# Stopping an ICBM with an orbital interceptor

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In a conversation I was having with a guy, he was going on about how the USA might have secret orbital anti-ballistic missiles.  I thought it was highly unlikely, but I can't prove the USA doesn't secretly have them, so I tried to argue it was basically unfeasible.

I only have a rough idea.  ICBMs from the main semi-unfriendly nation (russia) with a lot of them launch from various bases and come over the North pole on the way to the USA.  The ballistic trajectories have a very high apoapsis and the missile doesn't have the energy for orbit, at least not while carrying it's warhead.

As near as I can tell, your interceptors would have to be in low earth orbit, in some kind of polar orbit, flying the opposite direction from the tracks the ICBMs would take.  Essentially the parabola of the ascending and descending ICBM is going to intersect the orbital altitude of the interceptor twice.  So the interceptor needs to be there when it happens.   Err, maybe not, maybe the interceptor needs to use an energy minimization algorithm where it considers a number of points on the missile's ascending and descending arcs and the missile would need to use a gradient descent to find the point that requires the lowest energy for an intercept.  Essentially solving this problem with realtime numerical integration of different strategies to find the one to use this time.

That means you'd need a lot of interceptors, enough that one is passing by a given point every few minutes.  And they'd need high thrust engines and a lot of dV. Basically an entire rocket stage, in orbit.  I'm not quite sure roughly how much dV you'd need - I want to say it would be around a kilometer per second but I'm not sure how to go about calculating this.

How would you calculate the requirements?

Edited by SomeGuy123
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Forget about parabolas, they're only perfect escape trajectories in orbital mechanics, and even then they're impossible to get (like circular orbits).

You'd have to liken the trajectory of the missile to an orbit around the center of mass. Then you'd have to do rendezvous calculations.

Edited by Bill Phil
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Playing a bit with mechjeb intercept at selected time and adjust closes distance give you some ideas.
Its not so hard to get the dV requirements, harder to hit something at orbital speeds but it has been done by ground based interceptors.

Interceptor would be based in polar orbit or close to it, you then have to do plane changes and burning pro/ retro grade and normal to intercept target while within you dV budget.
No reason to be retrograde compared to the missiles, it would even make intercept harder as the relative speeds would be higher.
Most interceptors would be in wrong position so you would need lots of them just to have some positioned correctly, an pretty high orbit is also an benefit as it makes orbital adjustments easier.

None so system is operational we know as it would not be practical without many satellites.
Ground based interceptors looks cheaper, in space lasers would be more practical as it can start shooting during boost phase into atmospheric reentry.

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Terrible terrible idea. The key isn't the energy to intercept, it's the time. If interceptors are on known orbits (and they would be known, if not acknowledged), it would be utterly trivial to launch a missle in a window such that no orbital weapon could ever hope to intercept it, even if the sky were flooded with them.

It may, on the other hand, be a good location to base a laser net. Except the power requirements are the limitation for that.

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In all public plans the orbital interceptors, their amount varies from hudreds to thousands - and this is only for the case when ICBMs fly along one fixed direction (the shortest one). Both, with missiles or lasers.
As ICBM flight time is 20..40 min, while an orbital period is ~90, only, say, a quarter of them could be used in the required moment. And most of them at incorrect position angles.
Post-boost vehicles launch multiple false targets, which makes orbital anti-missiles almost useless.
So, the only realistic way to use them was protection of their carrier (Almaz-based orbital station) launching them head-on from the short distance into the directly incoming missile.

International treaties are written not by naive romantics, but by dull bureaucrats.
They almost always prohibit not something terrible, but something treated as useless but expensive by both sides, Just to avoid headache to themselves and each other, after numerous attempts to create it.

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13 minutes ago, kerbiloid said:

In all public plans the orbital interceptors, their amount varies from hudreds to thousands - and this is only for the case when ICBMs fly along one fixed direction (the shortest one). Both, with missiles or lasers.
As ICBM flight time is 20..40 min, while an orbital period is ~90, only, say, a quarter of them could be used in the required moment. And most of them at incorrect position angles.
Post-boost vehicles launch multiple false targets, which makes orbital anti-missiles almost useless.
So, the only realistic way to use them was protection of their carrier (Almaz-based orbital station) launching them head-on from the short distance into the directly incoming missile.

International treaties are written not by naive romantics, but by dull bureaucrats.
They almost always prohibit not something terrible, but something treated as useless but expensive by both sides, Just to avoid headache to themselves and each other, after numerous attempts to create it.

Decoys would be an serious challenge as you say, an direct energy weapon would do better as it would pop the decoy fast. It would also have much easier doing an intercept during burn phase.
Lots of the SDI ideas was not practical, part of it was also an obvious bluff like the SSTO idea, part of the idea was to push the arms race into space and advanced weapons where the US had an benefit, if they got an effective missile defense it would be an bonus.

The ABM treaty was limited to ground based interceptors, it has also expired.
Ground based interceptors is that has been easiest to make, know the US navy standard missile has abm and anti satellite capabilities, US also have another system for this, Russia has S-400.

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5 minutes ago, magnemoe said:

an direct energy weapon would do better as it would pop the decoy fast.

Boeing airborne laser distance stays unknown, but the program was closed, What probably means not so much successful results,
Chelomei's project meant 1500 orbital lasers to be effective,
The only real known practical orbital anti-ICBM laser plant massed 100 t and required an Energy launch.
So, looks like lasers are not so good, too.

9 minutes ago, magnemoe said:

The ABM treaty was limited to ground based interceptors

Was limited to 100 (?) ground interceptors in one region. This could intercept several occasional launches, just not to be Strangeloved.

12 minutes ago, magnemoe said:

it has also expired.

Orbital weapons are still prohibited, while ABM treaty is cancelled only by one side (which means, the another one still takes this sceptically).

14 minutes ago, magnemoe said:

the US navy standard missile has abm and anti satellite capabilities, US also have another system for this, Russia has S-400

Able to intercept tactical missiles, and mostly in tests.
Compare amount of successful ballistic tests against the amount of successful (?) ABM launches, The former arre routine, the latter are always events.

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2 hours ago, magnemoe said:

Ground based interceptors is that has been easiest to make, know the US navy standard missile has abm and anti satellite capabilities, US also have another system for this, Russia has S-400.

There is very serious doubt that the US has any practical anti-ballistic missile capability. The country has been spending a LOT of money trying to develop the capability to intercept even a single launch from a "rogue nation" (aka North Korea) and the tests have failed more often than they have succeeded. Note they have failed when the defense system knew the simulated attack was scheduled and also knew the approximate trajectory of the simulated attack.

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6 hours ago, kerbiloid said:

The only real known practical orbital anti-ICBM laser plant massed 100 t and required an Energy launch.

Are we even sure 1 MW of the Skif-D was enough for ABM work?

4 hours ago, mikegarrison said:

There is very serious doubt that the US has any practical anti-ballistic missile capability. The country has been spending a LOT of money trying to develop the capability to intercept even a single launch from a "rogue nation" (aka North Korea) and the tests have failed more often than they have succeeded. Note they have failed when the defense system knew the simulated attack was scheduled and also knew the approximate trajectory of the simulated attack.

One should distinguish between the three layers of US ABM. The massive mid-course interceptors are a total failure, there's only 16 of them or so. Terminal defense (THAAD, Patriot) is more credible, but still highly unreliable without Sprint and its neutron bomb warhead.

The only real hope is to deploy SM-3s close enough to beat ICBMs during the boost phase, back when the missile is big and full of fuel. Which is why Russian planes keep buzzing Aegis-equipped ships in the Baltic and the Black Sea:

Spoiler

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1 hour ago, DDE said:

Are we even sure 1 MW of the Skif-D was enough for ABM work?

One should distinguish between the three layers of US ABM. The massive mid-course interceptors are a total failure, there's only 16 of them or so. Terminal defense (THAAD, Patriot) is more credible, but still highly unreliable without Sprint and its neutron bomb warhead.

The only real hope is to deploy SM-3s close enough to beat ICBMs during the boost phase, back when the missile is big and full of fuel. Which is why Russian planes keep buzzing Aegis-equipped ships in the Baltic and the Black Sea:

THAAD was the other system, why have two systems, that and the other is SM-3s,
SM-3 hit that satellite, yes its an known trajectory and an larger target but relative speed would be higher.
Most of the focus is on slower and shorter range missiles anyway.

Think 1 MW is set as the requirement for ABM, you would want more of you can, think the heat shield on an icbm warhead make it an harder target.
One interesting thing here is the current trend with semiconductor lasers

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Skif-D probably doesn't tell you very much about what would be needed for orbital ABM work, given soviet laser tech of the time. The contemporary US equivalent, ZENITH STAR, was only to be about forty metric tons, and it'd probably be a good bit less with modern electronic lasers.

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9 hours ago, mikegarrison said:

There is very serious doubt that the US has any practical anti-ballistic missile capability. The country has been spending a LOT of money trying to develop the capability to intercept even a single launch from a "rogue nation" (aka North Korea) and the tests have failed more often than they have succeeded. Note they have failed when the defense system knew the simulated attack was scheduled and also knew the approximate trajectory of the simulated attack.

"Chasing" a launch from North Korea (with the anti-ballistic missile in South Korea*) is likely possible.  The big issue is time to launch, and just how expensive (read how much delta-v you require them to burn before go-nogo with the interceptors) any decoys would be be.  This wasn't really considered on Reagan's original Star Wars dream as the USSR was simply too big.

I wouldn't be too surprised if you could re-purpose an existing ICBM (with quick launch capability required in the cold war) by using a lighter warhead for more delta-v (a stern chase is a slow chase, but that makes it easier to hit in the end).  This might be too inexpensive for the DoD and partner/contractors.

* maybe in submarines.  Since Seoul is within artillery range of N. Korea, this might not be popular among the Koreans.  I wouldn't be surprised if the Chinese didn't at least have a bunch of proposals (i.e. they probably aren't ready to build it, just think about it) for building the same (i.e. stop N. Korea from firing an ICBM anywhere) simply to keep China and the rest of the world intact.

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After all, the problem is with MIRVs. One nuke is OK, but multiple nukes (MIRV) would be impossible to do. That's how deterrence and MAD works.

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5 hours ago, Kryten said:

US equivalent, ZENITH STAR, was only to be about forty metric tons

only forty tons... Still requires an Energy-class booster. Greater than shuttle's payload.
Also, relating to topic, not much 40-t peaceful satellites to cosplay

5 hours ago, magnemoe said:

SM-3 hit that satellite, yes its an known trajectory and an larger target but relative speed would be higher.

Speeds are almost similar, as ICBM speed is near-orbital.
And the target satellite moves along the predictable stable regular orbit, rather than the ICBM single-use trajectory.
Satellite trajectory is known, not estimated.
Satellite doesn't use jammers and decoys.
Unlikely the satellite is 200 kg heavy and 40 cm thick.
Also if a warhead would maneuver, things are even worse for the ABM.

1 hour ago, wumpus said:

I wouldn't be too surprised if you could re-purpose an existing ICBM (with quick launch capability required in the cold war) by using a lighter warhead for more delta-v

Afaik, some studies about Minutemans repurposing took place.

USSR unlikely was afraid of DPRK launches, As 70s USA also. But 100 ABM is enough to intercept an occasionally launched MIRV.

Edited by kerbiloid
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16 minutes ago, kerbiloid said:

only forty tons... Still requires an Energy-class booster. Greater than shuttle's payload.

They were initially going to use a bespoke Titan variant, Barbarian. A big vehicle for sure, but not Energiya-class. They later switched it to a dual-launch architecture with a pair of Titan IVs.

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You could do it, but it would take a lot of satellites. Whats hard is the MIRVs.

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5 hours ago, Kryten said:

They were initially going to use a bespoke Titan variant, Barbarian. A big vehicle for sure, but not Energiya-class. They later switched it to a dual-launch architecture with a pair of Titan IVs.

Barbarian looks AWESOME!!!

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Knocking down a few missiles is not implausible (i.e.: a small attack from a rogue state), and the technology should be pursued, IMO. The old 1980s idea of a "ballistic missile shield" was always silly, however. I knew people working on it at the time (many people paid off their student loans writing SBIRs for SDI stuff, lol), and they all knew that even given a magical weapon system that could kill targets X per minute, they'd not be able to parse the targets among various satellites given communications lag without many platforms deciding that the same target was the one to deal with first. So for a few targets, it's just an engineering problem, but for the notional "full strike" of the Cold War era, it just was;t ever going to happen.

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21 minutes ago, tater said:

Knocking down a few missiles is not implausible (i.e.: a small attack from a rogue state), and the technology should be pursued, IMO. The old 1980s idea of a "ballistic missile shield" was always silly, however. I knew people working on it at the time (many people paid off their student loans writing SBIRs for SDI stuff, lol), and they all knew that even given a magical weapon system that could kill targets X per minute, they'd not be able to parse the targets among various satellites given communications lag without many platforms deciding that the same target was the one to deal with first. So for a few targets, it's just an engineering problem, but for the notional "full strike" of the Cold War era, it just was;t ever going to happen.

This, now add jamming and asat weapons.
It was mostly an bluff, however it was an bluff they knew Soviet would follow up on and it would push the weapon race in an more hightech direction where the US had benefits.
It was other bluffs with weapon capabilities, the Soviet had always bluffed a lot however it was harder to do in the west as it was so open. You could however bluff with weapon capabilities and future plans.

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4 minutes ago, magnemoe said:

This, now add jamming and asat weapons.
It was mostly an bluff, however it was an bluff they knew Soviet would follow up on and it would push the weapon race in an more hightech direction where the US had benefits.
It was other bluffs with weapon capabilities, the Soviet had always bluffed a lot however it was harder to do in the west as it was so open. You could however bluff with weapon capabilities and future plans.

Countermeasures would always be cheaper than SDI itself, but they knew that even in the 1980s. Better to have a countermeasures arms race than piling up more weapons.

I think that the ability to knock out a small, or even an accidental attack would be a certain plus as a capability.

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19 hours ago, magnemoe said:

One interesting thing here is the current trend with semiconductor lasers

The current trend with semiconductors is because the requirements for combat lasers have been reduced drastically. They're now designed to kill plastic drones and thin-skinned mortar bombs; combined with improved laser technology, this has allowed for the first lasers to be deployed in the field, but it's far from factual that these improvements can be applied to ABM work. In particular, beam combiners cannot be used to match singular emitters in terms of effective range.

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5 hours ago, DDE said:

The current trend with semiconductors is because the requirements for combat lasers have been reduced drastically. They're now designed to kill plastic drones and thin-skinned mortar bombs; combined with improved laser technology, this has allowed for the first lasers to be deployed in the field, but it's far from factual that these improvements can be applied to ABM work. In particular, beam combiners cannot be used to match singular emitters in terms of effective range.

Another use, think they aim for 100-150 kw also for use on planes both for easy ground targets like cars and for defense against anti air missiles.
However good point about combined beams, the tactical version will have limited practical range to perhaps 10 km so you don't care if the beams is not perfectly aligned.
For ABM we talk some thousand km and 10 times as powerful

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I was always impressed by Escape Dynamics' work toward microwave powered flight (using a ground-based heating device to heat H2 in the rocket.  Instant 800 ISP).  Unfortunately, the microwave on the ground would be impossibly expensive (I doubt the company could really afford the vehicle, but the engine was the killer).  Last I checked, the Navy was developing a laser with the wattage needed by Escape Dynamics (note that a laser weapon likely needs full power for much less than a second, while the launch vehicle needs it the entire launch (or at least until it has reached a sufficient apoapsis and preferably an insertion burn (although that is likely through too much atmosphere).

Who knows, maybe such weapon research will find its way into a similar launcher.

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2 hours ago, wumpus said:

I was always impressed by Escape Dynamics' work toward microwave powered flight (using a ground-based heating device to heat H2 in the rocket.  Instant 800 ISP).  Unfortunately, the microwave on the ground would be impossibly expensive (I doubt the company could really afford the vehicle, but the engine was the killer).  Last I checked, the Navy was developing a laser with the wattage needed by Escape Dynamics (note that a laser weapon likely needs full power for much less than a second, while the launch vehicle needs it the entire launch (or at least until it has reached a sufficient apoapsis and preferably an insertion burn (although that is likely through too much atmosphere).

Who knows, maybe such weapon research will find its way into a similar launcher.

It seems that a given laser design can maintain continuous fire as long as power and cooling last.

I'm not sure about the Navy's Free Electron Laser.

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Orbital kill is easy, if you don't care too much about mucking up space for a bit.

Simply launch a few dozen rockets into suitable polar orbits, each dispenses a few hundred microsats.

Each microsat contains a hundred grams or so of ballbearings, on a spring load. And a teensy gyro for pointing, and a remote guidance and trigger.

you can basically *flood* an area of LEO several square kilometers with 1 gram ballbearings, evenly spread and with a relative velocity of about 18 km/s

No need for exacting timing, or aim. just dump enough mass in the path.

Each bearing will have the impact energy of TEN .50cal BMG rounds, enough to shred an armored truck, much less an icbm.

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