And technology would have been developed that could do the job significantly quicker. Even if it could be done today, you wouldn’t want to, since it’d make more sense to wait for the better tech first.
:mad:
Stop pointing out obvious things I should have mentioned in my posts, Pallas damn it!
Do you WANT me to unleash the bees?
Wow, I guess I asked the wrong question…
Is there anything technology could cause in the next 100-200 years that would quickly cause climate change or worldwide disaster? Basically, the world needs to be an inhospitable place to live, but still capable of supporting some human life.
A 100 km diameter object has a volume of 7.85 x 10[sup]9[/sup] m[sup]3[/sup]. If it has a density similar to Earth’s Moon (3.3464 g/cm[sup]3[/sup]) then it will have a mass of 26.3 x 10[sup]12[/sup] kg. If we are to assume that it is moving somewhere in the vicinity of Earth’s orbital speed (as it will have to be in order to m ake maximum effect of momentum transfer via gravitational swing-by) it will be moving at ~29.8 km/s, giving it a kinetic energy of 1.17 x 10[sup]13[/sup] GJ. To make a 1% change in any orbital characteristic would take about the equivalent of 28,000 megatons TNT, comparable to the total yield of all nuclear weapons produced by the major powers during the height of the Cold War, and the use of nuclear devices is the only feasible way to deliver and apply such energies to a moving celestial body. Applying this amount of impulse in some fashion without fracturing the object into fragments would require some kind of damped or buffered system which would distribute the impulse evenly across the surface and over an interval of time sufficient to allow stresses in the body to equalize before reaching shear limits. Such a damping system, based on something akin to the Project ORION pusher plate concept, with a maximum efficiency in the 10% range.
The propulsion system and propellant (tens of thousands of bomblets) would have to be delivered to the moving object via some conventional means, i.e. chemical rockets to lift it off the surface of the Earth and nuclear pulse propulsion to delivery it to rendezvous with the object. (Alternatively, you could establish a permanent manufacturing infrastructure and manned presence in space to mine, produce, assemble, and deliver the necessary components, at a cost of untold trillions of dollars.) All of this would have to be repeated on a periodic (presumably annual, or semi-annual) basis.
All of this would have the effect of transferring a fraction of the difference in momentum between the two bodies (at most twice the difference in relative momentum between the Earth and the object; in practice, significantly less). Since the difference in momentum is proportional to the masses, the gain factor for impulse transfer would be proportional to the ratio of masses, or Q=-113.6. This means to make a 1% change in Earth’s orbital characteristic and 100% transfer of relative momentum will take somewhere on the order of 2000 billion years, assuming you can perform a transfer maneuver twice per solar orbit. By this time, not only is the climatosphere of the Earth no doubt changed, the Sun itself has long turned into a greenish-white dwarf star.
None of this of course accounts for the fact that the close approach by a large body will cause huge seismic stresses that are likely to cause or amplify tectonic and volcanic activity, which is likely to cause more ultimate destruction than transitory climate change.
In short, not feasible nor desirable with any extant or conceptual technology.
Stranger
Quoth sylvernight:
You mean, other than what we’re doing now?
Quoth Stranger:
It would have to be going somewhere in that vicinity when it makes the swing-by, but it doesn’t have to be going that speed when you change its orbit. Like I said, you want to make your orbital changes near aphelion of a high-eccentricity object.
I doubt that such a small object would have such a noticeable effect on the planet, especially since the far larger Moon doesn’t despite producing enough tidal forces to create, well, tides. And even if it did, that’s still less damage than the death of all life on Earth besides some deep crust dwelling bacteria due to Earth going the Venus route. That’s neither temporary nor minor.
As for the rest of your post; I’m not a scientist, but the NASA people who are scientists thought it would work (and the scientists who didn’t like the idea complained about losing the Moon, not that it wouldn’t work), and with just chemical rockets at that. I suspect you misplaced a few decimal points somewhere.
But in order to make changes on an annual or semiannual basis, you’ll have to have an orbit that isn’t too elliptical. Of course you can make a very long elliptical orbit with a low momentum aphelion, but that means that your period of intercept will be on the order of decades or longer, which further extends the number of passes in order to effect a desired orbital change. Given that we’re already talking in multiples of hundreds of times the effective age of the Sun, I’d say it is a moot point. There is no practical way, even given an unlimited budget of labor and materials, to make a measurable change in the Earth’s orbital characteristics without incurring significant damage to the target.
Stranger
I was presuming infrequent interactions, and just taking a really long time to complete the move. But if you wanted to speed it up, you could send out multiple probes to multiple comets. Mind you, I don’t claim that it would be practical right now, but I do think it would be possible.
But in order to achieve a comparable momentum transfer with a lighter object you’ll have to swing closer to the Earth than with a heavier object; significantly closer than Earth’s Moon. This could have a very severe impact upon the geological stability of the Earth. If it increases volcanic activity, the suspended ash alone may offset any gains made from moving the planet. And in fact, even given tight control over the object’s trajectory, with millions or billions of swing-bys there is an almost certain chance that you’ll experience a direct impact. Direct impact upon the Earth by an object moving at an entrance speed of even a few km/s difference would most certainly of the same kind of apocalyptic destruction as you imagine a runaway greenhouse effect to be.
As you haven’t cited any study or reference to an article detailing the study I can only guess at the particulars of the proposal, but as an engineer working in the field of rocket propulsion I can assure you that the impulse provided by chemical motors is in no way sufficient to significantly move objects in the 1 km diameter range, much less 100 km diameter. The amount of propellant required to effect an impulse transfer of even a Near Earth Object of modest size (say 50 m diameter, four million times less massive than the 100 km diameter object you propose) to Earth orbit would tax the current state of the art and require a mass of several times the object itself, even using low energy maneuvers. A constant low thrust propulsion system with a high effective exhaust velocity could do it with less, but not at a very high efficiency (around 1-2%).
As for my calculations, while they certainly employed a number of broad assumptions, there are no missing decimal points. I have studied the use of nuclear pulse propulsion to divert a Potentially Hazardous Object from an Earth intercept (and have actually [POST=12775897]posted on the topic[/POST] in the past) which is a far easier problem than the kind or precision guidance required for orbital momentum transfer. In terms of the scale of our ability to alter the trajectory of an object, a 1 km diameter iron-nickel PHO is about the upper limit of what is feasible, and then not to the kind of precision necessary to perform a close enough approach to the Earth to provide effective momentum transfer while ensuring that it will not impact. There is currently no existing or proposed method of propulsion that will allow us to significantly and safely alter the orbital characteristics of the Earth in anything like human timescales, even if we expand the scale to thousands or millions of years. The amount of energy required is quite literally astronomical, far beyond anything we are or will conceivably be capable of producing in the foreseeable future.
Stranger
A self-replicating nanobot could work. It doesn’t even have to be aggressively harmful, if it can outcompete plants for the nutrients they need to survive. If the nanobots suck up every bit of usable nitrogen (ammonia, nitrite and nitrate) they can find, plants will die and most of the planet will revert to desert. (A desert crawling with a fine dust of nanobots). A few plants could survive thanks to nitrogen-fixing bacteria in their root systems. A few others would survive by getting just barely enough nutrients to survive. But clover and Venus fly traps are not going to prevent desertification.
But Dracoi, wouldn’t the nano-bots make it hard for humans to survive? Is there anything else that could destroy/harm most of the planet, but still allow a few small settlements to survive?
I remember reading about this about 10 years ago. IIRC, the timescale being contemplated was a few thousand years of fly-bys, and the intent of the maneuvers was to counter the increased luminosity (i.e solar energy output) of the Sun between now and its red giant phase.
It’s my understanding that the Sun has been increasing in solar output steadily for the last few billion years, and will continue to do so. Indeed, sometime in the next billion years or so, it is expected that this increased output will cause the oceans to completely evaporate, ending life on Earth.
The study I’m thinking of was a hypothetical one that envisioned a method to address the specific problem of increased solar output, not relatively short-term problems like the current global warming from increased carbon dioxide in the atmosphere.
Reality television?
Not necessarily. Remember, I’m not suggesting something aggressively harmful, just something that can outcompete plants for nutrients. The nanobots might try to get into our bodies to eat up components in our bodies, but we have various defenses that aren’t present in open soil. Immune systems in the blood, acid in the digestive tract, etc.
And you would still have plenty of plants that would grow. Any nitrogen-fixing plant would be able to produce its own fertilizer, and this include the whole legume family, as well as livestock feed such as alfalfa. Algae farms might be popular. (Here’s a Wikipedia page about it, with more plants: Nitrogen fixation - Wikipedia).
You’d still wind up with widespread deserts, though. The loss of all the non-nitrogen-fixing plants would lead to the same kind of desertification that unchecked logging can cause. Plus, it’s a good bet that all that plant material dying and decomposing would have an effect on atmospheric CO2 that could cause additional climate change.
Sailboat, I think that would be a different kind of story entirely. 
You would need to use a much larger mass than a 100 km asteroid, though. Ideally, you’d use something significantly larger than the Earth, so that a slow pass by the Earth would maximize momentum transfer without getting too close. Say, using Uranus or Neptune as the mass, with a massive fusion engine suspended on a cushion of atmosphere and using hydrogen from the atmosphere as fuel and propellant. Alternatively, you could have some kind of space tug which applied a small but continuous force coupled by the magnetic field, though the disruptions to the Earth’s magnetosphere may render it uninhabitable anyway (and you’d probably need magnetic monopoles or some other means to create a linear field over such a distance). All of this is far into science fiction, of course.
Really, if your concern is climate change the easiest mode of attack is probably to deal with the cause directly rather than trying to drag the planet around.
Stranger
Do you think it would be easier to start tinkering with the Sun and somehow keep its luminosity from increasing? 
No, but I think it would be much easier to place a filter or shield at the L1 libration point that would reduce solar incidence. That’s not even that far beyond conventional technology, requiring only a modest space mining and manufacturing infrastructure.
Stranger
Indeed, this is probably more feasible than trying to adjust the orbit of the Earth. I wonder how stable such a shield would be, though.
Of course, a shield or filter doesn’t help once the Sun gets to the red giant phase, but that’s a long way off.