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Old 01-19-2019, 10:47 PM   #11
Rupert
 
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Default Re: Orbital Lasers

Using Spaceships it'll probably have two TL9+ fusion systems, each massing 150,000 tons, and costing $30 billion.

Each of those forty 100GJ lasers masses ~15,000 tons and costs $1.5 billion.

Just the weapons and power supply for them costs $120 billion. The whole ship is probably about $400 billion (so about three years procurement spending for the US military). Even for a TL9-10 multi-system empire it's not a minor asset, and I suspect that with four secondary laser batteries it's a fairly specialised ship.
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Old 01-19-2019, 11:11 PM   #12
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Default Re: Orbital Lasers

Assuming the space laser works as the OP described, the Earth's best chance is to overaaturate the laser's defenses with massive nuclear assault. Have the US and Russia launch all their remaining nukes at it at once, assuming ICBMs could pull off that altitude. Depending on genre, that can be handwaved. It is doubtful it could shoot down a couple thousand missiles at once, if it is decked out the way the OP describes.

Of course, if it has even ine point defence system, that would fail, too, and Earth is just doomed.
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Old 01-19-2019, 11:44 PM   #13
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Assuming the space laser works as the OP described, the Earth's best chance is to overaaturate the laser's defenses with massive nuclear assault. Have the US and Russia launch all their remaining nukes at it at once, assuming ICBMs could pull off that altitude. Depending on genre, that can be handwaved. It is doubtful it could shoot down a couple thousand missiles at once, if it is decked out the way the OP describes.

Of course, if it has even ine point defence system, that would fail, too, and Earth is just doomed.
Just out of curiosity - how does this ship arrive in system? How long does earth have to respond to this potential issue?

Just curious.
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Old 01-20-2019, 02:04 AM   #14
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Assuming the space laser works as the OP described, the Earth's best chance is to overaaturate the laser's defenses with massive nuclear assault. Have the US and Russia launch all their remaining nukes at it at once, assuming ICBMs could pull off that altitude. Depending on genre, that can be handwaved. It is doubtful it could shoot down a couple thousand missiles at once, if it is decked out the way the OP describes.

Of course, if it has even ine point defence system, that would fail, too, and Earth is just doomed.
ICBMs don't have the reach to get to geosynchronous orbit altitude, so far as I can tell.

As for getting them shot down, The travel time will give plenty of time to shoot them with a battery capable for 120 shots per minute.
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Old 01-20-2019, 02:10 AM   #15
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Default Re: Orbital Lasers

With a spacecraft of these characteristics, anyone could get the governments of the world to accept all kinds of proposals as long as they are not eradicated.
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Old 01-20-2019, 02:22 AM   #16
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Neutron bombs have extremely low area of effect, their radiation has less penetration than standard nuclear weapons...
Nuclear blasts in space are extremely limited in effective radius, especially if the surface of the target has even light armor. Neutron bombs bypass that armor effectively, and therefore increase the effective radius of the warhead.

Whereas a small nuke might need to be within a few hundred meters to score a single-hit kill purely based on the thermal effects, the neutrinos and radiation would kill or sicken the crew if it goes off within kilometers of the target.

Considering the limited time to prepare, I'd recommend that everyone on the far side of the earth when the attack began should prepare literally every spaceflight capable rocket (from ICBMs to sounding rockets or even models) to launch simultaneously. As many of those as possible should be armed with nuclear warheads. As many of the armed missiles as is reasonably possible should have their re-entry shield replaced with graphite or other refractory materials, which will ablatively shield the missile.

Hopefully, the large scale of the wave will provide sacrificial targets that will take the initial brunt of the attack. The graphite will boil away, taking a great deal of energy with it. Hard to estimate how it will hold up to high-energy lasers (the spot size, pulse duration, wavelength, etc, etc, are unknown), but maybe it'll give you a chance.

This goes out the window with an alien ship, but still, people would give it a try.
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Old 01-20-2019, 03:08 AM   #17
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Nuclear blasts in space are extremely limited in effective radius, especially if the surface of the target has even light armor.
That's not really so. The energy that would go into the shockwave and a portion of the thermal pulse in an atmosphere remain as a very powerful x-ray pulse in space. X-rays have fairly good penetration and those that don't penetrate any armour will heat it greatly and very rapidly, quite possibly causing it to vaporise or turn into plasma. Given the extremely short time in which that will happen, that will cause a powerful shock to the ship.

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Neutron bombs bypass that armor effectively, and therefore increase the effective radius of the warhead.
Neutron shielding is fairly easy to install, and fuel tanks of hydrogen, etc., are quite effective neutron barriers.
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Old 01-20-2019, 06:37 AM   #18
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I agree. The neutrons produced by neutron bombs tend to be in the keV range, so a meter of liquid hydrogen will absorb them quite nicely. Also, any carbon-based armor would be quite fine, as it would also absorb the neutrons without issue.

Anyway, why would anyone want a neutron bomb? They are quite literally the most useless nuclear weapon. Their only utility in warfare was a marginal increase in the radioactivity of the detonation site, as the metals in the area become somewhat radioactive, but it greatly reduced the destruction power of a nuclear weapon to do so. It was why the US shelved the neutron bomb program after billions of dollars of development, because it was a less than useful weapon.
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Old 01-20-2019, 07:48 AM   #19
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Anyway, why would anyone want a neutron bomb? They are quite literally the most useless nuclear weapon. Their only utility in warfare was a marginal increase in the radioactivity of the detonation site, as the metals in the area become somewhat radioactive, but it greatly reduced the destruction power of a nuclear weapon to do so. It was why the US shelved the neutron bomb program after billions of dollars of development, because it was a less than useful weapon.
Actually, at the time they made sense as a tactical weapon - they could neutralisel the tanks of the 60s fairly effectively by killing their crews. However, later tanks were much less vulnerable to neutron flux, and so the bombs were no longer more effective than normal tactical nukes of the same size and mass.
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Old 01-20-2019, 08:06 AM   #20
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Just out of curiosity - how does this ship arrive in system? How long does earth have to respond to this potential issue?

Just curious.
Well, I am assuming that it is a FTL capable spacecraft that enters normal space at a 10 AU FTL limit. Assuming 1g acceleration, the Earth may have a week, if anyone detects it immediately. Of course, the spacecraft would have mobility, but it would be primarily a subjugation station, meant to keep the primitives out of the way while the aliens establish a military station around Saturn and mining stations throughout the Sol System.

In that case, the aliens would probably just want to make sure that nothing leaves the atmosphere of the Earth. They would probably vaporize anything substantial in orbit, just in case it was a hidden weapons platform, which would play havoc with communications, GPS, weather forecasting, etc. After cleaning out the orbits of Earth, it would proceed to remove any launch capabilities of the Earth, probably targeting any ICBMs or similar weapon systems. When it was done with removing launch capabilities, it would probably just maintain watch over the Earth from GSO, in case humanity tried anything clever.
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