Jan 172018

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.


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.

 Posted by at 9:31 pm
Jan 142018

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.

 Posted by at 2:38 am
Dec 202017

Mobile energy depot feasibility study: summary report


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.

Support the APR Patreon to help bring more of this sort of thing to light!




 Posted by at 10:15 am
Nov 142017

A while ago an ebay seller had a display model of a maneuverable re-entry vehicle, a warhead for an ICBM.There was apparently no documentation to go with it, so details are pretty much utterly lacking. Still, it does look reasonably likely to have been a “real” display model built by or for the USAF or a defense contractor. It’s simple… a cone with four sides shaved off with four added flaps for control. This basic geometry has been popular for maneuverable warhead concepts for decades; McDonnell-Douglas used a similar shape (explicitly stated as having been derived from their maneuverable MIRV studies) for their Delta Clipper SSTO, and an even closer shape for their X-33 and follow-on concepts.

 Posted by at 12:28 pm
Nov 052017

Currently being sold on ebay is a display model of a missile, a “Martin ASM.” ASM almost certainly means “Air to Surface Missile,” but otherwise there’s no further info. Seller seems to think it’s related to the Assault Breaker project, but it looks vaguely like a Skybolt-ish air-launched ballistic missile.





 Posted by at 5:59 pm
Sep 212017

Now available: two new US Aerospace Projects issues. Cover art was provided by Rob Parthoens, www.baroba.be

US Bomber Projects #20:XB-59 Special

US Bomber Projects #20 is now available (see HERE for the entire series). Issue #20 collects all the previously published articles and diagrams of the XB-59 antecedent designs and updates them. Additionally, more antecedent designs have been included as well as several designs that followed along after the XB-59. The biggest USXP publication yet!

USBP 20 includes twenty nine unique aircraft concepts (the usual issue of USXP has eight designs) from Boeing Models 484 and 701 showing how Boeing evolved the XB-59, their competitor to the Convair B-58 “Hustler.” Beginning with subsonic flying wings, the concept saw concepts both conventional and unconventional before eventually settling on Model 701-299-1, the final XB-59 design. This issue includes a half dozen Model 701 designs that followed along after the cancellation of the XB-59 program.


USBP #20 can be downloaded as a PDF file for only $8:



US Launch Vehicle Projects #04

US Launch Vehicle Projects #04 is now available (see HERE for the entire series). Issue #04 includes:

  • Space Carrier Vehicle: A US Army lunar rocket with 8 F-1 engines
  • Convair Reusable Helios: A stage-and-a-half monster with a gas core nuclear engine
  • Boeing Model 896-111: A 1980’s two stage transatmospheric vehicle
  • Project RAND Satellite Rocket 3-Stage: A 1947 satellite launcher
  • Convair Saturn V-R: An idea on how to make a fully reusable Saturn V first stage
  • Lockheed STAR Clipper: A 1968 stage-and-a-half lifting body Space Shuttle
  • Shuttle-C: The  Shuttle derived vehicle design that came closest to being built
  • Titan III Growth/156-inch boosters: A more powerful version of the Titan III for Dyna Soar launch


USLP #04 can be downloaded as a PDF file for only $4:


Also recommended, these previous Specials:

US Bomber Projects #14: System 464L Special

USBP#14 brings together the competitors to Weapon System 464L, the first major effort in the Dyna Soar program. These designs were previously shown individually in prior issues of USBP; here they are brought together, with some updates, as well as a few extra diagrams and a section of diagrams formatted for 11X17 printing. This issue includes info and diagrams of the Lockheed, Republic, General Dynamics, McDonnell, Boeing, Douglas, Northrop, North American and Martin-Bell entries as well as their various booster systems. Also included are detailed diagrams of the ultimate Dyna Soar design, the 2050E.

USBP#14 can be purchased for downloading for the low, low price of $6.


US Bomber Projects #16: The B-52 Evolution Special

Boeing Model 444 A: A late war turboprop heavy bomber
Boeing Model 461: An early postwar turboprop heavy bomber
Boeing Model 462: A large six-turboprop ancestor of the B-52
Boeing Model 462-5: A six-turboprop B-52 ancestor
Boeing Model 464-17: 1946 four-turboprop strategic bomber, a step toward the B-52
Boeing Model 464-18: a reduced-size version of the 464-17 turboprop strategic bomber
Boeing Model 464-25: a modification of the 464-17 turboprop bomber with slightly swept wings, among other changes
Boeing Model 464-27: a slightly-swept turboprop B-52 progenitor
Boeing Model 464-33-0: A turboprop B-52 predecessor
Boeing Model 464-34-3: A turboprop B-52 predecessor
Boeing Model 464-40: The first all-jet-powered design in the quest for the B-52
Boeing Model 464-40: The first all-jet-powered design in the quest for the B-52
Boeing Model 464-046: A six-engined B-52 predecessor
Boeing Model 464-49: The penultimate major design in the development of the B-52
Fairchild M-121:A highly unconventional canard-biplane
Convair B-60: A swept-wing turboprop-powered derivative of the B-36
Douglas Model 1211-J: An elegant turboprop alternative to the B-52
With additional diagrams of the B-47, XB-52 and B-52B

USBP#16 can be purchased for downloading for the low, low price of $6.



 Posted by at 7:51 am
Sep 102017

Recently on ebay were a set of 8X10 glossies, vintage Convair artwork depicting early spacecraft and launch vehicle concepts. I had my bid in… and was sniped in the last few seconds. Oh well. Anyway, one of the more interesting images was this one of the Convair “Helios” developed by or for Krafft Ehricke… a chemical rocket first stage equipped with wings for glide recovering and a nuclear powered second stage with a “tractor” arrangement to separate the nuclear engine from the payload – essentially a small manned laboratory to land on the moon. The second stage would unreel something like half a miles worth of cabling  and drag the payload along behind it, relying on distance rather than physical radiation shielding. The second stage would take the payload all the way to the lunar surface, gently lowering it down at the end of the cables, then land Way Over There Somewhere. A modern design would, I would hope, include electrical cables and would serve as a power generator.

A middling-resolution scan of the same image was posted back in January. One day I shall get a clean high-rez version. If that day is a particularly glorious day, it will come not only with the other images created for the Helios project… but they’ll also be in color.

 Posted by at 1:02 am
Jul 162017

Every month, patrons of the Aerospace Projects Review Patreon campaign are rewarded with a bundle of documents and diagrams, items of interest and importance to aerospace history. If you sign up, you get the monthly rewards going forwards; the “back issues” catalog lets patrons aid the APR cause by picking up items from before they signed on. The catalog, available to all patrons at the APR Patreon, has been updated to include everything from the beginning of the project back in 2014 on up to February, 2017.

Below are the items from 2016 (and the first two months of 2017):


If you are interested in any of these and in helping to fund the mission of Aerospace Projects Review, drop by the APR Patreon page and sign up. For only a few bucks a month you can help fund the procurement, scanning and dissemination of interesting aerospace documentation that might otherwise vanish from the public.

 Posted by at 12:49 am
Jul 012017

The Pluto nuclear ramjet is often considered one of the crazier (or perhaps more accurately, “badass”) weapons systems ever considered by serious people. In short, it used a nuclear reactor as the heat source for an airbreathing ramjet; it would fly at a few hundred feet altitude at Mach 3 with nearly unlimited range. Several American aerospace corporations vied for the contract; LTV won the contract to build the airframe in 1961. The “Tory” nuclear ramjet was static ground tested with some success, but the program was cancelled in 1964.

Convair gave the concept considerable study from the beginning of the program in 1957 until at least 1961. Their “Big Stick” concept has been reasonably well known, but they had another idea that was somewhat further from the basic idea. It was mentioned in at least two briefings that I’ve come across; some amount of serious work was done on it, but the information I have is fragmentary. The concept was called simply the “Submersible Nuclear Ramjet.”

Pluto and Big Stick were unmanned cruise missiles. They would be launched from the ground with solid rocket boosters (some though was given to launching from ships, subs and aircraft) and would fly “grand tours” of the Soviet Union, spitting out a number of individual nuclear bombs. They would leave in their wake a line of ruin… the shockwaves from their passage would likely shake apart civilian structures, and the reactors would constantly spit out radioactive particles. At the end of the mission the missiles would crash into one final target.

But the Submersible Nuclear Ramjet would work a little differently. For starters… it was manned. There would be a crew on board throughout the mission.

Rather than starting off at some Air Force base, the Submersible Nuclear Ramjet would actually start off as a submarine, floating around on its own in the ocean. Propulsion would be provided by the nuclear reactor, serving as a “water ramjet” by heating seawater and expelling it. Feeding salt water, diatoms, kelp, fish and all the rest of the junk  the ocean has to offer directly through a nuclear reactor seems a bit dubious.

When the order to begin an actual mission comes in, the propulsion system would be reconfigured from seawater-burning ramjet to seawater-burning rocket. The vehicle would expel stored seawater through the reactor, generating a large amount of thrust, enough to launch the craft vertically out of the water and up to high speed. The craft would then angle over towards the horizontal; the propulsion system would reconfigure once again, this time to an airbreathing nuclear ramjet. The vehicle would then fly a mission essentially similar to Plutos… low altitude, screamingly high speed, ejecting nuclear weapons as it goes. At the end of the mission, unlike Pluto it would *not* crash itself into one final target. Instead, the manned vehicle would return to secure waters and slow to subsonic speed. It would enter a vertical climb and slow to a stop; the ramjet would again reconfigure, this time back to rocket mode. Four drag brakes would deploy around the nose and the vehicle would back down into the water for a soft “splashdown.” It would of course land with nearly empty tanks, so it would be quite buoyant; until the tanks refill, it would likely sit tail-down in the water.

I’m going to try to find out more about this concept, but I have minimal hopes. I’ve gone all this time without hearing about it until just a few weeks ago.

Because why no, I’ve made a basic model of the concept. Complete accuracy is not assured… I have a top view and an inboard profile; as with a distressing number of concept aircraft diagrams, the views seem to conflict on things such as the cockpit canopy, and the inlet configuration is only partially shown. Still, it’s a really interesting concept.

If you’re interested in Pluto, take a look at Aerospace Projects Review issue V2N1. There is a very large, highly illustrated article on Pluto in that issue. If you are interested in the Submersible Nuclear Ramjet, keep an eye on US Bomber Projects… it will show up in the next issue or two.

The renders below show the Convair Submersible Nuclear Ramjet to scale with the LTV Pluto.

 Posted by at 12:36 am