Cassini Mission. Cassini Spacecra.

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2 Cassini Mission Lunch on 1997, OCT 15th Saturn rbit inser8on on 2004, JUL, 1st 11- years nominal mission (ended on June 2008 ) XM up to september 2010 XXM up to 2017 Mission ends with crash into Saturn athmosphere Cassini Spacecra. Lunch mass: 5574 kg SOI mass: 2800 kg height = 6,7m antenna diameter: 4m Mag boom: 11m 3 RTGs up to 13kW Main Engine= 2x445N

3 Titan R = 2575 Km a = km e = T = 16day Nominal: 76 orbits, 45 Titan Flbys XXM: 155 orbits, 54 Titan flybys

4 T33 h C/A = 1932 km Lat C/A = 8 Lon C/A = 297 T11 h C/A = 1812 km Lat C/A = Lon C/A = 110 T74 h C/A = 3650 km Lat C/A = 1 Lon C/A = 245 T22 h C/A = 1297 km Lat C/A = 41 Lon C/A = 338 T45 h C/A = 1613 km Lat C/A = 44 Lon C/A = 197 T68 h C/A = 1397 km Lat C/A = - 49 Lon C/A = 119 July 2011 Titan Surface Workshop - Caltech

5 Orbit Determina5on Program JPL so]ware for naviga8on of interplanetary missions Unix library of programs for orbit determina8on about 2 milion lines of fortran code, > 100 man- years Main models: Integra8on of rela8vis8c n- body problem Light- 8me solu8on Newtonian gravity and rela8vis8c correc8ons 8dal perturba8ons of the planet Solar radia8on pressure and torque planetary radia8on pressure (albedo and infrared emission) S/C anysotropic thermal emission Istantanous and finite burns Other type of accelera8ons: Periodic exponen8al sthocas8c

6 Ø Orbit determian5on is an itera5ve process Planetary and satellite ephemerides Trajectory integra5on Deep Space Network State transi8on matrix Observed observables Calibra5ons Dynamic model Ini8al state Final model update: Solu8on vector and covariance matrix Residuals and par5al deriva5ves OBS COMP EOP Planets and satellites gravity S/C components, ajtude and manuvers Differen5al correc5on: model parameters and state vector New itera5on Least squares filtering: Converge? Residuals

7 Ø PART 1: Defini5on of input files: export EOP_DIR="$HOME/EOP" export EOP_NL="$EOP_DIR/21MAY2005_22MAY.eop" export EOP="eop.nio export GIN_LOCK="$INP/GIN/ginlock.nio" export GIN_NL="$INP/GIN/gin_es5m.nl export PEFILE="$EPH/pe_DE421_29JUL1899_09OCT2053.nio" export PPFILE="$EPH/pp_DE414_30DEC1914_02JAN2050.nio" export SAT6="$EPH/se_SAT303_02JAN2004_06DEC2008.nio export CSP="$INP/CSP" export CSP1="$CSP/amc.csp" export CSP2="$CSP/edit.csp" export CSP3="$CSP/weights.csp export ATT_FILE="$INP/GIN/aJtude.nio export ODF="$INP/ODF/odf.nio export SIGMA_NL="$INP/SIGMA/sigma.nl" Earth Orienta5on Parameters Model parameters Ephemerides and Ephemerides par5als Obervables edi5ng: - selec5on - calibra5ons - weights S/C ajtude Observed observables Filter namelist

8 Ø PART 2: Itera5on process: FOR EACH ITERATION: #eop: eop2nio $EOP_NL $EOP #ginupdate ginupdate +LPARAM 16 $GIN_NL gin.nio $PEFILE #translate translate gin.nio csp.nio csp_all.txt #pvdrive pvdrive pv.nio gin.nio $PEFILE "" $ATT_FILE #twist twist pv.nio "" gin.nio $PEFILE #regres regres $ODF regres.nio pv.nio csp.nio gin.nio $PEFILE $PPFILE $SAT6 " #sigma sigma - nml $SIGMA_NL \ - reg regres.nio \ - pv pv.nio \ - ss smosol.nio \ - iapcov apcov_in.nio \ - apcov apcov_out.nio \ - sol sol.nio \ - sri sri.nio sh ud2cov.x sol.nio SOL Get EOP from IERS input Update model with ini5al state ( or from previous itera5on ) Generate data calibra5on and edi5ng file Integrate trajectory and compute par5al deriva5ves of S/C state vector w.r.t solve- for parameters Print trajectory (cartesian and oscula5ng elements at user selected 5mes) Compute residual and par5al deriva5ves of the observables with respect of the solve- for parameters Least squares filtering Print covariance and correla5on matrices

9 Structure of Orbit Data File (ODF) ORBIT DATA RECORD NUMBER = 7 TIMETAG = 27-FEB- 03:08: DTYPE = 12 DNLINK= 5 NET = 0 TRANS = 25 RCVR1 = 25 RCVR2 = 0 SC = 82 QUASAR= 0 LOCOMP= 0 HICOMP= 0 CAMERA= 0 UPLINK= 2 CHANEL= 0 WBMODE= 0 MODFLG= 0 SOBJSG= 0 SOBJID= 0 VALID = 0 PICTUR= 0 UPRCVR= 2 RERAMP= 1 VLBIFG= 0 RFQTYP= 1 DPLCNL= 7 ODFMT = 4 TIMTAG= E+08 OBSVBL= E+02 FREQCY= E+09 CMPTIM= E+01 MOD = 0.0 TA4RNG= 0.0 TB4RNG= 0.0 DDELAY= E-05 TRAXAZ= 0.0 UDELAY= E-05 RECORD NUMBER = 8 TIMETAG = 27-FEB- 03:09: DTYPE = 12 DNLINK= 2 NET = 0 TRANS = 25 RCVR1 = 25 RCVR2 = 0 SC = 82 QUASAR= 0 LOCOMP= 0 HICOMP= 0 CAMERA= 0 UPLINK= 2 CHANEL= 0 WBMODE= 0 MODFLG= 0 SOBJSG= 0 SOBJID= 0 VALID = 0 PICTUR= 0 UPRCVR= 2 RERAMP= 1 VLBIFG= 0 RFQTYP= 1 DPLCNL= 8 ODFMT = 4 TIMTAG= E+08 OBSVBL= E+02 FREQCY= E+09 CMPTIM= E+01 MOD = 0.0 TA4RNG= 0.0 TB4RNG= 0.0 DDELAY= E TRAXAZ= 0.0 UDELAY= E-05 OBSVBL = K * FREQCY - FSKY

10 DSS way DSS way Closest approach DSS way DSS way

11 Structure of Orbit Data File (ODF) RAMPS / STATION25 TYPE=D MAXLEN= 4 NRECS= 85 RANDOM=T 1 1 ** D D D D ** D D D D ** D D D D ** D D D+10 T_start (J2000) T_end (J2000) Start_frequency Frequency rate ORBIT FEB-//03:11: FEB-//03:12: FEB-//03:12: FEB-//03:13: FEB-//03:13: FEB-//03:14: FEB-//03:14: FEB-//03:15: FEB-//03:15: FEB-//03:16: FEB-//03:16: FEB-//03:17: FEB-//03:17: FEB-//03:18:08.5 Time (J2000) Sky frequency (X/Ka) Reference freq. Ancillary data.

12 Ø EXAMPLE : filter output Prefit SOS = E+08 Posnit SOS = E+03 Condi8on Number = E+05 Sum Of Squares SOS =!z T N z o c k " z k W!z = # $ N! 2 = N 2! k! 2 k=1 ( ) 2 *************************************************************************************** Name A priori Apriori Apriori Terminal Consider Delta Corrected Value Solu8on Sigma Solu8on Sigma Solu8on Nominal Epoch State Parameters: ( 6 ) X E E E E E E+04 Y E E E E E E+05 Z E E E E E E+04 DX E E E E E E+00 DY E E E E E E+00 DZ E E E E E E- 01 Constant Bias Parameters: ( 12 ) 606J E E E E E E C E E E E E S E E E E E C E E E E E E- 06

13 Radio science gravity experiment: Equatorial flyby Epoch: 27- Feb- 8:25:19 UTC Radius ~ 2575 km Al8tude ~ 1813 km SEP 147 i=180

14 Titan 11 flyby: Doppler residuals N points: 1136 µ 60s : e-04 60s : e-03 RMS 60s : e-03 T c : 300 s. 60 s. 10 s. C/A DSS X/X data s Hz DSS X/Ka data 60 s DSS DOY

15 Titan 11 flyby: case study Example: covariance matrix of Cassini posi8on at CA {r, H r, H} reference frame! H!r " 0.8 m V CA " 5.87 km/s! T! 0.13 ms! # P = # # " 4.30E E E E E E E E E-05 $ & & & % H 4387 km not in scale! r

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17 Cassini interplanetary phase experiments q In the early phase of the mission and for R<2.7 AU, the 4m HGA was continuously pointed to the Sun, acting as a heat shield and ensuring safety of bus instrumentation q Communications with ground were ensured by two LGAs q Attitude controlled by thrusters Use of LGA and thruster firings denied accurate measurements of non-gravitational accelerations before Jupiter encounter (2000)

18 Cassini s non- gravita8onal accelera8ons Except for orbital maneuvers, the two leading nongravitational accelerations are: q RTG s anisotropic thermal emission q Solar radiation pressure During three cruise radio science experiments (two solar opposition and a solar conjunction) the two accelerations were nearly aligned: a a RTG SP A M km s km s = 6 Their high correlation (0.96) makes impossible to separate the two accelerations with radio metric data. Disentangling the two effects is further complicated by variations of HGA thermo-optical coefficients. HGA thermo-optical properties have been inferred by temperature readings of two sensors mounted on the HGA back side m 2 kg

19 RTG s accelera8on The three on-board RTGs provide power through the natural radioactive decay of Pu 238 (half life = years - almost constant emission during time span considered). P = amc; P =13 kw; M=4600 kg r = ( A Zˆ β = R M R M R * 10 + s A X Xˆ * + A Yˆ Y * ) e βδt ratio of the spacecraft mass at injection to current mass

20 Solar pressure accelera8on Thermal Equilibrium Infinite thermal conduc8vity α spec value=0.15 ε = αφ 4 σt Thermal emission proper8es are mostly unaffected by radia8on and outgassing α = εσt Φ 4 Specular reflec8vity neglected Lamber8an diffuse reflec8vity SOI F SP ( 5 2α ) A 3 Source: S.C. Clark (JPL)