On page two of Neal Stephenson’s Snow Crash, the mighty car of the Deliverator is described as having “enough potential energy packed into its batteries to fire a pound of bacon into the Asteroid Belt.” How much energy is this? (I assume we start on Earth. Neal did.)
Well, assuming it’s aimed right, once it hits escape velocity, it’ll get to the asteroid belt eventually. Escape Velocity is 25,000 mph, and according to this site, it takes 7.89 KwHr to accelerate 1 pound to escape velocity. According to this, a typical car battery stores about 1 KwHr. So, we’re looking at a little less than eight car batteries worth of power.
I don’t have time to do the calculations right now, but don’t forget about the Sun’s gravitational potential, too. Still, that’ll be in the same ballpark, so it’s a plausible amount of energy for a near-future vehicle’s batteries.
It’s a trick question. It’s impossible to do, because it won’t happen until pigs fly.
Puts a new perspective on the “How long does bacon stay good?” thread, though.
8 batteries(given the above numbers) would provide enough power to reach escape velocity but would not be enough to maintain it long enough to escape the atmosphere.
You need a rocket scientist to give a more accurate answer.
But things you need to know:
What propulsion system? I’m not aware of a battery powered propulsion system that can focus enough power in a portable space to break atmo. Once you’re in space. An Ion drive is easily battery powered, but that’s useless in atmo. Don’t forget to account for the weight of the batteries. And AFAIK there does not exist a battery capable of lifting it’s own weight to space.
Pan, I don’t think I understand you comment about maintaining escape velocity. I thought escape velocity was the speed needed to “break free” from a gravitational field without any additional impulse. Why would you need to “maintain” escape velocity?
Ok, so your bacon is launched immediately to escape velocity at the surface of Earth. It’s been propulsed by a battery powered catapult. All the energy to set it going has been used and the bacon itself no longer has a propulsion generator, but it’s going escape velocity.
…At the surface.
By the time it reaches 100 miles up, it’s not going escape velocity anymore. It will still break atmo but it will settle into orbit or fall back down to earth without something to accelerate it back to escape velocity.
The calculations provided in the first few posts are valid from orbit, where things like wind resistance are not a factor, but not from the earths surface.
Attaining escape velocity is not enough to break orbit, you have to maintain it until you do. From orbit, theres not much to slow you down, but from the surface of the earth theres a hundred or so miles of atmosphere to get through.
This is a completely incorrect understanding of escape velocity. Ignoring, for the moment, drag caused by the air, if an object is moving at escape velocity for it’s given point in a gravitational field, it will never come back. Period. You don’t need to keep your speed up unless you have drag acting to slow down your object. You are correct in that the escape velocity is not the whole story, but it’s possible to figure out how much drag you need to overcome, and add that energy into your calculation so you get an escape speed adjusted for atmospheric drag. It is certainly possible to launch a ballistic object and escape the Earth’s gravity well. (Ballistic meaning it is not powered, obviously.)
Furthermore, there is fundamentally no difference between an object falling back to Earth and settling into orbit. If you drop, throw, or shoot an object it is in orbit, albeit an orbit that intersects with the planet itself. If you think back to the experiment of drilling a hole through the Earth, you would oscillate between the entrance and exit of the shaft – that’s an orbit too.
Escape velocity is apparently a completely misunderstood idea on this board. It is nothing more than the speed at which you need to be moving at that point in a gravitational field to never come back. Or more simply, how fast you need to throw your baseball so it never comes back (in a vaccuum).
When I hear “enough potential energy packed into its batteries to fire a pound of bacon into the Asteroid Belt”, I don’t think “powering an electrically driven propulsion system like an ion drive”. I think “that if set off in an explosion would make the pound of bacon fly through the air and space until it reached the Asteroid belt”. YMMV.
I think Stephenson’s intent was to emphasize a “boom” rather than suggest a practical means for delivering breakfast foods to space explorers. Not having read Snow Crash, however, I’m just guessing.
Obviously escape velocity is just a starting point. Since it neglects atmospheric friction, someone is going to have to estimate that. And someone is going to have to figure out blast efficiency - how much of that energy went into moving bacon upward vs how much went sideways away from the bacon, and how much was heat, and how much moved dirt out from under the bacon.
But at least there’s one advantage to this approach - the bacon arrives cooked and ready to eat.
Of course I’m incorrect if you ignore the drag caused by air. My whole point is that the earlier calculation didn’t account for drag caused by air.
And yes, an object must maintain escape velocity until its out of the gravity well. Just because it reaches escape velocity doesn’t free it from the effects of gravity forever. If it slows back down for some reason before exiting the gravity well, its going to get caught again.
Achieving escape velocity at 100 ft off the ground is not a free ticket to deep space. It still has to be travelling at escape velocity when it reaches space. Which it won’t be doing unless it was shot at a much greater speed than escape velocity. Since the whole point of my original argument was that the 8 car batteries math didn’t take that into account…providing just enough energy to reach escape velocity is simply just not enough energy - from the Earth surface. From Orbit, as I’ve said before, it is enough energy.
It’s fairly clear that he means the amount of energy you would have to impart to the bacon in order to launch it to the asteroid belt. The method of imparting that quantum of energy doesn’t matter, nor does its efficiency.
I guess if you’re just asking theoretically…but I was thinking too practically, I guess.
So if you can get all the energy out of 8 car batteries at once, you have the energy you need to launch bacon from earths orbit to the asteroid field (and beyond)
I didn’t say you were incorrect. I did say that, based on your post, you made it sound like you don’t understand escape velocity. It would have been much simpler to just say to you need to add the energy required to fight atmospheric drag.
Atmospheric drag causes various problems for the “bacon-on-a-railgun” scheme. When that bacon emerges at 11,000m/s or so, it rapidly heats and vaporizes. I say slow it down some - it won’t reach anywhere near the asteroid belt, but at least we might get some cooked bacon bits out of the deal.
Well, he/she did say “From orbit, theres not much to slow you down, but from the surface of the earth theres a hundred or so miles of atmosphere to get through.”.
You need more than Escape Velocity from Earth to reach the asteroid belt – you still have to overcome the gravitational potential due to the Sun between Earth’s Orbit and the Asteroid Belt (as Chronos has already pointed out). It’s a shallower curve, but by no means inconsequential. And if you don’t overcome it you will not get to the asteroid belt, no matter how long you wait.
I take it you haven’t been reading the news of late. Quite a few news stories about how the swine flu …