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Ground Tracking of

By FRIEDRICH 0.VONBUN NASA Goddard Space Flight Center

Ground, sea, and airborne stations strategically located around the world-the Manned Space Flight Network-will keep “track”of Apollo during the first flight to the

Immediately after liftoff of the 300-ton position and velocity (trajectory) can be deter- vehicle, a vast global complex of tracking and mined more accurately in a very short time (in communication stations will play a vital part in the order of minutes) by using ground-based our lunar-landing mission. This network of tracking data-range, range rate, and two angles ground stations, ships and aircraft-the so-called (azimuth and elevation or equivalent)-rather “Manned Space Flight Network” (MSFN)-will than onboard tracking information. Since both constitute the only link between the and systems will be needed and will be used to capacity the three in the Apollo Command when appropriate to fulfill Apollo navigation and Module. guidance requirements, the role of onboard sys- The MSFN will “track” the during tems should not be underestimated. its entire lunar mission, except for those portions of flight where the Moon occults the spacecraft a (approximately for 1 hr during each 2-hr lunar parking orbit). As defined here the word “track” well as in the quantities measured, which LJ means more than it does in the usual sense; it means the cumbersome “link” between the space- The onboard system, measuring craft and the Main Control Center at the Manned angles only between selected points on Earth, Spacecraft Center in Houston, Tex. This link con- planets, and stars, lacks two important quantities sists of the many information, tracking, voice, telemetry, and data channels necessary to keep up with the events of the flight. wxh more accuracy by using range, range rate, Besides handling communications between the and two angles than by using angles alone. Control Center and the spacecraft, the network The onboard system is, on the other hand, much must provide the extremely vital function of space less complicated than the MSFN. Therefore, the navigation. The decision to use the MSFN as a question of which system is “better” for space primary system for navigation, made some time guidance and navigation cannot be answered ago, was based on analyses which showed that unequivocally. An over-all description of the Apollo network and the tracking and communications functions will be presented here. Completeness is not FRIEDRICH 0. VONBUN, Chief of planned, inasmuch as a thorough description of Goddard’s Mission Analysis Office, the MSFN and all of its stations, equipment, and holds a Ph.D. in physics from Vien- na’s institute of Technology. Before functions would require a formidable number of joining Goddard In 1960, Dr. Vonbun pages. The graphs show spacecraft velocity errors, did research on antennas and mo- lecular-beam oscillators at Army which, in most cases, are more important than Signal Corps (For! Monmouth). He ’ position errors. This was done to keep the num- now directs mission analyses for the Anchored IMP and future space ber of graphs at a minimum. Work in this area missions for scientlfic spacecraft, and will, of course, .continue, and it is hoped that a Is responslble for analysis of NASA‘s worldwide tracklng network. better picture of the tracking and communications I04 Astronautics & Aeronaulirs problems will be obtained as time goes by. APOLLO- TRACKING

~ and Spacecraft Systems. Even AND TELEMETRY SYSTEMS though Saturn V with the Apollo spacecraft will STAGE SYSTEMS FUNCTION AND CHARACTERISTIC be capable of “flying” independently, numerous OOOP Tracking transponder-Range rate only, fre- types of tracking and telemetry systems will be quencies = 890 Mc (receiver), 960 Mc trans- carried on board to track, check, and test all vital mitter). systems during fight. During major phases of the Command (abort command transmit, range mission, the Unified S-Band System (USBS)- s-IC safety) frequency = 450 Mc (receiver) sensi- tivity = -90 dbm (min). tracking, telemetry, voice and TV transmission and reception combined to simplify the spacecraft VHF Telemetry, frequency 6 225-260 Mc, modula- electronics-carried aboard the Instrument Unit tion: PAM/FM/FM, SS/FM, PCMIFM. (IU) , the Command and (CSM) , MISTRAM Tracking or and the Lunar Excursion Module (LEM) will be AZUSA used for primary .communications, telemetry, and MISTRAM Transponder, frequency = 8,148 Gc/s (receiv- guidance.1-2 These onboard electronic systems en- er), 8,216 Gc/s (transmitter) power = 0.2 to able at Cape Kennedy, 0.5 W per channel. in Houston via MSFN,, s-ll AZUSA Transponder frequency = 5060 Mc (receiver), and the NASA Ground Communications System 5000 Mc (transmitter), power = 2.5 W. (NASCOM) to track the vehicle; command abort Command See S-IC. for crew safety as well as for protection of life and property; record engineering, biological, and VH F Telemetry, See SIC. scientific data; operate displays for flight control Command See S-IC. in real time; communicate by voice with the S-IVB VHF Telemetry, See S-IC. astronauts; transmit guidance and navigation data; and receive TV signals from the spacecraft MISTRAM Tracking transponder, See S-11. or and the lunar surface. The adjacent table lists AZUSA all tracking and telemetry systems used with the C-band Frequency = 5,690 Gc/s (receiver), 5,765 Apollo and Saturn V for each of the different radar Gc/s (transmitter) stages depicted in the illustration on page 106. trans- Power = 500 W (min, peak), single pulse, ponder Bdw - 10 Mc/s pulse width = 114 or 314 sec. As a tracking system for the Saturn V, either the IU Azusa or the Mistram system will be used, but not ODOP Tracking transponder, See S-IC. simultaneously. USBS Tracking (range and range rate), frequency = MSFN, the Manned Space Flight Network. 2,1018 Gc/s (receiver), 2,2825 Gc/s (transmit- MSFN’s complex of ground, sea, and airborne ter) (3~15 Mc). stations represents the counterpart of systems car- VH F Telemetry, See S-IC. ried aboard the Apollo ~pacecraft.~~*~~These sys - USBS Tracking (range, range rate) voice, voice- tems appear in the table at right. The MSFN biomedical telemetry, U-data, television, fre- stations that will be used for the lunar landing quency 2,1064 Gcls (receiver), 2,2725 Gc/s (transmitter), normal mode: 51,200 bitdsec, mission are listed in the table on page 107. (MSC- minlmum mode: 1600 bitslsec, (IU will be GSFC Technical Report 65-AN-1.0 presents the LEM separated when LEM is transferred), extra- vehicular telemetry, link for transmission of stations and systems essential to the space navi- suit telemetry and voice from backpack of gation tasks; that is, the primary Apollo site^.^) during lunar surface operation. Frequency 296.8 Mc, power = 0.1 W, link The stations are listed in sequence by longitude, from LEM to CSM; data rate = 1600 bitdsec. starting with the Cape Kennedy launch site which - is about 80 deg West. This has a certain advan- USES See LEM. tage if one wants to follow the stations that will VHF Telemetry, voice, frequency: 225 to 260 Mc/s. “see” the spacecraft as it circles the Earth going CSM HF Voice during Earth-orbital missions, recovery eastward from the Cape. Some of the stations are operation, frequency: 10 Mc/s, power = 5 W important only because of the launch phase. These (AM) and 20 W (SSB). are the ODOP receiver stations at the Cape, Mer- ritt Island, Titusville, Playalinda, Grand Bahama, Walker Cay, Little Carter Cay, and the transmitter stations at the Cape and Little Carter Cay. to the others). For instance, the impact of the first ODOP, a continuous-wave electronic tracking stage takes place 650 km down range along the system, utilizes integrated Doppler to obtain range trajectory approximately 12 min after liftoff, as sums and range differences. The ODOP stations shown on the graph on page 108. The burning time are not listed in the table on page 107, since only for the S-IC is about 150 sec.6 The same is true the S-IC stage carries an ODOP transponder (sys- for the Mistram stations at Valkaria and Eleu- tem in operation only a very short time compared thera, as well as for the Glotrack stations at the May 19GG 105

~~ APOLLO/SATURN V GROUND COMMUNICATIONS NETWORK I h

E 1 t I 1 I LL :"i - r- I ,III -11 I

IV/D ji I I I I I 211Y; 2V; IV/D' LJ I 211Y. IV I

Cape (C-band radars), and the range-rate stations SATURN V SYSTEMS ications network, has at Cherry Point, Antigua, and Grand Turk.7 been established in the The major stations of the network, indicated by form shown by the chart asterisks in the table on page 107 are: Cape Ken- at the top here. The ma- nedy, Grand Bahama Islands, Grand Turk Island, jor stations of the net- Bermuda, Antigua, Atlantic Ship (-49 deg W., work as well as thevoice, 28 deg N., insertion), Canary Islands, Ascension, telemetry, and data links Madrid, Indian Ocean Ship (-38 deg E., 18 are indicated in the il- deg S., post injection), Carnarvon, Guam, Pacific lustration. The links will Ocean Ship (-174 deg E., 8 deg N., post injec- provide information at tion), Canberra, Hawaii, Goldstone, Guaymas, the following rates: Tel- Corpus Christi, entry ships (two, Hawaii and etype, 60 words/min or Samoa area), and eight modified C-135 jets. 45.5 bits/sec; voice, 300 to 3000 cps; voice Only the areas directly connected with the or data, 300 to 3000 cps; high-speed data, 2400 MSFN and thus with Goddard Space Flight Center bits per sec; television channel, 500 kc per sec are discussed here. Neither the launch nor the bandwidth (Goldstone via commercial TV; Ma- recovery phase (opening of drogue parachute) as drid and Canberra, possibly via NASCOM) .4-s such are treated in detail. The prelaunch and Full duplex, four-wire voice circuits will be used launch phases will be handled by the Launch from all of the remote sites of the MSFN to the Control Center at Cape Kennedy. Obviously, the Manned Space Flight Control Center (MSCC) in Cape tracking and communications stations will order to communicate with the spacecraft. And be used for checkout of all systems before, during, full duplex teletype transmission and reception and shortly after liftoff. Accurate liftoff tracking facilities will be used at all sites for tracking and will provide data for post-flight analyses. telemetry data, updata and message traffic. Wide- The recovery phase, starting with the opening band (40.2 k bits/sec) and video circuits will be of the drogue parachute at about 25,000 ft, will be used between the Cape and MSCC for reception handled by the Air Rescue Service, which will use of prelaunch and launch telemetry data for sup- 63 propeller-driven HC-130H recovery aircraft. port of the SIV-B/IU orbital operations. After locating the landed Command Module, skin This somewhat "separate" network plays a vital divers will parachute from the aircraft to assist part, since the MSFN cannot operate and sup- in the final recovery. port a mission without NASCOM. In what fol- The NASA Comnzunications Network. To make lows, it is assumed that NASCOM is operating the Apollo network function-that is, to "con- and all necessary information is received at the nect" all the stations scattered around the world MSCC at the proper time in the correct format. into a network of stations-another system,4,* a Major MSFN Tracking Functions. The main logical extension of the original Mercury commun- purpose of the MSFN is to provide tracking, com-

1015 Astronautics G. Aeronautics ING MISSIONS~. STATION TRACKING STATUS STATION TRACKING I " COMMUNICATIONS 7 STATUS FPQ-6 Operational Pretoria MPS-26 FPS-16 Operational Considered AZUSA' Cape Kennedy* MISTRAM' Operational VHF - Voice, TM - Operational Operational Tanmarive receive (Merrit Island) ODOP Operational USBS dual 30' USBS Planned UHF - Up-data Indian Ocean Operationall same as Atlantic Ship VHF - Voice, TM Operational Ship* Planned Diaital Command Operational PCM - Data Separation " Operational FPQ-6 Operational USBS dual 30' USBS Planned " Operational ~ ~~ UHF FPS-16 Carnarvon' - Up-data Operational' UHF - Up-Data Operational VHF - Voice, TM Operational Wallops Island VHF - Voice, TM Digital Command Operational Digital Command PCM - Data Separation Operational "PCM - Data Separation USBS dual 30' USBS Planned " VHF - Voice, TM Planned Operational Digital Command Planned Grand Bahanla * UHF - Up-data Operational Planned VHF - Voice, TM PCM - Data Separation Operational 5ame as Atlantic ship " - Pianned GLOTRACK' Grand Turk ' Operational USBS Planned UHF - Up-data DSIF dual 85' USBS Planned VHF - Voice, TM (Standby) Digital Command, I" I Planned FPS- 16 Operational PCM - Data Separation Planned FPQ-6 CLOTRACK * Operational Operational USLlS dual 30' USBS Bermuda' USBS 30' USBS Planned UHF - Up-data Operationall UHF - Up-data Operational ' VHF - Voice. TM Operational VHF - Voice, TM Operational PCM - Data Separation Digital Command Operational " PCM - Data Separation Operational Operational Operational USBS dual 85' USBS Planned UHF - Up-data DSIF dual 85' USBS Antigua * Planned VHF - Voice, TM (Standby) PCM - Data Separation Digital Command Planned PCM - Data Separation Planned " FPQ- 6 Operational Arguello VHF Voice, TM USBS dual 30' USBS Planned - Operational Atlantic Ship* UHF - Up-data Planned USBS 30' USBS Planned VHF - Voice, TM Planned Guaymas* VHF - Voice, TM Operational Digital Command Planned Digital Command Operational PCM - Data Separation " PCM - Data Separation Operational MPS-26 VHF - Voice, TM Operational USBS 30' USBS USBS dual 30' USBS Canary Islands* UHF - Up-data Operational' Planned VHF Voice, TM UHF - Up-data Operational' - VHF Voice, TM Digital Command Onerational - Operational PCM - Data Separation PCM - Data Separation Operational " VHF - Voice, TM Operational TDQ- 18 Existing PCM - Data Senaration Ascension USBS dual 30' USBS [slatid* VHF - Voice, TM Planned Digital Command USBS Planned PCM - Data Separation VHF - Voice, TM Planned " PCM - Data Separation Planned iUSBS Pianned DSIF dual 85' 1JSBS Madrid' Planned (Standby) CSQ, RKV VHF - Voice, TM Planned IDigital Command Planned (Standby) I iPCM - Data Separation Injection. USBS - Voice, TM " Planned Aircraft \bHF - Voice, TM - VHF - Voice, TM Planned Cano Playback via VHF receive C-135) ;V< jEi Three are under time. FC NOTE: additional USBS consideration at this 'M

munications, telemetry, and voice capability in its use, and its capability for tracking the Apollo real time between the Apollo spacecraft and spacecraft. From here on, "tracking" will refer to the MSCC. the determination of the spacecraft's position and Both telemetry data and voice capability have velocity (or the six osculating elements of the been mentioned, including the stations and capa- orbits) or, better still, the estimation of the errors bilities. Tracking from the Cape and the down- based upon the data taken by the MSFN. range stations-in a firing with (Y greater than 90 Based on present data, the errors shown in the deg-with ODOP, Azusa or Mistram, and the graphs are believed to be realistic. The curves FPS-16 radars will yield spacecraft position and represent all pertinent information for comparing velocity to an accuracy in the order of a few cm/s other calculations and methods. Random errors, to 50 cm/s in velocity, as can be seen from the bias errors, and errors in the location of the track- Range Instrumentation Survey by B. G. Vin~ant.~ ing stations are most important and cannot be neg- Leaving this launch and liftoff phase as a special lected in an analysis of this kind. Errors assumed case, let us now concentrate more on the MSFN, are a bit pessimistic to prevent unpleasant sur- Muy 1966 107 prises from occurring in the f~ture.~(See table all error plots, “position and velocity errors” mean 5-1, GSFC-MSC Technical Report 65-AN-1.0.) the square root of the sum of the square of the Tracking the Insertion and Earth-parking-orbit components. This gives a maximum error and at 1 Phase. One of the first tracking tasks of the MSFN the same time reduces the number of necessary will be verification. of the orbital capability (Go, graphs.”12 A “perfect” ship’s navigation system- No-Go) achieved by the spacecraft shortly after no errors in ship’s location, curve B-would have, cutoff of the SIV-B stage. after 90 sec of tracking, no influence on the space- As can be seen from the graph at bottom, craft velocity error as compared to one with a only the insertion ship will be able to “track” the ship location error of 450 meters. The position spacecraft after insertion (burnout) into the Earth errors follow a similar trend but are not shown, parking orbit, shown in the graph on page 109. since they are secondary in importance-3.5 km Present plans call for a daily maximum variation for 1 min, 1 km for 1% min of tracking, all errors of the launch azimuth, 1~,of approximately 26 deg, included as per curve C in the graph. Similar or a launch window of 2 1/2 hr per day. If, during results were obtained in a previous GSFC study.13 this time, the launch cannot be made for some Another very important parameter for the so- reason, there will be no further attempts, and the called “Go, No-Go” decision is the error in peri- launch will be delayed until the following day. gee, since it is directly related to the spacecraft Three consecutive days are required for a “lunar orbital lifetime. The graph on page 110 depicts launch attempt” by definition. The graph below this error, again as a function of the ship’s track- shows that a launch azimuth variation from 73 ing time. Assuming a 200-km Earth parking orbit, to 100 deg can be covered by the ship stationed a perigee error of 0.4-0.5 km, as shown in this as indicated. For one variation of (Y,one ship graph, will certainly not alter the assumed orbital position is assumed. If the launch is delayed by lifetime. Thus a “Go, No-Go” decision check can one day, the ship will be moved slightly, as shown be made using the ship’s navigation and tracking in the graph. A ship’s velocity of 10 knots can be data indicated in the graph. For the cases con- assumed during a 24-hr period covering 240 n. mi. sidered, the available tracking times for E = 5 deg or 4 deg, which is adequate in this case. above the horizon is given in graph on page 110. The velocity errors to be coped with when this During the parking orbital phase this tracking ship is used with an FPS-16 radar type tracking is improved, and depicted as shown in the graph system are shown in the graph on page 110. For on page 110. This graph shows the spacecraft

INSERTION TRACKING FOR APOLLO a = 73 to 100 deg and a = 80 to 105 deg h = 200 km (100 n. mi.).

Astronautics & Aeronautics PARKING ORBITS 1 THI RO UGH 3 and a = 100 d eg (station coveragle).

velocity errors for a portion of the first Earth pler, since the orbits are closer together than €or parking orbit, The steps shown indicate the pro- injection near the equatorial region as shown on jection of the velocity error to the next tracking the previous example. Yet, coverage must be pro- station, which in turn improves the situation (a vided and enough aircraft must be on hand to similar curve applies for position). For this graph, cover the most unfavorable situation. a free flight was assumed. The influence of the The decision to choose the second parking venting14 of the SIV-B on position and velocity is orbit for injection is based on a probability for not included in the graph on page 110. success of 70%. The probability for injection dur- Tracking at Injection, Post Injection, and ing the first orbit is lo%, and during the third Lunar Transfer. No matter where injection occurs, orbit it is 20%. This difference exists because the Apollo spacecraft must be covered since this time is needed to make a complete systems check in is a mission requirement. This is possible only Earth orbit before starting the transfer maneuver. when the aircraft can fly fast enough to cover the Seven minutes after engine cutoff in the lunar injection from the three Earth parking orbits, transfer orbit, tracking and communications must which depends on the declination of the Moon at be made independently from the particular injec- that time. The required coverage includes those tion point along the three Earth parking orbits. systems functions listed at the end of the table on The graph at the top of page 112 shows outlines page 107. An example of very unfavorable cover- of all possible injection points for orbits 1 through age-a lunar declination of - 15 deg-is shown 3, having a launch azimuth between 72 and 108 by the hatched portions in the graph at the top. deg and covering a range of lunar declinations Coverage is needed 1 min before SIV-B ignition in from 4- 28% to -28% deg. The coverage circles the Earth parking orbit, during the burn, and 3 (approximate circles only near equatorial regions) min after engine cutoff in the lunar transfer trajec- are those with a height of 1100 km and a minimum tory. This covers approximately 5500 km (3000 tracking elevation angle (E) of 5 deg (radius of n. mi.) along the parking orbit chosen for transfer. this circle is 26 deg on the Earth surface). This The trajectory chosen for this example is that of requirement is almost fulfilled with the network Sept. 17, 1969.6For this particular case, the injec- and the Indian and Pacific Ocean ships, as shown tion burn starts over the eastern Pacific and ends in the graph at the top. Communications via over the western part of the United States. There- VHF and HF can be obtained for E = 0 deg or fore, as shown in the graph at the top, the injec- even negative. For this case, the total injection tion coverage for all three parking orbits is sim- area in the graph is covered by the network. May 19GG 109 INSERTION USING THE ATLANTIC SHIP VELOCITY ERRORS PERIGEE ERRORS

Tracking Time (minuter) Tracking Time (minuter)

1 .c

0

Time from Insertion (minutes) 110 irst portion of the lunar transfer, from be called upon to help in the checkout and lunar- second parking orbit, together with time and height orbit determination phase. The graph on page 114 points along the trajectory, is shown in the graph gives an example of how accurately spacecraft 0x1 page 112. Using these points and visibility con- velocity can be determined using the scheme shown tours in graph on page 113, it can be deduced in the graph top right on page 113.l” One prime when and where the large dish facilities at Gold- station and two or more slavc stations will bc stone, Madrid, and Canberra can ‘‘see’’ the space- used for the determination of the lunar orbit. craft above an elevation angle of 5 deg. It is The prime station employing a large dish will assumed here that “radio” visibility is identical send a continuous-wave (CW) signal to the space- with “optical” visibility. This, of course, is not craft transponder. The signal (actual frequency always true. For certain spacecraft positions translated) will be returned and mixed with the (attitudes), the onboard antenna pattern precludes similarly translated version of the transmitted sig- “radio” visibility (holes, side lobes). This is par- nal to extract the Doppler shift, which, to the first ticularly true during the Earth parking orbit when order, is proportional to the range rate. The trans- omnidirectional antennas are used. Madrid will mitted signal from the transponder will also be be able to contact the spacecraft first at about received by each of the two or more slave stations, 15 min at a height of about 3700 km. The Earth to be mixed with its local rubidium oscillators--ofT coordinates of the 15 min (3715 km) point of the by, say, 4 X 1O’Oto extract a kind of pseudo- lunar transfer trajectory shown in the graph on Doppler corresponding to a pseudo, but calculable, page 1 12 are approximately 20 deg N and 43 deg range rate. All three of these values are then used W. From graph on page 113, it can be determined for the trajectory determination. that this point lies within the 4000-km visibility From the graph on page 114, it is evident that region of Madrid and, therefore, is in that station’s the spacecraft velocity can be determined to field of view and will stay there for a few hours. within 0.5-3m/s. The cyclic behavior of these As can be seen in this graph, three large dishes errors is expected since they have to increase near cover almost the total lunar range of declinations the center of the Moon, where the range rate is a of +28% deg. The notches which occur on both very small component of the velocity; whereas sides of the visibility contours are due to the near the lunar periphery the range rate increases antenna keyhole, a mechanical obstruction of the and is almost equal to the spacecraft velocity. X-Y mounted antennas. Inasmuch as range rate can be measured accu- The graph on page 113 shows the errors in total rately, errors in spacecraft velocity should be spacecraft velocity for the referenced transfer small. Throughout the lunar operations-occulta- trajectory using Bermuda, Ascension, and Madrid tions excluded of course-both the Command tracking Again, in order to be “realistic” Module and the LEM will be within the beam- and sure during this analysis phase before installa- width of one of the large antennas, making simul- tion and testing of hardware, fairly large noise and taneous communications from both spacecraft pos- bias errors, particularly in range rate, have been sible. These dual capabilities are indicated in the assumed for a sampling rate of six measurements table on page 107. per minute. It is interesting to note that, despite Similar considerations apply to the LEM descent pessimistic assumptions about the tracking systems and ascent phases. For example, the graph on page and random and bias errors, the spacecraft posi- 114 shows the LEM position and velocity errors tion and velocity can be determined fairly accu- during the LEM ascent phase, using three-station rately during the first 30 min of the transfer range-rate tracking only. Again, all data assumed flight. These figures improve during the flight necessary are shown in this graph. The starting toward the Moon for velocity. Position errors go conditions are blown-up position and velocity through a minimum and increase slightly with time injection errors of the LEM guidance system. to a few kilometers on arrival at the Moon. Note the difference in the assumed errors of 3 Lunar Orbits, Landing, and TakeofJ. During and 6 cm/s of the master and slave stations, the flight toward the Moon, three midcourse respectively. Rubidium clocks are planned for maneuvers are planned to correct the spacecraft all of our stations, with a short time stability of trajectory and to bring it within the specified lunar 4 X 10”O-over 1 to 2 sec. Again, this figure is orbit of 150 2 8 km height.* The initial lunar- greater than that given in the manufacturer specifi- orbital phase starts with the shutdown of the cations for safety reasons, as mentioned previously. Service Module engine at 150-km circular lunar Assuming a frequency of 2 Gc/s, a shift of 4 X orbit. The geometry of the lunar tracking phases 10”O corresponds to 0.8 cps or 6 cm/s for a two is show in the graph on page 113. During the way Doppler mode. This means that even if the lunar stay time, the Command Module will make slave station is off frequency as much as 4 X 10“’ one or two orbits before the LEM descent begins. this analysis is still valid. During that time, the ground network will again It should also be pointed out that it is not a May 19GG 111 POST INJECTION COVERAGE OF THE MSFN (7 rnin after iniection. h = 1100 km. H = 5 dea).

LUNAR TRANSFER FROM THE SECOND PARKING ORBIT (a = 73 deg).

112 AJtronautics C Aeronautic$ I

TRACKING AND COMMUNICATIONS AT THE MOON

VISIBILITY CONTOURS FOR THE APOLLO 85-FT ANTENNAS VELOCITY ERRORS OF CSM IN LUNAR ORBITS ERRORS IN POSITION AND VELOCITY OF LEM ORBITAL PARAMETERS During lunar ascent using Earth tracking data. Equator of date coordinder - Moon centered ORBITAL PARAMETERS T = Sept. 20, 1969 Sh IO" 121.176 Moon centered equinox of dote XI = 306.76408 km SI = -1,5875100 km/rec X - -1702.6861 km X2 = -0.24903475 km/sac T = Scpt. 21, 1969 ?Ih 13" 24'.9b X: - 770.17548 km d3 = -0.081752615 km/rec X =- 383.68404 km kl = 1.65525258 km/rec TRACKER LOCATIONS - X - 1560.4722 km S2 = 0.369731788 km/sec Trosker Nome Latitude Longitude Ht (m) X 32: 705.9882 km X3 = 0.14009lll8 km/rec Canberra -35' 18' 41'!50 149' 08' 09:'OO 50 ' TRACKERS Camarvon -24" 53' 50!48 113' 42' 57X4 64 \----" Latitude Longitude Ht (m) Guam 13" 35' OO'!OO 144O 55' 30:'OO 20 Madrid 4E416667 N 30666667 50 Howoii 22' 09' 30'!96 -159O 40' OX43 I I42 -', W Canary 2f735522 N l5?600#5 W 29 \\Ascension 2972994 S 14?401694 W 143 \ TRACKER LOCATION ERRORS INJECTION ERRORS SAMPLING WT4 ljQ&gQj Latitude Longitude Ht (mi I maa/min. Madrid t 1.0" t1.2" *43 vel = t 10.4 m/rec Conary f4.6" t5.1" t32 "z,,Arcenrion t3.4" '-3.5" t32

\ A; ='3cm/ \,,Ar =tbcm/ \

- INJECTlON SX SX BX t4km 12= = = Skl Sk Sk *llm/r = 2 = = - HORIZON E ?. 50 Velocit SAMPLING RATEET\ I meas/min 0 I 2 3 i I I I I I I I I 3 6 9 12 15 18 21 24 Time from Lunor Orbit Inserfion (hours) Tracking Time (minuter)

ERRORS IN SPACECRAFT POSITION AND VELOCITY must to utilize a three-station solution. A one- Apollo return trajectory after first midcourse correction, station solution using a large dish with the speci- QfiElTAL PARAMETERS fied errors in range, range rate, and two angles T = Scpt. 22, 1969 21'' 59m 12l.25

X ~ 214186.74 km j( = -0.19846603 kmlscc (X-Y mount), shown on the graphs, may be used Xi (-234554.70 km k: 2 0.42912431 kmisec Xj =-121637.13 km = 0.26682065 kmlrcc in a similar manner. The position and velocity TRACKER LOCATIONS errors in this case are to be increased by a factor Tracker Nome Lotitude Longitude HI (m) Madrid 40?416667 N 30666667 W 50 of 5 to 10 when compared to the three-station so- Conberro 35?311528 S 149?135833 E 50 Goldrlone 35'?389639 N 116084878 W 1031 lution mentioned. Earth-Return Flight. This portion of the mission is similar to the lunar-transfer phase as far as the ground-network functions in generd are con- cerned. Again, three midcourse maneuvers are planned, the ground network being the primary SAMPLING RATE 1 meos/min system for navigation before and after them. The graph at the left shows the position and velocity errors, as a function of tracking time, for '."/ the first portion of the lunar-return trajectory. The starting covariance matrix is that of the blown- up burnout condition. The reason for this pro- cedure is to assure that the values shown have not been influenced unduly by the starting condition, thus making them optimistic. To make conditions extremely bad for the A-priori information at end of ground system, assume that contact was lost with first midcourse correction the spacecraft when it departed the Moon. Only qoor = t 8.93 km t/ 8 hr before entry into the Earth's atmosphere, contact, and thus tracking, was restored. Assuming that one ground station and one ship can track - 0.1 I I I I the spacecraft at one sample per minute, the entry 20 30 40 50 60 velocity error is approximately 1-1.5 m/s and Time from Transearth Injection (hours) the position error is approximately 1-2 km. Astronautics C Aeronautics APOLLO RE-ENTRY TRAJECTORIES

figures include Y ”. - 1 I( range rate and angular measurements taken once every 60 sec, using random and bias errors: 6C ur‘ = 3 cm/s, uLY - UE = 8.10-4 radii, A;. = 2 cm/s, An = Ae = 16. lo4 rad; stations Canberra, Carnarvon, and Guam can track this particular return. This is, by far, good enough for a proper atmospheric entry. Even “last-min-

ute” midcourse maneu- I I I I vers will not influence 0 loo0 2000 3000 4000 5000 Ronge (4.1) this situation very much.18 The use of a re-entry interferometer as ing its mission to and from the i~loon.~Apollo indicated in the report by the author, NASA tracking at this point shapes up as a very precise, TND-2880, is no longer planned at this time. well-controlled operation. now Radar-type acquisition methods are being References studied in some detail. Detection probabilities, 1. Jet Propulsion Laboratory, Research Summary Reports No. best radar scan, and optimum ship locations are 36-1, p. 39; 36-2, p. 26; 36-3, p. 42; 36-4, p. 64; 36-5, p. 46; 36-6, p. GO; 36-7, p. 62; 36-8, p. 52; 36-9, p. 51; 36-10, p. 26; 36-11, p. outlined for the numerous Apollo entry trajec- 31; 36-12, p. 66; 36-13, p. 42; 36-14, P. 51; 37-20, p. 1; 37-21, P. 5; 37-22, p. 7; 37-23, p. 8. tories in the report by Moore.IU 2. Painter, T. 1%.and Hondros, G., “Unified S-Band Teiecotn- rnunications Technique for Apollo,” Vol. 1, Functional Descrip- Atmospheric Entry. For the Sept. 17, 1969 tion, NASA TN D-2208, March 1965. mission, the spacecraft, nearing the Earth, flies 3. GSFC Manned Flight Operalions Branch, “Apollo Network,” ANWG-Note, Aug. 28, 1964. over the Pacific Ocean, the southern part of New 4. MSC-CSFC Apollo Navigation Working Group, Technical Report No. 65-AN-1.0, “Apollo Missions and Navigation Systems Guinea, the southern part of Java, east of Ceylon, Characteristics,” Feb. 5, 1965. crosses over Burma, China, and the southern part 5. Manned Flight Support Office, “A Revirw of Manned Space Flight Network Implementation Schedules,” GSFC Report X- of Japan, enters the Earth’s atmosphere near 512-65-186, April 21, 1965. 6. Grumman Aircraft Engineering Corp., “Design Reference Midway Island, and finally lands in the area of Mission,” Apollo Mission Planning Task Force, Vol. I, Contract NAS9-1100, Report No. LED-540-12, Oct. 30, 1964. Ha~aii.~The end portion of the atmospheric entry 7. Vinzant, B. G., “Range Instrumentation Survey,” General is shown in the graph at the right.ls During the Electric, November 1963. 8. Emmons, P. M., “NASCOM Network Support of Orbital last phase, the ground network will play a large ad...... Tvmslunar - .-. Apollo Missions,” GSFC Anollo Naviaation Work. ing Group Note, Aug. 3, 1964. role. Ships and aircraft will be deployed to track 9. Vonbun, F. 0. and Kahn, W. D., “Tracking Systems, Their .. h~~th-~~tical- . -... - Models and Their Errors. Part I. Theory.”.I NASA and communicate with the spacecraft during those TNP-1471, October 1962. portions where no radio blackout exists.1s,20 10. Kahn, W. D. and Vonbun, F. O., “Tracking Systems, Their Mathematical Models and Their Errors, Part 11, Least Square Using a tracking time of 90 sec with the entry Treatment,” to be published as a NASA TN. 11. Schmidt, S., “Interplanetary Error Propagation Program,” ship’s instrumentation yields a spacecraft position Philco WDL Div. Contract No. NAS 5-3342, Report No. WDL-TR- error of 1400 meters at point C. Projecting this 2184 and 2185, Nov. 15, 1963. 12. Cooley, J. L., “Tracking Systems, Their Mathematical Models error-over a ballistic path point #2-3, as shown and Their Errors,” Part 111, Program Description, GSFC Report No. X-513-64-145, May 20, 1964. (Gives description of program in the graph at top right, to the second entry used for Part 11, reference 10 of this paper.) 13. Marlow, A., “Error Analysis for Apollo Earth Parking point No. 3 yields an error of 10,000 meters. This Orbits Using Range Rate and Angle Measurements,” GSFC includes a ship’s position error of 1 km in latitude Report No. X-513.65-42, January 1965. 14. Cooley, J. L., “The Influence of Venting on the Apollo and longitude. Under the assumed conditions, the Earth Parking Orbits,” GSFC Report No. X-513-64-359, Nov. 24, 1964. crew can therefore compare and check the onboard 15. Vonbun, F. O., “Parking Orbits and Tracking for Lunar equipment and make corrections, if necessary, Transfrrs,” GSFC Report No. X-520.6243, June 7, 1962. 16. Bissett-Berman Corp., “Capabilities of MSFN for Apollo during this last critical phase of the flight. Guidance and Navigation,” Final Report, Contract NAS W-688, C 60-18, March 2, 1964. Concluding Remarks. The Manned Space 17. Vonbun, F. 0. and Kahn, W. D., “Tracking of a Lunar Transfer Orbit,” GSFC Report No. X-513-64-353, November 1964. Flight Network, as described in this article, is now 18. Vonbun, F. O., “Re-Entry Tracking for Apollo,” NASA (under construction, including the five ships and TND-2880, June 1965. 19. Moore, J. R., “Apollo Entry-Radar Acquisition Study,” eight jet aircraft which will support the critical GSFC Report X.513-65-225, May 25, 1965. 21). Lehnert, R. and Rosenbaum, B., “Plasma Effects on Apollo transfer burn. Studies and refined analyses are Re.Entry Communications,” NASA TND-2732, March 1965. being continued in close cooperation between the NASA Manned Spacecraft Center and the NASA Single-copy reprints of this article may be obtained free of Goddard Space Flight Center to perfect the task charge by writing on your organization’s letterhead to Dept. MG, Astronartics & Aeronautics, 1290 Sixth Avenue, New York, N.Y. of tracking and guiding the Apollo spacecraft dur- 10019. Multiple copy rates will be sent on request. May 196G