The Last Launch of the Saturn I

At this time there are several new heavy-lift launch vehicles being developed in the United States such as SpaceX’s Falcon Heavy, the recently announced Vulcan being developed by United Launch Alliance and NASA’s huge SLS to support new missions beyond Earth orbit. To one degree or another, these launch vehicles owe much to the lessons learned during the development of America’s first heavy lift launch vehicle, the Saturn I. And just like today, the lessons learned designing, building, testing and launching the Saturn I led to the successes of the uprated Saturn IB and its big brother, the Saturn V, which sent Apollo to the Moon. With an unprecedented perfect launch record, this capable launch vehicle was retired a half a century ago with the launch of the Pegasus 3 satellite and the last of the initial series of Apollo orbital test flights designated A-105.

The Apollo A-105 flight had been preceded by four earlier flights of Apollo program hardware launched as part of Saturn I development program. The objectives of the first two flights were to demonstrate the compatibility between the Apollo spacecraft and Saturn I launch vehicle as well as verify the design of the Apollo during launch and ascent into orbit. The first Apollo orbital test flight, called A-101, was successfully launched as part of the SA-6 Saturn I development flight on May 28, 1964 (see “The First Apollo Orbital Test Flight”). The second flight, designated A-102, was launched on September 18, 1964 by SA-7 and successfully met all of its major objectives as well (see “The Second Apollo Orbital Test Flight”).

The launch of SA-7 from LC-37B on September 18, 1964. (NASA)

The third flight, Apollo A-103, was launched using Saturn I designated SA-9 on February 16, 1965. In addition to carrying out measurements in support of Apollo and Saturn development programs, this mission also carried a NASA scientific satellite designed to measure the flux of micrometeoroids in the vicinity of the Earth. Called Pegasus 1, the measurements made by this satellite were meant to assess more accurately the hazards posed by micrometeoroids to manned spacecraft like Apollo. Designed for a one year orbital mission, Pegasus 1 return useful scientific data for over three years despite encountering a number of issues with its systems (see “The Mission of Apollo A-103/Pegasus 1”). The second Pegasus satellite was the primary payload of the launch of Saturn SA-8 on May 25, 1965 as part of the Apollo A-104 mission (see “The First Apollo-Saturn Night Launch”).

The Payloads

Like the earlier A-100 series test flights, the Apollo Command/Service Module (CSM) payload for Apollo A-105 consisted of a boilerplate spacecraft designated BP-9A. Boilerplate models mimic the mass, shape and dynamic properties of flight models but otherwise only carry systems and instruments needed for the tests being conducted.  Their low costs and adaptability make them ideal for early testing of a new spacecraft design. BP-9 had been used originally for dynamic ground tests of the Saturn I and was refurbished afterwards for this mission receiving the new designation, BP-9A. BP-9A was a 6.6 meter tall aluminum structure with a maximum diameter of 3.9 meters and total mass of about 4,580 kilograms. On top of BP-9A was a 7.7-meter tall Launch Escape System (LES) that would be jettisoned during ascent as would happen during an operational Apollo flight. Unlike the first three test flights in this series, no engineering tests were planned for the Apollo hardware save for the jettisoning of the LES during ascent. As in the previous four flights, no attempt would be made to recover the Apollo boilerplate spacecraft from orbit.

the Apollo BP-9A, with the Pegasus C satellite tucked inside, being lifted into place on top of SA-10 on July 6, 1965. (NASA)

Just as in the Apollo A-103 and A-104 missions, this flight also carried a scientific payload initially designated Pegasus C tucked inside the hollow interior of the BP-9A Service Module (SM) which essentially acted as a launch fairing for this satellite. Development of Pegasus, which was NASA’s largest scientific satellite to date, started in February 1963 under the responsibility of NASA’s Marshall Space Flight Center (MSFC) with the Aircraft-Missile Division of Fairchild-Hiller Corporation chosen as the prime contractor. The objective of this series of three satellites was to provide a better assessment of the hazards micrometeoroids in the 10^-5 to 10^-3 gram mass range would pose to manned spacecraft like Apollo which would spend up to a fortnight in space during lunar missions.

The 1,451-kilogram Pegasus C payload consisted of a box-shaped satellite bus which housed all of the systems for communications, power and control as well as a set of small solar panels to recharge the batteries that powered the spacecraft’s systems. Attached to the sides of the bus were a pair of extendable wings that were 4.3 meters wide with a total wingspan of 29.3 meters. On the standard Pegasus design, each wing consisted of seven hinged aluminum alloy frames holding a total of 208 sensor panels. Each 0.5-by-1.0-meter panel consisted of a sandwich-like structure that acted as a giant electric capacitor. The outer layer was a thin sheet of aluminum overlying a sheet of Mylar plastic dielectric coated with a thin layer of copper mounted on a foam core to provide a rigid surface. The aluminum sheets on the detector panels had thicknesses of 0.04, 0.2 or 0.4 millimeters to gauge the impact energy of different size particles. A micrometeoroid penetrating the aluminum layer would briefly short out and discharge the capacitor which would be detected and recorded by the onboard experiment electronics for subsequent periodic download to ground tracking stations.

Diagram showing the major components of the Pegasus satellite. Click on Image to enlarge. (NASA)

While there were some improvements made to Pegasus C based on experience with the previous two Pegasus satellites which continued to send data back to Earth, this flight also carried an additional engineering experiment to test how various materials would fare during long-term exposure to the space environment. Eight of the normal wing-mounted sensor panels on Pegasus C were replaced by dummy panels holding a total of 48 aluminum sub-panels or “coupons” 28 centimeters wide and 41 centimeter long. These coupons in turn carried a total of 352 items to test various materials and thermal samples possessing a range of surface finishes some of which were being considered for use on future missions. Although there was no officially approved mission at the time, the hope was that Pegasus C could be visited by a future manned mission at which time these samples could be recovered by an astronaut during an EVA and returned to Earth for study. In addition to assessing how these materials were affected by their exposure to space, it was hoped that some of these coupons would be pierced by micrometeoroids so that scientists could study the effects of such punctures first hand in the laboratory. At this time in July 1965, there were NASA planning documents that proposed that Pegasus could be visited during the Gemini 11 mission in late 1966.

During launch, the wings holding Pegasus’ detector panels were folded tight against the sides of the satellite bus so that they would fit inside the hollow boilerplate SM. Three minutes after reaching orbit, a spring mechanism would be triggered to separate the BP-9A CSM cleanly from the stack and safely into its own orbit so that it would not interfere with the Pegasus mission. About a minute later, motors would be activated to deploy the huge sensor wings over the course of about a minute. Pegasus 3, as the spacecraft would be called after reaching orbit, would remain attached to the spent final stage of its Saturn I launch vehicle for its mission. Since there was no active attitude control system, Sun and Earth sensors would provide information on the orientation of the slowly tumbling spacecraft. The total orbital mass of the satellite, its support structure and spent upper stage of the launch vehicle was about 10,480 kilograms.

An illustration showing the deployment sequence of the Pegasus satellite. Click on Image to enlarge. (NASA)

In order to make it easier for Pegasus to be reached by a manned spacecraft, the Saturn I launch vehicle would place the Apollo A-105/Pegasus C satellite into a circular 534-kilometer orbit that was lower on average and less eccentric than the orbits of the earlier two Pegasus satellites. After a year or more, the satellite’s orbit was expected to decay enough to make a rendezvous by Gemini or an early Apollo test flight easier. Because Launch Complex 37 used for the orbital Saturn I flights was scheduled for upgrades to support the upcoming series of Apollo-Saturn IB missions, the SA-10 needed to get off the ground no later than the end of July to keep the Apollo program’s tight schedule (see “From Apollo to Orion: Space Launch Complex 37”).

The Launch Vehicle

The launch vehicle for the A-105 mission was the Saturn I designated SA-10. This would be the last launch of the Saturn I before it was to be replaced by the upgraded Saturn IB which would be used for subsequent Apollo orbital missions. The Saturn I was developed for NASA at MSFC in Huntsville, Alabama by a team headed by famed German-American rocket pioneer, Wernher von Braun. SA-10 was the sixth flight of the improved Block II model of the Saturn I with a first stage, designated S-I, sporting eight uprated Rocketdyne H-1 engines generating a total of 6,700 kilonewtons at liftoff.  Unlike the first eight Saturn I launches which used first stages built in house at MSFC, the S-I stage of SA-10 was built by the Chrysler Corporation just as the S-I stage of the previous SA-8 Saturn I launch. The first stages of the last two Saturn I rockets and all those used by the Saturn IB were to be built by Chrysler at NASA’s Michoud Assembly Facility in Louisiana.

Diagram showing the major components of the S-I stage. Click on image to enlarge. (NASA)

The second stage of the Block II Saturn I, designated S-IV, was built by Douglas Aircraft Company and employed six hydrogen-fueled Pratt & Whitney RL-10A-3 engines to generate 400 kilonewtons of thrust.  The S-IV stage used on the SA-10 launch included a modified auxiliary non-propulsive vent system just like its predecessor. This was required to minimize the spin rate of the S-IV stage and the attached Pegasus satellite as an estimated 450 kilograms of unused cryogenic propellants evaporated from inside the tanks after orbit was achieved. The excessive tumbling noted in the older S-IV stages after they achieved orbit could damage the extended wings of Pegasus necessitating the new venting system. A new paint with an all-white scheme was also used on the newer S-IV stages to improve their thermal properties since it would remain attached to Pegasus during this satellite’s mission. The Saturn I stack was topped off by the Instrument Unit (IU) which provided guidance and control functions of the Saturn I during ascent.

Diagram showing the major components of the S-IV stage. Click on image to enlarge. (NASA)

The SA-10 with its Apollo BP-9A boilerplate and Pegasus C payloads was 57 meters tall with a launch mass of 512.6 metric tons. In addition to making measurements of the launch vehicle performance, the SA-10 was also equipped with a television camera which would transmit live images of the rocket’s exhaust plume during ascent as part of an engineering experiment. The total orbital mass of Apollo BP-9A along with the Pegasus satellite attached to the spent S-IV stage was 15.3 metric tons.

The Mission

The S-I stage of SA-10 arrived at Cape Kennedy from NASA’s Michoud Facility via barge on May 31, 1965 and was erected on Pad B of LC-37 on June 2. The S-IV stage, which had arrived by cargo aircraft on May 10, was added on June 6. Assembly of SA-10 was completed the following day with the addition of its IU. The Apollo BP-9A boilerplate model arrived at the Cape from MSFC on June 21 followed the next day by Pegasus C. The two payloads were mated and added to the waiting SA-10 at LC-37B on July 6 with the LES topping off the stack two days later. Three weeks of testing and flight readiness assessments then followed.

The launch of the last Saturn I, SA-10, from LC-37B on July 30, 1965. (NASA)

After an almost routine two-day countdown, SA-10 lifted off from LC-37B at 8:00 AM EDT on July 30, 1965 successfully placing BP-9A and Pegasus 3 into orbit. With this last flight, the Saturn I had an unprecedented ten successful launches in ten attempts at a time when launch failures were common especially during early developments flights of new rockets. After BP-9A was pushed clear, Pegasus 3 was in a 520 by 541-kilometer orbit with an inclination of 29°. Pegasus 3 dutifully extended it pair of wings and began operations.

Like its predecessors, Pegasus 3 started recording micrometeoroid hits on its detector panels shortly after reaching orbit. By December 21, 1965, a total of 196 events had been recorded. Combined with the data from the other two Pegasus satellites, NASA scientists had determined that the threat of micrometeoroids was much smaller than had been assumed. As a result, the Apollo spacecraft required less protection from micrometeoroids than originally thought leading to a savings of about 450 kilograms in total spacecraft mass.

Artist’s depiction of Pegasus in Earth orbit. (NASA)

Unfortunately, the hoped for rendezvous with a manned spacecraft to recover samples from Pegasus 3 never materialized. While the first short EVA during the Gemini 4 mission went well (see “The Forgotten Mission of Gemini 4”), subsequent EVAs experienced a multitude of problems resulting in dangerous astronaut fatigue. New EVA procedures and equipment had to be developed and were not successfully tested until the Gemini 12 mission in November 1966 – the last before the start of manned Apollo test flights (see “The Grand Finale: The Mission of Gemini 12“). The Apollo 1 fire two months later and the subsequent disruption in the original Apollo test flight schedule meant that Pegasus 3, with its quickly decaying orbit, would never be visited. Pegasus 3 was deactivated by ground controllers on August 29, 1968 and the satellite reentered the Earth’s atmosphere on August 4, 1969. With the successful completion of the Saturn I program, efforts turned towards test flights of the new Saturn IB and the much larger Saturn V as NASA continued its push towards the Moon.

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Related Reading

“The First Apollo-Saturn Night Launch”, Drew Ex Machina, May 25, 2015 [Post]

“The Mission of Apollo A-103/Pegasus 1”, Drew Ex Machina, February 16, 2015 [Post]

“From Apollo to Orion: Space Launch Complex 37”, Drew Ex Machina, December 5, 2014 [Post]

General References

Roger E. Bilstein, Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles, University Press of Florida, 2003

Alan Lawrie, Saturn I/IB The Complete Manufacturing and Testing Records, Apogee Books, 2008

“Pegasus C”, NASA Press Release 65-232, July 21, 1965

“Pegasus 3”, TRW Space Log, Vol. 5, No. 4, p. 35-36, Winter 1965-66

“The Meteoroid Satellite Project Pegasus: First Summary Report”, Technical Note D-3505, MSFC-NASA, November 1966