T - Sapienza

93 Pages·2013·6.87 MB·English

by  Luciano I.

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