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RESULTS OF THE SECOND U.S. MANNED ORBITAL SPACE FLIGHT, MAY 24, 1962

 

6. PILOT PERFORMANCE

 

By HELMUT A. KUEHNEL, Flight Crew Operations Division, NASA Manned Spacecraft Center; WILLIAM O. ARMSTRONG, Flight Crew Operations Division, NASA Manned Spacecraft Center; JOHN J. VAN BOCKEL, Flight Crew Operations Division, NASA Manned Spacecraft Center; and HAROLD I. JOHNSON, Flight Crew Operations Division, NASA Manned Spacecraft Center

 

[63] Summary

 

The results the MA-7 orbital flight further indicate that man can function effectively in a space environment for periods up to 4 1/2 hours. In general, the pilot can orient the spacecraft to a given attitude by using external reference provided sufficient time is available for determining yaw alinement. As with the MA-6 flight the results of this flight provide evidence that the man can serve as a backup to the automatic spacecraft systems. The pilot has demonstrated his ability to operate scientific apparatus successfully in a space environment and to obtain useful data for the analysis of scientific problems associated with a terrestrial space environment. The results of the MA-7 flight provide additional evidence that man is ready for a more extended mission in a weightless environment. Flight difficulties occurring during this mission, however, have served to emphasize that the primary attention of the pilot should be devoted to management of spacecraft systems and detailed attention to operational functions.

 

Introduction

 

The pilot's primary role during the MA-7 mission, as in the MA-6 mission, was to report and monitor systems operations and, if necessary, to take corrective action in order to achieve the mission objectives. The pilot's secondary responsibility during both of these missions was to conduct scientific experiments and to make observations that would further evaluate the spacecraft systems' performance. The purpose of this paper w ill be to discuss the pilot's performance in accomplishing the primary mission objectives. Only a few of the pilot's secondary tasks, such as scientific experiments and observations, are discussed here, since many of these are discussed in papers 1, 4, and 7 of this report.

 

Preflight Performance

 

A flight plan was formulated for the MA-7 flight to guide the pilot in carrying out the operational and experimental objectives of the mission. This plan defined the mission activities and established the sequence in which these activities were to be attempted. In preparation for the flight, the pilot participated in extensive preflight checkout activities and training sessions. In general, his preflight activities were similar to those accomplished by the MA-6 pilot as shown in table 6-I; however, the MA-7 pilot generally did acquire more time on the trainers and in the spacecraft than did the...

 

Table 6-1. Pilot Training Summaryskip to an accessible table

Flight

ALFA and Mercury procedures trainers

Time spent on spacecraft systems checks, hr:min

Time, hr:min

Number of simulated failures

Number of simulated missions

Number of simulated control maneuvers

MA-6 (Glenn)

59:45

189

70

162

25:55

MA-7 (Carpenter)

70:45

143

73

255

45:00

 


[
64] [MISSING] Figure 6-1. Astronaut Carpenter in the Langley procedures trainer.

 

...MA-6 pilot. It should be pointed out that this table summarizes only the pilots' specific preparation for their particular flight and does not include general training accomplished since their selection as astronauts.

It should be noted that Astronaut Carpenter had ad an opportunity to become familiar with the spacecraft and launch-vehicle operations during his period as backup pilot for the MA-6 flight. Thus, in addition to the experience indicated in table 6-I, he spent approximately 80 hours in the MA-6 spacecraft during its checkout period at the launch site. This period of familiarization provided him with an opportunity to increase his knowledge of the spacecraft systems and gave him a good background or his own MA-7 mission preparation activities.

 


[MISSING] Figure 6-2. Astronaut Carpenter practicing egress procedures.

 

The training activities, which were conducted in the Langley (see fig. 6-1) and Cape Canaveral procedures trainer and the air-lubricated free-attitude (ALFA) trainer, included a large number of attitude control maneuvers and simulated system failures. These trainers have been described in references 1 and 2. The pilot was also thoroughly rehearsed on egress and recovery procedures. (See fig. 6-2.) In addition to the above-mentioned training activities, the MA-7 pilot participated in several launch abort and network simulations during which the mission rules and the flight plan were rehearsed and discussed. Although the training as described above was extensive, it should be recognized that limitations in the Mercury procedures trainer precluded practice of certain activities, such as controlling attitude by using external references.

 

Control Tasks

 

Several control tasks and in-flight maneuvers were programed for the MA-7 flight to obtain information on orientation problems in space and the ability of the pilot to perform attitude control tasks. These control tasks included turnaround, tracking, maneuvering, drifting flight, and retrofire. It should be pointed out that the pilot s performance could not be quantitatively analyzed because:

1. The pitch horizon scanner circuit appeared to have malfunctioned.

2. The pilot deviated somewhat from planned procedures established prior to the mission.

3. The gyros were caged during much of the flight.

4. The spacecraft attitudes exceeded the viewing limits of the horizon scanners on a number of occasions.

 

With these limitations in mind, the attitude control tasks are discussed in the following paragraphs.

 

Turnaround Maneuver

 

The primary purpose in scheduling a manual turnaround after spacecraft separation was to conserve reaction control system fuel.

 


chart of pilot's time to correct spacecraft attitude.

[65] Figure 6-3.- Turnaround maneuver

 

The pilot used only 1.6 pounds of control fuel for the MA-7 turnaround, whereas past flight experience has shown that the automatic control system employs over 4 pounds of control fuel for this maneuver.

The shaded area of figure 6-3 displays the pilot's performance during turnaround training sessions, and the uncorrected gyro attitudes indicated during the actual flight maneuver are represented by the solid curves. The flight maneuver was performed in yaw approximately as planned, and the correct spacecraft orientation was achieved shortly after separation from the launch vehicle.

Although indicated roll attitude deviated to a greater extent during the in-flight turnaround maneuver than in training sessions, the pilot successfully brought roll attitude to zero by the end of the maneuver.

The pitch attitude indication initially varied from that of the trainer because of the malfunction in the pitch horizon scanner circuit described in paper 1. Therefore, the pilot was required to perform a correction in pitch which was considerably larger than planned, and as figure 6-3 shows he accomplished this correction in approximately the same time exhibited during training exercises. Then the pilot allowed the spacecraft attitude to diverge for a considerable period of time before stabilizing as planned at retroattitude, as shown in figure 6-3. However, it should be noted that an insertion "go" condition had been received from ground control during the turnaround, and it was not essential for the pilot to hold orbit attitude.

 

Sustainer Stage Tracking

 

The purpose of tracking the sustainer stage was to investigate the ability of the pilot to observe an object in space and to determine his capability to perform pursuit tracking of an object in a slightly different trajectory. The pilot readily sighted the sustainer stage through the spacecraft window after completion of spacecraft turnaround at a calculated distance of approximately 300 yards. He continued to observe and photograph the sustainer for 8 1/2 minutes at which time the sustainer stage was calculated to be at a range of 3 miles behind and below the spacecraft. During this period, the pilot noted a very slow tumbling motion of the sustainer and also observed small crystalline particles emanating from the sustainer nozzle.

Sufficient data were not obtained to permit a quantitative analysis of the pilot's tracking capability. However, the pilot stated that he believed precision tracking would not be a difficult task while using the low thrusters for control.

 

Use of External Reference for Maneuvering

 

This flight has further shown that manual control of spacecraft attitudes through the use of external references can be adequately accomplished under daylight and moonlit night conditions. Furthermore, the MA-7 flight provided evidence that spacecraft orientation about the pitch and roll axes could be accomplished manually on the dark side of the earth without moonlight by using the airglow layer as a horizon reference.

Manual control of the spacecraft yaw attitude using external references has proven to be more difficult and time consuming than pitch and roll alinement, particularly as external lighting diminishes . Although no precision [66] maneuvers were accomplished on the flight which could be quantitatively analyzed, the pilot did confirm that ground terrain drift provided the best daylight reference in yaw. However, a terrestrial reference at night was useful in controlling yaw attitudes only when sufficiently illuminated by moonlight. In the absence of moonlight, the pilot reported that the only satisfactory yaw reference was a known star complex near the orbital plane.

 

Drifting Flight

 

During the final portion of the MA-7 flight, the spacecraft was allowed to drift free to conserve fuel and to evaluate the behavior of the astronaut and vehicle during drifting flight. The spacecraft drifted for a total of 1 hour and 17 minutes during the mission, 1 hour and 6 minutes of which was continuous during the third orbital pass. Rates of 0.5 degree/second or less were generally typical of this period when the spacecraft was allowed to drift completely free of all control inputs. The pilot commented that on one occasion during drifting flight, he observed the moon for a significantly long period in or near the center of the window, indicating that attitude rates were near zero. Data showed that spacecraft attitude rates were less than 0.5 degree/second during this particular period. The pilot also reported that drifting flight was not disturbing and that he was not concerned when external references were temporarily unavailable. It would appear, then, that drifting flight, in addition to conserving fuel, affords a period when the pilot can be relatively free to accomplish many useful activities and experiments without devoting attention to spacecraft orientation.

 

Retrofire Maneuver

 

It was intended to have the automatic control system maintain spacecraft attitude during the firing of the retrorocket; however, the malfunction of the pitch horizon scanner circuit dictated that the pilot manually control the spacecraft attitudes during this event. Except for the late ignition of the retrorockets, the pilot reported that he believed the maneuver had proceeded without serious misalinement of the spacecraft attitude. However, the spacecraft overshot the intended landing point by approximately 250 miles.

The pilot backed up the automatic retrofire system by pushing the manual retrofire button when the event did not occur at the commanded time. Retrofire occurred 3 to 4 seconds late which accounted for approximately 15 to 20 miles of the total overshoot error.

In an effort to explain the major cause of the overshoot error, a review of the events just prior to and during the retrofire is presented. At approximately 11 minutes prior to retrofire, the pilot observed a possible source of the luminous particles previously reported by Astronaut Glenn during the MA-6 mission. This event followed by photographing of these particles delayed his completing the stowage of the onboard equipment as well as the accomplishment of the preretrosequence checklist.

At approximately 6 minutes prior to retrofire the pilot enabled the manual proportional (MP) control system as a backup to the automatic stabilization and control system (ASCS), as specified for an automatic retrofire maneuver. The pilot then engaged his automatic control system and almost immediately reported a discrepancy between the instruments and the external window references. In the 5 minutes prior to retrosequence (T-3O sec), he attempted to analyze the automatic control system problem, and rechecked his manual control systems in preparation for this event.

At 30 seconds before retrofire, the pilot again checked his ASCS orientation mode upon ground request. While the pilot was making this check, the spacecraft attained excessive pitch-down attitude; therefore, the pilot quickly switched from ASCS to FBW modes and repositioned the spacecraft to retrofire attitude using his earth-through-window reference. It was during this period that gyro outputs indicated a significant excursion in yaw attitude. As a result of switching to the FBW mode without cutting off the MP mode, the pilot inadvertently used double authority control. Because of the horizon scanner malfunction the pilot cross referenced between the gyro indications and the external references for attitude information during the firing of the retrorockets.

Figure 6-4 presents the gyro output attitude indications as well as the desired attitudes to he held during retrofire. Because of the horizon scanner malfunction, the gyro indications do...

 


chart of spacecraft position after separation

[67] Figure 6-4.- Indicated spacecraft attitudes during retrofire. Not corrected, gyros free.

 

...not necessarily represent the true spacecraft attitudes particularly; however, they do illustrate the trends in attitude as a function of elapsed time during retrofire. However, these are the indicated attitudes displayed to the pilot.

Radar tracking data have indicated that the mean spacecraft pitch attitude during the retrofire period was essentially correct. Thus the deviation in pitch attitude shown in this figure did not contribute to the overshoot error in landing. Some deviations are also shown in spacecraft roll attitude during retrofire; however, roll errors of this magnitude have a negligible effect on landing point dispersion. Thus, the error in landing position resulted primarily from a misalinement in spacecraft yaw- attitude (indicated in fig. 6-4). Radar tracking data have shown that the spacecraft had an average yaw error of 27° during retrofire. It should be noted, however, that the error in yaw was essentially corrected by the end of the retrofire event.

In review, the pilot, by manually controlling the spacecraft during retrofire, demonstrated an ability to orient the vehicle so as to effect a successful reentry, thereby providing evidence that he can serve as a backup to malfunctioning automatic systems of the spacecraft. The extensive review of this maneuver further serves to illustrate the desirability of assigning priority to flight requirements so that sufficient time will be available to perform the more critical operational activities.

 

Fuel Management

 

The fact that the fuel usage rate was greater shall expected was an area of major concern during this flight. This primarily resulted from the extensive use of high thruster control for orbit maneuvering, inadvertent actuation of two control systems simultaneously, and frequent engagement of the automatic system orientation control mode which generally uses high thrusters to reorient the spacecraft to orbit attitude.

As pointed out in paper 1, a systems modification has been incorporated on future spacecraft to preclude recurrence of high thruster usage for manual maneuvering in orbit. Further training emphasizing a more strict adherence to optimal operation of the control system, as well as simplified attitude maneuvering requirements and reduced control mode switching should also help reduce excessive fuel consumption for future Mercury flights.

 

Scientific Experiments

 

In addition to controlling the spacecraft and monitoring systems operations during the flight, the pilot also assumed a dominant role in accomplishing a number of in-flight experiments. One of these experiments consisted of deploying a multicolored inflatable balloon from the spacecraft while in orbit. The balloon was tethered to the spacecraft by means of a 100-foot braided nylon line. It was intended that the pilot should observe balloon motions and the various color patterns on the balloon to determine which appeared best suited for visual detection in space. Drag measurements were also to be taken at periodic intervals throughout the flight [68] The balloon was deployed as programed. The pilot was readily able to observe the balloon and attachment line as well as the balsa inserts used to hold the package prior to deployment. The pilot noted that both the orange and aluminum segments were visible and photographs confirmed this report. The pilot was also able to discern the irregular shape assumed by the balloon when it failed to inflate properly. The random motion of the balloon noted by the pilot was probably a result of large. attitude maneuvers of the spacecraft and unsteady aerodynamic loading because of the irregular balloon shape. The pilot was able to maintain visual balloon contact throughout the orbital daylight phases and on several occasions at night. Effective evaluation of the colors and meaningful measurements of the balloon drag were, of course, compromised by failure of the balloon to inflate fully.

Another experiment was conducted which was intended to define the earth's limb by photographing the d daylight horizon with a blue and red split filter over the film plane The pilot was able to maneuver the spacecraft into the correct attitude during the proper phase of the daylight pass and to expose a number of frames of film for microdensitometer evaluation by....

 


[MISSING] Figure 6-5.-Representative photograph of horizon definition.

 

....scientists of MIT. Of the 26 frames analyzed, 20 have yielded good data and 6 are questionable. Figure 6-5 is an example of one of the photographs taken during this experiment. The densitometer analysis has indicated that the earth s limb definition in the blue is very regular and this can be seen from the sample photograph ; however, the definition in the red is variable due partly to the distorting effect of the clouds. It is hoped that a complete analysis of these results will yield information on the height of the earth's limb; however, at the present results are still incomplete.


References

1. SLAYTON, DONALD K: Pilot Training and Preflight Preparation. Proc. Conf. on Results of the First U.S. Manned Suborbital Space Flight, NASA, Nat. Inst. Health, and Nat. Acad. Sci., June 6, 1961, pp. .53-60.

2. VOAS, ROBERT B. Manual Control of the Mercury Spacecraft. Astronautics, March 1962.


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