# Fictional Impact Scenario

1. Aug 11, 2012

### Groggen

Hi All,

I'm hoping some of you with more expertise in such matters can help me out with the plausibility of a scenario for a novel I'm working on. I know you guys must get stupid hypothetical questions like this frequently, so if I'm out of line just let me know and I'll just slink back to my word processor and keep working.

This is a somewhat near future setting without super advanced technology. All of the technology is based on at least either what we can do now or what we can speculate we can do in the near future. Basically, what's happening is that there are independent colonies spread throughout the solar system that are being conquered by earth. The colonies hatch a plan to deal with earth by creating a cloud of debris around the planet that makes space flight too hazardous to be practical for several years (or more). Space ships are still essentially tin cans but with more advanced propulsion, so a pebble can still punch right through one of them.

My idea for creating the cloud is this... A near earth asteroid (or comet) is going to make a pass by earth within a few earth-moon distances. A bomb (regular nuke or possibly antimatter) will be detonated on the surface, or under the surface of the asteroid to adjust the orbit enough to collide with the moon and knock massive amounts of regolith out of the moon's gravity well and into earth orbit.

I'm assuming such an impact done in a precise enough way could knock up a lot of rock and with enough velocity to escape the moons orbit, but how big would the impactor have to be to saturate the space around earth with hazardous amounts of debris? Would your average hazardous NEO be large enough if it hit just the right way? Say 1.5km to 10km? Or do I have to start looking at freakishly large unknown comets instead?

And could you create an explosion large enough to divert an asteroid (that's about a month away from a 1-2 earth-moon distance pass) so it would smash into the moon? The idea is, that the amount of time before impact should be short enough so that earth couldn't respond by detonating another bomb to make it miss. Keep in mind, large amounts (100's of kg) of antimatter atoms could be written in easily if nukes are insufficient.

Thanks in advance for whatever input you can offer.

2. Aug 11, 2012

### Staff: Mentor

With an object of 1.5km to 10km, what about a direct impact on earth? The first one is big enough to cause significant trouble to the whole industry network, and the second one is a serious threat to all life on the surface of earth.

I think I would not use the moon. Orbits of those particles would have an apogee at least comparable to the moon. Objects in low earth orbit (~500-1000km) are more dangerous. They have a higher velocity and you need less objects for the same density.

It is possible to track objects with a size of ~10cm with current technology, and you can shield the spacecrafts against objects <1cm. If it is a serious threat, it should be possible to track all dangerous objects in low earth orbit. Therefore, you need so many that it is nearly impossible to avoid all. Assuming rockets are still the usual way to launch stuff (something you should think about - space exploration with rockets is expensive), the shortest path through the debris is a vertical ascent. With ~100m^2 rocket surface area and a debris field between 500km and 1000km height, we need a volume of 500km*100m^2 = 0.05km^3 free of large objects. To avoid this, fill every cubic kilometer with ~100 objects. With ~1kg mass per object, this corresponds to 3*10^13kg, or an asteroid with ~1km radius. Quite large, and it does not even take into account that a spacecraft can steer around objects (the ISS does this sometimes). In addition, debris objects will frequently collide with other objects, giving more and more smaller particles, up to a level where you have something like a dust cloud around earth. Bad for unprotected solar cells, but not dangerous for spacecrafts.

Long story short: What about the direct impact? :D

3. Aug 12, 2012

### DennisN

Hi Groggen! (Posting here, in case you'll miss it) I posted a couple of links in another thread about SF (my reply is here).

4. Aug 13, 2012

### Groggen

Thanks for the replies. Yes, an earth impact was the first thing I considered. But I am wondering if that's something the colonists would do...they are my protagonists after all. I was trying to think of some way to clip earth's wings that didn't involve killing billions of people. If I did that, then I'd have to make the actions of earth leading up to the impact equally horrific in order for the impact to be justified in the reader's eyes.

But I can't think of an easy way to create a 100km thick sphere of evenly spaced debris around earth at exactly 500km. It's not like you could just setup a mass driver on an asteroid and slowly move it into orbit and start disassembling it 1kg piece by 1kg piece without being noticed. Especially when you're so close to a superior military force. That's why I'm favoring a quick big sloppy mess of an impact that would scatter debris throughout earth orbit between the moon and earth. But considering most of the mass of the impactor would stay on the moon, and based on your math, it sounds like I'd need an impactor many times larger than the largest NEO to do what I want. So maybe I'll go back to the original concept.

Yeah, the impact idea is a bit cliche nowadays, but it's still the most effective weapon that a small space based guerrilla force could use against a planet. Plus, it doesn't take up much of the story....as opposed to movies like Deep Impact (or that terrible one with Bruce Willis) where the asteroid is the story.

5. Aug 13, 2012

### Ryan_m_b

Staff Emeritus
You may want to read up on Kessler syndrome which is pretty much exactly what you are describing. In addendum to that you might want to think about what technologies may be in place in such a setting to deal with space debris, as this is a growing problem today I imagine it will be far worse in a world of widespread space travel. In such a scenario this enclosing action may be more temporary than originally proposed with interesting political plotlines as colonies observe increased efforts by Earth to clean up.

I wonder what the secondary effects of such an action would be? Presumably these colonies are self sufficient and are not reliant on Earth (which would imply very advanced technology) else they would be sealing their fates. Removal of LEO may have catastrophic effects for global ICT (especially if future increases in network coverage and bandwidth suck conventional communications into variants of VoIP), this would be especially bad if said communication black/brown outs disrupted the just-in-time logistics for global food distribution. The knock on effects of that being obvious.

Last edited: Aug 13, 2012
6. Aug 13, 2012

### Staff: Mentor

Well, there is a big difference between "make LEO unusable" (easy, the spacecrafts are designed to be years there) and "make space launches impractical" (hard, the spacecrafts can fly through this region within some minutes).

Get a big rubble pile (most smaller asteroids are those), direct it to a near miss. At perigee, blow it up. Some fraction of its mass will go in an orbit.

7. Aug 14, 2012

### Groggen

Yeah, that would would be good. But the impact comes at the end of the book, so this would have to wait until a sequel.

As I think about this, I'm liking it more and more. I didn't come in here expecting new ideas, just comments on what I'd already come with it. Maybe you guys should be writing the book?