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What would a Kinetic Orbital Bombardment Strike looks like?


RainDreamer

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1 hour ago, Jonfliesgoats said:

Fixed targets would still be doable with INS.

For manned capsules, there is a period of maximum aerodynsmic pressure which also corresponds to maximum heating and maximum ionization.  When you run the numbers for high angles, say 45, the reentry vehicle continues to accelerate all the way to the surface and generates tremendous heat and ionization.  It never slows down.

Check out formulae 4.1.7-7 and 4.1.7-8.  

https://www.faa.gov/other_visit/aviation_industry/designees_delegations/designee_types/ame/media/Section III.4.1.7 Returning from Space.pdf

 

Yes INS works not sure how large the error will be on impact, the shuttle used an antenna in the rear who communicated with satellites during the first part of decent but most of the braking here will be deep down. Will it be any better than an ICBM warhead? 
Looks like you will not get terminal guidance, you can get this on shorter range ballistic missiles but they don't reach reentry speeds. 
 

Edited by magnemoe
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3 hours ago, cantab said:

I don't think the projectile would be obscured by plasma all the way, would it?

Something "telephone pole" shaped would retain most of it's speed all the way to impact, so yes it will be obscured by plasma all the way down.
 

3 hours ago, cantab said:

Inertial guidance has relatively low precision though. A JDAM bomb has a Circular Error Probably of 30 m with inertial guidance


The CEP of an inertial system depends on a number of factors, such as the precision of the initial position, the precision of the control systems, and the precision of the inertial system itself.  You can only buy so much for $22k/unit (2007 dollars) even with mass production, and only fit so much into a space not much bigger than a coffee can.  (And I doubt that they're babied, calibrated, and aligned to the level we did in the Navy for SLBMs.)  Trident-II, which travels much (much) further than the JDAM (and spends most of it's flight time coasting with no controls whatsoever) has a CEP of 90 meters.  I can't find an exact number, but sifting through the web it seems a MK6LE Trident II guidance system (which is physically larger than the JDAM guidance system+electronics) runs somewhere in the neighborhood of $750k/unit.  (And unlike JDAM, that figure does not cover the control systems, which are part of the missile.)

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On 3.11.2016 at 11:14 PM, DerekL1963 said:

Something "telephone pole" shaped would retain most of it's speed all the way to impact, so yes it will be obscured by plasma all the way down.

The CEP of an inertial system depends on a number of factors, such as the precision of the initial position, the precision of the control systems, and the precision of the inertial system itself.  You can only buy so much for $22k/unit (2007 dollars) even with mass production, and only fit so much into a space not much bigger than a coffee can.  (And I doubt that they're babied, calibrated, and aligned to the level we did in the Navy for SLBMs.)  Trident-II, which travels much (much) further than the JDAM (and spends most of it's flight time coasting with no controls whatsoever) has a CEP of 90 meters.  I can't find an exact number, but sifting through the web it seems a MK6LE Trident II guidance system (which is physically larger than the JDAM guidance system+electronics) runs somewhere in the neighborhood of $750k/unit.  (And unlike JDAM, that figure does not cover the control systems, which are part of the missile.)

Yes, note that an jdam is supposed to use gps, inertial is an fallback if it looses the gps signal or get an weak one. As the gps will update the inertial system all the time so if gps is jammed or blocked the last kilometer it would not have much effect. 

is the nuclear warheads updated by gps while in space? Might not be needed as 90 meter should be close enough for an nuclear bomb. it would also be dangerous to depend to much on gps for nuclear weapons who is an fallback if everything else fails including gps. 

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8 hours ago, magnemoe said:

Yes, note that an jdam is supposed to use gps

True, but even so the effectiveness of it's controls limits what it can do.  (It's a kit that bolts onto the tail of something that was never meant to glide in the first place.)
 

8 hours ago, magnemoe said:

is the nuclear warheads updated by gps while in space?


No, mostly because the warhead is coasting at that point.

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On 03/11/2016 at 10:14 PM, DerekL1963 said:

Trident-II, which travels much (much) further than the JDAM (and spends most of it's flight time coasting with no controls whatsoever) has a CEP of 90 meters.

A 90 m CEP is good for a nuke, but it's not so great for a less powerful weapon. For a 10 ton impactor at Mach 10 (with kinetic energy equivalent to its own mass in TNT), the radius to damage "heavily built concrete buildings" is about 20 metres, while for more ordinary buildings it's about 100 metres. I'm not so sure about effectiveness against underground bunkers. Regardless, if you're targeting a reinforced structure you probably want much more precision. Laser-guided bombs can manage a CEP of *one* metre, and probably other systems where the projectile is able to 'see' the target can do the same.

Back to the original question of what a rods-of-god strike would look like, well before impact it would probably be just like a nuclear missile re-entry such as this famous(ish) Peacekeeper shot:

Peacekeeper-missile-testing.jpg

Although that's a long exposure, I don't know how bright the projectiles would look to the eye.

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@kerbiloid That's a really great find! And I think pretty much finalises answering @RainDreamer 's original question, because these unarmed re-entry vehicles are very much like an orbital strike projectile would be, impacting at the same kind of speed quoted as 16000 km/h (or Mach 13, or 4500 m/s). I can't find the mass of the re-entry vehicle, but changing mass should just scale up or down the effects anyway.

A bright bolide flying across the sky, then at the impact site a relatively small fireball and a larger cloud of debris thrown into the air, with fragments landing considerably further away. Almost surely an impact crater and probably a blast, but the video doesn't have close-ups or audio to confirm.

It's not dissimilar to my prediction on page 3, the biggest difference seems to be that hitting a real-world target throws up a lot more fine dust that lingers, compared to hitting a uniform bed of sand.

I think the video also demonstrates that if the guidance was precise enough, an ICBM with kinetic impact warheads would be an effective weapon. Value-for-money is another matter though, and there are concerns that the target and third parties might detect an ICBM launch and assume it was carrying a nuclear weapon and react accordingly.

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On 5.11.2016 at 3:43 PM, DerekL1963 said:

True, but even so the effectiveness of it's controls limits what it can do.  (It's a kit that bolts onto the tail of something that was never meant to glide in the first place.)

No, mostly because the warhead is coasting at that point.

Ok so jdam accuracy is mostly an control issue. Know that the small diameter bomb is far more accurate on gps. 

Looks to me that if the warhead could correct trajectory in space and also using ins during reentry it would boost accuracy a lot. 

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18 hours ago, cantab said:

I can't find the mass of the re-entry vehicle

Estimated ~200..300 kg in this case. Several different types.
Unlikely a ten times heavier one could make a Londocalypse.

13 hours ago, magnemoe said:

Looks to me that if the warhead could correct trajectory in space and also using ins during reentry it would boost accuracy a lot. 

But maybe not. Presuming that GPS gives exact coordinates and computer allows to build an ideal accurate trajectory, you still have atmosphere with air flows and ablation which makes parasite reactive propulsion, projectile's body oscillations and so on.
Maneuverable warheads were tested long ago, say http://space.skyrocket.de/doc_sdat/ogch.htm

Edited by kerbiloid
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