The Mission of Apollo A-103/Pegasus 1

With the recent Orion EFT-1 test flight and the anticipated test flights of the Boeing and SpaceX craft supporting NASA’s commercial crew transport program, these are exciting times for spaceflight enthusiasts. As important as these developments are, they seem to pale in comparison to the excitement surrounding the original Apollo test flights a half a century ago. Although the newer spacecraft are using the best proven technology available, Apollo was being developed from scratch using a range of untried technologies and techniques developed just after the dawn of the Space Age. The success of the more recent spacecraft programs owe much to the developments of the Apollo program and our first attempts to send humans beyond Earth orbit.

The Apollo A-103 Payloads

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 “50 Years Ago Today: The First Apollo Orbital Test Flight”). The objectives of the second test flight, A-102 launched on September 18, 1964, were similar to those of its predecessor: 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 (see “50 Years Ago Today: The Second Apollo Orbital Test Flight”).

Like the earlier A-101 and A-102 test flights, the Apollo Command/Service Module (CSM) payload for Apollo A-103 consisted of a boilerplate spacecraft designated BP-16. 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-16 was a 6.6 meter tall aluminum structure with a maximum diameter of 3.9 meters and total mass of about 4,500 kilograms. On top of BP-16 was a 7.7-meter tall Launch Escape System (LES) that would be jettisoned during ascent as would happen during an operational Apollo flight. BP-16 was fitted with a variety of sensors to transmit 179 different measurements during ascent and briefly once in orbit until its batteries ran out. As in the earlier Apollo A-101 and A-102 flights, no attempt would be made to recover the A-103 boilerplate spacecraft from orbit.

The Command Module of BP-16 being hoisted into place on top of the Service Module with Pegasus 1 inside. (NASA)

Unlike the earlier Apollo orbital test flights, however, this flight also carried a scientific payload initially designated Pegasus A tucked inside the hollow interior of the BP-16 Service Module (SM) which essentially acted as a launch fairing for this satellite. Development of Pegasus 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.

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

The 1,450-kilogram Pegasus spacecraft 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 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 detector area of NASA’s earlier Explorer 16 and 23 satellites which were dedicated to studying micrometeoroids.

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

During launch, the wings holding the detector panels were folded tight against the sides of the satellite bus so that they would fit inside the hollow boilerplate SM. SA-9 would place the Apollo A-103/Pegasus satellite into a 499-by-748-kilometer orbit inclined 31.7° to the equator with a period of 97 minutes. Three minutes after reaching orbit, a spring mechanism would be triggered to separate the BP-16 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 40 seconds. Pegasus 1 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 was 10,400 kilograms. While it was hoped that the solar-powered Pegasus 1 would operate for one year in orbit, program officials were reluctant to advertise this publicly since this was the first satellite in the series. Flight experience with Pegasus 1 with its 55,000 individual parts would allow modifications to be made to subsequent satellites to improve their chances of reaching the one-year lifetime goal.

The Launch Vehicle

The launch vehicle for the A-103 mission was a Block II Saturn I designated SA-9. This was the eighth test flight of the Saturn I program and the fourth destined for Earth orbit. 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. Launched out of sequence before SA-8, SA-9 was the fourth 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.  SA-9 was the last Saturn I flight to use a first stage assembled in house at MSFC with subsequent units manufactured by Chrysler Corporation. It was the delay in the final assembly and testing of the first Chrysler-built S-I that caused SA-9 to be launched before SA-8.

Diagram showing the major components of the SA-9 Saturn I. Click on image to enlarge. (NASA)

The second or S-IV stage of the Block II Saturn I was built by Douglas Aircraft Company and employed six hydrogen-fueled Pratt & Whitney RL-10 engines to generate 400 kilonewtons of thrust.  The S-IV stage used on the SA-9 launch included a modified auxiliary non-propulsive vent system. Even with a series of modifications, the earlier S-IV stages tended to increase their spin rate and tumble once in orbit as an estimated 320 kilograms of residual cryogenic propellants were vented. Since an excessive tumble rate could damage the Pegasus satellite with its wings extended, the new venting system was designed to keep the tumble rate of the satellite at a low level. A new paint was also used on this S-IV stage to improve its thermal properties since it would remain attached to Pegasus 1 during this satellite’s mission.

On top of the S-IV stage was a new Instrument Unit (IU) which controlled the Saturn I during ascent. This new IU had a mass of about 1,200 kilograms – almost 1,300 kilogram lighter than the IU used on the SA-7 flight. This lighter IU and other changes were made to accommodate the Pegasus mission. The SA-9 with its Apollo boilerplate and Pegasus payloads was 57 meters tall with a launch mass of about 508 metric tons. The total orbital mass of Apollo BP-16 along with the Pegasus 1 satellite attached to the spent S-IV stage and IU was just under 15 metric tons.

Diagram showing the major events of the ascent of SA-9 for the Apollo A-103/Pegasus 1 mission. Click on image to enlarge. (NASA)

The Mission

Saturn SA-9 lifted off from Launch Complex 37B at Cape Kennedy on February 16, 1965 at 9:37:03 AM EST after an unscheduled one hour, seven minute hold caused by a power failure in the Eastern Test Range flight safety computer. SA-9 successfully placed its payload into a 496 by 745-kilometer orbit (just a touch lower than nominal) after a near-perfect performance of its two stages. With its tasks completed, the BP-16 CSM separated to enter its own orbit of 500 by 736 kilometers. As planned, Pegasus 1 deployed its huge detector panel wings which was observed using an onboard remote controlled television camera. On its fourth orbit, telemetry from Pegasus 1 indicated the first signal from a micrometeoroid hit. After two weeks in orbit, nearly a score of hits were detected and by early May, a total of 70 penetrations had been recorded.

The launch of SA-9 on February 16, 1965 carrying Apollo A-103/Pegasus 1. (NASA)

While useful data were being returned, the performance of the system was not as good as was originally hoped. 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. 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. Within 20 days of launch, all of the panels covered with 0.2 millimeter-thick aluminum were deactivated as were 40% of the 0.4 millimeter panels. Only the panels with the thinner 0.04 millimeter aluminum layers continued to provide useful data. Problems with the Sun and Earth sensors also complicated the determination of the spacecraft’s attitude needed to analyze the impact data. Modifications to the detector panel power supply and logic circuitry as well as better quality control on the panels and attitude sensor system were instituted to avoid these problems in future Pegasus flights.

Pegasus 1 shown during ground testing with its wings deployed. (NASA)

Despite its issues, Pegasus 1 continued transmitting useful data back to Earth until it was deactivated by ground command on August 29, 1968 – 2½ years longer than its one-year design life goal when launched. Although it had experienced problems, it was possible to modify the two subsequent Pegasus satellites to avoid them. The silent Pegasus 1 satellite remained in orbit until it reentered the Earth’s atmosphere on September 17, 1978. This was followed almost seven years later by the reentry of the derelict BP-16 CSM on July 10, 1985. With the successful missions of Apollo A-103 and Pegasus 1, the United States was one step closer towards its goal of reaching the Moon.

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Related Video

Here is a brief video showing the deployment of the Pegasus 1 satellite as viewed by an onboard TV camera.

Related Reading

“50 Years Ago Today: The Second Apollo Orbital Test Flight”, Drew Ex Machina, September 18, 2014 [Post]

“50 Years Ago Today: The First Apollo Orbital Test Flight”, Drew Ex Machina, May 28, 2014 [Post]

“The First Apollo Little Joe Launch 50 Years Ago Today”, Drew Ex Machina, May 13, 2014 [Post]

“The Coolest Rocket Ever”, Drew Ex Machina, March 30, 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

“Saturn I to Launch Pegasus Meteoroid Detection Satellite”, Press Release 65-38, NASA, February 15, 1965

“Pegasus”, TRW Space Log, Vol. 5, No. 2, pp. 44-46, Summer 1965

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