F. J. Taylor G. W. Garrison - NASA...NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Technical Memorandum 33-535 Telecommunications System Design for the Mariner Mars 1971 Spacecraft

N A T I O N A L A E R O N A U T I C S A N D S P A C E A D M I N I S T R A T I O N

Technical Memorandum 33-535

Telecommunications System Design for the

Mariner Mars 1971 Spacecraft

F. J. Taylor

G. W. Garrison

J E T P R O P U L S I O N L A B O R A T O R Y

C A L I F O R N I A I N S T I T U T E O F T E C H N O L O G Y

P A S A D E N A , C A L I F O R N I A

May 1, 1972

https://ntrs.nasa.gov/search.jsp?R=19720017542 2020-02-27T12:55:52+00:00Z

N A T I O N A L A E R O N A U T I C S A N D S P A C E A D M I N I S T R A T I O N

Technical Memorandum 33-535

Telecommunications System Design for the

Mariner Mars 1971 Spacecraft

F. J. Taylor

G. W. Garrison

J E T P R O P U L S I O N L A B O R A T O R Y

C A L I F O R N I A I N S T I T U T E O F T E C H N O L O G Y

P A S A D E N A , C A L I F O R N I A

May 1, 1972

PREFACE

The work described in this report was performed by the technical

divisions of the Jet Propulsion Laboratory, under the cognizance of the

Mariner Mars 1971 Project.

JPL Technical Memorandum 33-535 iii

A CKNO WLE DGME NT

This report was compiled by Glenn W. Garrison and Francis H.

Taylor II, using many Interoffice Memorandums as source data. The follow-

ing people contributed to the lOM's and to the success of the telecommunica-

tions system:

W. Allen

A. Brejcha

W. F. Gillmore

D. R. Hersey

B. D. Trumpis

O. L. Irvin

C. T. Timpe

iv JPL Technical Memorandum 33-535

CONTENTS

I. Introduction 1

II. Spacecraft Configuration 2

A. Phase-Lock-Loop Receiver 2

B. S-Band Antenna Coupler and Medium-Gain Antenna 2

C. High-Gain Antenna 2

III. Telecommunications Requirements and Constraints 4

A. Cruise and Midcourse Maneuvers 4

B. Mars Orbit Insertion and Orbit Trim 5

C. Orbit Mission 6

IV. Telecommunications Design Control 8

A. Design Control Documentation 8

B. Telecommunications Prediction and Analysis Program 8

1. Predictions 9

2. Comparison 9

V. Telecommunications Performance Verification Tests 10

A. Telecommunications Developmental LaboratoryDescription 10

B. Overall Test Sequence 10

VI. Special Design or Analysis Problems 11

A. LGA/MGA Interferometer Effect 11

1. Launch phase 12

2. Early cruise phase 12

3. First midcourse maneuver 13

B. HGA/LGA Transmit Interferometer Effect 13

1. Cruise phase, at the switch from LGA to HGA 14

2. Second midcourse maneuver and Mars orbitinsertion 14

JPL Technical Memorandum 33-535

CONTENTS (contd)

C. Insertion and Orbital Doppler Rates 15

1. Signal levels 15

2. Doppler shift and doppler rates 16

3. Telecommunications strategies 16

TABLES

1. Mariner 1971 data rates and usage requirements 17

2. Mariner 1971 test matrix 18

3. Mariner Mars 1971 spacecraft antennacharacteristics 19

FIGURES

1. Simplified block diagram of Mariner Mars 1971telecommunications system 20

2. Engineering channel (33 1/3 bps) performance marginand tolerances, cruise phase 20

3. DSS 41 orbital doppler shift, 12-hour orbit 21

4. Performance loss due to increasing range and to antennaangle between earth and HGA 22

5. DSS 14 rise times 23

6. Variation in design value and tolerance with time for16. 2-kbps channel, referenced to Mars encounter 24

7. TPAP plot of engineering channel performance marginand adverse tolerances vs time 24

8. TPAP plot of earth clock and cone angles vs time 25

9. Typical TPAP plot of actual (MDDATA) vs predicted(PRDATA) performance 26

10. Typical TPAP plot of the difference between actual andpredicted performance 27

11. Typical TPAP histogram of the difference between actualand predicted performance 28

12. Telecommunications developmental laboratory floorlayout 29

VI JPL Technical Memorandum 33-535

CONTENTS (contd)

FIGURES (contd)

13. Telecommunications developmental laboratory functionalblock diagram 29

14. Mariner Mars 1971 spacecraft, antenna locations 30

15. LGA/MGA antenna system relative gain pattern 31

16. Nominal Mission A downlink power with interferometereffect, DSS 51 32

17. Intervals during which 10-dB peak-to-peak fading (ormore) is possible during initial minutes of mission(prior to sun acquisition) 32

18. Mission A downlink time history 33

19. Cone/clock trajectory of typical f irst midcoursemaneuver (2297 MHz) 34

20. Predicted performance during midcourse maneuver;relative change in downlink signal vs time 35

21. Mechanism of HGA/LGA transmit interferometer effect . . . . 35

22. Range of possible variation in downlink AGC due tointerferometer effect between HGA and LGA as afunction of GMT day (in LGA mode) 36

23. Positive yaws of 12-min duration 36

24. Range rate vs earth observed time (GMT): orbitinsertion 37

25. Range acceleration vs earth observed time (GMT):orbit insertion 38

26. Typical downlink receiver phase er ror due to rangeacceleration (doppler rate) only, in one- or two-waytracking mode 39

JPL Technical Memorandum 33-535 vii

ABSTRACT

The configuration of the Mariner Mars 1971 spacecraft telecommunica-

tions system is detailed, with particular attention to modifications performed

to accommodate the orbital mission. The report covers analysis and

planning to launch. Results of major analyses and tests are summarized.

viii JPL, Technical Memorandum 33-535

I. INTRODUCTION

The Mariner Mars 1971 telecommunications system was an adaptation

of the Mariner 1969 system, modified to meet the requirements of a Mars

orbital mission rather than a flyby. The Deep Space Instrumentation Facility

(DSIF) ground equipment was functionally identical to that used on Mariner

1969, but several new items of multimission modulation (command) and

demodulation (telemetry) equipment were developed during this time period

and first used on Mariner 1971.

The total launch period was from approximately May 5 through June 6,

1971. Planning was for two launches. Mission A, to be launched on May 7,

1971, was to be inserted in a Mars orbit on November 14, 1971. Mission B

was planned for launch on May 17, 1971, and for insertion on November 24.

Orbit periods for missions A and B were to be 12 and 20 hours, respectively.

Most of the discussion in this report is related to the 12-h orbit. Telecom-

munications problems for this orbit are similar to that encountered for a

20-h orbit.


II. SPACECRAFT CONFIGURATION

A simplified block diagram of the Mariner 1971 telecommunications

system is shown in Fig. 1. The overall system consisted of three subsys-

tems, the radio frequency subsystem (RFS), the command subsystem (FCS),

and the S-band antenna subsystem (SBA). Areas of modification from Mariner

1969 which were implemented to accommodate the orbital mission are shown

by asterisks. A number of other items were modified to improve performance

but were not specifically required for the orbital aspect of this mission.

They are discussed in separate reports for the individual subsystems. The

specific modifications for the orbital mission are discussed in the following

subsections.

A. Phase-Lock-Loop Receiver

The loop gain was increased by a factor of 10 to reduce loop phase

error with frequency offsets. This eliminates requirements for retuning the

uplink during the orbital phase, where doppler shifts on the uplink approach

40 kHz over one station pass.

B. S-Band Antenna Coupler and Medium-Gain Antenna

The medium-gain antenna (MGA) was added to the system using a

passive 6-dB directional coupler in the low-gain antenna (LGA) circuit. The

MGA was mounted to provide telemetry coverage and two-way doppler during

the orbit insertion and orbit trim phases of the mission. Although the MGA

has a bore sight gain of approximately 14 dBi, when installed with the 6-dB

coupler the effective peak gain was approximately the same as the LGA.

C. High-Gain Antenna

Mariner 1971 uses the same high-gain antenna (HGA) used on Mariner

1969, a 1.02-meter circular parabola. However, rather than being fixed in

position as on Mariner 1969, the antenna was used in two positions. The

first position was used preinsertion and for the first 60 days of orbit oper-

ations (assuming a November 14, 1971, orbit insertion). The second posi-

tion was used for the remainder of orbit operations and provides an effective

gain greater than the LGA until approximately 140 days in orbit (April 1,

1972).


The low-gain antenna, which is a shortened version of the Mariner 1969

LGA is always used for receiving the uplink signal and for transmitting

(downlink) during the early cruise phase and for maneuvers. The HGA is

used exclusively for transmitting during the late cruise and orbital phases.

Downlink telemetry modulation is provided by the flight telemetry sub-

system (FTS) as shown in Fig. 1. Telemetry data rates, required bit error

rates, and required periods of coverage are shown in Table 1. The high-rate

data at 1 to 16 kbps is block-coded. Low-rate data at 8 1/3, 33 1/3 or

50 bps is uncoded. Table 1 requirements covers only the standard mission

since the extended mission requirements are undefined.


III. TELECOMMUNICATIONS REQUIREMENTS AND CONSTRAINTS

A. Cruise and Midcourse Maneuvers

Cruise is the mission time beginning after launch transients have died

out until shortly before the Mars orbit insertion sequence. During cruise,

one or two midcourse maneuvers are planned, the first about one week after

launch, the second several weeks before encounter.

Telecommunications requirements during early cruise were to provide

33 1/3-bps telemetry data, ranging, doppler, and command capability. For

engineering telemetry and command communication between the earth and the

spacecraft, the broadbeam low-gain antenna provides coverage in the

hemisphere centered at 0 deg cone angle (in spacecraft coordinates). During

the latter part of cruise, and for orbital operations, high-rate science at

several kbps must be transmitted from the spacecraft through the high-gain

antenna. Downlink RF power of 20 W during the latter part of cruise and for

orbital operations together with 10 W for the launch and early cruise environ-

ment was provided by the radio frequency subsystem (RFS).

During the midcourse maneuvers, the spacecraft will be rolled off the

Canopus reference, then yawed off the sun. Engineering telemetry at 33 1/3

bps must be provided during the motor burn. In order to meet this require-

ment, the earth vector after the yaw turn must lie within approximately

90 deg of the LGA or within 35 deg of the MGA boresight for the first mid-

course maneuver. Owing to the greater distance to the spacecraft at the

time of the second midcourse maneuver, the corresponding angles are within

65 deg of the LGA and 30 deg of the MGA. This midcourse motor burn dura-

tion is less than 10 s. Doppler rates during these burns do not impose

special tuning or receiving bandwidth constraints.

Two telecommunications mode changes are planned during cruise. The

first, not later than 100 days after launch, is to switch the TWTA from its

low-power (10-W) state to the high-power (20-W) state. The second, about

110 days after launch, is to switch the downlink from the low-gain antenna to

the high-gain antenna. The first mode change is not time-critical. It can be

done as soon after launch as thermal and power considerations permit, and

should be done enough in advance of the antenna switch so that the radio is

well-stabilized in the high-power mode. The second mode change is more


time-critical. It cannot be done until the HGA boresight comes close enough

to earth so that the effective gain from the HGA at least equals the gain from

the LGA at the same time. It should not be delayed because (a) telecommuni-

cations performance will be better on the HGA, and (b) an interferometer

effect between the HGA and the LGA may degrade telecommunications per-

formance over the low-gain antenna below that predicted for either antenna

alone. This effect is described in a later section.

Representative telecommunications performance during cruise is shown

in Fig. 2. The upper curve indicates the design performance margin in dB

above minimum required signal-to-noise ratio (threshold) for the 33 1/3-bps

engineering telemetry channel. The lower curve shows the sum of the ad-

verse tolerances for this channel. These curves show that with design

(normal) telecommunications performance, the 33 1/3-bps channel is above

threshold throughout cruise. In the worst case, including the linear sum of

the adverse tolerances, the 33 1/3-bps channel drops below threshold briefly

before switch to the HGA. Thus, under worst-case conditions it may be re-

quired to switch to 8 1/3-bps telemetry to maintain a positive performance

margin.

B. Mars Orbit Insertion and Orbit Trim

The prime telecommunications requirement during these phases of the

mission is to provide engineering telemetry during the motor burn. Orbit

insertion maneuver turns require that the LGA be directed away from the

earth. Therefore, to provide telemetry during the motor burn, a medium-

gain antenna, passively coupled to the LGA, is oriented so as to be directed

toward the earth during the insertion. Orbit trim maneuvers will use either

the MGA or LGA, depending on the turns required, or fall outside the capa-

bilities of either antenna. The gain of the LGA is adequate for these maneu-

vers. The earth vector, however, is outside the useable range of the LGA.

Therefore, the boresight gain of the MGA (including coupling losses) was

made approximately equal to that of the LGA. As a result of the simultaneous

use of two antennas at the same frequencies (both are used for receiving the

uplink signal as well as transmitting on the downlink), an interferometer

effect is present in the areas between these two antennas. This LGA/MGA

interferometer effect and the results it has had on the planning for maneu-

vers are described in a later section.


C. Orbit Mission

Mariner 1971 is required to provide high-rate 8- or 16-kbps science

data for the first 90 days after orbit insertion. The planned orbit for Mis-

sion A is highly elliptical, with a periapsis (after trim) of 1250 km and a

period of 1 2 hours. The orbit causes a wide variation in the doppler shift

throughout the orbit period. In addition, throughout the orbit phase the dis-

tance between the earth and Mars will increase, continually decreasing per-

formance margins. The geometry between the sun- and Canopus-oriented

spacecraft and the earth also changes, making it impossible to have a fixed-

position high-gain antenna with sufficient gain to meet the stated orbit re-

quirements.

Figure 3 illustrates the doppler environment near the beginning and

end of the orbital phase for a 12-h orbit. The Mariner 1969 receiver would

not have maintained phase lock in the uplink doppler environment without

retuning of the uplink at least twice during each orbit. To preclude this

operational difficulty with the consequent possibility of dropping downlink

lock, the loop gain of the Mariner 1971 receiver was increased by a factor of

10 over that of the Mariner 1969 receiver. No uplink tuning will be required

during any single station pass, including the periapsis pass.

Analysis showed that the science bit rate requirement could be met by

allowing the Mariner 1969 HGA to assume a second boresight position about

two months into the orbital mission. The first position would take care of the

preorbit science and the first two-thirds of the orbital science. The second

position maintains the 16-kbps capability for the remainder of the 90-day

orbital phase, assuming design-point telecommunications performance.

Figure 4 shows the telecommunications performance margin (referenced

to 0 dB at insertion) variation over the mission, taking into account the shift

in HGA position on January 15, 1972. This decrease in margin must be

taken into account during planning for the orbital science sequences. Addi-

tional margin is gained by decreasing the science bit rate from 16 to 8 kbps.

Margin can also be provided by restricting the DSS 14 pass to higher and

higher elevation angles as the mission progresses. Some of these tradeoffs

are shown in Fig. 5. This figure compares fixed elevation angle rise times

of DSS 14 to performance-based rise times, taking into account the decrease

in margin shown in Fig. 4. The 0-dB reference curve shows design

JPL, Technical Memorandum 33-535

telecommunications performance at 1 6 kbps, with the other curves showing

the effect of having either better (by means of decreased bit rate) or worse

(through performance degradation) performance than design. Figure 5 shows

that design performance results in a useable 16-kbps pass at DSS 14 through-

out the planned 90-day orbital mission.

JPL, Technical Memorandum 33-535

IV. TELECOMMUNICATIONS DESIGN CONTROL

A. Design Control Documentation

The Mariner 1971 telecommunications design control document

(PD 610-57) titled Mariner Mars 1971 Project Telecommunications Link

Performance was the single authoritative source for the Mariner 1971 tele-

communications system, including spacecraft and DSIF elements. The

major items covered were:

(1) Spacecraft subsystems.

(2) Detailed characteristics of the spacecraft and DSIF elements.

(3) Link performance requirements and comparison to capabilities.

(4) Detailed link performance for major modes by mission phase,

using design control tables and plots of performance versus time.

(5) Parameters and calculation methods used in link calculations.

Two basic philosophies were followed. First, the document was to be

a comprehensive working level document in order to be of maximum use in

mission analysis and planning. Second, the document was to be released

early in the program, using design parameters, then updated prior to launch

when measured system parameters were available. A preliminary version

was published in May 1970. The first formal release was in August 1970;

the final issue was released in April 1971.

As an example of how design control techniques maintain link perfor-

mance through a project see Fig. 6. This figure illustrates how the per-

formance predictions of the prime 16,200-bps channel on Mariner 1971

changed through three issues of PD 610-57. The design value dropped

0. 3 dB, favorable tolerances were reduced 0. 5 dB, and adverse tolerances

were reduced 0.9 dB. Design control leads to consistent design values

through a project, and reduced tolerances as parameters are better under-

stood.

B. Telecommunications Prediction and Analysis Program

One of the major telecommunications efforts on Mariner 1971 was up-

dating the Telecommunications Prediction and Analysis Program (TPAP).

The connotations of "prediction" and "analysis" in this title are as follows:


Prediction is the generation of performance predictions for a link; analysis

is the comparison of predicted versus observed performance. The TPAP

program is an updated combination of the Mariner 1969 Predicts Program

(CP2M) and the Mariner 1969 Comparison Program (CMPM).

1. Predictions. The predicts portion of TPAP will, at the option

of the user, generate telemetry, command or ranging link predictions.

Major changes to this portion of the program on Mariner 1971 were as follows:

(1) The design control tables were reformatted to 8 1/2 X 11-in.

size such that they could be used directly in reports. This

modification has led to considerable cost savings.

(2) Performance and trajectory data is provided in tabulated or

plotted form for easy use by the telecom analysts.

(3) A data save tape may be generated to be used for comparing

actual versus predicted data.

Figures 7 and 8 illustrate typical telemetry and trajectory plots.

2. Comparison. The comparison, or analysis, version of TPAP

was extensively modified, using the Mariner 1969 CMPM program as a start-

ing point. The program compares data previously generated in a telemetry

prediction run with actual flight data. Comparison is made of uplink carrier

level, downlink carrier level, and telemetry (engineering and science)

signal-to-noise ratios.

Outputs provided are:

(1) Plots of actual and predicted data.

(2) Plots of the difference between actual and predicted (residuals).

(3) Histograms of the difference between predicted and actual.

This data is used to evaluate both spacecraft and DSIF performance

during mission operations. Typical plots are shown in Figs. 9, 10, and 11.


V. TELECOMMUNICATIONS PERFORMANCE VERIFICATION TESTS

One of the major activities of the telecommunications system group is

to verify proper link performance through testing. On Mariner 1971 there

were four major areas of test:

(1) Subsystem tests in the Telecommunications Developmental

Laboratory (TDL), which is operated by project personnel, and

in the Compatibility Test Area (CTA-21), a typical DSIF facility.

(2) System tests on the spacecraft at JPL and AFETR.

(3) Spacecraft/DSIF compatibility tests in CTA-21.

(4) Spacecraft/DSIF compatibility tests at DSS-71, a DSIF test sta-

tion at AFETR.

A complete description of all tests and results is beyond the scope of

this report. However, the overall program is outlined in summary form,

with major items emphasized. The data accumulated in these tests is in-

valuable in planning flight sequences and as backup data for anomaly investi-

gations.

A. Telecommunications Developmental Laboratory Description

The TDL was developed during Mariner 1971 to support the test effort.

For Mariner 1969 the TDL was located in CTA-21. Expansion of CTA-21

necessitated moving the TDL to new facilities in Building 161. Layout of the

TDL and a functional block diagram are shown in Figs. 12 and 13.

B. Overall Test Sequence

Table 2 is a test matrix showing tests performed during various phases

of Mariner 1971. Tests are shown as rather broad categories. In many

areas there were a large number of subtests. However, the matrix gives a

good feel for the overall test program.

The tests were intended to provide a comprehensive program, main-

taining a good awareness of system condition at all times and exercising the

equipment to the levels expected during the mission. In nearly all cases,

analysis of expected performance was performed prior to the test so that the

test results could be compared with predicted performance or design specifi-

cations.

10 JPL Technical Memorandum 33-535

VI. SPECIAL DESIGN OR ANALYSIS PROBLEMS

A. LGA/MGA Interferometer Effect

The MGA is connected electrically to the LGA through a directional

coupler such that the LGA and the MGA form an antenna system. This

antenna system can be considered as an array of two antennas separated

from one another by many wavelengths. Antenna theory predicts that such a

system will take on the gain of the individual elements of the array within the

main lobe of each of the elements. In the regions between the elements, an

interferometer or lobing effect will occur. Since the LGA and MGA are both

used for receiving the uplink at 2215 MHz and transmitting the downlink at

2295 MHz, the interferometer effect will be present at both frequencies.

Given the constraint that a medium-gain antenna is required, and its

location is determined by the probable orbit insertion parameters, the effect

of the interferometer nulling on other phases of the mission had to be ascer-

tained. The specific problems examined prior to launch included (a) the

probable profile of uplink and downlink signal strength during the launch,

sun acquisition, and Canopus acquisition sequences, (b) the possibility that

downlink telemetry might drop below threshold over some discrete range of

clock and cone angles of the tracking stations during the first two weeks of

the mission, and (c) the profiles of uplink and downlink signal strengths dur-

ing the roll and yaw turns associated with the first midcourse maneuver.

Figure 14 and Table 3 together define the main characteristics of the

Mariner Mars 1971 antenna system. The MGA is almost diametrically

opposed from the LGA, and the principal interferometer nulling would be

expected to occur in or near the plane of the solar panels. The insertion

loss of the MGA coupler is such that the overall antenna system gain is

approximately 7 dB near the boresight of both the LGA and the MGA.

Figure 15 shows a representative overall gain pattern of the LGA/MGA

system at the downlink frequency. With 90 deg cone angle representing the

spacecraft solar panels, this pattern was measured essentially in the plane

containing both the LGA and the MGA and passing through all cone angles

(roll cut). Since it was measured on a full-scale antenna test model with

flight antennas, this pattern closely approximates the actual Mariner 1971

pattern, including the effect of the spacecraft itself.

JPL Technical Memorandum 33-535 11

1. Launch phase. Analyses of the antenna pointing directions dur-

ing the powered-flight trajectory, during separation, and during sun and

Canopus acquisition sequences for launches on May 7 and May 15, 1971,

showed that severe fading was possible though not certain. The variable

preventing a definitive assessment was the tipoff forces and directions at

separation of the spacecraft from the Centaur. Figure 16 shows the extent

of variation in signal levels possible at DSS 51 (Johannesburg). If space-

craft orientation was such as to maintain the LGA boresight pointing contin-

uously at DSS 51, the upper curve indicates the signal level predicted. The

two lower curves indicate the envelope of the interferometer-effect fading,

assuming that zero tipoff rates occur. The lower limit of the envelope

assumes destructive interference between the LGA- and MGA-radiated sig-

nals. The upper limit assumes constructive interference. The spacing

between successive nulls in the interferometer pattern, as indicated by

Fig. 15, is 4 deg, but the phasing of the nulls is not known. Figure 16 as-

sumes a nominal Mission A launch date of May 7. A similar analysis was

made for the other near-earth phase station, Ascension Island. Figure 17

shows potential downlink loss times for these two stations. Because of

different antenna angles to the two stations and the absence of significant

time overlap, it was predicted that loss of downlink at both stations simul-

taneously was not likely.

2. Early cruise phase. For the Mariner 1971 mission, the later

the launch date the more favorable the geometry for maintaining adequate

downlink signal levels during the f irst 48 hours of the mission. A consider-

ation of the tolerances on the MGA and the LGA antenna gains, beamwidths,

and cabling losses showed that for a May 7, 1971, launch there would be

some risk of the downlink dropping below the threshold for 33 1/3-bps engi-

neering telemetry two days after launch,, should the phasing between the

LGA and the MGA also be worst-case, even with normal sun-Canopus orien-

tation (Fig. 18). No such potential loss of 33 1/3-bps downlink telemetry

was anticipated for the nominal Mission B launch or for a delayed launch

date. Figure 15 shows significant potential for interferometer-effect fading

at cone angles exceeding 90 deg. For comparison, the maximum earth cone

angle reached for a May 7 launch would be 102 deg; for a May 14 launch,

88 deg, and for the May 30 launch, 62 deg.


3. First midcourse maneuver. Planning for the f irs t midcourse

maneuver, to occur within one week of launch, again showed that the amount

of interferometer-effect fading occurring would depend on the launch date,

with lesser amounts for the later launches. The reason is that the first

midcourse event is a roll turn; the earth cone angle remains constant during

a roll turn, and the earth cone angle during the roll turn is larger the earlier

the launch and, hence, the maneuver date.

Figure 19 shows the "trajectory" of the earth cone and clock angles

during the turns of a typical midcourse maneuver sequence on June 4/5, 1971.

Note the long roll turn at a constant earth cone, followed by a yaw turn which

actually causes the earth vector to come nearer the boresight of the LGA.

During planning for the midcourse maneuver, a telecommunications con-

straint was to avoid turn sets (roll and yaw) which would pass through the

LGA/MGA interferometer region defined by the "crosshatched" region of

Fig. 19. This region is defined by a series of LGA/MGA patterns, such as

in Fig. 15, for various fixed clock angles. It is based on the antenna test

model measurements. The smooth envelopes in Fig. 19, which generally

follow the measured interferometer regions, are based on theoretical con-

siderations of the antenna system. Correlation between the two is good.

During this maneuver sequence [consisting of (a) the roll turn about the

spacecraft Z axis, (b) a yaw turn about the spacecraft Y axis, (c) a short

motor burn, and (d) yaw and roll "unwinds" back to the original sun-Canopus

stabilized position] little interferometer effect was predicted (Fig. 20).

Figure ZO is a good indicator of the influence of the interferometer effect at

this cone angle. The solid curve shows the gain of the LGA alone; the dotted

curve shows the gain of the LGA/MGA system during the maneuver.

B. HGA/LGA Transmit Interferometer Effect

This effect occurs because of imperfect isolation between the LGA and

the HGA outputs of the Mariner 1971 RFS and because of reflection of RF

from the antennas back into the transmission lines. The effect is dependent

on which combination of TWT and antenna is being used and on the specific

amounts of isolation between the two RFS ports (Fig. 21). The effect was

predicted to occur when the spacecraft is still transmitting via the LGA and

the HGA beam begins to swing onto the earth about 110 days after launch. It

might also be present during the second midcourse maneuver and during the


orbit insertion, from the moment the switch is made from the HGA to the

LGA until the HGA beam swings off earth at the beginning of the roll turn.

The physical mechanism of the HGA/LGA transmit interferometer

effect is the same as that of the LGA/MGA effect discussed in the previous

section. The HGA and the LGA form an antenna system consisting of an

array of two elements of different gains and beamwidths but transmitting at

the same frequency and separated by several wavelengths at S-band. The

HGA is "inefficiently" coupled to the system when the spacecraft is transmit-

ting via the LGA. However, the gain of the HGA is 19 dB higher than that of

the LGA at boresight (Table 3), and even with a typically specified 20 dB of

isolation between the LGA and the HGA ports of the RFS, a noticeable inter-

ferometer effect was predicted when the earth is near the HGA boresight.

1. Cruise phase, at the switch from LGA to HGA. The initial switch

from the LGA to the HGA was planned to occur on September 21, 112 days

after a May 30 launch, to maximize the earth-received signal level through-

out cruise. Trajectory calculations showed that the boresight of the HGA

would be moving toward the earth at about 0.4 deg per day at this time, with

the net gain of the HGA increasing by more than 1 dB per day. Analysis of

the LGA/HGA system showed that the spacing from one interferometer null

to the next is about 4 deg. Hence, any interferometer-effect fading occurring

before switch to HGA would take place very slowly and require many succes-

sive station passes to be seen. Figure 22 shows the magnitude of the pre-

dicted interferometer effect near the time of the initial switch to the HGA.

The greater the isolation between the two RFS ports, -the nearer the HGA

boresight the earth must come before a significant interferometer fading

occurs.

2. Second midcourse maneuver and Mars orbit insertion. The first

time a switch back to the LGA from the HGA is required prior to initiation of

the turns is during the second midcourse. Except by observation of the

amount of interferometer fading occurring just prior to the initial use of the

HGA (see paragraph above), it is not possible to predict whether the HGA/

LGA transmit interferometer will be a significant factor in the second mid-

course maneuver and the orbit insertion. The reason is that there is a rela-

tively narrow range of dB isolation between the ports required before inter-

ferometer fading can occur. The amount of isolation actually present is


difficult to measure; it is dependent on RFS temperature, and temperature is

variable through the mission. At most, it can be asserted that there may be

sufficient fading to cause loss of 33 1/3-bps telemetry when the switch to

LGA is made preparatory to a maneuver and before the HGA beam swings

off of the earth. Such fading is considered rather unlikely owing to the large

number of "worst-case" effects which must occur simultaneously. However,

planning for the second midcourse maneuver has included delaying the switch

to LGA to shortly after the roll turn start so as to eliminate loss of data dur-

ing the maneuver.

C. Insertion and Orbital Doppler Rates

The Mars orbit insertion sequence is monitored by the 64-meter

antenna at Goldstone, beginning about 2 hours before motor burn start and

concluding with the first occultation of the spacecraft, occurring about 15

min after motor burn end. During this sequence, the spacecraft will go

through a roll turn, a yaw turn which takes the earth from the LGA to the

MGA region of influence, a 1 5-min motor burn during which significant

doppler rates occur, and the beginning of the unwind turns. There are a

number of telecommunications problems involved in planning the insertion

sequence. Perhaps the most important of these is •whether to carry out the

entire sequence while the spacecraft is in two-way with DSS-14 or to allow

the high-doppler portions of the sequence to occur with the spacecraft in one-

way (downlink only). The downlink doppler offsets and rates are one-half as

large in one-way as in two-way, other factors being equal.

1. Signal levels. The magnitude of the doppler effect on the down-

link depends on (a) the signal levels present during the several phases.of the

sequence, and (b) the DSN strategy, including receiver and demodulator

bandwidths and tuning. Figure 23 shows the "trajectory" of the earth coordi-

nates (clock and cone) during the roll and the yaw turns. The earth coordi-

nates at roll start on the day of insertion (November 13) are known, and the

possible variation in roll and yaw turn magnitudes is also known. The roll

will keep the LGA boresight 43 deg from the earth, resulting in a worst-case

13-dB SNR in the downlink receiver loop bandwidth 2BT of 12 Hz. The yaw

turn will take the earth into the domain of the MGA as shown, and the worst-

case SNR in 2BT will be 16 dB at the end of the yaw turn. As shown, down-

link telemetry will be lost during the yaw turn regardless of whether


33 1/3- or 8 1/3-bps telemetry is chosen; 33 1/3 bps has been chosen to

maximize data return during the motor burn. Uplink lock (if two-way is

chosen) will also be dropped for 10 to 30 s during the yaw turn. These

dropouts are due to the LGA/MGA system gain being too low to support the

links throughout the yaw turn.

2. Doppler shift and doppler rates. Figure 24 shows the range rate

in km/s and the resulting uplink and one-way downlink doppler shifts during

the insertion sequence. Two-way downlink doppler would be twice the value

shown at each time. Figure 25 shows the range acceleration (in m/s^) and

the resulting uplink and one-way downlink doppler rates during the sequence.

Again, two-way doppler rate would be twice the values shown. Figure 26

shows the downlink phase error (2B - 12 Hz) resulting from the dopplerJ—lO

rate alone. The major contributor is the acceleration from the motor burn

itself, with the planetary effect at f irst periapsis (coincident with motor burn

stop) a secondary effect .

3. Telecommunications strategies. The plan for insertion is to

operate in the two-way RF mode. The two-way mode offers operational and

scientific advantages in that commanding will be possible through nearly the

entire insertion sequence, and two-way doppler permits a more precise and

timely determination of the orbit parameters than one-way doppler. On the

other hand, one-way tracking after the uplink drops out during the yaw turn

is operationally much less complex for the DSIF operators. In the two-way

tracking mode, the DSIF S-band receiver and engineering channel SDA will

be set to the medium bandwidth since this minimizes the possibility of

dropping lock due to high doppler rates. The penalty is several tenths of a

dB decrease in engineering channel SNR and receiver loop SNR. However,

the chosen insertion roll and yaw turns insure adequate margin to make this

penalty acceptable.


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JPL, Technical Memorandum 33-535 17

Table 2. Mariner 1971 test matrix

Unit(s)Tested

RFS

PCS §RFS

FTS §RFS

SYSTEM

TestDescription

1. RCVR Sensitivity

2. RCVR Acquisition

3. RCVR Tracking

4. RCVR Best- Lock §Aux. Osc. Frequencies

5. RCVR SPE

6. Downlink Spectrum

7. XMTR Power

8. XMTR Phase Jitter

9. Ranging Polarity

10. Ranging Threshold

11. Ranging DelayCalibration/Check

1. CMD Bit Error Rate

2. CMD Operational Check

3. VCO Frequency

4. CMD Acquisition

5. Modulation IndexOptimization

6. Command with Doppler

1. Block Coded TLM BitError Rate/SNR

2. Uncoded TLM BitError Rates/SNR

3. FTS Output Waveforms

4. Downlink Spectrum

5. Modulation IndexAdjust/Check

6. Subcarrier Frequency/Phase Jitter

1. TLM OperationalSoftware

2. Command Software

Test Type/Location

SubsystemTest

TDL

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

CTA-21

X

X

X

SystemTestsJPL/ETR

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

SC-DSIFCompatability

CTA-21

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

DSS-71

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X


Table 3. Mariner Mars 1971 spacecraft antenna characteristics

Antenna

Low gain

Medium gain

High gain(position 1)

High gain(position 2)

Boresight locations

Cone angle,deg

0

158

42.5

38. 3

Clock angle,deg

305

282.8

279.9

Gains and beamwidths

Boresight gain,dB

7

14

25

25

-3 dB beamwidth,deg

±45

±18

±4

±4


MODULATIONFROMTELEMETRYSUBSYSTEM

PHASE-LOCK-LOOP RECEIVER

RADIO FREQUENCY SUBSYSTEM (RFS)

FLIGHT COMMAND SUBSYSTEM (FCS)

COMMANDOUTPUTTO USERS

*ITEMS CHANGED FROM MARINER 1969TO ACCOMMODATE ORBITAL OPERATIONS

Fig. 1. Simplified block diagram of Mariner Mars 1971 telecommunicationssystem

zo

u

2C£.LLJ

Q_

_lLLJ

gu

Z UJ

ozz<

35

30

25

20

15

10

5

0

-5

-10

-15

NOM

LOW-POWER

LOW-GAIN ANTENNA

DAYS 150-233, 1971

TOL

I I I I

20

15

10

-5

-10

HIGH-POWER

LOW-GAINANTENNA

DAYS 233-264,1971

NOM

_TOL;

NOM\

HIGH-POWER

HIGH-GAIN ANTENNA(POSITION 1)

DAYS 264-318, 1971

ENGINEERING CHANNEL PERFORMANCEMARGIN (FOR SNR, ADD +4.3 dB)

26-m ANTENNA, ENGINEERING MODE,33-1/3 bps, RANGING CHANNEL OFF

MODES AS INDICATED. MARINER 9

NOMINAL (NOM) AND SUM OF ADVERSETOLERANCES (TOL) CURVES ARE SHOWN

140 160 180 200 220 240 260 260 270 280 290 300 310

GMT DAY OF YEAR (1971)

Fig. 2. Engineering channel (33 1/3 bps) performance margin andtolerances, cruise phase


NI_y

-120 -

-160 -

S- -200 -OQ

-240 -

-280 -

-320

FIRST DAYOF ORBIT,DAY 318, 1971

90TH DAYOF ORBIT,DAY 43, 1972

8 10

HOUR.OF DAY, GMT

Fig. 3. DSS 41 orbital doppler shift, 12-hour orbit


sg o

o

Z -1.0oQ_

5 -2.0

Z

Q

< -3.0LU

0

0 -4.0

LU

5

Z -5.0

o1—LU

CO

OLU

U

Z -7.0

OQCLU

\ POSITIOh

V

\

-J 1 ( FIRST

X

X

HALF OF

v

^x

MISSION)

^N

\

\\

^

\

^

— POSITION 1 SWITCH TOPOSITION 2 APPROXIMATELYJfu

\\

VNUARY IfA.LF OF OF

^

>, 1972 (SEtBITAL MIS

X. POSI

^X

CONDS1ON) -

'ION2

\\\

318 328 338 348

1971

358 13 23 33

1972

43 53

GMT DATE

Fig. 4. Performance loss due to increasing range and to antennaangle between earth and HGA


o

1—I—I—I I I I—I I—I

1930 -

1900-

1830 -

1800 -

318322 326 330 334 338 342 346 350 354 358 362 1 59 13 17 21 25 29 33 37 41 45 49 53

1971 1972

GMT DATE

Fig. 5. DSS 14 rise times


ADVERSETOLERANCES

DESIGNVALUE

-2 -1

PD 610-57MAY 1970

-2

PD610 10-57AUGUST 1970

-1

-2

PD 610-57APRIL 1971

-1

FAVORABLETOLERANCES

H dB

dB

H dB

Fig. 6. Variation in design value and tolerance with timefor 16. 2-kbps channel, referenced to Marsencounter

MARINER-MARS 1971 TELECOMMUNICATIONS PREDICTION AND ANALYSIS

< 30

£ 20O

2 10

O-5

-10140 160 180 200 220 240 260 280 300 320

GMT DAY OF YEAR, 1971

Fig. 7. TPAP plot of engineering channel perfor-mance margin and adverse tolerancesvs time


MARINER-MARS 197] TELECUMMICATIONS PREDICTION AND ANALYSIS

300

250

O)

•8

o

200

O 150

u

CLOCK

100

50

140 160 180 200 220 240 260 280 300 320


Fig. 8. TPAP plot of earth clock and cone anglesvs time


MARINER-MARS 1971 TELECOMMUNICATIONS PREDICTION AND ANYLISIS

< -1

u

5CO-o

of

UJU

-119.0

-119.5

-i?n n

-120.5

-121.0

-121.5

-122.0

-122.5

~MD,\

DATA"

^PRDX

\

V\JA \

\ \V\^\\\

A\

N^

v fy\

\

\

V\A\»,

A\\\^\\

— V>

v^\

>\l\\\\\

182 184 186 188 190


192 194

Fig. 9. Typical TPAP plot of actual (MDDATA) vspredicted (PRDATA) performance

26 JPL, Technical Memorandum 33-535

MARINER-MARS 1971 TELECOMMUNICATIONS PREDICTION AND ANALYSIS

<$

0.4

0.2

<J

U

-0.2

-0.4

-0.6

-0.8182 184 186 188 190


192 194

Fig. 10. Typical TPAP plot of the differencebetween actual and predictedperformance


MARINER-MARS l<\7\ TELECOMMUNICATIONS PREDICTION * ANALYSISMEASUREMENT VS. PREDICTS DISTRIBUTION

1.00

0.95

O.9O

O.85

a. so

O.75

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££0.55

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a:z

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o. is

o. 10

o.os

o.oo

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-

—

-

—

—

-

1

1O i n o i n o y i o i A c ô K m N o N l o N o

o w w f* (N ~ ••* »•I M

UPL.1

1Ko

INK C1

4-

1

1

\RRIER POWERi i i r i i i i i i i iSTATION(S)GMT-OAY 183 TO 1 <M _

13 DATA POINTS0 EXCEEDED 3.00 DB.0 LESS THAN-3. 00 DB. -

STD. DEVIATION .333 OB.MEAN -.035 DB.

1

—

-

—

—

1 I

—

—

—

—

—

—

i i i j J 1 I 1 1 1o Ui o tf) o if) o v) o y) o y) o 10 **îf) N o ^ if) ^ o 04 to ^ o î 10 r^ ^Ô O O O O O M » » « C 4 N N N ( < )

MEASURED - PREDICTED (dB)

Fig. 11. Typical TPAP histogram of the difference between actual andpredicted performance

28 JPL, Technical Memorandum 33-535

/

/

/

// /

1 1

/ / / / / / /

\ \

TESTEQUIPMEN(RAISED FLOORIf

;c

TJG)

/

X

/

OPERATIONALSUPPORT

EQUIPMENT

/ X X X X X/

X

\ ,/ / / / / / /

SCREENROOM

1 I-

MAINLAB J .^X 14m - 106. Om2 (25X46 ft = 1150ft2)SCREEN ROOM 3 . 6 X 2 . 7 m = 9.7m2 (9 X 12 ft - 108 ft2)

TOTAL 115.7m2 (1258ft2)

Fig. 12. Telecommunications develop-mental laboratory floor layout

TELEMETRYPROCESSING

\

COMPUTERINTERFACE

1TO XDS-930COMPUTER

S-B/RECEEXCISYS

i

\NDVERTERFEM

TELEMETRY/COMMAND

DATAGENERATION

GENERALTEST

EQUIPMENT

r—

1

1

* u11L

SCREEN ROOM

SPACECRAFTSUBSYSTEMS

DATAACQUISITIONAND STORAGE

Fig. 13. Telecommunications developmental laboratoryfunctional block diagram


LOW-GAIN ANTENNA

HIGH-GAIN ANTENNA

MEDIUM-GAIN ANTENNA

HIGH-GAIN ANTENNA

MEDIUM-GAIN ANTENNA

Fig. 14. Mariner Mars 1971 spacecraft, antenna locations


fllH

ni

C• r-t

60

<U

• H-4->

rir—IO

nitia1)

•4->flnJ

o

o

LT)

s

'})3MOd 3AI1V135I


o

10

5

0

-5

-10

-15

-20

-25

-30

-35

-40

-45

-50

J-a

ZO

-70

-80

-90

-100

-110

-120

-130 -

-140

IZERO dB

POINTINGLOSS

BEST(ACTUAL PL)

WORST\

I I I I I IDOWNLINK CARRIER POWER WITH 26-m DSS ANTENNA

AND NOMINAL SPACECRAFT ANTENNA GAINS ("0dB POINTING LOSS" IS AT LGA BORESIGHT), WORSTAND BEST LGA/MGA INTERFEROMETER RESULTANTANTENNA PATTERNS.

33-1/3 bps DATA THRESHOLD-156.3 dBmW (WORST-CASE)

CARRIER TRACKING THRESHOLD-156.0 dBmW FOR 48 Hz LOOPSNR OF 10 dB

SUN ACQUIRED CANOPUS ACQUIRED

10 20 40 60 80 100

TIME, min

I

200 400 600 1000

0.5 2

TIME, h

10

Fig. 16. Nominal Mission A downlink power with interferometer effect,DSS 51

I I I I I

MAY 7, 1971 LAUNCH

EZ!

MAY 15, 1971 LAUNCH

X///////////////A

VTA ASCENSION ISLAND

I I JOHANNESBURG

I I I I I I I20 22 24 26 28

TIME FROM LIFTOFF, min

30 32 34

Fig. 17. Intervals during which 10-dB peak-to-peakfading (or more) is possible during initialminutes of mission (prior to sun acquisition)


O<

O<

z

-12

-16

-20

-24

ACTUAL GAIN j BEST CASE

_ LIMITS \WORSTCASE

Z -28

-32

-36

-40

I I I I I I I IWORST LGA/BEST MGA TOLERANCES,

SPACECRAFT SUN/CANOPUS ORIENTED,33 1/3 bps TELEMETRY THESHOLD,26-m ANTENNA

GAIN REQUIRED,NOMINAL

GAIN REQUIRED,WORST CASE

J I I J I I I I I10 12 14 16 18 20

TIME FROM LAUNCH, days

22 24 26 28 30

Fig. 18. Mission A downlink time history


350°CLOCK ANGLE 340°

330°

120°

130°

140°

150°

300°

290°

INTERFEROMETEREFFECTFADING REGION

280°

270°

260°

250°

160°

210°

200° CLOCK ANGLE170°

Fig. 19. Cone/clock trajectory of typical first midcourse maneuver(2297 MHz)


RE

LATI

VE

CH

AN

GE

IN

SIG

NA

L, dB

12

10

8

6

2

0

-223,

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

PREDICTED FROM NOMINAL ATM ANALOG PATTERNS

ATM MEASUREMENTS OF LGA AND MGA COMBINED

*S

: f~:~ BEGIN MANEUVER /

~~"^v./\/< is/ .J\~rx-r^ / ~~

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1/47 50 54 58 0/0 4 8 12 16 20

JUNE 4 GMT, mm JUNES

Fig. 20. Predicted performance during midcoursemaneuver; relative change in downlinksignal vs time

TWTA1

TWTA2

CIRCULATOR^-^SWITCH

V

-n\^

j

' \-UNDESIREDTRANSMISSIONPATH V~

1

' I"T TO RECEIVER

HGA

LGA

NOTE: CIRCULATOR SWITCHES SHOWN IN POSITIONTO TRANSMIT FROM TWTA NO. 2 VIA LGA

Fig. 21. Mechanism of HGA/LGA transmitinterferometer effect

JPj_j Technical Memorandum 33-535 35

z~

6

0.

u_oLLJCL.

OUJ

z

3 -

PLANNED SWITCHTO HGAGMT DAY1971

262 264 266 268

GMT DAY OF YEAR (1971)

272

Fig. 22. Range of possible variation in downlinkAGC due to interferometer effectbetween HGA and LGA as a function ofGMT day (in LGA mode)

O

Z

8

1

180

160

140

120

100

80

60

40

20

0

1 1 1 1

POSSIBLE ~^>\N~ YAW TURN -J»\L END POINTS AN.

-""^v MGA^ N

^^ ^* "fm "-^ .*•'

i— """"•• « « _•• * '

-

ROLL TURN J- START ° 5

/30.1°-'

35. r-1

1 1 1 1

i 1 r i i i I i> t /^ ^ — —\ 1 / ^" ^-—~~\ \ \ f ^ ' ''[Ti.i4-*'f ENGINEERINGy j l j j / MODE BLACKOUT

iiiji (-33-1/2 bps!!!! 1 ENGINEERINGI j l j l 1 MODE BLACKOUT

Millj j i j i \\ \ \ \ \ POSSIBLE• ; ; : ; YAW TURNA<UJ> START POINTS

/ \\x-50.r/ \^- ROLL = 45.1°

^—40.1°1 1 1 1 1 1 1 1

240 260 280 300 320 340 0 20 40 60 80 100 120

EARTH CLOCK ANGLE, deg

Fig. 23. Positive yaws of 12-min duration


-123

-121

-* -119

oQ

-117

-115

-113

-inL

-134

-132

it "I30

§ -128

o

-126

o>-I -124UJ

O

-122

-120

17.5

17.3

17.1

16.9

16.7

16.5

_

16'3

O 16.1Z

15.9

15.7

15.5

15.3

15.1

14.921:30 22:00

GMT DAY 317

22:30 23:100

GMT

-110

-109

-108

-107

-106

-119

•118

-117

-116

•115

23:30 00:00 00:30

GMT DAY 318

Fig. 24. Range rate vs earth observed time (GMT); orbit insertion


zO -1.6

-2.4

O<

-3.2 I22:00

GMT DAY 317

_l_ I23:00

zg<uuO

fco

z_jQ-

0 ^

4 p

8 "J

O

12 lii

16

OO'OO 01:00

GMT DAY 318GMT

a.a.Oo

_Z

Oo

Fig. 25. Range acceleration vs earth observed time(GMT): orbit insertion


LLJ

16

14

12

c. 10•8Uj"

OO

RECEIVER 2B, = 12 HzLo

23:00

O Zo 2

Ocz

LGA-

23'-30

NOV13

00:00

-»

00:30

NOV 14

GMT

32

28

24

20

16

12

01:00

CD0>

•O

Uj"QO

>-

Ô

Fig. 26. Typical downlink receiver phase error dueto range acceleration (doppler rate) only,in one- or two-way tracking mode

JPL Technical Memorandum 33-535NASA - JPl - Conl., I.A., Calif.

39

Documents

F. J. Taylor G. W. Garrison - NASA...NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Technical Memorandum 33-535 Telecommunications System Design for the Mariner Mars 1971 Spacecraft