Wondering What the U.S. Air Force’s Secretive Spaceplane Can Do? History Offers Clues
Dyna Soar concept preceded X-37B by 50 years
On Oct. 17, one of two Boeing X-37B robotic spaceplanes in existence landed at Vandenberg Air Force Base in California after spending a record 675 days in orbit.
The U.S. Air Force has remained quite tight lipped about just what the small unmanned spaceplane was doing up there. In all likelihood, the payload and mission were both experimental, but what those experiments might have been remains the topic of speculation.
But strictly speaking, the X-37B is not the first design of its type. Boeing’s X-20 Dyna Soar proposal, now more than 50 years old, offers some clues as to what today’s X-37B could do.
The X-20 was the first serious attempt to build a spaceplane — and its roots stretch back all the way to the 1940s.
In 1948, the Bell Aircraft company began development of the manned intercontinental Bomber Missile, or BoMi, as a way to deliver a nuclear weapon into the heart of the Soviet Union with speed and some measure of precision.
It was a multistage reusable rocket vehicle, manned for the simple reason that unmanned systems were not considered capable of the accuracy needed. The development of the Atlas ICBM put an end to that belief … but not an end to the Air Force’s interest in a manned spaceplane.
In November 1959, Boeing began the laborious task of turning a paper design for a manned spaceplane, the Dyna Soar, into something that could fly. After two years of development and constant revision, in December of 1961 the Dyna Soar reached its ultimate form with the Model 844–2050E.
The Model 844–2050E was a flat-bottomed delta-winged configuration with wingtip fins and a distinct fuselage. Relatively small with a span of only 250 inches, it had a length of 424 inches. At liftoff the Dyna Soar weighed 11,390 pounds.
The Dyna Soar glider proper was not equipped with propulsion systems beyond reaction control jets for attitude control in space. The Dyna Soar, like the X-37B, would land unpowered.
The baseline launch vehicle for the Dyna Soar was the Titan IIIC. This booster could loft the spaceplane onto a once-around sub-orbital flight, from Florida’s Cape Canaveral to Edwards Air Force Base in California.
The Titan IIIC could also send the Dyna Soar into a certifiable orbit for a three-orbit mission—orbital altitude of 600,000 feet—and, it was planned, onto much higher, much longer orbits.
To provide on-orbit maneuver capability, the Dyna Soar would be connected via a “transition section” to a Martin Co. Transstage. This reliable upper stage survived the Dyne Soar program and became a standard feature on the Titan IIIc launch vehicle.
The purpose of using a lifting vehicle was two-fold—first was to gain cross-range capability. The lift capabilities of the Dyna Soar meant that it had a cross range of nearly 2,000 miles and a down-range capability of nearly 4,000 miles, giving it wide latitude in where and when to begin the de-orbit burn.
The second reason for lifting re-entry was that the deceleration could be greatly reduced and stretched over a longer period of time. This, it was thought, would make space travel easier on both the vehicles and the crew, allowing space to become a more “operational” environment.
Even though the Dyna Soar was granted the X-20 designation, it was never intended to be an entirely experimental craft; instead, the X-20 (suborbital flights) and X-20A (orbital flights) were meant to build a database that would allow the construction of operational Dyna Soar aerospacecraft.
Boeing designers presented the “Standard Glider” in mid-1963. Externally identical to the X-20, the interior was changed to permit payloads and expected improvements.
The monopropellant RCS thrusters were replaced with bipropellant jets burning N2O4 and Aerozine 50, the pilot’s instrument panel was re-arranged to let him interact with the payload and the equipment in the secondary power bay was re-arranged for compactness—with much of the power generation capability, such as the LH2 tank, transferred into the transition section.
Most importantly, the equipment bay was modified into a true cargo bay capable of seating up to four passengers. The topside access panel could be replaced with power actuated doors, much like on the later—and now retired—Space Shuttle.
Boeing documentation illustrated a number of payloads for the operational Dyna Soar.
The designers proposed two types of Dyna Soar bombers—the pre-emptive and second strike vehicles. The pre-emptive strike vehicle would carry a crew of three, with two hydrogen bombs strapped alongside the Transtage under aerodynamic fairings.
A large number of these bombers—30 or more—would wait in hardened silos near Vandenberg, ready for instant launch. They would launch on a southerly trajectory that would orbit them over targets in Russia or China.
More or less evenly spaced, they would provide minimal response time from weapons commit to impact—just two minutes.
The bomber would have a crew of three—a pilot-commander and two weapons monitors. Their mission would last around 24 hours, assuming it wasn’t interrupted by an actual nuclear apocalypse.
Additional equipment in the form of electro-optical sensors and a radar altimeter would deploy from the aft “ramp” above the secondary power bay. A secure two-way communications system would also be vitally important.
The “second strike” capability was quite different. Eleven Dyna Soars and their launch vehicles would form a single unit. Ten would be unmanned bombers with the 11th being a manned control vehicle.
Having launched into a storage orbit 100 nautical miles high, no further communications from the ground would be necessary. With a storage-orbit inclination of 28.5 degrees, the weapons would not overfly the Soviet Union. But if national authorities called them down, the vehicles’ cross-range capability was enough to allow them to reach targets as far north as 75 degrees.
The bombers would stay in orbit for 12 weeks. If Armageddon didn’t come, controllers could recall them to land at an Air Force base for recovery, refurbishment and relaunch.
Left unreported is the expected on-orbit mission time for the crewed command vehicle. Presumably, as with other Dyna Soar vehicles, it would have had a mission time of around 24 hours. Most likely the orbiting bombers would be left unattended, with command vehicles joining them only in times of crisis.
Each unmanned Dyna Soar bomber had a single 20-megaton hydrogen bomb, a 5,000-pound thrust turbojet and its fuel. On command, the bomber would re-enter, drop to subsonic speed and start the turbojet. After that it would fly the last 250 nautical miles at low altitude using terrain-mapping radar for guidance to within 400 feet of the target.
They were essentially cruise missiles that dropped down from space.
A version meant for high-altitude detonation replaced the jet engine with a 40-megaton bomb.
Slightly friendlier were several designs for satellite inspector and interceptor craft equipped with sensors and, for certain missions, “negation systems.”
The primary mission was to put the satellite inspector in the same orbit as the target, rendezvous with the target, scan the target with a multitude of sensors, record the data on tape and return the pilot, glider, sensors and data tape to the ground.
For some missions, the pilot would be required to make a judgment regarding the intent of the target satellite, and, if in his judgment it poses a threat, destroy that satellite.
Several slightly different payloads were proposed for satellite inspection. One concept from late 1963 called for a two-man crew, with the second crewman sitting in the unpressurized cargo bay and having the ability to swap places with the pilot. The inspection gear was located mostly in the aft boat tail, and would extend once in orbit and retract prior to re-entry.
This concept had a considerable store of expendables located within the transition section, and provided for a 14-day inspection mission. Little information is available on this concept, but it appears that the two crew were to have to stay within their suits for the entire length of the mission, as the vehicle would be unpressurized and the crew, especially the backseater, exposed directly to space.
Another series of concepts from mid-1963, and apparently the designs the Air Force selected for operational duty, called for a single-man satellite inspector.
The first design called for simple inspection. The inspection sensors were located on a turret that would extend from the cargo bay; this was separate from the cockpit, allowing a pressurized atmosphere. In any event, the mission duration was reduced to a more comfortable 16 hours.
Sensors included a targeting radar, cameras, electronic signals-interception gear and an infrared tracker.
The next design was very similar to the first, with the exception that a 48-inch dish replaced the smaller terminal guidance dish of the earlier model. Due to the larger dish there was a repositioning of the turret sensors and antennae, but everything else was much the same. Mission time was again 16 hours.
An interesting note is that this radar was meant to allow tracking of target satellites with radar cross-sections as low as 0.1 square meters. Stealth satellites were a concern even then.
The third design was a far more aggressive vehicle. The same sensor suite that the previous design had was provided here, but with the addition of “negation provisions.”
The Dyna Soar inspector would be backed off from the target satellite if the pilot judged it to be a threat. With the addition of a nuclear radiation detector and a mass measurement system, the pilot could determine whether the satellite in question was equipped with a nuclear power source or warhead. Mission time was up to 24 hours.
If the crew judged the target satellite to be an unhardened, non-nuclear target, the negation system to be used sounds quaint—a rifle. An AR-15, .223-caliber automatic rifle, to be exact.
The pilot wasn’t to simply roll the window down and take potshots at the satellite. Instead, the AR-15 was mounted to the sensor turret. The crew could fire it at the satellite from a range of 100 to 200 feet to damage solar panels, rocket motors and other delicate structures.
For hardened or nuclear targets, the craft could launch with three to six spin-stabilized, infrared-guided rockets weighing 370 pounds each. The rockets would have to hit a four-square-meter target from a standoff distance of up to five nautical miles, which the designers judged sufficient to protect the pilot from a nuclear detonation.
If the crew fired all the missiles and there was still uncertainty about whether the target was sufficiently damaged, the inspector would move back in to within a few hundred feet, inspect the target and if need be open fire with the rifle.
Almost as old a requirement as the manned rocket bomber was an equivalent reconnaissance platform. It would have the best of both worlds when compared the aircraft and satellite recon systems. It would have the immediacy of aircraft systems, while being as invulnerable and far-ranging as a satellite.
The basic reconnaissance variant of the Dyna Soar was a one-man multi-sensor platform. So many sensors were included that engineers had to cram many of them in the expendable transition section.
A large optical telescope/camera fit in the cargo bay. The basic sensor package included high-resolution cameras and radar. The biggest camera had a 105-inch focal length.
The camera system came with 1,000 feet of film, weighed 1,000 pounds and boasted a theoretical resolution of one foot, which would be quite competitive with modern satellite reconnaissance systems.
From Cape Canaveral, the Titan IIIC would have been able to launch the recon Dyna Soar into a 58-degree inclination, 70 nautical mile high circular orbit. The transtage would be able to provide another 1,400 feet per second while on orbit which could increase inclination to 61.2 degres.
Mission duration would be 24 hours, after which time the Dyna Soar would return with its payload of film and taped data. From Vandenberg, the Titan IIIC would launch the Dyna Soar into orbits with inclinations between 34.6 and 90 degrees.
After years of struggle and achievement, Secretary of Defense Robert McNamara cancelled Dyna Soar on Dec. 10, 1963. You can’t deny that the Dyna Soar program was an expensive one, nor can you argue that there were missions that Dyna Soar, and only Dyna Soar, could fulfill.
For every task anyone proposed for Dyna Soar, there was another, cheaper way of doing it. All of them could be made smaller, lighter, cheaper and at lower technical risk than Dyna Soar, and launched on smaller boosters.
While a vast amount of work was carried out during the existence of the Dyna Soar program—11 million man-hours of engineering, 14,000 hours of wind-tunnel testing, 9,000 hours in simulators—a definite mission for which the Dyna Soar proved demonstrably superior failed to materialize.
As of the stop-work order, construction was well underway on the first Dyna Soar. At that time, the Air Force had released 49 percent of the require production orders—14,660 of them. The first spaceframe was 40-percent complete.
Fifty years after Dyna Soar ended, the X-37B was orbiting Earth on its third mystery mission.
The X-37B is itself the end result of a development program longer than that of the Dyna Soar. The earliest recognizable antecedent of the X-37B was the Rockwell International “REFLY,” a small REusable FLYback satellite.
REFLY would go into orbit atop a Pegasus booster and would, as with the X-37B, provide power, maneuver and return capability for a payload meant to spend a short time in space. Rockwell submitted a patent application for REFLY in 1993, making the concept at least 21 years old at this point.
After Boeing acquired Rockwell, work on the REFLY continued, leading through the Military Space Plane and Space Maneuver Vehicle programs to the X-40 and finally the X-37B Orbital Test Vehicles. The configuration changed surprisingly little.
NASA chose Boeing to develop a reusable spaceplane in 1999. However, in 2004 NASA transferred the program to the Defense Advanced Research Projects Agency, which not only continued development but also clapped the cloak of classification over it.
While the configuration of the X-37B bears virtually no resemblance to that of the X-20, the cargo bay on the X-37B is larger than that of the X-20. It’s roughly the same cross section, and perhaps half again as long.
Fifty years of advancement in automation means that many missions like those planned for the Dyna Soar would now not need a crewman on-hand. The X-37B also benefits from advances in materials, both structural and thermal.
Where the Dyna Soar was built out of very dense nickel superalloys, the X-37B has a graphite/polymer composite main structure. The Dyna Soar had heat shielding that permitted massive heat loads to penetrate into the vehicle; the X-37B has a Shuttle-like cladding of silica ceramic tiles, effectively keeping the heat out.
The X-37B has a much lighter internal structure, with less need for the cooling systems needed around the Dyna Soar’s cockpit, cargo and equipment bays.
One important difference between the Dyna Soar and the X-37B is the inclusion of primary propulsion in the more recent vehicle. The Dyna Soar glider relied upon the Transtage for orbital maneuvers. The X-37B uses storable bipropellants for both reaction control thrusters and a single main engine in the tail.
The X-37B also has reaction wheels which use rotational momentum to provide attitude control without the expenditure of propellant.
The Dyna Soar used hydrogen/oxygen fuel cells to provide on-board electrical power. While this has proven a successful system on Apollo and the Shuttles, it does limit total energy. Once the cryogenic liquid hydrogen and liquid oxygen are consumed, the ship is out of power.
This was not a major problem for the Dyna Soar, as it was practical to provide enough consumables to outlast the crew who could hardly be expected to remain in their small craft for more than a few weeks. But for the robotic X-37B, far longer missions are—obviously—possible.
Thus a power source that won’t quickly deplete was provided in the form of a solar cell array that deploys from the cargo bay. Radiators are integrated into the payload bay doors, similar to the Space Shuttle.
The X-37B provides similar mission capabilities to the Dyna Soar, but seems to be a substantial improvement upon the earlier design in nearly all respects.
While the X-37B improves on Dyna Soar capabilities in most respects, there is one area in which it has not—what is its actual mission? The Dyna Soar died not because the technology wasn’t there, but because the mission wasn’t.
The one advantage that Dyna Soar offered was the ability to transport crew up and down, but crew are no longer necessary for the bulk of the missions that the military assigned to Dyna Soar.
And the question remains for the X-37B. What payload can it take up and provide for that would make sense to return safely to Earth? It’s generally assumed that the X-37B carries reconnaissance equipment. But all data collected by modern recon systems is transmitted digitally; so what actually needs to come back?
The X-37B could certainly carry out the offensive missions the military once planned for the Dyna Soar. The sensors and weapons needed would be much smaller today than in Dyna Soar’s day.
Additionally, various sources have suggested that the X-37B could carry weapons such as nuclear-armed re-entry vehicles and kinetic energy rods. The weapons could remain on orbit for an extended period and, if not used, return to the surface. This would, of course, be a treaty violation.
The X-20 prototype was left unfinished on the factory floor while at least two X-37Bs have not only been built but launched, even though the same questions of military utility remain unanswered. At least publicly.
Clearly the X-37B program succeeded on the political battleground where Dyna Soar ultimately failed.
Scott Lowther is the publisher of Aerospace Projects Review. The Model 844–2050E is the major feature of the latest issue of APR.