A Stellar Rendezvous

(NASA)

A Stellar Rendezvous

Steven R. Strom

The Gemini program brought two orbiting American spacecraft together for the first time—and Aerospace helped arrange the meeting.

As NASA's Project Mercury concluded its final flight in May 1963, America's future success in the space race was by no means assured. Although all of the program's major goals had been accomplished, an enormous amount of work still needed to be done before any attempt could be made to send an American to the moon—which was, at the time, the ultimate goal of the U.S. space program. Moreover, the United States was still lagging behind the Soviet Union, which had already completed a successful two-man flight in 1962 and sent the first woman into space, cosmonaut Valentina Tereshkova, the following year.

To bridge the gap between the Project Mercury flights and the planned Apollo moon landing, in December 1961 NASA announced plans for a series of flights carrying two astronauts using modified Mercury capsules. NASA planners had considered such an interim program, named Mercury Mark II, as early as 1959, but reached no clear consensus as to what its major goals should be. By the time Robert Gilruth, director of NASA's Manned Spacecraft Center, announced the creation of the program at a Houston press conference, the range of possible objectives had been narrowed to three, although many of the management and operations details were still not clearly defined.

The Genesis of Gemini

The first objective was to achieve rendezvous and docking of two vehicles in orbit and to maneuver the two spacecraft using the target vehicle's propulsion system. The second was to complete long-duration flights of up to two weeks. These objectives were chosen primarily because of their direct application to the upcoming Apollo missions. A third objective was to develop a means of landing the returning spacecraft on an airstrip in the United States, though this objective was later shelved after several tests of the proposed paraglider landing system ended in failure. On January 3, 1962, the Mercury Mark II program was formally designated "Project Gemini." The program acquired its new name from the Gemini constellation, which was itself named for the twins Castor and Pollux of ancient Greek mythology.

NASA chose the Titan II ballistic missile to launch the Gemini capsule. The Agena target vehicle would be launched by an Atlas rocket. The Air Force Space Systems Division (SSD) would serve as NASA's agent, responsible for the development, procurement, and launch of major articles of flight hardware except for the Gemini capsule. Thus, with NASA's overall funding and direction, SSD provided the Agena target vehicle, the Atlas launch vehicle for the Agena, the Titan II launch vehicle for the Gemini capsule, and the launch services for all of these. Separate contractors were selected for the Titan II, its first- and second-stage engines, the Agena, and the Atlas rockets.

A Titan II rocket boosts Gemini 3 into orbit on March 23, 1965. This flight, the first with an onboard crew, demonstrated that the Gemini spacecraft was qualified for human flight. (NASA)

The first step would be to reconfigure the Mercury capsule to support the Gemini mission. For example, the cabin needed to be much bigger to accommodate two astronauts while providing them the maneuverability needed to perform the planned docking procedures. The spacecraft contractor implemented a number of changes to allow greater pilot control, including simplified circuitry, redesigned instrumentation, and the addition of rendezvous radar and retrorockets. The Gemini capsule weighed about 2.5 times as much as its Mercury counterpart, with about a 20-percent increase in overall size, but with an approximately 50-percent increase in interior cabin space. The new capsule no longer contained an escape tower; instead, ejection seats were built in to provide a means of emergency escape.

SSD asked The Aerospace Corporation to assume responsibility for general systems engineering and technical direction for both the Titan II and the Atlas/Agena. Aerospace's primary responsibilities were to modify the Titan II to permit piloted spaceflight and to maintain the Pilot Safety Program, which had proved so successful during Project Mercury. Additional responsibilities included modifying Launch Complex 19 at the Atlantic Missile Range to accept the Gemini-Titan and erecting the rocket once it was on the launchpad. A Gemini Program Office was established at Aerospace in January 1962, just one month before John Glenn completed the first American orbital flight. The goal was to coordinate the work that Aerospace was performing at both the Atlantic and Western test ranges.

Rocket Science

At the time of its selection in December 1961, the Titan II was not fully operational. Some of the difficulties arose simply because the Titan II was far more advanced than the original Titan ICBM, and was in many ways an entirely new missile. For example, the Titan II was fueled by a hypergolic fuel-oxidizer combination. These fuels, consisting of unsymmetrical dimethyl hydrazine and nitrogen tetroxide, were in some ways easier to handle and did not require a complex ignition system. Although they were very dangerous in terms of their combustibility and toxicity, they could be stored at room temperature and preloaded into the rocket long before flight. The Atlas rocket, which used cryogenic liquid oxygen, did not offer that capability. In addition, the Titan II generated more than 31,100 newtons greater thrust at liftoff than the Mercury-Atlas, making it an attractive vehicle for the heavier Gemini spacecraft.

NASA intended to minimize modifications of the Titan II, but Aerospace soon recognized that important changes would be necessary. For example, Aerospace advocated the use of inertial (rather than radio) guidance and successfully argued for backup circuits for the electrical systems, backup flight controls, a redundant hydraulic system, and a malfunction detection system. While other proposals never made it beyond the analysis stage, the changes that were incorporated into the launch-vehicle hardware were of critical importance to the overall program.

One of the most important legacies of the Aerospace team was the solution to a major oscillation problem with the Titan II. These longitudinal oscillations were referred to as "pogo" because they resembled the motion of a pogo stick. Although the pogo vibrations might be acceptable for an armed missile, they would certainly prevent the astronauts from performing their in-flight duties, and could even be fatal. Following the initial discovery of this anomaly during the Titan II's first test flight on March 16, 1962, Aerospace engineers and other members of the Gemini team realized that a solution was needed before the rocket could be used.

Joe Wambolt, Tom Shiokari, and Jim McCurry of Aerospace meet with astronauts Gus Grissom and John Young at Cape Kennedy. The meeting took place in March 1965 shortly before the two astronauts were launched on the Gemini 3 craft, which Grissom had dubbed the "Molly Brown." Left to right: John Young, Jim McCurry, Joe Wambolt, Gus Grissom, and Tom Shiokari.

SSD asked Aerospace to guide the pogo investigations. After reviewing the static firing data from the previous year, Sheldon Rubin, a member of the Aerospace technical staff, believed he could solve the problem if he had access to the data of the transfer function of the Titan's engines. Aerospace convinced the Air Force to provide about $1 million to the engine manufacturer to conduct the necessary measurements. After receiving the data, Rubin developed an analytical model that solved the problem. By the end of 1963, Rubin's recommendations were fully adopted, and pogo suppression devices were added to the rocket. Subsequent flights over the next five months proved Rubin's modifications to be a complete success.

Another important Gemini activity under Aerospace direction was the Gemini Stability Improvement Program, also known as Gemsip. This program was developed by the contractor as a byproduct of the design reviews that were conducted for the Titan's first- and second-stage engines, originally as part of the pogo investigations. As a result of these reviews, Aerospace developed a new injector for the Titan II to reduce combustion instability during the second-stage engine's start transient. This was another serious problem observed during flight tests and ground tests. The manufacturer realized the value of an ongoing review process after the injector selected by Aerospace prevailed in tests over the manufacturer's proposed injector. By the end of 1964, Gemsip had become an established program at the manufacturing plant.

Aerospace also performed a vital "lessons learned" review with the Titan II contractor during the process of approving the Gemini launch vehicle for human flight. Aerospace had initiated successful rating procedures during the Mercury program for the Atlas rocket with its Pilot Safety Program, so it was only logical that SSD would ask the corporation to continue with the Titan II. However, the integrating contractor had by now changed. To complicate matters, Titan II parts were manufactured and designed in Denver, but the actual assembly took place in a Baltimore facility that had previously manufactured only airplanes. The change of contractors required Aerospace to assume an active role in virtually every step of the Titan II assembly procedure and to recommend numerous changes in manufacturing. These contributions added to the growing reputation of Aerospace as an impartial but vital observer and contributor. Ron Thompson, who began his Aerospace career in the Gemini Program Office in 1964, recalls, "Aerospace added a second set of eyes and ears to provide an independent review. This definitely caused contractors to be more diligent, and to some degree that legacy remains the same today."

In fact, the contractor's handbook for Gemini launch vehicle employees stated that, "As part of the Pilot Safety Program, SSD and Aerospace impose stringent requirements during the acceptance phase. Hardware is not accepted until SSD and Aerospace are convinced that the hardware and documentation comply with appropriate specifications and other contractual requirements. . . Acceptance is characterized by a methodical approach and an uncompromising attitude."

Fixing the Target

With Project Mercury wrapping up in the spring of 1963, Aerospace began phasing out its Mercury Program Office. Following the closure of the office that fall, Ben Hohmann and Ernst Letsch took over direction of the Gemini Program Office, which was officially known as the Gemini Launch Systems Directorate. By this time, the hard work of Aerospace engineers and the rest of the Gemini team was beginning to yield results, as the performance of the Titan II continued to improve in test launches. The first Gemini launch vehicle, GLV-1, was ready for testing in May 1963, but the vehicle was found to have defects, including serious problems with the wiring in the second stage. In July, Aerospace and SSD rejected GLV-1 after a combined systems test revealed numerous problems, including a lack of documented flight status for major components. After a second test in October, GLV-1 was approved and sent to Cape Kennedy to prepare for its launch as Gemini-Titan 1, the first of two scheduled flights without an onboard crew. Additional problems delayed the launch until April 8, 1964, but the flight was a complete success for both booster and payload, with the capsule remaining in orbit for nearly four days before reentering the atmosphere. Ben Funk, SSD Commander, described Gemini-Titan 1 as "just completely a storybook sort of flight."

As the process of approving the Titan II for passenger flight continued, Aerospace received a formal request from SSD to begin technical surveillance of the Gemini Agena Target Vehicle (GATV). The target vehicle was a standard Agena, modified to permit docking with the Gemini spacecraft.

Ed White demonstrates the Hand-Held Self-Maneuvering Unit to Ben Hohmann and Ernst Letsch of Aerospace and fellow Gemini astronauts prior to the flight of Gemini 4. White later used the device to move about in space during the first American space walk, which he performed on June 3, 1965. Left to right: James McDivitt, Ernst Letsch, Ben Hohmann, Jim Lovell, Frank Borman, and Ed White.

Work on the Agena started relatively late in the program because it was not scheduled for use until the fifth Gemini mission. Still, early development progressed very slowly, and the Air Force hoped that Aerospace could help the contractor sort out the problems. Indeed, SSD sought to alter its oversight strategy, applying Aerospace's technical expertise in all phases of the Gemini program that were operated under Air Force contracts. As such, Aerospace was responsible for monitoring the Agena vehicles from subsystem fabrication through testing through prelaunch and launch. Portions of the Pilot Safety Program were applied to the target vehicle, but the difficulties continued, and the first Gemini Agena Target Vehicle, GATV-5001, was not ready for tests until November 1964. From the very beginning of systems testing, the vehicle displayed serious problems.

Meanwhile, as Aerospace engineers grappled with the ongoing difficulties of the Agena, preparations continued for the launch of Gemini-Titan 2. Even though it experienced several near-disasters while sitting on the launchpad at Cape Kennedy—including being struck once by lightning and twice by hurricanes—the rocket was finally launched on January 19, 1965. This suborbital mission, the final launch without passengers, almost equaled the success of Gemini-Titan 1 and cleared the way for Gemini 3, the first piloted launch.

Bold Moves

NASA, in danger of falling behind schedule, decided to wait just two months before launching Gemini 3, which was now scheduled for March 23, 1965. Mercury veteran Gus Grissom and crewmate John Young made up the flight team. Following the Mercury tradition of giving official names to the spacecraft, Grissom dubbed his Gemini capsule the "Molly Brown," a reference to the Broadway play The Unsinkable Molly Brown. He chose the name because his Mercury spacecraft, the "Liberty Bell 7," sank shortly after landing in the Atlantic Ocean. Perhaps because NASA officials felt that "Molly Brown" was undignified, Gemini 3 was the last to receive an official name. Future Gemini spacecraft would only receive a numerical designation. With only a few minor problems during its three-orbit mission, Gemini 3 met all of its major objectives and proved that the Gemini/Titan II configuration was suitable for human flight.

Astronaut Ed White performs the first American extravehicular activity on June 3, 1965, during the flight of Gemini 4. White was attached to his spacecraft by an umbilical line and a 7-meter tether line, which were wrapped together to form a single cord. (NASA)

The first months of 1965 witnessed two successful Gemini launches, and the U.S. space program had now advanced well beyond the capabilities demonstrated during Project Mercury. Two additional successful missions followed with the launches of Gemini 4 on June 3 and Gemini 5 on August 21. The four-day flight of Gemini 4 was especially noteworthy, as it marked the first time that an American astronaut performed an extravehicular activity. Ed White's "space walk" was important for morale, because Soviet cosmonaut Alexei Leonov had achieved the world's first space walk on March 18. The ability of the Gemini team to duplicate this feat such a short time later meant that the U.S. space program was rapidly catching up with the Soviet program. Gemini 5, an eight-day mission, demonstrated the spacecraft's rendezvous, radar, and long-duration flight capabilities.

Gemini astronauts were now ready to try a rendezvous and docking with an Agena craft. The first attempt was scheduled for 1966, but was moved to the fall of 1965 to coincide with the launch of Gemini 6. On the morning of October 25, 1965, the Agena target vehicle (GATV-5002) was launched from Cape Kennedy. About two miles away, astronauts Wally Schirra and Tom Stafford were seated in their Gemini capsule awaiting their own launch so that they could begin pursuit of the Agena. In spite of a seemingly perfect liftoff for the Atlas rocket carrying the Agena, the initial joy of the flight controllers soon turned to confusion as they lost contact with the rocket just after six minutes into the flight. Radar observers reported several blips on their screens, and flight engineers were forced to conclude that the Agena had exploded over the Atlantic. Just 54 minutes after the countdown began for Gemini 6, NASA was forced to scrub the entire mission as a result of the Agena failure.

To get the problem-plagued GATV program back on track, SSD and Aerospace introduced Project Surefire in November 1965. This initiative, given emergency priority by SSD, was intended to ensure the flightworthiness of the Agena target vehicle. Project Surefire began by convening a symposium of propulsion experts, which concluded, in corroboration of the Aerospace analysis, that the vehicle's use of a fuel lead propellant (i.e., a quantity of fuel that precedes the oxidizer into the thrust chamber during ignition) had led to engine failure.

The Agena's engine would have to be redesigned, and members of Project Surefire would provide oversight and technical direction for this initiative. In one instance, Aerospace engineers prevailed upon the manufacturer to eliminate a lock-in relay in the pilot-operated solenoid-valve control circuitry, which they felt was unnecessary and could lead to potential problems. Joe Wambolt, who moved over to the Gemini Program Office following his work with Project Mercury, still feels pride in Aerospace's activities during this time. "Project Surefire culminated in the best configuration obtainable, from hardware, procedural, and performance standpoints. There were no further engine failures on Gemini Agena vehicles." Another benefit of Project Surefire was the close working relationship that it fostered among NASA, Air Force, Aerospace, and contractor personnel following the acceptance of many of Aerospace's technical recommendations.

A Second Try

Following the cancellation of Gemini 6, NASA boldly decided to make a second attempt before the end of the year; however, rather than launch another Agena, the first rendezvous would be achieved through a dual launch of Gemini 6-A (as the flight was now renamed) and Gemini 7. This joint mission, which garnered the unofficial nickname "Spirit of 76," began with the launch of Gemini 7 on December 4. Astronauts Frank Borman and Jim Lovell were scheduled for a 14-day flight, which would set a new world record and prove that humans could live in near-zero gravity for extended periods.

The launch of Gemini 6-A was set for the morning of December 12. But just one second after engine ignition, the launch vehicle automatically shut down, and the launch was canceled. Soon after Schirra and Stafford were removed from the capsule, the launch was rescheduled for December 15, and engineers began searching for the cause of the aborted launch.

Aerospace personnel, who were already working around the clock, helped review all the available data. They discovered a drop in oxidizer pressure and argued that the oxidizer system should be dismantled. Ron Thompson recalls that "There was reluctance on the part of the contractor, but the Air Force insisted on checking out the problem." The cause of the pressure drop was a dust cap that had been accidentally left in place between the oxidizer check valve and the injector.

Wambolt remembers this data review as a key lesson that still resonates in the work of Aerospace personnel. "Post-flight analysis is probably one of the cornerstones of our launch-vehicle readiness process that we have today for Atlases and Titans." Aerospace historian Everett Welmers neatly summarized this discovery: "Careful attention to oscillograph wiggles had prevented a potential disaster." With the dust cover removed, Gemini 6-A was launched on December 15, and the craft achieved rendezvous with Gemini 7 six hours after its flight began. The two capsules came within one foot of each other during the rendezvous operation. The next day, Gemini 6-A landed in the Atlantic Ocean, and Gemini 7 made its reentry on December 18. Funk sent his congratulations to Aerospace president Ivan Getting: "Even though faced with the disappointment of an aborted launch, a perfect countdown and a successful launch followed and made possible this nation's first rendezvous. Please convey my thanks to all the members of your organization for their participation in this achievement." In turn, Getting sent a telegram to Ben Hohmann, saying, "The contributions by you and your staff reflect great credit on The Aerospace Corporation."

As a result of the successful modifications made to the Agena target vehicle, on January 16, 1966, GATV-5003 was given the green light for launch in conjunction with the upcoming Gemini 8 mission. Gemini astronauts had so far demonstrated that humans could function in space long enough to accomplish a lunar mission and could maneuver one orbiting spacecraft to achieve rendezvous with another. NASA was now anxious to perform a docking with the assigned target vehicle, as this was the final Gemini objective. With the conclusion of Gemini scheduled before the end of the year, NASA's Gilruth wrote Funk in February to express his thanks for the contributions of Aerospace personnel and encourage their continued participation. "Aerospace has played a large part in making the Gemini Launch Vehicle (GLV) Programs successful to date, and we have come to respect and depend upon the services they provide the Government."

Docking and Rolling

On March 16, Gemini 8 was lifted into orbit carrying astronauts Neil Armstrong and David Scott. The first space docking in human history went smoothly at first, but the astronauts soon found themselves out of alignment with their original position. Armstrong and Scott were unable to locate the source of the problem and believed the fault lay with the Agena vehicle. Once they managed to separate their spacecraft, however, Armstrong and Scott found themselves spinning uncontrollably. Apparently, the fault lay with their own craft. With the astronauts in danger of blacking out and their fuel supply running low, NASA ordered an emergency termination of the mission. Armstrong realized that a malfunctioning thruster was the cause of their gyrations, and the orbital attitude maneuvering system was shut down. The craft was stabilized only after the reentry system was activated and bursts were periodically fired from the small thrusters. Gemini 8 made a safe splashdown in the Pacific Ocean, east of Okinawa, after beginning its seventh orbit. A near tragedy of major proportions had been averted, and the crew had made the U.S. space program's first emergency landing. Despite the problems with the Gemini craft and the early termination of the mission, the Agena target vehicle had performed extremely well in its first in-flight test after the Project Surefire modifications. The final objective of the Gemini program had now been achieved.

A Successful Close

The Agena target vehicle as seen from the Gemini 8 craft. On March 16, 1966, the crew performed the first space docking with the Agena, a maneuver that was critical to the success of any future moon mission. This operation was the final major Gemini program objective to be completed. (NASA)

During the remaining four flights, Gemini 9–12, astronauts performed additional rendezvous and docking maneuvers with the target vehicle and conducted more extravehicular activities. The reentry and recovery of the Gemini 12 craft on November 15, 1966, brought the program to a highly successful close. The list of accomplishments was staggering, considering some of the early problems that the program had faced. Ten passenger flights took place within the space of a mere 20 months, and the entire program came in on time and within budget. Astronauts acquired important experience working in conditions of near-zero gravity for extended periods and performed the U.S. space program's first space walks. Many of the problems of rendezvous and docking had been solved, and the modified Titan II had proved itself as a capable launch vehicle. Invaluable lessons were learned for the upcoming Apollo missions, and all of this was achieved with a 100-percent safety record. In addition, by Gemini's conclusion, the Soviet Union was no longer the clear leader in the space race. During the nearly two years of Gemini flights, the Soviets failed to launch a single piloted mission. The early post-Sputnik years of humiliation for the American space effort were largely forgotten by the time the Gemini program ended.

The entire space community made note of the Aerospace contributions to Gemini. The solid work performed alongside the Air Force and NASA made an outstanding contribution to The Aerospace Corporation's legacy of partnership and trust. Fifteen Aerospace representatives received Outstanding Achievement awards from the Air Force for their work with Gemini. In a ceremony held at the Manned Spacecraft Center, NASA presented awards to Wambolt, Hohmann, Letsch, J. W. McCurry, Newton Mas, and Leon Bush. Words of praise for the Aerospace team poured in from around the country, but Vice President Hubert Humphrey perhaps best summed up the nation's thanks in a letter he wrote to Getting on December 8, 1966. "Above all, this Gemini program has revealed how a team representing the Federal Government and private industry can work together and, in so doing, show the world in an open fashion the vitality and efficiency of our democracy and free enterprise system. I congratulate you and your associates for your contribution to Gemini. The American people are proud of your role and participation."

Acknowledgement

The author would like to thank Joseph Wambolt and Robert Yowell for the loan of photographs and documents that assisted in the preparation of this article.