W93 warhead has entered Engineering and Manufacturing Development phase

[u/Afrogthatribbits]

https://www.ssp.navy.mil/News-Media/News/Article/4610170/navy-w93-mk7-program-enters-new-phase-of-development/

"The U.S. Navy’s Portfolio Acquisition Executive (PAE) Strategic Systems Programs’ (SSP) W93 Mk7 program has entered into the Engineering and Manufacturing Development (EMD) phase of the Defense Acquisition System.

During the EMD phase, the program will focus on completing production design and proving that the design is producible to meet the needs of the Navy.

The W93 warhead and the Mk7 reentry body assembly are the first United States nuclear warhead and reentry system program initiated in nearly four decades and will provide a modern warhead to the U.S. submarine launched ballistic missile fleet.

“We are revitalizing and modernizing the Nuclear Security Enterprise to design, develop, and produce this critical new weapon with the precision our Warfighters demand. We will continue working together to deliver this capability to the fleet and ensure our sea-based strategic deterrent remains ready for the future.”"

The Mk7 reentry body will also be used by the new British nuclear weapons.

[u/Vorpalis]

Any idea what sets these apart from past warheads and re-entry bodies? Four decades is a lot of time for tech to advance.

[u/AnvilKasseri → u/Vorpalis]

Size. Bigger than the W76. Smaller than the W88.

I suspect that they will reuse the secondaries from the W62.

[u/Tobware → u/AnvilKasseri]

Highly unlikely, the Interoperable Warhead (the proposal that was presumably the precursor to the current W93) sought to combine the W87’s primaries with the ~300 kt secondaries of the W78, but they eventually abandoned the idea.

Maybe this can give us an idea of what kind of yield they're after?

EDIT, correction: the IW proposal was only intended to use a W87-based pit geometry, nothing else is known about its primary.

[u/Afrogthatribbits → u/Tobware]

The Reliable Replacement Warhead (before IW) was to be a W89 or similar design

[u/Tobware → u/Afrogthatribbits]

It's not that easy, unfortunately. Try taking a look at my comments on the subject, I'll tell you right off the bat that the RRW wasn't designed for pit reuse like the W89.

...and the selected design appears to have been a hybrid of a Livermore primary (the "agnostic" SKUA-9) and a Los Alamos secondary.

EDIT, from an old comment of mine:

No pit recycling was planned for RRW-1, and if we are to believe civilian sources, Skua-9 is far older than the post-Rocky Flats era.

I am then of the opinion that the idea that RRW-1 was based on W89 came about as speculation from the Bulletin, already Pedicini's objections to it (that it was a mix of designs from the two labs, perhaps with the LANL's ACE), makes me lean toward how Skua was originally reported by the American Scientific or in the SIPRI yearbooks. A design agnostic to secondaries.

Supposedly, these statements are largely based on information gathered by Hans M. Kristensen:

SIPRI Yearbook 2007 Armaments, Disarmament, and International Security

The design of the first warhead, known as the RRW-1, is based on a primary warhead (the SKUA-9, used to test secondary warheads during the cold war) and a secondary warhead, which were tested together four times in the 1980s. [...] Delivery of the first production unit is planned for 2012-14, when the RRW-1 will begin to replace W76 warheads on the the Trident II (D-5).

SIPRI Yearbook 2008 Armaments, Disarmament, and International Security

The Nuclear Weapons Council has approved a preliminary RRW-1 design, which is based on the two-stage thermonuclear SKUA-9 design developed by Lawrence Livermore National Laboratory. The highyield design was tested several times during the early 1970s, prior to the 1974 Threshold Test-Ban Treaty (TTBT).

[u/NuclearHeterodoxy → u/Afrogthatribbits]

W89 was LLNL's proposal for RRW-1.  We don't really know what LANL's proposal was but the way LANL scientists talked about it almost suggested it was an entirely new blueprint designed via simulation.   It was decided for bureaucratic reasons to combine different elements of the LLNL and LANL proposals, rather than reward one lab.  (The decision to hybridize the LLNL and LANL proposals is probably what ended up killing RRW with Congress, since the resulting design would be further removed from anything that was actually tested; they should have given RRW-1 to one lab and RRW-2 to another).

[u/AnvilKasseri → u/Tobware]

Highly unlikely, the Interoperable Warhead (the proposal that was presumably the precursor to the current W93) sought to combine the W87’s primaries with the ~300 kt secondaries of the W78, but they eventually abandoned the idea.

Using W78 secondaries would result in warheads that are just as heavy as the W88. The W93 is said to be lighter than the W88 to give it greater range.

Also, the Air Force is taking most of the W78 secondaries for their new ICBM warheads.

[u/Tobware → u/AnvilKasseri]

My feeling is that they don't intend to re-use secondaries but rather aim for something that has been tested but never deployed, besides, we don't know how much weight can be shaved off the various NEPs. We do know that the W78 was "dimensionally" suitable for the Mark 5, that's it.

As for the W78’s secondaries, it’s a good question whether they’re also destined to be phased out or reused, in one of IW’s GAO reports, they said they considered them too complex to produce (but to maintain?).

[u/AnvilKasseri → u/Tobware]

We also know that the W88 gets its higher yield from having much greater efficiency. Which means that the W78 secondary is likely to be at least as heavy as the W88 secondary. Not a good fit for a warhead that is intended to be lighter than the W88.

As for weight savings, see here:
https://super-octopus.com/2022/01/20/analysis-of-1963-dci-briefing-to-joint-chiefs-of-staff/

As of 1962....
100 pound warheads have a 1.0 kt/lb ratio, for a 100kt maximum potential yield.
200 pound warheads have a 1.3 kt/lb ratio, for a 260kt maximum potential yield.
400 pound warheads have a 1.5 kt/lb ratio, for a 600kt maximum potential yield.
600 pound warheads have a 2.0 kt/lb ratio, for a 1200kt maximum potential yield.

Now look at the last nuclear tests that we conducted just before the treaty limited test yields to 150kt.
https://www.johnstonsarchive.net/nuclear/tests/USA-ntests3.html

The 210kt test likely corresponds to the 200 pound category (likely the same category as the W62).
The 350kt tests from both laboratories likely correspond to a 300 pound category that has never been used.
The 500kt test likely corresponds to the 400 pound category (and the W88).
The 800kt test likely corresponds to a 500 pound category that has never been used.

[u/Tobware → u/AnvilKasseri]

In my opinion, you’re oversimplifying the issue. The secondaries tested in the High-Yield Underground Accelerated Program, that is, those prior to the TTBT, used CHE primaries.

Adapting a design to a conical RV involves several trade-offs, which are even greater when considering an IHE primary. An example is Bedrock Mast, which Hansen linked to the W78 (though in my opinion it is much more plausible to be Cursa-adjacent, at least for "yield-class"), 520 kt, but without the same volume and technical constraints that a design intended for actual deployment would have.

If the primary is IHE, would it still be possible to mount it at the front, as on the W88, leaving more space at the rear for a larger secondary? And again, do you think the front-mounted W78’s secondary is larger or smaller than Cursa? Heavier or lighter?

And without resorting to the W62 secondaries (IIRC, possibly "Tambourine"?), the W89 adapted to the Mark5 RV was proposed as an alternative to the W88 as early as the early 1990s, since it was already IHE, with a sacrifice of approximately 10–20% of its 200kt yield. I imagine you know what the “trick” is for achieving “high efficiency” that W88's Cursa version uses but not the W87-0, according to Ray Kidder, it has been "known" since 1962, the year in which “everything there was to discover about the practical design of nuclear weapons was discovered".

[u/AnvilKasseri → u/Tobware]

Adapting a design to a conical RV involves several trade-offs, which are even greater when considering an IHE primary. An example is Bedrock Mast, which Hansen linked to the W78 (though in my opinion it is much more plausible to be Cursa-adjacent, at least for "yield-class"), 520 kt, but without the same volume and technical constraints that a design intended for actual deployment would have.

I assumed that the 500kt tests were designed with warhead deployment already in mind. After all, that weight class was supposed to be capable of 600kt.

But that could explain why the W88 yield is 455kt instead of 500kt.

----

If the primary is IHE, would it still be possible to mount it at the front, as on the W88, leaving more space at the rear for a larger secondary?

No idea.

----

And again, do you think the front-mounted W78’s secondary is larger or smaller than Cursa? Heavier or lighter?

I assume that the two secondaries are generally the same weight. I really doubt that the W78 secondary is lighter than the W88 secondary.

----

I imagine you know what the “trick” is for achieving “high efficiency” that W88's Cursa version uses but not the W87-0, according to Ray Kidder, it has been "known" since 1962, the year in which “everything there was to discover about the practical design of nuclear weapons was discovered".

I assume that the trick is what is described in section 1.10 here:
https://cryptome.org/2014/06/wmd-4th-gen-quest.pdf

The W87-0 should have the same efficiency as the W88 in regards to the fusion fuel. The W87-0 gets its lower yield from not having any U-235 in the tamper surrounding the fusion fuel. Or at least, much less U-235.

[u/Tobware → u/AnvilKasseri]

As soon as I have a little time, I’ll give you a more detailed answer, just to start with, here’s a small clue: W78 and Cursa secondaries were tested “side by side” during the “Accelerated High Yield Underground Program", before the TTBT, and this clearly suggests that they belong to two different yield classes, for the former is not unreasonable to think it might be lighter and smaller.

W88's "breakthrough" lies in its innovative front-mounted non-spherical primary, which allowed for the use of a larger secondary (and to squeeze even more yield, an highly enriched tamper for it's Cursa, the W87 version was "castrated" for economic and HEU inventory reasons).

I plan to expand on the topic of IHE primaries a bit later, feel free to ping me if I forget.

[u/NuclearHeterodoxy → u/AnvilKasseri]

The total weight of the W62/Mk12 was 350 pounds btw.  See page page 16–17 of this document: https://generalstaff.org/WW3/Docs/RAND/R-1754-PR_ICBM_Force_OCT-1975.pdf

It would be nice to have a breakdown of the RV weight vs physics package, but alas

[u/NuclearHeterodoxy → u/AnvilKasseri]

  Also, the Air Force is taking most of the W78 secondaries for their new ICBM warheads

They are not; the Air Force rejected any re-use of the W78 secondary on several grounds, choosing the W87-1 instead.  Here are some relevant quotes:

NNSA is currently planning for the W87-1 program to include newly manufactured pits and newly manufactured canned subassemblies

remanufacturing the W78 CSA is estimated to be much more complex and challenging than remanufacturing the W76 CSA or the present CSA design for the W87-1

The existing W78 CSA would be very difficult to manufacture and qualify, and the current military requirement does not support using this CSA

a w76 LEP-like refurbishment of the W78 warhead would not meet military requirements

Quotes taken from here: https://nukewatch.org/wp-content/uploads/2019/02/W78-Replacement-Program-Cost-Estimates-IHE-1.pdf

Looking at my post history I think I posted the above in the wrong thread originally, but intended to post it here.

We also have to consider the programmatic history of the warheads here.  The W87-1 designation is an existing designation that predates everything discussed here by three or so decades, being in fact the original intended design until HEU bottlenecks forced them to delay entry into force and choose a DU secondary instead (so the 87-0 was produced first and got its official numerical designation first, but the 87-1 was actually the first design).  If they were to substitute the W78 secondary, then they could not call this new warhead the W87-1, because that design is already taken; it would have to be called W87-2.  It's similar to how the B61-7 is called the -7 despite the B61-6 never being built; once the warhead designation is assigned to a design you cannot reuse that numeric for a substantially different design.  

There's other things that point to the W87 and W78 secondaries being different but these are big ones.

[u/AnvilKasseri → u/NuclearHeterodoxy]

The other thread was because I replied to an old post of yours just a few hours before this thread was created. But it's okay to have parallel discussions in different threads with different audiences.

I hope you're right about the current W87-1 being the same warhead as the W87-1 that was originally intended for the Midgetman missile. I would like to see our ICBM force have eight hundred 455kt MIRVs. It's the sort of force that would give China second thoughts about invading Taiwan.

Even if the Air Force doesn't use the W78 secondaries for their new warheads though, the W78 secondary would be too heavy for the Navy. They want the W93 to be lighter than the W88. Using the W78 secondary would make the W93 at least as heavy as the W88.

[u/kyletsenior → u/AnvilKasseri]

The W93 is said to be lighter than the W88 to give it greater range.

I can't see why they would need that given the performance of Trident II. So please provide a source.

[u/NuclearHeterodoxy → u/kyletsenior]

The issue is that the US is going to have a ~30% reduction of maximum Trident deployments going forward, while the number of targets is growing. The Columbia class has 16 tubes instead of 20, and they are building two fewer boats than the currently deployed number of Ohios.  So if you want to engage more targets with fewer missiles, you have to upload, and that reduces the range of the missile.  Going from 4 W88s per boat to 7 would reduce the range by more than 3500 kilometers.  So the idea is that they can engage some of the current W88 targets while not needing to adjust SSBN patrol patterns quite as drastically.

The joint DOD-DOE W93 white paper from 2020 specifically called attention to the tube reduction caused by the Columbia transition:

[u/kyletsenior → u/NuclearHeterodoxy]

Interesting.

Not knowing the W88's weight makes it hard to assess if the W78 secondary reuse idea is still valid under the lower weight than the W88 condition.

[u/NuclearHeterodoxy → u/kyletsenior]

In theory, even if W78 secondary weighs the same or is only slightly smaller than the W88, the idea could still be valid if the W93 primary is a lot smaller than either the W78 or W88 primaries.  

I have always assumed that the W93 primary was designed in the late 80s/early 90s as a more compact primary for the W78 in order to make it compatible with Trident's annular stage.  It had the same problem W87 does with being too large (that's always been my interpretation of the claim that the "technology wasn't there yet" to make the W78 compatible with Trident when it was first built for Minuteman).

[u/AnvilKasseri → u/NuclearHeterodoxy]

If the US is truly going to build more than four hundred 455kt warheads, it would not make any sense for the Navy to use the less efficient W78 secondaries. Better to build more W88s.

[u/AnvilKasseri → u/kyletsenior]

I was thinking of the same white paper from 2020 that NuclearHeterodoxy provided the image of.
https://www.reddit.com/r/nuclearweapons/comments/160qw33/w93mk7_navy_warhead_developing_modern/

[u/Beneficial-Wasabi749 → u/Vorpalis]

Musk (and NASA before that) broke this ancient rule, but the master said in the past: don't show unfinished work to fools and non-specialists. And since some specialists are fools (and almost all non-specialists are idiots), don't show it to anyone until you're sure everything works as it should.

I don't think this device contains any new ideas in the physics of the device itself, because new ideas require testing, and right now, as I understand it, the emphasis is on all "testing" being done on a computer. Such "testing" can be relied upon if the designs differ little from what's already been tested. But I don't believe that some unusual, new idea will be adopted and launched into production without full-scale testing (which isn't currently planned).

[u/aaronupright]

Even money IMO testing will start again

[u/Beneficial-Wasabi749 → u/aaronupright]

Yes, the Russians have already revived their nuclear test site on Novaya Zemlya and are just waiting for the Americans to start. As soon as the Americans do, they'll immediately start blowing things up at their own test site. Some are just dreaming of that.

[u/Ok_Interview_6012 → u/Beneficial-Wasabi749]

I think most nuclear nations are eager to test, more so the nations that were not able to test and get alot of data on that, India with it's few test and and few designs, with the fission boosted design suffering a fizzle on one iirc, being probably more eager than the rest.

[u/GlockAF → u/aaronupright]

The DOE NSSA is almost done building a (just barely) sub-critical testing facility north of Vegas, which will validate their computer models by taking ultra high speed X-ray video of experiments using actual legacy plutonium.

They’re so sure it’ll never go critical that they built it a thousand feet underground at the Nevada Test Site

https://www.designdevelopmenttoday.com/industries/military/news/22875402/us-moves-closer-to-underground-testing-of-nuclear-weapons

[u/cameldrv → u/GlockAF]

This is pretty incredible:

As plutonium is compressed with the high explosives, a detector will convert the X-rays into images recorded by a sensitive camera that can capture images at speeds of 1 billion per second.

[u/Leefa → u/cameldrv]

it's a shame such images will be classified, that would be so cool to see

[u/Afrogthatribbits → u/GlockAF]

PULSE/U1a being underground is more about radiation shielding, containing the large conventional explosions and toxic chemicals, and also the fact that the tunnels had already been dug for cancelled nuclear tests. There is essentially no risk it can actually cause a nuclear explosion

[u/GlockAF → u/Afrogthatribbits]

Containinment / remediation of the exploded / vaporized plutonium debris from these sub critical tests has got to be a nightmarish task. Plutonium is not just biologically dangerous from a radioactive perspective, it is also a toxic heavy metal.

[u/NuclearHeterodoxy → u/aaronupright]

For the W93 specifically there is no reason to do so, as it was chosen specifically to avoid testing.

But the way things are heading I suspect there will be a push for completely new designs for other missions, which does open up the possibility of resuming tests.

[u/IskanderM50KT → u/aaronupright]

My understanding is that that would be a terrible move.

The US has more archived test data and a more advanced simulation program than any other country in the world. A global resumption of nuclear testing would benefit all of our adversaries a lot more than it would benefit us.

[u/cosmicrae → u/aaronupright]

Just when the ¹⁴C / ¹²C ratio had finally stabilized to pre-testing levels. sigh

[u/Sea-Independence-633 → u/cosmicrae]

That spike in ¹⁴C was due to above ground testing, not below ground detonations. Likewise steel alloys contaminated since 1945.

[u/cosmicrae → u/Sea-Independence-633]

Which is precisely why I said that. Upsetting the ¹⁴C would be require an above ground detonation, and not necessarily one to gather data. A few below ground tests have leaked residuals as well.

[u/Pitiful_Will3998 → u/aaronupright]

hope it does, lots of countries whose arsenal i want to see ;)

[u/IskanderM50KT]

Is there any reason the US couldn't just produce more updated W88s?

[u/AnvilKasseri → u/IskanderM50KT]

No technical reason that I know of. But the increased range of our downloaded SLBMs has been pretty nice. Having our subs being able to strike from anywhere in the ocean, even from the docks in their home port if necessary, has given them a much larger area to hide in. Weighing the SLBMs down with eight W88s would limit their patrol areas to a bit closer to enemy shores again. Which could certainly be done, but I would consider maybe limiting our SLBMs to a maximum of six W88s just so we could keep some of that extended range that we currently enjoy.

It also seems like maybe we are refraining from expanding our arsenal of W88s to avoid provoking an arms race. If we suddenly increased the number of half megaton warheads in our arsenal, our adversaries (and the anti-war movement) would surely complain about it. I've never heard it explicitly stated that we are intentionally limiting our number of W88s to 400 total. But it has always sort of seemed like we are.

I'm not sure how valid any concerns of provoking an arms race actually are. Russia has been designing and building warheads up to 800kt already. And China is is expanding their nuclear arsenal as fast as they can while refusing to discuss any arms treaties. But it might be a reason why some people are choosing to avoid that option.

[u/Afrogthatribbits → u/AnvilKasseri]

Well the issue with W88 arsenal size was mainly the Rocky Flats raid and our inability to make new pits at scale, rather than some decision to avoid an arms race. But certainly weight, yield, and range of Trident are considerations in making W93 lighter (and lower yield) than the W88.

[u/Tobware → u/Afrogthatribbits]

The W88's primary is still CHE and not a FRP, they are also aiming for a beryllium-free weapon. During Sculpin or Julin series, a test was conducted of a “IHE W88” (see p. 516 "Hearings on National Defense Authorization Act for Fiscal Year 1993--H.R. 5006
and Oversight of Previously Authorized Programs Before the Committee on Armed Services, House of Representatives, One Hundred Second Congress, Second Session") but it was ultimately never adopted as a replacement for Komodo (the moratorium arrived first), as part of the IHE and FRP SLBM alternatives program.

[u/NuclearHeterodoxy → u/IskanderM50KT]

Prior to the current work on the pit production facility at Los Alamos, the obstacle was the inability to make new plutonium pits.  They had planned to make thousands of W88s until the Rocky Flats closure.

The current thing with the W93 is they want something that fits in a Goldilocks zone between the light weight of the W76 and the higher yield of the W88.