Little Joe Mercury Escape Tower Test
Status: Retired 1961. Gross mass: 12,700 kg (27,900 lb). Height: 15.20 m (49.80 ft). Diameter: 2.03 m (6.66 ft). Apogee: 89 km (55 mi).
From This New Ocean: A History of Project Mercury, NASA SP-4201:
The search for better experimental methods in manned satellite research produced a concept by Purser and Faget for a new test rocket which would employ a cluster of four solid-propellant Sergeant rockets to provide a high initial thrust. Fired almost vertically and unguided except for large stabilizing aerodynamic fins, the rocket would be an inexpensive means of testing full-scale models of spacecraft in the most critical phases of an orbital mission - launch, abort, and escape at different speeds and under different stresses, parachute deployment, and recovery. Such a vehicle could also "toss" a man in a ballistic capsule to an altitude of perhaps 100 miles. Late in February, Purser and Faget received a job order and authorization to proceed with design work on the test rocket, which at that time they called "High Ride."
Meanwhile Faget's and Paul Purser's proposal made early in the year for a clustered-rocket test booster to be used in payload design research and in manned vertical flights had undergone a politic modification. After Dryden publicly drew his analogy between the Army's Project Adam and the circus lady shot from a cannon, the PARD research team leaders dropped the name "High Ride" and shelved their ideas for using the rocket to fire a man into space. In August, Faget asked William M. Bland, Jr., and Ronald Kolenkiewicz of PARD to prepare precise specifications for a vehicle to launch full-scale and full-weight capsules to a maximum altitude of 100 miles. Only a year would pass before the experimental rocket went into operation. When it did, the former "High Ride" would have acquired the new nickname "Little Joe."
Informed that the Atlas prime movers would cost approximately $2.5 million each and that even the Redstone would cost about $1million per launching, the managers of the manned satellite project recognized from the start that the numerous early test flights would have to be accomplished by a far less expensive booster system. In fact, as early as January 1958 Faget and Purser had worked out in considerable detail on paper how to cluster four of the solid-fuel Sergeant rockets, in standard use by PARD at Wallops Island, to boost a manned nose cone above the stratosphere. Faget's short-lived "High Ride" proposal had suffered from comparisons with "Project Adam" at that time, but in August 1958 William Bland and Ronald Kolenkiewicz had returned to their preliminary designs for a cheap cluster of solid rockets to boost full-scale and full-weight model capsules above the atmosphere. As drop tests of boilerplate capsules provided new aerodynamic data on the dynamic stability of the configuration in free-fall, the need for comparable data quickly on the powered phase became apparent. So in October a team of Bland, Kolenkiewicz, Caldwell Johnson, Clarence T. Brown, and F. E. Mershon prepared new engineering layouts and estimates for the mechanical design of the booster structure and a suitable launcher.37
As the blueprints for this cluster of four rockets began to emerge from their drawing boards, the designers' nickname for their project gradually was adopted. Since their first cross-section drawings showed four holes up, they called the project "Little Joe," from the crap-game throw of a double deuce on the dice. Although four smaller circles were added later to represent the addition of Recruit rocket motors, the original name stuck. The appearance on engineering drawings of the four large stabilizing fins protruding from its airframe also helped to perpetuate the name Little Joe had acquired.
The primary purpose of this relatively small and simple booster system was to save money - by allowing numerous test flights to qualify various solutions to the myriad problems associated with the development of manned space flight, especially the problem of escaping from an explosion midway through takeoff. Capsule aerodynamics under actual reentry conditions was another primary concern. To gain this kind of experience as soon as possible, its designers had to keep the clustered booster simple in concept; it should use solid fuel and existing proven equipment whenever possible, and should be free of any electronic guidance and control systems.
The designers made the Little Joe booster assembly to approximate the same performance that the Army's Redstone booster would have with the capsule payload. But in addition to being flexible enough to perform a variety of missions, Little Joe could be made for about one-fifth the basic cost of the Redstone, would have much lower operating costs, and could be developed and delivered with much less time and effort. And, unlike the larger launch vehicles, Little Joe could be shot from the existing facilities at Wallops Island. It still might even be used to carry a man some day.
Twelve companies responded during November to the invitations for bids to construct the airframe of Little Joe. The technical evaluation of these proposals was carried on in much the same manner as for the spacecraft, except that Langley Research Center itself carried the bulk of the administrative load. H. H. Maxwell chaired the evaluation board, assisted by Roland D. English, Johnson, Mershon, and Bland of the Space Task Group. English later became Langley's Little Joe Project Engineer, Bland the STG Project Engineer, and Mershon the NASA representative at the airframe factory. The Missile Division of North American Aviation won the contract on December 29, 1958, and began work immediately at Downey, California, on its order for seven booster airframes and one mobile launcher.
The primary mission objectives for Little Joe as seen in late 1958 (in addition to studying the capsule dynamics at progressively higher altitudes) were to test the capsule escape system at maximum dynamic pressure, to qualify the parachute system, and to verify search and retrieval methods. But since each group of specialists at work on the project sought to acquire firm empirical data as soon as possible, more exact priorities had to be established. The first flights were to secure measurements of inflight and impact forces on the capsule; later flights were to measure critical parameters at the progressively higher altitudes of 20,000, 250,000, and 500,000 feet. The minimum aims of each Little Joe shot could be supplemented from time to time with studies of noise levels, heat and pressure loads, heatshield separation, and the behavior of animal riders, so long as the measurements could be accomplished with minimum telemetry. Since all the capsules boosted by the Little Joe rockets were expected to be recovered, onboard recording techniques would also contribute to the simplicity of the system.
Unique as the only booster system designed specifically and solely for manned capsule qualifications, Little Joe was also one of the pioneer operational launch vehicles using the rocket cluster principle. Since the four modified Sergeants (called either Castor or Pollux rockets, depending upon modification) and four supplemental Recruit rockets were arranged to fire in various sequences, the takeoff thrust varied greatly, but maximum design thrust was almost 230,000 pounds. Theoretically enough to lift a spacecraft of about 4,000 pounds on a ballistic path over 100 miles high, the push of these clustered main engines should simulate the takeoff profile in the environment that the manned Atlas would experience. Furthermore, the additional powerful explosive pull of the tractor-rocket escape system could be demonstrated under the most severe takeoff conditions imaginable. The engineers who mothered Little Joe to maturity knew it was not much to look at, but they fondly hoped that their ungainly bastard would prove the legitimacy of most of the ballistic capsule design concepts, thereby earning its own honor.
Although Little Joe was designed to match the altitude-reaching capability of the Redstone booster system, and thus to validate the concepts for suborbital ballistic flights, it could not begin to match the burnout speed at orbiting altitude given by the Atlas system. Valuable preliminary data on the especially critical accelerations from aborts at intermediate speeds could be duplicated, but Little Joe could lift the capsule only to 100 miles, not put it at that altitude with a velocity approaching 18,000 miles per hour. For this task, a great deal more, some sort of Big Joe was needed. A Jupiter booster might simulate fairly closely the worst reentry heating conditions but ultimately only the Atlas itself could suffice.
STG shed no tears over cancellation of Jupiter and the balloon tests was that the Little Joe program was making good progress. Blueprint work for the Little Joe airframe had begun early in 1959. North American had assigned A. L. Lawbaugh as project engineer; Langley Research Center had appointed Carl A. Sandahl as its representative for support of this test booster program; and William M. Bland, Jr., was managing Little Joe for the Space Task Group. Throughout the year 1959 these three men were primarily responsible for Little Joe.
Two significant design changes for Little Joe early in 1959 undoubtedly delayed the program slightly but contributed greatly to its eventual success. The first change, decided upon by Gilruth and Faget in January, required a switch from straight to canted nozzles on all the forward-thrusting rocket motors. Little Joe had no guidance system, and such a redesign would minimize any upset from unsymmetrical thrust conditions. The other departure from the original design was the addition of a so-called "booster destruct system." In the interest of range safety there should be some provision to terminate by command the thrust of the main motor units. Therefore Charles H. McFall and Samuel Sokol of Langley devised a booster blowout system, which North American and Thiokol Chemical Corporation, the manufacturers of the rocket motor components, added to the forward end of each rocket combustion chamber.
By mid-February it was apparent that a development program for rocket hardware, even of such limited scope and relative simplicity as the Little Joe booster, demanded a far more sophisticated management organization than either Langley or the Task Group had envisioned. Although informal arrangements had sufficed to get the program started, funding allocations, personnel expansion, and contract monitoring problems began to weigh heavily. Carl Sandahl lamented in one weekly progress report that the transfer of Caldwell C. Johnson from Langley to the Space Task Group could "just about break up the Little Joe Project." Langley's loss was STG's gain in this respect, however, and cooperation continued to be encouraging. Indeed, in May, Bland reported that the delivery of the first Little Joe booster airframe could be expected approximately two weeks earlier than scheduled.
While the results of the Big Joe launch were being studied, a five-man investigating committee at Langley was trying to learn why the first Little Joe shot, on August 21, 1959, had miscarried so badly. Out at Wallops Island that Friday morning several weeks earlier, the first Little Joe (LJ-1) had sat on its launcher, tilted toward the sea, with a full-sized model capsule and escape system on top. Its test mission was to determine how well the escape rocket would function under the most severe dynamic loading conditions anticipated during a Mercury-Atlas launching. At 35 minutes before launch, evacuation of the area had been proceeding on schedule, and the batteries for the programmer and destruct system in the test booster were being charged. Suddenly, half an hour before launch time, an explosive flash and roar startled several photographers and crewmen into diving for cover.
No one was injured, but when the smoke cleared it was evident that only the capsule-and-tower combination had been launched, on a trajectory similar to an off-the-pad abort. The booster and adapter-clamp ring remained intact on the launcher. Near apogee, at about 2000 feet, the clamping ring that held tower to capsule released and the little pyro-rocket for jettisoning the tower fired.
The accident report on LJ-1, issued on September 18, blamed the premature firing of the Grand Central escape rocket on an electrical leak, or what missile engineers were calling "transients," "ghost" voltages or currents, or simply a "glitch" in a relay circuit. The fault was found in a coil. It had been specially designed as a positive redundancy to protect biological specimens from too rapid an abort and as a negative redundancy to prevent inadvertent destruction of the test booster. Again the problem of upgrading the machines to provide safety for animal payloads as well as to ensure mission success had created unexpected problems. This first trial of the brand-new Little Joe test booster apparently had been too ambitious. Fortunately the momentum of the Little Joe test series was not disturbed by the debacle of the boilerplate payload on Little Joe No. 1.
North American Aviation finished and shipped on September 25, 1959, its sixth and last airframe for the Little Joe booster as promised. The Space Task Group therefore had available at the beginning of October all the Little Joe test boosters it had ordered. Designed primarily to man-rate the escape system operating from a Mercury-Atlas already in flight, the Little Joe booster also was committed to perform some biological research before fulfilling its primary mission.
More by coincidence than by design, the next three Little Joe boosters were launched from Wallops Island exactly one month apart in the autumn of 1959. Still the primary aerodynamic test objectives remained unfulfilled. But the fourth shot, in January 1960, finally worked precisely as planned. STG was satisfied that its own pilot safety provisions were viable under the worst possible aerodynamic conditions. The same kind of test on McDonnell's finished product, rather than on boilerplate demonstration capsules, perhaps could be made the following summer.
On October 4, 1959, the same booster that had been jilted by the capsule and escape rocket in August was finally fired, this time with a double dummy - an uninstrumented boilerplate model fitted with an inert escape rocket system. After the fiasco of LJ- 1, the more modest purpose of this test, which later became known as Little Joe 6 (LJ-6), was to prove the "reliability" of the whole booster propulsion cluster. All four Pollux motors, plus four smaller Recruit motors, were set to fire in sequence. Little Joe 6, 55 feet tall and weighing 20 tons at liftoff, blasted up to a peak altitude barely short of 40 miles; then it was intentionally destroyed after two and a half minutes of flight to prove the destruct system. Impact was over 70 miles from Wallops Island. All went well.
Satisfied that Little Joe had proved itself as a booster, the supervisory team of NASA engineers, consisting of John C. Palmer from Wallops, and Roland English, James Mayo, Clifford Nelson, Charles McFall of Langley, and William M. Bland and Robert O. Piland of the Space Task Group, prepared for a new effort to check the correct operation of the abort escape system at maximum loading conditions. The region called "max q" (for maximum dynamic pressure) by aerodynamicists is the portion of the flight path at which relative speed between the vehicle and the atmosphere produces the greatest air resistance on the vehicle. Many variables were involved, but roughly both Little Joe and the Mercury-Atlas were expected to experience dynamic pressures of almost 1,000 pounds per square foot at an approximate altitude of six miles after about one minute of flight time.
For the second attempt at this primary mission, Little Joe 1-A (LJ-1A) needed to propel another dummy capsule and pylon to the max q region. Both drogue and main parachute behavior were to be carefully studied on this flight. Surprised by the insistent demands from the news media to witness these developmental flight tests, STG gave the press a careful enumeration of situations that might call for a "hold" or a "scratch" of the shot.
On November 4, 1959, when the second Little Joe booster was successfully launched, newspapermen could see nothing wrong. The flight looked straight and true until the rocket was out of sight. But the test engineers in the control center observed that the escape motor did not fire until 10 seconds after the point of maximum dynamic pressure. The parachutes and recovery operations performed well enough to fulfill secondary and tertiary objectives, but precisely why escape was too slow was never fully understood. Later analysis showed only that the delayed ignition of the escape rocket caused the separation of capsule from booster at a pressure only one-tenth of that programmed. Because the next scheduled launch of a Little Joe booster was already committed to a test for certain aeromedical objectives and was now in a late stage of preparation, the primary aerodynamic test of the escape system was postponed until January, when a third try, to be called Little Joe 1-B, could be made.
Back in May, STG had begun planning with the Air Force School of Aviation Medicine to include some biological packages in later Little Joe flights. The booster designated No. 5 was reserved specifically to qualify all systems in the McDonnell capsule, carrying a chimpanzee occupant and escaping from a simulated Atlas explosion at the point of max q.
After the disappointment of Little Joe 1-A, Donlan, Bland, and Piland decided to pull out the stops on Little Joe 2 and allow the aeromedical specialists to run all the experiments they wanted on a high-powered flight. The School of Aviation Medicine had made ready a biological package for its primate passenger, a small rhesus monkey named "Sam," after his alma mater. In addition to Sam's special capsule for rocket flight, the military physicians now prepared barley seeds, rat nerve cells, neurospora, tissue cultures, and insect packets to measure the effects of primary radiation, changes in appearance and capacity for reproduction, and ova and larvae responses to the space environment.
Little Joe 2 promised to be a spectacular flight if everything went as planned. The engineers could see how the capsule escape system would function under conditions of high Mach number and low dynamic pressure; more important technically, they could measure the motions, aerodynamic loads, and aerodynamic heating experience of the capsule entering from the intermediate height of about 70 miles. The Air Force medical specialists might also learn about other things, but their chief interest was to see how well Sam himself would withstand weightlessness during the trip. This was also the chief interest of Alan B. Shepard and Virgil I. Grissom, who came to see this launch.
On December 4, 1959, just before noon, the third Little Joe, LJ-2, ripped through the air under full power and burned out at an altitude of 100,000 feet. The tower and capsule separated as planned and the escape rocket gave an additional boost, throwing the capsule into a coasting trajectory that reached its zenith just short of 280,000 feet, or 53 miles. This peak height was about 100,000 feet lower than expected because of a serious windage error, so Sam experienced only three minutes of weightlessness instead of four. He survived the mild reentry, the not-so-mild impact, and six hours of confinement before he was recovered by a destroyer and liberated from his inner envelope.
All preliminary indications reflected a highly successful flight. For the first time Little Joe had achieved full success on all three orders of its programmed test objectives. Congratulatory letters sped around the circuit among those responsible. It was a satisfying way to close out the year. But STG engineers knew that this full-performance test of the Little Joe was not the most crucial case for man-rating the Mercury escape system. They still had to prove that at max q, where everything conspired to produce failure, the escape system could be relied upon to save the life of any man who ventured into this region aboard an Atlas.
Later evaluations of Little Joe 2 were somewhat less sanguine. Biologists were disappointed: although results were better than on any previous biological space flight, they were still not good enough. STG engineers still awaited the more crucial test of the escape system under maximum aerodynamic stress. And the Mercury managers were disappointed at the way the news media had dramatized the animal experiments at the expense of the equally significant demonstration of technological progress.
Public information officers John A. Powers of STG and E. Harry Kolcum of NASA Headquarters tried to correct the "misplaced emphasis" in the news stories before the fourth Little Joe shot, Little Joe 1-B, occurred in January. By this time, Gilruth wished the press would note "the relatively minor role of this particular task in the context of the total Mercury program." But again, to the reporters the star of the event was "Miss Sam," the female counterpart to the occupant of LJ-2, whose life was at stake and whose nervous system was to be tested in psychomotor performance tasks during the short but severe flight. Some of the newsmen perhaps knew or divined that several of the astronauts wanted to ride one of the next Little Joes into space.
Finally, on January 21, 1960, with the fourth launching of the Little Joe series, the escape system performed as planned at the point of max q. Propelled by two Pollux main motors, Little Joe 1-B blasted up to the nominal altitude of slightly less than nine miles and attained a maximum velocity slightly over 2,000 miles per hour. Then the escape rocket kicked on the overdrive for an additional 250 feet in one second to "rescue" the Mercury replica from a simulated booster failure at that point. Over a range of 11.5 miles out to sea, Miss Sam, in her biopack prepared by medical technicians from Brooks Air Force Base and its School of Aviation Medicine, not only survived these severe g loads but also performed well (except for a 30-second lapse) at her business of watching for the light and pulling the lever. After 8.5 minutes of flight, during which the sequence system and capsule landing systems worked perfectly, Miss Sam touched down. She was recovered almost immediately by a Marine helicopter, and was returned in excellent condition to Wallops Station within 45 minutes after liftoff.
For half a minute after the escape rocket fired, the little rhesus monkey had been badly shaken up and did not respond to stimuli, but otherwise Miss Sam acted the role of the perfectly trained primate automaton throughout the flight. Evidence of nystagmus after escape rocket firing and after impact on the water did cause concern, for it suggested that an astronaut's effectiveness as a backup to the parachute system might be impaired. The internal noise level proved to be higher than expected, likewise causing some other worries over the provisions for communications and pilot comfort.
To this point, the Little Joe series of five actual and attempted flights had expended four of the six test boosters North American had made for NASA and five prototype capsules made in the Langley shops. The primary test objectives for these solid-fuel-boosted models were an integral part of the development flight program conducted within NASA by the Space Task Group, with Langley and Wallops support. Now only two Little Joe boosters remained for the qualification flight tests. North American had manufactured seven Little Joe airframes, but one of these had been retained at the plant in Downey, California, for static loading tests. STG ordered the refurbishment of this seventh airframe so as to have three Little Joe boosters for the qualification flight program. The success of Little Joe 1-B in January 1960 meant that the next flight, the sixth, to be known as LJ-5, would be the first to fly a real Mercury capsule from the McDonnell production line. In passing from development flight tests with boilerplate models to qualification flight tests with the "real McDonnell" capsule, the Space Task Group moved further away from research into development and toward operations.
|Little Joe 1 4P American test vehicle. Two stage vehicle consisting of 4 x Recruit + 4 x Pollux|
|Little Joe 1 2P American test vehicle. Two stage vehicle consisting of 4 x Recruit + 2 x Pollux|
|Little Joe 1 4C American test vehicle. Two stage vehicle consisting of 4 x Recruit + 4 x Castor|
Credit: © Mark Wade
Paul E. Purser and Maxime A. Faget conceived of a solid-fuel launch vehicle design for the research and development phase of a manned satellite vehicle project. This launch vehicle was later designated Little Joe. When Project Mecury began in October 1958, the purposeof the Little Joe phase was to propel a full-scale, full-weight developmental version of the manned spacecraft to some of the flight conditions that would be encountered during exit from the atmosphere on an orbital mission. Also, Little Joe tests were used to perfect the escape maneuver in the event of an aborted mission.
A bidders' briefing for the Little Joe launch vehicle was held. As earlier mentioned, this launch vehicle was to be used in the development phase of the manned satellite project. The Little Joe launch vehicle was 48 feet in height, weighed (at maximum) 41,330 pounds, was 6.66 feet in diameter, consisted of four Pollux and four Recruit clustered, solid-fuel rockets, could develop a thrust of 250,000 pounds, and could lift a maximum payload of 3,942 pounds.
The letter-of-intent was placed with North American Aviation for the fabrication of the Little Joe Test vehicle air frame. Delivery of the air frames for flight testing was scheduled to occur every three weeks beginning in June 1959. Space Task Group had ordered all the major rocket motors, which were scheduled for delivery well ahead of the Little Joe flight test schedule. The spacecraft for this phase of the program was being designed and construction would start shortly. Thus the Little Joe program should meet its intended flight test schedule.
A Little Joe Project Coordination Meeting, attended by personnel from Space Task Group, McDonnell, and Wallops Island, was held for the first time. The purpose of the meeting was to determine the status of various developmental phases and whether or not proper coordination was being effected with other related projects in the Mercury program (Big Joe, Mercury-Atlas, Mercury-Redstone, and Mercury-Jupiter). The important factor with regard to the latter item was whether or not a reasonable launch schedule could be established and maintained.
Pigs were eliminated as Little Joe flight test subjects when studies disclosed that they could not survive long periods of time on their backs. However, McDonnell did use a pig, 'Gentle Bess,' to test the impact crushable support, and the test was successful.
North American Aviation delivered the first two Little Joe booster airframes, and noted that the four remaining were on fabrication schedule. The planned program was moving smoothly, for rocket motors to be used in the first flight were available at Wallops Station, Virginia, the test flight launching site. In addition, procurement of the test spacecraft incorporating Mercury flight items was on schedule, and the first spacecraft had been instrumented by Space Task Group personnel. Work was also in progress on other test spacecraft.
Space Task Group officials met with representatives of the School of Aviation Medicine to discuss detailed aspects of the bio-packs to be used in the NASA Little Joe Flight program. The packs were to be furnished by the school. The purpose was to gather life support data that would be applicable to the manned flights of Project Mercury.
Between June 28 and July 11, 1959, 12 heat-transfer tests were made in the Preflight Jet Test facility at Wallops Island on several ablation materials being considered for use on the spacecraft afterbody (not heat shield) for the Little Joe flights. Test conditions simulated those of actual Little Joe trajectories. Of the materials used, triester polymer and thermolag demonstrated the capability to protect the spacecraft against expected heat loads.
A boilerplate spacecraft, instrumented to measure sound pressure level and vibration, was launched in the second beach abort test leading to the Little Joe test series. The purpose of the instrumentation was to obtain measurement of the vibration and sound environment encountered on the capsule during the firing of the Grand Central abort rocket. Memo, Charles A. Hardesty to NASA Langley IRD files, subject: Sound Measurements on the Second Beach Abort Test on the Little Joe Capsule, Oct. 9, 1959.
A study was completed on the 'External and Internal Noise of Space Capsules.' This study covered the acoustic environments of missile and space vehicles including noise generated by the rocket engines, air-boundary layers, and on-board equipment. Data used included noise measurements compiled from the Big Joe I and Little Joe 2 flight tests. These tests were a part of the internal and external noise study that had been in progress since early 1959. NASA officials were still of the opinion that the internal noise level was too high for pilot comfort. Space Task Group felt that data were needed on noise transmission through an actual production-model spacecraft structure.
Little Joe was a booster lashed together by NASA Langley to test the Mercury escape tower abort system. In early NASA secretly considered a manned mission atop Little Joe but quickly dropped the idea when the dynamic pressures involved were reviewed (the concept nevertheless emerged in the trade press in 'Aviation Leak' (Aviation Week and Space Technology).
NASA wind tunnel data on the adaptation of the Project Mercury Little Joe booster to the Apollo launch escape system were analyzed. The booster fins were ineffective in maintaining the stability of the configuration and the project was canceled. The later Little Joe II depended on the inherent stability of the total vehicle to attain a successful ballistic trajectory to test altitude.