From the Summer 1961 Issue of the Collins Signal magazine.

Alan B. Shepard, Jr.

Washed by the gentle swells of the Atlantic Ocean northeast of Grand Bahama Island, the Mercury capsule “Freedom 7” awaited pick-up by a hovering helicopter. Inside the copter, Navy Commander Alan B. Shepard, Jr., America's first man in space, settled back for the brief airlift to the Aircraft Carrier Lake Champlain. As the 1 ½ ton capsule was hoisted from the sea, green dye, spilled by the recovery dye marker, swirled around the capsule's rubberized skirt. Months of work, study and practice had culminated in America's fastest, highest, manned flight.

The entire down range flight - lift off to Atlantic return - occupied just under 16 minutes. At Cape Canaveral a trailer-like van carried Shepard to Launch Complex 5 where the 69-foot Redstone missile stood poised like a giant bullet, blunted on top by the capsule which resembled a huge inverted television tube. Atop the capsule was the derrick-like superstructure of the escape system.

Before the first trace of dawn, Shepard entered the gantry elevator for the first part of his 115 mile climb. Reclining upon a contour couch inside the capsule, he sweated out a 120 minute countdown and still another 120 minute delay because of bad weather and minor mechanical troubles. Finally, at 9:34 a.m. E.S.T. with the morning sun breaking out of clouds to etch sharp shadows into the concrete base of Launch Complex 5, the steel service tower rolled away on railroad tracks and the zero hour arrived. The Redstone flashed life, showering the pad with flaming liquid fuel, and lumbered slowly away from the earth. During the 148 seconds of powered flight, Shepard endured an accelerative force six times his weight as the missile blasted him 115 miles high. At an altitude of 35 miles, the Redstone burned out and the escape tower jettisoned. Ten seconds after burn-out the small rockets at the base of the capsule fired to push the craft ahead and away from its booster. Five seconds later an automatic stabilization and control system flipped the space chariot around 180 degrees so the blunt heat-shielded base was in a forward position. Sitting upright, his back toward the direction he was traveling, Shepard raced along a weightless trajectory through space at a speed of 5,000 miles an hour.

Then, in five minutes it was over. The capsule plunged back into the thick atmosphere of space and G forces again gripped the man with nearly twice the strength as before.

Temperatures up to 600 degrees Fahrenheit built up on the conical section of the capsule as it dived earthward, but inside his double-walled hull, insulated, airtight and watertight, Shepard noted instrument recordings of less than 100 degrees Fahrenheit, easily tolerated in his air-conditioned spacesuit.

At 21,000 feet a small parachute popped out to stabilize the spacecraft. At 10,000 feet a 63-foot main chute blossomed and eased the spacecraft into the ocean 302 miles from its launching point.

As the brilliant red and white chute was jettisoned in the ocean wind, special rescue transmitters operated to permit aircraft and surface ships to “home in” with their direction finders to locate the capsule. This link to the recovery force, like the astronaut's link with earth, was provided by a highly miniaturized and rugged electronic communication system, designed and produced by Collins Radio Company in cooperation with a team of eight subcontractors of end-item equipments.

Launch of MR3

Communication in terms of human language and electrical language was vital to the success of the National Aeronautics and Space Administration's Project Mercury. The journey of the manned capsule involved several phases of flight - prelaunch, launch, flight, re-entry, and recovery and the communications system was developed to cover the requirements of all phases both functionally and environmentally.

Supplied by Collins under contract to McDonnell Aircraft Corporation of St. Louis, designers and builders of the Mercury capsule, the Mercury capsule communication system consisted of 30 components produced during two years of developmental work by Collins and its team of subcontractors. Areas of research included: the functional circuits necessary for the several phases of communication; the general problem of signal propagation; several special problem areas in manned-capsule electronics, and each piece of major equipment needed to serve the functions of the capsule system.

Mercury Communication Functions
The Mercury communication functions, as integrated into a complete system for the capsule and its ground counterpart, could be outlined as follows:

Voice Communication. It was necessary for the astronaut and ground personnel to talk to each other during all phases of the mission. Redundant equipment was used to give reliable voice communication in both flight and rescue operations.

Command Function. Redundant command receivers with a substantial number of on-and-off channels were provided to control various functions within the capsule during the launch, flight and re-entry.

Telemetry. Two telemetry transmitters were provided to transmit scientific, operational and aeromedical data from capsule to ground.

Precision Tracking. Two radar transponder beacons in the microwave frequency range were used for precision tracking during flight.

Rescue Beacons. Two rescue beacons, operating on international distress frequencies, were provided for determining the capsule's bearings during retrieval operations at sea. One of these was a “Sea Save” CW beacon. The other one was in the UHF range and used the pulsed “Sarah” principle. In addition, the UHF voice-communications transmitter permitted use of direction finding equipment.

The system in the capsule was compatible with the ground tracking and communication equipment at all locations planned for the tracking network by NASA. This phase of the project required considerable coordination by the designers of the equipment for the capsule and those responsible for the ground equipment. Every effort was made to insure adequate circuit margins over the distances contemplated for every function. System circuit margins were computed for distances of 700 nautical miles for the flight phase and 200 nautical miles for the rescue phase.

Signal propagation in the frequency spectrum (HF to microwave) covered by the Mercury system was thoroughly investigated, with no apparent propagation problems in the VHF, UHF and microwave ranges. Experience with unmanned satellites provided some degree of certainty for VHF, UHF and microwave circuit operation. Also, considerable thought was given HF propagation at satellite altitudes of approximately 100 miles or just below the “F” layer. Theoretical investigations by propagation experts at Collins and the National Bureau of Standards Propagation Laboratory in Boulder, Colorado, indicated that HF at those altitudes would give good long-range multihop communication.

The Reliability Program
Realizing that failure of communication electronics in a manned capsule would endanger the pilot and his ability to fulfill his mission, the Mercury communication project team headed by Robert Olson, head of Development Division B, Cedar Rapids Research Division, and Eugene Habeger, project manager, embarked on a comprehensive reliability program for the space Right. In this effort, the company's engineers teamed with consultants of Aeronautical Radio, Inc., to develop a reliability program for the Collins effort, as well as its subcontractors' efforts.

The reliability program included four basic areas of work - design review, equipment and parts testing, fabrication and assembly surveillance, and failure-recurrence controls. As a part of the quality-assurance measures, component parts were subjected to 100 per cent screening tests. Certain categories of parts, including semiconductors, were tested at elevated tem-peratures.

As a part of the reliability program, every consideration was given to equipment redundance. Nearly every major function package in the communication system was duplicated, and multiple use of equipment provided redundant paths. For example, one of the telemetry transmitters may be keyed in an emergency to provide outgoing CW coded signals; the UHF voice-communications transmitter doubles as a direction finding beacon and the command receivers are equipped with an emergency earth-to-capsule voice channel.

Design Problems
The nature of the capsule environment presented many design problems. Since the capsule contained an atmosphere of pure oxygen, special care was necessary in the design of electronic equipment that would operate in such an atmosphere and in avoidance of materials of construction that might liberate toxic gases in quantity sufficient to harm the astronaut. All relay and switch contacts were carefully sealed to avoid sparking.

All components were small and light, with much of the equipment foam-encapsulated. This permitted mounting components on lightweight structures such as printed boards and aluminum webs to give lightweight, rigid electronics packaging.

Power Demand
The total power demand of the communications system was kept low. Transistors and semiconductor devices were used wherever possible. Vacuum tubes were used only in areas where the power level precluded the use of transistors or in the higher frequency ranges where transistors were not yet applicable.

Environmental Performance
Extremely important in the various phases of the capsule mission was environmental performance of equipment. Each phase of Commander Shepard's Right had different requirements. Vibration, shock and acoustic noise were of paramount importance in the launch phase. Temperature and pressure became important in the Right and re-entry phase. Shock was a problem in the landing phase. The most serious factors were vibration and temperature, solved respectively by foam encapsulation and by heat sinks and water-cooled plates.

A thorough program of testing was accomplished in the Collins laboratories, at the McDonnell plant, and at the launch site. Testing was done at the subsystem or black box level and at the complete system level, both in the laboratory and in the field. Exhaustive checkouts of equipment were made during several unmanned Right tests of the capsule.

Mercury Equipment
Under ground rules laid down by NASA and McDonnell, it was necessary to provide highly reliable equipment in a short time. Although many existing techniques and off-the-shelf designs were used, some equipment had to be designed very rapidly from scratch. Collins was assigned overall system responsibility for all communication equipment.

UHF Orbital and Rescue Voice Equipment
This equipment consisted of a separate transmitter and receiver using a common antenna. The transmitter section, which used sub-miniature tubes, consisted of a crystal-controlled oscillator, a frequency tripler, and a power amplifier. A transistorized modulator provided amplitude modulation of the transmitter. Speech clipping was also incorporated. A transistorized power supply provided plate and filament voltage for the vacuum tubes. The receiver section was a completely transistorized, high-performance, singlecon version superheterodyne. Two UHF voice equipments were available; one was used for primary voice communication and the other was a backup. This voice equipment was utilized during both flight and rescue phases.

HF Orbital and Rescue Voice Equipment
The orbital or flight equipment consisted of a separate transmitter-receiver with a common antenna. The transmitter section consisted of a crystal-controlled oscillator, driver, and two-tube power amplifier. A four-transistor modulator furnished audio power for amplitude modulation. Speech clipping was incorporated in the audio circuits to increase the intelligence power. Provision was made for external-voice-operated or push-to-talk operation. The receiver section was a single conversion superheterodyne with a crystal lattice filter between the antenna and the first RF amplifier stage. A transistor power converter supplied power for all high-voltage circuits. The high frequency rescue equipment differed from the flight equipment in that the final amplifier and modulator stages were re-vised to reduce power output of the carrier for better battery economy during the rescue phase.

Command Receiver
This consisted of an FM superheterodyne receiver feeding a decoder which provided a number of command channels for capsule control functions. Each command channel was activated by a subcarrier tone transmitted on an FM signal. The receiver section used 11 germanium mesa transistors in a double-con version superheterodyne circuit. Following the discriminator, five audio transistors amplified the subcarrier signal, which was decoded by sensitive filters in the supersonic range. Relays were driven from transistors to perform each command function. There was also pro-vision for an emergency voice channel.

Telemetry Transmitters
This equipment consisted of two identical FM transmitters having transistorized stages except for the driver and parallel output amplifiers, which used ceramic tubes. Each transmitter had a linear FM oscillator and frequency-control circuit using a unique crystal discriminator to stabilize the center frequency. A transistor frequency multiplier increased the oscillator frequency to the final carrier frequency. Transistorized power units supplied filament and plate voltage for the output stages.

Radar Transponder Beacons
Two radar transponder beacons in separate but identical packages operated at different frequencies in the microwave range. Each beacon consisted of a superheterodyne receiver, pulse modulator, power-output stage and power supply. Most of the beacon circuitry employed transistors, except for the local oscillator and magnetron power-output stages. Provision was made for coding the beacons.

Rescue Beacons
Two beacons, packaged as a single unit, contained a “Sea Save” HF-MCW transmitter and a UHF “Sarah” pulsed-pair transmitter. The circuitry was entirely transistorized except for the UHF “Sarah” beacon output tube. In addition to these beacons, provision was made for “locar” type homing by using the UHF transmitter operated in the CW mode.

Audio Center
This completely transistorized unit centralized all of the audio frequency and control circuitry for the entire communication system. Dual-channel amplifiers were provided for the microphone and headset. A voice-operated relay (VOX) operated the press-to-talk circuits of the voice-communication transmitters when the microphone output reached a suitable output level. An audio amplifier, filter, and mixer were provided for the voice channel of the two command receivers.

1. S-Band Radar Beacon 6210-2.
2. Multiplexer 635H-l.
3. Bicone Isolator 635K-l.
4. UHF Rescue Antenna 237L-1.
5. C-Band Radar Beacon 621D-l.
6. Coaxial Switch “A” 184G-l.
7. UHF Voice Transmitter-Receiver (main) 618H-l.
8. UHF Voice Transmitter-Receiver (backup) 618H-l.
9. HF/UHF Rescue Beacon 56A-l.
10. Control Panel 714U-1.
11. Auxiliary UHF Rescue Beacon 56D-l.
12. Audio Center 346E-l.
13. HF Rescue Voice Transmitter-Receiver 618V-2.
14. HF Voice Transmitter-Receiver 618V-l.
15. Coaxial Switch “B” 184G-l.
16. Command Receiver “A” 50W-1A.
17. Command Receiver “B” 50W-1A.
18. Command Decoder “A” 50W-1B.
19. Command Decoder “B” 50W-1B.
20. UHF Voice Power Amplifier 548K-l.
21. HF Diplexer 635G-l.
22. Low Frequency Telemetry Transmitter 56B-lA.
23. High Frequency Telemetry Transmitter 56B-1B.
24. Telemetry Power Supply “A” 626B-l.
25. Telemetry Power Supply “B” 626B-l.
26. Telemetry Line Filter 635P-l.
27. C-Band Power Divider 2371-lC.
28. C- and S-Band Beacon Antennas 237J-1A.
29. S-Band Power Divider 237J-1B.
30. HF Antenna Z-Match 237U-1.

Control Panel
This unit, mounted within reach of the astronaut, provided three controls for adjusting the level of the audio signal delivered to the astronaut's headset. Audio controls were available for the HF and UHF voice equipment and the voice channel on the command receiver. These controls, of the vertical thumbwheel type, drove audio attenuators through a spur gear train. A push-button permitted emergency keying of one of the telemetry transmitters for emergency CW telegraph communication. A toggle switch permitted switching the UHF voice communication to the “locar” mode of direction finding.

There were four antennas in the capsule: The main antenna, the UHF descent-recovery antenna, the microwave antenna, and a whip antenna for the HF rescue transmitters.

The main antenna was formed by separating two portions of the capsule such that the junction made a discone. The junction was fed by a coaxial cable at its center. The structure acted as a discone in the UHF range and as an asymmetrically fed dipole at HF and VHF frequencies. This allowed simultaneous reception and/ or transmission of all frequencies except the microwave beacon frequencies. The main antenna was used during launch, flight and part of re-entry.

The microwave-beacon antenna system - actually two antennas in one - consisted of three dual-band radiators symmetrically arranged around the capsule, two sets of power dividers, and interconnecting coaxial cables.

Each radiator had two cavity-mounted helix antennas that operated on widely separated microwave frequencies. The radiation pattern of this antenna was circularly polarized and had omni-directional coverage around the axis of the capsule. The pattern coverage in the longitudinal plane was roughly a doughnut shape.

The UHF rescue antenna was a fan shaped monopole located at the top of the capsule and was exposed after jettisoning the bicone antenna fairing during re-entry. Its primary function was to provide a radiator for UHF functions during parachute descent and sea rescue operations.

There were two antenna multiplexers, one the main multiplexer and the other the high frequency diplexer. The main multiplexer consisted of a number of filters arranged so that six frequencies could be coupled to the single bicone-antenna feed line. This unit provided adequate isolation for each channel. The high-frequency diplexer consisted of one high-pass and one low-pass filter, arranged so that two HF frequencies might be operated on the single feed line to the HF whip antenna.

Project Mercury Capsule Communication Subsystem Equipment

Design for the Future
The communication system for the Project Mercury capsule represented the first approach for a manned space vehicle, just as Project Mercury represents America's first tentative step into space. With the achievement of Mercury behind it, NASA's Space Task Group, set up as a special unit two and one-half years ago to plan Project Mercury, could embark on more sophisticated probes of the solar sea. Later this year, the space agency will attempt to put a man into orbit using the Mercury capsule with an Atlas booster. This will be followed by an attempt to hit the moon and then by an effort to land instruments there which will radio back information. In 1962 there will be rocket payloads sent close to Mars and Venus and by 1964 NASA hopes to send a rocket around the moon and back to earth.

Providing space communication systems to meet the challenge of this space timetable is a task appropriate to Collins Radio, whose equipment transmitted America's first voice from space.

Collins Signal, Issue 42, Volume 9-1, 1961