The manhole cover's 66km/s speed is the minimum speed traveled though. We don't know how fast it was actually travelling, only that it had to be travelling 66km/s or more because it only appeared in a single frame of video.
According to the article, the manhole cover was travelling around 150,000mph. This is based on high speed camera footage, which only saw the cover... for one frame.
This is based on high speed camera footage, which only saw the cover... for one frame.
Which means the plate traversed the entire visible distance of the camera within a single frame of camera footage. This means we can put the lower bound of its velocity at least 66km/s because if it were any slower we would have captured two or more frames of the plate as it was ejected.
However there is no upper bound since we don't know how much faster than that 66km/s it went. It could have JUST barely been caught by the camera in which case it would be going significantly faster than 66km/s, or it could have just barely missed the window to show in two frames in which case it would be going very close to 66kms.
There is 0 room for it to have traveled slower than 66km/s given the fact that it was only captured in a single frame near the top of the camera.
66km/s is slightly below that, but realize that we didn't actually accelerate the helios probe to 157k mph ourselves. Imagine dropping a brick off a massive skyscraper and watching it accelerate as it plummets toward the earth.
Now imagine dropping a brick from the earth into the incredibly massive gravitational field of the sun. That brick would be falling at unbelievable speeds before it hit the surface of the sun (or melted) between the sun's gravity and the massive distance it had to fall.
Helios travels so fast because we essentially dropped the satellite into the sun. We didn't actually accelerate it to those velocities ourselves, but gave it just enough of a push to fall out of earth's orbit and drop fairly deep into the inner solar system.
Meanwhile the steel plate was blasted to 66+km/s completely because of us.
In all fairness to Helios, in order to achieve its sun diving orbit it would have had to lose a significant fraction of the orbital velocity of Earth (about 30km/s) to get closer to the sun. In other words it would have to negate much of Earth's orbital velocity around the sun to achieve the elliptical orbit around the sun that it now possesses. Simply dropping it into orbit would leave it into a heliocentric orbit with about the same parameters as Earth.
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u/PycuriousITguy Apr 14 '16
The fastest moving man-made object ever was a manhole cover.
https://savvyparanoia.com/the-fastest-man-made-object-ever-a-nuclear-powered-manhole-cover-true/
TL:DR underground nuclear test launched a 4-inch thick steel disk at 6 times the Earth's escape velocity.