The primary obstacle lying in the path of the Howitzers’ deployment was Draper’s continued inability to refine his guidance system. Data from the Port Matagorda launches helped, as did the input of Polish mathematician Stanislaw Ulam, more measurements of high-altitude weather and upper-atmosphere wind, but the primary obstacle he confronted was a technological one. Despite enormous advances in electrical and electronic controls, he was forced to rely upon mechanical linkages and controls for much of his work. Vacuum tube-based calculating machines were running at Oak Canyon, but their fragility, lack of reliability, weight, size, and the amount of electricity they required made using them in flight simply impossible.
Although Draper had hoped to improve upon his 10-kilometer CEP, events proved otherwise. Whenever he solved one problem, another would crop up, whether it was expansion and contraction of components from heating and cooling, flaws in the mechanical linkages leading to the control surfaces, or simply being blown off course by high-altitude winds. By June, events had come to a head. Draper’s work was creating only marginal gains, and a meeting of von Karman, Goddard, and Groves reached a verdict. Draper’s design would have to be frozen and put into production, even if it could only provide a CEP of 10 kilometers. All involved knew this was not good enough, so they turned to a solution they had discarded early on in the guidance discussion — terminal guidance.
The dictionary defines terminal guidance as “The guidance applied to a guided missile between midcourse guidance and arrival in the vicinity of the target.” To the Manhattan Project, this bloodless definition meant something would be required at or near the target area to provide that terminal guidance. This would be no easy matter, and one the scientists knew would be extremely impractical against a heavily defended target. But it was the only option they had, and they moved forward in the hope that a better solution might present itself.
The terminal guidance solution the Oak Canyon scientists came up with was something called Terminal Semi-Active Radar Homing, though the approach was simpler than its name indicated. In testing, and against Japan, a radar-equipped B-29 flew over the target and illuminated it with an onboard radar set. Sensors located in the forward sections of the Howitzer warheads would detect the reflected radar signals and steer the warhead toward the signal. Similar approaches had been used since 1940 with beam-guidance bomber systems, but these differed in several ways. In beam guidance, bombers flew a straight path along the line of a radio beam. If the radio signal faded, they could turn to the right or left until the signal strengthened to let them know they were on the right course. In the ballistic flight course of a long-range rocket, beam guidance was impossible because the course curved, and across three dimensions.
Still, a beam transmitted from the target area could provide guidance at the critical terminal phase, when it was needed the most. The obvious problem with this was that the target areas tended to be in enemy hands, and if the beam was placed aboard a bomber, an accurate missile might destroy the bomber supplying the beam signal. Therefore, the solution was to bounce the signal off the desired target. Four antennae aboard the warhead assembly received the bounced signals and turned the warhead toward the antennae recording the strongest signal. If all four antennae received a signal of approximately the same strength, the warhead was on target.
The collection of sensors and control systems needed to implement this terminal guidance system weighed more than 1,750 pounds, but it worked — most of the time. Testing revealed that the bounced signals were too weak beyond about 15 miles from the target, greatly limiting the ability of the incoming warhead — traveling at thousands of miles per hour — to adjust in time. Furthermore, if the signal was too weak, the warheads had an alarming tendancy to “hound dog,” or oscillate up, down, and side to side, as if sniffing the air while hunting for a stronger signal. Despite these drawbacks, it was put into production as a stopgap measure.
The TSARH system added another layer of complexity to an already hideously complicated weapon, but it successfully reduced the Howitzer CEP to 2 km, at the cost of requiring a B-29 to venture into harm’s way. Draper’s team continued to search for a new approach, but because time was running out for the program, the majority of their effort was devoted to improving the ease with which the guidance systems were built and used.
During this time, the designs for the warhead assembly were also finalized. As realized in the final design of the wartime Howitzer, the guidance and navigation system were housed in the section of the rocket just below its blunt-pointed nose. That nose itself would contain 17,200 pounds of explosives and the best proximity fuse America could build.
That fuse was one of the best-kept secrets of the war aside from the Manhattan Project. It used a special radar that measured the distance to the ground and ensured a detonation at the correct time. It was used in artillery and anti-aircraft shells in the last two years of the war, and a specialized version was developed for the Howitzer. That came as a result of calculations done for “Teller’s Rocks.” Those figures showed that if the Howitzer’s warhead used a kinetic fuse — contact with the ground causing detonation — the force of impact would drive much of the warhead’s explosive potential into the ground, making it worthless. Instead, James Van Allen of Johns Hopkins’ applied physics laboratory modified the proximity fuse design to ensure a warhead detonation with maximum destructive potential.
The first staged Howitzer arrived in Texas on May 28. It was almost the same as the production Howitzer, albeit with ballast instead of a warhead and a non-finalized guidance system. This early Howitzer also lacked several of the refinements in terms of more efficient control linkages and plumbing that were used on later wartime models. Nevertheless, from the outside, it appeared much the same as the missiles that were launched against Japan.
It stood 186 feet tall from the end of its first-stage engine bells to the tip of its rounded warhead point. It had a diameter of just under 22 feet at its widest and was left unpainted, the better to conserve weight. It was free-standing, with the launch gantry needed only to clamp its bottom portion and lift fueling hoses to the height of the upper stage fuel tanks. There were eight R-3 engines, each with a thrust of about 190,000 pounds, creating a total thrust of more than 1.5 million pounds for the first stage alone.
The second stage consisted of 6 much smaller engines, boasting a total thrust of just under 12,000 pounds. This lesser thrust was required because the rocket would be moving in vacuum when the second-stage engines were fired, and they were primarily for guidance correction after the main engines had cut off, 150 seconds into flight.
Although Draper had hoped to improve upon his 10-kilometer CEP, events proved otherwise. Whenever he solved one problem, another would crop up, whether it was expansion and contraction of components from heating and cooling, flaws in the mechanical linkages leading to the control surfaces, or simply being blown off course by high-altitude winds. By June, events had come to a head. Draper’s work was creating only marginal gains, and a meeting of von Karman, Goddard, and Groves reached a verdict. Draper’s design would have to be frozen and put into production, even if it could only provide a CEP of 10 kilometers. All involved knew this was not good enough, so they turned to a solution they had discarded early on in the guidance discussion — terminal guidance.
The dictionary defines terminal guidance as “The guidance applied to a guided missile between midcourse guidance and arrival in the vicinity of the target.” To the Manhattan Project, this bloodless definition meant something would be required at or near the target area to provide that terminal guidance. This would be no easy matter, and one the scientists knew would be extremely impractical against a heavily defended target. But it was the only option they had, and they moved forward in the hope that a better solution might present itself.
The terminal guidance solution the Oak Canyon scientists came up with was something called Terminal Semi-Active Radar Homing, though the approach was simpler than its name indicated. In testing, and against Japan, a radar-equipped B-29 flew over the target and illuminated it with an onboard radar set. Sensors located in the forward sections of the Howitzer warheads would detect the reflected radar signals and steer the warhead toward the signal. Similar approaches had been used since 1940 with beam-guidance bomber systems, but these differed in several ways. In beam guidance, bombers flew a straight path along the line of a radio beam. If the radio signal faded, they could turn to the right or left until the signal strengthened to let them know they were on the right course. In the ballistic flight course of a long-range rocket, beam guidance was impossible because the course curved, and across three dimensions.
Still, a beam transmitted from the target area could provide guidance at the critical terminal phase, when it was needed the most. The obvious problem with this was that the target areas tended to be in enemy hands, and if the beam was placed aboard a bomber, an accurate missile might destroy the bomber supplying the beam signal. Therefore, the solution was to bounce the signal off the desired target. Four antennae aboard the warhead assembly received the bounced signals and turned the warhead toward the antennae recording the strongest signal. If all four antennae received a signal of approximately the same strength, the warhead was on target.
The collection of sensors and control systems needed to implement this terminal guidance system weighed more than 1,750 pounds, but it worked — most of the time. Testing revealed that the bounced signals were too weak beyond about 15 miles from the target, greatly limiting the ability of the incoming warhead — traveling at thousands of miles per hour — to adjust in time. Furthermore, if the signal was too weak, the warheads had an alarming tendancy to “hound dog,” or oscillate up, down, and side to side, as if sniffing the air while hunting for a stronger signal. Despite these drawbacks, it was put into production as a stopgap measure.
The TSARH system added another layer of complexity to an already hideously complicated weapon, but it successfully reduced the Howitzer CEP to 2 km, at the cost of requiring a B-29 to venture into harm’s way. Draper’s team continued to search for a new approach, but because time was running out for the program, the majority of their effort was devoted to improving the ease with which the guidance systems were built and used.
During this time, the designs for the warhead assembly were also finalized. As realized in the final design of the wartime Howitzer, the guidance and navigation system were housed in the section of the rocket just below its blunt-pointed nose. That nose itself would contain 17,200 pounds of explosives and the best proximity fuse America could build.
That fuse was one of the best-kept secrets of the war aside from the Manhattan Project. It used a special radar that measured the distance to the ground and ensured a detonation at the correct time. It was used in artillery and anti-aircraft shells in the last two years of the war, and a specialized version was developed for the Howitzer. That came as a result of calculations done for “Teller’s Rocks.” Those figures showed that if the Howitzer’s warhead used a kinetic fuse — contact with the ground causing detonation — the force of impact would drive much of the warhead’s explosive potential into the ground, making it worthless. Instead, James Van Allen of Johns Hopkins’ applied physics laboratory modified the proximity fuse design to ensure a warhead detonation with maximum destructive potential.
The first staged Howitzer arrived in Texas on May 28. It was almost the same as the production Howitzer, albeit with ballast instead of a warhead and a non-finalized guidance system. This early Howitzer also lacked several of the refinements in terms of more efficient control linkages and plumbing that were used on later wartime models. Nevertheless, from the outside, it appeared much the same as the missiles that were launched against Japan.
It stood 186 feet tall from the end of its first-stage engine bells to the tip of its rounded warhead point. It had a diameter of just under 22 feet at its widest and was left unpainted, the better to conserve weight. It was free-standing, with the launch gantry needed only to clamp its bottom portion and lift fueling hoses to the height of the upper stage fuel tanks. There were eight R-3 engines, each with a thrust of about 190,000 pounds, creating a total thrust of more than 1.5 million pounds for the first stage alone.
The second stage consisted of 6 much smaller engines, boasting a total thrust of just under 12,000 pounds. This lesser thrust was required because the rocket would be moving in vacuum when the second-stage engines were fired, and they were primarily for guidance correction after the main engines had cut off, 150 seconds into flight.
Great job, Amerigo.