There are those in NASA who have had the crazy idea that maybe, just maybe, NASA should live up to its mandate and actually move outwards into the cosmos. In order to do that, you need power, and until magic comes along, nuclear power is best power. Yesterday there was a media event in support of the “Kilopower” initiative to develop one-to-ten kilowatt nuclear power reactors. Given that the SP-100 project to develop 100 kilowatt reactors began on the order of 40 years ago, one kilowatt seems kinda unaggressive…but given that right now the United States has *no* kilowatt reactors under development for space power… I’ll take it.

The Soviet Tsar Bomb, dropped in 1961 and with a yield of around 50 megatons (backed down from the design yield of 100 megatons) is acknowledged as the biggest bomb ever tested. But is it the most powerful bomb ever designed, or ever built? I’ve discovered some snippets of evidence that the US *may* have designed, and even built, an even bigger bomb.

Several frustratingly unenlightening reports give bits and pieces of information on a bomb code-named “Flashback.” This device was apparently air-dropped near Johnston Atoll. “Flashback” was designed by Sandia Labs and flown from Kirtland Air Force Base to Oahu, Hawaii and then to Johnston Atoll. There are some Terrible Quality Photos:

The Flashback bomb was so big that it could not quite fit within the confines of the B-52 bomb bay, and required the removal of the bomb bay doors.

Of course, this could have been purely an aerodynamic shape. Or perhaps it was a large conventional bomb, a giant “Daisy Cutter.” Or perhaps it wasn’t an actual bomb as such, but just some sort of science experiment to be dropped from an aircraft. Lots of possibilities. But those possibilities drop away with some of the hints that are provided, such as:

This came from an electromagnetic radiation effects report, describing – seemingly – the effect of radio emissions from the B-52 upon the electronics of the Flashback bomb. Since the bomb projected well below the belly, it was subject not only to very cold temperatures but also to intense radio transmissions from the antennae below the B-52 fuselage, so it makes sense they’d test for that. You don’t want the B-52’s communications to cause the bombs fuzing to go screwy. In this particular test, the parachute was not packed within the tail of the Flashback; instead test instruments were fitted there. More tellingly, “All HE (high explosive) and nuclear components were deleted.” Emphasis mine. Additionally, “A simulator was used to replace the warhead.”

You don’t have a warhead in a science package. You don’t have nuclear components in a conventional bomb. and if this was simply an aerodynamic and mass simulator of a proposed bomb… you wouldn’t remove the nuclear materials, because you wouldn’t have installed them in the first place. You don’t fill a mockup full of jet fuel, after all.

Such details as the weight of the unit and the yield of the device are seemingly not given. But they can be guessed at. A report on testing of the tailfin has this:

I’m not quite sure how that load of 36,000 pounds would relate to any actual forces applied to an actual bomb, but it *may* indicate the weight.

Other reports list the sizes and weights of items to be shipped to Oahu (and then to Johnston Atoll) for the test. Some of them are intriguing… what is “EMPTV?” TV certainly means “test vehicle.” But does “EMP” mean Electromagnetic Pulse? If so, does that mean another bomb-like unit, or just a science package, meant to be *hit* with an EMP to see how it reacts? Or is it a specific EMP generator, to be dropped out of an aircraft? Whatever it is, it weighed 14,500 pounds and was around 221 inches long and perhaps 59 or so inches in diameter, and was quite classified (SRD = Secret Restricted Data… “Data concerning the design, manufacture, or utilization of atomic weapons; production of special nuclear material; or use of special nuclear material in the production of energy“).

And there’s 38,000 pounds of “test equipment,” which could be anything:

There was also this:

Here, the “BTV” is the “Big Test Vehicle,” 25,000 pounds, 309 inches long by up to 76 inches in diameter, also classified SRD. Big as this is, though, it’s possibly not the device hanging below the B-52’s belly; the BTV is referenced several times in a way that seems to make it distinct from the Flashback Test Vehicle. But perhaps they are the same thing.

The Flashback Test Vehicle, fortunately, was shown in a fair diagram of a wind tunnel model. Full scale, it was 297 inches long (not counting parachute pack or what appear to be antennae) and was ~96 inches in diameter. This makes it bigger, and presumably heavier, than the BTV. So 36,000 pounds is not unreasonable.

Other ill-described tests show the Flashback as a much smaller unit than the bomb. This, *perhaps,* is merely the “physics package” of the device. This test, illustrated with one of histories worst-quality photos, was carried out in a very cold high altitude chamber, and shows two more mysteries: the “Companion Test Vehicles,” or CTVs, which are unexplained. Speculating wildly, they might have been designed to have the same ballistic properties as the Flashback, so if you drop them from the B-52 along with the Flashback, they’ll fall along with it, following the same trajectory and staying reasonably close. Perhaps thy had cameras. perhaps they had sensors. Perhaps they had transmitters. Who knows.

And there was also the “UTV.” No further data.

Perhaps the Flashback, BTV, EMPTV and UTV were all different sizes of new gigantic bombs…?

Code names generally have no relationship to the subject, but are chosen essentially at random. One would never know that “Copper Canyon” was a program to develop a scramjet SSTO. Similarly, “Operation Paddlewheel” tells nothing. But perhaps, just barely, “Flashback” might have some meaning. Comparing the Flashback to the Tsar Bomb, it it remarkable how similar they are in terms of both size and shape. One might be forgiven for wondering if Flashback was the end result of someone trying to design a Really Big Bomb based on nothing more than a verbal description of the Tsar Bomb, given, perhaps, by a spy or defector. So *perhaps* this project was a “flash back” to the earlier Soviet design. If so, what was the purpose? Was it to give the United States the same insanely pointless capability? Or was it just to find out what the capabilities and limitations the Soviets had gifted or saddled themselves with?

Using the wind tunnel model diagram, I’ve reconstructed the Flashback to scale with the Tsar Bomb:

As can be seen, the Flashback had much the same configuration, but was substantially “fatter.” Impossible to say if that was because the US designers needed the extra diameter to get the same yield (theoretically 100 megatons), or if Sandia Labs went head and designed themselves an even bigger bang. What use is a 200 megaton bomb? Not much. But then, neither is a 100 megaton bomb, especially one so big that the carrier aircraft essentially has to *lumber* to the target all the while carrying the worlds largest bullseye.

As always, if anyone has any further info, I’d love to see it.

PS: I’ve taken the Flashback model and have turned it into 2D CAD diagrams, including scale comparison with the Tsar and showing it stuffed into the B-52’s belly. This diagram will be one of this months rewards for Patrons of the APR Patreon. A simplified version will be included at the $5 level; the full diagram will be in the $8 level rewards package. So if you’d like access… sign up for the APR Patreon.

UPDATE:

It’s good to get a fresh perspective. Sadly, the perspective emailed to me was that the Flashback sure looked like a missile nosecone. So I pulled up the Flashback diagram I made from the wind tunnel model diagrams and put the RV from the Titan II ICBM on top of it. It’s not an exact match, but it’s distressingly close. If it wasn’t for the noticeably larger radius of the Flashbacks nose, I’d say it was spot-on… the outer diameter and angle are incredibly close matches.

So…what would be the point of that? Some sort of science experiment, clearly, rather than a weapons test. But what point would there be in dropping a Titan RV from a B-52? Why dangle it from a chute? Why add the heavy tail & fin assembly?

If it turns out that this was an experiment with the Titan RV, that would be less interesting than the revelation that the US developed a 50 to 100 megaton nuke. But it’s still interesting. Just not *as* interesting.

Just stumbled across some *terrible* quality photos from circa 1967 showing a B-52 with its bomb bay doors removed and a bomb stuffed in and partly protruding since it was too big to actually fit within. This was the “Flashback,” best as I can tell, and seems to have been designed as an actual nuke, and perhaps built as an actual nuke. It was apparently tested somewhere near Oahu without the nuclear bits. The reports I have are stunningly unenlightening, but this seems to have been a full-up weight & aerodynamics & instruments/electronics test for a bomb that was just way too damn big. Currently working on putting together diagrams, because why wouldn’t I.

This seems new to me. But is it just something I seem to have missed in my reading, something everybody always knew about?

A 1966 Aerojet concept for a space probe with a nuclear reactor and ion engines. Note the largish thermal radiator “wings;” such things are usually left off spacecraft in science fiction, but they are a vital part of any nuclear spacecraft. Nukes, after all, are simply heat sources; in order to get useful electrical power out of them, the heat must be used to boil a working fluid which runs a turbogenerator; and the hot gas then needs to be condensed back to a liquid by radiating the heat way to space. And thermal radiation is a terribly slow and weak process, necessitating large radiators. Electricity can also be created with thermionic systems, which generate electricity across a thermal differential… hot on one side, cold on the other. But unless the cold side it attached to some radiators, the cold side will soon be just as hot as the hot side, and then… no thermal differential, no power generation.

Note also that even with a substantial powerplant and the sizable bank of ion engines, acceleration is going to be creakingly slow. Thus you can get away with spindly structures. The reactor itself is the tiny little tin can-looking thing, top and centerline; the U-shaped structure around it is a radiation shield protecting the electronics, structure and radiators from the radiation spat out by the reactor.

The Hawaii Emergency Management Agency just sent out a helpful text message:

There is a small issue with the message. Guess what it might be. Go on, guess.

A video of the 27 May 1956 “Yuma” test from Operation Redwing. This was a small “boosted” fission bomb… 5 inch diameter, designed for air defense use (back when nuking formations of Soviet bombers seemed like it was going to be a thing). The process was that a small fission explosion would set off a small fusion booster… not quite a true H-bomb. In an H-bomb, the fission bomb is “merely” the trigger… a several kiloton fission bomb sets off up to many megatons of fusion explosion, with the fusion yield being up to 20 times that of the fission. In a boosted weapon, a sub-kiloton or low-kiloton fission bomb sets off the fusion booster which doesn’t itself amount to a whole lot of “bang,” but it releases a flood of neutrons which makes that fission explosion a whole lot more efficient and powerful. The neutrons released by the initial fission explosion can cause the lithium-6 in the lithium deuteride booster to fission into tritium; the conditions next to the fission blast are hot enough that the tritium will happily fuse with the deuterium, spitting out neutrons which will race back into the fission explosion and cause more of the plutonium to fission. (Done right, a surrounding case of non-fissionable depleted uranium can add to the power of the blast, as the high energy neutrons from the booster are powerful enough to cause U-238 to fission.)

It’s all well and good, but the resulting bang is a little less impressive when the fusion booster doesn’t actually go off. Which is what happened during the Yuma test, resulting in a paltry 0.19 kilotons yield. Data is sketchy, but I’d imagine the goal was to get close to one kiloton out of the device.

While poking around one of my old computers I found the partially finished 3D CAD model of the Martin “Aldebaran” I made some years ago for my NPP book. I’ll use the model to create diagrams for the book, in hopes that someday I’ll finish the damn thing, but I’m curious if there might be interest in physical models of the thing. Let me know. I might take a stab at this with Shapeways or some such.

Mobile energy depot feasibility study: summary report

Description:

Declassified 28 Aug 1973. Various methods of producing and using nuclear power for military land vehicles and other military equipment were investigated and evaluated. A nuclear-powered mobile energy depot (MED) would move with advancing armies and produce vehicle fuels from materials readily available in the field. This would make mechanized units independent of external fuel supplies for extended periods, and permit them to move quickly and easily to areas impossible for units that depend on the customary fuel supply lines. Many possible MED systems were evaluated on the basis of energy sources, fuel manufacturing (by both conventional and chemonuclear processes), fuel storage and transportation, and fuel utilization in both present-day internal-combustion engines and power units of the future (i.e., fuel cells). The applications of more than a dozen MED systems to vehicular propulsion were studied.

The report can be downloaded directly from HERE.

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Cherenkov radiation is something you are unlikely to experience in the natural world.This visible blue light is the “shock wave” produce when something travels faster than the local speed of light. The speed of light in transparent substances such as glass and water than be substantially lower than it is in a vacuum, so high energy particles can easily be FTL in those media.

Nuclear reactors generate just such high energy particles. And they are often immersed within pools of water for both shielding and cooling. Thus… Cherenkov radiation, and thus this spiffy collection of videos showing just how fast reactors start cranking out the rads upon startup.

Also:

https://www.youtube.com/watch?v=UxQdS0pbpKo

This sort of thing is unlikely to appear outside of a reactor environment. If you are in space, high energy cosmic rays that penetrate your eyeballs can create tiny flashes of Cherenkov radiation within the vitreous humor, an effect that astronauts have note since the earliest days of spaceflight, something sure to freak the fark out of space tourists. But these are instantaneous phenomena, not steady state ghostly glows. If you do stumble across something out in the wild causing the water, air or glass around it to glow like Dr. Manhattan, you may well have stumbled across something that it would be best to stumble away from.

And as to how good that water shielding is? Your average human would probably look at that Cherenkov radiation and assume that the water ain’t doin’ diddly. But things like electrons *aren’t* photons, and they don’t pass through water as easily as simple light does. This “What If” from XKCD explains it well.

There is apparently some discussion about parking some THAAD missiles along the west coast to protect against the likes of a Nork missile. The THAAD isn’t a full-up anti-ICBM system, but it’s the best the US currently has for land-based systems. It’s also the only missile in operation that has an important subsystem (the igniter) designed by *me.* So there.