Hi
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.
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.
He also selected the Florida coast as the ideal launch site. He got that bit right.
Though he got the wrong coast of Florida.
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.
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).
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.)
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
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.
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.
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.
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.
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.
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.
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.
While Stapp didn’t have a stroke or break any bones, he probably did have a fair bit of brass clanging.
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.