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A Side Affect of Planetary Bombardment

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Re: A Side Affect of Planetary Bombardment
Post by Loren Pechtel   » Sat Nov 12, 2022 12:06 am

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ThinksMarkedly wrote:
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.


DART had a long lead time and lead to a tiny deflection.

What happens when they go out in the Oort cloud and grab something a mile across. Spend a while boosting it to .01c, way off from the ecliptic. We've never seen what happens when something like that hits a wedge, the Honorverse has nothing else that can stop it. Something like that might very well only be picked up at light seconds out.
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Re: A Side Affect of Planetary Bombardment
Post by Loren Pechtel   » Sat Nov 12, 2022 12:29 am

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Somtaaw wrote: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.


Agreed. I don't think they could even throw them out of the Moon's SOI--it takes a bit less energy to eject to L1.

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.


They had no choice, the impact would be the 11 km/sec that Earth imparts as it falls in. Ejecting it faster would have almost no effect on the impact velocity.

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.


1 extra and the impact location is far more timing than energy.

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.


This. Radar needs r^4 energy, long range detection isn't an option (but note the rebels can put a cornercube reflector on their side of the rock--they can track it from much, much farther away than Earth can.) I would say the book is below current tech levels except he didn't realize how hard a lot of space stuff is. IIRC the impacts were around 10kt. I don't know what's going to happen at they hit atmosphere, if there wasn't atmosphere in the way there wouldn't even be time to get the President out. One minute of warning requires detection at 420 miles up. Nearby bunker, yes, escape, no. And note that they destroyed the hardest bunker of the time, Cheyenne Mountain. On the other hand, there was absolutely zero chance they would shoot at the President. (And, yes, they could have destroyed Cheyenne Mountain--it was never built to survive a direct hit.)
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Re: A Side Affect of Planetary Bombardment
Post by ThinksMarkedly   » Sat Nov 12, 2022 12:32 am

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Loren Pechtel wrote:DART had a long lead time and lead to a tiny deflection.

What happens when they go out in the Oort cloud and grab something a mile across. Spend a while boosting it to .01c, way off from the ecliptic. We've never seen what happens when something like that hits a wedge, the Honorverse has nothing else that can stop it. Something like that might very well only be picked up at light seconds out.


The Oort Cloud is over 6 light-hours away. Something moving at 0.1c from there would take 60 hours to reach the inner system, which is plenty of time to detect and do something in the HV, It might be enough to bolt a regular rocket to its surface and impart a lateral acceleration vector. You don't need to actually destroy the object, you can simply deflect it like we did with Dimorphos. In fact, you should thank whoever sent you an asteroid closer so you could mine it!

A planet is actually a pretty tiny target. Assuming the object is aimed at the centre of the planet, you'd need to deflect it by about 7,000 km to miss. Rounding up to 10,000 km, if the rocket is emplaced 15 hours before impact (one quarter of the travel time), it needs to add a Δv = 185 m/s. If the rocket can only push that much mass at a tenth of a gravity, it only needs to work for 3.14 minutes. At one hundredth of a gravity, 31.4 minutes.

It can also just decelerate or accelerate the object a little. Earth covers its own radius in just over 210 seconds. So the best bet is actually to accelerate it in either direction of a vector that is pointing ahead of the planet. That is, either decelerate it and push it anti-spinward, or accelerate and push it spinward.

BTW, the Manticore Binary System doesn't have an Oort-like cloud that close because the two stars are only 13-15 light-hours apart. There are no stable orbits after about 6 light-hours until the orbits that are stable around the common barycentre. Those aren't going to be less than what, 30-35 light-hours? Something launched at 0.1c from there would take over 2 weeks to arrive. While detection much further out is difficult, the object would spend an awful lot of time where it can be detected. And given that they must have observation satellites in both components, anything moving towards one system would be moving across the sky in the other.
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Re: A Side Affect of Planetary Bombardment
Post by Loren Pechtel   » Sat Nov 12, 2022 7:29 pm

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ThinksMarkedly wrote:
Loren Pechtel wrote:DART had a long lead time and lead to a tiny deflection.

What happens when they go out in the Oort cloud and grab something a mile across. Spend a while boosting it to .01c, way off from the ecliptic. We've never seen what happens when something like that hits a wedge, the Honorverse has nothing else that can stop it. Something like that might very well only be picked up at light seconds out.


The Oort Cloud is over 6 light-hours away. Something moving at 0.1c from there would take 60 hours to reach the inner system, which is plenty of time to detect and do something in the HV, It might be enough to bolt a regular rocket to its surface and impart a lateral acceleration vector. You don't need to actually destroy the object, you can simply deflect it like we did with Dimorphos. In fact, you should thank whoever sent you an asteroid closer so you could mine it!


Detect it with what?? We see hyper footprints. We wedges. We see things at a 1Mkm by radar. Big radar installations can probably do better, but not all that far.

Grabbing something from out there means it has no wedge. No hyper footprint. It's going to be found when someone happens nearby (note that there are very few wandering around outside the hyper limit) or in the last seconds of it's flight.

Consider Oyster Bay. Nobody saw the missiles until a ship passed nearby and they didn't realize what they had seen in time to do anything about it. Those missiles were going far faster and thus had a far more visible particle shockwave.

A planet is actually a pretty tiny target. Assuming the object is aimed at the centre of the planet, you'd need to deflect it by about 7,000 km to miss. Rounding up to 10,000 km, if the rocket is emplaced 15 hours before impact (one quarter of the travel time), it needs to add a Δv = 185 m/s. If the rocket can only push that much mass at a tenth of a gravity, it only needs to work for 3.14 minutes. At one hundredth of a gravity, 31.4 minutes.


And where in the Honorverse can you find a rocket with that kind of spec? There's nothing remotely like it. And I would be amazed if it didn't simply come apart under .1g. I wouldn't be surprised if it came apart under .01g. (Accelerating it originally is going to be a very long, slow process.)

It can also just decelerate or accelerate the object a little. Earth covers its own radius in just over 210 seconds. So the best bet is actually to accelerate it in either direction of a vector that is pointing ahead of the planet. That is, either decelerate it and push it anti-spinward, or accelerate and push it spinward.


Disagree--for a perfectly aimed object it doesn't matter which direction you deflect it, all have equal effects.

BTW, the Manticore Binary System doesn't have an Oort-like cloud that close because the two stars are only 13-15 light-hours apart. There are no stable orbits after about 6 light-hours until the orbits that are stable around the common barycentre. Those aren't going to be less than what, 30-35 light-hours? Something launched at 0.1c from there would take over 2 weeks to arrive. While detection much further out is difficult, the object would spend an awful lot of time where it can be detected. And given that they must have observation satellites in both components, anything moving towards one system would be moving across the sky in the other.


I was figuring a lot more than 2 weeks to carry it out. This is probably a project of years. And how would they be detecting said bodies? We have seen a few that are close and many miles across. Nobody's sitting there continually rescanning space, even if it's within a theoretical detection range doesn't mean it will actually be seen in time.
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Re: A Side Affect of Planetary Bombardment
Post by ThinksMarkedly   » Sun Nov 13, 2022 3:51 pm

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Loren Pechtel wrote:Detect it with what?? We see hyper footprints. We wedges. We see things at a 1Mkm by radar. Big radar installations can probably do better, but not all that far.


Telescopes. We're not talking about a stealth craft with active camouflage, heat sinks, and directed irradiation. We're talking about a rock. Low albedo is not invisible, it's just low. With enough exposure, you can detect low reflectivity objects.

I'm assuming any space-faring civilisation has telescopes. Moreover, a system like the MBS has thousands of sensor platforms in the form of all the ships going through the system. None of them may be paying attention to the specific location where the object is coming from, but that's what software is for. All the Manticore-flagged ships probably download their records when they dock, and some background process scans.

Grabbing something from out there means it has no wedge. No hyper footprint. It's going to be found when someone happens nearby (note that there are very few wandering around outside the hyper limit) or in the last seconds of it's flight.


Not seconds. Even if it isn't detected before, when it comes in the inner system, near the hyperlimit, it will likely be detected by someone. There are a lot of ships crawling around and their vectors can't be accurately predicted weeks in advance. Even if it is aiming at Sphinx at 4 light-minutes from the hyperlimit, that's a 40-minute warning.

Consider Oyster Bay. Nobody saw the missiles until a ship passed nearby and they didn't realize what they had seen in time to do anything about it. Those missiles were going far faster and thus had a far more visible particle shockwave.


But were MUCH smaller and were artificial. Each pod is a thousand tonnes, maybe? Dimorphos is 5 million tonnes and wouldn't be big enough to cause an extinction-level event. It's within the the capabilities of wedge destruction too.

And where in the Honorverse can you find a rocket with that kind of spec? There's nothing remotely like it. And I would be amazed if it didn't simply come apart under .1g. I wouldn't be surprised if it came apart under .01g. (Accelerating it originally is going to be a very long, slow process.)


The ones that accelerated half a million tonnes of cruisers in Honor's defence of Cerberus at 50 gravities. That's something I've had issues with, but is canon.

The same force that accelerates half a million tonnes at 50 gravities accelerates Dimorphos 5 gravities or Didymos (which is 52 million tonnes) at half a gravity. It only needs to work for one minute under those conditions.

Disagree--for a perfectly aimed object it doesn't matter which direction you deflect it, all have equal effects.


Well, not exactly. My point is that this is actually a two-dimensional problem (the third is not helpful). Think of all cartoon characters that run from a tumbling boulder in the direction it's going and then get smashed. What they should have done is go sideways. And the perpendicular direction is the best.

I was figuring a lot more than 2 weeks to carry it out. This is probably a project of years. And how would they be detecting said bodies? We have seen a few that are close and many miles across. Nobody's sitting there continually rescanning space, even if it's within a theoretical detection range doesn't mean it will actually be seen in time.


You're underestimating our current detection capability. According to Wikipedia, we know of over 30,000 near-Earth asteroids. Of the 2304 that cross Earth's orbit and are larger than 140 m wide, only 153 are larger than 1 km across.

All of those have been detected with ground or NEO telescopes, so from a single vantage point. If you can cheaply emplace big telescopes in space, you get better resolution. This type of service is something that the Manticore Astro Control would have been doing for centuries, as it's required for proper navigation in the system.

You're probably thinking of what happened in The Expanse, where Marco Inaros' faction coated the asteroids with Martian stealth technology and launched them in an orbit such that they'd arrive on Earth from sunwards, making detection difficult. It is possible for such a thing to happen, but it also requires complacency on the target, assuming they'd have mapped everything and the picture was static. And even then, only three rocks landed on Earth, neither of which was extinction-level; all others were intercepted further out. Book Seven also told us the Earth economy had recovered within 30 years. Plus, none of the polities in the Alliance would be as vulnerable, given that they have multiple planets in each one (even the Republic of Beowulf) and the one that doesn't is also the one where the population is living inside domes and wouldn't be affected by ecological damage (Grayson). not to mention, of course, they have each other.
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Re: A Side Affect of Planetary Bombardment
Post by Loren Pechtel   » Sun Nov 13, 2022 7:40 pm

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ThinksMarkedly wrote:
Loren Pechtel wrote:Detect it with what?? We see hyper footprints. We wedges. We see things at a 1Mkm by radar. Big radar installations can probably do better, but not all that far.


Telescopes. We're not talking about a stealth craft with active camouflage, heat sinks, and directed irradiation. We're talking about a rock. Low albedo is not invisible, it's just low. With enough exposure, you can detect low reflectivity objects.


I'm sure they have telescopes. Detecting something that far out takes a mighty telescope, though. And there's an awful lot of space to check.

I'm assuming any space-faring civilisation has telescopes. Moreover, a system like the MBS has thousands of sensor platforms in the form of all the ships going through the system. None of them may be paying attention to the specific location where the object is coming from, but that's what software is for. All the Manticore-flagged ships probably download their records when they dock, and some background process scans.


Except most of those ships are in the plane of the ecliptic. That's why I said to bring it in far from the ecliptic. And note that the traffic thins out a lot once you reach the hyper limit. A mining ship just might pass nearby but their likely locations could be plotted. (A mining ship will normally be going to a mine.)

Not seconds. Even if it isn't detected before, when it comes in the inner system, near the hyperlimit, it will likely be detected by someone. There are a lot of ships crawling around and their vectors can't be accurately predicted weeks in advance. Even if it is aiming at Sphinx at 4 light-minutes from the hyperlimit, that's a 40-minute warning.


Not many ships crawling around at high angles. And it has to pass very close to a ship for them to take note.

And where in the Honorverse can you find a rocket with that kind of spec? There's nothing remotely like it. And I would be amazed if it didn't simply come apart under .1g. I wouldn't be surprised if it came apart under .01g. (Accelerating it originally is going to be a very long, slow process.)


The ones that accelerated half a million tonnes of cruisers in Honor's defence of Cerberus at 50 gravities. That's something I've had issues with, but is canon.

The same force that accelerates half a million tonnes at 50 gravities accelerates Dimorphos 5 gravities or Didymos (which is 52 million tonnes) at half a gravity. It only needs to work for one minute under those conditions.


I'm talking about something considerably larger but I'll concede they have insane rockets. However, that leaves the real problem that applying that kind of force simply results in it coming apart and does nothing to save the planet.

Disagree--for a perfectly aimed object it doesn't matter which direction you deflect it, all have equal effects.


Well, not exactly. My point is that this is actually a two-dimensional problem (the third is not helpful). Think of all cartoon characters that run from a tumbling boulder in the direction it's going and then get smashed. What they should have done is go sideways. And the perpendicular direction is the best.


The third dimension counts--speeding it up or slowing it down cases a miss, also. I'm just saying that with perfect aim the deflection needed in each direction is equal.

I was figuring a lot more than 2 weeks to carry it out. This is probably a project of years. And how would they be detecting said bodies? We have seen a few that are close and many miles across. Nobody's sitting there continually rescanning space, even if it's within a theoretical detection range doesn't mean it will actually be seen in time.


You're underestimating our current detection capability. According to Wikipedia, we know of over 30,000 near-Earth asteroids. Of the 2304 that cross Earth's orbit and are larger than 140 m wide, only 153 are larger than 1 km across.

All of those have been detected with ground or NEO telescopes, so from a single vantage point. If you can cheaply emplace big telescopes in space, you get better resolution. This type of service is something that the Manticore Astro Control would have been doing for centuries, as it's required for proper navigation in the system.


They'll have a pretty good map of inner-system asteroids. That doesn't mean they'll pick up an intruder the instant it enters the inner system, though.

You're probably thinking of what happened in The Expanse, where Marco Inaros' faction coated the asteroids with Martian stealth technology and launched them in an orbit such that they'd arrive on Earth from sunwards, making detection difficult. It is possible for such a thing to happen, but it also requires complacency on the target, assuming they'd have mapped everything and the picture was static. And even then, only three rocks landed on Earth, neither of which was extinction-level; all others were intercepted further out. Book Seven also told us the Earth economy had recovered within 30 years. Plus, none of the polities in the Alliance would be as vulnerable, given that they have multiple planets in each one (even the Republic of Beowulf) and the one that doesn't is also the one where the population is living inside domes and wouldn't be affected by ecological damage (Grayson). not to mention, of course, they have each other.


Never watched it.
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Re: A Side Affect of Planetary Bombardment
Post by Jonathan_S   » Mon Nov 14, 2022 9:37 am

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Loren Pechtel wrote:
ThinksMarkedly wrote:Well, not exactly. My point is that this is actually a two-dimensional problem (the third is not helpful). Think of all cartoon characters that run from a tumbling boulder in the direction it's going and then get smashed. What they should have done is go sideways. And the perpendicular direction is the best.


The third dimension counts--speeding it up or slowing it down cases a miss, also. I'm just saying that with perfect aim the deflection needed in each direction is equal.
Obviously if it was aimed through the dead center of the planet then you'd need to deflecting it somewhat over one planetary radius in any direction to cause a miss.

However, not all vectors of acceleration you could apply to the rock will result in the same amount of lateral deflection per newton of applied force. So are more efficient than others.

Let's start with something obvious. The rock is on a ballistic course calculated to reach a point on the planet's orbit at the same time the planet does. But you could calculate a wide range of other courses where you adjust the rock's speed and the correct its trajectory in order to meet the planet at a different point and time in its orbit.

The closer your deflection vector is to one of those alternate intercept courses the less the rocks point of impact will shift for a given acceleration. So you'd want to apply acceleration in an efficient direction. I suspect that any direction direction perpendicular to the current vector would be pretty close to optimal. (But fortunately you don't need to actually work one of those optimal vectors out by eye, or longhand, that's what computers are for ;) -- or just apply enough brute force that it doesn't matter if you're inefficient about it :D)
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Re: A Side Affect of Planetary Bombardment
Post by ThinksMarkedly   » Mon Nov 14, 2022 10:51 pm

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Loren Pechtel wrote:I'm sure they have telescopes. Detecting something that far out takes a mighty telescope, though. And there's an awful lot of space to check.
...
Except most of those ships are in the plane of the ecliptic. That's why I said to bring it in far from the ecliptic. And note that the traffic thins out a lot once you reach the hyper limit. A mining ship just might pass nearby but their likely locations could be plotted. (A mining ship will normally be going to a mine.)
...
Not many ships crawling around at high angles. And it has to pass very close to a ship for them to take note.


Indeed, the vast majority of ships, if not the near totality, is going to be on the ecliptic. We're also told that arriving on the ecliptic from hyperspace is easier on the generators, so that's where all civilian traffic will arrive at, short of exigent circumstances.

What I meant is that all those ships have sensors and, while focused on the ecliptic, would have captured all-sky data. Not good data, but that's where software adds up.

You've got a point though that the quality of the data off the ecliptic is going to suffer a lot. So scanning off it is where Astro Control needs to focus its own telescopes. The interesting thing is that scanning off the ecliptic is easier, because your satellite that is orbiting on the ecliptic can simply rotate around the axis that connects it to the system's primary, thereby keeping its solar panels facing the star and its cold side facing away (like the Gaia and the James Webb telescopes).

I do grant you that they won't be scanning for defence purposes. Astro Control is not the military, their job is not scan for external threats. I am saying, though, that with a travel time measured in weeks to months, such a rock has a very good chance of being picked up by routine scanning. If space travel is cheap enough that people commute to space for work, it's cheap enough to seed your near-planetary space with satellites to scan for impactors.

As Larry Niven said, "the dinosaurs became extinct because they didn't have a space program."

I'm talking about something considerably larger but I'll concede they have insane rockets. However, that leaves the real problem that applying that kind of force simply results in it coming apart and does nothing to save the planet.


If you break a 52-million tonne asteroid into 10 5-million tonne chunks, you can destroy each with wedges. We know that 5 million tonnes is within the wedge-destroying capability. We've only talked about deflecting a large asteroid because we don't know what size limit a powerful wedge could still apply to.

The third dimension counts--speeding it up or slowing it down cases a miss, also. I'm just saying that with perfect aim the deflection needed in each direction is equal.


Yes and no. It counts, but you can ignore it because the optimal deflection reduces the problem to two dimensions. See Jonathan's reply for details.

They'll have a pretty good map of inner-system asteroids. That doesn't mean they'll pick up an intruder the instant it enters the inner system, though.


ʻOumuamua was detected by the Spaceguard survey when its brightness was less than magnitude 20. That was a fast-moving object, small and not very luminous.

According to the ESA's website, Gaia performs one rotation every 6 hours. It has a narrow field of view, so it takes just short of half a year to scan all of it. But it's trying to keep track of one billion stars. The FAQ says "Gaia detects and measures celestial objects (stars, galaxies, quasars and Solar-System bodies) down to magnitude 20.5." That's just one telescope.

As I said above, for them it would be cheap to have lots of telescopes, to provide a full sky survey every week or two.

Plus, something large enough to be a planetary danger will be brighter than something small like 'Oumuamua. I really doubt it wouldn't be picked up at 4 light-minutes.
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Re: A Side Affect of Planetary Bombardment
Post by Loren Pechtel   » Tue Nov 15, 2022 12:29 am

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Jonathan_S wrote:The closer your deflection vector is to one of those alternate intercept courses the less the rocks point of impact will shift for a given acceleration. So you'd want to apply acceleration in an efficient direction. I suspect that any direction direction perpendicular to the current vector would be pretty close to optimal. (But fortunately you don't need to actually work one of those optimal vectors out by eye, or longhand, that's what computers are for ;) -- or just apply enough brute force that it doesn't matter if you're inefficient about it :D)


I don't think any of those alternate intercepts are close enough to the target trajectory to matter.
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Re: A Side Affect of Planetary Bombardment
Post by Loren Pechtel   » Tue Nov 15, 2022 12:37 am

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ThinksMarkedly wrote:ʻOumuamua was detected by the Spaceguard survey when its brightness was less than magnitude 20. That was a fast-moving object, small and not very luminous.

According to the ESA's website, Gaia performs one rotation every 6 hours. It has a narrow field of view, so it takes just short of half a year to scan all of it. But it's trying to keep track of one billion stars. The FAQ says "Gaia detects and measures celestial objects (stars, galaxies, quasars and Solar-System bodies) down to magnitude 20.5." That's just one telescope.

As I said above, for them it would be cheap to have lots of telescopes, to provide a full sky survey every week or two.

Plus, something large enough to be a planetary danger will be brighter than something small like 'Oumuamua. I really doubt it wouldn't be picked up at 4 light-minutes.


Detected at 2 light minutes. Spreading carbon dust on the leading edge of your attack object should get it that close against equivalent telescopes.

And note the problem with pushing it with ships--you just push right through it. If a wedge can survive such an impact it would be destroyed--but if a wedge can survive that starships pose an extreme threat to planets and wouldn't be allowed anywhere near them.
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