RESULTS OF THE THIRD U.S. MANNED ORBITAL SPACE FLIGHT, OCTOBER 3, 1962

 

4. PILOT PERFORMANCE

By Richard E. Day, Asst. Chief for Training, Flight Crew Operations Division; and John J. Van Hockel, Flight Crew Operations Division

 

[37] Summary

 

The results of the MA-8 orbital flight of Astronaut Walter M. Schirra, Jr., further verify that man can function effectively in a space environment, in this instance for a period of up to 9 hours. The pilot was able to position the spacecraft to a given attitude and to complete attitude maneuvers with a high degree of accuracy and a minimum amount of control-system fuel by using only visual references as seen through the spacecraft window. This flight provided additional evidence that man can perform primary control tasks and serve as an effective backup to the automatic control modes provided. During the MA-8 mission, the pilot also demonstrated that he can efficiently perform the role of an engineering test pilot while orbiting in a space environment if the pilot devotes his primary attention to the management of spacecraft systems and the operational aspects of the mission.

 

Introduction

 

The pilot's primary responsibility during the MA-8 mission, as in the previous orbital missions, was to monitor and manage systems operations and, if necessary, to take corrective action in order to achieve the prescribed mission objectives. The pilot's secondary responsibility during this mission was to accomplish various in-flight activities that would further evaluate the spacecraft systems as well as provide a basis for evaluating man's performance in space. Experimental scientific activities were somewhat reduced for this mission in view of the greater emphasis placed on operational objectives. The purpose of this paper is to report on the pilot's effectiveness in achieving the primary mission objectives. The pilot's performance in conducting certain scientific experiments, secondary objectives for this mission, are not described in this paper since they are discussed in the Scientific Experiments section of paper 1.

 

Flight Plan Description

 

A flight plan was designed for the MA-8 flight to guide the pilot in carrying out the mission objectives with particular emphasis upon systems' management and control-fuel conservation. Only a few scientific activities were scheduled late in the mission on a flexible basis so as not to interfere with operational mission requirements. Control systems were to be evaluated prior to extending the flight duration beyond three orbital passes.

The pilot's adherence to the flight plan was excellent, and all major activities were accomplished within the time periods scheduled. The spacecraft control systems were completely checked out during the first three orbital passes; and the drifting flight phase, as well as the automatic-control-system evaluation scheduled during the final three passes, was completed as planned. Observations of the ground flares at Woomera, Australia, and of the high intensity lights at Durban, South Africa, were attempted at the proper times; but, poor weather conditions prevented the pilot's observation of both light sources.

 

Preflight Performance

 

In preparing for this flight, Astronaut Schirra participated in extensive training and spacecraft checkout activities. In general his preflight activities were similar to those accomplished by the pilots of the previous orbital flights, except that more time was devoted to becoming familiar with the spacecraft systems through briefings and discussions and less time was spent in using the Mercury procedures trainer.

As a result of the experience gained from previous Mercury flights, the pilot was able to prepare for this flight in a more efficient manner than has been possible in the past. The flight plan was more flexible and was finalized at an earlier date, operational requirements were emphasized, and nonoperational objectives were [38] reduced. Consequently, the pilot kind the necessary additional time to become more familiar with the spacecraft and launch-vehicle systems.

The major preflight pilot activities in the period from July 11, 1962, to the date of launch are given in table 4-I. During the preflight preparation period, the pilot was engaged in a diversity of activities often requiring considerable travel and resulting in a crowded schedule. As can be seen from this summary table, the pilot spent a large portion of his time in briefings and meetings concerning every aspect of the mission. For example, the pilot became familiar with the hand-held camera used during the flight (see fig. 4-1). In addition, he completed such required training activities as recovery training, survival-pack exercises, acceleration refamiliarization on the centrifuge, and review of the celestial sphere at the Morehead Planetarium, Chapel Hill, N.C. The pilot also logged 35 hours in the T-33-, F-102-, and F-106-type aircraft during his preflight preparation period. Flights to maintain proficiency in high performance fighter aircraft are considered an important phase of training because the pilot must maintain the ability to....

 

Table 4.I. Pilot Preflight Preparation History.

Date (1962)

Day

Activity

July 11

Wed

Flight plan meeting, flight film meeting.

July 12

Thurs

Flight plan review.

July 13

Fri

Scheduling meeting.

July 14

Sat

Flying (T-33)

July 16

Mon

Flight plan review.

July 17

Tued

Scientific panel meeting.

July 18

Wed

Mission rules review; flying (T-33)

July 20

Fri

Camera and onboard equipment briefing.

July 23

Mon

A.m.: Flight activities discussion, scheduling meeting.
P.m.: TV interview (Telstar)

July 24

Tues

Blood pressure cuff discussion, systems briefing (ASCS)

July 25

Wed

System briefings (ASCS and RCS)

July 26

Thurs

System briefing (sequential)

July 27

Fri

Flight plan presentation.

July 28

Sat

Flying (T-33)

Aug. 1

Wed

A.m.: Systems briefings (communications and environmental control system)
P.m.: Ultraviolet camera briefing.

Aug. 2

Thurs

A.m.: Systems briefing.
P.m.: Weather briefing.

Aug. 3

Fri

Geology briefing (terrestrial photography).

Aug. 4

Sat

Flying (F-106)

Aug. 6

Mon

Scheduling meeting, flying (T-33)

Aug. 8

Wed

Flying (T-33)

[39] Aug. 10

Fri

Review of contractor documents.

Aug. 11

Sat

Systems tests.

Aug. 12

Sun

Systems tests concluded.

Aug. 13

Mon

Sequential system checks.

Aug. 14

Tues

Sequential system checks concluded

Aug. 15

Wed

Survival equipment meeting, flying (F-106)

Aug. 16

Thurs

Recovery training.

Aug. 17

Fri

Weight and balance.

Aug. 20

Mon

Mercury procedures trainer, flying (F-106)

Aug. 21

Tues

Survival pack exercise.

Aug. 22

Wed

A.m.: Flight plan activities meeting.
P.m.: Mercury procedures trainer.

Aug. 23

Thurs

Mercury procedures trainer.

Aug. 24

Fri

Johnsville centrifuge Atlas "g" refamiliarization.

Aug. 25

Sat

Morehead Planetarium celestial review.

Aug. 27

Mon

Meeting on checklists.

Aug. 28

Tues

Mercury procedures trainer, flying (F-106).

Aug. 29

Wed

A.m.: Mercury procedures trainer.
P.m.: Scheduling meeting.

Aug. 30

Fri

Flight plan meeting.

Sept. 1

Sat

Flying (T-33).

Sept. 4

Tues

Flight controller briefing.

Sept. 5

Wed

Flying (T-33).

Sept. 6

Thurs

Systems briefings (ASCS and RCS).

Sept. 7

Fri

A.m.: Systems briefings (electrical and sequential).
P.m.: Launch vehicle meeting.

Sept. 8

Sat

Mercury procedures trainer.

Sept. 10

Mon

Mercury procedures trainer.

Sept. 11

Tues

A.m.: Simulated flight no.1.
P.m.: Brief the President of the United States; Mercury procedures trainer.

Sept. 12

Wed

A.m.: Readiness examination.
P.m.: Mercury procedures trainer.

Sept. 13

Thurs

Flight plan activities review, checklists review, flying (F-102).

Sept. 14

Fri

Simulated flight no.2 and flight acceptance test, air-ground communications check.

Sept. 15

Sat

Mercury procedures trainer.

Sept. 17

Mon

Questionnaire review, air-ground communications check, flying (F-102).

Sept. 18

Tues

Mercury Control Center-Bermuda simulation.

Sept. 19

Wed

Flight configuration sequence and aborts.

Sept. 20

Thurs

A.m.: Mission review.
P.m.: Mercury procedures trainer.

Sept. 21

Fri

Launch simulation and RF compatibility, flying (F-102).

Sept. 22

Sat

Network simulation.

Sept. 24

Mon

Training facilities meeting (Houston), flying (T-33).

Sept. 25

Tues

Mercury procedures trainer.

Sept. 27

Thurs

A.m.: Flight plan discussion, mission review.
P.m.: Mercury procedures trainer.

Sept. 28

Fri

Launch simulation and RF compatibility, flying (F-102).

Sept. 29

Sat

Simulated flight no.3.

Sept. 30

Sun

Mission review.

Oct. 1

Mon

A.m.: Mercury procedures trainer.
P.m.: Physical examination.

Oct. 2

Tues

Pilot briefing, study

Oct. 3

Wed

Launch

[40] Table 4-II. Pilot Time in Spacecraft 16 During Hangar and Launch Complex Tests from August 11, 1962, to Flight Date

Date (1962)

Spacecraft tests

Duration, hr:min

Aug.11

Systems tests (Hangar S)

02:15

Aug.12

Systems tests concluded

05:15

Aug.13

Sequential system checks

02:45

Aug.14

Sequential system checks concluded

02:17

Sept.11

Simulated flight no.1

03:25

Sept.14

Simulated flight no.2 and flight acceptance test

02:20

Sept.19

Flight configuration sequence and aborts

03:20

Sept.28

Launch simulation and radio frequency compatibility

03:20

Sept.29

Simulated flight no.3

06:30

Total

31:27

 

...make rapid and accurate decisions under actual operational conditions.

Astronaut Schirra achieved a high level of skill on the procedures trainer in performing the turnaround and retrofire maneuvers. Use of the transparent gyro simulator and a very good understanding of the spacecraft control systems and their operation prepared him adequately for scheduled in-flight activities, such as control mode switching, flight maneuvering, drifting flight, and the gyro caging and uncaging procedures that cannot be properly simulated on the procedures trainer. Preparation in such areas as emergency procedures, mission anomalies, egress from the spacecraft, and recovery procedures was also satisfactorily accomplished.

Active participation in spacecraft checkout activities enabled the pilot to become familiar with the systems of the MA-8 spacecraft and the Atlas launch vehicle. This familiarity permitted him to manipulate and evaluate his flight equipment along with the various modifications to flight systems and switching procedures specific to the Sigma 7 spacecraft. Table 4-II summarizes these activities from August 11 to October 3, 1962, during which period the pilot spent 31 hours and 27 minutes in the spacecraft itself and many additional hours before and after each checkout operation in preparation, observation, troubleshooting, and discussion. In addition, Astronaut Schirra, as the backup pilot for the MA-7 mission, spent 45 hours in the Aurora 7 spacecraft during the MA-7 preflight period. This experience added significantly to his knowledge of the Mercury spacecraft and launch vehicle systems.

The pilot's training activities using the Cape Canaveral procedures trainer from August 20 to October 1, 1962, are summarized in table 4-III. This table does not include the 28 hours spent in this trainer during the MA-7 preflight period, or the 8 hours spent in the Langely procedures trainer during June 1962 in which manual control of possible reentry-rate oscillations was practiced and flight plan control tasks were evaluated. During the training period at Cape Canaveral, the pilot spent 29 hours and 15 minutes in the trainer accomplishing 37 simulated missions which included 40 turnaround maneuvers, 53 retrofire maneuvers, and 68 simulated failures. The pilot devoted nearly as much time to briefings and debriefings in conjunction with each training session as he spent in the trainer. The greatest emphasis during these simulations was on the more basic operational aspects of the mission because of their relative importance and because the procedures trainer is best equipped to accomplish these requirements. The pilot participated in several simulated launch aborts and network exercises during which the mission rules were rehearsed and discussed.

The pilot received three series of formal briefings which were oriented as much as possible towards the operational requirements of the mission. In addition, he spent well over 100 hours in reviewing informally the operation of spacecraft systems with specialists during the 2 months prior to launch in order to establish mission operational procedures.

 

Click here to go to the accessible version of table 4.3.

[41] Table 4-III. Pilot Training Summary in the Mercury Procedures Trainer No.2 (Cape Canaveral)

[68 simulated failures, 40 turnaround maneuvers, 53 retrofire attitude control maneuvers]

Date (1962)

Type of training

Time, hr:min

No. of missions

Failure number and type

Special training activities1

ECS

RCS

Sequential system

Electrical system

Communication system

Other

Aug.20

New switch function familiarization

01:30

1

-

-

-

-

-

-

1,4,5

Aug.23

One-orbital-pass mission

01:30

1

-

-

-

-

-

-

1,4,5,6

Aug.28

Flight plan familiarization, simulated systems failures

01:45

1

-

-

1

1

-

-

3,4,6

Aug.29

Flight plan familiarization

00:35

1

-

-

-

1

-

-

1,4,6

Sept.8

Simulated systems failures

03:00

4

-

1

3

3

1

1

1,2,3

Sept.10

Simulated systems failures

01:35

3

-

1

3

3

-

-

1,2,3,6

Sept.11

Simulated systems failures

01:30

3

1

-

2

3

-

3

2,3,4

Sept.12

Simulated systems failures

01:15

4

3

-

2

1

-

1

2,3,4,5

Sept.15

Simulated systems failures

02:25

3

2

-

5

1

1

-

2,3,6

Sept.18

MCC-Bermuda simulation

03:35

4

1

2

2

2

3

2

2,3

Sept.19

MCC-Bermuda simulation

00:30

1

1

-

-

-

-

1

2

Sept.20

Simulated attitude control system failure

02:30

4

2

1

1

-

-

3

1,2,3,4,5

Sept.22

Network simulation

01:00

1

-

-

-

-

-

-

1,4

Sept.25

Flight plan work

02:00

1

-

-

-

-

-

-

1,4,6

Sept.27

Simulated attitude control system failure

01:05

1

-

-

-

-

-

-

1,5,6

Oct.1

Network simulation, simulated systems failures.

03:30

4

-

-

3

-

-

-

1,2,4

Total

29:15

37

10

5

22

15

5

11

1 Training activities key:

1- Normal launches and reentries.
2- Launch aborts.
3-Orbital and reentry emergencies.
4- Turnaround maneuvers.
5- Retrofire attitude control.
6-Flight plan activities (equipment manipulation, control mode switching, yaw maneuvering, et cetera)
 
 

[42] Control Tasks

 

Several in-flight maneuvers and control tasks were programmed for the MA-8 flight to obtain additional information on possible orientation problems in space and the ability of the pilot to perform various attitude control tasks using accuracy and fuel expenditure as the primary criteria of performance. These tasks are discussed in the following paragraphs.

The primary purpose in accomplishing a manual turnaround maneuver using the fly-by-wire control mode, low thrusters only, was to conserve control-system fuel. Therefore, it w as planned that, if the flight was proceeding normally, the turnaround would be executed at a leisurely pace using a 4-degree-per-second rate about the yaw axis.

The pilot performed this maneuver identically as it has been practiced on the procedures trainer prior to the flight. Figure 4-2 shows the spacecraft attitudes as indicated by the gyros and a background envelope of five turnaround maneuvers accomplished on the procedures trainer for comparison. The pilot...

 


Figure 4-2.- Turnaround maneuver.

 

....performed the maneuver smoothly and with precision. Only 0.3 pound, or less than 1 percent, of the automatic-control-system fuel supply was used. This quantity amounts to approximately 10 percent of the total control fuel typically required by the automatic control system for accomplishing this same maneuver.

The pilot reported that the turnaround maneuver proceeded just as it had on the procedures trainer. In accordance with practice in the trainer, Astronaut Schirra used only the rate and attitude indicators for reference, and he resisted the temptation to look out the window when the horizon first came into view.

A series of yaw maneuvers were planned for this flight to obtain quantitative information on the use of the window and periscope as independent references for determining and acquiring the proper spacecraft attitude about the yaw axis. The yaw indicator was to be covered and the spacecraft displaced in yaw. However, this maneuver was planned so that the yaw attitude would be retained within gyro and repeater stop limits. These maneuvers were to be performed during both daytime and nighttime phases of the orbit in which the views through the window and the periscope were used independently as external references.

The pilot stated very early in the flight that he could accurately estimate yaw attitude during periods when either the automatic stabilization and control system (ASCS) mode was operating or when in a drifting flight mode.

The first yaw maneuver on the daylight side of the earth in which the view through the window was used as a reference was performed at a ground elapsed time (g.e.t.) of 1 hour and 41 minutes over Bermuda during the second orbital pass. This maneuver was followed at 01:50 g.e.t. by a similar exercise using the view through the periscope as a reference. In addition yaw maneuvers on the night side of the earth in which the view through the window was again used as a reference were performed in sequence over Muchea, Australia, during the second orbital pass at 02:26 and 02:28 g.e.t. The results of these yaw maneuvers are presented in figure 4-3, which gives the variation in spacecraft roll, pitch, and yaw attitudes. Table 4-IV lists the fuel usage, time required, control....

 

[43] Table 4-IV. Yaw Maneuvers

Maneuver

Visual Reference

Control mode

Automatic fuel usage, lb

Gyro switch position

1

Window

Fly-by-wire, low

0.39

Normal

2

Periscope

Fly-by-wire, low

0.32

Free

3

Window

Fly-by-wire, low

0.23

Free

4

Window

Fly-by-wire, low

0.30

Free


Figure 4.3. Yaw maneuvers.

 

[44] ...mode, and visual reference used for these yaw maneuvers, which are discussed below in the order tabulated.

The first yaw maneuver on the day side of the earth consisted of three separate yaw displacement and realinement maneuvers accomplished in rapid sequence. The pilot did not, however, record an attitude "MARK" on the voice tape until the end of the final maneuver of the sequence. The pilot yawed the spacecraft approximately 8° to 10° from 0° in each case, holding pitch and roll attitudes reasonably close to retroattitude as intended. At the termination of this maneuver yaw misalinement was +4°, with roll and pitch attitudes at the nominal 0° and -34°, respectively. As a result of this maneuver, the pilot reported that yaw errors could be readily recognized and corrected by using the terrain features or any available type of cloud formation through the window. The pilot reported, and the results of this maneuver verify, that yaw realinement could be accomplished while holding the nominal retroattitude of-34° in pitch. This attitude in pitch makes the horizon available for maintaining proper attitudes in pitch and roll while the spacecraft is being oriented in yaw.

In the second yaw maneuver on the daylight side of the earth, the pilot yawed 23° to the right while holding pitch and roll within ±5° of the desired attitudes. At the termination of this maneuver, the spacecraft was in error by only +2° in yaw, with pitch and roll at -33° and 0°, respectively.

The pilot reported that yaw misalinements were readily apparent and that realinement to 0° could be effected rapidly by using only the periscope reference. However, as a result of the two daytime yaw maneuvers, he reported that the window provided an adequate yaw reference and that the periscope constituted a redundant external reference system.

In the third and fourth yaw maneuvers accomplished on the nightside of the orbit, the astronaut employed the window as a reference because he found the periscope to be ineffective at night. In performing each of these maneuvers, the pilot yawed approximately 20° left and then was able to realine in yaw very close to 0°. At the termination of the third maneuver, the yaw error was +3°; and at the end of the fourth maneuver, the yaw error was -1°. In the course of completing both of these maneuvers, pitch attitude was increased from the nominal -34 ° to approximately -22 °; however, pitch attitude was returned to about -34° by the end of each maneuver. Excursions in roll were somewhat larger for these maneuvers than they had been during the daylight yaw maneuvers; however, these errors were also reduced to nearly zero at the completion of the maneuver. The pilot used the Moon and the planet Venus as visual references in performing both of these maneuvers.

Astronaut Schirra reported that yaw determination on the nightside was more difficult than during the daylight phase because of the small field of view available for the acquisition of star patterns. He reported that only through concentrated effort could he acquire attitude alinement about all axes by using, the airglow layer as his reference in pitch and roll and a known celestial body for yaw reference.

The results of these four maneuvers indicate that for yaw misalinements of the order obtained during this flight, the spacecraft can be realined in yaw during the day or during moonlit night conditions by using the window view as the only visual reference. Quantitatively, these maneuvers were accomplished in a 2- to 3-minute time period with an average usage of between 0.2 and 0.3 pound of control fuel, and realinement of spacecraft attitudes to within - 5° of the nominal retroattitude was readily achieved. Yaw alinement on the daylight side in which the periscope was used required approximately the same amount of control fuel and time as was required when the window reference was used with little or no improvement in accuracy.

 

Drifting Flight

 

The spacecraft was permitted to drift completely free in attitude on two different occasions to conserve control fuel. During this time, power to the ASCS was switched off (powered down) to conserve electrical power. On three additional occasions, the pilot maintained the spacecraft attitudes within the limits of the horizon scanners with a minimum amount of control inputs. This flight mode is referred to as limited drifting flight. A total of 2 hours and 29 minutes was spent in both types of drifting flight during this mission, with the longest continuous period extending for 1 hour and 42 minutes. Most of the drifting period [45] was devoted to flight in the attitude-free state. The total control fuel usage directly associated with the drifting flight phases was approximately 1 pound, and this was almost entirely consumed in reestablishing attitudes at the termination of each period of drifting flight. Drifting flight was not disturbing to the pilot, and the flight results verify that this operational technique provides an excellent means of conserving fuel and electrical power.

 

Gyro Realinement Maneuvers

 

The gyros were realined to an early reference through the window by using fly-by-wire on two different occasions. At the completion of both maneuvers, the gyros and horizon scanners were alined quite closely, and torquing of the gyros to the horizon scanners quickly corrected any remaining disparities. The first gyro realinement required 1.71 pounds, but the second maneuver required only 0.66 pound of automatic control fuel.

The first maneuver was accomplished entirely during the night period of the orbit and required two separate gyro caging and uncaging operations to obtain the correct alinement. The procedure used was to determine attitude by observing available star patterns and to acquire and track the horizon by using 2-degree-per-second rates or less until the proper position was indicated in the window. The gyros were then caged and uncaged. At this point, roll and pitch were quite well alined; however, all error of approximately 35° in yaw attitude existed at this time. By using the constellation Cassiopeia as a visual reference, the pilot quickly recognized this yaw error and maneuvered to the proper heading.

The procedure used by the pilot in performing the second gyro realinement was: (1) to cage and uncage the gyros at -34° in pitch and 0° in roll and yaw, and (2) to pitch up to an indicated attitude of +34°, while simultaneously holding roll and yaw attitudes at 0°, and again cage and uncage the gyros The maneuver was performed during the daylight phase of the orbit, and again the earth horizon reference through the window was used. The errors in slaving the gyros to the horizon scanners were within ±7° for all axes at the completion of this maneuver, and the scanners required less than a minute to correct remaining gyro errors.

On four occasions during the flight, the pilot maneuvered from retroattitude to reentry attitude in pitch prior to selecting the automatic reentry-select control mode. Typical fuel usage for this pitch attitude change was 0.20 pound of the automatic fuel supply. During the final pitch maneuver to reentry- attitude, the pilot simultaneously checked his fly-by-wire high thrusters, and this action resulted in a much higher fuel usage than the 'previous pitch maneuvers. The pilot performed these maneuvers with precision, and at the completion of each maneuver he engaged the automatic control system without actuating the high reaction control thrusters.

The pilot completed stowage of the items on the preretrofire checklist and was prepared well in advance of the retrosequence event. Just before the last sunrise prior to this event, the pilot used Jupiter, Fomalhaut, and the constellation Grus to verify that his gyro indicators were functioning properly. As planned, the automatic control system was used to control the spacecraft attitudes during retrofire, with the manual proportional control mode selected as a backup had it been required. During retrofire, he cross-checked his window reference and reported that his attitudes were constant within less than 1° about all axes. Just prior to retrosequence, he reported that the glare of the Sun through the periscope was blinding and therefore placed the dark filter over the Iens.

 

Reentry

 

As planned, the pilot used the rate stabilization and control system mode for controlling the reentry phase of the flight. Although this system was consuming large quantities of control system fuel at a rate which was expected (for example, 50 percent of the manual supply was expended from 0.05g to drogue parachute deployment), this fact almost led the pilot to select the auxiliary damping control mode of the ASCS.

 

[46] Systems Management and Operational Procedures

 

Throughout the mission, the pilot exhibited an excellent monitoring technique and operational procedure in managing the spacecraft systems. During the entire flight, the pilot reported clearly and accurately on the status of systems and maintained a verbal commentary on the in-flight activities, such as the yaw maneuvers, control mode usage, spacecraft elapsed time, and visual observations The pilot exercised sound judgement and procedure in resolving the suit-circuit-temperature control problem The procedure for switching off (powering down) and switching on (powering up) the ASCS inverter was performed exactly as planned. The pilot maintained an effective surveillance for possible discrepancies between true vehicle and gyro attitudes as well as the overall operation of the spacecraft's electrical systems. The proper fuse control switch positions were selected throughout the mission, and the drogue parachute and snorkle inlet valves were manually activated at the proper time.

 

Control Mode Switching

 

The pilot's use of his control systems, as well as his control mode switching operations, was excellent. He was able to accomplish these switching operations with a very minimum amount of fuel usage.

Table 4-V lists the control modes and combinations of control mode configurations together with the total time and frequency that each control system was used during the flight. The pilot used a total of 14 single or dual control combinations and switched control modes 54 times during the mission The automatic control system controlled the spacecraft during 60 percent of the total orbital flight time, whereas the pilot manually controlled the spacecraft 16 percent of this total. During the remaining 24 percent of the flight, the spacecraft was permitted to drift in an attitude-free mode.

The pilot selected the automatic control system on 23 different occasions. Only in one case did he inadvertently activate the automatic control system high thrusters, and this was....

 

Table 4-V. Control Mode Utilization [Does not include gyro switch position]

Control mode configuration (a)
Total time used in rank order,
hr:min:sec
Maximum time used any one time,
hr:min:sec
Frequency used

ASCS, retroattitude select

04:57:34

01:15:29

16

Free drift

02:11:56

01:41:56

2

FBW, low

00:40:59

00:06:36

20

ASCS, reentry select

00:35:09

00:19:11

6

Drift and FBW, low

00:17:00 (approx.)

00:09:22

3

MP

00:07:05

00:02:54

4

RSCS

00:06:28

00:06:28

1

FBW, normal

00:02:17

00:01:21

2

ASCS, orientation, low

00:01:06

00:00:10

17

MP and ASCS

00:00:53

00:00:53

2

FBW, low, and RSCS

00:00:31

00:00:31

1

ASCS, orientation, high

b00:00:36

00.00:23

3

MP and FBW, low

00:00:07

00:00:07

1

ASCS, auxiliary damping

00:00:04

00:00:04

1

a Key:

ASCS - Automatic stabilization and control system.
RSCS - Rate stabilization control system.
MP - Manual proportional.
FBW - Fly-by-wire.
Retroattitude and reentry select - Pitch attitude command by the ASCS as determined by the attitude select switch.
ASCS orientation - Orients spacecraft to either retroattitude or reentry attitude. High or low thruster actuation dependent upon deviation of rates and attitudes from those commanded by the orientation mode control logic.

b Includes the 23-second retrofire period.

 

 

[47] ...because he engaged the automatic control system while the spacecraft was in proper retroattitude, but the attitude-select switch was in the reentry-attitude position. The only other time that automatic control system high thruster operation occurred, other than during the retrofire period was just prior to 0.05g. This activation resulted when the ASCS in orbit mode failed to keep the spacecraft attitudes within the attitude limits.

The pilot selected trouble authority control on four occasions during the flight. Only the first case was inadvertent and occurred when the pilot changed from the manual proportional control mode to the fly-by-wire mode, low thrusters only. The pilot noticed the greater than normal response for the fly-by-wire, low, and immediately returned to a single control configuration.

The second case of double authority control occurred just subsequent to the single instance in which the pilot inadvertently actuated the automatic-control-system high thrusters. The pilot analyzed the situation as a stuck thruster in the automatic control system and therefore selected rate command in conjunction with fly-by-wire, low, to counteract the effect of the automatic-mode high thrusters.

In the third case, the manual proportional system was intentionally utilized to override the automatic system in order to correct for an error of approximately 10° in roll at the end of the horizon scanner test.

The final case of double authority control occurred during the ignition period for the retrorockets. The pilot selected manual proportional control, as planned, to back up the automatic control system in case it failed to control the spacecraft attitudes properly during this event.

 

Fuel Usage

 

The amount of fuel used during the maneuvering flight phase and control-mode switching exercises was much less than the amount which had been predicted from calculations based on the prescribed flight plan. A fuel usage history is presented in paper 1 in the section entitled "Spacecraft Control System." The fuel reserve at retrofire was approximately 80 percent of initial levels for both the manual and automatic fuel supplies, which represented a total fuel consumption of only 12 pounds for almost 9 hours of flight. The automatic control system controlled the spacecraft attitudes during 60 percent of the mission, and all of the scheduled maneuvers and control system operations were accomplished. The fuel economy exhibited on this flight can be attributed to the following:

1. The pilot performed the turnaround maneuver using only the fly-by-wire, low-thrust, control. Fuel usage for this maneuver was approximately 1O percent of that nominally required by the automatic control system to accomplish the same task.

2. The high thrusters of the automatic control system were activated only on two very brief occasions prior to retrofire, only one of which resulted from an oversight on the part of the pilot and which he quickly corrected.

3. The fly-by-wire mode, low thrusters only, was used for most of the manual maneuvers.

4. The pilot executed each maneuver smoothly and with minimal control inputs.

5. The pilot used a systematic procedure for fuel conservation, particularly during control system checks.

 


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