Saturday, July 30, 2016

A Brief History of the Soviet Space Shuttle Buran, Part One: Guest Post by Jay Chladek

Occasionally this blog features writing by other space historians and figures. During the next two weeks, I am proud and honored to present a history of the Soviet Buran space shuttle by someone who knows an awful lot about it. Here's the dirt on everybody's favorite shuttle, by space historian Jay Chladek:
A Brief History of Soviet Space Shuttle Buran, Part One (CLICK FOR MORE AFTER THE JUMP!) 

It has been said that imitation is a form of flattery. During the Cold War between the United States and the Soviet Union from the late 1940s until the beginning of the 1990s, there was a bit of what one could describe as industrial espionage going on between these two countries which would ultimately end up becoming global superpowers. The two most visible aspects of that were the Tu-95 (NATO codename "Bull") bomber, a copy of the Boeing B-29 Superfortress reverse engineered from captured airframes and the nemesis of the Korean war, the MiG-15 powered by a copy of the Rolls Royce Nein jet engine.

During the early days of the space race, it was felt that the Soviets might also be copying American spacecraft and rocket designs as well. But over time it was revealed that this was not the case. The R-7 rocket, along with the Vostok, Voskhod and Soyuz spacecraft were completely original and the Soviets took great pride in their achievements. So when pictures of what apparently looked like a nearly identical copy of NASA's space shuttle were seen sitting on a launch pad at the Baikonur Cosmodrome in 1988, it was greeted by the Western press with a combination of excitement, bewilderment and concern. Had the Soviet Union really copied the most technically complex manned space vehicle ever built? If so, why?

The Seeds of Buran

For an answer to that, we have to go back to the early 1970s. As we know today, but was a closely guarded secret at the time, the Soviets were working on a lunar program in the form of the N1 moon rocket, and things were not going well. A bit of sideways thinking got the first civilian space station, "Salyut," off the ground, but it was not the brain child of Vasili Mishin, the head of Sergei Korolev's old bureau and he resented it. Ultimately when the fourth N1 launch attempt ended in failure, it took some extreme arm twisting by Defense Minister Dimitri Ustinov to get Mishin to fall in line and focus on developing Salyut. 

As time went on, Salyut would mature and ultimately develop into a very successful series of stations. But at the time the decision was made, no one knew how successful it would be. Even with Mishin agreeing to back Salyut, higher ups in Soviet government decided that Mishin was not the long term answer for Korolev's bureau and ultimately replaced him with Valentin Glushko, a rival designer with his own bureau that focused on the development of rocket engines.   

From Wikimedia Commons: "OK-GLI Buran programme spacecraft at the Technik Museum Speyer, Germany on exhibition during 2013." Image taken from Flickr user pasukaru76's photostream, marked as CC0 1.0. (public domain) by its author.
During the 1960s, Korolev despised Glushko, but had to work with him as Korolev needed Glushko's rocket engine designs to power his firm's own missiles and rockets. It really came to a head with the N1 as Korolev felt that Glushko was stonewalling on the development of engines that used cryogenic fuels (liquid hydrogen), such as the H-1 and J-2 motors used to power the upper stages of the Saturn boosters. Glushko favored engines powered by kerosene and liquid oxygen (LOX) or hypergolics. 

They were easier to develop and in the case of hypergolic fuels, they didn't require refrigeration equipment to prevent them from boiling off. Liquid hydrogen (LHX) is a much more powerful fuel, but it required much more extreme refrigeration than LOX as its liquid state is only about 20 degrees above absolute zero. Gaseous hydrogen's small atomic size also requires special handling and materials to keep it from leeching out compared to oxygen or nitrogen. Even with proper equipment and the best refrigeration, liquid hydrogen is still prone to boiling off at a rate of about 1% a day. Worse than that though, liquid hydrogen had been known to combust on contact with almost anything if there is an oxidizer present. Hence the difficulty with taming it for use in rocket engines. 

Ultimately Korolev went with less efficient motors from a different design firm and many believe this is a key contributor as to why the N1 rocket failed to send a payload into orbit, let alone the moon. The engines were a sound design, but having to cluster 30 of them in the first stage and almost as many in the second stage meant the chances for failure were amplified many times compared to the much smaller number of motors in the Saturn V. By comparison, the S-II stage of the Saturn V used five LHX/LOX powered J-2 motors.

When Glushko took over Korolev's bureau in 1974, he decided to merge the two design firms into one, renaming it NPO Energia. Even though memories of Korolev and Glushko's feud were still relatively fresh, many engineers at Energia considered this move a good one as the new firm had a strong hand which many felt it lacked under Mishin. But now the question became what to do with a firm this massive. For that, the Soviets looked to what the Americans were doing.

The Decision

Congress had approved NASA's plan to develop a reusable space shuttle in early 1972 and by 1974, the agency had settled on a vehicle with a winged orbiter, solid rocket boosters and a huge external fuel tank housing fuel and oxidizer to power the orbiter's LHX/LOX engines. The vehicle had the potential to deliver some very large payloads into Earth orbit and in order for NASA to proceed with development, they needed backing from the United States Air Force and the Department of Defense. While NASA planned to fly the vehicle from Cape Canaveral, the Air Force put plans into motion to launch the shuttle into polar orbits from their facility at Vandenberg Air Force Base in California. Polar orbits are ideal for reconnaissance of the Soviet Union due to how far north it is located, but what concerned the Soviets greatly is the same polar orbits could also be used for attack as well. 

When the space shuttle was designed, the USAF had a requirement for a 1,500 mile cross range capability, meaning a returning orbiter could land at a runway up to 1,500 miles to either side of its orbit track. By comparison, space capsules don't have very much cross range. If NASA were the only user of the space shuttle, a lifting body vehicle based on the X-24 would have been ideal. But polar orbit launches need a higher cross range if a problem develops. As the Earth rotates under a spacecraft in orbit, the orbit track shifts west. Orbits with a lower inclination (the angle of the orbit relative to the equator of the Earth) are easier to return from if the vehicle has to make a pinpoint landing at a specific place, such as its launch site. The shuttle's cross range requirement was needed to allow for a shuttle to land at Vandenberg after only one polar orbit, usually if an emergency required a shuttle to return right away. But, it also meant that the USAF could theoretically launch, deploy a payload and land before anyone in the Soviet Union would know what was going on and such a payload might be an offensive weapon rather than a simple reconnaissance satellite.

In the 1970s, the Soviet intelligence and military agencies were very paranoid by Western standards. Just to give you some idea of how paranoid they were, the Soviet Almaz military space station, which in modified form became the basis of the civilian Salyut station program, was equipped with a 23 mm automatic cannon as a defense against any prying U.S. spacecraft that might want to take an up close look. The weapon thankfully was never utilized in anger, but it was test fired in orbit and showed just to what lengths the Soviets were willing to protect their assets because of a perceived threat. 

So when the design specifications for the shuttle were published, the Soviet military looked at them with great concern and decided they needed a similar capability. While they didn't know exactly what the USAF were planning to do with the space shuttle, the Soviet military figured it must be important enough that they should have their own shuttle type vehicle and they should start work as soon as possible since the Americans already had a head start on them. So the Soviet military made the decision to require development of their own MKS (Soviet acronym for "Reusable Space System") in June, 1974 and NPO Energia was given responsibility for it in October of that year.

Rocket Booster Development

Remember how I said Glushko was reluctant to develop rocket engines which utilized cryogenic fuels? While Apollo had made use of LHX for the second and third stages of the Saturn V rocket, NASA was planning to use it to power the orbiter the entire way from launch to orbit and make those engines re-useable. The shuttle was also designed to make use of two very large solid rocket boosters to give it the added thrust it required and the Soviets had no equivalent capability.

With Glushko merging his bureau with Korolev's old one, he decided to focus it on developing a new rocket booster powered by LHX/LOX engines. Unlike shuttle, this new rocket wouldn't be intended exclusively for use with the new space plane. Instead it could be used to launch several different payloads into orbit and perhaps the moon or other planets. At the time, the Soviets had a heavy lift booster in the form of the Proton rocket. But Proton was developed by a different design bureau, not Korolev's and Glushko must have felt the need to eclipse his rivals now that he had the full resources of what were once two design bureaus. On paper, this new booster would make Proton look relatively puny. This new booster design was originally called "Vulkan". 

Looking at Vulkan's core, it looks very much like a space shuttle external tank with four rocket engines strapped to the bottom. Additional power would be provided by strap-on rocket stages powered by RD-170 engines fueled by LOX and Kerosene as an alternative to the SRBs of NASA's space shuttle. For use with the Soviet shuttle, four boosters were needed, but the core rocket could be powered by anywhere from two to eight boosters depending on the size and weight of the payload that needed to be flown. The engines of the Vulkan, designated RD-0120, were about the same size and power class as the SSMEs used in shuttle, but the Soviets weren't concerned with making them reusable. The engines were also capable of being throttled and represented a leap in Soviet rocket design technology. Development was long and difficult, but the first production rocket motors were ready for flight by 1987.

Soviet Shuttle Development

So why does the Soviet shuttle look so much like the American one? The answer is aerodynamics, although there is a bit of that Soviet industrial espionage hiding under the surface. By the time NASA settled on the final shape of their orbiter, they had undergone hundreds of hours of wind tunnel testing and simulation to work out as many bugs in the design as possible. The shuttle's double-delta wings were needed for its cross range capability. Technically, given the massive size of the Soviet Union, they probably could have gone with a design that had less cross-range, but at the time there were no launch and support facilities as large as Baikonur to the east or west of it.

In a spacecraft system as complex as a shuttle, the shape is only the start though and the Soviets had a lot of catching up to do and come up with their own solutions to problems not encountered with the American shuttle. It took five years of development before the designers settled on a shape that very much was a mirror of the space shuttle, but with differences. For one thing, since the Soviet design lacked SSMEs, its rear end contained only the orbital maneuvering engines and due to the change in the shuttle's center of gravity, the nose gear was moved further back from the nose into the belly. Even with these changes, the basic dimensions of the Soviet shuttle were about the same, although the shapes appeared a bit cruder in spots. 

The shape was settled on in 1980 and to test the design, the Soviets began building several test airframes for both structural and flight testing in much the same way that the Americans built STA-99 (which became Challenger) and OV-101 Enterprise. Instead of developing an aircraft to piggy-back the shuttle to altitude for glide testing, the Soviets instead powered one of their test airframes with four turbojet engines. This orbiter became the OK-GLI test vehicle and it made 25 flights from 1985 to early 1988. The Antonov AN-225 cargo plane was developed with the capability to transport the shuttle. But it wasn't finished until 1988. Prior to that, shuttle airframes and portions of the rocket stages were transported on the backs of specially modified M-4 Bison bombers. But the shuttle airframes were stripped-down and unfinished as a fully completed shuttle was too heavy for air transport by an M-4.

Preparations For Flight

Even with a relatively high priority dedicated to the shuttle program, the Soviets had a long and difficult road getting it ready for flight. By the mid-1980s, the orbiter, the rocket booster and the launch facilities had fallen behind schedule. So additional money was allocated and a crash program was undertaken to get everything ready. Manpower on the orbiter, rocket booster and launch pad was increased many times over to finish the vehicle.

In an interesting parallel to NASA's shuttle, the preparation facilities and launch pad for Buran was converted from one used to launch the N-1 moon rocket. So final assembly took place in a massive hangar which once housed parts for the Soviet lunar program. When assembled, the stack would be transported to the pad horizontally on the same transporter and dual railroad lines used to carry the N-1 as well and it would be rotated to a vertical orientation at the pad. 

As with America's shuttle, development of the booster's rocket engines and the heat resistant tiles were the two items that took the longest time to refine and install. Some short cuts also took place as the rocket booster first flew without any major testing of the full stack on the ground. The first launch in 1987 sent up a payload called "Polyus" which was a test bed of technology related to the Soviets answer to Ronald Reagan's Strategic Defense Initiative. The booster worked perfectly, but the payload failed to enter orbit as it instead commanded itself to deorbit rather than boost itself into a higher orbit. With the successful test of the rocket, all that was needed was the orbiter.

Stay tuned for part two of the Buran saga next week. 
Jay Chladek is a freelance space historian and model builder who has written chapters in various books about plastic models of aircraft and spacecraft, both real and fictional. He has also won awards at various levels for his model building work, and has had an interest in space since he was a child growing up in the 1970s. Outposts on the Frontier: A Fifty Year History of Space Stations is his first book in the subject of space history, and will be published as part of the University of Nebraska’s Outward Odyssey series in 2017.