A Side Affect of Planetary Bombardment

Bluesqueak wrote:Rereading The Moon is a Harsh Mistress at the moment and the ‘rocks’ are encased in steel. The rock is basically providing the mass for a kinetic missile.

True, but I'm sure back then nobody realized that a piece of rock would simply go boom and do nothing to people on the ground. He didn't do a good job with the numbers in that book.

Bluesqueak wrote:Rereading The Moon is a Harsh Mistress at the moment and the ‘rocks’ are encased in steel. The rock is basically providing the mass for a kinetic missile.

Loren Pechtel wrote:True, but I'm sure back then nobody realized that a piece of rock would simply go boom and do nothing to people on the ground. He didn't do a good job with the numbers in that book.

Without saying anything about the numbers; he must have known something of the properties of rocks, if he bothered to encase them in steel. This was several years after people realized that giant meteorites could impact Earth. The Arizona crater might have been to first to be recognized.

tlb wrote:

Bluesqueak wrote:Rereading The Moon is a Harsh Mistress at the moment and the ‘rocks’ are encased in steel. The rock is basically providing the mass for a kinetic missile.

Loren Pechtel wrote:True, but I'm sure back then nobody realized that a piece of rock would simply go boom and do nothing to people on the ground. He didn't do a good job with the numbers in that book.

Without saying anything about the numbers; he must have known something of the properties of rocks, if he bothered to encase them in steel. This was several years after people realized that giant meteorites could impact Earth. The Arizona crater might have been to first to be recognized.

No. The rocks were encased in steel because the catapult needed the steel case. It wasn't a purpose-built planetary bombardment system, it was a cargo system repurposed as a weapon.

The numbers were clearly wrong because in the normal use they were using some small solid rockets to decelerate the cargo. Nope--it would really take something not much smaller than a Saturn V to do it and is all but impossible with solids.

Bluesqueak wrote:Rereading The Moon is a Harsh Mistress at the moment and the ‘rocks’ are encased in steel. The rock is basically providing the mass for a kinetic missile.

Loren Pechtel wrote:True, but I'm sure back then nobody realized that a piece of rock would simply go boom and do nothing to people on the ground. He didn't do a good job with the numbers in that book.

tlb wrote:Without saying anything about the numbers; he must have known something of the properties of rocks, if he bothered to encase them in steel. This was several years after people realized that giant meteorites could impact Earth. The Arizona crater might have been to first to be recognized.

Loren Pechtel wrote:No. The rocks were encased in steel because the catapult needed the steel case. It wasn't a purpose-built planetary bombardment system, it was a cargo system repurposed as a weapon.

The numbers were clearly wrong because in the normal use they were using some small solid rockets to decelerate the cargo. Nope--it would really take something not much smaller than a Saturn V to do it and is all but impossible with solids.

Personally I am reasonably forgiving for mistakes that do not directly impact the outcome of the story. The possibility that the cargo system might not have worked as advertised before it was turned into a weapon is fine for me, because I am already suspending disbelief. If the story grips me, then I will even forgive some things that do impact the outcome; an example I gave before was the treatment of ships in the David Drake RCN series, because I so enjoy the way his characters interact (I deeply regret that his writing has come to an end).

If a big rock is accelerated at a planet, how much time would there be to evacuate the impact zone? The impact zone should be easily determined.

Reminds me of a certain thread.

cthia wrote:If a big rock is accelerated at a planet, how much time would there be to evacuate the impact zone? The impact zone should be easily determined.

Because of the Earth's rotation, once the impact area is determined, so is the time to impact; it is all part of the same calculation. If anything, you probably calculate time to impact first and see where that puts the impact.

cthia wrote:If a big rock is accelerated at a planet, how much time would there be to evacuate the impact zone? The impact zone should be easily determined.

Reminds me of a certain thread.

Depends on how fast the rock was accelerated to, and how far out you detected it. (So, basically, the exact same problem as "how much time would you have to evacuate an asteroid impact zone?")

It might be anywhere from seconds (nobody saw it until it touched atmosphere) to weeks. Hell, there's no particular reason someone couldn't put it on a course that would take over a year to intersect the planet.

Though, of course, the less time until impact the more accurately you can determine the course (and hence the exact impact time/location). At a year from impact they may not be immediately sure whether it'll even hit the planet. (And, of course that'd leave lots of time for a tramp freighter to wander through -- who you can beg to deal with the inbound)

Jonathan_S wrote:

cthia wrote:If a big rock is accelerated at a planet, how much time would there be to evacuate the impact zone? The impact zone should be easily determined.

Reminds me of a certain thread.

Depends on how fast the rock was accelerated to, and how far out you detected it. (So, basically, the exact same problem as "how much time would you have to evacuate an asteroid impact zone?")

It might be anywhere from seconds (nobody saw it until it touched atmosphere) to weeks. Hell, there's no particular reason someone couldn't put it on a course that would take over a year to intersect the planet.

Though, of course, the less time until impact the more accurately you can determine the course (and hence the exact impact time/location). At a year from impact they may not be immediately sure whether it'll even hit the planet. (And, of course that'd leave lots of time for a tramp freighter to wander through -- who you can beg to deal with the inbound)

Good points. I think it would depend on how the rock is accelerated as well. If the original suggestion of using tractor beams is employed, I think it would take a significant amount of time to get a large enough rock up to planet crushing speed. Which means the starting point would have to be quite some distance from the planet. And I would think the perpetrators would want to remain as anonymous as they can; so they would want the point at which they detach from the rock to be as far away from the planet as possible.

Conclusion. Plenty of time to evacuate the impact zone.

cthia wrote:Good points. I think it would depend on how the rock is accelerated as well. If the original suggestion of using tractor beams is employed, I think it would take a significant amount of time to get a large enough rock up to planet crushing speed. Which means the starting point would have to be quite some distance from the planet. And I would think the perpetrators would want to remain as anonymous as they can; so they would want the point at which they detach from the rock to be as far away from the planet as possible.

Conclusion. Plenty of time to evacuate the impact zone.

Plenty of time to get a minor deviation too so it misses the planet.

You may have seen in the last month that we have the technology for it NOW.

tlb wrote:The first story to suggest throwing stones at a planet (that I am know about) was 1966's The Moon is a Harsh Mistress (the story that also popularized the phrase "There is no such thing as a free lunch"), where the Moon's inhabitants revolt against rule from Earth. So the idea predates the Honorverse by far.

It has been suggested that just throwing rocks would not be effective, since they could disintegrate in the atmosphere. So it is necessary to choose metallic objects to strike the surface.

Note that I was only mentioning this as an alternative to using a marginally traceable KEW.

Well the velocity of the rock also comes into question. My memory on TMiHM is a bit hazy, but iirc the velocity the Moon's original catapults lofted rocks was extremely low. They were literally using the Earth's own gravity to do the most of the work, the original magnetic catapult was just imparting enough velocity to get it out of the Moon's Sphere of Influence, and to 'land' the rocks in the ocean. The steel-coated Moon catapult rocks had to be large enough to carry Moon-grown wheat or as they did later in the book 3 full-grown adults which puts the minimum rock size at minimum as approximately the size of an Apollo command capsules if not larger. If smaller rocks can come in at high velocity and impact Earth's surface, then a larger but much slower rock specifically calculated to hit ocean and not land is easily going survive atmosphere and not explode.


After the Moon slaves/workers revolted, and built a few extra catapults off the books, they changed the landing zones from oceans to cities by altering the velocity they launch at by a small margin. But I'm fairly certain they were still primarily relying on Earth doing most of the heavy work of pulling the rocks in rather than the catapults impacting considerably higher velocities.

And the described technology of the time is still very much modern era... "invasion fleets" took multiple days to traverse from Earth to the Moon, just like our latest craft from SpaceX would take. The magnetic catapults would launch from the dark side of the Moon, and after the catapult powers down Earth literally couldn't even see the rocks until they were practically hitting atmosphere. At which time they were only minutes from impact due to having traveled with a measly acceleration of not much higher than 9 or 10 mps squared. You'd have enough time to evacuate a President, Premier or Prime Minister but everybody else is pretty much screwed.


About the only thing I remember being off, was the destruction effect of these rocks. Unless they were loaded with heavy metals, or stuff like uranium or liquid mercury, they had a rather high destructive effect for something coming in so slowly, relatively speaking. Maybe my memory is playing tricks but I recall them being somewhat more dangerous and a little closer to what Frontier Fleet using single KEWs to take out entire (small) towns, rather than something like say Terekhov using a KEW to kill Yucel with only a few blocks worth of damage.