56.

THOR VS. JUPITER

The success Jacobson wrought came none too soon. That August, Eisenhower, as part of a renewed campaign to constrict the military budget, had instructed Wilson to end the absurd expense of two IRBM programs. Wilson had established a committee consisting of Schriever and Medaris, with Wilson’s special assistant for guided missiles, William Holaday, as chairman, to decide whether the nation’s IRBM was to be Thor or Jupiter.

Eisenhower and Wilson were not naive men and it is difficult to believe they thought that either Schriever or Medaris would consent to the cancellation of his own missile. The committee appears to have been structured as it was so that Holaday could permit each of the contestants to argue his case, examine the test results at Canaveral, and then render judgment for one side or the other. Disagree the two contestants did. On September 25, 1957, Medaris sent Holaday a lengthy, point-by-point memorandum, thickened with nine attachments, which extolled Jupiter as the superior missile, its worth demonstrated by its testing record and guaranteed by superior rocket makers under Wernher von Braun. His recommendation was:

a.  The JUPITER be continued as the IRBM and,

b. The THOR project be cancelled as expeditiously as possible.

Schriever countered in his brief that Thor was the better choice for the country because it could be fielded faster than Jupiter. The prototype Jupiters were being built individually at the Redstone Arsenal. The final design of the missile would subsequently have to be farmed out to industry for production. (Medaris intended to use the Chrysler Corporation, which was manufacturing Redstone.) In contrast, because the test model Thors were being created by Douglas on production tooling, the Air Force had the ability to move right into full production and then deployment as soon as the problems common to any new missile were solved. Furthermore, Schriever argued, the Army was building only a missile, not an IRBM weapon system that could be fielded. The Jupiter project lacked provisions for ground support equipment, such as tanks for the LOX and RP-1, shelters to protect the missile from the weather, and other equipment necessary for deployment. By the time the Army got around to furnishing this equipment, more delay would ensue.

Holaday, who submitted his report on October 8, 1957, after Jacobson had begun to rescue the test launches with Thor 105’s 1,495-mile flight on September 20, decided not to place himself in the middle of a nasty interservice row. He beat a bureaucrat’s retreat. He said that unless Thor showed marked improvement, “the spectacular success which has been achieved by the Jupiter test flights” might eventually force its choice. But he recommended that in the meantime the Defense Department “continue both programs until we have a better basis for resolving the various problem areas.”

In his report he did, however, state “a firm requirement” that whichever missile might eventually be chosen must have the capacity for upgrading “to a 2,000 nautical mile [2,301 statute mile] range from the present design” of 1,500 nautical. Medaris claimed that while Jupiter could easily achieve 2,020 nautical miles (2,324 statute), Thor would never be able to fly more than 1,660 nautical (1,909 statute) because of its heavier reentry vehicle. Thor’s reentry vehicle, designated the Mark 2, weighed 3,500 pounds and was the same RV designed for Atlas. In the hustle to put Thor together, it had been adopted without any remodeling to size it down for the smaller rocket. It was a heat shield, or “heat sink,” type. Its nose consisted of a massive, conical shield of solid, machined copper, five eighths to three quarters of an inch thick and six feet in diameter. Behind the shield was a stainless steel compartment in which the one-megaton hydrogen bomb was to ride. The shield alone weighed more than a thousand pounds. As this blunt nose RV descended back into the atmosphere, the shield absorbed the extreme heat generated by the friction of the air and protected the bomb behind it. Because of its shape and the size of the shield, it was also aimed to enter the atmosphere at a shallow angle, thereby slowing itself down as it descended and reducing heat that way as well.

Jupiter’s reentry vehicle, which weighed 3,000 pounds, was the one technological advance the Army missile had over Thor. It was an ablative type, the first of its kind to be mounted on an American ballistic missile and a tribute to the knowledge gleaned from experience by von Braun’s team. The word, originally a grammatical term for nouns or pronouns indicating separation, later also denoted the removal of tissue by a surgeon, the melting of ice or snow, typically from a glacier, or the erosion of rock by wind action. In this age of guided missiles coming into being, “ablative” referred to a reentry vehicle coated with a compound of plastic and other heat-absorbing elements. As the RV plunged back into the atmosphere and friction built up from the density of the air, the coating was enveloped by the red-hot abrasion and progressively burned away, thereby diverting the heat that would otherwise destroy the reentry vehicle and the hydrogen bomb inside it. Usually conical-shaped, or rounded like the nose of a torpedo (Jupiter’s was conical, if much smaller in diameter than Thor’s), an ablative RV had distinct advantages. It descended at a steep angle and retained its speed, making it more accurate because it was less subject to deflection from its course by the winds of the upper atmosphere. For this reason, an ablative RV was later adapted for Atlas. In the case of Thor and Jupiter, any minor difference in accuracy was largely academic, as both were first-generation area-destroying weapons referred to as “city busters” in the language of nuclear weaponry.

Thor was stuck with its 3,500-pound reentry vehicle, Medaris contended. There was no practical way to shave off the 500 pounds necessary for the missile to reach the required 2,000 nautical mile range. “This would mean a complete nose cone redesign with attendant high cost and extensive re-test programs,” he wrote. What he did not calculate was that an IRBM, flying a far shorter distance than an ICBM, also flew at considerably less than an ICBM’s speed, about 10,000 miles per hour. The higher the speed, the greater the heat generated on reentry. Thus the warhead on Thor did not need anything approaching the heat protection afforded by the copper heat shield designed for the Atlas, which was six feet in diameter.

Jacobson, because of his knowledge of guided missiles, understood this. When Schriever, who was in Washington at the time, passed the word to Jake that he had to fly Thor 2,000 nautical miles, Jacobson responded, “Hell, that’s easy.” He instructed Mettler to trim hundreds of pounds (later he could not recall the precise figure) off both the heat shield and the bomb compartment behind it. When the engine of Thor 107 was ignited on October 24, 1957, the rocket flew flawlessly on past the 1,725-mile mark and over the Windward Islands, the last of the West Indies, to plunge into the Atlantic Ocean 3,043 miles from its launching pad on Cape Canaveral. The issue was never raised again. For some reason, Neil McElroy, the Procter & Gamble executive who succeeded Wilson as secretary of defense that October, never enforced Holaday’s requirement to extend the reach to 2,000 nautical miles. The 1,500-nautical mile range was retained. Jake flew the subsequent Thors with the original Atlas heat sink reentry vehicle. There was no necessity to fashion a lighter one. Holaday’s recommendation to wait and see turned into permanent hesitation. The Army and Air Force went on duplicating money and effort as each continued to build its own IRBM. Major General John Medaris had lost his power play. Bennie Schriever’s ICBM program was safe.

If you find an error please notify us in the comments. Thank you!