Sidebar: Sonnengewehr, the “Sun Gun”

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Illustration of the Sonnengewehr “Sun Gun” as published by Life magazine on July 23, 1945. Image copyright status unknown, possibly owned by Time, Inc.. Click for a larger view.

At the end of World War II the United States famously snapped up as many German scientists as it could with Operation Paperclip. While they were from a wide variety of disciplines, the ones most remembered today were the rocket designers and, as London and Amsterdam were still sporting spectacular V-2 craters, public interest in them was high at the time.

By the end of 1945 most of them would relocate to the United States, but in the period immediately following the end of fighting in Europe they were still in Western Europe and being interrogated by US intelligence personnel keen to learn about a line of weapons development in which the Nazis had jumped far ahead of the rest of the world.

It was in this setting that a few articles were published in major US newspapers and magazines (Time, Life, the New York Times and others) during July 1945 outlining one bit of information the US was getting from the captured scientists. All the articles were based on a single news conference held in Paris at the end of the previous month. While the conference apparently covered a wide variety of weapons that had been under development when the war ended, the articles picked up on one spectacular one and focused on it: the Sonnengewehr, quickly dubbed the “Sun Gun”.

The Sun Gun idea had been brought to the attention of the US by a group of scientists and engineers at Hillersleben, Germany (now part of the town of Westheide in Saxony-Anhalt, which was once part of East Germany). Though mostly unassociated with Wernher von Braun’s more-famous group they too had experience with rocketry, having worked on rocket-assisted artillery weapons and tank shells during the war.

As reported, in an unfortunately garbled way that makes it clear the reporters didn’t understand the underlying physics, the Sun Gun would have been a disc-shaped space station in a 3100-mile (5000-kilometer) orbit; some sources say 5100 miles, but this seems unlikely as German engineers would have expressed themselves in kilometers and that would be an unwieldy 8208 of them. Either way, neither would have been geosynchronous, an oddity pointed out even by some of the reporters in 1945.

Regardless, the station would have been coated with metallic sodium—chemically reactive and so easy to tarnish in the atmosphere, but which would stay clean in vacuum—polished into a mirror. The mirror would be pointed at a receiver off the coast of Europe and used to boil ocean water for power, but when the need arose it could be used on military targets—it had a projected ability to heat anything on the surface to 200 Celsius. Other numbers are scant and not clearly from the scientists themselves, but one that raises an eyebrow is that the mirror would have had an area of 5000 square miles (a round number in non-metric units, which is suspicious, and matches a diameter of 128.4 kilometers). Other sources suggest a much more realistic 9 square kilometers.

Life magazine was the most expansive on the topic, and published several drawings on the construction and operation of the station. Unfortunately their accompanying text and some of the details in the illustrations themselves suggest that the article’s authors were engaging in speculation on both topics. For example, they have the station being built of pre-made sections—cubes, oddly enough, which makes it a bit hard to produce a disk—when there’s reason to believe that it would have been made on a skeleton of long cables reeled out from a central station. Also contrary to this, Life has the inhabitable area around the edge of the disk, though this would have turned the Sonnengewehr into a “filled-in” version of the torus-shaped stations so favoured by von Braun during his lifetime

Immediate post-war reports to the contrary, it’s very unlikely that there was any sort of official work done on the Sonnengewehr beyond some tentative memos and discussions. If nothing else, consider the sheer mass of material that would have to be lifted into high orbit to build it. One source suggests one million tonnes of sodium metal, a figure considerably larger than the mass of everything ever lifted into orbit by all the world’s nations between 1957 and the present day.

Instead it seems to have been at best something batted around as a possible ultimate destination—even the scientists involved were thinking along the lines of the year 2000—in the culture of grandiosity that Nazism embraced and that also produced things like the Landkreuzer P. 1500 and Hitler’s architectural enabler Albert Speer. Even the mainstream rocketry program at Peenemünde was looking to run before it learned to walk, and this was just an extreme example of this attitude in the embryonic German space program. It may not have even been as tentative as that: at worst, it was merely discussions of an idea floated by the father of German rocketry, Hermann Oberth, in 1929.

Any gloss of reality the Sonnengewehr got likely came once the war was over and the Hillersleben group were under the control of the American military. In that precarious situation they would have been searching for anything to impress their captors of their usefulness and the Sun Gun inflated from cafeteria-table discussions to the preliminaries of a project. It did get them a little attention at the time, to be sure, but its sheer fantasticalness made it quickly drop back out of the limelight.

Sidebar: Von Braun’s Moonship

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Detail from the diagram of Wernher von Braun’s conjectural Moon ship published in the Collier’s Magazine issue of October 18, 1952. Click for a larger, complete view of the whole diagram.

Wernher von Braun, Willy Ley, Fred Whipple, and others famously jump-started American interest in space with their series Man Will Conquer Space Soon!, published over eight different issues of Collier’s Magazine between March 1952 and April 1954. This is from the second one, October 18, 1952′s “Man on the Moon”.

Though unsigned, it is likely the work of magazine artist Rolf Klep—Chesley Bonestell is remembered for the paintings he did for the series, but Klep did most of the more diagrammatic images. It depicts two variants of the same basic ship, one a passenger ship and one a cargo ship. Both would have been built in orbit after a space infrastructure of orbital rockets and a space station had been put in place.

Two of the “passenger” version would have carried a total of 50 scientists and technicians between them, while the “cargo” version would have been on a one-way trip to the Moon carrying the supplies the 50 men (and the title of the series leaves little doubt that it would have been only men) would need for a six-week stay on Earth’s nearest neighbour. Their goal would have been the Sinus Roris near the Moon’s North Pole—and later used by Arthur C. Clarke as the setting of his A Fall of Moondust, in all likelihood because of its mention in this article.

The ships are 160 feet tall, which is to say just about the same height as the entire Space Shuttle stack. They were to have burned nitric acid and hydrazine, which was quite prescient on the part of Dr. von Braun as that’s one of the three most popular rocket fuel combinations (along with LOX/LH2 and LOX/Kerosene) down to the modern day. Less prescient is its mercury-vapour powered turbine, which uses the parabolically concentrated light from the Sun to evaporate liquid mercury and generate 35 kilowatts. They were the hot new thing in 1952, but fell out of favour not long after. So far as I know there’s never been one in space.

Naturally on arriving at the Moon, the astronauts would set about building a Moon base using the cargo they brought as well as the one ship that brought it. From there von Braun confidently predicted that it would not be too much longer before the first manned trip to Mars ensued.

While this ship was never a serious proposal like all the other posts to this blog have been, it’s historically significant. Though published in 1952 it originally dates back to a non-fiction book written by von Braun in 1948, Das Marsprojekt. Bearing in mind that this is only three years after he was forced to leave Germany, it likely reflects his long-term goals for the German V-rocket program. As is well-known, he was highly interested in diverting it from focusing solely on weaponry into space exploration—indeed the winged rocket ships used to get von Braun shipwrights into orbit to builld these Moon ships look like a hybrid of the most speculative and advanced idea Peenemünde floated, the A12 and the winged A6. Who knows? In a different, more peaceful world we may have seen Germany sending something like this to the Moon in 1980, dedicated to the memory of the recently deceased father of the German space program.

X-15B: Shortcut to Space?

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A cutaway diagram of the X-15B. While the shape of the plane was the same as the original, a large number of changes would have been necessary to send it into orbit. Space was carved out for a second crew member, who also had a canopy of his own. A small payload bay was put directly behind him. Image from the NASA publication SATURN/X-15 Flight Research Program Report. Click for a larger view.

What it was: A North American Aviation proposal to build an orbital spaceplane based on the same aerodynamic shape as the X-15 and boosted by leftovers from the cancelled Navaho cruise missile program or a Saturn. Initially proposed as a single-orbit craft in 1956-57, in the short period post-Sputnik I but before the responsibility for manned space exploration was given to NASA it was one of three ideas seriously considered by the US Air Force to get a man into space before the Soviet Union.

Details: In February 1956 the US Air Force’s Air Research and Development Command (ARDC) began work on a follow-up to the X-15 research craft, Project 7969, with a specific goal of putting a man into space. As this was pre-Sputnik I progress was leisurely, but before long there were two main lines of approach being studied: the Manned Ballistic Rocket Research System, which would work on a ballistic capsule (probably to be launched on an Atlas missile), and the Manned Glide Rocket Research System, which was to work on a rocket-boosted spaceplane. There were no funds for any of this research, so contractors were enlisted to work on it themselves and were paid with the hope that it might lead to lucrative contracts

North American Aviation was one of those that responded to the Glide Rocket specifications. Their work on the X-15 was already well underway, so they suggested an interesting shortcut to getting something into orbit. The aerodynamic properties of the X-15’s shape were already understood from wind tunnel work, and within a few years there would be a plethora of data from the actual flights it would make, so why not build on that? The X-15B would need no further aerodynamic testing—NAA could proceed right to redesigning the craft for orbit.

Once built, this iteration of the X-15B would be launched on a bundle of four G-38 Navaho missiles—also a product of NAA. The X-15B would make a single orbit (and no more: while its apogee was 120 kilometers its perigee was only 75, and that would force re-entry whether they wanted to stay up for a second orbit or not), and then the pilot would parachute to safety while his craft crashed into the Gulf of Mexico. Total cost? US$120 million over thirty months.

While not entirely keen on the specifics of this mission, the Air Force realized that there might be something there worth investigating. Work on the X-20 Dyna-Soar had already started but it was still years away from flight. Why not slot the X-15B into the space between the end of the regular X-15 flights and the start of the X-20’s in order to slowly build up to the latter?

The level of the Air Force’s interest rose radically in the months following Sputnik I. Project 7969 morphed into Man in Space Soonest (MISS), and proposals were once again solicited. There were eleven in all, but three were picked as likeliest to succeed: one of the ballistic capsules proposed by six of the defense contractors, accelerating the Dyna-Soar, and building the X-15B.

The general consensus, though, was that a ballistic capsule was the way to go. Man in Space Soonest was an entirely political exercise: beat the Russians to the punch by getting a man into space as quickly as possible. Whether there was any more practical reason for him to be up there was irrelevant. The Dyna-Soar and X-15B would have uses like reconnaissance and bombing, but that didn’t matter in context. The former would take too long no matter how many resources were thrown at it, and the X-15B suffered from the problem that it needed to be piloted: learning if an astronaut could function as a pilot in the conditions of space would take extra time. In a ballistic capsule, he’d just have to sit there.

Their preference was confirmed in October 1958 when MISS was absorbed by the newly created NASA. It became Project Mercury, and NASA focused on its Mercury capsule.

That didn’t mean that the X-15B would not be built at all, though. Returning to the idea that it could fit between the regular X-15 (which was now NASA’s baby) and the X-20, NAA continued to pitch it to the new agency. In the past this phase of the X-15B’s existence has been overlooked, mostly because it was classified Secret in 1959 and dropped out of sight. NAA’s final 1961 reports to NASA did come out a few years ago though, and gives us a clear idea of how it might have flown.

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Diagram of the unusual materials needed for the X-15B’s structure so that it could resist re-entry temperatures. The skin would have been even more exotic. Click for a larger view.

Like the original X-15B proposal, the next iteration of the craft would have had the same shape as the plain X-15. The biggest difference between the two planes was the materials used to make them. While the X-15 could get by with aluminum and steel for its frame, the X-15B’s orbital re-entry would have caused it to deal with much higher temperatures: as high as 2700 Celsius on the leading wing edges. Regular structural metals would sag and melt when subjected to that.

As a result the nickel alloy Inconel X, which was used only for the heat-resistant skin of the X-15, was restricted to the area of the plane’s frame behind the nose and above the belly. Those other two areas, as well as the wings and tail fins, had to use more exotic refractory materials like graphite, molybdenum, and beryllium oxide. Where the heat was worst, NAA planned on using thorium(IV) oxide, which means that—like its predecessor the Douglas Model 684—the X-15B would have been somewhat radioactive. Unlike the Douglas plane only structural elements for the tail fin edges and the roots of the wing edges would have used the stuff, not the whole skin.

The skin of the plane would have been even more exotic, including molybdenum, tungsten, the René-41 alloy used for the shell of the Mercury capsule, and niobium. The last of these was a particularly interesting call as at the time the Dyna-Soar was also looking as if it were going to made out of the same metal, and together they would have used up more than the world’s annual production of the metal for a few years.

Inside the plane was rather different too. Space was carved out for a second crew-member, who was also given a canopy, while instrumentation was stuffed into an area behind him (in the X-15 you could have instrumentation or a second crew, not both, and if you went with the latter he couldn’t see out). Behind that the X-15B’s oxidizer tank could be accessed through a payload door on the top of the craft; the tank could either take up the whole space for missions where more fuel was needed, or a smaller tank could be fitted and part of the space be used for a small satellite payload.

The extra space for this arrangement was available because while the X-15B was to have the same shape as the X-15, it would have been somewhat bigger. Oddly enough, how much bigger is not clear—two figures are 57’ 4” and 52’ 4”, and one presumably incorrect NAA illustration even shows it as taking up approximately 42 feet of a Saturn/X-15B stack even though the original X-15 was seven feet longer than that. However much it was, this extra space would also have been used for one more purpose: instead of bringing oxygen bottles as was done on the short flights of the basic X-15 or as would have been done for the earlier single-orbit X-15B, the final X-15B plan had a regenerative oxygen system.

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Saturn/X-15 stack for the first mission. In later missions to higher altitudes, the S-IV would be swapped out for the more-powerful S-II. Click for a larger view.

They couldn’t carry bottles because the weight of them needed for the final plan’s missions was too great: even the first X-15B launch was going for 32 orbits over the course of two days (thus giving the 90-minute orbit that was ubiquitous in early space mission designs). The craft would be perched on top of two-thirds of a Saturn V rocket stack and would be launched to 150 kilometers. For the first mission the second stage would be deleted, but for later, higher missions would have taken out the smaller third stage instead. Using equipment stowed in the payload bay, they would engage in some optical and radio telescopy, measure the Earth’s gravitational field, and study the planet’s surface with infrared and radar.

Once their two-day mission was done, the crew would retro-fire the X-15B’s rockets to get them down to 105 kilometers where the residual atmosphere would cause them to re-enter. Though they’d have to bleed off 28,000 kilometers per hour of speed, before too long they’d be back to velocities more typical of the original X-15 and glide back to base like that more-staid craft did. Unlike the original X-15B proposal, this version of the craft was almost fully recoverable—no parachutes and dips into the Gulf of Mexico now. The only blemish was the need to jettison its ventral tail fin so that the plane’s aft landing skid could touch the landing strip.

North American Aviation promised that if they started work in December 1959, the first manned orbital flight in the X-15B would take place in June 1964.

What happened to make it fail: It turned out that the time-saving of re-using the X-15’s shape wasn’t nearly enough to turn the X-15B into a useful program. Once NAA worked it all out and came up with that target date of June 1964, it meant that the X-15B wasn’t going to fly until nearly two years after the X-20 Dyna-Soar was supposed to make its first suborbital flight. The idea of using it to build up to the X-20 was a complete impossibility.

What was necessary for it to succeed: At first blush it seems like the X-15B might have had room to fit into the gap between the X-15 and the X-20 anyway, once delays are worked in The Dyna-Soar didn’t fly in mid-1962 like it was supposed to, and didn’t even come close. When it was cancelled in December of 1963, Boeing hadn’t even begun building it, and the first flight had been pushed back until January 1, 1966.

The X-15B still wouldn’t have been able to catch up. What was delaying the X-20 was the work needed to develop the materials for its frame and skin; exactly the same work would have been needed for the X-15B; its worked-out aerodynamics and the time saved there were irrelevant to the problem, so all the real-world delays that affected the more advanced craft would have affected its hypothetical predecessor too.

Ultimately the X-15B was an interesting idea, but it couldn’t fill any of the niches it was supposed to fit—first orbital craft or interim test-bed—and so there was no reason for it to get built.

It did give history one interesting legacy, though. Astronaut selection for MISS was completed on June 25, 1958. Nine astronauts were selected and several would be pilots for the vanilla X-15 instead (one, Joe Walker, would reach space that way), and a couple would be selected for the X-20. But more important from a historical standpoint is the one who moved on to NASA from MISS via the X-15: Neil Armstrong.

M-46/M-48 (VKA-23): The First Soviet Spaceplane

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The VKA-23′s two designs, Vladimir Myasishchev third attempt in the 1956-60 period to propose a small spaceplane to Soviet leadership. The one on the left was based on his second try, the M-48, while the second design, on the right, was the ancestor of several other Soviet attempts at a lifting body re-entry vehicle in future years. Based on two images of unknown source, believed to be from the USSR–if you know of their source, please contact the author. Click for a larger view.

What it was: Four interrelated, but different, designs for a small Soviet spaceplane. While almost all Russian spacecraft descend from Sergei Korolev’s R-7 and Vostok, they began as an independent line of approach pre-dating 1957, building up to orbital operations by creating ever more extreme airplanes. Only after Korolev’s crowning achievement of orbiting Yuri Gagarin in a ballistic capsule was it definitively folded into the main line of Soviet space exploration. Even after that its descendants repeatedly threatened to split back off again right up until the collapse of the Soviet Union.

Details: We’ve previously discussed Eugen Sänger’s Silbervogel and how it was the first serious attempt to build a spacecraft by an alternative means to ballistic rocketry—building a plane so extreme that its speed and height qualified it for orbit. After WWII ended there was some interest in his work in the United States, but as designing a spaceplane is relatively difficult as compared to a ballistic capsule, it never went anywhere interesting until the development of the X-15.

In the Soviet Union, however, airplane designers kept their eye on the possibility starting as soon as they discovered Sänger and Bredt’s work. Stalin is reported to have been very interested in the possibility of an orbital bomber, and in 1949 tried to have a Soviet Air Force officer, Grigoriy Tokaty-Tokayev, kidnap Sänger from his home in post-war Paris (Tokaty-Tokayev chose to defect instead). Long before this, though, in November 1946 Stalin directed Mstislav Keldysh—arguably his most talented plane designer and one of the three men (along with Sergei Korolev and Mikhail Tikhonravov) who suggested in 1954 that the Soviet Union launch an artificial satellite—to build something like the Silbervogel.

Keldysh concluded that the Silbervogel was entirely too advanced for Russian industry to build any time soon. Nevertheless he went for a somewhat less-extreme ramjet-and-rocket-powered craft that kept the same basic suborbital boost-glide approach suggested by Sänger. What he comes up with is still too sophisticated for Russia to make, so it’s not hard to conclude that it wasn’t a serious proposal and more just a way of getting Stalin off his back.

In the years immediately following this, Vladimir Myasishchev was the most serious of early Russian spaceplane designers. Well before Sputnik I his design bureau, OKB-23, was working on radical weapons like supersonic bombers and the Buran cruise missile. When Korolev demonstrated to the Soviet leadership’s satisfaction that ballistic missiles were the best delivery system for nuclear weapons, Buran was cancelled in November 1957, but Myasishchev was still interested in going faster and higher with his planes. So he continued working on an idea he’d had while working on his missile for a suborbital reconnaissance spaceplane called the M-46. Note the date: he was already working on it prior to the launch of Sputnik I, which makes it one of the select few spacecraft seriously considered before the dawn of the Space Age.

Not a lot is known about the M-46 other than its existence, as the work was done entirely on Myasishchev’s own accord; when he was found out he was sanctioned and told to pay back the funds he had spent. Archive materials on it were apparently destroyed some time thereafter. Nevertheless, there’s reason to believe that it would have been a manned version of the Buran missile, which is to say a ramjet-driven, delta-winged craft some 23 meters long, boosted up to speed by four nitric acid/kerosene rockets. The ramjets would have gone out for lack of oxygen long before it reached space, but it would have had enough speed for a suborbital hop above 100 kilometers with an intercontinental range.

Two years after being slapped down for his initiative, Myasishchev’s situation changed. Early reports of the US Air Force’s Dyna-Soar inspired the Russian military to counter with a spaceplane of their own. Korolev’s OKB-1 worked with Pavel Tsybin to develop one possibility, the PKA, while Myasishchev’s OKB-23 was given the go-ahead to develop a new one of his own, which he called the M-48. Both were designed to be boosted by Korolev’s R-7, just like the Vostok spacecraft for which they were considered an alternative. As it’s much easier to build a ballistic re-entry capsule, Yuri Gagarin made his historic flight in the relatively unsophisticated Vostok 1, but work continued on both the PKA and the M-48 until October 1959 and October 1960 respectively.

Myasishchev’s first attempt at this commission produced the M-48 proper, about which again not very much is known. One day the Soviet archives may open enough to give us more details, but for now our best idea is that it was long, flat-bottomed, triangular craft (with the two forward sides of the triangle much longer than the other one,) with a relatively simple faceted crew cabin for one attached to its upper surface. Its flat underside is particularly interesting, as it makes the M-48 one of the first waveriders, which is to say it took advantage of the shockwave on the belly of the craft to provide lift. The whole concept of doing this had only been discovered in 1951, and its discoverer (Terence Nonweiler) was only just developing a plan to use it (in the never-built British Nonweiler Waverider re-entry vehicle) as OKB-23 was doing the same. Waveriding is a difficult and sophisticated technique, and even in the 21st century only one aircraft has ever been built that used it, the 60s-era XB-70.

Perhaps it was that sophistication, as well as the general audacity of designing a spaceplane, that got the M-48 into trouble. When Myasishchev submitted his design for approval, it was savaged by governmental engineer/bureaucrats, and he had to head back to the drawing board. This time he came up with two designs. Though technically still the M-48, they’re sufficiently different from the original (and from each other) that they’re usually referred to by their alternate designations: VKA-23 design 1 and VKA-23 design 2.

The first of the two designs was similar to what he had done with the M-48, but with changes intended to address the objections to the previous design. It would have been 9.4 meters long and built of steel and titanium, which would then be covered with ceramic foam tiles embedded in a frame made of silicon and graphite. It would have been able to carry one pilot and 700 kilograms to orbit, with the entire loaded and fuelled craft weighing an additional 3500 to 4100 kilograms. This is very small, smaller than even SpaceShip One and only a few hundred kilograms heavier than the unmanned X-37 spaceplane. This size was dictated by the fact that it was to be lifted by one of Korolev’s R-7 boosters, which would do most of the work of getting it into orbit.

The second design is the particularly interesting one, though. In contrast with the first design’s faceted appearance, this one was a rounded lifting body, recognizably like almost every small winged re-entry vehicle developed since then. On the Russian side this is not coincidental. The chain of proposed Soviet mini-spaceplanes running from Raketoplan to Spiral to LKS to MAKS are all dependent in one way or another on the work done on it, or the engineers who developed it. Like design 1, it had to be light to go up on an R-7, and so it rang in at 3600 to 4500 kilograms, and its payload was the same—700 kilograms. It likewise used the same ceramic tiles and silicon/graphite frame as a heat shield. It was slightly shorter than its brother, at 9.0 meters.

Both would have been fitted with a small turbojet engine for maneuverability once they had reached the lower atmosphere during re-entry.

Despite its numerous descendants, the VKA-23 was still quite primitive. In both designs its one astronaut actually had to take a trick from the similarly basic Vostok and parachute out from it to safety once he dropped below 8 kilometers (but before getting to 3 kilometers); the plane itself would have had landing skids (design 1) or had a parachute to bring it safely to ground (design 2).

What happened to make it fail: In 1959-60 Khrushchev starting reducing the size and complexity of the Soviet military establishment. OKB-23 was dissolved in October 1960, and many of the VKA-23 engineers were re-assigned to Vladimir Chelomei’s OKB-52, where they became an important part of his Raketoplan spaceplane design team. When that too was cancelled, they were moved to Mikoyan, where they worked on Spiral.

What was necessary for it to succeed: None of the original four designs was ever going to fly. Spaceplanes have turned out to be considerably harder than anyone ever suspected, and even the United States was far away from building one in the late 1950s and early 1960s. The Soviet Union was even less able to do so.

But In a sense, Myasishchev’s little plane came very close to succeeding in the long run. During all their travels through various Soviet design bureaus, a variable group of Myasishchev engineers kept a recognizable core of VKA-23 design 2 knowledge moving forward. A scale testing model of Raketoplan was launched on a suborbital re-entry experiment in 1961, and another model tested the design’s hypersonic maneuverability in 1963. The Spiral spaceplane got to the point of a full-scale subsonic version, the MiG-105, which was used to study its low-speed handling. Two sub-scale versions of Spiral, BOR-2 and BOR-4, were launched into orbit. Even the larger-scale Soviet shuttle that did finally fly in 1988 had its cockpit designed by the Myasishchev bureau, which was reconstituted in 1967. It had the name Buran, which was a nice callback to the manned Buran cruise missile plans that started it all in 1956-7.

Incredibly, the Myasishchev design bureau was still chugging along on their own distant descendant of the VKA-23 (after a long fallow period) as late as 2009—this time with the aim of using the result for space tourism. That dream finally died when they were acquired by the Russian government’s United Aircraft Corporation in that year.

Army/RAND World-Circling Spaceship: War is Over, Space Is Just Begun

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Three views of the World-Circling Spaceship. On the left is the two-stage LOX/LH2 version, while in the centre is the more-developed four-stage LOX/Alcohol version. On the right is a view of the four-stage rocket as it might be assembled on the pad (support vehicle shown, far right). Images from Preliminary Design of a World-Circling Spaceship. Click for a larger version.

What it was: The first attempt to build a ship that could actually reach orbit by an organization that had the wherewithal to do it. Proposed in May 1946, the World Circling Spaceship was in fact two of them: a four-stage Liquid Oxygen/Alcohol rocket whose 500-pound (227-kilogram) upper stage would reach orbit, and an alternative two-stage LOX/Liquid Hydrogen rocket with a similar 500-pound upper stage. While primarily intended for unmanned payloads, putting a man into space with either was considered.

Details: The WWII German rocket team had a design, but no backing. Right after the war, the US Navy could have come up with the funds, but their design (actually several designs) to build a single-stage-to-orbit vehicle would never have worked—SSTO was beyond the technology of the 1940s.

The US Army Air Force, however, could have had both sometime immediately following the spring of 1946. In March they arranged for Douglas Aircraft to put together Project RAND to study intercontinental warfare by means of missiles. Their list of consultants was stellar, and even included Luis Alvarez, later much more famous for his paper proposing an asteroid strike as the cause of the extinction of the dinosaurs, and who would also be on the commission looking into the Challenger disaster.

By May 2, 1946 they had produced the first of what would be a very long line of reports from what would soon be the Rand Corporation. This one was devoted to artificial satellites and was called Preliminary Design of an Experimental World-Circling Spaceship. In it they studied the various issues standing between the present state of the art in rocketry and putting something into orbit, and they came to the conclusion that it could be done with 1946-era engineering. Working backwards from a goal of putting 500 pounds into orbit, they then proceeded to lay out two preliminary designs: a four-stage rocket using liquid oxygen and alcohol for fuel (the same fuels used by the V2 rocket) and an all-cryogenic two-stage rocket using liquid oxygen and liquid hydrogen. They also noted that their initial analysis’ conclusion that a rocket burning LOX/LH2 would be best if it had two stages had turned out to be wrong, and that if time permitted they would have redesigned the second concept to use three stages—not a bad result for 1948, as this prefigures any number of successful three-stage rockets developed since then.

The first actual all-cryogenic three-stage rocket didn’t come about until the Delta IV in the early 21st century, though, as liquid hydrogen is a bit of a bear to handle. In 1946 the knowledge of how to do so simply didn’t exist, so the alcohol fuelled rocket was considered the more conservative choice. As a result the report focused on the four-stage vehicle. Its length was 60 to 70 feet, and its width at its maximum was 12 to 14 feet. Altogether before launch (and including fuel) it would have weighed about 100 tonnes. Promisingly, this makes it quite similar in size to the two-stage Atlas B, a late 1950s rocket which had a payload of 70 kilograms.

A hypothetical launch of one of these rockets would begin on an equatorial Pacific Island, an idea we’d see again a few years later in the Army’s proposal to use Christmas Island as a spaceport for a lunar base. As with that future plan, this was to take advantage of a long downrange area clear of human life as well as getting the maximum possible boost from the Earth’s rotation.

The rocket’s four stages, from largest to smallest and first-firing to last, were charmingly named Grandma, Mother, Daughter, and Baby, with the final one being the orbiting section; in the cryogenic rocket, Baby was perched on one single large stage (unnamed in the report, but call it “The Mother of All Stages” if you like). Each of these stages would have been stripped-down accumulations of fuel and rocket engines with the exception of Baby; it was in charge of guidance for itself and any earlier stage still attached to it and firing, an approach taken by the Proton K/D used for the Soviet circumlunar Zond spacecraft.

Baby’s payload cone would have been 3 feet (0.9 meters) in diameter and 7 feet (2.1 meters) in length, with an internal space of 20 cubic feet (0.57 cubic meters), and the payload’s weight would be no more than 500 pounds. While the assumption was that at first the Baby would be unmanned, a short chapter in the report—almost an aside, not even two full pages long—suggests that this would be big enough for a man and a vivarium to provide him with oxygen. Considering that the cramped Mercury capsule, by far the smallest manned craft ever made, had 60 cubic feet (1.70 cubic meters) of internal space, this was probably optimistic.

Baby’s instrument payload would be swapped in and out to fill a variety of roles. Fundamental research of the near-Earth environment was first, and RAND also pointed out the usefulness of a satellite for geodesy, ultraviolet astronomy, and communications. They even discuss the advantages of a satellite in geostationary orbit, but never actually mention that there’s a considerable difference between 500 pounds to LEO and 500 pounds to 35,786 kilometers up. Probably bearing in mind that RAND was funded by the Army Air Force, they also suggested that Baby could watch the weather over enemy territory, act as a spotter for a nuclear missile in a co-orbit, and send back pictures after an attack to assess its effect. There’s also a surprisingly prescient prediction, eleven years before the Sputnik 1 flap, that Baby would provide value simply by existing, so that it could increase world opinion of the United States.

Though they do mention using television to return images, they considered how best to return Baby to Earth with photographs until such time as radio downlinks were up to the task (and not incidentally so our previously mentioned claustrophilic astronaut could come home). Their solution was to add small wings about 30 square feet in area (2.8 square meters) to the orbiting capsule. This is particularly interesting as it only highlights that Harvey Allen’s discovery that a blunt shape actually reduced re-entry heat with its bow shock—one of the fundamental discoveries of space exploration—was still several years in the future. Lacking that knowledge, RAND suggested that Baby could use its wings to slow the craft’s descent and cut the temperature that way. Both the wings and the capsule’s skin were to be made with stainless steel, which is worrisome in hindsight and appears to be the only place where their analysis missed out on a good understanding of what would be necessary to launch and retrieve an orbital satellite.

RAND suggested that, once given the go-ahead, designing and launching the World-Circling Spaceship would cost US$150 million and take 5 years.

What happened to make it fail: RAND’s report came out at a time when rockets were on the upswing with the Army Air Force (and the independent USAF that followed in 1947). In particular, they were headed by General Carl Spaatz, who was believer in the future role of rocketry in war.

He retired in February of 1948, however, and in October of the same year General Curtis LeMay took over the Strategic Air Command—and they were in charge of any Air Force missiles on American soil. LeMay was of the opposing school to Spaatz, and believed that the future of air war was in bombers. As a result his influence stalled any and all long-range missile projects, let alone one that was as speculative as an orbital launcher in a time of military budget austerity. The World-Circling Spaceship never gained the backing it needed, and soon withered away.

What was necessary for it to succeed: If it had been launched as designed, with stainless steel leading edges on the wings, the first few Babys may have made it into space but weren’t coming home. Apart from that, though, Preliminary Design of an Experimental World-Circling Spaceship is remarkably close to something that could fly considering that it was spec’d out in the Precambrian of the Space Age. With the right personnel (say if Wernher von Braun and his crew had gone along with the Air Force during the divorce from the Army) and someone other than Curtis LeMay in charge of the Strategic Air Command, it’s not hard to see an upgraded Baby beeping its way around the Earth by the end of 1952—a tight schedule, but not out of the question.

Even if they didn’t pull it off by then, after the election of Eisenhower in November of that year it’s an open question if the new president’s preference for civilian control of space exploration would have been enough to stop a project that hadn’t yet put something into orbit but was getting close.

Douglas Model 671/684: The X-15′s Shadow

Model 684

A schematic diagram of the Douglas Model 684. It was submitted to NACA in 1954 as part of the X-15 design competition. Though evaluation suggested it would be the superior suborbital spacecraft, it lost to North American Aviation’s bid. Image from “USAF Project 1226, Douglas Model 684 High Altitude Research Airplane”. Click for a larger view.

What it was: Douglas Aircraft’s 1954-55 attempt at a suborbital spaceplane, with support from the US Navy and eventually NACA, intended for testing high Mach numbers in the atmosphere. Launched from a bomber, it would use a ballistic flight to get as high as 344 kilometers and then use the drop back down into the atmosphere to build up speed.

Details: NASA’s predecessor, the National Advisory Committee for Aerospace (NACA), was devoted to basic aerospace research programs whose results could be used by industry to make better aircraft. By the 1950s hypersonic travel was in the cards and they resolved to develop a research aircraft that could reach Mach 7, solely for the purpose of studying the aerodynamic and heating problems of moving through the atmosphere at that speed. Interestingly, they were not interested in studying spaceplanes or re-entry, as they considered manned space travel something for the 21st century, but the speeds involved were creeping up on those issues regardless of their intentions. With that in mind engineers at their Langley Research Center roughed out a basic design that is recognizably the X-15.

A lot of NACA’s work was done in conjunction with the US Air Force and Navy, partly because they were the groups most interested in cutting-edge aviation and partly because the Department of Defense had a budget roughly 150 times larger than NACA did. Accordingly, basic design in hand, NACA met with the other two organizations on June 11, 1954 to discuss where to go next.

The Air Force had been working with Bell Aircraft—builders of the X-1 and X-2—but the Navy had been working with Douglas Aircraft on two successive planes, the D-558-1 and the D-558-2. At the meeting they revealed that they were in the early stages of getting Douglas to work on what the manufacturer called the Model 671 (informally known as the D-558-3 in years since, though that name was never actually assigned to it).

Unlike the NACA idea, the Model 671 was designed for height as well as velocity. Although the work done on it was still preliminary, Douglas had already come to the conclusion that they could make it reach 1,130,000 feet—or, in more modern terms, 344 kilometers. The International Space Station is actually allowed to drop as low as this before being boosted again, so this is well into space; Douglas did admit that the pilot would probably not survive the G forces of that flight and so recommended nothing higher than 770,000 feet (237 kilometers). The plane’s downrange capability was 850 kilometers for both high and low flights, which is suborbital, but for both in height and distance this is considerably farther than Alan Shepard went in Freedom 7.

Given that NACA and the Air Force were now looking at similar programs, the Navy cancelled the Model 671 and joined up to launch a design competition. On December 30, 1954 twelve contractors were invited; only four came up with proposals, probably because of the risk involved and the minimal profits that would stem from the two airplanes that NACA wanted built. Three of the replies were from Bell Aircraft, North American Aviation, and Republic Aviation.

Douglas replied with the Model 684. Their proposed craft would hit a maximum of 7300 kilometers per hour, and reach heights of 114 kilometers—in other words, they had to tone down the Model 671 just to meet the NACA requirements. Even at that, this is still the edge of outer space: the Model 684 would have been the first suborbital spaceplane.

As it was headed for space, the pilot compartment was completely pressurized, and could carry two if the research instrumentation was removed. Anyone onboard would wear a pressure suit (the X-15 program would actually develop the space suit used by Mercury astronauts), and in case of a dire emergency the entire forward fuselage would cut loose, push away from the main body of the craft on a small jet, and drift down to Earth under a parachute.

The Model 684 would have been lifted to about 30,000 feet by a B-50 Superfortress bomber where it would be dropped. At that point it would have ignited its liquid oxygen and ammonia engine and taken off on a trajectory for either speed or height. After reaching its apogee it would glide back to Earth, eventually landing at a long conventional airstrip at about 300 kilometers per hour.

Like the other proposals this was a “hot structure” craft, which is worth explaining. The Space Shuttle’s fuselage, for example, is built mostly of aluminum. As a result it’s completely incapable of standing up to the heat of re-entry and must be kept cool. In the particular case of the Space Shuttle this was done by covering it with ceramic heat tiles, but other cold structure options include ablative coverings (which the Model 671 would have used) or cooling using some sort of liquid inside the skin that would be allowed to boil off.

A hot structure, on the other hand, approaches the problem head on: build the fuselage out of a material that holds up to high temperatures. NACA had suggested to the design competitors that they might want to look at Inconel X, a nickel-chromium alloy that doesn’t begin to soften until very high temperatures. Three of the bidders took the hint.

The Model 684 would have used HK31, an alloy of magnesium, thorium, and zirconium which is no longer in use since the three percent that is thorium makes the alloy radioactive. At the time its relatively low radioactivity was not considered much of a problem, though, and it had the advantage of being much lighter than Inconel X. This meant that the Model 684’s skin could be much thicker, which would reduce costs and would dramatically increase the heat capacity of the plane and keep it from pushing 1000 Celsius on re-entry. The leading wing edges would be made of copper, which would conduct heat away quickly into the rest of the plane.

The total estimated cost for research and development, then the production of three planes, came to US$36.4 million, with the first flight anticipated by March of 1958.

What happened to make it fail: This one actually came quite close to existing, as it was a strong second in the NACA competition to the North American Aviation ESO-7487; in the formal evaluation it actually outscored its rival 152 to 150. Essentially the decision came down to unhappiness with the choice of the HK31 alloy for its fuselage over Inconel X. As a research craft, they wanted the X-15 to be subjected to the heat of hypersonic travel. Inconel X would go up over 800 Celsius when at the heights and speeds NACA wanted; HK31’s higher heat capacity would have kept the Model 684 to about 300 Celsius during the relatively short flights the X-15 would undertake. It was a better solution if one were just making this aircraft, but not if the whole point was to study high temperatures in flight for future aircraft.

Basically it came down to what NACA was looking to build. They didn’t want a spaceplane, they wanted a regular, if extreme, aircraft. The NAA ESO-7487 may not have been able go as high as the Model 671, but that was OK. In looking to make something that would be relatively easy to develop into something the Navy would want to buy later for service, Douglas was too ambitious for their own good. The ESO-7487 would become the X-15.

What was necessary for it to succeed: North American Aviation actually asked to withdraw from the X-15 competition in October 1955, after it had informally been awarded the contract but before it was official. A slew of new design work had come their way and they no longer thought they could make the 30 month deadline for first flight that the contract would impose.

NACA, the Air Force, and the Navy mulled over two options. Either they could award the contract to the Model 684 if it was switched to an Inconel X skin, or they could give NAA an eight-month extension. They decided on the latter course, but if they hadn’t the Model 684 would have flown.

Sänger-Bredt Silbervogel: The Nazi Space Plane

Sänger-Bredt Silbervogel spaceplane

Image of the Silbervogel taken from the 1952 translated edition of Eugen Sänger and Irene Bredt’s 1944 A Rocket Drive for Long Range Bombers. An inset of the entire craft at launch is at upper left. Public domain image.

What it was: A boost-glide intercontinental spaceplane. It would reach space, if not orbit due to lack of speed, but manage to get all the way around Earth once by repeatedly skipping off the upper atmosphere to gain more altitude. During World War II it was positioned as an extreme long-distance bomber (capable of, for example, carrying a 3600-kilogram bomb to New York City from a launch site in Germany), but it also would have made an interesting surveillance vehicle—utterly immune to being shot down and the next best thing to a spy satellite.

Details: Ever since space travel became even marginally possible doing so has been torn between two approaches. One is to stick a one-shot capsule of some sort on top of a rocket and then let it return ballistically after the mission is over; the other is to build a spaceplane which either gets to space under its own power or is launched on a rocket, and then is capable of gliding back to Earth. Theoretically planes are cheaper because of their reusability while capsules are easier to build. In practice, though, no-one’s ever been able to develop a spaceplane that could undercut a capsule because the added complexity of the plane adds back on to the saved costs. As a result, with the exception of the Americans’ long excursion into the Space Shuttle program, all spacecraft that were successful for more than one or two flights have been capsules.

Both approaches date back to the first time and place that had any chance at all of putting something into space, which is to say Germany in the 1940s. Wernher von Braun’s ballistic rocket approach has been the one followed by the USSR and China, while the United States used it into the 1970s and is returning to it now with the upcoming Orion MPCV.

Less well-known is Eugen Sänger and Irene Bredt’s Silbervogel (“Silverbird”) which was the first serious attempt at building a spaceplane, work on which contributed to the success of several other later spaceplanes that flew, and which itself was refactored and raised as a possibility as late as the 1980s.

Sänger began work on the concept in his original engineering thesis for the Vienna Polytechnic Institute. When it was rejected as too radical in 1931, he submitted a second, more acceptable thesis on a different subject, but arranged for the original to be published by a different route in 1933. At the same time he perfected a regeneratively-cooled rocket engine (which is to say that it used the expansion of the rocket fuel’s gases to carry away heat and keep the engine from overheating). His research couldn’t secure funding in his native Austria, but an article in the journal Flug (“Flight”) in 1935 attracted the attention of the Luftwaffe in Germany. He was invited to set up a research facility there, which he did in 1936 and then the real work on Silbervogel began.

By 1942 he had advanced the rocket engine which would power the craft, worked on the rocket sled and track which would be used for its initial boost launch, and worked out the aerodynamics of a plane that would be both subsonic and supersonic as well as flying in the near-vacuum of space.

The Silbervogel would have been a two-part ship. The spacecraft itself was to have been a 10-ton, streamlined plane with two stubby wings and two tailfins, both raked upwards at about ten degrees. Four fuel tanks took up most of the fuselage and contained liquid oxygen and kerosene which would burn in a single rocket engine over the course of 168 seconds. On the ground the plane would be mated with a rocket sled which would give it an initial boost from behind along a rail track for a mere ten seconds but with nearly five times the thrust as the spaceplane’s engine.

Once the Silbervogel completed both burns it would be moving at a minimum of Mach 13 (15,926 km/h) and as much as Mach 20 depending on its mission and payload, and reach a maximum altitude of anywhere from 31 to 121.5 kilometers, the latter value being well into space. Just to put this in perspective, the air speed record in 1944 was 1130 kilometers per hour (Mach 0.92), while the altitude record in an aircraft was 17.3 kilometers. Sänger and Bredt did not think small.

The Silbervogel would then begin a roller-coaster-like ride up and down into the Earth’s atmosphere, using its wings and angle of attack to skip off the denser air at about 20 kilometers up and regain altitude for another distance-eating hop. An example diagram in the 1944 paper discussed below shows no less than eight such skips before settling into a steady flight at 20 kilometers and a return to base after a complete trip around the world.

What happened to make it fail: It was too advanced for the time, and even Sänger (who underestimated the technical difficulties of the heat Silbervogel would have to endure when skipping into the atmosphere) thought that it would not fly for many years. As World War II heated up, the Nazi government officially put the program on hold in 1942 to save money and resources for weapon systems that could be used before the end of the ongoing fighting. Oddly enough, despite the stop Sänger was still assigned to it and continued work on it until 1944, as the Nazis looked at several possibilities for being able to bomb the United States from the Azores if fascist Spain and Portugal could be brought into the Axis.

In that year he and Bredt published their final version of their research, which was published as Über einen Racketantrieb für Fernbomber (translated after the war as A Rocket Drive for Long Range Bombers, a copy of which can be downloaded as a PDF). This remarkable document outlines how the Silbervogel would have looked and worked, as well as how it might have been used in a variety of ways—for example avoiding the difficulty of having to go the whole way around the Earth by setting up a second Silbervogel landing and launching base in the Japanese Marianas Islands or, better, in the occupied territory in California which the Japanese would helpfully conquer for the Nazis. A cheerful diagram showing the complete destruction of Manhattan from roughly Union Square north to the corner of 27th Street and Broadway and south to Houston Street is included, as this would be possible with a mere 84 sorties with 3600-kilogram bombs. Note that the Space Shuttle Discovery holds the record for the most flights above 100 kilometers by any one spaceplane, 39, racked up over the course of 27 years.

What was necessary for it to succeed: Under any reasonable circumstances, it wasn’t going to work as initially designed.  The design was simply too far advanced for the time, and Germany couldn’t come up with the physical resources or money to build one.

That said, if there had been no war, and if the Germans had had access to high melting-point molybdenum for its belly (or developed heat-resistant ceramic tiles as would be used on the US’s Space Shuttle), and if there had been the political will to spend those marks and metals—and that’s an awful lot of “ifs”—something like the Silbervogel could have flown around 1960. It likely would have been heavily redesigned by then.