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"Breakaway" physics

Greetings all! I was showcasing episiode 1 to my nephew and a thought/question came into my mind at the point where area 2 goes up. Am I correct in thinking that the physics would be that the moon would accelerate to the point where area 2 stops exploding then stop accelerating and continue on at that speed? Or would it continue to accelerate? My physics is a bit fuzzy..it's been a while.

Cheers!
 

Odahs

Alphans
The breakaway conforms to Newton's third law, essentially an acceleration occurs whilst the nuclear waste in in fission (like a giant rocket motor being fired). The moon would reach a constant velocity then maintain that velocity at the end of the reaction.

Whether or not the moon could withstand the acceleration necessary to break orbit in one short burst is open to question. ;)
 

KevinD

Alphans
It's Newton's third law that means the explosion of waste fuel provides the thrust, it's Newton's first law that says the moon will stop accelerating when that thrust stops.
 

KevinD

Alphans
We don't know the angle of the explosion, so it could have pushed it out of orbit, not just into the Earth. Mind you, in every shot you ever see of the moon in the show, it never looks damaged.:think:
 

boatshewsd2

Alphans
"The Bent and Brok'n Moon..."

True enough. That noted, Catacombs' Breakaway episode guide serves up an intriguing what-if: if you look in the section with SFX shots that did not appear in the episode's final version, there is a depiction of what the erstwhile-far side might've looked like following those infamous explosions...

We don't know the angle of the explosion, so it could have pushed it out of orbit, not just into the Earth. Mind you, in every shot you ever see of the moon in the show, it never looks damaged.:think:
 

Odahs

Alphans
It's Newton's third law that means the explosion of waste fuel provides the thrust, it's Newton's first law that says the moon will stop accelerating when that thrust stops.

Indeed, for OP who's forgotten all those physics lessons, essentially the Third Law is "For every action, there is an equal and opposite reaction", hence the initial acceleration.

The period of constant velocity is the First Law "An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction UNLESS acted upon by an unbalanced force" in other words as there is nothing to slow the moon down or speed it up once the fission reaction is over, it carries on at a constant velocity.
 
One law for some, another law for the rest.....

Right, I've just watched the much-lauded Gravity (on the small screen). Sorry for hi-jacking this thread, but.....

If you're a well-made film about survival in space against all the odds, and just happen to win a clutch of Oscars, then all of the glaring scientific inaccuracies seem to be swept under the carpet. If you're a well-made TV series about survival in space against all the odds, made by "The puppet guy" then everybody and their dog has a go at the glaring scientific inaccuracies....

Once again, apologies for interrupting you guys, but felt compelled to make comment. As Gerry once said, "it's science FICTION we're making, not a documentary...."

Kindest regards,

Patrick
 

Boldman

Alphans
I think you'll find that there are many places on t'internet where Gravity's scientific inaccuracies are dissected minutely, but not here as this forum isn't about Hollywood sci-fi movies, but about Gerry Anderson productions.
 

Odahs

Alphans
I think we are doing a fairly good job of showing that the breakaway conformed to Newtons First and Third Laws and was therefore scientifically at least feasible. The only issue I can see is whether or not the moon as a 'structure' could have taken the acceleration in a very short burst. I'm quite happy to except though that in the Space 1999 universe, it did! (else it would have been a very short series of one episode where the moon and alpha were scattered all over space!)

Reminds me a little of one of my lecturers years ago who set a problem regarding the deceleration involved of a jet landing on an aircraft carrier. The math was easy enough, the only problem was that not only was I not convinced the aircraft's hook would have taken the strain, I didn't think the pilot's head would have stayed on his shoulders either! Fortunately in real world landings the velocity involved is substantially lower than the problem set by the lecturer.

So all we need to do is give Gerry his dues and accept the relatively short and violent burst would have needed to occur over a longer time period. I'm happy to accept it wasn't shown as such for dramatic effect, which works better for television.

Gerry might not of been making documentaries, but he certainly wasn't clueless about how things work either.
 

Howard

Forum Supporter
I've known about Isaac's comments for years, so I copied and pasted this from 1999 Wiki:

Isaac Asimov criticised the scientific accuracy of the series by pointing out that any explosion capable of knocking the Moon out of its orbit would actually blow it apart, and even if it did leave orbit it would take thousands of years to reach the nearest star. He did, however, praise the programme for the accuracy of the representation of movement in the low gravity environment of the Moon, and for its realistic production design (Asimov's responses were based on the pilot episode only). Subsequent episodes (such as "The Black Sun", third in production order, and "Another Time, Another Place", sixth in production order) suggest the Moon reaches the stars by passing through wormholes and hyperspatial tunnels, a plot point made more overt in second season episodes, notably "The Taybor" and "Space Warp".[23]
 

boatshewsd2

Alphans
Doing the Space Warp (Again)...

:2c:

Metamorph, too; notwithstanding that the Moon's passage through the warp is only "mentioned in dispatches" (by Helena) rather than actually depicted on screen.


I've known about Isaac's comments for years, so I copied and pasted this from 1999 Wiki:

Isaac Asimov criticised the scientific accuracy of the series by pointing out that any explosion capable of knocking the Moon out of its orbit would actually blow it apart, and even if it did leave orbit it would take thousands of years to reach the nearest star. He did, however, praise the programme for the accuracy of the representation of movement in the low gravity environment of the Moon, and for its realistic production design (Asimov's responses were based on the pilot episode only). Subsequent episodes (such as "The Black Sun", third in production order, and "Another Time, Another Place", sixth in production order) suggest the Moon reaches the stars by passing through wormholes and hyperspatial tunnels, a plot point made more overt in second season episodes, notably "The Taybor" and "Space Warp".[23]
 
True enough. That noted, Catacombs' Breakaway episode guide serves up an intriguing what-if: if you look in the section with SFX shots that did not appear in the episode's final version, there is a depiction of what the erstwhile-far side might've looked like following those infamous explosions...
I would love to see that- can you tell me where to find it?
(Catacombs I am unfamiliar with)
 

boatshewsd2

Alphans
"...(Hanging) silent on the purple walls of Heaven..."

Think this link will get you there - as most hereabouts are aware, I'm just about hopeless at posting images! :D

Seriously, I simply cannot say enough good thing about Martin and the extraordinary all-things-Alpha archive he's assembled. I find myself referring to it almost constantly! :yes:

So - look, read and enjoy (any issues, pls advise):

http://catacombs.space1999.net/main/pguide/obs/upsfx01b2.html


I would love to see that- can you tell me where to find it?
(Catacombs I am unfamiliar with)
 

Ham Salad

Alphans
I think we are doing a fairly good job of showing that the breakaway conformed to Newtons First and Third Laws and was therefore scientifically at least feasible. The only issue I can see is whether or not the moon as a 'structure' could have taken the acceleration in a very short burst.


They did seem to accelerate to more than 3 gravities, judging by the way the characters were flattened by the force in main mission....the real issue is how much time did it actually take? I son['t seem to remember the time period mentioned in the show, but I seem to remember it was hours.


The issue of the structure of the moon and what acceleration it could take really depends on what that structure actually is: the moon has taken some enormous hits in it's past, and this didn't break it up (viz: tycho crater)
.

It seem to me form memory of the episode that the acceleration built up gradually and then sustained for some time...the 'explosion' was more of a burn rather than one huge blast....
 

Odahs

Alphans
They did seem to accelerate to more than 3 gravities, judging by the way the characters were flattened by the force in main mission....the real issue is how much time did it actually take? I son['t seem to remember the time period mentioned in the show, but I seem to remember it was hours.


The issue of the structure of the moon and what acceleration it could take really depends on what that structure actually is: the moon has taken some enormous hits in it's past, and this didn't break it up (viz: tycho crater)
.

It seem to me form memory of the episode that the acceleration built up gradually and then sustained for some time...the 'explosion' was more of a burn rather than one huge blast....

The problem then becomes would there have been enough acceleration to break orbit? Being hit by something is not easily comparable with withstanding an acceleration sufficient for a body with the mass of the moon to break orbit with the earth.

I'm bogged down with work and various projects at the moment, but if I get a chance I would be interested in doing the maths involved to shed light on the question. What is immediately apparent is there would be an enormous force required in accordance with Newton's Second law (summed up as F=ma). The question then is, could the moon in terms of a structure withstand such a force?
 

Boldman

Alphans
The time it takes is easily calculated:

Escape velocity from earth = 11200 m/s
Moon's existing orbitaly velocity = 1032 m/s

So let us assume the acceleration was in the same direction as orbital velocity (it actually doesn't make that much difference in the end)

if was take the acceleration they experienced as 3g as has been mentioned before, this is 28.44 m/s/s

The equation of motion is easy

V= Vstart +at

where
a is acceleration
t is time
Vstart is the initial speed
V is the end speed

which becomes

t = (V-Vstart)/a

If you plug the numbers in that gives a value of 357 seconds to acceperate form lunar orbital velocity to Earth Escape velocity with a constant acceleration of 3 G.

Next we need to calcualte the force required to do that. Agains its simple

F = ma

m is the mass of the Moon which is 7.3 x 10^22 kg

so F = 2.07 x 10^24 N

So the eruprion of the nuclear waste provided *at least* 2 x 10^24 N thrust over *at least* a 357 second window to allow the moon to escape from Earth orbit.

However it also escape from Solar orbit which is 42 m/s so here we see that the time would have been 1440 seconds (24 minutes) at 3g to achieve this. We didn't see it last that long but it could have been artistic licence :)

From memory the acceleration lasted about 2 minutes - this would lead to the force having to be 36G which is of course not survivable.

Feel free to check my calculations :)
 

martin

Alphans
There's a detailed discussion of the physics in the catacombs:
http://catacombs.space1999.net/main/pguide/xrsfb.html

Also see the linked discussion by astronomer Phil Plait:
http://www.blastr.com/2012/03/astronomer_explains_what.php

moon's velocity after the blast = 80 m/s/s x 150 s = about 12,000 m/s = 12 kilometers/second.

The mass of the moon is 7.4 x 1022 kilograms, and we calculated the velocity as 12,000 m/s. So:
Energy needed = 0.5 x (7.4 x 1022 kilograms) x (12000 m/sec) 2 = 5 x 1030 Joules
To put it in terms that might be easier to grasp, a one-megaton nuclear bomb explodes with an energy of about 4 x 1015 Joules. So those nuclear waste dumps exploded with the energy yield of 1 quadrillion one-megaton bombs! In other words, take a million one-megaton bombs and blow them up. Now do that a billion more times.



The Moonbase Alpha crew wouldn't have been pinned to the floor. They would've been a cloud of very rapidly expanding vapor.


Of course, Space: 1999 is science fiction. And in the opening episode they make a big deal of this explosion being of a new kind of previously unknown magnetic energy, and later episodes make it clear Higher Forces were at work. But man. They must've been working hard.
 
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