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#1
11-02-2009, 10:03 PM
 Member Join Date: Jun 1999 Location: Near the GT eeehhhh... Posts: 27,706

## So, how much energy *does* it take to fire a pound of bacon into the Asteroid Belt?

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.)
#2
11-02-2009, 10:40 PM
 Guest Join Date: Mar 2008 Location: Minneapolis Posts: 996
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.

Last edited by Silophant; 11-02-2009 at 10:41 PM. Reason: formatting
#3
11-02-2009, 11:13 PM
 Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 83,206
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.
#4
11-02-2009, 11:13 PM
 Guest Join Date: Mar 1999 Location: Montreal Posts: 20,200
It's a trick question. It's impossible to do, because it won't happen until pigs fly.
#5
11-03-2009, 12:03 AM
 Guest Join Date: Aug 2005 Location: California Posts: 38,776
Quote:
 Originally Posted by matt_mcl It's a trick question. It's impossible to do, because it won't happen until pigs fly.
#6
11-03-2009, 07:27 AM
 Charter Member Join Date: Jan 2003 Location: Saskaboom Posts: 9,211
Puts a new perspective on the "How long does bacon stay good?" thread, though.
#7
11-03-2009, 08:39 AM
 Guest Join Date: Sep 2009 Posts: 845
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.
#8
11-03-2009, 08:54 AM
 Guest Join Date: May 2002 Posts: 911
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?
#9
11-03-2009, 09:43 AM
 Guest Join Date: Sep 2009 Posts: 845
Quote:
 Originally Posted by tullsterx 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.
#10
11-03-2009, 09:43 AM
 Guest Join Date: Oct 2008 Posts: 165
Quote:
 Originally Posted by tullsterx 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?
Atmospheric drag
#11
11-03-2009, 10:03 AM
 Guest Join Date: Nov 2008 Posts: 1,742
Quote:
 Originally Posted by pan1 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).
#12
11-03-2009, 10:13 AM
 Guest Join Date: Dec 1999 Location: Denton, TX, USA Posts: 12,486
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.
#13
11-03-2009, 10:21 AM
 Guest Join Date: Sep 2009 Posts: 845
Quote:
 Originally Posted by ivn1188 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).
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.
#14
11-03-2009, 10:25 AM
 Guest Join Date: Nov 2008 Posts: 1,742
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.
#15
11-03-2009, 10:30 AM
 Guest Join Date: Sep 2009 Posts: 845
Quote:
 Originally Posted by ivn1188 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)

Last edited by pan1; 11-03-2009 at 10:32 AM.
#16
11-03-2009, 10:32 AM
 Guest Join Date: Nov 2008 Posts: 1,742
Quote:
 Originally Posted by pan1 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.
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.
#17
11-03-2009, 11:10 AM
 Guest Join Date: Mar 2002 Posts: 12,104
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.
#18
11-03-2009, 11:13 AM
 Guest Join Date: Mar 2002 Posts: 12,104
Quote:
 Originally Posted by ivn1188 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.
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.".
#19
11-03-2009, 11:17 AM
 Member Join Date: May 2000 Location: Massachusetts Posts: 44,053
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.
#20
11-03-2009, 11:49 AM
 Charter Member Join Date: Aug 2001 Posts: 14,642
Quote:
 Originally Posted by matt_mcl It's a trick question. It's impossible to do, because it won't happen until pigs fly.
I take it you haven't been reading the news of late. Quite a few news stories about how the swine flu ...
#21
11-03-2009, 12:27 PM
 Member Join Date: Jun 1999 Location: Near the GT eeehhhh... Posts: 27,706
Okay... we have an elecrically-powered pork-product projector on the earth's surface, which fires indestructible (i.e. perfect) pound-sized pork pieces into orbit. We have to supply energy to reach earth escape velocity, plus additional energy to compensate for the drag of the atmosphere, plus some additional amount to take us from earth orbit to the asteroid belt. I had an image of the pork piece coasting upwards, away from the earth and sun through the solar system, and moving slower and slower until at the centre of the asteroid belt, it comes to a halt for an instant, then slowly starts to fall backwards. It would probably fall back to land in the sun and lend a hint of pork flavour to the solar wind for a moment.

Is it possible to do this with one well-aimed shot? What if we wanted the pork to take up orbit in the belt, rather than just pausing there?

Last edited by Sunspace; 11-03-2009 at 12:30 PM.
#22
11-03-2009, 12:35 PM
 Guest Join Date: Nov 2008 Posts: 1,742
No, the bacon will likely end up in orbit around Jupiter or Mars or one of the bigger asteroids. Each body has a region of space where it is the dominant gravitational well, called the Hill Sphere. I suppose it might be possible to time your shot so that you can slingshot around but if it stops in the asteroid belt, it's going to stay near there.
#23
11-03-2009, 12:35 PM
 Guest Join Date: Sep 2009 Posts: 845
Quote:
 Originally Posted by Sunspace Is it possible to do this with one well-aimed shot? What if we wanted the pork to take up orbit in the belt, rather than just pausing there?
Yes it's possible. Do I know the precise mathematical numbers involved, no. But, keep in mind that its probably just launched into orbit around the sun, so actually hitting the sun on the return trip is a bit tricky. You'd have to aim it close enough to another object, like Ceres, that the interaction would slow the bacon down and alter the trajectory to hit the sun.

Ditto, for settling into orbit in the asteroid belt.

Possible, yes. Easy, even to a rocket scientist, no. I don't know any nasa engineers that would want to try it without the possibility of correction thrusters.
#24
11-03-2009, 12:50 PM
 Member Join Date: May 2000 Location: Massachusetts Posts: 44,053
Actually, after you get to the asteroid belt you'll have put the bacon into an elliptical orbit. It'll come back, cross the earth's orbit, and drop down to a minimum somewhere (I'd have to figure it out, and I ain't got the time right now -- probably still further out than Venus' orbit) before going back up towards the asteroid belt. It's not going to end up around Jupiter or Mars anytime soon.

Incidentally, there are ways to shoot a small package up into space without benefit of a rocket. The Laser Propulsion project I worked on for a few years was meant to do precisely that -- getting small packages into orbit, with only an outer shell and a block of Reaction Mass. Leik Myrabo's Apollo Lightship was supposed to do the same thing, but without the reaction mass -- he concentrated the light on the surrounding atmosphere.
#25
11-03-2009, 01:41 PM
 Guest Join Date: Dec 2000 Location: temperate forest Posts: 7,093
Quote:
 Originally Posted by CalMeacham Incidentally, there are ways to shoot a small package up into space without benefit of a rocket. The Laser Propulsion project I worked on for a few years was meant to do precisely that -- getting small packages into orbit, with only an outer shell and a block of Reaction Mass. Leik Myrabo's Apollo Lightship was supposed to do the same thing, but without the reaction mass -- he concentrated the light on the surrounding atmosphere.
If technology has progressed enough that we have batteries nearly an order of magnitude better (actually, not nearly as technologically crazy as the auto-adjusting wheels on the skateboard), then we can just put the bacon on the Space Elevator, then catapult/railgun it out to the asteroids. Avoids atmosphere issues, and requires only the energy to counteract the gravity well (although the pre-cooking no longer happens)
#26
11-03-2009, 02:02 PM
 Guest Join Date: Feb 2007 Location: Challenger Deep Posts: 11,832
Quote:
 Originally Posted by pan1 And yes, an object must maintain escape velocity until its out of the gravity well.
Not true.

Quote:
 Just because it reaches escape velocity doesn't free it from the effects of gravity forever.
Actually, it does. That's the whole definition of escape velocity.

Steps:

1. Derive the equation for gravitational force on 1 lbm of bacon as a function of distance from earth's center.

2. Integrate from the earth's surface to a distance of infinity; this gives the total gravitational potential energy of the bacon after it has been moved infinitely far from the earth's surface. This is the amount of kinetic energy that must be imparted to the bacon, at the earth's surface, for it to keep moving away from the earth forever.

No matter what your object - porcine or otherwise - if you neglect atmospheric effects, escape velocity from the earth's surface is in the neighborhood of 25,000 MPH. Bacon launched with this initial velocity will continuously decelerate as it moves away from the earth, but barring interference from other celestial objects, it will indeed continue moving away from the earth forever.
#27
11-03-2009, 02:16 PM
 Guest Join Date: Jul 2008 Posts: 153
Quote:
 Originally Posted by Xema Atmospheric drag causes various problems for the "bacon-on-a-railgun" scheme.
My mission for this week is to find a way to plausibly work the phrase "like bacon on a railgun" into a serious conversation.

Amusingly enough, this is not the first time that an attempt has been made to answer this exact question:

Bacon in the Asteroid Belt

It looks like they ignore the atmospheric effects, though.
#28
11-03-2009, 02:22 PM
 Member Join Date: Jun 1999 Location: Near the GT eeehhhh... Posts: 27,706
So, as you move farther and farther from the centre of the earth, the escape velocity at that point gets less and less? I'm imagining the bacon coasting slower and slower, but never quite stopping and falling back. This is in a universe where the bacon and the earth are the only two objects.

For going from the earth to the asteroid belt, would there also be calcualtion for the escape velocity from the sun, starting at the distance of the earth's orbit? And if we don't actually want to escape, but just go to the asteroid belt, we don't need to supply as much velocity?
#29
11-03-2009, 02:26 PM
 Member Join Date: Jun 1999 Location: Near the GT eeehhhh... Posts: 27,706
Quote:
 Originally Posted by Stathol My mission for this week is to find a way to plausibly work the phrase "like bacon on a railgun" into a serious conversation. Amusingly enough, this is not the first time that an attempt has been made to answer this exact question: Bacon in the Asteroid Belt It looks like they ignore the atmospheric effects, though.
Cool! It turns out that you need much more energy to go from earth's oerbit to the asteroid belt than you need to only escape from the earth. Interesting.
#30
11-03-2009, 02:26 PM
 Guest Join Date: Sep 2009 Posts: 845
Quote:
Originally Posted by Joe Frickin Friday
Quote:
 And yes, an object must maintain escape velocity until its out of the gravity well.
Not true.

Quote:
 Just because it reaches escape velocity doesn't free it from the effects of gravity forever.
Actually, it does. That's the whole definition of escape velocity.
So you're saying that if I manage to shoot a bb at 25,000 mph (defined as escape velocity earlier in the thread) from my back yard - it will leave earths gravity well. Even, when atmopheric drag reduces its speed to 24,999 after a small distance?

Think about what you're saying when you say what I said wasn't true.

You're saying that a satellite orbiting at orbital speed, that accidentally hits the wrong thruster and accelerates to 25000, then corrects itself back to orbital speed is screwed and cannot possibly return to orbit - no matter what amount of thrusting manuvers it undertakes.

Last edited by pan1; 11-03-2009 at 02:28 PM.
#31
11-03-2009, 02:32 PM
 Guest Join Date: Feb 2007 Location: Challenger Deep Posts: 11,832
Quote:
 Originally Posted by Sunspace So, as you move farther and farther from the centre of the earth, the escape velocity at that point gets less and less? I'm imagining the bacon coasting slower and slower, but never quite stopping and falling back.
Ayup, that's pretty much it. Like rolling up a hill whose slope gets more and more gentle as you approach the summit.

Quote:
 This is in a universe where the bacon and the earth are the only two objects.
A lonely, but oh-so-delicious universe.

Quote:
 For going from the earth to the asteroid belt, would there also be calcualtion for the escape velocity from the sun, starting at the distance of the earth's orbit? And if we don't actually want to escape, but just go to the asteroid belt, we don't need to supply as much velocity?
The sun would affect things. How much is hard to say without doing the math. I looked up the earth's orbital velocity around the sun, and figured out that the centripetal acceleration (and therefore the sun's gravitational acceleration at the earth's orbital radius) is about 0.006 meters per second, just a tiny fraction of earth's surface gravity. I'm too lazy to calculate solar escape velocity from the earth's orbital distance, but I'll WAG it doesn't add much to the 25K MPH we're already imparting to the bacon.
#32
11-03-2009, 02:45 PM
 Member Join Date: Nov 2001 Location: Madison, WI Posts: 36,997
You are all missing important factors

1. the bacon will probably fry on the way up. Atmospheric drag will heat the bacon, and the fat/grease will bubble up and be blown away in the wind.

So, in order to get a pound of bacon to the asteroid belt, you will need to start with quite a bit more bacon. How much? I dunno, but the fat content will be a variable in determining what the initial pile of bacon must weigh.

2. And, it might be what starts as bacon on the ground, won't be bacon by the time it gets into space. Can you call a hunk of charred carbon bacon?

So, I contend you need some kind of shell to protect the bacon from thermal destruction during the first few minutes of launch. Possibly, with the right material, the shell might weight less than the initial bacon mass that would be needed for an unshielded launch.

3. And then, once it gets into space and is subjected to near absolute zero temperature and possibly cosmic ray bombardment, can it survive as bacon the remainder of the journey? I don't know this either, but I am shocked that all you big brains haven't considered this. So I contend it will need some kind of environmental support system to maintain its essential baconness. All of which will add a great deal of weight to the initial launch.

I also contend that the point of the whole exercise is to deliver edible bacon to the asteroid belt. Otherwise, you might as well ask what it takes to deliver a pound of mass to the asteroind belt.

Fortunately we have the technology. It's called the Saturn V rocket.

Last edited by Boyo Jim; 11-03-2009 at 02:46 PM.
#33
11-03-2009, 02:45 PM
 Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 83,206
Quote:
 Actually, after you get to the asteroid belt you'll have put the bacon into an elliptical orbit. It'll come back, cross the earth's orbit, and drop down to a minimum somewhere (I'd have to figure it out, and I ain't got the time right now -- probably still further out than Venus' orbit) before going back up towards the asteroid belt. It's not going to end up around Jupiter or Mars anytime soon.
Assuming you're doing this the most efficient way, with a Hohmann transfer orbit, then the perihelion of the elliptical orbit will be exactly as far from the Sun as the Earth's orbit.

And since the original quote said nothing about efficiency, and since there are ways to make energy loss from atmospheric drag arbitrarily small, I think we're justified in ignoring the atmosphere.
#34
11-03-2009, 03:28 PM
 Member Join Date: May 2000 Location: Massachusetts Posts: 44,053
Quote:
 Assuming you're doing this the most efficient way
Well, I didn't -- I figured they're just tossing it up there. The perihelion will be different.
#35
11-03-2009, 03:42 PM
 Guest Join Date: Jul 2008 Posts: 153
Quote:
 Originally Posted by Chronos And since the original quote said nothing about efficiency, and since there are ways to make energy loss from atmospheric drag arbitrarily small, I think we're justified in ignoring the atmosphere.
As a mental exercise, I agree. However, I don't think we're quite justified in ignoring it with respect to the OP's question:

Quote:
 enough potential energy packed into its batteries to fire a pound of bacon into the Asteroid Belt.
This definitely implies some sort of ballistic bacon and rules out more efficient, but exotic solutions like a space bacon elevator.
#36
11-03-2009, 03:48 PM
 Guest Join Date: Mar 2008 Location: Minneapolis Posts: 996
Quote:
 Originally Posted by Stathol space bacon elevator.
Band Name!
#37
11-03-2009, 06:21 PM
 Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 83,206
Sure, but you still can't really take air resistance into account without more information than we have. What shape is the bacon? If it's a long, thin strand of bacon, then the air resistance might be very low (though it'd make it harder to fire it, but that's an engineering problem). If it's a roughly-spherical lump, or even something like a parachute shape, air resistance would be much greater.
#38
11-03-2009, 06:57 PM
 Guest Join Date: Dec 2000 Location: Boston, MA Posts: 3,222
Quote:
 Originally Posted by pan1 So you're saying that if I manage to shoot a bb at 25,000 mph (defined as escape velocity earlier in the thread) from my back yard - it will leave earths gravity well. Even, when atmopheric drag reduces its speed to 24,999 after a small distance? Think about what you're saying when you say what I said wasn't true. You're saying that a satellite orbiting at orbital speed, that accidentally hits the wrong thruster and accelerates to 25000, then corrects itself back to orbital speed is screwed and cannot possibly return to orbit - no matter what amount of thrusting manuvers it undertakes.
Hi, physics grad student at your service. There are a lot of hidden assumptions going on here that are complicating the issue. I'm going to deal with the three different scenarios that have been intermixing themselves in this escape velocity side discussion.

1) An inert mass (such as bacon) is launched ballistically from Earth's surface with an instantaneous initial velocity of 25,000 mph. There is no atmosphere.

In this simple scenario, the only relevant numbers are the bacon's kinetic energy and its gravitational potential energy. Joe Frickin Friday's post above explains why the bacon, assuming nothing else interferes, will never return to Earth.

2) An inert mass of bacon is launched ballistically from Earth's surface with an instantaneous initial velocity of 25,000 mph. The Earth has its usual atmosphere.

Here, the atmosphere gives us velocity-dependent drag, which will reduce the bacon's KE as it rises. This is not a problem, since the required KE for escape also reduces as the bacon rises. Offsetting it is a matter of using a higher initial velocity. This is your bb scenario, and 25k mph would be slightly insufficient to prevent it from falling back down.

3) An electronic satellite already in Low Earth Orbit misfires a thruster and reaches a speed of 25,000 mph.

This is a totally different scenario. As I pointed out above, escape velocity is not equal for all positions near Earth. An LEO satellite is already traveling at about 17k mph, so first of all it would have to be an accident exceeding the design specs of the satellite to bring it to 25k mph. Second, escape velocity for an LEO satellite is lower than 25k mph. Assuming an orbital altitude of 1,000 km, escape velocity is now about 23k mph.

Finally, and most importantly, a satellite with thrusters is not a ballistic object like the bacon was. If it does accidentally thrust itself into an escape trajectory, it can thrust itself back into orbit at the price of burning fuel. The word "ballistic" I keep using means that the object gets one impulse and then moves only under the influence of gravity. Any statement to the effect of "an object which reaches escape velocity never comes back" should be understood to apply only to ballistic objects.

Ok. I hope that clears things up.

Last edited by Spatial Rift 47; 11-03-2009 at 06:59 PM. Reason: clarifying LEO
#39
11-03-2009, 08:02 PM
 Guest Join Date: Feb 2007 Location: Challenger Deep Posts: 11,832
Quote:
 Originally Posted by Chronos Sure, but you still can't really take air resistance into account without more information than we have. What shape is the bacon? If it's a long, thin strand of bacon, then the air resistance might be very low
If it's long and thin enough, you could use it like a cape to slow your descent.
#40
11-03-2009, 09:12 PM
 Charter Member Join Date: Aug 2002 Location: Colorado Posts: 213
To expand on what Spatial Rift 47 said, the whole idea of escape velocity is that it's the initial velocity needed by an object to escape the gravitational well, without further impulse. Because it's still affected by gravity, the object will obviously slow down as it escapes, but the point is that it won't slow down enough to return to Earth (neglecting air resistance, of course).

In contrast, if we had a magic rocket that was able to provide a constant acceleration to exactly counter the gravitation of earth at any particular height above the surface, if I were to give it an upwards push of 1 m/s it would (again neglicting air resistance) eventually escape, even though it never reaches escape velocity, since there's a constant thrust being provided. (Okay, eventually it'll get far enough away to reach a point where the escape velocity is reduced to 1 m/s, but you get the picture.)

To go back to the original point of the thread, there's a few things I'm wondering about. First, how much initial velocity could a car battery impart to a one-pound object, assuming all its potential energy were magically converted to kinetic energy of the bacon? How does this speed compare to escape velocity at the surface? Second, how much initial speed can be saved due to the fact that we only need to reach the asteroid belt before allowing the bacon to cease its outward journey? I mean, if we consider an isolated system with just the earth and a pound of bacon, shooting it at escape velocity will get it to an infinite distance from the earth eventually. However, we just need to get it to a distance of the astroid belt. This will take a smaller initial velocity, although I suspect it'll turn out to be a miniscule difference. I would suppose the same holds true for moving the bacon within the sun's potential well. Again, we don't have to have it escape entirely, just get far enough to reach the asteroid belt. These savings might (and I emphasize "might") be more substantial.
#41
11-03-2009, 09:43 PM
 Guest Join Date: Sep 2009 Location: The Internet. Since '84. Posts: 6,460
He's obviously insane to send bacon away from himself.
#42
11-03-2009, 11:28 PM
 Guest Join Date: Nov 2008 Posts: 1,742
Quote:
 Originally Posted by Heller Highwater Okay, eventually it'll get far enough away to reach a point where the escape velocity is reduced to 1 m/s, but you get the picture.
Just FYI that would be somewhere in the middle of the Oort cloud, about 10,000 AU out.
#43
11-04-2009, 09:20 AM
 Guest Join Date: Mar 2002 Posts: 12,104
Quote:
 Originally Posted by Spatial Rift 47 2) An inert mass of bacon is launched ballistically from Earth's surface with an instantaneous initial velocity of 25,000 mph. The Earth has its usual atmosphere. Here, the atmosphere gives us velocity-dependent drag, which will reduce the bacon's KE as it rises. This is not a problem, since the required KE for escape also reduces as the bacon rises. Offsetting it is a matter of using a higher initial velocity.
I don't think this works with any practical projectile (and certainly not for one consisting of bacon). Even at 25k mph, the energy lost to drag, and the destructive effects of the heating, would be enormous. At higher velocities, these problems are worse.

It's certainly not impossible - meteors (often with velocities greater than 25k mph) occasionally survive a plunge through the atmosphere). But a great many of them don't, and those that do expend serious energy heating themselves and the atmosphere. It takes some significant initial mass for a meteor to have a good chance of reaching the ground at high velocity.

Quote:
 Meteorite Impact Velocities The average velocity of meteoroids entering our atmosphere is 10-70 km/second. The smaller ones that survive the trip to the Earth's surface are quickly slowed by atmospheric friction to speeds of a few hundred kilometers per hour, and so hit the Earth with no more speed than if they had been dropped from a tall building. For meteorites larger than a few hundred tons (which fortunately are quite rare), atmospheric friction has little effect on the velocity and they hit the Earth with the enormous speeds characteristic of their entry into our atmosphere. Thus, for example, it is estimated that the meteorite that produced the Barringer Crater was still travelling at 11 km/second when it struck what is now the Arizona desert 49,000 years ago.
#44
11-04-2009, 09:33 AM
 Charter Member Join Date: Aug 2002 Location: Colorado Posts: 213
Quote:
 Originally Posted by ivn1188 Just FYI that would be somewhere in the middle of the Oort cloud, about 10,000 AU out.
Wow, that's closer than I realized. Neat!
#45
11-04-2009, 09:45 AM
 Member Join Date: Jun 1999 Location: Near the GT eeehhhh... Posts: 27,706
Quote:
 Originally Posted by Boyo Jim You are all missing important factors 1. the bacon will probably fry on the way up...
But I already postulated indestructible bacon. You post dioes lead to a good question, thoiugh; what is the most efficient shape for bacon passing through the atmosphere, especially at 25000 mph?
#46
11-04-2009, 09:56 AM
 Member Join Date: Nov 2001 Location: Madison, WI Posts: 36,997
Quote:
 Originally Posted by Sunspace But I already postulated indestructible bacon. You post dioes lead to a good question, thoiugh; what is the most efficient shape for bacon passing through the atmosphere, especially at 25000 mph?
I see you got to the indestructible thing in a later post.

But if it's indestructible, it's not edible! Bacon is the most delicate flower of meats. Do you really want to go to all this effort and trouble to deliver a lump of "thing that looks like bacon" to the starving natives of the asteroid belt? Won't someone think of the alien children?
#47
11-04-2009, 11:37 AM
 Guest Join Date: Sep 2005 Location: Huntsville, AL Posts: 2,569
This has been quite interesting, but I would like to point out another thing that the OP missed.

The character in the book is talking about his car. I was deeply involved in hot rodding back int he sixties and seventies, and stay a little in it even today. And if there's one thing that is true about guys and their cars, it is that everybody lies about their car!

People used to ask me why my 1966 Mustang would only go 125 mph while everyone else's would go 145 mph. I told them it was because I was telling the truth.*

So, I have to say that while we've got answers on how much energy the Deliverator's car would need, we need to be very about it actually having that much.

* And the true top speed of that car was actually 120 mph...see what I mean?
#48
11-04-2009, 11:45 AM
 Guest Join Date: Jul 2008 Posts: 153
Quote:
 Originally Posted by Sunspace what is the most efficient shape for bacon passing through the atmosphere, especially at 25000 mph?
If my calculations are correct, when this bacon hits 25000 mph, you're going to see some serious shit!

I'm sorry, but someone had to say it.
#49
11-04-2009, 12:24 PM
 Member Join Date: Aug 2001 Location: Bedrock Posts: 26,079
I'm thinkin' once it arrives we'll have to let the ol' Asteroid Belt out a notch.
#50
11-04-2009, 01:05 PM
 Guest Join Date: Nov 2009 Location: San Francisco, CA Posts: 1

## Propellant

When the bacon heats up and begins too cook, perhaps we could get some small boost by using the burning grease as a propellant. That way the projectile is not simply ballistic in nature. In a very inefficient sense, the bacon is itself, a fuel.

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