GOQDARD SPACE FLIGHT
I-\rtIIi(THRU)PI/ . .e-7'4'y"it(PAOES)ICO'DE)(NASA CR OR TMX OR AD NUMBER)(CATEGORY1zII14'I,II\IMATHEMATICAL COMPUTATIONSFOR THE AUTOMATIC PICTURETRAN SMISS IO N SY STEM-TIROS YIIII,I-.ROGER D. WERKINGGPO PRICE CFSTl PRICE(S) Hard copy (HC)30\IMicrofiche (MF)ff1APRIL 1965653 July 6 5-IGOQDARD SPACE FLIGHT CENTERGREENBELT, MD.
X-547-65-181MATHEMATICAL COMPUTATIONSFOR THE AUTOMATIC PICTURE TRANSMISSIONSYSTEM-TIROSVIIIbyR o g e r D. WerkingApril 1965T h e o r y and Analysis OfficeData Systems DivisionTracking and Data Systems D i r e c t o r a t e
ft Configuration11IV.Information Requirements of the APT Ground Stations21V.VI.VII.A.Tracking Information21B.Picture Time Information28C.Picture Orientation Information3037FormulationsA.APT Definitions37B.Mathematical Formulation38Formatting of APT Messages57A.Message Distribution57B.APT Computer Program Format of Daily and Weekly Message58C.Format of the Daily Teletype Message64Schedule for Preparation and Sending of the APT Messages71A.Preparation Flow Chart71B.APT Message Schedule73C.Message Check List77Appendix A79References84iii
IllustrationsFiguresI- 1Map of APT Ground Stations4II-1Celestial Sphere8I1-2Illustration of Orbital Elements9I1-3Illustration of Satellite Angles10111-1TIROS VI11 Spacecraft12I11-2TIROS VI11 Baseplate Assembly13111-3Comparison of Camera Systems16111-4Sun Sensor - APT Camera Location17111-5Determining Effective Location of Sun Sensor18I11-6Geometry of APT System19IV-1APT Tracking Data Sheet29IV-2"R" and "S" Angles on the APT Picture31IV -3Oblique Equidistant Cylindrical Projection Chart33IV-4Perspective Grid34IV-5Transfer Grid35V-l"R" and40v-2Orientation of Spin Axis41v-3Radius and velocity Vectors of the Satellite41v -4Definition of theE Vector42v-5Orientation of T;43V-6Dot Product of r * and v*44v -7Definition of the ?Vector45v-8Dot Product of r * and q*46v-9Image Plane Coordinates47"S" AnglesV
nlustrations (cont'd)v-10Dot Product of q* and G *48v-11Projection of Tangent Plane Onto the Image Plane ( T * , h*)49v-12Projection of the Principal Line Onto the Image Plane50V-1351V-14Projection of the Heading Line Onto the Image PlaneDefining 5 and "R"V-15Relation between5 and "R"5354VI-1APT Computer Program Output Format59VI-20ctant Limits62VI-3APT Teletype Format65VI-4Sample of APT Teletype Message69VII-1APT Message Preparation Flow Chart72VI1 -2Schedule for APT Daily Message74VII-3Time Scale for Weekly MessageVI1 -4Schedule for Preparation of APT Weekly Message7576VII-5Operational APT Message Check List78vi
TablesTable1-1I11- 1APT Ground Stations2Camera ComparisonElevation Angle as a Function of Great Circle A r c Lengthand Altitude23VI-1Octant Limits63VI-2Explanation of Code Symbols66IV-1vii15
Section IINTRODUCTIONWith the successful launching of TIROS VIII, a completely new method ofreal time weather forecasting was put into operation. The system aboardTIROS VI11 which permits this real time operation is the Automatic PictureTransmission (APT) System. The APT System enables approximately 50 APTground stations throughout the world to receive the TIROS pictures giving thereal time capability. A list of these stations a r e given in Table 1-1 and areshown on a world map in Figure 1-1. A s can be seen, the number is quite largecompared to the three Command and Data Acquisition (CDA) stations used withthe conventional TIROS cameras.To meet the real time capabilities of the APT system, it is very importantthat each APT ground station have aids and information available which make itpossible to track the spacecraft and to orientate the pictures as soon as they arereceived. The meteorologist can analyze the picture with a minimum delay andmake weather predictions for the local area.The aids and information which a r e supplied to the ground station a r edivided into three groups:1.A package of materials which include instructions, tables , maps, nomograms , overlays , etc.2.Daily teletype messages containing predictive data required by the APTstation.3.Weekly messages containing long range satellite predictions of orbitand attitude which can be used for planning purposes, and to provide abackup in case the teletype communications fail. This message'is sentto the APT stations by mail.1
It is the responsibility of the Theory and Analysis Office, Data SystemsDivision, Goddard Space Flight Center, to prepare the daily and weekly messages which are sent to the APT stations.The purpose of this report is to present, in detailed form, the methods usedin meeting the requirements of the APT messages.Table 1-1APT Ground StationsHONGKOKowloon, Hong KongSAIGONSaigon, Viet NamPEARLHPearl Harbor, HawaiiOTTAWAOttawa, OntarioMONTRLMontreal , QuebecPATRKPatrick A i r Force Base, FloridaSARTOGU.S. S. Saratoga, Norfolk, VirginiaFRANCEParis, FranceMALVRNMalvern, EnglandGERMNYOffenback am Main, GermanyHANSCOHanscom Field, Bedford, Mass.PMRWEACDA Station, Port Mugu, CaliforniaSANDGOSan Diego, CaliforniaCHRISTChristchurch, New ZealandMCMURDMcMurdo Sound, AntarticaHIGH W YHigh Wycombe, EnglandVANDENVandenburg AFB , CaliforniaTORRE JTorrejon AFB, Madrid, SpainCOLORAPeterson AFB, Colorado Springs, Colo.OFFUTTOffutt AFB, NebraskaWESTOVWestover AFB, Mass.RDLAWAFort Monmouth, New J e r s e y2
RCAHNJCDA Station, RCA, P r i n c e t o n , N. J.FCHILDF a i r c h i l d Stratos, Bayshore, N. Y.SFCAPTGoddard Space Flight C e n t e r , Greenbelt, Md.WEABURNational Weather Satellite C e n t e r , Suitland, Md.ULASKACDA Station, Gilmore C r e e k , AlaskaDENMRKCopenhagen, DenmarkRIEDRNB e r n e , SwitzerlandWISCONMadison, WisconsinCALCOMAnaheim, CaliforniaSANK0Osan, KoreaEVREAUE v e r e a u , FranceBRAZILSao P a u l o , B r a z i lCHICAGChicago, Ill.BOSTONBoston, Mass.IDLEWIJohn F. Kennedy Memorial A i r p o r t , N. Y.NEWORLNew Orleans, La.MIAMIFMiami, Fla.SANJUASan Juna, Puerto RicoKANSASKansas City, Mo.SEATTLSeattle, Wash.ANCHORAnchorage, AlaskaHONOLUHonolulu, HawaiiPTMUGUPort Mugu, Calif.AGANAGAgana, GuamADANAAdana, TurkeyCLARKC l a r k AFB, PhilippinesLAJESL a j e s Field, AzoresKINDLEKindley AFB, B e r m u d aKUNIAKunia Camp, HawaiiLANGLELangley AFB, Va.ELMENDElmendnrf, AlaskaKADENAKadena, OkinawaRAMSTERamstein AFB, GermanyFUCHUFuchu AFB, Japan3
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Section 11DEFINITIONSThe following terms are used in this report and in papers connected withthe TIROS satellite.Argument of Perigee (W)-The geocentric angle of the perigee measured inthe orbital plane from its ascending node in the direction of motion.(See Figure 11-2.)Ascending Node-The point at the equator at which the satellite, in its orbitalmotion, crosses from the southern to the northern hemisphere. (SeeFigure 11-2.)Attitude World Map Program (ATMAP)-AGSFC computer programdesigned to compute the earth oriented picture center and boundariesalong with station acquisition information.Celestial Equator-Thegreat circle along which the plane of the earth'sequator intersects the celestial sphere. (See Figure 11-1.)Celestial Sphere-An imaginary sphere of infinite radius with i t s centerlocated a t the observer o r at the center of the earth. In satellitemeteorology, the center of the celestial sphere is a t the center of theearth. Lines o r points a r e projected into the celestial sphere usingradials through the center of the earth. (See Figure 11-1.)Data Acquisition Station (CDA)-Aground station which performs variousfunctions to control satellite operations and to obtain data from thesatellite. The CDA station transmits programming signals to thesatellite and commands the transmissionf data to the ground. Proc-essing of data electronically and manually is accomplished a t the CDA5
station. Raw and processed data a r e disseminated from the CDAstations.Declination (6)-The angular distance of an object north ( ) o r south (-)from the celestial equator measured along the hour circle passingthrough the object. (See Figure 11-1.)Fiducial Line-Thefiducial line connects the central cross-mark in thepicture with the "T" fiducial mark on the right side. (See Figure 111-3.)Fiducial Marks-Indexmarks rigidly connected with the camera optical sys-tem so that they form images on the negative. The fiducial marks of theTIROS vidicon cameras and the APT vidicon camera a r e marked differently. (See Figure 111-3.)GAMMA Angle (y)-The angle measured from the spin axis vector to thevector directed to the sun. The limits are '0 y5 180'.(SeeFigure II-3.)Heading Line (h)-The direction of the component of the velocity vectornormal to the radius vector to the satellite from the center of theearth. (See Figure V-4.)Image Plane-Aplane parallel to the object plane on the vidicon camera.(See Figure 11-3.)Inclination (i)-The angle measured from the celestial equator to theorbital plane of the satellite. The angle is measured in a counterclockwise direction at the ascending node. (See Figure 11-2.)Magnetic Attitude Program (MGAP)-AGSFC computer program designedto determine the orientation of the satellite spin axis, NON, and TOTof each orbit.Nadir Angle (q)-The angle measured at the satellite between the radiusvector and the direction of the spin axis of the satellite. (SeeFigure 11-3.)NON-TeletypeObject Plane-Acode for the minimum nadir angle for a given orbit.plane perpendicular to the camera axis tangent to theprincipal point. (See Figure 11-3.)6
,Orbit-The path which a celestial object follows in i t s motions throughspace, relative to some selected point. (See Figure 11-2.)Principal Line @)-The line in the picture plane that connects the principalpoint and the image subsatellite point. (See Figure V-7.)Principal Plane-Theplane which includes the optical axis of a camera andthe local vertical through the front nodal point of a satellite cameralens.Principal Point-The point of intersection of the optical axis of the camerawith the earth. (See Figure 11-3.)"R" angle-The"R" angle is the counterclockwise angle from the image ofthe heading line to the image principal line. "R" is defined as zero forthe special case where the nadir angle equals zero. (See Figure IV-2.)Right Ascension @)-The a r c measured eastward along the celestial equator from the vernal equinox to the great circle passing through thecelestial poles and the object projected onto the celestial sphere.(See Figure 11-1.)ITS" angle-The"S" angle is the counterclockwise angle between thefiducial line in the picture and the direction in the picture of the imageof the forward heading line. (See Figure IV-2.)Spin Axis-The axis about which the satellite spins. The positive directionalong the spin axis is designated from the floor to the top of thesatellite. (See Figure 11-3.)Subpoint Track-Locusof subsatellite points on the earth.Subsatellite Point-Intersectionof the local vertical passing through thesatellite with the earth's surface. (See Figure 11-3.)TIROS- Abbreviation for Television Lnfrared Observation Satellite.TOT-Teletypecode f o r the time of minimum nadir angle; time afterascending node when NON occurs.True Anomaly (V)-The geocentric angle of a Satellite measured in theorbital plane from its perigee in the direction of motion. (SeeFigure 11-2.)7
Vidicon-A photoconductive image pickup o r television type tube.Each television camera in the satellite consists of a set of optic lenses,a focal plane shutter and a vidicon tube. The image i s focused on thevidicon screen by the lens, and the vidicon scanner transforms theimage into an electric signal which can be transmitted o r recorded onmagnetic tape.World Map and Station Acquisitior, Data Program (WMSAD)-A GSFC computer program designed to determine the subsatellite points withstation acquisition times and acquisition characteristics.NorthPol eCelest ia IEquatora - right ascension6 - declinationFirst Point of AriesT--Figure 11-1.Celestial Sphere8
Orbitiw- inclination- Argument of- Right Ascension ofVPerigeeFigure- True Anomaly11-2. Illustration of Orbital Elements9the Ascending Node
ObjectPlane/ImagePlanePri nc ipaPointwFigure 11-3. Illustration of Satellite Angles10Satel Iite
Section 111SPACECRAFT CONFIGURATIONThe configuration of the spacecraft is important when making some of thelater calculations concerning the orientation of the TIROS pictures. Therefore,this section has been included in this report.The TIROS VI11 spacecraft is of polyhedron configuration with 18 sides,see Figure 111-1. The structure of the spacecraft consists of a baseplate ontowhich most of the electrical and mechanical components a r e attached and acover o r cap assembly onto which the solar cells a r e attached. The cameralenses extend through the baseplate and are aligned parallel to the spin axis ofthe spacecraft. A sketch of the baseplate assembly i s shown in Figure ID-2.Two types of camera systems a r e aboard the TIROS VI11 satellite. CameraNo. 1 i s a conventional TIROS camera and Camera No. 2 i s an APT camera. Acomparison of the cameras is shown in Table 111-1 and Figure 111-3. This reportis concerned only with the latter of these systems and the relative locations ofsome of the components in the system.The main components of the APT system a r e (1) a sun sensor, (2) APTcamera, (3) picture transmission equipment, and (4) clock alarm equipment.The function of the sun sensor mechanism, in effect, is to trigger the APTcamera. The camera shutter i s activated after a delay which begins when sunlight impinges on the sensor. If this delay is known along with the angle betweenthe sun sensor and the camera, the spin rate, the location of the sun, and thetime when the picture i s taken, the picture orientation can be determined.Calibrations of the TIROS VI11 spacecraft were made a t varying spin ratesfrom 8 to 12 rpm and gamma angles between 20 and 7 0 degrees. The Sun OffsetTime was found to be 5.475 0.005 seconds.11
,Figure 111-1.TIROS Vlll Spacecraft12
Figure111-2. TlROS Vlll Baseplate Assembly13
The location of the sun sensor with respect to the APT camera is shown inFigure 111-4. However, since the sensor is of a finite size, the effective position of the sun sensor must be determined. The sensor is activated when thesun's rays strike the edge of the sensor as in Figure III-5. The actual angularlocation of the sensor in the baseplate reference radial system is 220'5.5'.Theangle of the sun's rays can be referenced to the radial reference system by subtracting the angle (A B) from 220'.This angle, (A B), is the angle throughwhich the satellite would have to rotate to align the center of the sun sensorwith the sun. The angle w a s found to be 13 27.5', hence, the effective angle inthe baseplate reference radial system, of the sun sensor is 206'38',as shownin Figure 111-4.The Sun Sensor Reference Angle o r the angle which the sun's rays make withthe picture fiducial line at the time when the sun sensor is activated can now bedetermined.From Figure 111-6, the geometric relationships used in determining theSun Sensor Reference Angle a r e a s follows:A-Theangle between the zero reference line and the camera radialreference line.B-Theangle between the zero reference line and the effective loca-tion of the sun sensor radial reference line.C-Theangle between the fiducial line and the right fiducial mark.D-Theangle between the camera radial reference line and the rightfiducial mark.E-Theangle between the fiducial line and the line to the sun measuredat the central fiducial mark of the camera.From measurements made during the calibration of the spacecraftA 170 17.0'B 206 38.0'C 0'19.3'.And, by definitionD 90 00'.14
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21483216644- Sun AngleDigital Display270'r1IIDirect ionto Spin 4Axis!& SunAnglcLIZeroRef,zerolCamera 1DirectClock00r - r - r - r i1Writtenby.)i S A x i1FiducialLine0003-(Date Time)HandFacsimile Reproduction ofPicture from Camera No. 2 (APT)Figure 111-3. Comparison of Camera Systems16
"SunAngle"Zerov\I on,,/ZeroReferenceDirection ofSa tel I iteI--@--Of Camera No. 1of Rotation SensorOrientationof Camera No.Test Chartc t i v e Position2Note:Angles shown in orientation of cameras refer to numbers on distortion target as theyappear in the subject plane.Figure 111-4. Sun Sensor- APT Camera Location17
Figure111-5, Determining Effective Location of Sun Sensor18
To SunTo SunEffective LocationReferenceLinejFigure 111-6.Geometry of APT System19
F-Theangle between the effective location of the sun sensor radialand the camera radial reference line is:F B-AF 36'21'G-The angle between the right fiducial line and the camera radialreference line is:G D-CG 89'40.7'H-Since the sum of the interior angles is equal to 180 , the angle His :H H 180 00' - (G F)53O58.3'Thus, by definition of parallel lines intersected by a transverse line:E HTherefore, the Sun Sensor Reference Angle i s equal to 53'58.3'and ismeasured in a counterclockwise direction.With the time delay and the relative location of the camera and sensorcalibrated later calculations can be made to orient the APT pictures.20
Section IVINFORMATION REQUIREMENTS OF THE APT GROUND STATIONSThe ground stations must have orbital information so that the satellite canbe tracked and the pictures received. Once the acquisition is made and thepictures have been received, information concerning the location at which thepictures were taken and the orientation of the camera must be supplied. Thissection will specify what data is needed and the way this data is used at the APTground station.A.Tracking InformationThe interrogation of the TIROS APT system is the first step in real timeweather forecasting via TIROS pictures. This interrogation requires that theground station receiving antenna be pointed in the general direction of the spacecraft. To point the antenna it is necessary for the station to know the azimuthand elevation of the satellite with respect to the antenna at a given time. Amethod has been devised by which, with the use of overlays, a station can determinethe subpoint track given only the longitude and time of the ascending node. Thisapproach to solving the problem was decided upon because this information issent to the APT station daily via teletype.The overlay consists of a subpoint track of the spacecraft drawn on a transparent rotating disc which is superimposed over a polar projection of the earth.The latitude indicators are circles evenly spaced outward from the pole of onehemisphere t o 30' of the other hemisphere. From the pole, radials are extendedand the longitudes a r e labeled. Hence, if the hatch mark indicating the ascendingnode on the subpoint track is rotated until it is coincident with the longitude ofascending node, provided in the daily APT message, the subpoint track of thesatellite can be determined.21
Once the subpoint track of the satellite has been determined, the azimuthand the elevation angle of the satellite with respect to the station must be determined. To accomplish this task, the satellite height and the geographic latitudeof the local tracking antenna a r e required. The height of the satellite i s suppliedto the station in the APT daily message. An azimuth-great circle a r c lengthtracking diagram is drawn on the polar projection with the origin at the geographic location of the antenna. To obtain tracking data, the user reads thevalues of azimuth and great circle a r c length from the overlay. A r c length isthen converted to elevation angle by noting the satellite height at the desireddata point. Table IV-1 contains satellite elevation angles as a function of greatcircle arc length (degrees) and height. Hence, a t the points where the satellite'ssubpoint track intersects the acquisition diagram, the azimuth and elevation canbe determined.The final tracking information which is required by the APT station is thetime of acquisition. To accomplish this, hatch marks are drawn on the subpointtrack representing two minute time intervals referenced to the ascending node.The time of the ascending node referenced to Greenwich mean time for a giventime is supplied to the station in the APT daily message. Thus, for a given timewhen the satellite can be interrogated by a station the tracking information isknown.In summary, the following steps a r e followed to determine which orbitscan be locally acquired and to derive tracking data points:1.Set ascending node of subpoint track on the transparent overlay to thelongitude of the ascending node given for the reference orbit in thedaily message.2.Determine which orbit can be interrogated by the station.3.The daily message provides the longitude and time interval betweensuccessive ascending nodes. Thus , the operator can determine specificascending node data by incrementing successive longitudes and timesto the reference orbits.22
23
24
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a,a3,.c.c,., 2ama)E-PI4926
Table IV-1 (Continued)Elevation Angle as Function of Great C i r c l e A r c Length and AltitudeHeight(Naut. Mi.)ArcLength1001251501752002252502753003253503 754004254504755005255505756006 256 506 757007257507758008258508 7590013.615.216.617.919.120.221.227.223.124 32.733.333.834.334.835.335.836.236.737.137.627
4.Rotate the transparent overlay until the subpoint track intersects theascending node of the first orbit which can be acquired locally. Readthe times on the subpoint track, - minutes referenced to ascending node,at the two intersections of the subpoint track with the 0' elevationcircle (or minimum elevation circle after it has been empiricallydetermined). Convert the time referenced to ascending node to GMTby adding the time of ascending node (of orbit being tracked) to the timeread on the subpoint track. This provides the operator with approximate antenna elevation, azimuth, and time at which the first signal willbe received.5.Antenna azimuth and elevation data points for tracking may then beobtained at convenient time intervals along the subpoint track whichfalls within the tracking limits of the local station.6.B.A tracking data sheet, as in Figure IV-1, is completed.Picture Time InformationWith the TIROS satellite being a spin stabilized spacecraft and the camerassituated in such a way that the field of view of the camera is parallel to the spinaxis, good picture taking conditions exist f o r only a portion of each orbit. Withthis limiting factor existing, it is necessary to notify the APT station when goodpicture taking conditions occur. The following factors determine the criteriafor good picture taking conditions:000.Nadir angles between 70.0 and -70 .OReal intersection between the camera axis and the earth.0Sun elevation angles at the picture center point greater than 1 2The picture time information supplied to the station contains the latitudeand longitude of the subpoint track at two minute intervals during the time offavorable conditions. This time i s referenced to the time after the ascendingnode of the orbit in question.Since the APT system does not have picture storage capabilities, thepictures must be transmitted to the receiving station as they are taken. Thus, bycomparing the times after ascending node f o r favorable picture taking conditions28
SIGNAL ACQUISITION:TIME:ELEV:AZIMUTH:TIMEASC.NODE REF( 2)GREAT ELNATION AZI MUTHCIRCLEDISTANCEPICTURE-5.9-5-f3-93-3.0- F 6-2.0-3.2. - / . 0drbpFigure IV-1STOP. APT Tracking Data Sheet29 /e v.
with the time after ascending node when the satellite is within range of thereceiving station on a particular orbit, the operator can determine when totrack and interrogate the satellite and expect to receive pictures.C.Picture Orientation InformationCertain information is needed by the APT ground station to orient thepictures once they a r e received. This information is supplied to the stationin the APT daily message.One of two possible conditions exists when the picture is received. Thefirst and most common is the condition when the horizon is visible in thepicture. When this condition occurs, the values of NON, TOT, the nadir angle,and the time at which the picture was taken are needed to f i t the grids to thepicture, and hence, orient the picture. The values of NON, TOT, and the nadirangle at two minute intervals during the time of favorable picture taking aresupplied to the station.The second condition is when the horizon is not visible0in the picture. This condition occurs when the nadir angle is l e s s than 1 0.When this condition occurs, additional information is required. This information consists of two angles, "R" and "S", which are used to ascertain the principal line orientation in the picture. These angles are shown in Figure IV-2.The "R" and "S" angles are supplied in the daily message at two minuteintervals during the time for favorable picture taking.The "S" angle i s measured counterclockwise from the fiducial line in thepicture. The line drawn at an angle "S" to the fiducial line with the origin atthe center of the received picture is the projection of the heading line onto thepicture plane. The principal line is then drawn at an angle "R" to the headingline. Once the principal line is drawn, the same technique is used to matchgrids to the pictures as that used when the horizon is visible.Figures 1V-3,4, and 5 are samples of the grids used to orient the pictures.A detailed discussion on the use of these grids can be found in the "APT Users'Guide" written by Leon Goldshlak. A short description of each of the grids issupplied in the following paragraphs.30
Satel I itePrincipalLineIF iduc ia ILineFigureIV-2. "R" and "S" Angles on the APT Picture31
.Oblique Equidistant Cylindrical (OEC) Projection Chart (Figure IV-3)The OEC chart is constructed with the satellite orbit as the projectionequator, along which a cylinder makes contact with the earth's surface. Theprojection then results in an equidistant projection along the projection equator.A simplified way of looking at this chart is to assume it to be a mercator chartwith the earth's equator tilted to the satellite orbital track and the geographicareas near the track a constant scale of equal dimensions.Perspective Grid (Figure IV-4)Due to the wide field of view of the TIROS APT camera, the horizon willfrequently be photographed at nadir angles greater thanloo,as w a s statedearlier. Since the position and shape of the horizon curve on the image formatis a function only of camera altitude and nadir angle, it is possible to projectthe horizon curve onto the perspective grid. The horizon image position provides the means of orienting the perspective grid on the picture. The centralline of the perspective grid, which is orthogonal to the horizon curve, is theprojection of the principal plane onto the image format. This central line isalso the "image" of the great circle a r c which has been defined as the centralline of the square grid of the earth's surface.Transfer Grid (Figure IV-5)A grid representing 180 nautical mile squares has been drawn for the OEDprojection chart. The grid is centered at the location of the picture centerpoint which is indicated by the "X" on the grid and oriented from the subpointon the orbital track, the direction of which is indicated by an arrowhead.In summary, the data required in the daily message to orient the picturesconsists of (1) NON, (2) TOT, and (3) nadir angles, "S" angles, and "R" angles,at two minute intervals along the time of favorable picture taking.32
FigureIV-3. Oblique Equidistant Cylindrical Projection Chart33
FigureIV-4. Perspective Grid34
Figure IV-5. Transfer Grid35
Section VFORMULATIONSIn most cases, the information supplied to the APT ground station was computed for previous TIROS satellites. Therefore, this section is intended only topresent the formulations which a r e peculiar to the APT system.A.APT DefinitionsSince vector notation will be used to present the APT formulations, it isimportant that the terms used are well defined. The following are the definitionof t e r m s which will be used:P*-Spin axis vector which lines along the principal axis of the satellite and pointsfrom the base to the top of the satellite. (See Figure V-1.)q*-Cameraaxis vector which lies along the principal axis of the camera and inopposite direction of the spin axis vector. (See Figure V-7.)G * S u n vector which lies along the direction to the sun and points from the lenstoward the sun. (See Figure V-10.)T -Velocity vector which lies along the direction of the satellite's motion. (See-rFigure V-3.)-Radius vector which lies along the direction from the center of the earthtoward the satellite. (See Figure V-3. )CY-Right ascension of the spin axis. (See Figure V-2.)6 -Declination of the spin axis.Sun Offset Time-The(See Figure V-2.)fixed time delay between the sun-pulse signal and theshutter opening.Sun Sensor Reference Angle-An angle of orientation of the camera fiducial linewith respect to the sun-pulse signal mechanism.37
h*-Unitvector describing the heading of the satellite from the subpoint forwardalong the orbit. (See Figure V-14.) -Unitvector describing the principal line from the subpoint toward the princi-pal point. (See Figure V-14.)h*-Unit vector along the projection of h* in the image plane. (See Figure V-14.)P#-Unit vector along the projection of inthe image plane. (See Figure V-14.)PB.Mathematical FormulationIn addition to the special constants, Sun Offset Time and Sun ReferenceAngle, five basic elements a r e needed to produce the desired APT user data:0Satellite spin rate, u0The spin axis vector, p*0The vector to the sun, G*0The satellite inertial velocity vector, v*The satellite radius vector, r*.The TIROS attitude determination system has the capability of determiningthe spin axis vector, p: both historically and predictively. Taking the ri
Map of APT Ground Stations Celestial Sphere Illustration of Orbital Elements Illustration of Satellite Angles TIROS VI11 Spacecraft . Offutt AFB, Nebraska Westover AFB, Mass. Fort Monmouth, New Jersey 2 . RCAHNJ FCHILD SFCAPT WEABUR ULASKA DENMRK RIEDRN WISCON CALCOM SANK0 EVREAU BRAZIL CHICAG BOSTON
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Flight Center will participate in flight training activities to verify safe and effective flight training. 2.2 Chief Flight Instructor The Chief Flight Instructor is responsible for the day-to-day operations of the Flight Center. He is the principle point-of-contact to the FAA for the University of Dubuque. He ensures
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