By JOHN D. HODGE, Asst. Chief for Flight Control, Flight Operations Division, NASA Manned Spacecraft Center; and DANIEL T. LOCKARD, Flight Operations, NASA Manned Spacecraft Center




[253] An organization was established It the beginning of Project Mercury to provide support to the astronaut in all phases of the mission This organization was to monitor and direct the mission to insure a greater margin of safety for the astronaut, provide support necessary for mission success by extending the analysis capability of the astronaut, and record data for detailed postflight analysis.


To be able to accomplish the assigned tasks it was necessary to plan operational requirements, generate documentation for real time use, and train personnel specifically for the job of flight control.


As the program progressed from the planning stages through manned orbital flight, flight control progressed in its ability to provide better support.


All Mercury flights were successfully supported by flight controllers at the Mercury Control Center and sites located throughout the world. During, the program a number of difficulties occurred which required changes and improvements to methods used in the early flights. Most of these difficulties were corrected and flight control provided the necessary support to contribute significantly to the success of the program. Because of the experience gained in the Mercury program the flight control organization is now mole qualified to progress to the more complex programs planned for the future.


Purpose of Flight Control


At the beginning of the Mercury program, it was recognized that a ground based crew would be needed to aid the astronaut in monitoring the spacecraft systems, to evaluate systems performance, and to advise the astronaut on the proper action necessary in case of a spacecraft malfunction. Also, the ground crew would have the capability to command reentry of the spacecraft in unmanned vehicles and in manned vehicles should the necessity arise. In addition, it was necessary that the flight control organization record information for postflight analysis. The major objectives of flight control were::

(1) Assist the astronaut during critical mission phases where additional close monitoring and direction would insure a greater margin of safety.

(2) Provide support as required in conducting the flight plan to contribute to mission success.

(3) Extend the system analysis capability of the crew and make available experts in all vehicle systems should they be needed to support the crew .


Flight control is the team work existing between the spacecraft crew and a worldwide ground crew to accomplish manned space flight. This task covers the entire premission preparation phase and terminates with the recovery of the spacecraft and crew. Flight control was broken into five separate tasks:

(1) Preparation of the ground and flight crews prior to launch, which includes the detailed development of Flight Plans, countdowns, Mission Rules, and training of personnel in vehicle systems and ground network operations.

(2) Execution of mission control, which includes the direct supervision and coordination of all aspects of mission real time ground support and the control of the launch vehicle and spacecraft crew during flight.

(3) Supplement the vehicle systems analysis capability of the spacecraft crew, primarily by the compilation, reduction, and evaluation of telemetered and voice data from the spacecraft and its crew.

[254] (4) Assistance to the spacecraft crew in attaining the mission objectives. This task requires participation in the development of an optimum flight program, provision and coordination for real time ground support necessary for execution of this optimum Flight Plan, modification of the Flight Plan in real time as required, and assistance in preparation for subsequent mission phases.

(5) Participation in postmission analysis, recommendations, and the preparation for subsequent flight programs.


History of Communication Between Ground and Pilot


The development of a complex vehicle requires the parallel development of a test and control organization to provide the support necessary to accomplish the test objectives.


The advent of air ground data links has allowed a ground based crew to monitor the test in progress, to modify the flight if necessary, and to recommend the most expeditious course of action to be taken in the event of a contingency situation. The missile age brought about the development of a ground to air data link by which information and commands could he sent from a monitoring ground crew to the vehicle to modify its flight plan.


In the early planning stage of Project Mercury, it became evident that an extensive tracking and data acquisition network would be required. The presence of man in all orbiting satellite demanded that considerably different requirements be placed on the tracking network than had previously been necessary for unmanned vehicles. The most significant of these requirements was that it was now imperative that the network respond rapidly to contingency situations to insure adequate safety of the astronaut. In order to meet the new requirements and to analyze the progress of the flight, the tracking network combined previously used methods of monitoring. These methods are telemetry and radar and voice communications which are discussed as follows:

(1) Telemetry, and radar, which were used to monitor and track satellite and missile systems, provided a means in Project Mercury not only of analyzing launch vehicle performance and trajectory progress but also of monitoring spacecraft systems and making medical analyses of the astronaut's physical status.

(2) The voice conversations between the astronaut and the spacecraft communicators around the world proved to be invaluable. The ability of the astronaut to make observation and relay them to the control center, to verify telemetry data, to update the retrofire timer, to exchange information with the ground, and to carry on discussion of problem areas proved to be the best tool for flight control analysis. Voice communications also proved to be a primary method of making a medical analysis of the astronaut's physical status.


Development of Flight Control Operations

Network Requirements


In the planning stages for manned flights, the design criteria for the tracking network were established. These requirements were:

(1) At central control facility able to coordinate a worldwide network of tracking stations.

(2) Continuous monitoring of the powered flight phase of the mission.

(3) A worldwide network capable of monitoring a spacecraft while in orbit.

(4) Voice, telemetry, radar tracking and command capability at the time of retrofire for a planned reentry.

(5) A recovery force capable of astronaut rescue in case of all emergency as well as recovery after a normal reentry.


Development of Detailed Flight Control Operational Planning



As preparation began for manned space flight, it became apparent that a need existed for a well trained control organization in order to perform the flight control tasks previously mentioned. As in the case with any engineering or scientific undertaking, the ability to control a mission successfully is primarily a result of premission planning.


Documentation. At the beginning of the project, the different organizations connected with the Mercury program published a number of documents in which the method that should be used to accomplish the flight control task was described in detail. Some of the documents were revised and used in Astronaut Cooper's [255] flight. However, the majority of the documents proved to be too cumbersome for real time use and too difficult to keep updated for use by the flight control organization. Consequently, some of these documents were revised, others were discontinued, and new ones which would tee more adaptable to use in real time were written. As a result of the experience gained by the use of these documents, several specifically designed for flight control were published.


The most difficult task of flight control is that of being prepared to make a real time decision. A real time decision by flight control could result in an action to change the entire mission. The action based on this decision may range from a slight variation of the flight plan to immediate termination of the mission. The documentation to be used by flight control personnel not only must have all necessary information available to research a problem, but also must contain information that can be quickly located, if time is limited. The most significant documents that evolved through experience and use were Mission Rules, Flight Plan, Flight Controller Handbook 1, and the Trajectory Working Paper.


Mission Rules: A fundamental approach to the analysis of systems failures in any flight test program is to formulate a set of probable component failures and their respective countermeasures which may either rectify the problem, provide for the safety of the occupant, or protect the equipment. This compilation of preplanned actions for each flight is called Mission Rules. In no other document are the actions of the crew and the flight control teams so well defined. Each rule is carefully scrutinized by the flight controllers and astronauts for possible ramifications which need more clarification. This document shows the integrated actions of the spacecraft crew and ground support personnel which are required to establish an efficient team that may be called on to take life saving actions should an emergency situation arise.


These Mission Rules Ire put to the final test during the extensive series of simulations prior to the mission. Some of the rules may be modified as a result of the realistic situations created by the simulation. A Mission Rule Review is held the day before launch to assure a consistent interpretation and a complete understanding of the rules. A page from the Mission Rules for orbital reentry is shown in table 15-I.


Flight Plan. The Flight Plan for the manned Mercury missions consisted of a time referenced step by step list of the astronaut's activities during an individual mission and the necessary supporting information. It was basically written as a guide for the astronaut in conducting the mission, but it also served as a focal point for the coordination of all the inputs into the mission and the coordination of the ground controller activities with those of the astronaut. In addition, it served as a basis for premission training, simulations, system tests, and detailed management in meeting the mission objectives.


The formulation of the Flight Plan required the coordination of inputs from many organizations into a sequence that not only met the mission objectives and ground rules, but also could readily be performed by the astronaut. The inputs into the Flight Plan were concerned with the astronauts, the spacecraft systems, flight controllers, medical requirements, and experimental considerations. As these inputs were received, they were arranged to meet the requirements of astronaut usage, reliability, priority, Mission Rules, and ground control. In order to obtain the maximum amount of useful information from the flight, the Flight Plan was continuously coordinated with and reviewed by the various input organizations and finally approved by the Operations Director.


The Flight Plan, as an operational document, served several purposes. Primarily, it provided the astronaut with a coordinated schedule of his activities during the mission. It also outlined part of the astronaut's preflight training. The Flight Plan further served to inform the flight controllers of the astronaut's planned activities and was used as a tool to help coordinate the activities. In addition to the activity schedule' the Flight Plan provided the normal and emergency procedures and checklists for the control of the spacecraft and procedures for conducting experimental and medical activities. During the mission it provided a basis from which changes could he made because of system malfunctions or alterations in the requirements. Also, it provided nonoperational organizations with information concerning the activities scheduled for an individual mission. See table 15 II for sample page from flight plan.

Table 15-I. Mission rules- Orbital reentry.


Item condition-Malfunction


Notes, Comments, Standard Operation Procedures

8. Failure of one suit fan.

8. Continue mission.

9. Failure of both suit fans.

9. Select EMER O2 rate ASAP and reenter at next planned landing area.


10. Smoke, fumes, unusual or annoying odors in suit circuit.

10. Switch suit fans. If this does not clear up the fumes or smoke, go to EMER O2 rate and try further to isolate cause. If cannot isolate, reenter next planned landing area.

10. Check suit PCO2 reading.

11. Smoke, fumes, unusual or annoying odors in cabin.

11. Close faceplate, attempt to isolate cause. If source isolated and no other Mission Rules are violated, continue mission. If fire, decompress.

12.Faceplate will not reseal.

a. Cabin pressure above 4.6 psi.

b.Cabin pressure below 4.6 psi.

12a. Reenter next planned landing area.

b. May require contingency landing area reentry or ASAP reentry if cabin pressure below 4.0 psi.

12. Astronaut should get spacecraft in RETRO ATTITUDE and prepare to reenter.

13. Conditions for selection of EMER O2 rate.

13. Astronaut should select EMER O2 rate when:

a. Suit pressure below 4.0 psi.

b. Respiration rate increasing to 40 breaths/min.

c. Unsatisfactory operation of suit heat exchanger that is not corrected.

d. Rise in partial CO2 reading to 7.5mm Mercury.

e. Smoke, fumes, unusual or annoying odors in suit circuit.

Table 15-II. Excerpt From Flight Plan.



Site mode







A - Turn ON cabin fan and cabin coolant flow for precooling prior to reentry.





A - Radiation experiment ON for 5 minutes period.




A - Tape recorder-PROGRAM. Take horizon definition photographs.





A - TV ON for pass.
Oral Temperature.
Blood pressure.

The astronaut cannot talk for a period pf 3-5 minutes during oral temperature taking.









A - Tape recorder. CONTINUOUS. Complete stowage and preretrosequence checklists. Check manual proportional and FBW-high thrusters if required. Readout fuel and O2 quantities.





A- TV ON for pass.
C and S-band radar beacons.
CONTINUOUS. Report checklists-COMPLETED.
CSQ- Confirm astronaut ready for retrosequence. Confirm retrosequence time setting.
A- Squib switch ARM at retrosequence minus 5 seconds.


[258] Flight Controllers Handbook. The first document designed specifically for flight controllers was published in December 1960. This book was designed to contain operational information needed by a flight control team to analyze spacecraft systems problems. Schematics, logic diagrams, and other publications were used to prepare schematics oriented for operational utilization. This document entitled Flight Controllers Handbook No.1 (FCH-1), was used from the MA-3 mission until the end of the Mercury Project. During this time, the FCH-1 was modified and revised to include more system details. The final document contained highly detailed functional schematics of spacecraft systems, yet the arrangement of these schematics along with notes explaining details provided information very adaptable to real time use. The schematic diagram, shown in figure 15-1 was taken from the Flight Controller's Handbook.


Trajectory Working Papers. Real time decisions concerning flight dynamics are of paramount importance to the astronaut's safety and to mission success. Should the flight trajectory vary from the precalculated nominal during launch, there is no time for analysis, and corrective action must be immediate. In order to aid the flight controllers in making these fast decisions, a flight dynamics document was prepared to provide n ready reference of charts, curves tables and other data illustrating the expected normal trajectories, calculated allowable limits, and timed sequence of events. This document contained not only information pertaining to all the conditions necessary for insertion of the spacecraft into orbit, but it also contained curves for calculating retrofire times and making reentry landing predictions. Table 15-III and figure 15-2 are examples of information contained in the Trajectory Working Paper.


Training. In November 1960 training courses were organized for NASA personnel who were to become flight controllers. The classes covered basic spacecraft systems. Because of the limited number of personnel available to man a worldwide tracking network, it was necessary to borrow personnel from other organizations to be used as flight controllers on a part time basis. However, it was soon discovered that this arrangement was not adequate. Since these people were responsible to their own organizations except during a mission, they were not available for premission planning and postmission analysis. In addition, the flight control tasks interfered with their responsibilities to their own organizations. As a result, it was determined that full time flight controllers were needed. The first full time team of systems monitors came to NASA in January 1961, and new techniques of instruction were incorporated through the experience gained in the preceding class. These systems monitors learned the spacecraft and ground systems and conducted the succeeding flight controller training classes. The following facilities and aids were used in the flight controller training program: classroom lectures, Mercury procedures trainer, and training documentation.


An updated formal training course was held in April 1962 and consisted of 156 hours of classroom lectures on spacecraft and ground systems. The original NASA flight controllers were the instructors and were responsible for the training lesson plans. The FCH-1 manual was the primary source of information for the lectures on spacecraft systems. Within one year, a total of six classes were conducted without any significant changes in the format.


The Mercury procedures trainer was utilized in training flight controllers in network operational procedures, spacecraft communications, and systems analysis. The first Mercury procedures trainer was installed at Langley Air Force Base, Va., in 1960 and became operational the latter part of the year. The remote site console simulator was also installed at Langley. For a description of the procedures trainer and the simulator, see paper 10. This remote site simulator was designed to operate from outputs of the spacecraft procedures trainer for simultaneous site vehicle training. Initially, the procedures s trainer was used primarily by the astronaut for systems training, and there was limited availability for use by the flight controllers. In 1961 a Mercury procedures trainer was installed at Cape Canaveral, and more time was then available for the Flight Controllers to train on the one at Langley. The trainer configuration was continuously updated to make it identical with the spacecraft used for the realtime operation.


259] Figure 15-1. Schematic diagram of 0.05g sequence.

260] Table 15-III. Sequence of Events for Abort Trajectoriesa


Time of abort, min:sec

Time of event, min:sec

Recovery Area

Tower jettison

Retropack jettison

Blackout (start)

Begin reentry (0.05g)

Reentry flight-path angle at 0.05g, deg

Blackout (end)

Drogue parachute automatic deploy at 21,000 ft

Main parachute deploy at 10,000 ft
















































































































































02:35 7

03:24 7

02:35 7








a Times based on normal abort trajectories. For dispersed trajectory, the sequence changes.


graph of separation distances

[261] Figure 15-2. Separation distance as a function of incremental time from SECO for different thrust sensing levels during nominal thrust conditions.


A flight plan was written which deviated from the normal Flight Plan in order to give the flight controllers experience in a contingency situation. A typical simulation picked up the last five passes of the spacecraft and during that time three flight controllers practiced simultaneously: one as the astronaut, one as the spacecraft communicator, and the third as the systems monitor.


In order to apply some of the defined procedures and to gain experience in the operation of the spacecraft systems, the Mercury procedures trainer at the Mercury Control Center (MCC) was used for launch and network simulations involving the MCC and the remote sites.


The primary objective of the launch simulations was to train the MCC flight controllers and the astronauts as a team by means of simulated launch experiences in order to develop their ability to perform correctly in any situation during the launch phase. In order to provide a realistic simulation, the launch trajectory was determined and prerecorded on tape with the additional capability of introducing an abort at any time by the operations staff, the astronaut, or a simulated automatic launch vehicle abort. A complete voice network was exercised within the MCC and to the astronaut for complete familiarization of communication procedures. The telemetry backups of the MCC trainer allowed the flight controllers at MCC to view actions taken by the astronaut without a fixed simulation program. This practice resulted in a more realistic flight simulation than that afforded by the taped simulations used at the remote sites.


A full network simulation was first used for the MA 3 mission and was the basic final mission preparation tool utilized in all subsequent flights. The flight controllers were sent to their stations approximately 2 weeks before the scheduled launch date. Before the launch, three or four simulations were conducted to give the flight controllers experience in the use of correct procedures, coordination of the efforts of all support groups, and to exercise systems analysis capabilities. For the MA 9 mission, a real time simulation of 18 orbital passes was performed to determine if any network operational difficulties existed which could affect the success of a long duration mission. Thus, the problem areas were uncovered and solved before deployment for the MA-9 flight. After each simulation, there was a briefing in which the flight controllers explained their actions and any problems were reviewed. As a result, many changes to operational procedures and documentation were made.


The flight controller's detailed systems analysis capability coupled with his understanding of the network equipment were the basic requirements necessary to perform his job. A brief examination of all orbital station passage will permit a better understanding of the real time aspects of flight control.


Prior to radar and voice acquisition of the spacecraft at a particular site, the flight control team at that site received systems status reports and monitored the air to ground transmissions between the spacecraft and other network sites. Trend plots were prepared and acquisition messages were received from the Goddard computers. The flight controllers at the site were generally briefed by the Mercury Flight Director prior to contact. At the expected acquisition and the approximate horizon time, the spacecraft communicator attempted UHF contact with the astronaut. Almost simultaneously the telemetry supervisor announced contact, and shortly thereafter, solid telemetry lock was obtained. The spacecraft communicator took the astronaut's systems status report; the aeromedical and spacecraft monitors evaluated systems status. After completion of the preliminary systems assessment, the flight control team concentrated on any potential problem areas. If a problem existed, the data were rapidly evaluated and notification was sent to the MCC [262] and network by either voice or teletype. If time did not permit or if loss of communications with the MCC did not allow instructions to be given by the Flight Director, the flight controller had to be prepared to advise the astronaut. In order to provide the proper advice to the astronaut, the flight controller must rely on his knowledge of Mission Rules and spacecraft systems.


Flight Control Chronology


The ability of the ground crew and the astronaut to work together as a team has contributed greatly to the success of Project Mercury. The astronauts' confidence in the flight control organization and its ability to advise and direct their actions when problems occurred greatly simplified the flight control task.




America's first manned space flight, Astronaut Shepard's flight (MR-3), was performed satisfactorily despite the tension involved with the first manned launch.


The flight control operations of Astronaut Grissom's flight (MR-4) were smoother than those of the MR-3 flight, indicating the benefits obtained from flight test experience. Information provided by all sources allowed a good analysis of the flight to be made in real time. From launch through landing, the flight was completely normal from the standpoint of flight control. However, early release of the spacecraft hatch caused the spacecraft to flood with water after landing and it was not recovered.


MA-3, MA-4, AND MA-5


Although the MA-3, MA-4, and MA-5 flights were unmanned, they provided valuable experience to the flight control team. In MA-3 and MA-4 a mechanical man was used to exercise the Environmental Control System. In MA-5, a chimpanzee was on board.


The MA-3 flight of April 25, 1961, was the first attempt to orbit a Mercury spacecraft; however, because of a launch vehicle guidance malfunction, the mission was aborted shortly after lift off. From the viewpoint of the flight control organization, a tremendous amount of experience was gained from this orbital attempt. For the first time, flight controllers were deployed to remote sites. As a result, many difficulties were experienced with logistics and communications. Originally, the MA-3 mission was to have been a suborbital flight, but 3 weeks prior to the actual launch, the mission profile was changed to an orbital flight. As a result, problems were encountered with transportation, currency, passports, and travel orders.


The remote site flight controllers on the MA-4 mission were able to acquire, evaluate, and transmit real time data; however, problems developed because of the delay in preparation of summary and postpass messages. The major concern during this mission was the inability of the sites to acquire C and S band radar tracking The inability of the sites to acquire C band radar tracking was attributed to poor spacecraft antenna radiation pattern which was corrected for later flights. Failure to track S band at several sites was determined to be the result of personnel error. This difficulty was corrected by further training of the maintenance and operational personnel at the remote sites.


For the MA-5 mission, the telemetered data from the spacecraft were of good quality and all sites received total coverage. Data transmission from all sites was good, and the Goddard conference loop was utilized for the first time to provide real time voice data to MCC from sites that had access to a telephone cable for voice capability. The MA-5 mission was originally scheduled for a three orbital pass mission, but a series of problems caused termination of the flight. At the end of the second pass, the apparatus used to measure the chimpanzee's psychomotor responses malfunctioned. In addition, there was a suit and cabin temperature increase; however, a control system malfunction causing high fuel usage was the reason for termination of the flight. If the flight had been allowed to continue an insufficient quantity of fuel would have been available for retrofire and reentry. The decision to terminate was made and executed in 12 seconds in order to be able to bring the spacecraft into a planned landing area. The decision was made, and the California spacecraft communicator commanded retrofire. The MA-5 flight proved to be a fine example of the importance of being prepared [263] to make a real time decision and to act on it immediately.




Because MA-6 was the United States' first manned orbital flight, the events which occurred are quite familiar. At the beginning of the second orbital pass over Cape Canaveral, the telemetry data indicated that the heat shield had become unlatched. This indication caused a great deal of concern to the ground crew because of the possibility that the heat shield was loose. While he was in contact with the Hawaii station during the third pass, Astronaut Glenn was asked to put the landing bag switch in the automatic position to determine if the landing bag deploy light would come on. The astronaut did not get an indication which meant that the problem was probably an instrumentation failure. However, after further analysis it was decided that the safest approach was not to jettison the retropackage so that the retropackage straps could hold the heat shield in its proper position during reentry until sufficient aerodynamic force was exerted on the shield to hold it in place. .Another problem was a partial failure of the automatic stabilization and control system (ASCS), but this problem was handled very adequately by the astronaut's using manual backup and fly by wire (FBW) control.




For the MA-7 mission, the air ground contact procedures were reviewed and negative reporting procedures were initiated to eliminate unnecessary conversation with the pilot and network teletype traffic. The only major systems problem was the improper functioning of the ASCS. Astronaut Carpenter was forced to perform a manual retrofire since attitudes could not be controlled by the ASCS.




As far as the flight was concerned, the MA-8 mission was a "textbook flight,'' in which no problems of any importance developed. As a result of the excellent performance of Astronaut Schirra and the spacecraft, the flight control task became one of monitoring, gathering data, and assisting the astronaut with the Plan.




Permission. The flight controllers began deploying for the MA-9 mission on April 30, 1963, and by May 5 all teams were at their sites.


Onsite prelaunch preparation began with launch simulations at Cape Canaveral and Bermuda. A total of ten launch simulations were conducted, five on May 2 and five on May 4


The network simulations began on May 7 with two simulations being conducted on that day. In the first simulated mission, the systems analysis capabilities of the flight controllers were exercised by a failure of the FBW high thruster control followed by a loss of cabin and suit pressure integrity. The second simulated mission contained a 1 second late sustainer engine cut off resulting in an overspeed insertion which caused a higher shall normal apogee. These conditions tested the ability of the flight dynamics officer and retrofire monitors to calculate new reentry areas and retrofire times. Also, all the flight controllers were tested in their ability to adjust to an abnormal sequence of acquisition of signal and loss of signal times.


On May 8 the first simulation contained noisy and intermittent telemetry data, and the flight controllers were required to obtain data from backup recorders. The second mission contained a leaking regulator in the manual fuel pressurization system. During the second orbital pass a Military alert was simulated, which caused a reevaluation of the Mission Rules concerning loss of two way communication with the spacecraft.


The first mission of the third day of simulations, May 9, was primarily an aeromedical monitor exercise with the astronaut experiencing a simulated heart attack. The second mission of the same day contained another systems problem with a failure of the main fans inverter and the standby inverter. Reentry was initiated by the California station when the Guaymas station experienced a failure of the air ground transmitting capability. Landing was approximately 1,100 miles downrange from nominal because of a failure of the third retrorocket to fire.


The last simulation was on May 12 and an attempt was made to exercise both the range maintenance and operations personnel and the [264] flight controllers. During the mission the 10.5kc voltage controlled oscillator drifted in frequency, and this action required the telemetry ground station operators at the remote sites to adjust the discriminator center frequency control constantly, and the flight controllers to analyze the pulse amplitude modulation wave train on the backup recorders.


Throughout the simulations, the intent was to provide the flight controllers and support personnel with the atmosphere of an actual mission. For that reason, each mission began with liftoff, and reentry was determined by the condition of the spacecraft and the astronaut without regard to any set pattern of orbital or reentry simulations.


The performance of the site simulation teams, and particularly the astronaut simulators, was outstanding throughout the MA 9 simulations. Probably the most often heard criticism of the MA-D simulations was the fact that 3 consecutive days of network simulations were scheduled. This rigorous schedule imposed extremely long hours on the maintenance and operations personnel as well as the flight controllers.


Mission. The network countdown for MA-9 was initiated on May 14 at 2:00 a.m. e.s.t. The spacecraft launch vehicle countdown proceeded normally. The network radar computer data test was completed on schedule, and the mandatory equipment at all stations was operating satisfactorily with the exception of the Bermuda FPS 16 radar, which had failed the slew tests in both azimuth and range. The slew tests were scheduled to be rerun for Bermuda, and the "C" computer at Goddard was standing by to check the Bermuda data. Bermuda estimated that it would take an hour to isolate the problem. Reruns of the radar computer data tests indicated the azimuth and elevation data were good; however, some dropouts were experienced in range.


At T-60 minutes, a series of short duration holds, eventually totaling 2 hours, were called because of problems with the diesel generator used for moving the gantry. The fuel system on the diesel was changed and the count was resumed at 9:09 a.m. e.s.t.


The Bermuda radar had passed the test performed during,, the hold; however, there w as still a 14 percent error rate in the range data. Continual status reports were obtained from Bermuda, and the performance of the radar was marginal for the T-45 minute liquid oxygen status check. A final slew test was performed with Bermuda at T-20 minutes, and the error rate on these data was unacceptable. It was determined at this time that the radar would not be able to support the mission and the launch attempt was canceled at 10:00 a.m. e.s.t.


The Bermuda station began immediate troubleshooting of the FPS-16 system, and the Goddard computer was placed on a standby status to run data slew tests with the radar when it was repaired. The problems were isolated to the preamplifier in the azimuth digital data channel and the shift register in the range digital data channel.


The count was recycled for 24 hours and the network count was resumed at 2:00 a.m. e.s.t. On May 15. All primary network systems were operational when the countdown was initiated.


The confidence summaries transmitted by the network to verify the site patching and calibrations were very good. No major discrepancies were noted in the network voice communications; however, Zanzibar, Canton Island, Rose Knot Victor, and Coastal Sentry Quebec stations were influenced by propagation and several repeats were required from the stations. The May 15 countdown was continuous except for a short hold for the launch vehicle ground support equipment. The countdown was resumed within approximately 4 minutes and liftoff occurred at 8:04:13 a.m. e.s.t.


The powered flight phase was normal, and all launch events occurred at the expected time. The performance of the guidance and data systems was excellent. A clear go condition was evident at insertion, and orbit lifetime was not considered to be a problem. All vehicle systems performed satisfactorily through launch and the air ground communications were better than those of the previous mission.


After spacecraft separation from the launch vehicle, the astronaut manually performed a FBW low turnaround maneuver. Shortly after the completion of this maneuver, the Bermuda station advised the MCC that they had observed approximately a 6° F rise in cabin and suit dome heat exchanger temperatures. The astronaut was informed of this situation and increased the coolant flow. When the astronaut [265] acquired voice communications with the Canary Islands station, he said that the dome temperature warning light had come on, which indicated that the suit dome temperature was below 51° F. The astronaut v as required to monitor this temperature throughout the flight and to make frequent adjustments to the coolant control valve. The cabin temperature rose from 94° F at launch to approximately 118° F when the spacecraft passed over Muchea as a result of the exit heat pulse ; subsequently, this temperature began to decrease slowly to a value of between 90° F and 100° F. All spacecraft systems were functioning normally, and MCC advised the Guaymas station to transmit to the astronaut the go decision for seven orbital passes. Throughout the flight, cabin air temperature appeared to vary slightly as a function of the spacecraft a c power configuration. During the periods when the ASCS 115v a-c inverter was powered for an appreciable time, the temperature rose to a maximum value of 105° F ; and when this inverter was powered down, the temperature decreased slowly over a period of several orbital passes to a value between 85° F and 95° F.


The first discrepancy occurred over Cape Canaveral at the beginning of the second orbital pass. When the telemetry was commanded by the ground, a series of repetitive telemetry calibration signals occurred. It was decided that the programed telemetry calibration function would be turned on during the sleep period so that it would not interfere with normal telemetry.


At the beginning of the fifth orbital pass, the astronaut turned the cabin fan and cabin heat exchanger off as indicated by the Flight Plan. It was noted subsequently that turning off the cabin cooling did not materially affect the cabin temperature. The astronaut opened the outlet port of the condensate trap, and whenever this trap was activated, it is believed that the system performed satisfactorily. It was noted early in the flight that the actual power consumption was less than predicted. This surplus electrical power was utilized to obtain more beacon tracking during the later phases of the flight. The C band beacon was powered up three times prior to passes over the Hawaii station to enable tracking by the Range Tracker ship.


Fuel usage was also less than expected, and all reports indicated that the astronaut was managing his fuel supplies exceptionally well. The astronaut made several attempts to deploy the tethered balloon, in support of air density studies and visual tests ; however, all attempts were unsuccessful. After ground analysis of this system, it was decided that no further attempt would be made to deploy the balloon.


The most serious trouble of the flight was reported over Hawaii during the 19th orbital pass. The Hawaii spacecraft communicator contacted the astronaut and received a report that the 0.05g green telelite had come on and that the astronaut had placed the ASCS 0.05g fuse switch and the emergency 0.05g fuse switch to off. The main concern at MCC was to establish the state of the amplifier calibrator (auto pilot) unit and to determine what functions of the ASCS were lost as a consequence. There was no need for planning early mission termination at this time as no Mission Rules had been violated and there was an effective control mode remaining on both the automatic and manual control systems.


After analysis and discussion of the problem, it was decided that the first step was to have the astronaut power up the ASCS bus as the spacecraft passed over Guaymas. Subsequently, over Cape Canaveral, the gyros were slaved to the horizon scanners ; and after about a minute of operation, no gyro or scanner deviation from the gyro caged condition was noted. This situation indicated that the gyro and scanner power actually was off and that the 0.05g circuit was latched up. It was realized at this time that a manual retrofire would be required and that a checklist must be prepared for the astronaut. The remote site flight control personnel on standby status were called to their stations and advised to be prepared to attempt to relay communications to the astronaut if directed by the MCC.


While he was in contact with the Coastal Sentry Quebec, the astronaut was requested to turn on the telemetry and C band beacon to allow the Range Tracker to check its radar data. These data were very important since the retrofire maneuver would be performed manually. While the spacecraft was passing over the Hawaii station, the astronaut was requested to place the ASCS 0.05g and emergency [266] 0.05g fuse switches to the on position and to select the ASCS automatic mode to verify the 0.05g event. If the spacecraft began to roll as it would normally do when the 0.05g indicators were valid, the ASCS would be latched in the reentry mode. The astronaut verified this roll rate and the 0.05g event which were again confirmed by telemetry over the Guaymas station.


At this point the flight controllers knew the exact configuration of the ASCS logic and the required configuration for reentry after completion of these tests, it was determined that the ASCS would provide proper attitude control and roll rate for reentry after the normal 0.05g event time. The manual retrofire checklist was completed and thoroughly reviewed by the MCC flight control team. This checklist was relayed to the spacecraft via the spacecraft communicator on the Coastal Sentry Quebec and written down by the astronaut. The astronaut was advised to "take Green for go" which was a coded means of telling him to take a dexadrine pill. The purpose for taking the pill was an added precaution to be sure that he was alert for the manual retrofire maneuver. The flight surgeon was not concerned over the astronaut's condition but he was not certain the astronaut was thoroughly rested from his sleep. On acquisition by the Zanzibar station on the 22nd orbital pass, the astronaut reported that the ASCS inverter had failed and the standby inverter would not start. These failures meant that the pilot could no longer have automatic control after 0.05g but would have to introduce the reentry roll rate manually. The failure of the inverters to start required that a revision be made to the checklist previously transmitted to the astronaut. The revision consisted of changing only one switch position on the earlier checklist.


Prior to retrofire, the Coastal Sentry Quebec acquired the spacecraft and the reentry procedures were reviewed. The astronaut was given time hacks at retrofire minus 60 seconds, minus 30 seconds, and a 10 second terminal countdown. The telemetry immediately confirmed the retrofire and the astronaut indicated that his attitudes were good and confirmed that all three retrorockets had ignited. Reentry blackout was confirmed by the Range Tracker ship within 2 seconds of predicted time which indicated that the landing point would be close to nominal.


The network flight control teams performed well during this flight. Communications between the ground and the astronaut u were precise and conveyed the necessary information. The flight control teams utilized the proper contact and reporting procedures that were developed for this flight test. The operations messages provided much useful real time data, and no difficulty existed in determining the precise status of the spacecraft the astronaut, or the mission. The entire mission period from deployment through recovery was an extremely smooth and well coordinated effort. The cooperation between the flight astronauts and the flight control personnel had a significant influence on the success of the MA-9 mission.


Concluding Remarks


The flight control organization has played a significant role in the first space flights and has made a major contribution to the success of the Mercury program. A wealth of experience and information has been gained from the project. Some of the more important are as follows:

(1) Documentation used by flight control had to be easy to update, contain detailed information yet be put together in such a manner that the information could be found quickly in real time.

(2) People could not be borrowed from other organizations on a part time basis to be flight controllers. It not only disrupted their own organizations but prevented them from being able to devote the required amount of time to the flight control] task. As a result, it was learned that full time flight controllers were a necessity.

(3) It was also discovered that a flight controller had to have the following special qualification: The flight controller must be a technically trained individual. It became apparent he should be an engineer or oriented toward engineering with a wealth of experience in system analysis.

(4) It was also found that a continuing program of training was necessary to keep flight controllers proficient in knowledge of spacecraft systems and operation procedures.

(5) The network and launch simulations held prior to the actual mission were found to be a necessity. In simulations, mistakes are made [267] and corrected. Simulations are run until the entire network is functioning as a team and complete confidence is gained in the ability of the flight controllers to respond correctly to any emergency.

(6) Because of the experience gained in Mercury it has become obvious that the more complex missions of Gemini and Apollo will require more automation. In order to be able to process the information in real time and arrive at a proper decision, it is necessary that more data processing aids be utilized.

Previous Index Next