Orbital Lasers

[Anthony]

Originally Posted by ericthered

Is it? Its my understanding that modern nuclear decoys are essentially very fancy balloons.

For objects in space that are using thrust, it is very hard to disguise their mass. For objects on a ballistic course it is not all that hard.

Originally Posted by AlexanderHowl

Balloons pop in the vacuum of space.

A balloon pops if the pressure difference between inside and outside exceeds the strength of the balloon. Put 1 atmosphere of pressure inside a balloon in space and it almost certainly pops, but there's no reason to do that, it will inflate just fine with much less pressure.

[Anaraxes]

The decoys would need the same mass as a real warhead in order to properly mimic their orbits*. Forcing replacement of a real warhead with a decoy counts as an automatic warhead kill for the defense. If the defense is less than 100% accurate, the offense might as well throw 2 warheads as 1 warhead and 1 decoy. If the decoys mass far less than a real warhead, then you can discriminate them and ignore them (which means they were wasted space, and again might as well be replaced with a real warhead).

--
* I can remember claims from the old SDI arguments about drag and cross-sectional density and momentum, or observing recoil from a relatively low-powered probe pulse, for instance. (One counterargument is of course that the defense might as well go ahead and fry the decoys, too. Why not -- unless you assume some limitations on the defense such as ammunition or tracking or RoF limits in the time available.) One-sentence bullet point arguments like these conceal a great many assumptions, rather than being universal truths.

[Anthony]

Originally Posted by Anaraxes

The decoys would need the same mass as a real warhead in order to properly mimic their orbits*.

After the launch phase you'll be in atmosphere thin enough that atmospheric drag should be moot (and interactions with the solar wind might be below detection threshold, or maskable somehow). Being shot down during launch would be a problem, though if there's only one laser platform it's likely the actual launch will occur on the far side of the planet.

[ericthered]

Originally Posted by Anaraxes

The decoys would need the same mass as a real warhead in order to properly mimic their orbits*

Any discussion you can point to on that star? from my reading, mylar balloons released from an IMBC aren't just an extant technology, they seem to be a standard technology and if there is an easy way to distinguish them from nukes in space, it doesn't show up in a shallow internet search.



If you have negligible atmospheric interference and you don't maneuver the objects, the mass of the orbiting object doesn't matter. Those are two strict requirements, and put a lot of constraints on what you can do, but I never said this was an attempt to hit them. The purpose of such an action is to divert resources away from figuring out where you're hiding your tanks, ammo depots, troops, and so forth. And if they don't respect the threat, maybe I will get a hit in.



If you have some time to do R&D first, you can make course corrections on the far side of the planet, where the aliens can't see how big the burn on each object is. Unless they have satellites stationed all over the globe . In which case you've got targets you can fight more fairly.

[AlexanderHowl]

The problem though is that the spacecraft can just get out of the way (and the decoys are going to spread away from the warheads over 30,000 km of travel unless they also have rockets and guidance systems).

[Michele]

Originally Posted by Anaraxes

The decoys would need the same mass as a real warhead in order to properly mimic their orbits*. Forcing replacement of a real warhead with a decoy counts as an automatic warhead kill for the defense.

That assumes you have to have a 1 for 1 replacement rate. The reason why some posters are discussing balloons and inflatables is, I believe, that they can occupy much less volume during launch, and weigh much less than a warhead. So, they inflate once deployed, and you can have, say, 100 decoys for sacrificing a warhead.
If you calculate that over the time of the attack, the opposition can shoot down 1000 targets, and you have 500 missiles, replacing 10 warheads with 1000 decoys you will be attacking with 1490 targets, of which 490 will be actual warheads. Chances are some will get through.

(One counterargument is of course that the defense might as well go ahead and fry the decoys, too. Why not -- unless you assume some limitations on the defense such as ammunition or tracking or RoF limits in the time available.)
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In fact, the whole basic assumption is that saturation will work: i.e. that those laser batteries cannot fire continuously because they will overheat. if they have no such problem, then no attack will ge through.

[Michele]

Originally Posted by AlexanderHowl

The problem though is that the spacecraft can just get out of the way

Yes, but see post #41. The space station might cover significant distances through hyperspace jumps, and then be very slow in normal space. The possibility of its slowly maneuvering away is covered by the "shotgun" approach of the proposed kinetic and nuclear attack.

(and the decoys are going to spread away from the warheads over 30,000 km of travel unless they also have rockets and guidance systems).

"Ballistic" implies that once the boost phase is over, the thing travels as an artillery round.
That is not true of MIRV missiles, which maneuver to release each individual reentry vehicle on a new course. But of course, in this case (with one target) each MIRV missile can be programmed to work just as a MRV missile, firing all individual warheads together on a pattern-making course. Then the individual warheads would also be simply on a ballistic course.
The only warheads that would be clearly distinguishable from ballistically moving decoys are the MaRVs, which are maneuverable. I say, fire those too, if any are still on inventory.

[Michele]

I just realized that each ICBM available actually could be modified, if there's the time to do that, to carry more payload.
Because a sizable part of the weight of each warhead is the reentry shield that is necessary because of the attrition with the atmosphere, while going down towards a ground target.
With a target in space, the shielding can be significantly reduced and that weight can be taken up by small-sized stuff that can be shaped to take its place, such as chaff packages or more small kinetic projectiles. Once the warhead is on its terminal course, the thinned-down shielding opens up and disperses the additional stuff.

[Rupert]

Originally Posted by Michele

That assumes you have to have a 1 for 1 replacement rate. The reason why some posters are discussing balloons and inflatables is, I believe, that they can occupy much less volume during launch, and weigh much less than a warhead. So, they inflate once deployed, and you can have, say, 100 decoys for sacrificing a warhead.

If the cold war ICBM systems are anything to go by, while they mass much less than a warhead, their volume isn't much less, so one warhead is only replaced by a few decoys. The exchange rate is low enough that there were strong arguments over whether it was worth bothering with decoys over warheads.

[Michele]

Originally Posted by Rupert

If the cold war ICBM systems are anything to go by, while they mass much less than a warhead, their volume isn't much less, so one warhead is only replaced by a few decoys. The exchange rate is low enough that there were strong arguments over whether it was worth bothering with decoys over warheads.

Pity, that.