The Armstrong Whitworth Pyramid: For an Empire on the Up

pyramid-diagram

A diagram of the Pyramid re-entry vehicle as presented to the British Commonwealth Space Flight Symposium in August 1959. The basic design with is on the left, while the variant with caret wings is on the right. The crew would have resided in the small cylinder outlined with dashes in the centre of the craft. Click for a larger view.

What it was: A proposal put forward in 1959 by Armstrong Whitworth, a British aircraft manufacturer, to build a pyramidal spaceplane to put on top of a two-stage rocket composed of a Black Knight rocket poised on a Blue Streak missile (this latter arrangement actually becoming official less than a year later, as the Black Prince launch vehicle).

Details: The UK is the only country in the world to have developed a space launch capability and then give it up (one could make an argument for France as well, as the Ariane is technically European, but that rocket is clearly France’s baby). That said, at the end of 1945 the UK was one of the few countries on the cutting edge of rocketry—like the US and Soviet Union they benefited from the ransacking of the German rocket programs. For a period of roughly twenty-five years after that up to 1971 the UK did try to keep within striking distance of the pace set by their two rivals, and in the period immediately following Sputnik there were grand plans to get men into space too, plans only struck down by Britain’s poor economy as compared to the US and an inability to shoot dissenters as the USSR had in its favour. To paraphrase Dean Acheson, it was all part of Britain losing an empire and trying to find a role.

The ultimate expression of this was the Pyramid. The basic idea behind the craft actually dates to 1951, when as we’ve discussed previously the University of Belfast’s Terence Nonweiler invented the concept of waveriding: increasing lift by riding the shockwave generated by a hypersonic aircraft. By 1956 the British had begun slowly working on this; after Sputnik I was launched they greatly increased their pace.

In 1957-58 Armstrong Whitworth, part of the Hawker Siddeley aircraft consortium (which also included Avro Canada, of Avro Arrow fame) worked out a shape that would be able to waveride back to Earth from orbit and, more importantly, orbital speeds. At that time the equations used to model hypersonic aerodynamic flow were crude, and the answers they gave had to be calculated by hand, so the shape was as simple as possible: take a regular tetrahedron and push its top point down to produce a squat pyramid. Then take one of the base points and pull it out by about half until you have something resembling the platonic ideal of an airplane. For simplicity’s sake, the underside stays completely flat. The only wrinkle is the addition of two rudders on horizontal tail structures at the aft end of the craft, and in one variant two small caret wings (the designers also realized that the real Pyramid would have to have rounded edges and a blunted nose to keep sharp edges and points from burning off during re-entry).

As designed, the Pyramid would have weighed 1876 kilograms, somewhat larger than a Mercury capsule’s 1104 kilograms, but in the same range (a Gemini capsule weighed 3396kg). It would have been 7.7 meters long and 5.2 meters wide, with a height at its point of 2.8 meters—though as it was a flat pyramid much of its length was considerably lower than that. Under the point and the rear facet of the pyramid was the crew capsule itself, which would be cylindrical and contain two men. As was typical for very early spacecraft designs, its engineers were overly optimistic about how many astronauts could be crammed into a small space.

The craft would have been launched on a proposed launcher involving a Blue Streak missile (an IRBM being developed by the UK for their nuclear weapons) as the first stage and a Black Knight rocket as the second. This was actually proposed more formally a few months later by the British government and given the name Black Prince, and so while it’s slightly anachronistic to call it that in the context of Pyramid, we’ll use that name here.

pyramid-on-black-prince

A view of the Pyramid on its rocket (though this one looks more like a US Titan than the Black Prince). The “mirror Pyramid” added to the Pyramid-proper for aerodynamic stability can be seen here. Originally published in Flight magazine, August 1959, and so believed to be in the public domain. Click for a larger view.

The Black Prince wouldn’t have been capable of getting very much into orbit (it would have been hard-pressed with a payload of 100kg), so Armstrong Whitworth suggested killing two birds with one stone. The Pyramid would also be much too wide to fit into an aerodynamic fairing on top of its rocket, and as it generated lift at low altitudes it would try to push the rocket off course and make the climb into orbit all that more difficult. So the Pyramid would have been paired with an identically shaped fuel tank mated to its underbelly, balancing its aerodynamics and supplying more propellants to the first stage. Once the first stage had lifted the whole arrangement as high and as fast as it could take it, it and the mirror-Pyramid would be jettisoned and the second would carry the real Pyramid into a 130 by 650 kilometer orbit.

Once the mission was done, the Pyramid carried just enough fuel (only a few kilograms) to perform a retro-rocket burn at perigee, which would knock it down to 100 kilometers and allow it to re-enter. Here the waveriding aspect of the craft would kick in. At a high angle of attack a lifting shockwave would form on the flat underbelly and let the Pyramid guide its path; it could even perform a sinusoidal flight following successive great circle paths to minimize the amount of heat the underbelly had to absorb.

The designers were concerned that their original design was unstable at speeds below 130 km/h, and they didn’t know enough to make it so, so the plan was for the crew to eject out of a hatch in the rear of the Pyramid once they were low and slow enough to parachute to safety. The ship would then crash, obviously reducing its reusability. Armstrong Whitworth believed that after harvesting data from a few flights, though, they would have learned how to proceed so the future Pyramids could land safely. Then the hatch would serve for emergency exits only.

Long term planning-borderline-dreaming for the Pyramid was to upgrade the Black Prince with a cruciform set of ten engines and then stick a nuclear second stage on top of it. With that booster, the Pyramid could be given a landing engine and head for the Moon. As seems surprisingly common for early proposale, they even had a landing site picked out: Piazzi Smyth Carter near the eastern edge of the Mare Imbrium. After a few unmanned cargo launches, the manned mission would consist of several Pyramids landing their crew simultaneously nearby and getting to work on a Moon base.

pyramid-on-the-moon

An image of a Pyramid on the Moon, from “Surface Exploration of the Moon” in Spaceflight magazine, August 1961. Image believed to be in the public domain. Click for a larger view.

What happened to make it fail: The Pyramid can be broken down into two pieces, the re-entry vehicle and the rocket on which it was perched.

The crewed section failed for the usual reason: it was a paper proposal looking for government funding and it didn’t get it. The window for it to get that funding was particularly small too, as it was a primitive design and would have been completely obsolete based on what had been learned the previous few years if it had got underway by, say, 1963. That said, there were some wind tunnel tests on it, and Hawker Siddeley did study another, more sophisticated waverider in 1971; that system was radically different, being lofted by a winged booster and having an on-board ramjet.

The 1959 Pyramid’s rocket was more successful, bearing in mind that “successful” here is a relative term. As mentioned earlier, the Black Prince was actually given the go-ahead a few months later, but the reason for this was complex. The UK had been pouring money into the Blue Streak missile and, out of embarrassment at its cancellation with no return on that investment, allowed it to go ahead as a civilian rocket. Political embarrassment or not, the Treasury was uninterested in funding space, and repeatedly tried to cancel every ballistic missile and space launcher project until an attempt stuck—and in the case of the Black Prince and its follow-ons, no-one was actually interested in sticking up for it. Ultimately it came down to a struggle between expensive British independence and prestige, or cheaply relying on the US for technology.

What was necessary for it to succeed: The Pyramid re-entry vehicle had a lot going against it. First of all, waveriding has never been well-developed, not even in the 21st century: only one craft has ever used it, the American XB-70, and that plane never went much above Mach 3. Furthermore, the Pyramid’s design was too small for the two men it was supposed to carry, so it would inevitably have had to undergo a radical redesign. It also became obsolete very quickly as manned space travel took several great leaps forward in 1960-65. The Pyramid also wasn’t an official government project, being a proposal from private industry that Armstrong Whitworth then had to convince the UK government to fund. With the Treasury opposing everything to do with space, it wasn’t going to get that. Altogether it was never going to fly, either because of money problems or because the design was not going to work as planned.

The rocket had a chance, though. The turning point there was probably the Nassau Agreement of 1962. After the cancellation of the Blue Streak, the UK had been planning to use the American Skybolt missile and when that was cancelled as well they were left in a dire situation as far as nuclear deterrent was concerned. Expensive or not, it looked for a while as if the UK was going to have to spend their way out of the problem and uncancel the Blue Streak. If so, the British would have had a much easier (and much better funded) path to the Black Prince that they could have taken.

Instead PM Harold Macmillan convinced John F. Kennedy to sell Polaris missiles to the UK. The Blue Streak stayed dead, and all of the UK’s independent space plans went with it over the course of the next few years. Change the course of history there and you might get the UK in space using Pyramid’s launcher

The Blue Streak cancellation notwithstanding, the launcher half of the Pyramid system did move ahead for a while. The embarrassment-driven Black Prince derivative proceeded until the end of 1960. The British couldn’t convince Australia or Canada to help finance it, though, so it too was cancelled, signalling the end of Britain’s large-scale ambitions in space.

It still stumbled along for several more years, morphing into two different projects, the British/French/German European Launcher Development Organization’s Europa (which was cancelled and replaced with Ariane in 1971-3) and the Black Arrow—both of which suffered from lack of support from the UK to the point of deliberately being set up for failure. Nevertheless the latter of these was launched four times, with the last being the first successful British launch of a satellite, Prospero, in October 1971. It was also the last: the Black Arrow program had already been cancelled in July, and the launch had only gone ahead because the final rocket had already been built and shipped to Woomera in Australia for its flight.