TNT.

But when they ran the test, the bomb exploded with the force of nearly 300 metric tons of TNT. Those two tons of concrete vaporized, building pressure in the chute and blasting the metal cover right off the top. The high speed camera only caught it in one frame. From there, the researchers calculated that the steel plate had been moving at about 70 kilometers per second. That's six times Earth's escape velocity. The steel plate wouldn't have gotten to space though, it probably burned up in the atmosphere like a meteor in reverse, or just slowed down enough that it eventually landed somewhere. 

So that record setting hunk of metal could still be somewhere in the Nevada desert. Since it's speed could only be estimated and was never truly verified, the manhole cover shares the title of fastest human made object with another, more sophisticated, piece of metal, the Helios 2 probe, which reached 70 kilometers per second as it zipped around the Sun.

There were actually 2 Helios probes, launched in 1974 and 1976, but the second one flew 5 million kilometers closer to the Sun, 43 million kilometers away at closest approach, so it was slightly faster. An object in an elliptical orbit speeds up as it gets closer to the body it's going around, and slows at it moves farther away, because it's angular momentum, the momentum of it's motion around the ellipse, has to stay the same. Angular momentum just depends on mass, velocity, radius, and angle, and if the radius gets shorter, like it did when Helios 2 was closest to the Sun, the velocity goes up.

Scientists wanted the Helios probes to have an elliptical orbit so that they could get close enough to the Sun to conduct experiments with high energy particle detectors, plus measure things like solar wind and the Sun's magnetic field. And because they got super close, they also went super fast. The Helios probes don't actually work any more, but they're still in orbit around the Sun. And soon, NASA's Juno mission will be breaking the Helios/manhole cover tie.

Juno won't reach Jupiter until 2016, but it's expected to hit speeds of about 74 kilometers per second, relative to the planet. And scientists at the Applied Physics Laboratory at Johns Hopkins are preparing another spacecraft, set to launch in 2018, Solar Probe Plus.

This probe will get closer to the Sun than any human-made object ever has before, only six million kilometers away. At such a close range, Solar Probe Plus will be able to examine where the highest energy solar particles come from, and figure out why the Sun's outer atmosphere, or corona, is so much hotter than it's surface. And as it swings by the Sun, it will be going as fast as 200 kilometers per second. With that kind of speed, you could fly from Earth to the Moon in half an hour. And right now, there are no plans to have any sort of manhole cover break that record. 

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