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N A S A ' s MANNED SPACE FLIGHT NETWORK

Tracking, command and communication--Apollo' s v i t a l l i n k sw i th t h e ea r th - - a r e p er fo rm ed i n t w o broad phases ,

For t h e f i r s t pha se , t h e Manned Space F l i g h t Network (MSFN)d ep en ds l a r g e ly on i t s w orldw id e ch a in of s t a t i o n s equ ipp ed w i t h30-foot an tenna s wh i le Apol lo i s l a un c he d a nd o r b i t i n g n e a r t h ee a r t h . The second phase beg ins when th e sp ac ec ra f t moves ou tmore than 1 0 , 0 0 0 m i l e s above e a r t h , when t h e 85-foot-d iametera nt en n as b r i n g t h e i r g r e a t e r power and p r e c i s i o n i n t o p l a y .

The Network m ust f u r n i s h r e l i a b l e , i n s t an t an eo u s c o n t a c tw i t h t h e a s t r o n a u t s , t h e i r l a un ch v e h i c l e and s p a c e c r a f t , froml i f t o f f t hr ou gh e a r t h o r b i t , moon l a n d in g and l u n a r t a k e o f f t osplashdown i n t h e P ac i f i c O cean .

The Network c o n s i s t s of 1 2 g r o u n d s t a t i o n s , o n e s h i p , a n df o u r j e t a i r c r a f t - - a l l d i r e c t l y o r i n d i r e c t l y l i nk e d w i t h M i s -s i o n C o n t r o l C e n te r i n H ou sto n. W hile t h e e a r t h t u r n s on i t sa x i s , and t h e moon t r a v e l s i n o r b i t n e a r l y o n e - qu a rt e r m i l l i o nm i l e s away and th e Apol lo s p a c e c r a f t moves between them, groundc o n t r o l l e r s w i l l b e k e p t i n th e c l o s e s t p o s s i b l e c o n t a c t . T hus,on ly fo r some 45 m in ute s a s t h e s p a c e c r a f t f l i e s beh ind t h emoon i n each o r b i t , i s t h i s l i n k wi th e a r t h o u t of r ea ch .

A l l e lements of t h e netw ork g e t r e a d y e a r l y i n t h e c o u nt -down, A s th e Apo llo lau nch es from Cape Kennedy, v oi ce and d a t aa r e t r a n s m i t t e d i n s t a n t a n e o u s l y t o H ouston. The d a t a a r e s e n td i r e c t l y t hr ou gh com puters f o r v i s u a l d i s p l a y t o f l i g h t con-t r o l l e r s

Depending on t h e l aunch az imuth , t h e 30- foo t an tenn as keept a b s o n A p o l lo , b eg inn in g w i th t h e s t a t i o n a t M e r r i t t I s l a n d ,F l a , , thence Bermuda; t h e t r a ck in g s h i p V an gu ard : t h e C ana ryIs la n ds ; Tananar iv e , Madagascar ; Carnarvon, A u s t r a l i a ; Guam;Hawai i; and Corpus C h r i s t i , Texas .

To i n j e c t A po ll o i n t o t r a n s l u n a r f l i g h t p a t h , M is si on Con-t r o l s en d s a s i g n a l t hr ou gh on e of t h e l a nd s t a t i o n s , A s t h es p a c e c r a f t h ea ds f o r t h e moon, t h e e n g i n e b u rn i s moni to red byt h e gro und s t a t i o n s and a n A p o ll o r a ng e i n s t r u m e n t a t i o n a i r -c r a f t ( A R I A ) * The AR I A p r o v id e s a r e l a y f o r th e a s t r o n a u t s 'vo ice s and d a ta communication wi th Hous ton .

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When the spacecraft reaches an altitude of 10,000 milesthe more powerful 85-foot antennas join in for primary supportof the flight, although the 30-foot ''dishes" continue to trackand record data, The 85-foot antennas are located about 120degrees apart at Madrid, Spain; Goldstone, Calif.; and Canberra,Australia.

With the 120-degree spacing around the earth, at least oneof the large antennas always has the moon "in view." As theearth revolves from west to east, one 85-foot station hands overcontrol to the next 85-foot station as it moves into view of thespacecraft. In this way data and communication flow is con-t nuous

Data are always relayed back through the large antennas andtransmitted via the NASA Communications Network (NASC0M)--a two-million mile hookup of landlines, undersea cables, radio circuitsand communication satellites--to Houston. This information isfed into computers for visual display in Mission Control--forexample, a display of the precise position of the spacecraft ona large map. Or, returning data may indicate a drop in power orsome other difficulty in a spacecraft system, which would ener-gize a red light to alert a flight controller to action.Returning data flowing through the earth stations give thenecessary information for commanding midcourse maneuvers to keepApollo ip a proper trajectory for orbiting the moon.is in the vicinity of the moon, these data indicate the amountof retro burn necessary for the service module engine to place

the spacecraft in lunar orbit.

While Apollo

Once the lunar module separates from the command module andgoes into a separate lunar orbit, the MSFN is required to keeptrack of both spacecraft at once, and provide two-way communica-tion and telemetry between them and the earth. The prime antennaat each of the three 85-foot tracking stations handles one space-craft while a wing, qr backup, antenna at the same site handlesthe other spacecraft during each pass.

Tracking and acquisition of data between earth and the twospacecraft provide support for the rendezvous and dockingmaneuvers. The information also is used to determine the time

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and duration of the service module into a precise trajectoryfor reentering the earth's atmosphere at the planned location,

As the spacecraft comes toward earth at high speed--morethan 25 ,000 miles per hour--it must reenter at the proper angle.To make an accurate reentry, information from the tracking air-craft and stations is fed into the MCC computers where flightcontrollers make decisions that will provide the Apollo crewwith the necessary information,

Appropriate network stations and aircraft in the Pacificare on hand to provide support during the reentry. An ARIAaircraft relays astronaut voice communications to MCC, andantennas on reentry ships follow the spacecraft,

Through the journey to the moon and return, television isreceived from the spacecraft at the Goldstone, Madrid, and Can-berra 85- foot antennas. In addition, 210-foot-diameter antennasin California and Australia are used to augment the televisioncoverage while the Apollo is near and on the moon, Scan con-verters at the stations permit immediate transmission of com-mercial quality TV via NASCOM to Houston, where it is thenreleased to TV networks,NASA Communications Network

The NASA Communications Network (NASCOM) consists ofseveral systems of diversely routed communications channelsleased on communications satellites, common carrier systemsand high frequency radio facilities where necessary to providethe access links.The system includes both narrow and wideband channels, andsome TV channels. Among these are a variety of telegraph, voice,

and data systems (digital and analog) with several digital datarates- Alternate routes or redundancy provide added reliability.A primary switching center and intermediate switching andcontrol points provide centralized facility and technical con-trol, and switching operations under direct NASA control.. Theprimary switching center is at the Goddard Space Flight Center,Greenbelt, Md. Intermediate centers are located at Canberra,Madrid, London, Honolulu, Guam, and Kennedy Space Center..

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The Kennedy Space Center is connected directly to theMission Control Center, Houston, via the Apollo Launch DataSystem and to the Marshall Space Flight Center, Huntsville,Ala., by a Launch Information Exchange Facility.

After launch, all network tracking and telemetry data hubsat GSFC for transmission to MCC Houston via two 50,000 bits-per-second circuits used for reuundancy and in case of dataoverflow.Two Intelsat communications satellites are used for Apollo.The Atlantic satellite services the Ascension Island unifiedS-band ( U SB ) station, the Atlantic Ocean ship and the Canary

Islands site.The second Apollo Intelsat communications satellite overthe mid-Pacific services the Carnarvon, Australia, USB site.These stations transmit simultaneously through the satellite toHouston via Brewster Flats, Wash., and the Goddard Space FlightCenter.

Network ComputersAt fraction-of-a-second intervals, the network's digitaldata processing systems, with NASA's Manned Spacecraft Center

as the focal point, "talk" to each other or to the spacecraft.Highspeed computers at the remote site (tracking ships included)issue commands or "up-link" data on such matters as control ofcabin pressure, orbital guidance commands, or "go-no-go" indi-cations to perform certain functions,When information originates from Houston, the computersrefer to their pre-programmed information for validity before

transmitting the required data to the spacecraft,Such "up-link" information is communications by ultra-high-frequency radio at about 1,200 bits-per-second. Communi-cation between remote ground sites, via high-speed communica-tions links, occurs at about the same rate. Houston readsinformation from these ground sites at 2,400 bits-per-second,as well as from remote sites at 100 words-per-minute.

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The computer systems perform many other functions, s u c has:

- Assuring the quality of the transmission lines bycontinually exercising data paths.- Verifying accuracy of the messages by repetitive

operations.- Constantly updating the flight status.For "down link" data, sensors b'iilt into the spacecraftcontinually sample cabin temperature, pressure, physical infor-mation on the astronauts such as heartbeat and respiration,among other items. These data are transmitted to the groundstations at 51.2 kilobits (12,800 inary digits) per second.A t MCC the computers:- Detect and select changes or deviations, compare withtheir stored programs, and indicate the problem areas

or pertinent data to the flight controllers.- Provide displays to mission personnel.- Assemble output data in proper formats.- Log data on magnetic tape for replay for the flightcontrollers.- Keep time.

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The Apollo Ship and AircraftThe mission is supported by one instrumentation shipoperating as an integral station of the Manned Space FlightNetwork (MSFN) to provide coverage in areas beyond the rangeof land stations, and four instrumented jet aircraft on sta-tion over the South Pacific.The ship, USNS Vanguard, performs tracking, telemetry,and communication functions for the launch phase, and earth-orbit insertion

Vanguard is stations about 1,000 miles southeast ofBermuda (25 degrees N., 49 degrees W,) to bridge the Bermuda-Ascension Island gap during earth-orbit insertion. Vanguardalso functions as part of the Atlantic recovery fleet in theevent of a launch phase contingency. In the event the launchdate slips, the ship normally moves in a northeastward direc-tion to cover the changing translunar injection location.The Apollo ship was developed jointly by NASA and theDepartment of Defense. The DOD operates the ship in supportof Apollo and other NASA and DOD missions on a non-interfer-

ence basis with Apollo requirements.Management of the Apoflo ship is the responsibility ofthe Military Sea Transport Service, with maritime crews andthe Federal Electric Corp., International Telephone and Tele-graph, under contract providing the technical instrumentationcrews.The technical crews operate in accordance with joint NASA-DOD standards and specifications which are compatible with MSFN

operatianal procedures.The Apollo Range Instrumentation Aircraft or ARIA, areused primarily to fill coverage gaps between Australia andHawaii during the translunar injection interval, Prior to andduring the burn, the ARIA record telemetry data from Apollo andprovide real-time voice communication between the astronauts

and the Mission Control Center at Houston.

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Four a i r c r a f t p a r t i c i p a t e , o p e r a t i n g from P a c i f i c , Aus-t r a l i a n , and I n d i an Ocean a i r f i e l d s i n p o s i t i o n s u n d e r t h eo r b i t a l t r a c k of t h e s p a c e c r a f t and l au nc h v e h i c l e . The a i r -c r a f t a r e de pl oy ed i n a no rth we st wa rd d i r e c t i o n i n t h e ev en tof launch day s l i p s ,

F o r r e e n t r y , t w o AR IA are dep loyed t o t h e l a nd i ng a r e a t oco nt inu e communications between Apol lo and Mission C ontr o l a tHouston and p rov ide p os i t io n in fo rm at ion on t h e s p a c e c ra f t a f t e rt h e b l a c k o u t p h a se o f r e e n t r y h a s p a s se d . 4

T h e t o t a l AR I A f l e e t f o r A p ol lo m i ss i o n s c o n s i s t s of f o u rEC-135A (Boeing 707) j e t s equipped s p e c i f i c a l l y t o m e e t miss ionn eed s, They ca r r y s even -f o ot p a r ab o l i c an t en n as i n t h e noses e c t i o n , g iv in g them a l a r g e , b u lbo u s l o o k ,The a i r c r a f t , a s w e l l a s f l i g h t and i n s t r u m e n t a t i o n c re w s,p rov ided by th e A i r F o r ce , a r e equ ip ped t h r o ug h jo i n t A i r Force-

NASA c o n t r a c t a c t i o n t o o p e ra te i n acco rdance w it h MSFN proce-d u r e s .Miss ion Con t ro l Cen te r

The Miss ion Con t ro l C en te r a t t h e Manned Spa ce cr af t Cen ter ,Houston, i s t h e f o c a l p o i n t f o r Apollo f l i g h t c o n t ro l a c t i v i t i e s ,The c e n t e r r e c e i v e s t r a c k i n g and t e l e m e t r y d a t a fro m t h e MannedS pace F l i g h t N etw ork , p r o ces s e s d a t a t h r ou g h t h e M is sio n C o n t r o lCe nte r Real-Time Computer Complex and di s p l a y s th e da t a t o t h ef l i g h t c o n t r o l l e r s and e n g in e e rs i n t h e Mission Operations Con-t r o l Room and s t a f f sup por t rooms.

The Manned Space F l i g h t Network t ra ck in g and da ta ac qu is i -t i o n s t a t i o n s l i n k t h e f l i g h t c o n t r o l l e r s a t t h e c e n t e r t o t h es p a c e c r a f t ,

F or A po ll o a l l ne tw ork s t a t i o n s a r e r em ote s i t e s , t h a t i s ,w i th o u t f l i g h t c o n t r o l te am s. A l l up -l in k commands and v o ic ecommunica tions o r ig in a t e f rom Hous ton, and te lem et ry d a t a a res e n t bac k t o Houston a t h i g h s p ee d r a t e s ( 2 , 4 0 0 b i t s - p e r - s e c o n d ) ,on two s e p a r a t e d a t a l i n e s , They c an be e i t h e r r e a l t i m e o rp layback in fo rmat ion .

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Signal flow for voice circuits between Houston and theremote sites is via commercial carrier, usually satellite,wherever possible using leased lines which are part of theNASA Communications Network.Commands are sent from Houston to NASA's Goddard SpaceFlight Center, Greenbelt, Md., on lines which link computersat the two points. The Goddard communication computers pro-vide automatic switching facilities and speed buffering forthe command data. Data are transferred from Goddard to remotesites on high speed (2,400 bits-per-second) lines. Commandloads also can be sent by teletype from Houston to the remote

sites at 100 word per minute. Again, Goddard computers pro-vide storage and switching functions.

Telemetry data at the remote site are received by the RFreceivers, processed by the pulse code modulation ground sta-tions, and transferred to the 642B remote-site telemetry com-puter for storage. Depending on the format selected by thetelemetry controller at Houston, the 642B sends the desiredformat through a 2010 data transmission unit which providesparallel to serial conversion, and drives a 2,400 bit-per-second mode.The data mode converts the digital serial data to phase-shifted keyed tones which are fed to the high speed data linesof the communications network.Tracking data are sent from the sites in a low speed

(100 words) teletype format and a 240-bit block high speed(2,400 its) format. Data rates are one sample--6 secondsfor teletype and ten samples (frames) per second for highspeed data.

A l l high-speed data, whether tracking or telemetry, whichoriginate at a remote site are sent to Goddard on high-speedlines. Goddard reformats the data when necessary and sendsthem to Houston in 600-bit blocks at a 40,800bits-per-secondrate. Of the 600-bit block, 480 bits are reserved for data,the other 120 bits for dddress, sync, intercomputer instruc-tions, and polynominal error encoding,

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~ l lideband 40,800 b i ts -p e r- se co n d d a t a o r i g i n a t i n g a tHous ton a r e conve r t ed t o h igh speed (2 ,400 bi t s -per - second)d a t a a t Goddard b e f o r e b ei n g t r a n s f e r r e d t o t h e d e s i g n a te dremote s i t e .

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