How is Gravity Explained?
on the ship, is it gravity plating, or what? what do the crew and passengers believe is holding them down? is it ever explained?
thanks
People seem to say it is a one G acceleration of the ship, but not sure if the show ever explains it thusly.
shareThat would only work if they were continuously accelerating, but that is physically impossible. They would be at light speed now if it was that way.
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Continuous acceleration on the Orion scale was only expected to be used for interplanetary flights. For an interstellar voyage, the expectation was to accelerate for a period of time, then use rotation to produce "gravity" for most of the duration.
That couldn't be done for a fake ship that was still on Earth though, because the Earth's natural gravity would interfere.
So they basically had to pretend like the ship was using constant acceleration, and hope that even the people who were supposedly smart enough and trained to be pilots etc, wouldn't figure out that it wouldn't work that way.
Pretty serious flaw.
How about this?
Accelerate for 1G as long as you can when the ship is pointing toward the Centauri system. When you reach the limit, everybody hangs on to something as they point the ship toward the Solar system, andit decelerates for a while (1G worth again). Point the ship again toward the Centauri system and repeat those steps until you get there, and be sure you are doing the decelerating drill when you're getting close to a planet so you do not overshoot.
1G gravity practically all the way !
Using some rotation makes more sense for a variety of reasons, including that you wouldn't need such a huge amount of fuel - or number of bombs - to make the trip.
They just couldn't do it on the fake, because it wouldn't work inside Earth's gravity.
For rotation they would need a different layout for the ship. The footing/ground would be on the lateral "walls"/fuselage.
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For rotation they would need a different layout for the ship. The footing/ground would be on the lateral "walls"/fuselage.
Yes, which is one reason why the early promos were bogus.
But rotation couldn't be used for a FAKE ship anyway, since it wouldn't have the proper effect while still on Earth. share
What kind of fuel was there available in the 50s that would make it possible for such maneuvers for 100 years? Just look how much rocket fuel is burned during a liftoff of a tiny spaceship nowadays. Besides that, such constant acceleration-deceleration cycles would make the voyage much, much longer.
I think this problem was intentionally omitted by the writers because it couldn't be logically explained and wasn't that important to the story.
Atom bombs, lots of them.
Read more about it here:
http://www.projectrho.com/public_html/rocket/realdesigns.php#id--Project_Orion
That's close to how it works. It's an old idea. Accelerate up to about half way, turn around and decelereate for the second half.
shareWhile they could never quite reach lightspeed (Einstein), I would have thought that the blue and red shift of the stars would have become obvious, and after 50 years, there would be VERY advanced time dilation.
Given a constant 1g of acceleration, you just pick a star most anywhere in our galaxy, and to those inside the spaceship only 100 years would have passed by the time you get there.
http://en.wikipedia.org/wiki/Space_travel_using_constant_acceleration
It's not physically possible to reach the speed of light using a force (gravity is not actually a force in the normal sense, by the way), and as you get very close, your additional energy expended tends to go towards increasing your mass compared to the external world (which might be useful against high velocity hydrogen atoms) and for traveling more quickly into the future. The time dilation effect itself functionally works as if you are traveling faster than the speed of light, as it cuts down on transit time by making your velocity work over a longer period of time in the external world as compared to what you'd observe inside the ship. A 1G acceleration using force-based propulsion for half the trip, then 1G deceleration for the second half would work. It would have to use something like nuclear propulsion or laser-based solar sails, as chemical propulsion is impractical due to fuel reasons. Even continuous half a G of acceleration would be a pretty big deal. You don't need anything too exotic like artificial quantum gravity providing real superluminal propulsion to get to nearby star systems. That would be nice, but it could be done using existing physics and in people's own lifespans.
shareSome people have argued that the 1G acceleration isn't realistic because even if you could somehow do it, they would end up going too fast and get to Proxima in less than the 100 years laid out in the show.
The real reason, as I've pointed out, is that they were going to always have actual 1G anyway, because they're really still on Earth. So any kind of faking pretty much has to be forgiven under those circumstances. At least forgiven by the writers, and maybe by the larger audience, but not by ME.
Using a lower acceleration on an interstellar trip might seem like a good idea just in terms of fuel requirements etc, but assuming you're going to have at least one generation born along the way, I'd still say you would be better off using rotation for the living-quarters parts of the ship and have those at 1G, in order to avoid arriving at your destination with a ship-full of people who spent their whole lives in reduced gravity and now can't function properly on a planet.
1G acceleration and then deceleration for travel within the solar system would be more sensible, both for passenger comfort and to minimize the time required to make such trips. And it wouldn't require the huge "fuel" supplies that would be needed for pushing a "city in space" to another star.
If you had constant 1G acceleration all the way to the destination, yes you'd be going too fast at the end.
The way to resolve this is to turn the ship around half way into the journey and decelerate at 1G for the remainder of the journey. That would result in constant gravity for the entire trip with all the energy for maintaining gravity going into propulsion.
That's the "in show" explanation, but in "real life" it would make a lot more sense to use rotating sections. They couldn't do that for the show because the ship was actually on Earth the whole time, and everything/everyone inside would experience at least 1G regardless.
shareYes, but if you accelerate at a constant 1g towards the destination for 50 years you'd already be way past Proxima Centauri (which is only 4ly away) when you turn on the brakes.
shareSince they were actually on Earth the whole time, they had no option but to pretend that constant 1g acceleration was normal.
shareSure, it's just another flaw in the script. But that one could've been solved easily by chosing a more plausible destination for a 100 year journey.
Assuming that's even possible. They would get increadibly far in a 100 years (their time) at close to the speed of light.
Actually there's terminal velocity to consider too. Something like exploding atomic bombs behind you gets you going quickly, but its terminal velocity is going to be significantly less than the speed of light. Beyond that terminal velocity, whatever it is, you just won't go any faster no matter how much you try. At that point if you're not still accelerating, your fake gravity goes away too. (And it would be decreasing already before then.)
So they would have to tell the people that somehow they can keep accelerating forever, and/or the people would have to be too stupid to know better. Because once again, even if the people "in the ship" knew that they'd already reached terminal velocity, there would have to be some explanation for why they still feel acceleration. (Which isn't really acceleration, it's just the 1G that comes from actually being on Earth the whole time.)
That's true but is there any credible theory that can estimate it? If there isn't, then it's not a big deal. They would be convinced that the terminal velocity is reached sometime beyond 50 years.
shareMaybe if they didn't really know much about physics, or what's supposed to be powering their "ship." Which might be understandable for regular passengers and "stewardesses" but crew people for a spaceship should be more educated than that.
shareIf space was perfect vacuum there wouldn't be any terminal velocity, but it's not so there must be. It should be very high though?
I have honestly never heard of any theory estimating terminal velocity in space, but I'm no physicist! :)
Well, terminal velocity on Earth/in the atmosphere is just for a free fall. If you were firing a rocket towards the ground you could go a lot faster than "terminal velocity" of a free fall.
And even in space, you've got the speed of light as "terminal velocity."
But I was referring in terms of the propulsion source being used. For example, no matter how good your chemical rocket is, your forward velocity will never exceed the velocity of exhaust from the rocket.
Some kind of ion "rocket" could eventually get to a decent fraction of the speed of light, if you had enough "fuel" - actually mass - to throw backwards, because the electrical fields involve can propel the ions in the "exhaust" at near light-speed.
But anything else, even exploding atomic bombs behind a shock-absorbing plate a la Orion from the 60s, has a terminal velocity in terms of the expanding explosion. And it's not a huge fraction of light-speed. At some point you'll get to where your forward speed is equal to the "backward speed" of the explosion, and you won't go any faster no matter how many more bombs you detonate.
Like I've posted elsewhere, something like Orion could get you fast enough to deploy something like a Bussard ramjet and go even faster. But you couldn't accelerate to close to lightspeed using Orion, and even before reaching its terminal velocity your acceleration - and hence your sense of "gravity" inside - should begin to decrease and eventually reach zero.
That's a misconception, because the engine is moving along with the ship and the ship is moving through vacuum.
F=ma still holds true (disregarding relativistic effects) no matter what the speed is at the moment. Apply the same force and you will accelerate with the same amount as long as the mass is constant.
Consider floating in empty space. What is your speed? You have nothing to measure it against. In your frame of reference you are at rest. Apply some force with a rocket and you will feel the acceleration. Turn the rocket off and you are again at rest. Apply it again and you will feel the same force. You can keep doing that forever.
Relativity doesn't really change that except that there will be other weird effects happening as you approach the speed of light.
There's only a problem if you have external forces acting against you, like the atmosphere. Then it would become increasingly more difficult to continue to accelerate.
Actually the larger problem is having to bring all that fuel mass with you, and the chemical reactions aren't terribly efficient as these things go. Even if you're not fighting wind resistance or gravity, you still have the mass - weight, under acceleration - of your fuel supply to deal with.
One big advantage - theoretical at least - to something like a Bussard ramjet is that you only bring along a power source. The "fuel" - or actually reaction mass - is taken from the space you're traveling through.
> "But I was referring in terms of the propulsion source being used. For example, no matter how good your chemical rocket is, your forward velocity will never exceed the velocity of exhaust from the rocket"
That's absolutely false and physically illiterate. A rocket - i.e. a vehicle that propels itself by ejecting a portion of its own mass backward - is not in any way tied to the velocity of that ejected mass. As long as the rocket keeps ejecting the mass backwards, the rocked will keep to accelerate continuously. A rocket has no terminal velocity of that kind.
A faster ejection is more efficient in a sense that it generates more acceleration. But even a very very very slow ejection still accelerates the rocket forward.
At certain point the speed of the rocket will get higher than the backwards speed of the "exhaust", which means that for the external observer it will look like the exhaust actually continues to follow the rocket after ejection (instead of travelling in opposite direction). But that's is completely inconsequential. As long as a rocket has something it can throw backwards (at any velocity), the rocket accelerates.
The show is totally unrealistic for other reasons:
I am a physicist. You'll never reach the speed of light. The more you accelerate, the faster you will get to your destination, ...period. With an unlimited power source, a spaceship and the ability to accelerate as fast as you like, you can get anywhere in the universe within your own lifetime, or even within seconds. The problem is that no matter what, from an external point of view (like from Earth's point of view), you appear never to go faster than the speed of light. So, you can never get to Proxima Centauri in under 4.2 Earth-based years, no matter how fast you think you are going from your point-of-view inside your spaceship. You might get there within seconds in your own time, but 4.2 years will have always passed on Earth. A round-trip will take 8.4+ years even if you complete it within an hour of spaceship time.
That's the odd and tested reality of the Theory of Relativity.
Show's major malfunctions:
1) A spaceship accelerating at 1G for half the duration and decelerating for the other half would reach Proxima Centauri in 5.2 years, not 100 years.
2) An Orion class Starship of any configuration using nuclear fuel has been proven to never be able to exceed perhaps 10% of the speed of light. Certainly not one as large as shown in that show and so 1G cannot be maintained. Pure antimatter fuel would be required to reach up to 80% of the speed of light. We are far from being able to accomplish something like that.
3) The budget required to build a ship of that size would have destroyed the economy of any country. At least several years of gross domestic GDP would be required to build something like that.
The show *does* explain using constant acceleration. It is buried in a couple of lines in the first episode:
"Ascension's been hit with cosmic rays before."
"How's this different?"
"That was before we reached our current speed. The radiation caused by our fractional speed-of-light velocity will cause fireworks."
Those lines imply that they have been accelerating a long time and thus using the constant acceleration method to create gravity.
good catch there!
share