creationists are killing my fossil shell google searches.
I think I’ve found the earliest scientific mention. It’s in Kepler’s novel Somnium, published posthumously in 1634.
His hero, Duracotus, flies to the moon literally carried by demons. That’s the equivalent of unobtanium, allowing him to narrate a tale of what is encountered. The telling line is:
Being at the point in space where the gravitational pulls of the Moon and the Earth equalize is not the same as being in free fall, I realize. Still, the math has been there since Kepler and needed only someone to apply it. Newton was able to predict orbiting satellites after figuring out why the Moon doesn’t fall to earth. I believe that no science or technology was as completely mapped out mathematically before it came into being as space travel.
Russians were afraid Gagarin might go crazy in weightlessness. That’s why his craft was highly automated. He only could gain manual control by retrieving a code from a safe: they apparently thought he can’t do it if he has gone bonkers.
Isn’t that also where the concept of “escape velocity” comes from? Basically you have to exceed some minimum speed to quit falling past the earth and keep on going.
Kepler didn’t know enough about the science to make any sort of accurate description. That would have to wait until Newton.
Which is not in any way to belittle the enormous progress Kepler did make in the science, of course, and Newton couldn’t have done it without Kepler’s work.
Whence his quote about “standing on ye sholders of Giants”.
I’ve been watching a kids series from 1955 where they had some stuff floating in space. No people - they didn’t have the budget. And the people who wrote that series weren’t exactly rocket scientists. I’m fuzzy, but I’m pretty sure Destination Moon from 1951 got it right - but they had Heinlein as an adviser.
Sure they did. A hyperbolic orbit is still an orbit. They entered the moon’s sphere of influence and returned.
Not exactly – if you think about an elliptical orbit, the satellite is well exceeding the curve of the earth on it outbound path, but it still keeps coming back. But I think an elliptical orbit is a good way of visualizing escape velocity. The satellite is constantly exchanging its kinetic energy for gravitational potential energy, so that it’s moving fastest (most kinetic energy) at its closest approach where it has the least GPE, and moving slowest at its furthest point when it has the most GPE. If it’s given more speed the high point of its orbit gets further and further away until it eventually becomes infinite.
The mathematical way to calculate it is to arbitrarily define gravitational potential per unit mass to be zero at infinity, and therefore increasingly negative as the object approaches (because it’s speeding up, gaining KE, and therefore losing GPE). Escape velocity at any point is the speed required such that the sum of the object’s kinetic energy and the gravitational potential energy thus calculated equals zero. Or to put it more simply, a ball released from any given height will hit the ground at a speed dependent on the height and (ignoring air resistance) shooting it upward at that speed will reach exactly that height – escape velocity is the speed at which a ball would hit the earth if it started off from an infinite height (distance) and will therefore keep going until it reaches infinity.
Great fucking work on this find.
It’s not entirely arbitrary to define potential energy as zero at infinity. You can, of course, define it to be zero at any given point, and it’s equally valid for any such choice… but making it zero at infinity makes the calculations a fair bit simpler, in a way that no other choice does.
Appreciated, but it was a serendipitous find. I was looking through Ron Miller’s magnificent The Dream Machines: A Pictorial History of the Spaceship in Art, Science and Literature. When I saw this I remembered this thread.
Miller lists many examples of 19th century authors mentioning weightlessness in space in one form or another, though few seem to have cared about the technical details that real-live space travelers have to be concerned with. The more important point is that the knowledge was there decades, if not centuries, before anyone entered space. It’s fascinating that people today don’t realize this, to the point of praising 1950s tv shows for getting it right. I’m not sure what an equivalent example would be today. Maybe that people on television talk about black holes despite our never having visited one.
I don’t mean to insult anybody who doesn’t know the history; hardly anyone does.
Agreed. I meant “arbitrary” only in the literal sense that it was a choice, to emphasize that other reference points are possible.