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Old 10-19-2019, 10:11 AM
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Question regarding the physics of Jules Verne's "From the Earth to the Moon"


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Regarding the physics of Jules Verne's "From the Earth to the Moon", from what can be gleaned from the novel, what physics/aeronautics/mathematics makes sense and what is sheer nonsense/fly in the face of Newtonian physics principles. I look forward to your feedback.
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Old 10-19-2019, 10:25 AM
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He got the general idea that you need to achieve a very high velocity to escape gravity right, but that is pretty much it. Since the capsule which he would have fired from the Columbiad would be launched vertically, he would have to use a method called direct ascent - basically, aiming straight for the moon. This method was considered in the early days of the Apollo programme, but soon replaced with an alternative method whereby the top stages of the Saturn V would first be placed in an orbit around the Earth, then expand that orbit to approach the moon (trans-lunar injection), then enter into an orbit around the Moon. You can't do that with a projective which gets one initial boost from being fired vertically and has no propulsion afterwards.

The "most wrong" bit, IMHO, was, however, the method by which he wanted to compensate for the enormous acceleration when the cannon is fired. He envisaged a mechanism whereby the capsule has a layer of water between its outer shell and a movable inner floor floating on that water; this water would be pressed out of the capsule by the inner floor being pushed down upon launch, thereby absorbing the acceleration. This method would not work, and would not prevent the passengers inside from being smashed to pulp.

IIRC, he also envisaged a short state of weightlessness at a point between the Earth and the Moon at which the gravitational forces of the two bodies cancel each other out. This is superficially somewhat reminiscent of Langrangian points, but still wrong.
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Old 10-19-2019, 10:40 AM
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He got the general idea that you need to achieve a very high velocity to escape gravity right, but that is pretty much it. .
He also selected the Florida coast as the ideal launch site. He got that bit right.
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Old 10-19-2019, 11:11 AM
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Though he got the wrong coast of Florida.
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The "most wrong" bit, IMHO, was, however, the method by which he wanted to compensate for the enormous acceleration when the cannon is fired.
He tries to build up on the fluid chamber by describing it as having multiple crumple-disc baffles -- a sensible one-time shock-absorber in normal industrial applications but absolutely inconsequential for the kind of acceleration he posits. This was one of his most awkward and forced proto-technobabble explanations -- probably because (as opposed to, say, the Nautilus' power source) it did not lend itself as easily to "say to yourself it's only a SF novel" handwaving as sudden explosive acceleration IS something even relatively unsophisticated readers may be able to visualize. So he tried to baffle us with BS and here you can see him flailing.

Verne was not really a SF writer, of course, he was an adventure-genre writer who would sometimes use the "science genius inventor" trope to make the story happen. And some times it shows more than others.

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Old 10-19-2019, 12:23 PM
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Though he got the wrong coast of Florida.
That is not a minor mishap, by the way. Since the Earth rotates eastwards, it makes sense to launch rockets in the same direction - that way, you save a little thrust which you would otherwise need to achieve with propulsion by having the rocket make use the eastward impetus which it already has. But then you want your launch site to be on the east coast of whatever continent you launch it from, so that discarded rocket components or debris falls into the sea. A launch from the west coast, as in Verne's novel, risks having those parts come down on inhabited areas. Which for Verne might not have been a major issue, since he has the projectile launched vertically, and without its own onboard propulsion, so the debris issue would not arise. But that is simply because his method for going to the Moon was so far off from what was done subsequently.

Nonetheless, the Florida location includes one fascinating bit which Verne got right in a stunning coincidence: The map of Florida that was included in the book edition of "From the Earth to the Moon" has Cape Canaveral labelled with that name (though not as the launch site).
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Old 10-19-2019, 01:09 PM
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Nonetheless, the Florida location includes one fascinating bit which Verne got right in a stunning coincidence: The map of Florida that was included in the book edition of "From the Earth to the Moon" has Cape Canaveral labelled with that name (though not as the launch site).
Not a coincidence at all. Cape Canaveral is the most prominent geographical feature of the Florida east coast. It'd be unusual if it were not named on that map.

I expect Verne used Florida because it's a part of the US that the Moon goes directly above at times. Further north and it's never directly overhead. At the time, the east coast of Florida was not developed significantly, but there was a city on the west coast at Tampa Bay.

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Old 10-19-2019, 02:45 PM
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Not a coincidence at all. Cape Canaveral is the most prominent geographical feature of the Florida east coast. It'd be unusual if it were not named on that map.

I expect Verne used Florida because it's a part of the US that the Moon goes directly above at times. Further north and it's never directly overhead. At the time, the east coast of Florida was not developed significantly, but there was a city on the west coast at Tampa Bay.
Right, that astronomical part was explicitly stated in the book.

OTOH Verne's description of what the club finds going inland into Florida to find a suitable launch site does tell of someone not working from reliable sources. They are looking for high land to avoid the water table, but in our world there are no such highlands in peninsular Florida. Looked it up and saw that Verne writes that Stone Hill's elevation is "1800 feet above sea level" which is one of his best laugh lines (real highest elevation in state: 345 feet, in the Panhandle).

And even granting that inland Florida were treated like a "Lost World" scenario at the time, then the map Schnitte linked, placing Stone's Hill south of Lake Okechobee, is wrong even for the book, since the text describes the site as barely a half day's ride East from Tampa for a crew on horseback and boats, while the map plants it at the edge of the Everglades over 160 miles away. (That last bit is probably the illustrator falling victim to the still-to-this-day common misapprehension of the territorial scale of US states by outsiders.)

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Old 10-19-2019, 04:04 PM
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To illustrate the futility of the shock absorbers, let's make the highly optimistic assumption that a cannon for launching humans has been designed to give constant acceleration over its entire length of 274 meters. The acceleration needed to reach Earth's escape velocity is about 23,000 g's, more than a factor of 1,000 beyond the human limit for sustained acceleration. At best, the shock absorber would lower the acceleration by the same amount as extending the length of the cannon by the distance by which the shock absorber deflects. Of course you'd need to extend the cannon by approximately that amount to accommodate the shock absorber.

The only way to make the cannon work is to make it very long. If you assume humans can survive the wildly optimistic value of 15 g's (5 times the maximum g of the space shuttle), the cannon would need to be about 400 kilometers long.

Verne could have gotten weightlessness right. He correctly understood that the dog outside the capsule would travel along with the craft, but he still thought weightlessness only occurred when the capsule was at the point at which the Moon's gravity cancelled the Earth's gravity.
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Old 10-22-2019, 04:25 PM
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To illustrate the futility of the shock absorbers, let's make the highly optimistic assumption that a cannon for launching humans has been designed to give constant acceleration over its entire length of 274 meters. The acceleration needed to reach Earth's escape velocity is about 23,000 g's, more than a factor of 1,000 beyond the human limit for sustained acceleration. At best, the shock absorber would lower the acceleration by the same amount as extending the length of the cannon by the distance by which the shock absorber deflects. Of course you'd need to extend the cannon by approximately that amount to accommodate the shock absorber.

The only way to make the cannon work is to make it very long. If you assume humans can survive the wildly optimistic value of 15 g's (5 times the maximum g of the space shuttle), the cannon would need to be about 400 kilometers long.

Verne could have gotten weightlessness right. He correctly understood that the dog outside the capsule would travel along with the craft, but he still thought weightlessness only occurred when the capsule was at the point at which the Moon's gravity cancelled the Earth's gravity.
Thank you all. Ver helpful
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Old 10-22-2019, 04:36 PM
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To illustrate the futility of the shock absorbers, let's make the highly optimistic assumption that a cannon for launching humans has been designed to give constant acceleration over its entire length of 274 meters. The acceleration needed to reach Earth's escape velocity is about 23,000 g's,...
And in fact, the cannon would have to fire the capsule at much higher speed than escape velocity. As soon as it exits the barrel of the cannon, it starts slowing down from air resistance. And the capsule needs to still be moving at escape velocity after it's gone all the way through the earth's atmosphere.
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Old 10-22-2019, 06:11 PM
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The only way to make the cannon work is to make it very long. If you assume humans can survive the wildly optimistic value of 15 g's (5 times the maximum g of the space shuttle)
15 gees is pretty pessimistic. With healthy, young subjects, an "eyeballs-in" launch, body-conforming seats, and a few other amenities, 50 gees can be tolerated for the duration of a launch. The astronaut's lungs will likely collapse, but that's ok for the 25 seconds it takes to launch.

Still requires a 150 km launch tube, though.
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Old 10-22-2019, 06:35 PM
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15 gees is pretty pessimistic. With healthy, young subjects, an "eyeballs-in" launch, body-conforming seats, and a few other amenities, 50 gees can be tolerated for the duration of a launch. The astronaut's lungs will likely collapse, but that's ok for the 25 seconds it takes to launch.
John Stapp survived an acceleration (deceleration) of 46.2 G, and that seems to be considered the world record. I'm sure some people have survived higher G forces during vehicle crashes, but I don't think we know how likely it is for a human to survive 50G.

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Old 10-22-2019, 07:15 PM
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John Stapp survived an acceleration (deceleration) of 46.2 G, and that seems to be considered the world record.
That was eyeballs-out--not the configuration you'd want for a launch situation. Instead of the force being distributed into a nice conforming seat, it was concentrated into the straps of a harness.

Despite this, he survived 46 gees with minimal damage. Plus there's little reason to believe Stapp was particularly well-suited to surviving high gee loads (he was in his mid-40s by then--probably not at peak fitness).

The experiments were designed around designing better ejection seats, flight harnesses, seating arrangements, and so on in aircraft. 50 gees should be fairly easy to achieve when engineering for that alone, without the extra requirements that normal aircraft impose.
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Old 10-22-2019, 08:07 PM
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And, heck, there are amusement park rides that go higher than 3 g, just for fun (it looks like the record might be the Do-Dodonpa, at 3.27 g). You can certainly go higher than that for astronauts in peak physical condition and with a high risk tolerance.
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Old 10-22-2019, 09:12 PM
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Any grandma can take 3 gees. The Gravitron amusement park ride (a big centrifuge) does 3 gees for minutes at a time and they'll let anyone on.

Fighter pilots can do 9 gees. Here, we have to assume peak physical condition. But they're pulling that gee load while sitting in a chair, with a big helmet and flight suit, and while remaining fully conscious and in control of the aircraft. So that, at least, is an extreme lower bound to the possibilities here.

But our test subjects don't need to stay in control of the craft, or even conscious. They just need to not break any bones or have a stroke. Stapp showed that forces in the 40 gee range were entirely doable, and he didn't think he was close to the human limit.

Just take a look at the picture of Stapp's rocket sled setup. That's probably a pretty good way to test an airplane ejection seat, but it's not how you would design a system for achieving maximum acceleration. And that's without any high-tech stuff like liquid breathing.
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Old 10-22-2019, 09:57 PM
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Thanks for the information about tolerable acceleration levels. I stand corrected.
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Old 10-23-2019, 12:01 AM
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Thanks for the information about tolerable acceleration levels. I stand corrected.
Your main point is still correct, of course. 150 kilometers isn't any more practical than 400 km. Not to mention that, assuming a small 1000 kg craft being accelerated at 50 gees up to 12 km/s (escape velocity plus some margin), 5.9 GW of power is required. Just powering this thing is a huge challenge.
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Old 10-23-2019, 06:58 AM
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But our test subjects don't need to stay in control of the craft, or even conscious. They just need to not break any bones or have a stroke. Stapp showed that forces in the 40 gee range were entirely doable, and he didn't think he was close to the human limit.
While Stapp didn't have a stroke or break any bones, he probably did have a fair bit of brass clanging.
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Old 10-23-2019, 03:09 PM
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Not to mention that, assuming a small 1000 kg craft being accelerated at 50 gees up to 12 km/s (escape velocity plus some margin), 5.9 GW of power is required. Just powering this thing is a huge challenge.
And that’s another one — Verne claims the vehicle will be a little under 10 tons, and for propulsion he proposes 100 tons of a type of some formulation of guncotton. No idea how well he may have calculated for that to deliver the appropriate muzzle velocity.
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Old 10-23-2019, 03:22 PM
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And that’s another one — Verne claims the vehicle will be a little under 10 tons, and for propulsion he proposes 100 tons of a type of some formulation of guncotton. No idea how well he may have calculated for that to deliver the appropriate muzzle velocity.
I did some very quick maths, but at least that part doesn't sound so far off:

If we apply the standard formula for kinetic energy, E = 0.5mv², then a mass of 10,000 kg accelerted to 12,000 m/s would have a kinetic energy of 720 gigajoules.

Guncotton provides explosive heat of about 5,500 kilojoules per kg (I'm taking that from the German Wikipedia article. A hundred tons of it would yield 550 gigajoules.

Of course that is a very, very rough calculation, ignoring completely air drag, the efficiency of energy conversion, and lots of other things. But at least it's not entirely wacky.
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Old 10-23-2019, 11:18 PM
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Question regarding the physics of Jules Verne's "From the Earth to the Moon"


Ah good, so he was at least in a realistic ballpark for how thinly he’d have smeared the crew against the aft bulkhead, in spite of his technobabble shock absorber...

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Old 10-24-2019, 01:31 AM
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I read a review of FtEttM once that said that Verne had correctly anticipated all the problems with his proposed flight, and then explained them all away, with handwavium of necessary.

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Old 10-24-2019, 08:49 AM
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I take issue with JR's saying that Verne "wasn't a science fiction writer, of course". There's no "of course" about it. Verne definitely was a science fiction writer, even if folks like Walter B. Evans try to make out that he wasn't. He clearly researched his topics heavily, extrapolated from known facts, and tried to show how they affected people and how people reacted to them. He ran into problems whgen there wasn't enough easily accessible material on his topic, as in thus case.

Verne correctly chose Florida as his launch site (and had sort of "mission control" in Texas, amazingly enough, where they set up a large telescope to watch). His projectile was made of aluminum, chosen for its combination of strength and light weight. They had chemicals on board for scrubbing carbon dioxide and releasing oxygen. And his bullet-shaped ship was just about the size of the Apollo craft (without the LM). Verne painstakingly plotted the course around the Moon, describing the features it passed over, had the ship use rockets to adjust its orbit, and had it come down in the ocean for a relatively soft landing. Verne even had a "count up" at launch, with the crowd chanting from zero to ten, instead of a "countdown" going to zero*

Of course, his "lunar cannon" was a ludicrous way into orbit, because the acceleration would've been more than lethal. I suspect that Verne was well aware of this, and simply ignored it so that he could go on with his story. This was years before Konstantin Tsiolkovsky or any of the early rocket pioneers wrote their speculations about the practicalities of rocket flight, and at least a giant cannon was more realistic than any of Cyrano de Bergerac's proposed methods of flying to the moon. (Edward Everett Hale wrote a four-part story about the first artificial satellite, which was manned, in 1869 -- The Brick Moon -- four years after Verne's book. It's sadly pretty neglected. He had his launched using a sort of giant slingshot, which would still have the same problems of acceleration.)

Verne must have realized how his "assumption for the sake of the story" appeared, or had it pointed out to him too often, because he wrote a much-neglected second sequel to From the Earth to the Moon, Sans dessus dessous (translated as "Topsy Turvy" or "The Purchase of the North Pole"), in which the Baltimore Gun Club plans an even more outrageous undertaking, and carries it along for a time, until someone does the calculations and shows them that their idea is completely unworkable.

Apparently the length of the gun barrel in From the Earth to the Moon is too short to let them achieve escape velocity.

Also, Verne really had no good idea about how orbital dynamics worked. He imagined that they basically had to go to the L1 Lagrange point between the Earth and the Moon, give the craft a push, and then "fall" into the Moon's gravitational potential well. (That's the reason they were at that point to experience Verne's mistaken idea of weightlessness). I have a book on orbital dynamics that points to this as a classic mistake in thinking about orbital paths, although it doesn't actually name Verne**.

Exactly why Verne had this odd idea that you would only have weightlessness at L1 is something I don't understand. As observed above, Verne correctly observed that the body of the dog that had died, thrown out of the ship (through the airlock) did not drift away, but stayed with the ship. He similarly properly explained in Hector Servadac ("Off on a Comet", his other outer space adventure) that the breakup of the cometary body would not result in any changes of velocity, since all the components would still travel at the same speed next to each other. From all of this you'd think he would realize that the bodies of the space travelers, even though inside the space ship, would have been effectively weightless.

Maybe he simply didn't want to deal with having his characters floating around inside the ship for the whole story. Unlike the writers of Star Trek, he didn't have he concept of Artificial Gravity to play with, so he simply ignored it, except for a brief Lagrangian interlude.






*As far as I know, the first "countdown" in science fiction was in Fritz Lang's Die Frau im Mond ("Woman in the Moon"), made with the help of rocket pioneer Hermann Oberth.

**I wonder if Verne got his weird notion of how gravity worked from Edgar Allen Poe. Verne was a big fan of Poe and admired his proto-science fiction efforts. Verne's "get to L1 and turn around" orbital dynamics resemble those used by the protagonist in Poe's The Unparalleled Adventures of One Hans Pfaall, who got to the moon in a balloon made of old newspapers.
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Old 10-24-2019, 09:37 AM
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...assuming a small 1000 kg craft being accelerated at 50 gees up to 12 km/s (escape velocity plus some margin), 5.9 GW of power is required. Just powering this thing is a huge challenge.
To elaborate, Verne envisioned explosive power but even modern rail gun technology is nowhere near the energy required. To accelerate Verne's "10 ton" vehicle to escape velocity would require about 263 gigajoules, and that assumes 100% efficiency. The most powerful magnetic rail gun tested thus far is about 32 *mega* joules or very roughly 1/10,000th the energy: https://www.popularmechanics.com/mil...a2289/4231461/

But the actual energy isn't that great - 263 gigajoules is "only" 73 megawatt hours or less than 10% the output of a typical power plant for 1 hr. However storing that and productively releasing it is another matter.

There is no technology that can store and release that amount of energy within the approx. 22 sec. a 50-g boost to escape velocity would require, so it would have to be generated "on line". That would require 3.6 gigawatts electrical at 100% efficiency, or probably 5 gigawatts including some losses. So just to power the apparatus would require five 1 gigawatt plants (gas turbine, nuclear, etc) in parallel.

Even at 50 g acceleration, the gun "barrell" would be about 80 miles long and would likely have to be pumped down to a vacuum. Maybe if the end was open that would suffice since 80 miles altitude is space.

In theory humans using fluid breathing and fluid immersion can tolerate much higher g forces. I have seen speculation that maybe 1,000 g might be survivable but even at 500 g the "gun" would still be eight miles long. Since exiting the barrell would still be within the atmosphere there would be tremendous deceleration and thermal factors, far worse than an Apollo capsule returning from the moon.

The shorter boost time also worsens the energy generation problem since 263 gigajoules must be released within 2.2 sec at 500 g, which equates to about 119 gigawatts for 2.2 sec at 100% efficiency.

An airbreathing aerospaceplane, a space elevator, an Orion nuclear pulse rocket, or almost any other conceivable method - however outlandish and expensive - would be more achievable.
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Old 10-24-2019, 09:59 AM
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In theory humans using fluid breathing and fluid immersion can tolerate much higher g forces.
The one thing I have never seen addressed with liquid breathing while immersed in a liquid environment is dealing with air trapped in middle ear chambers or sinuses. A SCUBA diver can equalize his/her ears during a slow, controlled descent/ascent in the ocean, increasing the ambient pressure on their body by maybe 1 atmosphere every 15 seconds. And they have the ability to pause their ascent/descent if they are having trouble with equalization.

The equivalent acceleration ramp rate during a rail-gun launch would need to be no more than 1 g every 15 seconds, dramatically increasing launch time and rail gun length - and there likely wouldn't be any pause in acceleration ramp-up if any if the passengers complained about trouble equalizing their ears. So if you're going to be exposed to extreme accelerations and/or rapid acceleration buildup rates (high jerk), while immersed in liquid you need to completely fill your tympanic cavities and Eustachian tubes with liquid. If there's more than a smidge of air left in there, then when you and your liquid bath accelerate, the increased liquid pressure on your body will compress that trapped air and rupture your tympanic membranes.
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Old 10-24-2019, 10:18 AM
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I read a review of FtEttM once that said that Verne had correctly anticipated all the problems with his proposed flight, and then explained them all away, with handwavium of necessary.

Handwavium it is. It would be a very short novel otherwise...

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"We want to go to the moon."
"We don't have the technology to do that."
The End.
Many science fiction writers expound ideas which require some "suspension of disbelief". For example, calculating escape velocity is a waste of time considering how hot a capsule gets on re-entry - a capsule going miles-per-second at sea level probably would be cinders before it reached the upper atmosphere, plus would slow down dramatically. Anyone who knew about meteors would know about this. Ignore these because they simply make the story complicated.

I think the launch Verne knew instinctively was a lethal idea, but figured with gargantuan sizes and handwaving the calculations could make it seem plausible enough to get past it an into the rest of the story.

Verne made some best guesses with the facts known at the time.

Last edited by md2000; 10-24-2019 at 10:18 AM.
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Old 10-24-2019, 12:01 PM
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Many science fiction writers expound ideas which require some "suspension of disbelief". For example, calculating escape velocity is a waste of time considering how hot a capsule gets on re-entry - a capsule going miles-per-second at sea level probably would be cinders before it reached the upper atmosphere, plus would slow down dramatically. Anyone who knew about meteors would know about this. Ignore these because they simply make the story complicated.
A speculative answer from history, going in the "correct" direction:
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Originally Posted by Wikipedia
Propulsion of steel plate cap
During the [Operation Plumbob] Pascal-B nuclear test, a 900-kilogram (2,000 lb) steel plate cap (a piece of armor plate) was blasted off the top of a test shaft at a speed of more than 66 km/s (41 mi/s; 240,000 km/h; 150,000 mph). Before the test, experimental designer Robert Brownlee had estimated that the nuclear explosion, combined with the specific design of the shaft, would accelerate the plate to approximately six times Earth's escape velocity. The plate was never found, and Dr. Brownlee believes that the plate left the atmosphere, however it may have been vaporized by compression heating of the atmosphere due to its high speed. The calculated velocity was sufficiently interesting that the crew trained a high-speed camera on the plate, which unfortunately only appeared in one frame, but this nevertheless gave a very high lower bound for its speed.
From https://en.wikipedia.org/wiki/Operat...teel_plate_cap

So attempting to attaining escape velocity while still in the meaty part of the atmosphere would almost certainly end badly.
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Old 10-25-2019, 05:02 PM
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Meteors going the other way tend to become spectacular vapor, I don't see why starting from the ground would end any differently.

The meteor which was captured on a number of assorted video cameras in Russia a few years ago was allegedly the size of a 5-story building, and yet there was no evidence any of it reached ground level. What hope for a hollow metallic object? All that kinetic energy converted to heat...

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Old 10-25-2019, 05:08 PM
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Originally Posted by md2000 View Post
Meteors going the other way tend to become spectacular vapor, I don't see why starting from the ground would end any differently.
It's much worse starting from the ground. Coming in from above, you hit the least dense part of the atmosphere first, slowing you down slightly before you hit the more dense part of the atmosphere. Starting at the ground, you hit the most dense part of the atmosphere at the highest speed.
  #30  
Old 10-25-2019, 05:12 PM
md2000 is offline
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Originally Posted by scr4 View Post
It's much worse starting from the ground. Coming in from above, you hit the least dense part of the atmosphere first, slowing you down slightly before you hit the more dense part of the atmosphere. Starting at the ground, you hit the most dense part of the atmosphere at the highest speed.
Yes, not just friction but deceleration forces from wind resistance like hitting a brick wall at 7 miles a second. The projectile would probably pancake before it disintegrated and vaporised.
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Old 10-25-2019, 05:16 PM
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Originally Posted by md2000 View Post
The meteor which was captured on a number of assorted video cameras in Russia a few years ago was allegedly the size of a 5-story building, and yet there was no evidence any of it reached ground level.
Actually, they recovered quite a bit of material. The largest piece they found was 1442 pounds.
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