Spacecraft are generally not constructed to be able to penetrate deeply into an atmosphere at high velocity - reentry vehicles do, but witness what happened when the Hayabusa spacecraft and its small sample-return capsule hit the atmosphere together. The bit meant to reach the ground keeps going, everything else shatters into lots of tiny fragments immediately.
As such I can't help but think that anything human-constructed will tend to fall apart very high up, and dump its energy many kilometers from the ground and in many pieces. Consider the recent meteor in Russia - that was probably a solid lump 15+ meters wide weighing in at 10,000 ish tons, and it lost integrity and fell apart 30 kilometers up. Not to mention that that object was 50-100 times as massive as a 747 and carried ~200 times as much kinetic energy as the total chemical energy of the best rocket ever built. You need some truly epic spacecraft before they become dangerous as anything but (potentially radioactive depending on contents) litter downrange of where they smack the air.
Redirecting small already-earth-crossing rocks by a quarter meter per second such that their path coincides with the Earth ten years later could be another matter all together. But that would be patently obvious as something with enough delta V approached a known object. And if something unofficial can move it, something official can doubtlessly move it back...
The point is not that the spaceship itself is a significant danger, but that at its distant position it could slightly nudge an asteroid on a trajectory strait to earth.
Almost nobody wants to do terrorist attacks.
There are very few terrorist attacks, even though doing a terrorist attack is not very hard. A smart person who really wants to blow up a building, and doesn't mind death or life imprisonment, can generally do so. But very few buildings are blown up. Therefore, even though terrorist attacks are highly available thanks to news reports and fiction, almost nobody wants to do them.
For a crime to occur requires means, motive, and opportunity. We can consider these to be factors of production, or the reagents that go into making a crime happen. Which of them is the limiting reagent on the production of terrorist attacks? Not the means; guns, explosives, and other weapons aren't difficult to come by or create. Not the opportunity; we do not armor all possible terrorist targets nor track every potential terrorist. Rather, the limiting reagent on the production of terrorist attacks is motive — people's interest in doing them.
Which of them is the limiting reagent on the production of terrorist attacks? Not the means; guns, explosives, and other weapons aren't difficult to come by or create. Not the opportunity; we do not armor all possible terrorist targets nor track every potential terrorist. Rather, the limiting reagent on the production of terrorist attacks is motive — people's interest in doing them.
That depends on your location. There is no shortage of would-be suicide bombers in the Palestinian territories (or so I have been led to believe). There is, however, a shortage of explosives and access to targets within Israel.
So I suppose the question is, for what value of harm does (harm per terrorist * small number of terrorists) become so large that very harsh interventions affecting large numbers of innocents start to seem actually reasonable? (Even considering that actual terrorists are not quite like the media's image of them, I think we should probably be willing to pay a rather large cost to keep x-risk-level weapons out of the hands of the terrorists we have today, so clearly there is some line...)
To prevent catastrophe, do not install utility functions that value occupying lots of citizen attention with anxiety as the operators of your media and government.
Aside from ground targets, if lots of people are in space, then there are space-borne targets of high value.
They'll have to look out a lot more carefully.
A reality of physics, and one that doesn't get much play in science fiction, is that as soon as humanity gains space travel, anyone in the asteroid mining or space travel business will have city-busting capabilities at their fingertips.
How do you know that's the reality? Could you go into more detail? Especially if you have enough telescope satellites to monitor all mining activities and some nuclear weapons to attack asteroids that get redirected?
Will a company like Planetary Resources, Inc have the ability to blow up a city when it gets it's mining working?
I think the idea is that active defensive measures (as opposed to just watching with telescopes) are a lot more difficult to set up, and there's little motivation considering that the space activities aren't military-oriented. Although I suppose if we'd be far enough in space exploration to have asteroid mining there'd also be some contingency plans for extinction-grade bricks on a collision course; plans that can probably be adapted to include 'hostile local' handling.
Regarding the physics, do not underestimate heavy things flying very fast, especially if they're good at staying in one piece - a ship/asteroid may well destroy a city when dropped at 10~30km/sec, and attackers will aim.
Things flying very fast through the atmosphere of the earth have the habit of insinuating in it. Would the kind of technology that you would need to do astroid mining really give you the ability to blow up a city?
Yes. You just need to nudge an existing sufficiently large asteroid onto a collision course. (Targeting a specific city is harder but I don't know how much harder.) There are how many near-earth and earth-crossing asteroids over 100m diameter?
Would the kind of technology that you would need to do astroid mining really give you the ability to blow up a city?
Almost certainly. Whether it is practical to get the asteroid involved rather than adapting the large scale propulsion technology is a whole different question.
I was mainly thinking about Project Thor, which roughly means that going at mach 10 (~3km/s) is like being made of TNT energy-wise. Now, current space-shuttles and the ISS weigh around 100 tons, and I'd imagine being able to get at least 10km/s, if not 30 with asteroid mining-level space tech, which should bring spaceships into the kiloton TNT range, that while far from a hydrogen bomb, packs the punch of a smallish fission nuke. So, while it probably won't be easy to wipe out big cities, immense damage is guaranteed.
What I can't estimate properly due to insufficient knowledge is the atmosphere's ability at stopping/limiting such threats, for all I know spaceships/rocks going at too steep an angle might blow up very high up, while stuff going at a gradual entry might be significantly slowed, Although as a rule, bigger things should care less about the atmosphere.
Edit: CellBioGuy's comment points out that spaceships aren't (and probably won't be) built to withstand reentry at dangerous velocities, making at least spaceship-jacks less of a threat.
Note that we have made agreements to not weaponize space, so putting nuclear missiles in space would be difficult.
Not to mention that nuclear weapons in space is a cure that may be worse than the disease.
Furthermore, once you get to fractional-c levels of space technology, the defensive problem becomes much more difficult, and city-busting kinetic weapons turn into planet-busting.
If you have the basics that you need for to fractional-c levels of space technology I think you make a mistake by thinking that "space" is very important. With that kind of technology you can do damage in a lot of ways.
If you have fractional-c level tech for objects larger than very small mass accelerator gun rounds, things are entirely different and you can probably just make a damn nuke.
The principles involved here are not dependent on spaceflight or any new technology, but apply with current technology just as much. In fact, almost twelve and a half years ago, terrorists actually did this exact thing, but with airplanes rather than spaceships.
From this, we can try to extrapolate to the possibility of this happening on a larger scale. So I have two points: The first is that that attack was by far the largest and most destructive terrorist attack ever. If it involved spaceships rather than airplanes, it would have been even larger and more devastating. The second is that since then, not a single attack has managed to get even close to that one in devastation. Modern security measures against attacks like that one seem to be working, and that shows that effective measures against attacks like this are possible.
Modern security measures like fellow passengers not accepting the line that they're hostages, instead fighting vigorously.
The air would already have been safe on September 12, if anything had been in the air by then.
Yes, true. I agree that that is the most effective part of modern airplane security. I doubt all the crazy TSA stuff has any real impact. But resistance by the passengers seems to be working so far in preventing another 9/11. So, hopefully, the same will extend to spacecraft. Of course, nothing is preventing someone, now or in the future, from buying their own airplane/spaceship and crashing it into something. So it is true that this still doesn't absolutely assure safety.
Of course, nothing is preventing someone, now or in the future, from buying their own airplane/spaceship and crashing it into something. So it is true that this still doesn't absolutely assure safety.
See Joe Stack. I recall the media at the time being very careful to not call it a terrorist attack, oddly enough.
I'm not an expert on astrophysics, or millitary technology. Luckily, I have a friend who is an expert on both and has super-hard science fiction world building as his hobby. So I'm just going to quote him on why this isn't as big a deal as people think.
A related issue is the use of spacecraft as weapons against ground targets. This is unlikely, to say the least. As mentioned above, a sectional density of 10 tons/m2 is required to make it through the atmosphere with a reasonable amount of velocity remaining. While common ships might reach this threshold, they are almost certain to fail structurally long before impact. When they break up, the pieces are unlikely to retain sufficient sectional density to do damage. The result is a high-altitude airburst, which, given expected vessel sizes, is unlikely to do significant damage. It has even been suggested that vessels be intentionally designed to break up on atmospheric entry to reduce the risk to people on the ground.
This is from a recent paper meant as an introduction the theoretical space warfare community -of course that is a thing- consensus with an emphasis on what are called plausible mid-future scenarios.
This is from a recent paper meant as an introduction the theoretical space warfare community -of course that is a thing- consensus with an emphasis on what are called plausible mid-future scenarios.
Of course it's a thing. It's actually much more interesting than regular space opera stuff like Honor Harrington. If you have a spare day, read through Project Rho. (I drew on them a bunch for my own space warfare essay.)
I love Project Rho!
Weaponization of engines is also possible although since we lost the promise and the peril of the 1950s it looks like there are going to be no high-power non-chemical engines.
What about private nuclear cores? Could be an issue.
Asteroid strikes are an entirely different issue of course.
Well, something like this was the motivation for the space race: if you can send a rocket to the moon, you can send a bomb around the world. Even though this reason isn't usually raised by space advocates.
How effective is a spaceship as a kinetic weapon, anyway? They're not very massive.
Generally, not very effective (reentry vehicles are a quasi-execption), and they can be intentionally designed to be ineffective as weapons without seriously compromising their effectiveness at space travel. However, this isn't so much about mass per se, but about sectional density and structural integrity, see me and CellBioGuy's upstream comments for details.
I think we need to be specific about scenarios here. For example, right now we don't need to worry about extremely high speeds, so defending against inbound objects should be fairly easy. I think for the near future, (US, Russian, and Chinese) interceptor missile technology will outpace abuse-of-spaceships technology, so once there are a bunch of spaceships flying around and/or mining operations get started, it may be easiest to just keep track of relevant objects and shoot them down. I think that should be more than enough, since I just don't think there are very many people who'd want to use spaceships as makeshift weapons who don't have access to better weapons already. If we make it to the far future (where we might expect significant-fraction-of-c speed ships) without singularity things happening for some reason, on the other hand, more authoritarian external control may become necessary.
A reality of physics, and one that doesn't get much play in science fiction, is that as soon as humanity gains space travel, anyone in the asteroid mining or space travel business will have city-busting capabilities at their fingertips.
It's there in classic sci-fi, but not so much recently.
This discussion was started in the comments to:
http://lesswrong.com/lw/gln/a_brief_history_of_ethically_concerned_scientists/
In the "Ethically Concerned Scientists" post, Izeinwinter commented:
A great start to a discussion here.
You've considered people going loons and some general security, but it would then become a hacker war along the lines of who could break the security and gain control of the space ships.
It doesn't address the problem of the leaders using the ships as threat weapons, since they have legitimate control, but can still make terrorist decisions.
And I'm terrified of your idea of turning spaceflight, which I see as the ultimate freedom, along the lines of Niven's Belters, into a state-controlled affair like the Soviet navy with political officers.
Now, one thing I think is a useful safety control that doesn't lead to worse problems is the destruct option. All major rockets have them right now, since if it goes out of control it's a huge hazard for a great distance. And although I don't like the idea of all personal spaceships being under a safety officers thumb, it might be better than the alternative of terrorist groups gaining control of asteroid mines and holding the world hostage.
You're right about great story potential though, in any of these scenarios.