Sapienza  University  of  Rome       The  largest  European  university,  with  a  variety     of  curricula  in  many  fields.       Department  of  Mechanical  and  Aerospace  Engineering     >65  professors  and  staff  researchers,  >60  PhD  students   and  research  assistants.       Research  acCviCes  in  space  systems,  aerospace  structures,     propulsion,  flight  mechanics  and  fluidodynamics. EducaNon  and  Degrees   -­‐  F        A  E     IRST LEVEL DEGREE IN EROSPACE NGINEERING -­‐  SECOND  LEVEL  DEGREE  IN  SPACE  ENGINEERING   -­‐  SECOND  LEVEL  DEGREE  IN  AERONAUTICAL  ENGINEERING   -­‐  M      S    O  P   ASTER COURSE IN ATELLITES AND RBITING LATFORMS -­‐  M      S  T  S   ASTER COURSE IN PACE RANSPORTATION YSTEMS -­‐  P D      S    A  T   H PROGRAM IN PACE AND ERONAUTICAL ECHNOLOGIES -­‐  >  1500     STUDENTS -­‐  M              E   ANY SECOND LEVEL COURSES ARE TAUGHT IN NGLISH -­‐  M    P D        E   ASTER AND H COURSES TAUGHT IN NGLISH                                      hFp://www.ingaero.uniroma1.it/ Outline  of  seminars   Tuesday morning 1) Deep Space Navigation Systems: Where do we stand? 2) The European Delta-DOR correlator Tuesday afternoon 3) Bepicolombo: The ESA mission to Mercury; Mercury Orbiter Radio science Experiment (MORE) Wednesday morning: 4) The scientific use of deep space tracking systems Wednesday afternoon: 5) Radio science in deep space missions D  S  T  S   EEP PACE RACKING YSTEMS       ?   WHERE DO WE STAND   L  I       UCIANO ESS D .             EPT OF MECHANICAL AND AEROSPACE ENGINEERING   U  L  S NIVERSITÀ A APIENZA BITTT  -­‐  29/01/2013 Outline  –  Seminar  1   -­‐  O             S   VERVIEW OF DEEP SPACE TRACKING SYSTEM -­‐  O :   ,     ,  ΔDOR   BSERVABLES RANGE RANGE RATE -­‐  C   :           URRENT ACCURACIES EXAMPLES FROM PAST MISSIONS -­‐  E              ΔDOR   RROR BUDGET FOR RADIO METRIC OBSERVABLES AND -­‐  R     :        10       OADMAP FOR IMPROVEMENTS HOW TO DO TIMES BETTER The  History  of  Deep  Space  NavigaNon  Accuracy     6 Basic  concepts State of a dynamical system: the set of parameters required to predict the future motion of the system. For OD, the minimal set are (r,v) at a given time. Dynamical model: the dynamical laws governing the evolution of a system in time The dynamical state is almost never directly measurable. One uses measurements linked in some way to the dynamical state, such as range, range-rate, angles, etc. When an estimate of the trajectory is obtained, the orbit can be predicted using the dynamical model. The predicted values differ from the true ones because of: Basic  concepts   •  Errors or inadequacy of the dynamical model •  Measurement noise, limiting the accuracies of the observations •  Errors in the numerical procedure (including truncation and roundoff errors) As a consequence the state determination must be repeated. It is virtually impossible to propagate the state of a spacecraft for very long times without incurring in serious discrepancies. The time interval between updates depends on the accuracy of the dynamical model, the quality of the observations, and the needs of the user. In this seminar I will focus on item 2 and 3 (measurement noise and numerical noise). DifferenNal  correcNons   Accelerometer Radio Tracking readings Dynamical Computed Observed model observables observables - Observation model Residuals NO Differential corrections Cost function at a of parameters and state local minimum? YES Updated state vector and dynamical model, estimation errors Measurements   Good  results  start  from  good  data   •  For  interplanetary  missions,  the  following  measurements  are  used   •   Doppler  -­‐frequency  shiR  in  the  carrier    -­‐    measures  the  range  rate  from  the   ground  antenna  to  the  spacecraR  antenna     •   Cassini  used  X  and  Ka  band  with  accuracies  up  to  0.5  mm/sec  (1s   integraCon  Cme);  best  results:  0.001  mm/s  (Cassini  radio  science,  1000  s)   •   Since  the  Earthʼs  moCon  affects  the  range  rate,  informaCon  on  the  right   ascension  and  declinaCon  can  be  obtained.   •   Accuracy  depends  up  the  stability  of  the  ground  reference  signal  (clock),   spacecraR  down  link  is  coherently  locked  to  the  uplink  signal.   •   Range  -­‐  Measurement  of  the  round  trip  light  Cme   •   Range  typical  accuracy  of  1  meters  (1s)  -­‐    subject  to  long  term,  systemaCc   effects