I still remember the night of December 6, 1972. I was in fifth grade at the time and my parents let me stay up well past my normal bedtime to watch the night launch of the final manned mission to the Moon, Apollo 17. Problems with the launch sequencer resulted in a two hour, forty minute delay in lift off which finally occurred at 12:33 AM EST in the early morning hours of December 7. Needless to say, I was a bit bleary eyed when I went to school the next morning but at least I got to witness yet another historical event involving NASA’s Apollo program.

As spectacular as this night launch of a Saturn V had been, it was not the first such launch in the Apollo-Saturn program. While the majority of launches for this program had taken place during daylight hours, launch window requirements dictated the need for one other night launch 7½ years before the liftoff of Apollo 17. This was the launch of the what was known as the Apollo A-104 mission. Although this flight involved “only” a Saturn I rocket, it was the very first night launch of a heavy lift rocket since the beginning of the Space Age over seven years earlier.

The Payloads

The Apollo A-104 flight had been preceded by three 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 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 better assess the hazards posed by micrometeoroids to manned spacecraft like Apollo. Designed for a one year orbital mission, Pegasus 1 returned 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”).

Like the earlier A-100 series test flights, the Apollo Command/Service Module (CSM) payload for Apollo A-104 consisted of a boilerplate spacecraft designated BP-26. 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-26 was a 6.6 meter tall aluminum structure with a maximum diameter of 3.9 meters and total mass of about 4,400 kilograms. On top of BP-26 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 earlier test flights in this series, no engineering tests were planned for the Apollo hardware save for the operation of the LES. As before, no attempt would be made to recover the Apollo boilerplate spacecraft from orbit.

Just as in the Apollo A-103 mission, this flight also carried a scientific payload initially designated Pegasus B tucked inside the hollow interior of the BP-26 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 1,452-kilogram Pegasus B 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. 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. The total area of the detector panels was 214 square meters which was a factor of 80 times larger than the area of the detectors on NASA’s earlier S-55 series satellites, Explorers 16 and 23, which were also dedicated to studying micrometeoroids.

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. The Saturn I launch vehicle would place the Apollo A-104/Pegasus B satellite into a 510-by-750 kilometer orbit inclined 31.8° to the equator with a period of 97 minutes. Because the Pegasus B used the same frequencies as its predecessor for communications with the ground, it was necessary to keep the two satellites 120° apart in their respective orbits to ensure that they would not interfere with each other. For the planned mid-May launch, this necessitated a night-time liftoff – the first of the Saturn I flight program.

Three minutes after reaching orbit, a spring mechanism would be triggered to separate the BP-26 CSM cleanly from the stack and safely into its own orbit so that it would not interfere with the Pegasus B mission. About a minute later, motors would be activated to deploy the huge sensor wings over the course of about a minute. Pegasus 2, 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 10,480 kilograms.

During the Pegasus 1 mission launched in February 1965, the satellite experienced a number of issues that curtailed its ability to measure micrometeoroids. It had been expected that the temporary shorts caused by a penetration of the detector panels would “heal” themselves as the bits of the aluminum causing the signal would burn away as a result of the current flow. Unfortunately, the panels were shorting out at a faster rate than preflight predictions possibly due in part to unwanted inclusions in the Mylar dielectric sheet. And some of the shorts proved to be intermittent in nature causing spurious impact signals. Such shorts seemed to be more common when the temperature of the panels exceeded 71° C as would happen when the panels faced the Sun. Because of the design of the logic network monitoring groups of detector panels, it was not possible to isolate the shorted panels from the network resulting in a faster than expected loss in effective detector area.

For the Pegasus B spacecraft changes were made to overcome the difficulties experienced by the first spacecraft. The detection panels, which were divided into 62 logic groups, incorporated a new fusing arrangement that permitted individual panels or entire logic groups to be disconnected from the detection electronics by ground command. Improvements in manufacturing techniques used for the detection panels were implemented so that they would perform better under conditions of elevated temperature. Other changes in quality assurance of various spacecraft systems were instituted in order to avoid some of the issues experienced by Pegasus 1 and improve the overall reliability of the spacecraft.

The Launch Vehicle

The launch vehicle for the A-104 mission was the Saturn I designated SA-8. This would be the second to last launch of the Saturn I before it was to be replaced by the upgraded Saturn IB which would be used for subsequent Apollo Earth 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-8 was the fifth 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 6,700 kilonewtons at liftoff. Unlike the earlier eight Saturn I launches which used first stages built in house at MSFC, the S-I stage of SA-8 was the first to be built by the Chrysler Corporation. The first stages of the last Saturn I and all those used by the Saturn IB were to be built by Chrysler at NASA’s Michoud Assembly Facility in Louisiana. Because of delays in the final assembly and testing of this first Chrysler-built unit, SA-8 was launched out of sequence and after the last MSFC-built SA-9.

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-8 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.

On top of the S-IV stage was a Instrument Unit (IU) which controlled the Saturn I during ascent. Just as on the SA-9 flight, SA-8 used a new lighter weight version of the IU which was needed to accommodate the Pegasus mission. With a mass less than half of the earlier versions used on the SA-5 to 7 flights, the new 1,212-kilogram IU used lighter unpressurized compartments to house the components of the rocket’s ST-124 guidance system. Like the other Saturn I flights in the series, the performance of various systems were monitored during this flight. A total of 1,394 different measurements were telemetered to ground stations during ascent.

The SA-8 with its Apollo BP-26 boilerplate and Pegasus B payloads was 57 meters tall with a launch mass of 512.5 metric tons. The total orbital mass of Apollo BP-26 along with the Pegasus 2 satellite attached to the spent S-IV stage and IU was 15.3 metric tons.

The Mission

Saturn SA-8 lifted off with its Apollo A-104 and Pegasus 2 payloads from Launch Complex 37B at Cape Kennedy on May 25, 1965 at 2:35:01 AM Eastern Time. The spectacular launch in the early morning hours resulted in Pegasus 2, with the spent S-IV stage still attached, being placed into a 506.5 by 751.2 kilometer orbit with an inclination of 31.8° after just over ten minutes of powered flight – just a touch below the targeted orbit but still well within the acceptable limits for the mission. After a three minute coast in orbit, the Apollo BP-26 successfully separated from the S-IV stage to enter its own independent orbit and expose the Pegasus payload. One minute later, motors were activated to extend the detector panel wings with the procedure monitored from the ground using a television camera mounted on the payload. Pegasus 2 was now ready to start its mission.

Although the Pegasus 2 satellite experienced intermittent issues with its analog and digital telemetry systems which were eventually traced to the circuits becoming wet during a prelaunch thunderstorm, ground controllers were able to iron out the problems well enough so that the mission was considered a success. Two micrometeoroid hits were recorded during the first day in orbit with another 71 hits recorded after 40 days in orbit. During the first four weeks of operation, 36 panels shorted out and were disconnected either singly or in groups by ground command. Because of the new fusing arrangement on Pegasus 2, these shorts did not present as great a problem as they had on the earlier Pegasus 1 mission.

Pegasus 2 continued to transmit useful data until it was deactivated by ground command on August 29, 1968. Its three years and three months of operation easily exceeded the one-year design goal of the satellite. Although it had experienced some issues, the valuable data returned by Pegasus 2 and its predecessor indicated that micrometeoroids were not as big a threat to the Apollo spacecraft as had been originally thought. As a result, the Apollo spacecraft required less protection from micrometeoroids resulting in a savings of about 450 kilograms in total spacecraft mass.

The orbit of the silent Pegasus 2 finally decayed on November 3, 1979 with the inert Apollo BP-26 hardware following almost a decade later on July 8, 1989. With the successful completion of this mission, only one more flight of the Saturn I remained which would carry the last Pegasus payload into orbit. After this launch, operations would transition to test flights of the Saturn IB and flight-certified Apollo hardware as NASA continued its push to send Apollo to the Moon.

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Related Video

Here is a brief video of a 1965 newsreel of the launch of SA-8 carrying Pegasus 2.

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Related Reading

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

“The Second Apollo Orbital Test Flight”, Drew Ex Machina, September 18, 2014 [Post]

“The First Apollo Orbital Test Flight”, Drew Ex Machina, May 28, 2014 [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

“NASA to Launch Second Pegasus Meteoroid Satellite”, Press Release 65-151, NASA, May 17, 1965

“Pegasus 2”, TRW Space Log, Vol. 5, No. 2, p. 46, Summer 1965

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