‘GAS BAG’

Despite the hatch malfunction, Grissom’s flight validated the Mercury capsule sufficiently to encourage the Space Task Group to do away with plans for two more suborbital Redstone missions; in fact, MR-6 had already been discarded from consideration since early June. Although Bob Gilruth was happy with this plan, NASA’s head of spaceflight programmes, Abe Silverstein, felt that the Liberty Bell 7 data should be fully appraised before abandoning MR-5. Moreover, the public knew that three astronauts – Shepard, Grissom and Glenn – were in training for Redstone missions and fully expected each to fly. On the other hand, by expediting Project Mercury and accomplishing a five-hour, three-orbit mission, the achievement of Yuri Gagarin would be eclipsed. To do this, the abilities of the Redstone were simply insufficient; the larger Atlas missile, a rocket with a long history of development problems, would be needed. Then, on 7 August 1961, less than three weeks after Grissom’s mission, all hopes of beating Gagarin were quashed when Gherman Titov completed 17 circuits of the globe in the day-long Vostok 2.

After the analysis of the Liberty Bell 7 data, it became clear that little more could be accomplished with the Redstone and, on 14 August, the Space Task Group’s Paul Purser drafted a termination recommendation for Gilruth to submit to Silverstein. In it, Purser argued that the Redstone had successfully qualified the Mercury spacecraft, had validated NASA’s training hardware and, despite problems, had not presented anything that could hinder a manned orbital flight. Four days later, NASA Headquarters announced the effective termination of Mercury-Redstone and the decision was made that the next manned mission would orbit Earth three times. However, although the capsule was ready, the Atlas rocket had a very bad habit of exploding either on the pad or shortly after liftoff and would require further qualification before it could be entrusted with a human pilot.

Unlike the Redstone, which owed its genesis to the Army and Wernher von Braun, the Atlas was an Air Force effort, inaugurated in 1946 to develop the United States’ first intercontinental ballistic missile. Initial studies were awarded to the Convair Corporation of San Diego and led to Project MX-774 or what was described as “a sort of Americanised V-2’’. Its novel design would control the rocket by swivelling its engines, using hydraulic actuators which responded to commands issued by gyroscopes and an autopilot. Unfortunately, President Harry Truman’s administration offered the Air Force the choice of having funding cut for either its intercontinental manned bombers and interceptors or its advanced weapons designs; the latter option was taken and, as the first MX-774 test vehicle neared completion, it was abruptly cancelled. This left the United States with no intercontinental ballistic missile, a problem made all the more worrisome when the Soviets detonated their first live nuclear device in 1949. A dramatic turnaround followed, with Truman ordering the development of hydrogen-fusion warheads on a priority basis and the outbreak of the Korean War boosting military budgets overnight. The Army began planning the Redstone and the Air Force, at last, was able to resume efforts to build an intercontinental missile which, in 1951, assumed the name ‘Atlas’.

An initially cautious approach to its development was altered dramatically late the following year, when the Atomic Energy Commission conducted the world’s first thermonuclear explosion on Eniwetok Atoll in the Pacific Ocean and increased emphasis was imposed on the Air Force to give its highest consideration to work on long-range ballistic missiles. By 1955, Convair’s rocket gained a new lease of life with a long-term contract for its fabrication: Atlas truly became a high-profile, ‘crash’ project. During its development, another Air Force missile, the intermediate-range Thor, was designed by Douglas Aircraft Company as a stopgap nuclear deterrent, while the Army and (at first) the Navy assumed joint responsibility for a rocket dubbed ‘Jupiter’.

Convair, meanwhile, was busy tackling several fundamental problem areas with the Atlas, one of which led to an entirely different airframe. The principle of this airframe, nicknamed ‘the gas bag’, utilised stainless steel sections thinner than paper, which were rigidised through helium pressurisation at between 1.7-4.2 bars. This led to a huge reduction in the ratio between the Atlas’ structure and total weight – its ‘empty’ weight was less than two per cent that of its propellant weight – and yet the airframe remained capable of withstanding heavy aerodynamic loads. Meanwhile, a three-engine design for the missile, employing two boosters and one sustainer, producing a total thrust of 163,000 kg, together with small vernier jets, was devised by the Rocketdyne Division of North American Aviation.

The technique of igniting the boosters and sustainer on the ground provided an advantage of avoiding the need to start the Atlas’ second stage in the high atmosphere. Firing the sustainer at liftoff also meant that smaller engines could be used. These would be fuelled by a combination of liquid oxygen and a hydrocarbon mixture known as Rocket Propellant-1 (RP-1) – a highly-refined form of kerosene – brought together by an intricate system of turbopumps, lines and valves, which fed them into the Atlas’ combustion chambers at a rate of 680 kg per second. Appearance-wise, it also made the Atlas ‘fatter’ than the Redstone or Thor. Its original length was nearly 23 m, its diameter at the fuel tank section was 3.3 m and its fully-loaded weight was around 118,000 kg. At burnout, it was capable of a speed of some 25,750 km/h and a range of 14,480 km. Later Atlas variants, including those used for Project Mercury’s orbital missions (the Atlas-D), were thicker-skinned and employed radio-inertial guidance systems to detect aerodynamic forces and calculate and adjust position, speed and direction.

A key stumbling block, though, involved preventing the warhead inside the Atlas nosecone from burning up as it entered the denser atmosphere at several times the speed of sound; this also had important ramifications from a man-in-space standpoint. During the development of Project Mercury, discussion flared over whether to include a beryllium heat sink or an ablative shield, with both concepts being developed in tandem for a time, until the latter option was finally selected. The Atlas’ role as an orbital rocket became more acute when the Soviets launched the first Sputniks in 1957, by which time it was only partway through its verification programme, plagued by turbopump and fuel-sloshing problems. Nonetheless, on 8 December 1958, the Space Task Group formally approved it as the launch vehicle for its orbital missions and ordered nine flight units.

Since the Mercury-Atlas combo was taller than the weapons-carrying version of the missile, the gyroscopes had to be installed higher in the airframe, in order to more precisely gauge attitude changes during flight. The Mercury spacecraft would use its own posigrade rockets to separate from the Atlas, but because there was a chance that they could burn through the thin-skinned liquid oxygen dome, a fibreglass shield was affixed to the capsule-to-rocket mating ring. Also, the two small vernier jets were adjusted to reduce weight and complexity and increased aerodynamic loads and buffeting problems with the attached capsule forced engineers to thicken the skin of the Atlas’ forebody. New instrumentation was installed to carefully monitor liquid oxygen and differential tank pressures, attitude rates about all three axes, engine manifold pressures and primary electrical power, all of which had the potential to lead to catastrophe.

Its maiden suborbital flight with a capsule, dubbed Mercury-Atlas 1 (MA-1), got underway on the morning of 29 July 1960. Despite holds for heavy rainfall, the cloud ceiling rose high enough to be considered acceptable and, after other delays caused by problems topping-up the Atlas’ liquid oxygen tanks and ensuring telemetry was sound, the rocket lifted-off at 9:13 am. The early part of ascent went like clockwork, but, around a minute into the flight, the pressure difference between the liquid oxygen and fuel tanks went to zero and all contact with the Atlas was lost. Unfortunately, cloud cover over the Cape was so thick that visual and photographic evidence was virtually impossible, although it subsequently became apparent that the Atlas’ walls had ruptured due to vibrations set up by mechanical resonance in the capsule-to-rocket adaptor. The rocket and spacecraft reached a peak altitude of 13 km, before descending to impact the Atlantic. One of the few saving graces was that the Mercury capsule maintained its structural integrity until it hit the ocean.

A stainless steel reinforcing ‘belly band’, strapped around the upper part of the

The crumpled MA-1 spacecraft after its ill-fated Atlas launch.

rocket, was implemented and the capsule-to-Atlas adaptor was stiffened. The MA-2 suborbital mission was duly launched at 9:12 am on 21 February 1961, passing successfully through ‘Max Q’ a minute later, and after reaching an apogee of 183 km, the now-separated capsule commenced its ballistic fall towards the South Atlantic. Splashdown occurred 18 minutes after launch and a proud NASA described the mission as ‘‘nominal in nearly every respect’’, with MA-2 recovered in good condition. When asked at a press conference later that day if an astronaut could have survived the test, Bob Gilruth beamed with a resounding ‘‘Yes’’.

Nine weeks later, at 11:15 am on 25 April, MA-3 lifted-off on what should have been an orbital flight, carrying an electronic mannequin capable of ‘inhaling’ and ‘exhaling’ man-like quantities of gas, heat and water vapour. This time, however, the Atlas failed to properly follow its roll and pitch manoeuvres due to a transient voltage. ‘‘The roll and pitch program normally changed the initial vertical trajectory of the launch into a more horizontal one that would take the Atlas out over the Atlantic,’’ wrote Gene Kranz. ‘‘This Atlas was still inexplicably flying straight up, threatening the Cape and the surrounding communities.’’ It was remotely destroyed after just 43 seconds, but, fortunately, the LES tower saved the Mercury capsule by pulling it free as planned. It impacted the Atlantic seven minutes after launch and was in such good condition that it was used on the very next Atlas flight. That flight was itself repeatedly postponed, firstly by delays in the delivery of its rocket to the Cape and also by the need to extensively overhaul the old MA-3 capsule back at McDonnell’s St Louis plant. During its time in Missouri, the spacecraft was meticulously cleaned, its heat shield replaced and other repairs implemented.

At length, at 9:04 am on 13 September, only weeks after Gherman Titov’s 17- orbit mission, MA-4 succeeded where its predecessor had failed, splashing down safely 280 km east of Bermuda. Finally, on 29 November, the chimpanzee Enos was blasted aloft in MA-5 to evaluate the capsule’s life-support systems and the Atlas’ performance with a living passenger. NASA Administrator Jim Webb’s office had questioned the Manned Spacecraft Center (MSC) about the need for this and, indeed, Washington newspapers suggested that another such mission would invite Soviet ridicule. However, the decision was taken for a ‘‘necessary preliminary checkout’’ of the hardware before committing a human pilot. Enos, one of four chimps shortlisted for the flight, owed his name to the Hebrew word for ‘man’, hopefully indicative that the next Mercury-Atlas would be flown by a somewhat less hairy hominid. He underwent 1,250 hours of training – more than Ham, because Enos would be exposed to a much longer period of weightlessness and higher G loads – which included psychomotor preparations and aircraft flights. President Kennedy drew laughs from the Senate when he announced that the just-launched Enos ‘‘reports that everything is perfect and working well’’.

The Atlas successfully placed MA-5 into an orbit of 159 x 237 km. Originally intended to fly three orbits – the same as was planned for John Glenn on MA-6 – the capsule encountered difficulties with its attitude-control system when a metal chip in a fuel line caused one of its roll thrusters to fail. This allowed the spacecraft to drift from its normal attitude and, although the automatic system worked to correct this, some 4 kg of fuel was wasted trying to keep it properly aligned during its second orbit. Coupled with this problem, the environmental system experienced glitches and the temperature of Enos’ pressure suit rose to 38.1°C. The problem later resolved itself, but engineers’ concerns over fuel consumption prompted them to request a re­entry at the end of the second orbit. As Enos hurtled over Point Arguello in California, Flight Director Chris Kraft decided to bring MA-5 home early and the retrofire command was transmitted to the spacecraft.

Three hours after launch, Enos’ capsule was bobbing in the Atlantic, just off the coast of Puerto Rico. It was hauled aboard the destroyer Stormes and its hatch explosively detonated. Enos, who, like Ham, had been ‘rewarded’ with electric shocks for operating the correct controls, thanks to an equipment malfunction, was bloodied and ‘‘excitable’’, but nonetheless alive and happy to see his rescuers.

Significant though it was, the flight of Enos – who would die of dysentery less than a year later – quickly faded as public attention became riveted on the impending mission, tentatively scheduled for 19 December. At around the same time, some members of the media speculated that Glenn, Shepard and Scott Carpenter had been selected as candidates for the first orbital mission. Glenn, however, having served as backup for the last two missions, had already been picked by Bob Gilruth to fly. Barely a day after Enos splashed down, his launch vehicle, designated ‘Atlas 109D’, arrived at the Cape and Mercury’s operations director Walt Williams told journalists that three shifts were now working around-the-clock, seven days a week, in a bid to get an American into orbit before the end of the year. That plan evaporated on 7 December, when it was announced that ‘‘minor problems dealing with the cooling system and positioning devices in the Mercury capsule’’ had obliged a postponement until January. Admittedly, many senior managers had known since October that the timeframe for a December launch was tight. Said the agency’s deputy administrator, Hugh Dryden: ‘‘You like to have a man go with everything just as near-perfect as possible. This business is risky. You can’t avoid this, but you can take all the precautions you know about.’’

With the completion of MA-5, NASA felt confident and ready for the manned orbital mission. By the end of February 1962, a somewhat different hominid – a Marine pilot, transcontinental record-holder and ‘Name That Tune’ winner named John Herschel Glenn Jr – would ride the temperamental Atlas not only into space, but into orbit and into the history books. Yet the risks were pervasive and enormous. The success of Enos’ mission did not detract from the reality that the rocket had exploded on a number of occasions. ‘‘John Glenn is going to ride on that contraption?’’ asked the Redstone’s designer, Wernher von Braun. ‘‘He should be getting a medal just for sitting on top of it before he takes off!’’