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

 

2. MERCURY NETWORK PERFORMANCE

 

By James J. DONEGAN, Manned Space Flight Support Division, NASA Goddard Space Flight Center; and James C. JACKSON, Manned Space Flight Support Division, NASA Goddard Space Flight Center

 

[15] Summary

 

The Mercury Network performed very well in support of the Mercury Atlas-7 mission. All systems required to support the mission were operational at the time of launch and in some instances utilized backup equipment in the place of primary equipment. No problems were encountered with computing and data flow. The computers at the Goddard Space Flight Center accurately predicted the 250 nautical mile overshoot immediately after the FPS-16 tracking data from Point Arguello, California, were received Radar tracking was generally horizon to horizon, and the resulting data provided to the Goddard computers resulted in good orbit determination during the mission.

The ground communications network performance was generally better than that of the MA-6 mission. The ground-to-spacecraft communications were slightly inferior to MA-6 performance, particularly when patched onto the conference network to allow monitoring by other stations. Telemetry reception, as in the MA-6 flight, was good.

 

Introduction

 

The purpose of this paper is twofold. The first is to present a description and the performance during the MA-7 mission of the Mercury Network and its associated equipment. The second is to describe briefly the Mercury real-time computing system of the network and to give a brief account of its performance during the MA-7 mission.

 

Mercury Network

 

The Mercury Network configuration for the MA-7 flight shown in figure 2-1, was the same as that for MA-6 , with but minor exceptions. For MA-7 there was no Mid-Atlantic Ship, the Indian Ocean Ship was repositioned in the Mozambique Channel as shown in figure 2-1.

The Mercury Network consists of 15 Mercury sites supplemented by several Atlantic Missile Range (AMR) stations, and the Goddard Space Flight Center communication and computing facility. The major functions of this Network during the MA-7 mission were to:

(1) Provide ground radar tracking of the spacecraft and data transmission to the Goddard computers.

(2) Provide launch and orbital commuting during the flight with real-time display data transmitted to the Mercury Control Center.

(3) Provide real-time telemetry display data at the sites and summary messages to Mercury Control Center (MCC) for flight control purposes.

 


world map with Mercury Network locations indicated

Figure 2-1.-Mercury Network configuration for MA-7.

 

[16] (4) Provide command capability from various stations for astronaut backup of critical spacecraft control functions.

(5) Provide ground-to-spacecraft voice communications and remote station-to-MCC voice and teletype communications.

 

The major equipment subsystems located at each site are shown in table 2-1. Generally the overall performance of all major equipment of the Mercury Network during the MA-7 mission was excellent. A brief description of the performance of each specific network subsystems and an introduction to the equipment is presented in the following sections.

 

Radar Tracking and Acquisition

 

Two principal types of precision tracking radars are used in the Mercury ground range to track the spacecraft: the AN/FPS-16 and Verlort radars. The AN/FPS-16, shown in figure 2-2, is a precision C-band tracking radar with a 12-foot dish. It operates on a frequency of 5,500 to 5,900 mc and has a beam width of approximately 1.2°. It is the most accurate of our tracking devices. The S-band, or Verlort, radar, shown in figure 2-3, is a very long-range tracking radar with a 10-foot dish. It operates on a frequency of 2,800 to 3,000 mc and has a beam width of approximately 2.5°. The redundancy provided by both of these radar systems supplies the computers with sufficient data to determine the orbit, should one of the spacecraft beacons fail. The active acquisition aid has a quad-helix antenna, which is shown in figure 2-4. It has a broad beam width of 20°, operates on telemetry frequencies (215 to 265 mc),...

 


[MISSING] Figure 2-2. AN/FPS-16 radar installation at Bermuda.

[MISSING] Figure 2-3. Verlort radar installation at Guaymas, Mexico.

 

...and normally acquires the target first. The acquisition aid console and equipment racks are shown in figure 2-5.

This acquisition capability is most critical at sites with the FPS-16 radar since this radar is a narrow-beam device requiring precise pointing information to locate the target. Once the radar has acquired the spacecraft, the radar...

 


[MISSING] Figure 2-4. Acquisition air quad-helix antenna at Bermuda.

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[17] Table 2-1. Ground Communications.

Station

Orbital-pass coverage

Command control

Telemetry reception

Air-ground voice

FPS-16

Verlort radar

Acquisition aid

Computer

Ground Communications

Timing

Voice

Telemetry

Mercury Control Center (MCC)

1, 2, and 3

X

X

X

-

-

X

B/GE IP7090

X

X

X

Cape Canaveral (CNV)

-

-

-

-

X

-

-

-

-

-

-

Grand Bahama (GBI)a

1, 2, and 3

X

X

X

X

-

-

-

X

X

X

Grand Turk (GTI)a

1, 2, and 3

X

X

X

-

-

-

-

X

X

X

Bermuda (BDA)

1, 2, and 3

X

X

X

X

X

X

IBM-709

X

X

X

Grand Canary Island (CYI)

1 and 2

-

X

X

-

X

X

-

X

X

X

Kano, Nigeria (KNO)

1 and 2

-

X

X

-

-

X

-

-

X

X

Zanzibar (ZZB)

1 and 2

-

X

X

-

-

X

-

-

X

X

Indian Ocean Ship (IOS)

1, 2, and 3

-

X

X

-

-

X

-

-

X

X

Muchea, Australia (MUC)

1, 2, and 3

X

X

X

-

X

X

-

X

X

X

Woomera, Australia (WOM)

1 and 2

-

X

X

X

-

X

-

X

X

X

Canton Island (CTN)

1 and 2

-

X

X

-

-

X

-

-

X

X

Kauai Island, Hawaii (HAW)

2 and 3

X

X

X

X

X

X

-

X

X

X

Point Arguello, Calif. (CAL)

1, 2, and 3

X

X

X

X

X

X

-

X

X

X

Guaymas, Mex. (GYM)

1, 2, and 3

X

X

X

-

X

X

-

X

X

X

White Sands, N.M. (WHS)b

1, 2, and 3

-

-

-

X

-

X

-

X

X

X

Corpus Christi, Tex. (TEX)

1, 2, and 3

-

X

X

-

X

X

-

X

X

X

Eglin,Florida (EGL)b

1, 2, and 3

-

-

-

X

MPQ-31

X

-

X

X

X

Goddard Space Flight Center (GSFC)

-

-

-

-

-

-

-

IBM-709

Comm. Center

-

a No monitoring facilities; downrange antennas for MCC.
b Radar tracking station only.
 
 

[
18] [MISSING] Figure 2-5. Acquisition aid console and equipment racks.

 

....system begins automatic tracking and does not require additional acquisition assistance unless the tracking is interrupted.

The acquisition system performance was very good; The only difficulty encountered was the failure of the elevation drive motor at the Zanzibar station. This failure did not influence the reception of data since the operator was able to operate successfully the antenna elevation in the manual mode. The coverage periods of the acquisition system for the Network are shown in figure 2.6.

A comparison of the radar coverage for MA-6 and MA-7, for both C- and S-band systems, is shown in figure 2-7. From an examination of this figure, it can be ascertained that the acquisition system received signals beyond the meaningful limits of horizon-to-horizon track. The standard errors in range, azimuth, and elevation as a result of noise in the radar data collected by the Goddard computers and the quantity of data received are given in table 2-II....

 


chart of geographical locations and their ability to track the Mercury spacecraft

Figure 2-6. Acquisition system coverage.

 

... for the MA-7 flight. These data reveal that the radar tracking was comparable with the horizon-to-horizon coverage obtained during MA-6.

Tracking was consistent from horizon to horizon. The spacecraft beacons functioned very well during the launch phase and satisfactorily throughout the flight. Some amplitude modulation and slight beacon countdown were noted at times. However, these conditions caused no noticeable deterioration of data presented to the computers. Signal strengths received by the radars were noticeably weaker than the MA-6 flight. The radar data transmission (via automatic teletype) was excellent with only minor errors in transmission of several lines of data from Muchea, Australia, during the first orbital pass. There was a total of 67,354 characters transmitted by the network radars with no error.

 

Computing

 

By way of introduction to the Mercury real-time computing system, a brief description is given. Data from the worldwide Mercury Tracking Network are transmitted to the Goddard Communications Center via the data circuits shown in figure 2-8. From the Communications Center, the data are transmitted to the Goddard Computing Center, shown in figure 2-9, which is located in an adjacent room. Here, real-time equipment places the radar data from each tracking station automatically in the core storage of the computers. Two IBM 7090 computers operating independently but in a parallel fashion process the data. Should a computer malfunction during the mission, the other computer may be switched on-line to support...

 


[
19] Figure 2-7. Comparison or radar coverage MA-6 and MA-7.


data flow chart for Mercury tracking information

Figure 2-8. Data circuits for Project Mercury.

 

...the mission while the malfunctioning computer is taken off-line and repaired.

The Mercury computing program is a real-time automatic computing program designed to provide trajectory information necessary to the flight control of the Mercury mission. The heart if the real-time computing system is the monitor system which is shown schematically in figure 2-10. This monitor control system directs the sequence of computer operations in real time. Simply stated, the monitor system accepts data from the remote sites, places the data in the correct block of computer memory, calls on the correct processor (whether it be...

 


[MISSING] Figure 2-9. Goddard Computing Center.

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[20] Table 2-II. Standard Deviations of MA-7 Low-Speed Radar Data

Station

Radar

Total points

Standard Deviations

Range, yards

Azimuth, mils

Elevation, mils

First orbital pass

Bermuda

FPS-16

74

31.0

0.11

0.54

Bermuda

Verlort

74

62.8

1.28

2.15

Canaries

Verlort

68

18.5

1.18

0.67

Muchea

Verlort

84

17.8

1.05

1.15

Woomera

FPS-16

79

4.5

0.17

0.14

Guaymas

Verlort

52

11.0

1.44

1.58

White Sands

FPS-16

29

4.9

0.23

0.41

Texas

Verlort

72

31.9

2.55

2.20

Eglin

FPS-16

82

10.0

0.35

0.24

Eglin

Verlort

81

40.1

1.67

1.78

Cape Canaveral

FPS-16

61

7.6

0.12

0.56

Second orbital pass

Bermuda

FPS-16

76

10.1

0.16

0.57

Bermuda

Verlort

71

62.2

1.65

2.71

Canaries

Verlort

61

12.0

2.31

1.80

Muchea

Verlort

82

22.9

1.28

1.34

Woomera

FPS-16

74

2.5

0.10

0.22

Hawaii

FPS-16

53

5.4

0.24

0.21

Hawaii

Verlort

52

16.7

1.33

1.23

California

FPS-16

45

10.1

0.30

0.40

California

Verlort

45

12.0

1.42

1.56

White Sands

FPS-16

38

17.7

0.14

0.39

Texas

Verlort

70

76.7

2.50

2.44

Eglin

FPS-16

88

7.0

0.54

0.29

Eglin

FPS-16

89

89.1

1.82

2.53

Cape Canaveral

FPS-16

59

6.6

0.16

0.73

Third orbital pass

Bermuda

FPS-16

66

8.2

0.30

0.50

Bermuda

Verlort

66

34.7

1.84

2.09

Muchea

Verlort

64

8.8

0.74

0.60

Hawaii

FPS-16

62

11.5

0.19

0.34

Hawaii

Verlort

64

21.8

1.83

1.71

Reentry

California

FPS-16

61

11.6

0.84

0.66

California

Verlort

61

20.5

1.93

1.64

White Sands

FPS-16

41

21.7

0.23

1.14

Texas

Verlort

61

91.6

2.37

2.19

Eglin

Verlort

74

39.4

1.17

0.32

Cape Canaveral

FPS-16

20

10.0

0.14

0.43

San Salvador

FPS-16

14

30.8

0.21

0.36

 


schematic of the monitor control system

[21] Figure 2-10.-Real-time monitor control system.

 

...launch, orbit, or reentry) to perform the proper computation on the data, then provides the required output quantities to be transmitted to the proper destination at the correct time.

During the MA-7 mission the computing system at Goddard performed well. The equipment, the launch subsystem, and the high-speed line functioned properly during the entire mission. Especially gratifying was the performance of the Bermuda high-speed data system and computations which were implemented after the MA-6 mission. The new dual-compilation system also worked well.

Launch.- All the computing and data transmission equipment was operational during the entire countdown. High-speed input data were continuous during the powered phase of the flight from each of the three data sources, the AMR range safety computer, the launch-vehicle guidance computer, and the Bermuda range....

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Table 2-III. Launch Phase Discrete and Telemetry Events.

Event

Time "tag" of arrival at GSFC, sec since lift-off unless indicated

General Electric/Burroughs line

Nominal

Lift-off

7:45:16 e.s.t.

-

BECO

128.964

130.1

Tower release

153.464

152.2

Tower separation

153.464

142.0

SECO

310.464

304.7

Spacecraft separation

313.964

306.3

Posigrade 1

317.964

-

Posigrade 2

318.464

-

Posigrade 3

318.964

-

Orbit-phase switch

350.964

-

 

....station- See figure 2-11. The data received from the Atlantic Missile Range sources during the launch were excellent. At lift-off FPS-16 data processed through the AMR IP 7090 computer were used as the data source for the Goddard computers for approximately the first 35 seconds of launch. Mark II Azusa data processed by the AMR IP 7090 computer were used for the next 37 seconds as source data for the Goddard computers. The launch-vehicle guidance complex acquired the vehicle in both rate and track at 00:01:02 g.e.t. and was used throughout the powered flight phase and during the "go-no-go" computation as the selected data source by the Goddard computers. Minor deviations in flight-path angle, for example, 1.2° at booster-engine cutoff, and altitude during powered flight were recorded by steering prior to insertion by the Atlas guidance system. Time of the telemetry discretes observed by Goddard during launch are shown in table 2-III. Insertion conditions computed on the basis of the three independent launch sources of data were in close agreement. The data from all sources during the launch were excellent. From a trajectory point of view it was a nearly perfect launch.

Orbital phase.- As a result of the extremely good insertion conditions provided by the Atlas launch vehicle, the orbit phase was nearly nominal. The orbit was determined accurately and verified early in the first pass. The orbital computation equipment functioned normally and automatically during the mission. A basic parameter which is usually indicative of the performance of the tracking-computing network is the computed time for retrorocket ignition for a landing in the normal mission recovery area. This parameter varied a maximum of 2 seconds from launch throughout the mission after the Bermuda correction. As stated previously, the tracking data were plentiful and accurate during the orbit.

Reentry phase.- A retrofire time of 4 hr 32 min 58 sec g.e.t. was recommended by the Goddard computers based on a nominal landing point of 68°W. longitude. The retrofire time actually used was 4 hr 33 min 06 sec g.e.t. based on a more realistic reentry weight because of the actual fuel usage. The retrorockets were fired at approximately 04:33:09 g.e.t. Point Arguello, Calif., tracked the spacecraft during...

 


[
22] Figure 2-11. Computer data sources during launch.

 

....and after retrofire. Based on the Point Arguello FPS-16 tracking information, the Goddard computers immediately predicted an overshoot of 246 nautical miles. The overshoot point was confirmed by the data from the White Sands and Texas stations and all subsequent tracking data. The position of the spacecraft was continuously and accurately displayed on the wall map of the Mercury Control Center in real-time to an altitude of 60,000 feet.

From an analysis of the data, it appears the tracking and computing systems performed their primary tasks normally and without exception. No computer or equipment problems were encountered during the mission.

 

Telemetry and Timing

 

The telemetry system provides reception of the aeromedical data for display of astronaut hearbeat rate, respiration, ECG, blood pressure...


[MISSING] Figure 2-12. Telemetry antenna installation at Kano, Nigeria.


[
23] [MISSING] Figure 2-13. Typical telemetry receiving equipment.

 

..., and body temperature. It also provides the reception and display of data indicative of spacecraft performance for use by the Flight Control team at each tracking station.

A typical telemetry antenna installation is shown in figure 2-12, and the associated electronic receiving and decommutation equipment is shown in figure 2-13. A typical arrangement of display consoles for Flight Control at remote sites is shown in figure 2-14. Although not all spacecraft systems quantities are displayed at the Flight Control consoles, all data received are recorded either on magnetic tape or on direct-writing oscillograph recorders. The timing system provides time marks on all records for later verification and also provides time "tags" with the radar data transmitted to the computers.

In general, all tracking stations received telemetry signals from horizon to horizon. Because the telemetry transmission frequency is severely attenuated by the reentry ionization sheath, a blackout of ground reception results. This effect was recorded for MA-7 as commencing at a ground-elapsed time of 4 hours, 13 minutes and 58 seconds. Signal contact was regained at 4 hr 48 min and 47 sec for approximately 12 seconds at Grand Turk Island. Final loss of telemetry during the landing phase was the result of extreme range and low elevation angle.

A comparison of telemetry reception coverage for each site for MA-6 and MA-7 is given in figure 2-15 and the received signal strengths are given in table 2-IV. The reception periods for each station, identified in figure 2-15, are almost identical to the results shown for the MA- 6 mission.

 

Command

 

The dual ground command system was installed at specific command sites shown in table 2-I. This system provides ground command backup to critical spacecraft functions such as abort and retrofire. Out of a total of 16 command functions transmitted to the spacecraft, 15 were effectively received. The one exception was a calibration command transmitted from Muchea Australia, which was attempted when the spacecraft had passed beyond the optimum transmitting time.

As backup means of voice communications from the ground to spacecraft, the ground command...

 


[MISSING] Figure 2-14.-Typical display consoles at remote stations.

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[24] Table 2-IV. Telemetry Receiver Signal Strengths.

Station

Estimated mean, microvolts

Low

(receiver 1, model 1415)

Low

(receiver 2, model 1434)

High

(receiver 1, model 1415)

High

(receiver 2, model 1434)

First orbital pass

Mercury Control Center

-

-

-

-

Bermuda

100

100

100

100

Canaries

90

275

60

80

Kano

90

70

150

70

Zanzibar

37

90

50

40

Indian Ocean Ship

80

70

20

30

Muchea

195

175

195

180

Woomera

300

300

300

250

Canton

100

120

100

150

Hawaii

Not in range

Guaymas

80

80

75

80

California

30

30

30

30

Texas

300

300

195

300

Second orbital pass

Mercury Control Center

-

-

-

-

Bermuda

150

150

100

110

Canaries

110

170

40

40

Kano

40

30

60

30

Zanzibar

46

46

48

26

Indian Ocean Ship

80

200

50

60

Muchea

195

185

180

165

Woomera

300

190

160

120

Canton

45

45

40

50

Hawaii

100

50

45

40

Guaymas

70

75

60

55

California

80

Not recorded

75

Texas

30

80

30

50

Third orbital pass

Mercury Control Center

-

-

-

-

Bermuda

60

60

40

40

Canaries

Too low to estimate

Kano

Not in range

Zanzibar

Not in range

Indian Ocean Ship

120

200

65

90

Muchea

135

100

150

95

Woomera

30

60

54

59

Canton

Not in range

Hawaii

200

100

100

200

Guaymas

70

70

50

60

California

Not recorded

100

80

80

Texas

200

300

50

325


[
25] Figure 2-15.- Comparison of telemetry coverage times for MA-6 and MA-7.

 

....system employs a voice modulator which may be utilized in the event both the HF and UHF voice systems are inoperative. This backup technique was tested successfully during the first orbital pass over Muchea, Australia .

Standby systems were called upon to maintain command coverage at two stations. Minor trouble was experienced at the California station during the first orbital pass when a fuse opened in the primary system, and the transmitter in the primary command system at Guaymas failed during the third pass. In both cases the standby system functioned satisfactorily. The command system operated normally in spite of several minor malfunctions and had no effect on the mission.

 

Communications

 

The communications facilities for the Mercury- Network consist of:

(1) Teletype between all remote stations and the Mercury Control Center through the Goddard Space Flight Center.

(2) Direct-line telephone communications between selected stations and Mercury Control Center.

(3) HF and UHF communications from all stations except Eglin, Fla., and White Sands, N. Mex., to the spacecraft.

The teletype circuits are utilized for flight message traffic and radar data from radar tracking stations to the Goddard computers. This sharing of circuits restricts all but priority messages from a station during the radar tracking period.

The voice communications circuits between the Mercury Control Center and selected remote stations provide a direct and rapid means of information transfer between the Flight Control personnel at these locations.

The HF and UHF receiving and transmitting equipment permits direct and successive voice contact during the flight between the astronaut and the Flight Control team over each station. A patching arrangement permits all stations which have ground voice communications to the Control Center to monitor all ground-to-spacecraft communications during the flight

Teletype and ground voice .- All regular, part-time, and alternate circuits were active and operative on launch day. The propagation ion prediction was for good conditions for those teletype circuits which utilize radio links to reach certain stations. The teletype network performance well with only three difficulties occurring:

(1) The teletype circuit between Goddard and Guaymas was open for a 7-minute period beginning at 00:36 g.e.t. The spacecraft was not over Guaymas at the time, and retransmission assured message continuity.

(2) The Australian cable gave trouble for a short period at 01:00 g.e.t., which resulted in loss of four dines of Woomera radar data.

(3) Teletype traffic to the Indian Ocean Ship was interrupted for about 6 minutes due to propagation; However, the interruption...

 


[
26] Figure 2-16. HF and UHF coverage for MA-6 and and MA-7.

 

...occurred at a time when the spacecraft was approaching the west coast of the United States and did not interrupt critical traffic.

HF and UHF voice.- The quality of the ground-to spacecraft communications was acceptable throughout the mission; however it was not as good as that for the MA-6 mission. A study of the character of the average signal strength at the ground systems reveals that the majority of the stations reported a lower signal level for MA-7 than was experienced during MA-6. In some of these cases the signal level was 2 to 5 times greater for the earlier mission.

It was noted that when the ground-to-spacecraft circuit was patched to the between-stations voice conference the quality was not as good as the MA-6 mission. This effect is being investigated by studying the recordings made at various locations on the circuits. The generally weaker signal strength may account for part of this problem. Figure 2-16 shows the HF and UHF coverage for both the MA-6 and MA-7 missions.


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