Earlier this week we celebrated the 50th anniversary of John Glenn’s orbital flight, marking our full entry into the space race with the Soviets.Â Signatory of the mission was our first use of an ICBM to launch Glenn into orbit — the previous missions had been suborbital and used the Redstone missile, itself an SRBM (operational range: 323 km) and not altogether too far removed from the V-2 (as well as a kissing cousin to the SCUD-series SRBMs).Â Modified SRBMs were all well and good for tossing â€œgrapefruitsâ€ (as Krushchev dismissively referred to the Vanguard satellite) into orbit, but to lift a nearly 4,000 lb space capsule (gross launch weight off the Mercury capsule w/escape tower) off the launch pad into orbit would require something much more powerful â€“ and already designed to loftÂ a nuclear warhead and RV weighing over 3,000 lb on a 5,500 mile trajectory as an ICBM.Â That missile was the SM-65 Atlas (and specifically for Project Mercury, the SM-65D), Americaâ€™s first ICBM.
April 1946 â€“ not even a year since the end of WWII and the after effects are still in play.Â The post-war, post-colonial era is well underway as Syria declares its independence from France, the League of Nations meets for the last time to dissolve itself and parts of East Prussia are absorbed into Russia.Â In the US, 400,000 miners go on strike, the Montreal Canadiens beat the Boston Bruins 4-1 for the Stanley Cup and 11 players are named to baseballâ€™s hall of fame. The boys â€œover thereâ€ are very much anxious to be â€œback hereâ€ and make no bones of it and in the Southwest desert of the US, the surviving output of half a decade of war industry begins to line up for the scrappers.
Even still, the newly formed Strategic Air Command of the Army Air Forces is pressing for new means to meet its mission of conducting â€œlong range offensive operations in any part of the world either independently or in cooperation with land and naval forcesâ€¦ employing the latest and most advanced weapons.â€ The previous month, Northrup Aircraft Inc. had been awarded one-year study and research project for a subsonic (SNARK) and supersonic (BOOJUM), long-range (1,000 â€“ 5000 mile) surface-to-surface missile and North American, likewise for 500 mile supersonic, hybrid (rocket/ramjet) missile that would eventually be increased to 5,500 miles and be called Navaho.Â In April, Consolidated Vultee (Convair) Aircraft Corporation was awarded a similar research and study contract for a 1500-5000 mile missile, also in subsonic and supersonic form.Â This study would form the basis of the Atlas ICBM project.Â Three versions or â€œstagesâ€ of missile were to be produced; Stage A (â€œTeetotalerâ€) was a sub-sonic, self-guided cruise missile, Stage B (â€œOld Fashionedâ€), was a test missile using V-2 technology but incorporating new concepts planned for the next phase â€“ Stage C (â€œManhattanâ€), which was to be an ICBM.
By December 1946, however, significant budget cuts to all of the War and Navy departments meant the cancellation of many of those research and study contracts, including the one awarded Convair.Â To soften the blow, Convair was allowed to use the remaining money to complete and flight test three rocket research vehicles for guidance and nose-cone re-entry study.Â These were the Stage B missiles which were launched from White Sands, NM.Â Unfortunately, all three test flights ended in failure, but important concepts were tried, including the use of pressurized fuel and oxidizer tanks, a separating warhead and gimbaled engines.Â The former addressed one of the serious shortcomings of the V-2; its weight, by removing its double walled liner, reducing internal bracing (the interior was pressurized by nitrogen gas instead) and increasing the volume available for propellant and oxidizer.Â A separating warhead ensured that the only part of the vehicle that needed to survive atmospheric re-entry was just the warhead â€“ not the entire missile as was the case with the V-2, reducing weight further and, in the process further increasing range of the missile.Â Finally, use of gimbaled engines enabled the missile to be steered more precisely than through the use of thrust vanes, a simpler system but one which reduces effective thrust by up to 17% (but still in use on the SCUD-family today).Â The net result was essentially a stack of pressurized tanks with a rocket motor at one end and a warhead at the other, setting the major design elements in place for future missiles.
(source: Encyclopedia Astronautica)
|Â Gross mass: 2,800 lb
Â Height: 31.40 ft
Â Diameter: 2.49 ft
Â Thrust: 7,868 lbf
Â Apogee: 31 mi
Â First Launch:
14 July 1948
Â Last Launch:
02 Dec 1948
Â Number: 3
By the end of the decade, the sharp elbows being thrown among the Services while competing for increasingly limited funds became an all out brawl.Â Appointed Secretary of the recently formed Defense Department in 1949, Louis Johnson embarked on a major cost cutting program that exacerbated the roles and missions controversies, highlighted by major weapons programs cancellations including the Navyâ€™s new class of super carriers, the United States, in favor of funding for the Air Forceâ€™s B-36 Peacemaker.Â However, the Air Force, assigned responsibility for long-range surface-to-surface â€œstrategicâ€ missiles (i.e., those that would not have an immediate effect on the battlefield) in 1950, was forced to look hard at existing aircraft programs and developmental missile programs to allocate ever dwindling funds.Â Opting to meet near term goals of improving the nationâ€™s ability to delivery nuclear weapons from a variety of platforms (not just long-range manned bombers like the B-29 and B-36), the Air Force chose to place funding on cruise missile and aircraft carried missiles, placing long-range ballistic missiles as low eighth on the JCS list of missiles to be developed.Â Even at that, more programs fell by the wayside as MATADOR and Firebird missiles were cancelled.Â By the time the Soviets had exploded their bomb and the North Koreans had invaded the South, the Air Force was left with three funded missile programs in toto â€“ Navaho (ground launched cruise missile), Rascal (short-range air-to-ground missile launched by bombers) and Falcon (for air-to-air intercepts).
Not all of the issues faced were fiscal â€“ there were issues with nuclear weapons themselves.Â Up front, there amount of fissionable material was still very much in short supply and what there was went in to designs that were not far removed from the fission-based â€œFat Manâ€ plutonium bomb.Â Smaller weapons were on the visible horizon for TACAIR (notably the LASL-developed Mk7 which entered the stockpile in 1952), but the small but powerful (megaton-range vs. kiloton) weapons that would support the development of an ICBM force were still a theory, awaiting the development of thermonuclear weapons.
Â Hitting the â€˜Resetâ€™ Button
The new decade brought with it a restart of sorts for long-range missiles in general, and Convairâ€™s ICBM design in particular.Â Mindful of the twin geopolitical shocks (Soviet bomb and Korean invasion) and building on promising technical developments like those revealed with the MX-774B, RAND released a report in late 1950 informing the Air Force that long-range missiles were increasingly technically feasible.Â One of the immediate results was a January 1951 contract let to Convair to study whether that weapon should be a ballistic missile or boost-glide missile.Â The required capabilities entailed a range of 5,000 nm carrying an 8,000 lb warhead and a CEP of 1500 ft.Â Designated Project MX-1593, the study was divided into two phases â€“ Phase 1 determined the time and cost to build both versions, a configuration analysis and assessment of potential problems for each.Â Phase 2 would be â€œan intense studyâ€ of those problems to arrive at â€œnecking downâ€ to one design.
Noteworthy was that unlike previous studies which had pitted air-breather cruise missiles (sub- and supersonic) vs. missiles, this study established that a non-air breather missile would be the platform â€“ what differed was the method for flight.Â A Boost-glide missile uses aerodynamic features (e.g., wings) to extend its range following booster burnout.Â The stuff of Nazi rocket scientist plans for a â€œBerlin-to-New Yorkâ€ missile and popular sci-fi dreams in the immediate post-war era, the reality of the limitations of boost glide missiles were such that by 1951, the bloom was well off the bud.Â With boost-glide, smaller, less efficient motors could be clustered to provide the initial kinetic boost and since the entire path would be in the atmosphere, re-entry problems would not be an issue.Â However, given the size of the vehicle and speed, questions were already being raised (as they were in the manned aircraft realm) of survivability â€“ not to mention the weight penalty entailed in carrying the necessary aerodynamic features (like wings).Â With the appearanceÂ of ever more powerful rocket engines then, boost-glide would become moot as an option for long range missiles (until the advent ofÂ hypersonic vehicles that is â€“ but thatâ€™s for another time).
For its part, Convair had been working off company funds in the interregnum between the cancellation of MX-774B and the award of MX-1593, concentrating on key technologies and problem areas identified by the MX-774B.Â In particular, their focus was on pressurized tanks, warhead separation from the missileâ€™s airframe, and thrust vector steering using the gimbaled engines first flown on MX-774B.Â Taken together, it was clear that Convairâ€™s focus, should funding be made available (as it was with MX-1593) would be on a ballistic missile.Â In like manner, North American, builder of the Navaho, had spent a good $1 million of its own money (no mean figure in 1950 dollars) on further development of rocket engines and a high energy test stand in a remote part of California to test them on.
Mk 14 and CASTLE UNION test shot
Bearing this in mind, Convair focused on developing a ballistic missile design that was 160ft in length, 17 ft in diameter and supported as many as 7 rocket engines, developed by North American producing 120,000 lbf of thrust and 20,000 lbf thrust engines produced by Reaction Motors â€“ all necessary to deliver the 8,000 lb warhead the requisite distance (or reference, the still to be designed MK14, the first weaponized thermonuclear device (stockpile entry: 1954) would weigh between 28,000 and 31,000 lb with a yield of 5-7 Mt).Â To put all of this in perspective, the 2-stage Saturn 1B (sans payload), first flown in 1966, and later serving Apollo and Apollo-Soyuz earth orbit missions, was 141 ft long and ~21ft in diameter and used a cluster of 8 H-1 engines to produce 1.16 million lbf of thrust.Â About this same time, the Air Force learned that the Russians were deep into their own missile programs, with several models in development and most disturbingly, had developed a rocket engine that more than doubled ours, outputting in the neighborhood of 265,000 lbf thrust.
Saturn 1B Launches
So here was the conundrum Convair and the Air Force found themselves in.Â A missile design 5 times the size of the MX-774B that would likely struggle to deliver a huge, heavy weapon half a world away â€“ a veritable Everest of a technological challenge for 1951.Â But a way ahead was offered â€“ reduce the size of the payload and raise the CEP, in this case, to 7,000 lb and one mile respectively.Â Why would Convair offer such a seemingly drastic modification to the original specifications?Â In large part it revolved round expectations of a new generation of weapons that would indeed be smaller (i.e., weigh less) and more powerful (reducing the need for a tight CEP for the vast majority of targets).Â The question, if accepted, was would the Air Force press for an accelerated schedule, with its attending risks, or take a more deliberative approach â€“ an approach that the developer of the Navyâ€™s Aegis weapons system, Wayne E. Meyer, would later call â€œbuild a little, test a little, learn a lot.â€Â Under this approach, individual elements would be incrementally tested, then integrated into a larger whole.Â Using this process, IOC would be about 15 years down the road, or around 1965/66.Â In the end, it came down to the threat â€“ that given the albeit limited knowledge extant over the Sovietâ€™s progress in their own missile programs (and using a bit of mirror imaging, projecting our development to date progress on offensive and defensive systems on the Soviets) the Air Force assessed that the Soviets could be first to the ICBM finish line and an emergency system would be helpful to hold the line until a fully operational ICBM could be fielded.Â To that end, a missile could be built for $3 million (FY52) that would loft a 3,000 lb warhead 2,000 nm (or a 1,500 lb warhead 3,000 nm) â€“ in sum, roughly half the size (and cost) of the original MX-1593.Â Pushing back was the Air Staff director of R&D, Major General Don Yates who continued to argue for the slower and technologically safer approach.Â The issue was briefed to the Guided Missile Committee (the JCS body that was supposed to prioritize, coordinate and oversee missile development across all the Services) that approved the smaller design as a study and/or development project whose further development was tied to demonstrated progress.Â Ergo â€“ if progress were rapid, development would likewise be sped up.Â Project Atlas, as it came to be called, was approved for $850,000 in FY52 and $3 million in FY53 as a result and ARDC was tasked to draw up the detailed specifications.Â Delivered in August 1952, those specifications centered on a missile that would have a range of 5,500 nm, carry a warhead weighing 3,000 lb and deliver it to a CEP of 1,500 ft or less.
The next year saw a continued back and forth within the Air Force between ARDC and any one of several committees established to review and make recommendations on advanced technology weapons, including long-range missiles.Â Over the course of this requirements assessment and analysis process (and you thought JCIDS was painfulâ€¦) several important changes were made to the detailed specifications that would have major impact later in the missileâ€™s career.Â Included in these changes were a requirement to use inertial vice radio-assisted navigation, a shift from alcohol-LOX to hydrocarbon (gasoline) and LOX and implementation of a 3-phase, 10 year developmental program that stepped from single- to three and then a final five-engine configuration, generating more than 650,000 lbf of thrust.Â Cost of the program would be $378 million ($3.1 billion in 2011 dollars).Â At long last, by October 1953 the final form of WS-107A (WS = â€˜Weapons Systemâ€™) emerged:
|Convair SM-65A Atlas A
(Source: Neufeld, The Development of Ballistic Missiles in the U.S. Air Force: 1945-1960)
|Â Gross mass: 440,000 lb
(409,000 lb in gasoline-LOX)Â Height: 110 ft
Â Diameter: 12 ftThrust: 656,000 lbfStages: 1.5Range: 5,500 nm
Next up: Part II â€“ A â€œNew Lookâ€ and Trials by Fire