Table 1-1. SOOBDF specification. Variable length SOAC Header Record: 129 byte fixed TACC-Normalized Observation Data: Equivalent to OBDF

Transcription

1 SOAC OBSERVATION DATA FILE SOOBDF) ) GENERAL The SOOBDF is reated for the purpose to save traking data in SELENE Observation Data Arhive Center SOAC). The SOOBDF onsists of SOAC Header and OBDF. 2) FILE SPECIFICATION The SOOBDF is desribed in Table -. Table -. SOOBDF speifiation Item File Identifiation File Type File Format Reord Length Maximum Number of Reords Data File Creator SOAC Observation Data File SOOBDF) Content Files reated for eah spaeraft/station/data type Text file Charater Code = ASCII) Variable length SOAC Header Reord: 29 byte fixed TACC-Normalized Observation Data: Equivalent to OBDF N/A SOAC Header and TACC-Normalized Observation Data SELENE Information Sub-System / SOAC Data Conversion Program Note

2 3) FILE STRUCTURE Table -2. SOOBDF struture Blok Reord Item SOAC Header TACC-normalized Observation Data SOAC Header Reord File Classifiation, Creation Date and Time, Data Blok Length, Spaeraft ID, Spaeraft Name, Storage Start/End Date and Time, Station Name, Data Type Name Detailed Desription Table -3 Equivalent to OBDF. See 2 Observation Data File for detailed desription. 4) RECORD Detailed Desriptions of Reords in the SOOBDF are provided in Table -3. [Convention] : Spae 9999 : Number with zero padding ex., 000 ). ZZZ9 : Number without zero padding ex., ). S : Sign positive: +, negative: - ). s : Sign positive:spae, negative: - ). PE22.5 form: s es99 form. To maintain 6-digit preision, integer in the base shall not be zero.) Ex., E-02 shall not be expressed as E-0. 2

3 Table -3. SOAC Header Reord File SOOBDF SOAC Header Reord 0 SOAC Header ID C 8 #!Head: fixed 8 C Blank 9 File Classifiation C 8 SOOBDF fixed 7 C Blank 8 File Creation Date C 0 Mahine date when the file is reated YYYY-MM-DD format UTC) 28 C Blank 29 File Creation Time C Mahine time when the file is reated 8 hh:mm:ss format UTC) 37 C Blank 38 Data Blok Length C File size without SOAC Header 2 ZZZZZZZZZZZ9 format byte) 50 C Blank C 5 Spaeraft ID 2 34 : Main 35 : Rstar 36 : Vstar 53 C Blank 54 Spaeraft Name C 6 SELENE-M : Main SELENE-R : Rstar SELENE-V : VstarS 70 C Blank 7 Storage Start Date C 0 YYYY-MM-DD format UTC) 8 C Blank 82 Storage Start Time C 8 hh:mm:ss format UTC) 90 C Blank 9 Storage End Date C 0 YYYY-MM-DD format UTC) 0 C Blank 02 Storage End Time C 8 hh:mm:ss format UTC) 0 C Blank Station Name C 8 OKN : Okinawa Traking and Communiation Station KTU : Katsuura Traking and Communiation Station MSD : Masuda Traking and Communiation Station SNT : Santiago Traking and Communiation Station PRT : Perth Traking and Communiation Station MSP : Maspalomas Traking and Communiation Station KRN : Kiruna Traking and Communiation Station KSC34 : Uhinoura Spae Center UDSC64 : Usuda Deep Spae Center 9 C Blank 20 Data Type Name C 8 RA2 : 2-Way Range DP2 : 2-Way Doppler SDP4 : 4-Way Doppler Rstar) 28 Line Feed Code C 0x0A 3

4 5) Appendix A N/A 4

5 2 OBSERVATION DATA FILE OBDF) ) GENERAL The OBDF ontains engineering data of range and Doppler measurements. 2) FILE SPECIFICATION The OBDF is desribed in Table 2-. Table 2-. OBDF speifiation Item Content File Identifiation File Type File Format Reord Length Maximum Number of Reords Data File Creator Observation Data File OBDF) Files reated for eah spaeraft/station/data type Text file Charater Code = ASCII) Variable length End of eah reord is Line Feed Code.) File Control Information Reord: 25 byte, 36 byte Pass Control Information Reord: 37 byte, 37 byte), 29 byte, 3 byte, 25 byte, 22 byte, 22 byte, 44 byte, 44 byte Preproessing Information Reord: 43 byte, 43 byte, 27 byte, 27 byte, 44 byte, 26 byte Observation Data Information Reord: 92 byte N/A Engineering data of range and Doppler measurements Orbit Determination Sub-System / Format Conversion Program from data obtained by ISAS ground-stations Orbit Determination Sub-System / Format Conversion Program from data obtained by GN ground-stations Note 5

6 3) FILE STRUCTURE Table 2-2. OBDF struture Blok Reord Item Detailed Desription File Control Blok Pass Control Information Preproessing Information Observation Data Information File Control Information Reord Pass Control Information Reord Preproessing Information Reord Observation Data Information Reord # Observation Data Information Reord #n File Classifiation, File Creation Date and Time Table 2-3 Spaeraft Name,Station Name, Pass ID, Data Type, Uplink Band, Downlink Band, Referene Frequeny, Station Delay Data Start/End Time, Number of Stored Data, Number of Rejeted Data, modulo-m, Count Interval Time Tag, Observation Data, Azimuth Angle at Observation, Elevation Angle at Observation, Temperature at Observation, Relative Humidity at Observation, Pressure at Observation Repeat of Observation Data Information for the number of data) Time Tag, Observation Data, Azimuth Angle at Observation, Elevation Angle at Observation, Temperature at Observation, Relative Humidity at Observation, Pressure at Observation Table 2-4 Table 2-5 Table 2-6 4) RECORD Detailed Desriptions of Reords in the OBDF are provided in Tables 2-3, 2-4, 2-5, and 2-6. [Convention] : Spae 9999 : Number with zero padding ex., 000 ). ZZZ9 : Number without zero padding ex., ). S : Sign positive: +, negative: - ). s : Sign positive:spae, negative: - ). PE22.5 form: s es99 form. To maintain 6-digit preision, integer in the base shall not be zero.) Ex., E-02 shall not be expressed as E-0. Table 2-3. File Control Information Reord File OBDF File Control Information Reord 0 File Classifiation Label C 20 file_name = format 20 File Classifiation C 4 OBDF fixed 24 Line Feed Code C 0x0A File OBDF File Control Information Reord 0 File Creation Date and Time Label C 20 file_reate = format 20 File Creation Date and Time C 5 yyyymmdd hhmmss format 35 Line Feed Code C 0x0A 6

7 Table 2-4. Pass Control Information Reord File OBDF Pass Control Information Reord 0 Spaeraft Name Label C 20 spaeraft_name = format 20 Spaeraft Name C 6 36 Line Feed Code C 0x0A SELENE-M SELENE-R Note ) SELENE-V Left justifiation File OBDF Pass Control Information Reord 0 2nd Spaeraft Name Label C 20 spaeraft_name_2nd= format 20 2nd Spaeraft Name C 6 SELENE-M Note 2) Left justifiation 36 Line Feed Code C 0x0A File OBDF Pass Control Information Reord 0 Station Name Label C 20 station_name = format 20 Station Name C 8 28 Line Feed Code C 0x0A OKN : Okinawa Traking and Communiation Station KTU : Katsuura Traking and Communiation Station MSD : Masuda Traking and Communiation Station SNT : Santiago Traking and Communiation Station PRT : Perth Traking and Communiation Station MSP : Maspalomas Traking and Communiation Station KRN : Kiruna Traking and Communiation Station KSC34 : Uhinoura Spae Center UDSC64 : Usuda Deep Spae Center Left justifiation File OBDF Pass Control Information Reord 0 Pass ID Label C 20 pass_id = format 20 Pass ID C 0 yymmddnnmm format nn: Visible pass number of the day mm: Division number Default = 00) 30 Line Feed Code C 0x0A File OBDF Pass Control Information Reord 0 Data Type Label C 20 data_type_name = format 20 Data Type C 4 RA2 : 2-Way Range DP2 : 2-Way Doppler SDP4 : 4-Way Doppler Rstar) 24 Line Feed Code C 0x0A 7

8 File OBDF Pass Control Information Reord 0 Uplink Band Label C 20 uplink_band = format 20 Uplink Band C S : S band 2 Line Feed Code C 0x0A File OBDF Pass Control Information Reord 0 Downlink Band Label C 20 downlink_band = format 20 Downlink Band C S : S-band X : X-band 2 Line Feed Code C 0x0A File OBDF Pass Control Information Reord 0 Referene Frequeny Label C 20 standard_freq = format 20 Referene Frequeny C E+2 Hz) 43 Line Feed Code C 0x0A File OBDF Pass Control Information Reord 0 Station Delay Label C 20 station_delay = format 20 Station Delay C E+2 Appliable if Data Type is RA2 and orretion seond) is required; otherwise Line Feed Code C 0x0A Note ) If Data Type is SDP4, this reord is fixed to be SELENE-R. Note 2) If Data Type is SDP4, this reord is fixed to be SELENE-M. Otherwise this reord is blank. 8

9 Table 2-5. Preproessing Information Reord File OBDF Preproessing Information Reord 0 Data Start Time Label C 20 data_start = format 20 Data Start Time C 22 yyyymmdd hhmmss.ssssss format 42 Line Feed Code C 0x0A File OBDF Preproessing Information Reord 0 Data End Time Label C 20 data_end = format 20 Data End Time C 22 yyyymmdd hhmmss.ssssss format 42 Line Feed Code C 0x0A File OBDF Preproessing Information Reord 0 Number of Stored Data Label C 20 stored_data_no = format 20 Number of Stored Data C format 26 Line Feed Code C 0x0A File OBDF Preproessing Information Reord 0 Number of Rejeted Data Label C 20 rejeted_data_no = format 20 Number of Rejeted Data C format Note 3) 26 Line Feed Code C 0x0A File OBDF Preproessing Information Reord 0 modulo-m Label C 20 modulo_m = format 20 modulo-m C E+2 format 43 Line Feed Code C 0x0A File OBDF Preproessing Information Reord 0 Count Interval Label C 20 t = format 20 Count Interval C format For Doppler data, ount interval in seonds is multiplied by 00; otherwise '00000'. 25 Line Feed Code C 0x0A Note 3) Rejeted data have already been removed from the file. 9

10 Table 2-6. Observation Data Information File OBDF Observation Data Information 0 Time Tag C 22 yyyymmdd hhmmss.ssssss format UTC) 22 C Blank 23 Observation Data C E+2 format See Appendix B [Traking Data Format] 46 C Blank 47 Azimuth Angle at Observation C format degrees) 55 C Blank 56 Elevation Angle at Observation C format degrees) 63 C Blank 64 Temperature at Observation C format C) 72 C Blank 73 Relative Humidity at Observation C format %) 8 C Blank 82 Pressure at Observation C format mb) 9 Line Feed Code C 0x0A 0

11 5) Appendix B [Traking Data Format] # UTC time tag. datase,hz,rad) Azdeg), Eldeg),tempC), humid%),pressmb) # yyyymmdd hhmmss.ssssss E Observation Data Angle Data, Weather Data For 2-way range se) Azdeg), Eldeg), tempc), humid%), pressmb) For 2-way Doppler Hz) Azdeg), Eldeg), tempc), humid%), pressmb) For 4-way Doppler Hz) Azdeg), Eldeg), tempc), humid%), pressmb) *) Data Blok length is fixed to be 92 byte for reord. The last byte has to be Line Feed LF). **) The time-tag, tt, on the data file refers to the mid-interval value of the ount interval T of the data file. If ta is the start and tb the end of the ount interval, then and tb - ta = T tt = tb + ta ) / 2. The observation value as given on the file is omputed from Doppler ount values ID as IDtb) - IDta) ) / T ***) Weather data are listed, but are not measured every seond. And they are available only for UDSC64 data. [2-way and 4-way Data Conversion] For proessing SELENE traking data, for example, further averaging 2-way data or onverting from frequeny into range rate, anillary information about onboard instruments and transmitter at ground station is required. See Iwata et al. 200) and Namiki et al. 200) for details of instrumental design and estimated auraies of the observation. As for omputational algorithm, see an attahed doument by Goossens. When using the four-way data, the following should be taken into aount. There is a bias frequeny involved: bias frequeny= F REF - K2 + K5 * K6 ) * f sent, with F REF = MHz. And with this, the full observable beomes 4-way range rate = 0.5 * average frequeny - bias frequeny ) * / K5 * K6 * f sent ) Note that the fator 0.5 is inluded to make the distintion between round-trip measurements, and "one leg" measurements. See the attahed doument by Goossens for turn-around ratios, K2, K5, and K6. Referene frequeny, f sent, is given in the SOOBDF Table 2-4). Goossens, S., Doppler data proessing for orbit determination, 20. Iwata, T., M. Takahashi, N. Namiki, H. Hanada, N. Kawano, K., Heki, K. Matsumoto, and T. Takano, Mission Instruments for Lunar Gravity Measurements using SELENE Sub- satellites, J. Geod. So. Japan., 47, , 200. Namiki, N., T. Iwata, N. Kawano, F. Fuke, N. Tateno, K. Asari, H. Noda, Y. Kono, H. Hanada, Y. Yahagi, Z. Yamamoto, K. Tanaka, M. Yamada, K. Matsumoto, S. Goossens, Ground ompatibility tests for gravity measurement of SELENE: Auraies of two- and four-way Doppler and range measurements, Spae Si. Rev., 54, 03 2, doi:0.007/s , 200.

12 Doppler data proessing for orbit determination Sander Goossens Abstrat This brief report desribes some basis about Doppler data proessing for the purpose of orbit determination. The goal is to write down the formulation for the speifi 4-way link for the SELENE measurement. This an then be used when loading the data into GEODYN. The start is a reap of a 2-way data link, whih an serve as the basis for the 4-way link. Two-way Doppler In a non-relativisti formulation, the observed frequeny is expressed as: f obs = v ) f sent ) with f obs the observed frequeny, f sent the transmitted frequeny at the station, v the line-of-sight veloity, and the speed of light. In a relativisti formulation, the fator /γ needs to be added, with γ = v/) 2. It is assumed here that v. For a two-way link, there is usually a turn-around ratio T at the satellite to prevent interferene from the upand downlinks. This ratio is inluded here. In order to onstrut the reeived frequeny f r as a funtion from the transmitted frequeny f t at the station, the signal is traed bak. Firstly, the reeived frequeny depends on the frequeny as transmitted by the satellite, f sent, sat, aording to equation ): f r = v 2 ) f sent, sat 2) with v 2 the line-of-sight veloity for the downlink. However, the frequeny of the signal sent at the satellite, equals the observed frequeny at the satellite, times the turn-around ratio T : f sent, sat = Tf obs, sat 3) The observed satellite frequeny itself is Doppler shifted, aording to f obs, sat = v ) f t 4) with v the line-of-sight veloity for the uplink, and f t the transmitted frequeny at the station. Combining all these equations together yields: f r = v ) 2 T v ) f t 5) This an be simplified, when it is taken into aount that v = v 2 = v the delay at the spaeraft is negleted here, and in any ase, it is assumed that the signals are re-transmitted bak to the station almost instantaneously), and that quadrati terms v/) 2 an be negleted, sine it is assumed that v non-relativisti formulation). This then leads to a well-known formula: f r = 2 v ) Tf t 6) In general, the reeived frequeny is not measured diretly, but instead, zero-rossings of the reeived frequeny ompared with a referene frequeny f ref are. These are integrated along a ertain time interval t 2 t = T, the ount interval. This then leads to a Doppler ount, from whih the average range-rate an be determined. This is used in GEODYN as an observable. The Doppler ount N is defined as e.g. Montenbruk and Gill [2000]): N = t2 t f r f ref ) dt 7) Using equation 6) for the reeived frequeny, remembering that t 2 t = T, and assuming a onstant transmitter frequeny and referene frequeny, this an be written as N = t2 t 2 vt) )Tf t dt T f ref 8) The average range rate is defined as v = /T ) t 2 t vt)dt, so the above equation an also be written as: { v } N = Tf t T 2T T f ref 9)

13 In the ase that f ref = Tf t, this an be simplified further, and the onstant term Tf t T T f ref drops out. This then finally yields for the average range-rate v: v = N 0) 2 Tf t T whih equals equation 6.9) of Montenbruk and Gill [2000]. 2 Four-way Doppler In the ase of SELENE, there is an extra link between two satellites, the main satellite and the relay satellite. This ompliates the measurement link somewhat, as there are also different turn-around ratios in the satellites. The final downlink is also a mix of a reeived signal from the relay satellite and the station uplink. The measurement senario is first desribed, and then the measurement link is worked out, following the 2-way Doppler approah. 2. Measurement link In the SELENE senario, a transmitter frequeny is sent to the relay satellite. This is an S-band signal. This signal is then forwarded to the main satellite, after a multipliation using the fator K 5 = This signal is then retransmitted bak from the main satellite to the relay satellite, with a multipliation fator of K 6 = This signal is reeived in the relay satellite, and mixed with K2 times the original reeived frequeny, with K 2 = This results in the last link from the 4-way measurement being in the X-band instead of in the S-band. Apart from that, a normal 2-way link is also inluded, with the standard turn-around ratio of K = for S-band signals. 2.2 Modelling the 4-way observable The signal is again traed bak as was done for the 2-way model. For eah leg, a veloity will be defined, aording to figure. Figure. The SELENE 4-way measurement links and veloities definitions The station transmits again at a frequeny f t. In the relay satellite the traking satellite), this link is reeived at a Doppler shifted frequeny f 3 : f 3 = v ) f t ) with v the veloity of the the relay satellite with respet to the station on the uplink. Now working bakwards along the signal path, the reeived frequeny at the station f r is reeived at a Doppler shifted frequeny, depending on the signal as broadast finally from the relay satellite: f r = v ) 4 f sent, relay-to-station 2) with v 4 the veloity of the relay satellite with respet to the station on the final leg. Thus, v and v 4 onstitute a two-way link, as they don t onern the traking of the main satellite. For now, all veloities are written separately, and it is not neessarily assumed that v = v 4 as was done in the two-way ase), as there is some time in between these veloities, namely, the time it takes the signal to go from the relay satellite to the main satellite and bak. Aording to the lay-out of the SELENE measurement, on-board the relay satellite, the inoming signal from the main satellite the traked satellite) is mixed with f 3, and then it is sent to the station as f sent, relay-to-station : f sent, relay-to-station = K 2 f 3 + f reeived, relay-from-main 3) With the expression for f 3 as given in equation ), this beomes f sent, relay-to-station = K 2 v ) f t + f reeived, relay-from-main 4) Working bakwards again along the signal path, the frequeny f reeived, relay-from-main arrives, Doppler shifted, from the main satellite, and an be expressed as: f reeived, relay-from-main = v ) 3 f main, sent 5) 2

14 with v 3 the veloity between the main and the relay satellite, on the downlink from the main satellite to the relay satellite. For the main satellite, there is a turn-around ratio K 6 suh that f main, sent = K 6 f main, reeived 6) The reeived frequeny at the main satellite finally is again Doppler shifted and omes from the relay satellite: f main, reeived = v ) 2 f relay, sent-to-main 7) with v 2 the veloity between main and relay satellite on the uplink between them. The signal as sent by the relay satellite to the main satellite, finally, is given aording to f relay, sent-to-main = K 5 f 3 = K 5 v ) f t 8) Now, all frequenies an be traed bak to the initial, transmitted frequeny, by subsequently olleting the above equations, and bak-substituting them. This then yields for the reeived frequeny: f r = v ) 4 {K 2 v ) f t + v ) 3 K 6 v ) 2 K 5 v The above equation an be expanded, and quadrati and higher order terms of v/ are negleted, due to the assumption v. This then yields f r = {K 2 v v ) 4 + K 5 K 6 v v 2 v 3 v )} 4 f t 20) Equation 20) is ready to be used in the formula for the Doppler ount N as given in the setion dealing with the two-way data, equation 7). The referene frequeny is briefly left out of the disussion now, so that the fous will be on the integral t 2 t f r dt, with again t 2 t = T, the ount interval. Integrals of veloities give an average range rate aording to v i = t2 v i t) dt 2) T t For now, they are not grouped together, as was done for the two-way signal. Instead, eah leg is left apart, so that the final result an be ompared diretly with the way that the 4-way observable is defined in GEODYN. Expanding the integral over the reeived frequeny f r, and taking into aount the definition of the average range-rates for the separate legs aording to equation 2), the integral beomes: t2 v f r dt = K 2 + K 5 K 6 )f t T K 2 T f t t K v 4 v 2T f t K 5K 6 T f t + v 2 + v 3 + v ) 4 22) This equation an be leaned up for now, if it is assumed that the referene frequeny against whih the reeived frequeny is beat, equals K 2 + K 5 K 6 )f t, similar as in the two-way ase. In this ase, the onstants drop out of the equation again. This isn t ompletely neessary; they an be maintained, but a bias would be added or subtrated) from the Doppler ount variable N. For brevity and larity, this is assumed for now. This then yields the following formula: ) f t } v + v 2 + v 3 + v 4 ) + K 2 K 5 K 6 v + v 4 ) = K 5 K 6 N T f t 23) This is the observation equation for the 4-way Doppler observable, expressed in the ount interval T, the transmitted frequeny f t and the several turn-around ratios. Namely, aording to the GEODYN manual, the 4-way satellite-to-satellite relay Doppler measurement is expressed as being omputed along the lines of [Rowlands et al., 995]) T3 S3 S S2 T2 + SF T2 S2 T2) In the ase of SELENE, S3 = S2 and T3 = T2, and that means that the above measurement link mathes the sequene as given in equation 23). This also shows readily whih value to use for the sale fator SF: 9) SF = K 2 K 5 K 6 24) In the ase of SELENE, using the values for K 2, K 5 and K 6, the sale fator beomes SF = Equations 23) and 24) an thus be readily used when pre-proessing the data, making them suitable for importing into GEODYN. These equations an also be used when transforming frequeny values to metri values, for the use in GEODYN. Referenes Montenbruk, O., and E. Gill 2000), Satellite Orbits, Springer, Heidelberg. Rowlands, D., J.A. Marshall, J. MCarthy, D. Moore, D. Pavlis, S. Rowton, S. Luthke, and L. Tsaoussi 995), GEODYN II system desription, Vols. -5, Contrator report, Hughes STX Corp., Greenbelt, MD. 3