LGM-35A Sentinel - Ground-Based Strategic Deterrent (GBSD) program

[Josh_TN]

Well, Falcon-9 Block 5 could launch about 5.800 kg on GTO. More than enough for a bus, several warheads, and retro-rocket booster (since the system is space-based, we could afford to use storable liquid-fuel and get more specific impulse than solid fuel could).

For example: let's use the old "Chevaline" missile bus for our calculations (there are a lot of data for it). It's about 318 kg fueled, and designed for 400 kg payload (warheads, decoys, chaffs, ect.). So we could safely fit three W76 warheads on it, and have enough mass for decoys.

Extracting 750 kg of payload mass from 5800 kg allowance, we are left with about 5 tons for propulsion. Let's assume that we use RD-864 hypergolic rocket engine, with a specific impulse of 300 s and dry mass of 200 kg. Let's also assume that tanks, frames, ect. are about 800 kg of total mass.

So we are left with 4000 kg of propellant for a 1800 kg of everyting else, and we have 300 s ISP engine. We could have delta-v supply around 3.4 km/s - more than enough for de-orbiting and even some maneuvering.

And how many LEO satellites could you have for the same cost/effort? And how much cheaper is it to build the ASAT weapon that will engage the RV, since it only has to go up not back down? What does this buy you over a silo solution?

 

[Dilandu]

And how many LEO satellites could you have for the same cost/effort?

LEO warheads are much worse solution; the reaction time is very short for both sides. I.e. the opponent have little time to react on your bombs (which made them a perfect first-strike weapon) and you have very little time to react on attack on your bombs (which made them poor retaliatory weapon).

 

[Forest Green]

Well, if the warhead on high orbit, they aren't very destabilizing - the long delivery time (hours/days) and easy observation made them totally unsuitable for any kind of first strike (i.e. making them a purely retaliation weapon).

Any warhead in orbit is already an attack in progress IMO.

 

[VishnuOsiris]

Any warhead in orbit is already an attack in progress IMO.

FWIW, at one point they had nuclear-armed B-52 Chrome Domes orbiting the Soviets for a ~decade. Dr. Strangelove told me they were 2hrs away from their targets by design. IMO, through clear, overt and signaled doctrine, one can normalize warheads in orbit the same way Launch-on-Warning ICBMs were normalized. I think the space/time dimensions of where/when these weapons are on standby or deployed is relative.

 

[Josh_TN]

FWIW, at one point they had nuclear-armed B-52 Chrome Domes orbiting the Soviets for a ~decade. Dr. Strangelove told me they were 2hrs away from their targets by design. IMO, through clear, overt and signaled doctrine, one can normalize warheads in orbit the same way Launch-on-Warning ICBMs were normalized. I think the space/time dimensions of where/when these weapons are on standby or deployed is relative.

Normalization of warheads constantly in the air/orbit hardly seems like a good idea.

Some additional issues with orbital weapons: what do you do if one fails? How do you retire them? How secure is your command link to those satellites? Every other deployment scheme involves a human launch officer colocated with the weapon turning a key or entering a PAL code. Orbit removes that safeguard.

 

[VishnuOsiris]

Normalization of warheads constantly in the air/orbit hardly seems like a good idea.

More of less agreed, but if it's going to happen anyway due to wide proliferation, better to get ahead of the curve.

Some additional issues with orbital weapons: what do you do if one fails?

Going back to the Chrome Dome example, we have these incidents C/O wiki:

• 1961 Goldsboro B-52 crash (project "Cover All")
• 1961 Yuba City B-52 crash (project "Cover All")
• 1964 Savage Mountain B-52 crash
• 1966 Palomares B-52 crash
• 1968 Thule Air Base B-52 crash. The Thule accident signaled the end of the program on January 22, 1968.

IMO, with the exclusion of Thule, you cross that bridge when you come to it. Accidents will happen, but they will be the exception not the norm. Perhaps there will be great luck involved if (AFAIK) most debris will land in an ocean.

 

[Forest Green]

FWIW, at one point they had nuclear-armed B-52 Chrome Domes orbiting the Soviets for a ~decade. Dr. Strangelove told me they were 2hrs away from their targets by design. IMO, through clear, overt and signaled doctrine, one can normalize warheads in orbit the same way Launch-on-Warning ICBMs were normalized. I think the space/time dimensions of where/when these weapons are on standby or deployed is relative.

Disagree, it's about timescales and also relative danger. Bombers are slow and even ICBMs take 25-30mins. Satellites don't always stay in orbit either and whilst a crash might not cause detonation, nukes randomly landing in random countries isn't a particularly good idea.

 

[Dilandu]

Any warhead in orbit is already an attack in progress IMO.

On high orbit, I repeat. From which the descent time is significant.

 

[Dilandu]

Satellites don't always stay in orbit either and whilst a crash might not cause detonation, nukes randomly landing in random countries isn't a particularly good idea.

Try to calculate the delta-v required to deorbit a satellite from semi-stationary orbit, for example.

 

[VishnuOsiris]

Disagree, it's about timescales and also relative danger.

Fair enough. But it's not just the timescales that are relative. One also must account for the psychology of your adversary's decision-making. Risk/Reward, Pros/Cons, the Stakes and how much one stands to lose if they make the wrong call, etc.

IMO, the psychology of a weapon on standby in orbit isn't any less existential threat than the BMs, however to both of your points, it is admittedly more terrifying and destabilizing (initially ). I don't think this is an unbreachable barrier to entry for the concept though.

I'm more or less riffing here, so no shame in dismantling this. I'm not married to the idea.

 

[Josh_TN]

More of less agreed, but if it's going to happen anyway due to wide proliferation, better to get ahead of the curve.


Going back to the Chrome Dome example, we have these incidents C/O wiki:

• 1961 Goldsboro B-52 crash (project "Cover All")
• 1961 Yuba City B-52 crash (project "Cover All")
• 1964 Savage Mountain B-52 crash
• 1966 Palomares B-52 crash
• 1968 Thule Air Base B-52 crash. The Thule accident signaled the end of the program on January 22, 1968.

IMO, with the exclusion of Thule, you cross that bridge when you come to it. Accidents will happen, but they will be the exception not the norm. Perhaps there will be great luck involved if (AFAIK) most debris will land in an ocean.

Aircraft losses at least involve a bomb landing in an area that can be searched. There were accidents at U.S. silos as well. What if you broken arrow is in orbit? How do you safely bring that back, or else eject it from orbit altogether?

And that was only one of the several complications I brought up.

I suspect the U.S. will never base its own nuclear weapons on orbit just for control reasons alone. That means it will almost certainly actively engage attempts to orbit nuclear weapons instead .

 

[VishnuOsiris]

Aircraft losses at least involve a bomb landing in an area that can be searched. There were accidents at U.S. silos as well. What if you broken arrow is in orbit? How do you safely bring that back, or else eject it from orbit altogether?

I addressed this earlier. AFAIK most debris or "losses" will land in an ocean, the exception will be land masses. I'm presuming I have that right. Along the same line of thinking, one could consolidate losses and broken arrows in a similar fashion. IMO it may be preferrable to otherwise deorbit and dump them in the ocean. To your other questions, I don't know. That will require someone with greater expertise to articulate.

Also, I never said anything about Nukes in orbit. I was referring more or less to Brilliant Pebbles. Re: BMs, I was thinking Prompt Global Strike.

 

[Josh_TN]

I addressed this earlier. AFAIK most debris or "losses" will land in an ocean, the exception will be land masses. I'm presuming I have that right. Along the same line of thinking, one could consolidate losses and broken arrows in a similar fashion. IMO it may be preferrable to otherwise deorbit and dump them in the ocean. To your other questions, I don't know. That will require someone with greater expertise to articulate.

Also, I never said anything about Nukes in orbit. I was referring more or less to Brilliant Pebbles. Re: BMs, I was thinking Prompt Global Strike.

Conventional weapons seem off topic and I have no problem basing them in orbit. It seems quite clear China will do so as soon as it is able.

 

[uk 75]

We were fortunate right up to the end of the Cold War that US and Soviet leaders were men who had experienced the horrors of World War 2. They were rational and intimidated by the apparatus of nuclear deterrence.
Unfortunately today the reverse is true. Most leaders have not experienced war at first hand. Nuclear deterrence is discussed either in historical or polemic language.
To be blunt Xi and Trump have led war free lives compared with Bush Sr and Gorbachev or Kennedy and Kruschev.

 

[Forest Green]

Fair enough. But it's not just the timescales that are relative. One also must account for the psychology of your adversary's decision-making. Risk/Reward, Pros/Cons, the Stakes and how much one stands to lose if they make the wrong call, etc.

IMO, the psychology of a weapon on standby in orbit isn't any less existential threat than the BMs, however to both of your points, it is admittedly more terrifying and destabilizing (initially ). I don't think this is an unbreachable barrier to entry for the concept though.

I'm more or less riffing here, so no shame in dismantling this. I'm not married to the idea.

The psychology is such that it will likely result in the immediate shoot-down of such an object, hell I certainly would. Nobody is prepared to live under that threat and the Outer Space Treaty prohibits it.

As for events in the '60s, insanity was rife at the time when it came to nukes.

Try to calculate the delta-v required to deorbit a satellite from semi-stationary orbit, for example.

What's the purpose of placing one at 20,200km altitude?

 

[VishnuOsiris]

The psychology is such that it will likely result in the immediate shoot-down of such an object. Nobody is prepared to live under that threat and the Outer Space Treaty prohibits it.

As for events in the '60s, insanity was rife at the time when it came to nukes.

Maybe... maybe not. Rational actor, maybe. Maybe not. We can't take into consideration future circumstances of decision-making until they happen, because we cannot predict the future.

As for the events in the current era, insanity is rife when it comes to nukes (and war in general)

META: I would prefer to move on from this topic and get back to the thread. You win.

 

[Forest Green]

Maybe... maybe not. Rational actor, maybe. Maybe not. We can't take into consideration future circumstances of decision-making until they happen, because we cannot predict the future.

It's unmanned and a treaty breach, plain and simple. The vast majority of nations will support such a disposal.

As for the events in the current era, insanity is rife when it comes to nukes (and war in general)

I don't actually think it is, bluffing is rife.

 

[VishnuOsiris]

It's unmanned and a treaty breach, plain and simple. The vast majority of nations will support such a disposal.


I don't actually think it is, bluffing is rife.

That's great. Think what you want. We have differing opinions. Regardless, both of our opinions are irrelevant with regards to how the future unfolds. No one knows anything to a certainty. This includes whether or not an entity decides to abide by a treaty or not. The INF Treaty is an example that comes to mind as something that was, and is no longer. I never thought I would see a 3rd European land war... ever.

No more of this please. I'm tapped out FR.

 

[NMaude]

There's one problem with orbital nuke RVs (And their associated bus) and that's the issue of accuracy, unless the RV is equipped with a terminal homing seeker it's going to be very inaccurate necessitating a multi-megaton yield warhead.

Another problem with a high earth orbit that no one has considered here are the Van Allen radiation belts, the inner belt in particular.

 

[Dilandu]

There's one problem with orbital nuke RVs (And their associated bus) and that's the issue of accuracy, unless the RV is equipped with a terminal homing seeker it's going to be very inaccurate necessitating a multi-megaton yield warhead.

Another problem with a high earth orbit that no one has considered here are the Van Allen radiation belts, the inner belt in particular.

True. On the other hand, with flight time in hours (or even days) warhead could use celestial navigation to get a near-perfect descend trajectory. Also, since its a retaliatory weapon by definition, the use of megaton-class warheads is perfectly justified.

Another problem with a high earth orbit that no one has considered here are the Van Allen radiation belts, the inner belt in particular.

Its a problem if warhead orbit inside the belt. If its merely cross it two times (first when launched, second when deorbited) its of no consequence. A short run through belt would not affect the warhead much.

More actual problem is a logistic of servicing the orbiting warhead. Its likely that space deterrence warhead would need to be designed very specifically to last long without needed to be serviced. Which would require... unorthodox design solutions, and maybe the whole warhead architecture.

P.S. Or, we could replace the warheads often, using a robotic crafts to launch warheads up & re-entry them. In diassembled state, of course, with final accembly only when warhead is loaded on carrier platform.

 

[Josh_TN]

Tritium replacement surely would problematic, but as I noted there are a huge number of life cycle concerns to address assuming such an action did not immediately lead to orbital conflict.

 

[Scott Kenny]

As is, warheads cross the Van Allen belts twice. Particularly the inner.

 

[bobbymike]

A good discussion by my learned SPF associates but given this is the Sentinel thread specifically maybe move to

https://www.secretprojects.co.uk/threads/nuclear-weapons-discussion.40043/

 

[Forest Green]

That's great. Think what you want. We have differing opinions. Regardless, both of our opinions are irrelevant with regards to how the future unfolds. No one knows anything to a certainty. This includes whether or not an entity decides to abide by a treaty or not. The INF Treaty is an example that comes to mind as something that was, and is no longer. I never thought I would see a 3rd European land war... ever.

No more of this please. I'm tapped out FR.

One of the main reasons the INF failed was because only two parties were signed up to it and it was also poorly written banning both conventional and nuclear weapons of that range but with dubious loopholes. The Outer Space Treaty is much clearer and far more people are signed up.

Outer Space Treaty - Wikipedia

en.wikipedia.org

 

[Kat Tsun]

Space basing nuclear warheads is an incredibly destabilizing idea. If some other country begins doing so, the U.S. will hand choice but to respond, but it is a road best avoided if possible.

"Destabilizing" is the path ahead regardless. The weaponization of low orbit is inevitable given the costs of lift to orbit dropping. Brilliant Pebbles and SDI for a Soviet-style attack are almost doable for a strategic, Apollo or Manhattan-type program nowadays. GPALS is trivial in terms of cost and USA has achieved 80-90% of it with decreasing year on year defense spending. A Chinese PLARF (1,000 warheads) attack would be right in the middle of the two.

Space basing of nuclear warheads, or basing on the Moon as a second strike, are simply the long term knock on effects of this.

Simply shooting them down would be the easier option. Then what?

You shoot back with your surviving warheads, bombers and SSBNs. It's not much different than being attacked by stealth bombers over a missile field or having a SSN attack a SSBN during a trail.

How technically feasible would it be for any advancing nation to send a spacecraft to grab some warheads from orbit?

For what purpose? The general threat of "snatching" warheads has always been protestors and anti-nuclear groups looking to embarrass powerful people and basically nothing else. An SOF team would just blow up the TEL with LAWs or grenade machine guns and leave. Terrorists prefer to go to the Third World to buy yellowcake direct to refine in safehouses using homebuilt centrifuges. An attack on an orbital satellite carrying strategic weapons would be like attacking an SSBN. You just don't do it.

The idea of a terrorist group snatching a warhead from an orbital missile silo and secreting away in some abandoned capsule is pretty cool but also very science fiction-y. Actual space incidents involve high level diplomacy between secretaries of state and ministries of foreign affairs and a lot of questions being asked about what the fuck is that thing doing in our orbital band. Grabber arms and net launchers are optional.

The U.S. PLA Strategic Support Force "dogfight" exercises that happened last year are public record now.

https://www.cnn.com/2025/03/21/china/china-space-force-dogfighting-satellites-intl-hnk/index.html

Suffice to say they aren't interesting in stealing warheads but would absolutely be interested in inspecting them with baby Canadarms.

One of the main reasons the INF failed was because only two parties were signed up to it and it was also poorly written banning both conventional and nuclear weapons of that range but with dubious loopholes. The Outer Space Treaty is much clearer and far more people are signed up.

Outer Space Treaty - Wikipedia

en.wikipedia.org

Someone will make the fatal mistake of claiming SDI is against the Outer Space Treaty, and it will collapse, like the ABM Treaty before it. Europe is probably conscripting entire acres of forest to tell the world why a net launcher and an oversized shotgun are "weapons of mass destruction" for the purposes of the Outer Space Treaty.

Tritium replacement surely would problematic, but as I noted there are a huge number of life cycle concerns to address assuming such an action did not immediately lead to orbital conflict.

The militarization of space will lead to permanent basing of maintenance and combat personnel in space.

Most likely they're just pure fission bombs for extremely accurate first-strikes against hard targets and SSBNs shift to the population annihilators with high yield warheads. An on-orbit W76 Mod 2 would alleviate the Navy of the need to expend partial missile loads on hard targets and allow them to expend all available warheads on every city in range.

 

[Josh_TN]

I think it’s important to split out two concepts: militarization of space and nuclearization of space. Yes, space is a military domain and will remain so, and it would be foolish for the U.S. to not firmly and explicitly establish both offensive and defensive systems in orbit. However basing nuclear weapons there comes with a raft of problems, most of which no one has addressed. More over I believe the U.S. would be unwilling to allow warheads to overfly it territory on a daily basis and would have the means to both inspect satellites for nuclear materials and engage those suspected of carrying warheads.

 

[Scott Kenny]

I think it’s important to split out two concepts: militarization of space and nuclearization of space. Yes, space is a military domain and will remain so, and it would be foolish for the U.S. to not firmly and explicitly establish both offensive and defensive systems in orbit. However basing nuclear weapons there comes with a raft of problems, most of which no one has addressed. More over I believe the U.S. would be unwilling to allow warheads to overfly it territory on a daily basis and would have the means to both inspect satellites for nuclear materials and engage those suspected of carrying warheads.

The US allows overflight by kinetic WMDs daily already.

 

[Josh_TN]

The US allows overflight by kinetic WMDs daily already.

Not familiar with what you’re referring to.

 

[flateric]

Can you tell me what it all has to do with LGM-35A Sentinel ICBM?

 

[Scott Kenny]

Not familiar with what you’re referring to.

Any 2000+lb satellite, if dropped at the correct angle, will impact the earth. And land at sufficient speed that we're getting into "packing its own weight in TNT" or higher.

 

[Dilandu]

Any 2000+lb satellite, if dropped at the correct angle, will impact the earth. And land at sufficient speed that we're getting into "packing its own weight in TNT" or higher.

It would require 3+ km/s to make an energy equivalent of its mass in TNT. Which is hardly WMD-grade damage.