RENDEZVOUS AND DOCKING OF SPACECRAFT -...
Transcript of RENDEZVOUS AND DOCKING OF SPACECRAFT -...
RENDEZVOUS AND DOCKING OFSPACECRAFT
1. INTRODUCTION TO RENDEZVOUS & CAPTURE IN SPACE
2. VERIFICATION PRIOR TO FLIGHT, CONCEPTS & TOOLS
By
Wigbert Fehse
Tutorial Lectures on LEO & GEO Rendezvous at the 4th ICATT, Madrid 2010
This course is based to a large extent on the book’Automated Rendezvous and Docking of Spacecraft’,published by Cambridge University Press(ISBN: 0521824923).
No part of this lecture must be copied or used in any formwithout stating the source.
1
WHERE DO WE NEED RENDEZVOUS, CAPTURE AND
COUPLING IN SPACE?
RENDEZVOUS, CAPTURE AND COUPLING IN SPACE WILL BE REQUIREDIN MOST SCENARIOS WHERE MORE THAN ONE SPACECRAFTIS INVOLVED, e.g.:
• ASSEMBLY OF STRUCTURES IN ORBIT,
• SERVICING OF SPACECRAFT, i.e. SUPPLY WITH CONSUMABLES,EXPERIMENTS AND OTHER GOODS,
• TRANSPORT OF CREW & GOODS TO / FROM A MANNED SPACESTATION,
• LANDING ON CELESTIAL BODIES AND RETURN TO EARTHOF (UN)/MANNED SPACECRAFT.
WITHIN THE FRAME OF THIS LECTURE WE WILLCONCENTRATE ON APPLICATION OF RENDEZVOUS & CAPTUREIN LOW- AND GEOSTATIONARY EARTH ORBITS (LEO & GEO).
Dr. W. Fehse — Introduction to RVD — Where is RVD needed — Version 2009
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PART 1: INTRODUCTION TO RENDEZVOUS & DOCKING
THE MOST IMPORTANT QUESTIONS TO BE
ANSWERED
1. WHAT ARE THE TASKS, WHAT IS THE SCENARIO, WHO ARE THEMAJOR PLAYERS IN A RENDEZVOUS MISSION ?
2. HOW DOES THE APPROACHING VEHICLE GET FROM GROUNDTO THE TARGET ?
3. WHAT ARE THE MAIN ISSUES OF CAPTURE IN SPACE ?
4. WHICH FUNCTIONS MUST BE AVAILABLE ABOARD TO DO ITAUTOMATICALLY (LEO) ?
5. WHAT IS THE ROLE OF MAN IN THE AUTOMATIC RENDEZVOUSPROCESS (LEO)?
6. WHAT ARE THE MAIN ISSUES OF RENDEZVOUS & CAPTURE IN GEO ?
Dr. W. Fehse – Introduction to RVD – Tasks, Scenario, Players – Version 2009
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THE TASK
A VEHICLE SHALL MEET IN ORBIT ANOTHER VEHICLEAND CONNECT TO IT.
BOTH VEHICLES MUST HAVE AT THE SAME TIMEWITHIN CLOSE TOLERANCES:
• THE SAME POSITION
• THE SAME VELOCITY VECTOR
• A PARTICULAR ATTITUDE RELATIVE TO EACH OTHER
ONLY UNDER THOSE CONDITIONS COUPLING CAN BE PERFORMED.
Dr. W. Fehse – Introduction to RVD – Tasks, Scenario, Players – Version 2009
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THE SCENARIO IN LEO
THE LEO SCENARIO, IN WHICH THE AUTOMATIC RVD TAKES PLACE,CONSISTS OF THE FOLLOWING ELEMENTS:
• A MANNED SPACE STATION IN LOW EARTH ORBIT,
• MANNED SPACECRAFT, WHICH REGULARLY BRING CREW FROMGROUND TO THE STATION AND BACK,
• UNMANNED TRANSPORT VEHICLES, WHICH SUPPLY THE STATIONWITH CONSUMABLES AND PAYLOAD,
• GROUND CONTROL CENTRES, WHICH MONITOR AND GUIDE THEFLIGHT OF THE APPROACHING VEHICLE AND OF THE STATION,
• RELATED INFRASTRUCTURES FOR COMMUNICATION BETWEENGROUND STATIONS AND SPACECRAFT AND BETWEEN THE VARIOUSGROUND CENTRES THEMSELVES.
Dr. W. Fehse – Introduction to RVD – Tasks, Scenario, Players – Version 2009
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SYSTEM AND FUNCTIONS IN LEO ARD (SCHEMATIC)
Ground/Ground
Space/G
round
Gro
und/S
pace
Com
munic
ations
Space/G
round
Gro
und/S
pace
GNC, MVM , FDIRONBOARD CONTROL SYSTEM:
AOCS
SENSOR FUNCTIONS:
GPS
TM/TC COMM’s SYSTEM
VOICE COMM’s WITH GROUND
CHASER SPACECR. CONTROL
COMM’s WITH TARGET CC
CHASER MISSION CONTROL
COMM’s LINK CONTROL
TARGET MISSION CONTROL
COMM’s WITH CHASER CC
COMM’s LINK CONTROL
VOICE COMM’s WITH TARGET
TARGET SPACECR. CONTROL
Interfaces
GROUND SEGMENT
SPACE SEGMENT
CHASER
TM/TC COMM’s SYSTEM
THRUSTERSREACTION CONTROL SYSTEM
GPS, RGPS, RADAR, OPT. SENSORSRENDEZVOUS SENSORS:
CHASER CONTROL CENTRE TARGET CONTROL CENTRE
ONBOARD CONTROL SYSTEM:
TARGET
CommunicationsSpace/Space
Docking Mechanism
Rendezvous SensorInterfaces
Communications
Com
munic
ations
Dr. W. Fehse – Introduction to RVD – Tasks, Scenario, Players – Version 2009
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THE INTERNATIONAL SPACE STATION (ISS) SCENARIO
THE PRESENT SPACE STATION SCENARIO CONSISTS OF:
• THE INTERNATIONAL SPACE STATION ’ISS’
– USA, RUSSIA, JAPAN, WESTERN EUROPE AND CANADA WILLCONTRIBUTE MODULES / ELEMENTS TO THE ISS
• CREW TRANSPORT- AND RESCUE VEHICLES:
– THE US SHUTTLE,
– THE RUSSIAN SOYUS CREW TRANSPORTER
– (CREW TRANSPORT VEHICLES STUDIED BY NASA CEV - ORIONAND BY RUSSIA AND EUROPE CSTS )
• UNMANNED TRANSPORT VEHICLES:
– THE RUSSIAN PROGRESS,
– THE AUTOMATED TRANSFER VEHICLE (ATV) OF ESA (2008)
– THE JAPANESE H-2 TRANSFER VEHICLE (HTV) (2009)
Dr. W. Fehse – Introduction to RVD – Tasks, Scenario, Players – Version 2009
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THE COMMUNICATION SATELLITE
SERVICING SCENARIO
THE GEO RENDEZVOUS SCENARIO CONSISTS OF:
• A COMMUNICATION OR EARTH OBSERVATION SATELLITE,WHICH NEEDS:
– FUNCTIONAL SUPPORT IN AOCS or
– REMOVAL FROM THE GEOSTATIONARY RIM.
• A SERVICE VEHICLE,WHICH WILL PROVIDE TO THE TARGET SATELLITE:
– ATTITUDE CONTROL, E-W & N-S STATIONKEEPING SERVICES or
– TRANSPORT TO A GRAVEYARD ORBIT.
Dr. W. Fehse – Introduction to RVD – Tasks, Scenario, Players – Version 2009
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SYSTEM AND FUNCTIONS IN GEO RVD (SCHEMATIC)
Sp
ace
/Gro
un
d
Gro
un
d/S
pa
ce
Co
mm
un
ica
tio
ns
Sp
ace
/Gro
un
d
Gro
un
d/S
pa
ce
GNC only
GROUND SEGMENT
SPACE SEGMENT
CHASER
TM/TC COMM’s SYSTEM
REACTION CONTROL SYSTEM
RENDEZVOUS SENSORS:
CHASER CONTROL CENTRE TARGET CONTROL CENTRE
ONBOARD CONTROL SYSTEM:
CommunicationsGround/Ground
OPT. SENSORS only
TARGET SPACECR. CONTROL
COMM’s WITH CHASER CC
COMM’s LINK CONTROL
CHASER MISSION CONTROL
CHASER SPACECR. CONTROL
RENDEZVOUS & DOCKING CONTROLimage processing, GNC, MVM, FDIR
no dedicated interfacesfor sensors and docking
Camera
Launcher Interface Ring
TARGET (Comm’s Satellite)
COMM’s LINK CONTROL
COMM’s WITH TARGET CC
Capture Tool
ApogeeBoost
Motor AOCS
TM/TC COMM’s SYSTEM
THRUSTERS & WHEELS
Co
mm
un
ica
tio
ns
THRUSTERS & WHEELS
Dr. W. Fehse – Introduction to RVD – Tasks, Scenario, Players – Version 2009
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PART 1: INTRODUCTION TO RENDEZVOUS & DOCKING
THE MOST IMPORTANT QUESTIONS TO BE
ANSWERED
1. WHAT ARE THE TASKS, WHAT IS THE SCENARIO, WHO ARE THEMAJOR PLAYERS IN A RENDEZVOUS MISSION ?
2. HOW DOES THE APPROACHING VEHICLE GET FROM GROUNDTO THE TARGET ?
3. WHAT ARE THE MAIN ISSUES OF CAPTURE IN SPACE ?
4. WHICH FUNCTIONS MUST BE AVAILABLE ABOARD TO DO ITAUTOMATICALLY (LEO) ?
5. WHAT IS THE ROLE OF MAN IN THE AUTOMATIC RENDEZVOUSPROCESS (LEO)?
6. WHAT ARE THE MAIN ISSUES OF RENDEZVOUS & CAPTURE IN GEO ?
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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MAIN PHASES OF A RENDEZVOUS MISSION
chaser and target S/C, absolute navigation
GROUND
TARGET STATION
Achievement of stable orbital conditions
Reduction of orbital phase angle between
Achievement of rigid structural connection
Attentuation of shock & residual motion
Achievement of capture conditionsApproach to capture point
Reduction of relative distance to targetAcquistion of final approach line
Transfer from phasing orbit to first aim pointin close vicinity of target, relative navigation
Insertion into structural latch interfaces
Injection into orbital plane of target
Prevention of escape of capture interfaces
LAUNCH
PHASING
FAR RANGE RENDEZVOUS
CLOSE RANGE RENDEZVOUS
CLOSING
FINAL APPROACH
CAPTURE
STRUCTURAL CONNECTION
MATING (DOCKING OR BERTHING)
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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CO-ORDINATE FRAMES
To describe rendezvous orbits and trajectories we use
three different co-ordinate frames:
3
γ
Equator
a
aa
12
N
a = y
a = x
3 op op2
i
1 op
N
a = z
Inclination
Equator Ascending Node
3
orbital motiona = z
2 lo
Earth
a = x1
lo
lo
a = y
Earth Inertial Frame
orbit angles w.r.t.
inertial space
Orbital Plane Frame
position&velocities
in orbit
Local Orbital Frame
relative position &
velocities to target
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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LAUNCH INTO THE ORBIT PLANE OF THE TARGET
• OWING TO THE ROTATION OF THE EARTH, TWO TIMES A DAY THELAUNCH SITE MOVES INTO THE ORBITAL PLANE OF THE TARGETVEHICLE.
• HOWEVER, BECAUSE OF SAFETY RESTRICTIONS (NO FLIGHT OVERINHABITED AREAS), MOST LAUNCH SITES CAN ONLY LAUNCH IN ONEDIRECTION, e.g. OVER OPEN SEA.
• ALSO, WITH A LAUNCH IN EAST-DIRECTION, THE VEHICLEBENEFITS FROM THE ROTATION OF THE EARTH, WHICHPROVIDES A GRATIS ∆V OF ≈ 463 m/s AT THE EQUATOR.
• THIS RESULTS IN ONE OPPORTUNITY PER DAY, WHERE THE LAUNCHDIRECTION MEETS THE ORBIT PLANE AND ORBIT DIRECTION.
• BECAUSE OF THE DEVIATION OF THE EARTH FROM A TRUE SPHERE,THE ORBIT WILL DRIFT WITH TIME (DRIFT OF NODES).
AS A RESULT, THE CHASER SPACECRAFT HAS TO BE LAUNCHED INTOA VIRTUAL TARGET ORBIT PLANE, SUCH THATAT THE TIME OF ARRIVAL, CHASER AND TARGET VEHICLESWILL HAVE DRIFTED INTO THE SAME ORBITAL PLANE.
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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Definition of Orbital Elements
Earth Centred Inertial Frame
EARTH
N
ASCENDINGNODE
Ω
EQUINOXMEAN OF VERNAL
i
Ω
i
= RIGHT ASCENSION OF ASCENDING NODE (RAAN)
= INCLINATION
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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DEFINITION OF PHASE ANGLE
Orbital Plane Frame
PHASE ANGLE
TARGET ORBIT
CHASER ORBIT CHASERPOSITION
TARGETPOSITION
EARTH
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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APOGEE AND PERIGEE RAISE MANOEUVRES
Orbital Plane Frame
Perigee p∆
rp
ra
rp
Orbit 2
Earth
ApogeeV∆ a
Perigee 1
Perigee 2
Apogee 1
Apogee 2
Orbit 1 ra2a
2a1
2a 12
2
Earth
Orbit 1
2a
Orbit 2V
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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TRAJECTORIES IN EARTH CENTRED AND
TARGET CENTERED FRAMES
x
z
TARGET ORBIT
∆
PERIGEE
TARGET ORBIT
CH
AS
ER
OR
BIT
ORBITAL PLANE FRAME
TARGET CENTERED ROTATING FRAME
(local orbital coordinates move with the target)
(Earth−centred coordinates in the orbit plane)
CHASER ORBIT
TARGET POSITIONV−bar APOGEE
h
∆ h
R−bar
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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HOHMANN TRANSFER
=
=
Vp∆ ∆Vx1
∆Vx2
X (V−bar)
∆Vx1
∆Vx2
2a
Va
Orbit 1
Transfer
Orbit
Apogee
Perigee
Earth
∆
Z (R−bar)
∆ z =4
ω∆
∆ x =3 π
∆Vx
Vx1
1ω
Orbit 2
Orbit 1
TransferOrbit
r
Orbit 2
a
rp
IN ORBITAL PLANE FRAME IN TARGET CENTRED FRAME
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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Hill Equations
For circular orbits, the motion between a body in orbit and the origin of thelocal orbital frame (e.g. that of the target) is described by the Hill Equations.
x− 2ωz =1
mcFx
y + ω2y =1
mcFy (1)
z + 2ωx− 3ω2z =1
mcFz
Parameter:ω = orbital ratemc = mass of body (e.g. chaser)
The right side of the equations describes the imposed accelerations
Fx,y,z
mc= γx,y,z
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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Clohessy-Wiltshire Equations
x(t) =
(4x0
ω− 6z0
)sin(ωt)−
2z0
ωcos(ωt) + (6ωz0 − 3x0)t +
(x0 +
2z0
ω
)· · ·
+2
ω2γz(ωt− sin(ωt)) + γx
(4
ω2(1− cos(ωt))−
3
2t2
)y(t) = y0 cos(ωt) +
y0
ωsin(ωt) +
γy
ω2(1− cos(ωt)) (2)
z(t) =
(2x0
ω− 3z0
)cos(ωt) +
z0
ωsin(ωt) +
(4z0 −
2x0
ω
)· · ·
+2
ω2γx(sin(ωt)− ωt) +
γz
ω2(1− cos(ωt))
The Clohessy-Wiltshire Equations are a particular solution of the Hill Equations.This form of the equations is valid- for pulses (instantaneous changes of velocity at start and end) and- for constant values of γx,y,z.
Results are sufficiently accurate for distances in z-direction between chaser and targetof up to a few 1000 m.
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2010
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USE OF
CLOHESSY-WILTSHIRE EQUATIONS
AND OF HILL EQUATIONS
THE CLOHESSEY-WILTSHIRE (CW) EQUATIONS PROVIDE ANEASY WAY TO CALCULATE POSITIONS AND VELOCITIES ANDTHE DELTA-V OF TRAJECTORIES.
THEY ARE EXTREMELY USEFUL TO e.g.
• DEVISE APPROACH STRATEGIES,
• ASSESS TRAJECTORY SAFETY,
• CALCULATE OVERALL DELTA-V BUDGETS etc.
WE MUST NOT FORGET, HOWEVER, THAT THE CW-EQUATIONS AREONLY APPROXIMATIONS (PULSES, CONSTANT FORCES).
FOR EXACT RESULTS (REAL THRUSTERS & DISTURBANCES)NUMERICAL INTEGRATION OF THE HILL-EQUATION IS INEVITABLE.
THIS WILL BE NECESSARY IN PARTICULAR FOR MOSTVERIFICATION TASKS.
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2010
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PHASING STRATEGY IN LEO, EXAMPLE
FIRST AIM
POINT
LAUNCH
PHASING
FAR RANGE RV
MANOEUVRE
MANOEUVRE
MANOEUVRE
MANOEUVRE
MANOUEVRE
HOHMANN
TRAJECTORY
LAUNCHER
PERIGEE RAISE
PERIGEE RAISE
PERIGEE RAISE
APOGEE RAISE
GROUND
TARGET ORBIT
LOCATION
TARGET
TRANSFERS
CIRCULARISATION
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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IMPULSIVE TRAJECTORIES
TANGENTIAL MANOEUVRES RADIAL MANOEUVRES
Vx1 ∆Vx2
X (V−bar)
Z (R−bar)
∆ x =ω
π∆
6 Vx∆ 1
Z (R−bar)
∆ =ω
∆_z1
X (V−bar)
∆
∆ x =ω
∆_4
∆Vz Vz2 1
Vz
Vz
1
1
X (V−bar)
Z (R−bar)
fly−around to
R−bar approach
on +R−bar side
∆
∆
∆
∆
∆ z =4
ω∆_
∆ x = 3
ω
π∆
_ Vx
Vx2
1Vx
Vx1
1
Vx
Vx
1
2
on −R−bar sideR−bar approachfly−around to
X (V−bar)
Z (R−bar)
∆ x =ω
∆_2
∆
∆
∆ =ω
∆_z1
Vz
Vx
1
Vz
Vz1
1
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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STRAIGHT LINE AND QUASI-STRAIGHT LINE
TRAJECTORIES
V-bar LINE
∆Vx2 ∆Vx1
Continuous force
Motion Vx
X (V−bar)
Z (R−bar)
2ωVx
Z
R−bar
X
V−bar Target
∆V∆V
∆V ∆V∆V∆V
R-bar LINE
1z
z 2
z0
t
z
Mo
tio
n V
z
+ +
Z (R−bar)
Co
ntin
uo
us x
−fo
rce
2
2ω
3ω
z−
forc
e
∆
∆
V
VV
(V+
Z
)
X (V−bar)
V−bar
V
∆V
∆V
∆V
∆V
∆V
∆V
∆V
∆V
∆V
∆V
Target
Z
R−bar
X
∆
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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THE PREDOMINANT DISTURBANCES IN LEO AND GEO
ALWAYS OPPOSITE TO THE FLIGHT DIRECTION
DRAG
FDRAG
V−bar
R−bar
THE DIRECTION OF THE DRAG FORCE IS
CoP
γ
ALWAYS OPPOSITE TO THE SUN DIRECTION
DRAG
V−bar
R−bar
γSUN
THE DIRECTION OF THE SOLAR FORCE IS
Sun
α. =24 h
360 deg
CoP
F
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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LONG TERM TRAJECTORY WITH DIFFERENTIAL DRAG
EXAMPLE: 0.5 m/s R-BAR CAM IN 400 km ORBIT, z0 = 15m, CBc
CBt= 5,
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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EFFECTS OF THE SOLAR PRESSURE IN GEO (repeated)
Important:(Figures are obtained by numerical integration of the Hill equations.The Clohessy-Wiltshire equation are valid only for constant forces.)
1. Motion after releasedue to solar pressure,start 12:00 h
2. Tangent. boost traject.diff. solar press., 3 rev.+0.002 m/s, start 12:00 h
3. Radial boost traject.,diff. solar press. 3 rev.+0.01 m/s, start 12:00 h
Note: These are just 3 examples !Shape of trajectories depends highly on starting timeand boost size and direction !
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2010
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DRIVERS FOR RENDEZVOUS STRATEGIES IN THE
SHORT RANGE
THE MAIN DRIVERS FOR AN APPROACH STRATEGY ARE:
• LOCATION OF DOCKING/BERTHING PORTS w.r.t. V-BAR AND R-BAR
• DIRECTION OF APPROACH AXIS & ATTITUDE OF TARGET
• CAPABILITIES (RANGE, FOV, ACCURACY) OF SENSORS
• TRAJECTORY SAFETY CONSIDERATIONS
• APPROACH CONTROL ZONES IMPOSED BY THE TARGET
• COMMUNICATION WINDOWS WITH GROUND
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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DRIVERS FOR RENDEZVOUS STRATEGIES IN THESHORT RANGE:
DOCKING AND BERTHING PORT LOCATIONS
DOCKING PORT LOCATIONS
line of final
and other apendages
not shown !
R−bar
V−bar CoM
m
m
m
m
m
mm
+ V−bar Port
− R−bar Portsensor interfaces
docking ports can have
a significant distance
from the actual V−bar
or R−bar
sensor interfaces sensor interfaces
line of final
translation
line of final
translation
line of final
translation
line of final
translation
line of final
translation
line of final
translation
sensor interfaces
sensor interfaces
−V−bar Port
− V−bar Port+ V−bar Port
+ V−bar Port
+ R−bar Port
translation
solar arrays
BERTHING BOX & PORT LOCATIONS
transfer to
R−bar Port
R−bar Port
+ V−bar Port
R−bar Port
− Vbar Port
acquired by
R−bar approach
R−bar
V−bar
+ V−bar Port
+ V−bar Port
m
m
sensor interfaces for
final translation and
berthing box acquisition
CoM
berthing port
by manipulator
transfer to
Berthing Box
acquired by
V−bar approach
Berthing Box
by manipulatorberthing port
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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DRIVERS FOR RVD STRATEGIES IN THE SHORT RANGE:
OPERATIONAL RANGE OF RENDEZVOUS SENSORS
1 m
10 m
100 m
1000 m
0.1 m
1 m 10 m 100 m 1 km 10 km 100 km
1 % of range
AGPS and RGPSlimited by multipath andshadowing effects
Relative GPS
Radar
Camera Type S
ensor
0.01 m
Laser Range Finder
Absolute GPS w. S/A
Absolute GPS w/o S/A
accuracy
range
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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DRIVERS FOR RVD STRATEGIES IN THE SHORT RANGE:
APPROACH CONTROL ZONES OF THE ISS
+V−bar
APPROACH ELLIPSOID
2000m
1000m
APPROACH ELLIPSOID
half cone angle 10 − 15 degr.
KEEP−OUT ZONE
APPROACH CORRIDORS
KEEP−OUT ZONE 200m
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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ONBOARD FUNCTIONS AND COMMUNICATION LINKS
CONTROL CENTER CONTROL CENTER
CHASER
DOCKING
SYSTEMH.O.
TARGET
H.O.
H.O. = HUMAN OPERATOR
PROPULS.
CONTROLGYROS
COMPUTER
GPS
COMM’s
SYSTEM MGMT
& SOFTWARE
SOFTWARE
OPT. RVSENSORS
RV SENSOR
DRS GPS
CHASER
ONBOARD GNC
ONBOARD RVD CONTROL SYSTEM
H.O.TARGETGROUND LINK INFRASTRUCTURE
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
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COMMUNICATION RANGE OF GROUND STATIONS
(Example: DEOS 400 km, i = 87, RAAN = 0, day = 01 - 02 January)
Dr. W. Fehse — Introduction to RVD — From Ground to Capture — Version 2010
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APPROACH STRATEGY EXAMPLE (ATV-TYPE)
(FROM PHASING)
(FAR RANGE RV)(CLOSE RANGE RV)
V−BAR APPROACH
V−BAR
CORRIDOR
TRANSFER
R−
BA
R
FINAL
RVS RGPS RGPS GPS
S1
S2
COMMUNICATIONRANGE
S3
250−500m
> 3000 m S0
2000 m
APPROACH
KEEP−OUT ZONE 200m
HOMING PHASECLOSING PHASEAPPROACH
TRANSFER
APPROACH
ELLIPSOID
TARGET
RADIAL BOOST
HOHMANN
WAITING POINT3000 − 5000 m
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
34
APPROACH STRATEGY EXAMPLE
(JAPANESE HTV-TYPE)
V−BAR
KEEP−OUT ZONE
AP
PR
OA
CH
CLOSING PHASE
RGPS
CORRIDOR
APPROACH
3000 − 5000 mWAITING POINT
S0S1
TRANSFER
HOHMANN
TRANSFERRANGE
COMMUNICATION
200 m S2
S3S4
GPSRGPS
HOMING PHASE
> 2500 m
R−
BA
R
2000 m
HOHMANN
APPROACH
ELLIPSOID
RV
S
FIN
AL
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
35
APPROACH STRATEGY EXAMPLE(GEO SERVICING TYPE)
150°
165*
R−bar, z
270°
315°
330°
S1
Earth ShadowEclipse
70°
9°9°
V−bar, x
S3
S4
Target satellite
(Source: SENER, Smart-OLEV project)
Dr. W. Fehse – Introduction to RVD – From Ground to Capture – Version 2009
36
PART 1: INTRODUCTION TO RENDEZVOUS & DOCKING
THE MOST IMPORTANT QUESTIONS TO BE
ANSWERED
1. WHAT ARE THE TASKS, WHAT IS THE SCENARIO, WHO ARE THEMAJOR PLAYERS IN A RENDEZVOUS MISSION ?
2. HOW DOES THE APPROACHING VEHICLE GET FROM GROUNDTO THE TARGET ?
3. WHAT ARE THE MAIN ISSUES OF CAPTURE IN SPACE ?
4. WHICH FUNCTIONS MUST BE AVAILABLE ABOARD TO DO ITAUTOMATICALLY (LEO) ?
5. WHAT IS THE ROLE OF MAN IN THE AUTOMATIC RENDEZVOUSPROCESS (LEO)?
6. WHAT ARE THE MAIN ISSUES OF RENDEZVOUS & CAPTURE IN GEO ?
Dr. W. Fehse – Introduction to RVD – Capture Issues – Version 2009
37
DOCKING AND BERTHING (DEFINITION)
lateralmisalignm’t
motion
attitude
lateralmotion
motion
appr. velocity
attitude angleof target
rel. attitude
lateral
TARGET
CHASER
residual
rel. attituderesidualattitudemotions
STATION
TARGET
HALVES
residual
motions
translational
motions
attitude
GRAPPLE FIXTURE
CHASER
BERTHING BOX
MANIPULATOR
GRAPPLE MECH.
BERTHING
MECHANISM
. DOCKING BERTHING
CAPTURE & CONNECTION CAPTURE & TRANSFER TO. ATTACHMENT POSITION
Dr. W. Fehse – Introduction to RVD – Capture Issues – Version 2009
38
THE PROBLEM OF CAPTURE
LAW OF CONSERVATION OF MOMENTUM:
FREE BODIES CONTACTING EACH OTHER WILL REBOUND AND SEPARATEAGAIN.
TOTAL MOMENTUM Σ (M x V) OF THE COMPLETE SYSTEM REMAINSCONSTANT, IF NO MOTION ENERGY HAS BEEN CONVERTED INTO HEAT.
v
d
AS A RESULT OF THE REBOUND, ONLY LIMITED TIME IS AVAILABLE TOPERFORM CAPTURE.
Dr. W. Fehse – Introduction to RVD – Capture Issues – Version 2009
39
Momentum Exchange at Contact
The motions between two bodies after contact can be derived from the momentumlaw.
For translational motion ∫ t1
t0Fdt = m ·∆V
If the point of impact is not located on a line connecting the CoM’s of the twobodies, also the change of angular momentum must be taken into account:
I ·∆ω =
∫ t1
t0(r× F)dt
CoMb
Vb1
F(t) Va0
CoMb
CoMa
CoMa
F(t)
r
b1V
Va0
ωb1
Non−CentralImpact
Central Impact
Dr. W. Fehse – Introduction to RVD – Capture Issues – Version 2009
40
Shock Attenuation Dynamics
Basic Spacecraft Features Important for Contact Analysis
Mfe = mass of front−end
Mfe
Mb Ma
Mb >/= Ma
Ma = mass of chaser s/c
Mb = mass of target s/c
Mfe << Ma
1x0
v
∆
fixed wall
xmax
x
e
x
compressionmaximum
Point ofcontact
0
m
spacecraft mass and damping features equivalent mass system
∆x = −(D∆x + C ∆x)1
me
me =ma ·mb
ma + mb
Dr. W. Fehse – Short Introduction to ARD – Capture Issues – Version 2009
41
FUNCTIONS OF A DOCKING MECHANISM
RECEPTION : PROVIDES AFTER FIRST CONTACT THE MECHANICALGUIDANCE OF THE CAPTURE INTERFACES INTO A POSITION WHERECAPTURE TAKES PLACE.
CAPTURE: ENSURES THAT THE CAPTURE INTERFACES WILL NOTESCAPE AFTER CONTACT DUE TO REBOUND.
SHOCK ABSORPTION: REDUCES THE CONTACT SHOCK AND INCREASESTHE TIME FOR CAPTURE, DUE TO THE SPRING-DAMPER EFFECT ON THEMOTION OF THE CONTACT INTERFACES.
MECHANICAL ALIGNMENT: REDUCES THE ALIGNMENT ERRORS TO ADEGREE NECESSARY FOR THE ENGAGEMENT OF STRUCTURAL LATCHES.PROVIDES PRECISION ALIGNMENT DURING STRUCTURAL LATCHING.
STRUCTURAL LATCHING: ESTABLISHES A STIFF STRUCTURALCONNECTION, AS NECESSARY TO SUSTAIN AND TRANSMIT THE LOADSOF THE COMBINED VEHICLE.
SEALING: ESTABLISHES A GAS- TIGHT CONNECTION BETWEEN THE TWOSPACECRAFT.
Dr. W. Fehse – Introduction to RVD – Capture Issues – Version 2009
42
TYPES OF DOCKING MECHANISM
TWO BASIC TYPES OF DOCKING SYSTEMS HAVE BEEN DEVELOPED:
DOCKING SYSTEMS WITH CENTRAL CONTACT INTERFACESDOCKING SYSTEMS WITH PERIPHERAL CONTACT INTERFACES
THE CENTRAL DOCKING SYSTEMHAS ON THE ACTIVE SIDE AN ELASTICALLY SUSPENDED ROD (PROBE),WHICH ENTERS A HOLLOW CONE (DROGUE) ON THE PASSIVE SIDE.IT WILL BE CAPTURED AT THE CENTRE OF THE CONE BY PASSIVE(SPRING ACTUATED) LATCHES.
THE PERIPHERAL DOCKING SYSTEMUSES PETAL-TYPE GUIDING STRUCTURES AT ITS CIRCUMFERENCE.THERE ARE SPACES BETWEEN THE PETALS, WHERE THE PETALS OF THEOPPOSITE SIDE FIT IN.
WHEN INTERFACES ARE ENGAGED AT A CERTAIN DEPTH, CAPTURE ISEFFECTED BY PASSIVE OR ACTIVE LATCHES.
Dr. W. Fehse – Introduction to RVD – Capture Issues – Version 2009
43
TYPES OF DOCKING MECHANISM (DIAGRAM)
CENTRAL DOCKING MECHANISM PERIPHERAL DOCKING MECHANISM
IN CASE OF CENTRAL DOCKING MECHANISM
PETALS CAN BE INSIDE
AT HATCH OPENING, MECHANISM IS IN THE WAY
OR OUTSIDE
Dr. W. Fehse – Introduction to RVD – Capture Issues – Version 200944
PART 1: INTRODUCTION TO RENDEZVOUS & DOCKING
THE MOST IMPORTANT QUESTIONS TO BE
ANSWERED
1. WHAT ARE THE TASKS, WHAT IS THE SCENARIO, WHO ARE THEMAJOR PLAYERS IN A RENDEZVOUS MISSION ?
2. HOW DOES THE APPROACHING VEHICLE GET FROM GROUNDTO THE TARGET ?
3. WHAT ARE THE MAIN ISSUES OF CAPTURE IN SPACE ?
4. WHICH FUNCTIONS MUST BE AVAILABLE ABOARD TO DO ITAUTOMATICALLY (LEO) ?
5. WHAT IS THE ROLE OF MAN IN THE AUTOMATIC RENDEZVOUSPROCESS (LEO)?
6. WHAT ARE THE MAIN ISSUES OF RENDEZVOUS & CAPTURE IN GEO ?
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
45
ONBOARD FUNCTIONS AND COMMUNICATION LINKS
(repeated)
CONTROL CENTER CONTROL CENTER
CHASER
DOCKING
SYSTEMH.O.
TARGET
H.O.
H.O. = HUMAN OPERATOR
PROPULS.
CONTROLGYROS
COMPUTER
GPS
COMM’s
SYSTEM MGMT
& SOFTWARE
SOFTWARE
OPT. RVSENSORS
RV SENSOR
DRS GPS
CHASER
ONBOARD GNC
ONBOARD RVD CONTROL SYSTEM
H.O.TARGETGROUND LINK INFRASTRUCTURE
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
46
THE AUTOMATIC ONBOARD CONTROL SYSTEM
FOR RVD IN LEO
THE MOST IMPORTANT TASKS, THE AUTOMATIC CONTROL SYSTEM OFTHE APPROACHING VEHICLE HAS TO FULFIL, ARE:
• GUIDANCE, NAVIGATION and CONTROL (GNC),i.e. IMPLEMENTATION OF THE MANOEUVRES, THE TRAJECTORIESAND THE ATTITUDES ACCORDING TO THE APPROACH STRATEGY.
• MISSION and VEHICLE MANAGEMENT (MVM),i.e. THE SEQUENCING OF GNC MODES FORTRAJECTORY AND ATTITUDE ANDTHE ENGAGEMENT OF THE RELEVANT H/W AND S/W FUNCTIONS.
• FAILURE DETECTION, ISOLATION and RECOVERY (FDIR)
• COLLISION AVOIDANCE MONITORING ANDCOLLISION AVOIDANCE MANOEUVRE (CAM) ACTUATION
• COMMUNICATION WITH GROUND AND WITH TARGET, i.e.SELECTION & TRANSMISSION OF ONBOARD DATA TO GROUND/TARGETAND RECEPTION, PROCESSING AND EXECUTION OF DATA FROM GROUND.
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
47
CONTROL HIERARCHY AND SPACECRAFT FUNCTIONSIN AUTOMATED RENDEZVOUS AND DOCKING
DATA MANAGEMENT SYSTEM
COMMUNICATIONS SYSTEM
TH
ER
MA
L C
ON
TR
OL
SY
ST
EM
(VO
LT
AG
E)
(TE
MP
.)
CA
M
PO
WE
R C
ON
TR
OL
SY
ST
EM
SPACECRAFT
ONBOARD
SYSTEMS
MODES
ACTUA−
TORS
(POSITION, VELOCITIES
ATTITUDE, ATTITUDE RATES
OF CHASER)
HIGH LEVEL CONTROL
BY OPERATORS IN CC
PLANT (ATV)
GNC (SPACECRAFT STATE CONTROL)
SP
AC
EC
RA
FT
ST
AT
E
CO
NT
RO
L F
OR
CE
S/T
OR
QU
ES
PL
AN
T
PL
AN
T
AUTOMATIC ONBOARD RV−CONTROL SYSTEM
TCTM
MONITORING &
AUTOMATIC FDIRFAILURE DETECTION, ISOLATION
& RECOVERY SYSTEM
AUTOMATIC MVMMISSION & VEHICLE MANAGEMENT
(MODE SWITCH./ EQU’PT ASSIGNM.)
SENSORS GNC
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
48
CLOSED LOOP GNC BLOCK DIAGRAM
−
+
MANAGEMENTCONTROLLERNAVIGATION
FILTER
GUIDANCE
MEASUREMENT
ENVIRONMENT& DISTURBANC.
DISTURBANCES
DYNAMIC
SENSORS GNC FUNCTIONS ACTUATORS
SPACECRAFT
DYNAMICS, KINEMATICS
& ENVIRONMENT
SPACECRAFT STATE
BY SENSORS
STATE AS SEEN DYNAMICS
& KINEMATICS
ACTUATOR
FORCES & TORQUES
RENDEZVOUS
SENSOR
GPS RECEIVER
ATTITUDE
SENSORS
THRUSTERS
WHEELS
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
49
GNC SYSTEM FOR ARD, DEGREES OF FREEDOM
THERE ARE 6 DEGREES OF FREEDOM (DOF) TO BE CONTROLLED, i.e.3 TRANSLATIONS AND 3 ROTATIONS.THE COMPLETE GNC SYSTEM, THEREFORE, CONSISTS OF6 CONTROL LOOPS.
AS LONG AS TARGET AND CHASER ARE AT LARGE DISTANCE ANDMOVEMENTS ARE INDEPENDENT OF EACH OTHER, THE6 DOF CAN BE CONTROLLED TO A FAR EXTENT INDEPENDENTLYOF EACH OTHER.
IN THE LAST PART OF THE APPROACH, i.e.WHEN THE DOCKING INTERFACE OF THE APPROACHING VEHICLE HASTO BE ALIGNED TO THAT OF THE TARGET STATION,ALL MOTIONS WILL EVENTUALLY BE COUPLED.
FOR THIS CASE MULTIPLE-INPUT-MULTIPLE-OUTPUT (MIMO) CONTROLOR OTHER TECHNIQUES HAVE TO BE APPLIED FOR THE CONTROLOF THE COUPLED MOTION.
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
50
THE MISSION + VEHICLE MANAGEMENT (MVM)
FUNCTION FOR ARD
THE TASK OF THE MVM FUNCTION IS TO SCHEDULE THE VARIOUS
• S/W MODES FOR FOR NAVIGATION, GUIDANCE AND CONTROL(PHASE + MODE MANAGEMENT) AND
• THE EQUIPMENT CONFIGURATION FOR EACH STEP OF THEAPPROACH.
THE MVM FUNCTION IS DRIVEN BY A MISSION TIMELINE TABLE,WHICH IS UPDATED ACCORDING TO THE ACTUAL EVENTS.
THE MVM IS VERY CLOSELY INTERACTING WITH THE FAILUREDETECTION, ISOLATION + RECOVERY (FDIR) FUNCTION.
ON REQUEST OF THE FDIR FUNCTION, IN CASE OF FAILURE OF ANEQUIPMENT OR OF FAULTY BEHAVIOUR OF THE COMPLETE STRING,IT EXECUTES THE REDUNDANCY SWITCHING OF SENSOR ANDACTUATOR EQUIPMENT.
IT REGISTERS THE INSTANTANEOUS CONFIGURATION OF MODESAND EQUIPMENT AND THE REDUNDANCY STATUS WITHIN THATCONFIGURATION.
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
51
PRINCIPLE OF MVM FUNCTION (simplified)
NAVIG.
ALGO’S ALGO’S
CONTROL
ALGO’S
GUIDANCE
ALGORITHM SCHEDULER
EQUIPMENT SCHEDULER
EQU’T A EQU’T BEQU’T C EQU’T D
LLFDI−ALG. LLFDI−ALG. LLFDI−ALG.
HEALTH STAT. HEALTH STAT.HEALTH STAT. HEALTH STAT.
INSTANT.
GNC
CONFIG.
MODE MANAGEMENT
FDIR
TC
DISTRIB.MISSION
TIME LINE
MODE
TABLE
FUNCTION
TRANS.CRIT.
TC TM
PHASE/MODE
MODE & EQUIP’T CONFIG. MONITORING
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
52
FAULT TOLERANCE AND RECOVERY CONCEPT
THE FOLLOWING FAULT TOLERANCE REQUIREMENTS HAVE BEENESTABLISHED FOR OPERATIONS AT OR IN PROXIMITY OF A MANNEDSPACE STATION:
• AFTER ANY COMBINATION OF 2 SINGLE FAILURES, CREW ANDSTATION MUST REMAIN SAFE.
• AFTER ANY FIRST SINGLE FAILURE THE MISSION MUST STILLBE ACHIEVED.
THIS HAS IMPORTANT REPERCUSSIONS ON BOTH TRAJECTORY DESIGNAND REDUNDANCY DESIGN OF THE ONBOARD SYSTEM.
FOR THE ESSENTIAL FUNCTIONS THE ONBOARD SYSTEM MUST BETWO-FAILURE TOLERANT.
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
53
RECOVERY FROM CONTINGENCIES
THE FOLLOWING ACTIONS ARE POSSIBLE:
• SWITCH TO REDUNDANT EQUIPMENT, IF FAULTY EQUIPMENTHAS BEEN IDENTIFIED.
• SWITCH TO REDUNDANT STRING, IF FAILURE COULD NOT BEISOLATED. THIS INCLUDES SWITCHING TO A REDUNDANTPROCESSOR WITH IDENTICAL S/W.
• EXECUTION OF A COLLISION AVOIDANCE MANOEUVRE (CAM)OR INHIBITION OF TRAJECTORY CONTROL ACTUATION TO LEAVETHE VEHICLE ON A SAFE DRIFT ORBIT (IF AVAILABLE).
RECOVERY FROM FAILURES OF COMPUTER- AND DATA BUSFUNCTIONS WILL BE HANDLED (VOTING) BY THE DATA MANAGEMENTSYSTEM RATHER THAN BY THE MVM FUNCTION.
FOR S/W FAILURES, A SEPARATE MORE ROBUST AND SIMPLEPROCESSOR MAY BE USED FOR MONITORING, FAILURE DETECTIONAND RECOVERY.
FUNCTIONAL REDUNDANCY HAS TO BE USED TO THE EXTENTPOSSIBLE, TO REDUCE THE COMPLEXITY OF THE SYSTEM.
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
54
COLLISION AVOIDANCE MANOEUVRE (CAM)
THE CAM IS A SINGLE RETROGRADE BOOST, WHICH MOVES THEVEHICLE IN THE FIRST INSTANCE IN A DIRECTION OPPOSITE TO THEAPPROACH DIRECTION.
THE DELTA-V OF THE CAM HAS A CONSTANT VALUE(AT LEAST PER APPROACH PHASE).
THE CAM MUST BE STRONG ENOUGH TO ENSURE THAT THERESULTING TRAJECTORY MOVES OUT OF A SAFETY ZONE AROUNDTHE TARGET STATION (e.g. THE APPROACH ELLIPSOID IN CASE OF THEISS) AND DOES NOT RETURN TO IT WITHIN A GIVEN TIME.
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
55
THE NAVIGATION REQUIREMENTS FOR ARD
VALUES TO BE MEASURED (LONG RANGE):
AS LONG AS CHASER AND TARGET VEHICLE ARE AT FAR DISTANCEFROM EACH OTHER, IT IS SUFFICIENT TO MEASUREPOSITION AND ATTITUDE INDEPENDENTLY FOR EACH VEHICLEIN AN ABSOLUTE FRAME ,
• POSITION IN AN EARTH FIXED COORDINATE SYSTEM,
• ATTITUDE EITHER EARTH ORIENTED OR INERTIAL(e.g. SUN POINTING).
WHEN THE CHASER HAS COME CLOSER TO THE TARGET VEHICLE(ORDER OF MAGNITUDE OF A FEW 10 KM)AND MANOEUVRES REQUIRE HIGHER ACCURACY,THE DIFFERENCE OF ABSOLUTE POSITION MEASUREMENTSWOULD LEAD TO TOO LARGE ERRORS.
RELATIVE POSITION MEASUREMENTS BETWEEN THE TWO VEHICLESNEED TO BE PERFORMED FROM THEREON.
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
56
THE NAVIGATION REQUIREMENTS FOR ARD (cont’d)
PERFORMANCE REQUIREMENTS FOR ABSOLUTE AND RELATIVEATTITUDE:
DURING ALL APPROACH PHASES PRIOR TO THE FINAL APPROACH,ONLY ABSOLUTE ATTITUDE NEEDS TO BE MEASURED(e.g. w.r.t. LOCAL VERTICAL / LOCAL HORIZONTAL).
THE ABSOLUTE ATTITUDE HAS TO BE CONTROLLED TO ≤ 1 DEG.,MOSTLY BECAUSE OF THE NECESSARY ALIGNMENT OF THRUSTERS FORTRAJECTORY CONTROL.
ABSOLUTE ATTITUDE MEASUREMENT ACCURACY MUST BE OF THEORDER OF 0.1 DEG.
RELATIVE ATTITUDE MEASUREMENT IS REQUIRED WHEN THE CHASERVEHICLE HAS TO ACQUIRE THE DOCKING AXIS OF THE TARGETSPACECRAFT.
RELATIVE ATTITUDE MEASUREMENT ACCURACY REQUIREMENT IS OFTHE ORDER OF 1 - 2 DEG.
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
57
MEASUREMENT PRINCIPLES: GPS
NAVIGATION SATELLITE CONSTELLATION
N
19
13
18
5
1
2
9
20
23
11
21
22
14
7
24
10
8
3
15
4
12
6
16
17
LOCUS OF EQUAL DISTANCES
S3
S1 S2
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
58
MEASUREMENT PRINCIPLES: RGPS
RELATIVE GPS (RGPS) MEASUREMENT PRINCIPLE:
IN CASE OF DIFFERENTIAL GPS (AS USED e.g. FOR AIRCRAFT ANDSHIPS) ALL MEASUREMENTS ARE RELATED TO ONE RECEIVER,THE POSITION OF WHICH IS PRECISELY KNOWN.
HOWEVER, THERE IS NO FIXED POSITION AVAILABLE IN SPACE.BOTH CHASER AND TARGET ARE MOVING WITH HIGH VELOCITYRELATIVE TO THE EARTH.
THEREFORE, WITH RELATIVE GPS, THE RAW DATA OF THEGPS RECEIVERS OF CHASER AND TARGET ARE RELATED TO THEPOSITION ESTIMATES OF THE CHASER’S NAVIGATION FILTER.
THE NAVIGATION FILTER PRODUCES A RELATIVE POSITIONESTIMATE, USING ALL NAVIGATION INFORMATION AVAILABLE,INCLUDING:
• THE GPS RAW DATA OF BOTH VEHICLES,
• ORBIT PROPAGATION WITH THE PRESENT STATE VECTOR,
• THE COMMANDED THRUSTS .
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
59
MEASUREMENT PRINCIPLES: RGPS
− rel. clock drift
− rel. position− rel. velocities− rel. clock bias
RGPS NAVIGATION FILTER
THRUSTER
MANAGEM.
RELATIVESTATE VECTOR
GPS RAW DATA CHASER
GPS RAW DATA TARGET
GPS SAT.
GPS SAT EPHEMERIS
INITIAL PARAMETERS
CONTROL FORCES
GPS RXCHASER
GPS RXTARGET
SELECTIONGPS SATEL.
DIFFERENTIAL
PROPAGATIONCOVARIANCE
PROPAGATION,STATE
UPDATECOVARIANCE
&
STATE UPDATE
CALCULATION
(e.g. TARGET ORBIT EPHEMERIS)
RELATIVE GPS
MEASUREMENTDATA
COMMANDED
ABSOLUTE
FILTERNAVIGATION
ABSOLUTE ATTITUDE & POSITION
VECTOR
COMPARE BOXES ’SENSORS’ AND ’NAVIGATION FILTER’ ON CHART 47.In RGPS the sensor function includes GPS Receivers and Navigation Filter.
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
60
MEASUREMENT PRINCIPLE OF LASER RANGE FINDER
(PULSE TYPE)
OUTGOING
RANGE
LOS−DIRECTION
REL. ATTITUDE
(t)
(t)
LASER BEAM
INCOMING
MIRROR 2
MIRROR 1
OUTGOING PULSE
INCOMING PULSE
∆ t
PROCESSOR
SIGNAL
RECEIVER
TRANSMITTER/ψ
ϑ ψϑ
RELATIVE ATTITUDE
ψ, ϑ
R
R3
R2R1
RANGE & DIRECTION
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
61
MEASUREMENT PRINCIPLE OF CAMERA SENSOR
(SCHEMATIC)
CCD CAMERA
CAMERA SENSOR MEASUREMENT CONCEPT
E
R = RANGE
A
Pitch
Yaw
Roll
A = AZIMUTH
E = ELEVATION
CCD
ELECTRON.PROCESSOR
PATTERNEVALUATIONALGORITHMS
RANGEDIRECTIONREL. ATTITUDE
ILLUMINATOR
LENS
CCD
RING
R
TARGET REFLECTORS
Dr. W. Fehse – Introduction to RVD – Automatic RVD Onboard Functions – Version 2009
62
PART 1: INTRODUCTION TO RENDEZVOUS & DOCKING
THE MOST IMPORTANT QUESTIONS TO BE
ANSWERED
1. WHAT ARE THE TASKS, WHAT IS THE SCENARIO, WHO ARE THEMAJOR PLAYERS IN A RENDEZVOUS MISSION ?
2. HOW DOES THE APPROACHING VEHICLE GET FROM GROUNDTO THE TARGET ?
3. WHAT ARE THE MAIN ISSUES OF CAPTURE IN SPACE ?
4. WHICH FUNCTIONS MUST BE AVAILABLE ABOARD TO DO ITAUTOMATICALLY (LEO) ?
5. WHAT IS THE ROLE OF MAN IN THE AUTOMATIC RENDEZVOUSPROCESS (LEO)?
6. WHAT ARE THE MAIN ISSUES OF RENDEZVOUS & CAPTURE IN GEO ?
Dr. W. Fehse – Introduction to RVD – Role of Man in Automatic RVD – Version 2009
63
FUNCTIONS AND OPERATORS INVOLVED IN ARD
(repeated)
CONTROL CENTER CONTROL CENTER
CHASER
DOCKING
SYSTEMH.O.
TARGET
H.O.
H.O. = HUMAN OPERATOR
PROPULS.
CONTROLGYROS
COMPUTER
GPS
COMM’s
SYSTEM MGMT
& SOFTWARE
SOFTWARE
OPT. RVSENSORS
RV SENSOR
DRS GPS
CHASER
ONBOARD GNC
ONBOARD RVD CONTROL SYSTEM
H.O.TARGETGROUND LINK INFRASTRUCTURE
Dr. W. Fehse – Introduction to RVD – Role of Man in Automatic RVD – Version 2009
64
WHY DO WE WANT TO HAVE AN AUTOMATIC
ONBOARD SYSTEM?
COULDN’T WE DO IT BETTER REMOTELY CONTROLLED FROMGROUND?
ANSWER:
FOR THE APPROACH AND COUPLING OF THE CHASER TO THE TARGET,A LARGE NUMBER OF MANOEUVRES AND OPERATIONS ARE NECESSARY.
• DUE TO THE LIMITED COMMUNICATION POSSIBILITIES BETWEENGROUND CONTROL CENTRE AND SPACECRAFT
• AND BECAUSE OF THE RISK OF LINK FAILURES
MANOEUVRES AND OPERATIONS HAVE TO BE PERFORMED TOA LARGE EXTENT AUTOMATICALLY ABOARD THE VEHICLE.
Dr. W. Fehse – Introduction to RVD – Role of Man in Automatic RVD – Version 2009
65
WHY DO WE WANT TO HAVE HUMAN OPERATORS
INVOLVED ?
ANSWER:
WE WANT TO HAVE HUMAN OPERATORS INVOLVED,WHEREVER THEY CAN DECREASE COMPLEXITY OF THE SYSTEMAND IMPROVE SAFETY AND MISSION SUCCESS.
AUTOMATIC DOES NOT MEAN COMPLETELY AUTONOMOUS !
MONITORING AND ’GO-AHEAD’ COMMANDS ARE PART OF THENOMINAL OPERATIONS.
THUS, THE ONBOARD SYSTEM MUST BE CAPABLE OF PROVIDINGAND RECEIVING INFORMATION TO AND FROM REMOTE OPERATORS.
ALSO, INTERACTIONS BY GROUND AND BY CREW ARE PART OFTHE OVERALL RECOVERY CONCEPT IN CASE OF FAILURES.
Dr. W. Fehse – Introduction to RVD – Role of Man in Automatic RVD – Version 2009
66
THE ROLE OF HUMAN OPERATORS IN
AUTOMATIC RENDEZVOUS AND DOCKING
IN AN EARTH ORBIT THERE IS NO NEED TO PERFORM THERENDEZVOUS AND DOCKING PROCESS COMPLETELY AUTONOMOUSLY.
ON THE CONTRARY, INTERACTION BY HUMAN OPERATORS ISALWAYS DESIRABLE, IF THIS LEADS TO
• INCREASE OF SAFETY
• INCREASE OF MISSION SUCCES PROBABILITY
• DECREASE OF COMPLEXITY
FOR THIS REASON, BOTH
OPERATORS ON GROUND AND IN THE TARGET STATION
WILL BE INVOLVED IN THE RENDEZVOUS AND DOCKING PROCESS.
Dr. W. Fehse – Introduction to RVD – Role of Man in Automatic RVD – Version 2009
67
THE CONTROL HIERARCHY IN AUTOMATED RVD
(GROUND & TARGET S/C)
REMOTE
AUTOMATIC ONBOARD RV−CONTROL SYSTEM
AUTOMATIC FDIRFAILURE DETECTION, ISOLATION
& RECOVERY SYSTEM
AUTOMATIC MVMMISSION & VEHICLE MANAGEMENT
GNC (SPACECRAFT STATE CONTROL)
SENSORSGNC
MODES
ACTUA−
TORS
PLANT
ATTITUDE, ATTITUDE RATES
(POSITION, VELOCITIES
TMTC
SP
AC
EC
RA
FT
ST
AT
E
CO
NT
RO
L F
OR
CE
S/T
OR
QU
ES
OF CHASER)
MONITORING & CONTROL
BY OPERATORS
(MODE SWITCH./ EQU’PT ASSIGNM.)
Dr. W. Fehse – Introduction to RVD – Role of Man in Automatic RVD – Version 2009
68
THE TASKS OF GROUND OPERATORS IN ARD
IN THE NOMINAL MISSION CASE
DURING THE NOMINAL MISSION, THE TASKS OF THE HUMAN OPERATORSIN THE GROUND CONTROL CENTRE ARE:
• MONITORING OF
– TRAJECTORY, ATTITUDE, RATES ANDSTATUS OF ONBOARD SYSTEM,
– TIMELINE (ADJUSTMENT OF TIMELINE , IF NECESSARY),
– VIDEO PICTURES IN THE LAST METRES OF FINAL APPROACHAND DOCKING (RUSSIAN APPROACH),
• INPUT OF DATA AND COMMANDS TO THE CHASER VEHICLE
– UPDATED ORBIT DATA OF TARGET VEHICLE ,
– GO-AHEAD- (MISSION CONTINUATION) COMMANDINGAFTER HOLD POINTS,
• VOICE COMMUNICATION WITH TARGET CREW AND WITHOPERATORS OF OTHER CONTROL CENTRES INVOLVED.
IN ADDITION, IF NECESSARY, GROUND OPERATORS MAY HAVE TOPERFORM CALIBRATION AND TRIMM MANOEUVRES.
Dr. W. Fehse – Introduction to RVD – Role of Man in Automatic RVD – Version 2009
69
TRAJECTORY MONITORING DISPLAY
actual position
PITCH
YAW
ROLL
POSITION VELOCITYX
Y
Z
DEVIATION FROM PLANNED
XXXXXXX XXXXXXX
XXXXXXX XXXXXXX
XXXXXXX XXXXXXX
XXXXXXX XXXXXXX
XXXXXXX XXXXXXX
XXXXXXX XXXXXXX
MISSION
SYSTEM
GNC
SENSOR
−4000
0
200
400
600
800
X (LVLH)
Z (
LV
LH
)
−1500 −2000 −2500 −3000 −3500−200
X
Z
Y
Z
GMT METxx:xx:xx xx:xx:xx
lineTime
DISPLAYS
HELPMENU
ORBIT
NNN NNNHohmann
xx:xx:xx
xx:xx:xx
ANGLE ANG.RATE
PHASE
START
END
R Y P
Traj.
trajectory
hold pointS2
holdpointmargin
trajectory continuationif no S2 boost
corridor
actual position orb. night
DEVIATION
CONTINGENCY
WARNING Syst. Thrust Com.
Messages concerning mission events
Messages concerning system events and warnings
mode
type
Dr. W. Fehse – Introduction to RVD – Role of Man in Automatic RVD – Version 2009
70
RENDEZVOUS CONTROL SYSTEM DISPLAY
Gyro 4
MISSION
SYSTEM
GMT METxx:xx:xx xx:xx:xx
lineTime
DISPLAYS
HELPMENU
ORBIT
NNN NNNHohmann
xx:xx:xx
xx:xx:xx
PHASE
START
END
RVS 1 RVS 2
Video 1 Video 2
Traj.
FTC 1 FTC 2 FTC 3 FTC 4
Gui.modeTraj. mode Traj. mode
Att. mode
NAVIGAT. GUIDANCE CONTROL
OPTICAL
SENSORS
local linkAtt. mode
Th
r.m
an.
Illumin.
Therm.
Power
DockingSystem
CONTINGENCY
WARNING
DATA MANAGEMENT SYSTEM
LargeThr. 1
LargeThr. 2
Small SmallThr. 1 Thr. 2
MVM / FDIR S/W
PROPULS. SYSTEM
RV−CONTROL
SYSTEM
COMM’s
SYSTEM
S−Band 2
UHF 1 UHF 2
Nav.Sat.1 Nav.Sat.2
S−Band 1
ATTITUDE SENSORS
Com.
Messages concerning mission events
Messages concerning system events and warnings
Syst. Thrust
Sun S.Earth S.
Gyro 1 Gyro 2
Gyro 3
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PART 1: INTRODUCTION TO RENDEZVOUS & DOCKING
THE MOST IMPORTANT QUESTIONS TO BE
ANSWERED
1. WHAT ARE THE TASKS, WHAT IS THE SCENARIO, WHO ARE THEMAJOR PLAYERS IN A RENDEZVOUS MISSION ?
2. HOW DOES THE APPROACHING VEHICLE GET FROM GROUNDTO THE TARGET ?
3. WHAT ARE THE MAIN ISSUES OF CAPTURE IN SPACE ?
4. WHICH FUNCTIONS MUST BE AVAILABLE ABOARD TO DO ITAUTOMATICALLY (LEO) ?
5. WHAT IS THE ROLE OF MAN IN THE AUTOMATIC RENDEZVOUSPROCESS (LEO)?
6. WHAT ARE THE MAIN ISSUES OF RENDEZVOUS & CAPTUREIN GEO ?
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WHAT IS DIFFERENT BETWEEN RVD IN GEO AND LEO ?
THE MAJOR DIFFERENCES ARE IN THE FOLLOWING AREAS:
1. ORBITAL DYNAMICS DURATION, DELTA-V
2. ORBITAL DISTURBANCES: DRAG IN LEO, SOLAR PRESSURE IN GEO
3. ILLUMINATION: PRACTICALLY NO ECLIPSES
4. COMMUNICATION WITH GROUND: PERMANENT LINK POSSIBLE
5. NAVIGATION: NO GPS, NO INTERFACES FOR SENSORS
6. CAPTURE & LATCHING: NO DEDICATED INTERFACES
THESE DIFFERENCES WILL BE DISCUSSED IN MORE DETAIL
IN THE FOLLOWING CHARTS.
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THE MAJOR DIFFERENCES: ORBITAL DYNAMICS
Typical two-pulse manoeuvres with a duration of half an orbitalperiod will take 12 h in GEO as compared to 46 min in LEO(factor of 15 - 16).
This makes the approach very slow and results in a duration of many daysfor the rendezvous phase in GEO, as compared to a couple of hours in LEO-RVD.
The ∆V is proportional to ω, the orbital rate→ the required ∆V for the same distance is in GEO about 15 - 16 times smallerthan in LEO.
• The fact that the required forces for a certain trajectory size are smaller, doesnot only imply less propellant but alsothat the thrusters must be smaller to keep thrust errors low.
• In the same way the trajectory becomes alsomore sensitive to orbital disturbances.
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THE MAJOR DIFFERENCES: ORBITAL DISTURBANCES
THE PREDOMINANT DISTURBANCES IN LEO AND GEO
ALWAYS OPPOSITE TO THE FLIGHT DIRECTION
DRAG
FDRAG
V−bar
R−bar
THE DIRECTION OF THE DRAG FORCE IS
CoP
γ
ALWAYS OPPOSITE TO THE SUN DIRECTION
DRAG
V−bar
R−bar
γSUN
THE DIRECTION OF THE SOLAR FORCE IS
Sun
α. =24 h
360 deg
CoP
F
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THE MAJOR DIFFERENCES: ILLUMINATION
There will be no occurrence of an orbital night during the major part of a year.
Only at ± 23 days around the equinoxes there will be at midnight relatively shortperiods of eclipses (of a maximum of 74 min at the day of the equinox).
There is no need in any of the envisaged GEO missions to perform RVD on thoseparticular days at that time.
According to the 24 h orbit, for an Earth-pointing satellite in GEO the Sun directionchanges along the day the same way as for a fixed position on the equator on ground.
The maximum lateral Sun-angle for an equatorial orbit is that of the ecliptic,changing over the year by ± 23.5 deg, with 0 deg at the equinoxes.
Optimal illumination conditions for -R-bar docking around 9:00 h or 15:00 h.
At those times sunlight comes from behind the chaser and from the side,illuminating optimally the target docking port.
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THE MAJOR DIFFERENCES:
COMMUNICATION WITH GROUND
If the ground station of the servicer is near to the foot point of the
target vehicle, direct and continuous communication with ground
will be possible during RVD.
There are no systematic interruptions as in LEO.
This is an important advantage over LEO RVD, where even under
best conditions and availability of a relay satellite a part of the orbit
will be without communications with ground.
Also, due to the quasi-fixed position over ground,
high bandwidth communication is possible in both directions,
including video transmission from space to ground.
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THE MAJOR DIFFERENCES: NAVIGATION
No useful navigation satellite reception in GEO.
No sensor interfaces on GEO satellites.
GEO rendezvous vehicles will have to use either RF-sensors of the radar-type oroptical sensors.
• RF-sensors are both heavy and bulky, when there areno active interfaces on the target.
• Optical sensors generally have a much shorter range than RF-sensors, butrequire less power, since they can use Sun illumination.
As RF-Sensors have probably to be excluded for mass, size and power consumption,there is in principle a gap in the medium range between a few 10 km and ≈1 km.
Since in GEO servicing missions no dedicated interfaces will beavailable on the target for optical rendezvous sensors,not the same performance can be expectedas known from LEO rendezvous missions.
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THE MAJOR DIFFERENCES
GENERAL PROBLEM: NO TARGET INTERFACES
Satellites in GEO for communications and for
monitoring of phenomena on the Earth
(Weather and Earth Observation)
are not designed to support rendezvous and docking.
As additional equipment for RVD results in additional cost,
not only for the equipment but also for
the launch of the additional mass,
and as RVD is not required for the nominal mission,
GEO satellites will also in future not be designed to support RVD.
NO DEDICATED DOCKING- AND SENSOR INTERFACES
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POTENTIAL CAPTURE INTERFACES
As a result, only the nozzle of apogee boost motor is available as suitablecapture interface, unless the entire satellite body is captured e.g. by large arms orby a net.
The principle of capture using the ABM nozzle as interface is shown below.
Also in case of spinning satellites, this will be the sole interface available for capture.However in this case the capture interface on the chaser or even the entire chaservehicle would have to be spun up.
OF GEO SATELLITEAPOGEE BOOST MOTOR
SERVICING VEHICLECAPTURE TOOL OF
SERVICING VEHICLE
Principle of Capture Tool for Apogee Boost Motor
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ALLOCATION OF TASKS TO SPACE- AND GROUND
SEGMENT IN GEO RVD
Owing to the possibility ofcontinuous communicationand toslow trajectory dynamics,most of control tasks can beallocated to ground.
The objective is to have asfew as possible functions on board,in order to keepcomplexity, mass & power consumptionof the vehicle low,and to keep the cost forspacecraft, launch and operationas low as possible.
MAN−MACHINE INTERFACE PROCESSING
CLOSED LOOP
CAM
SYSTEM
ATTUDE CONTR.
TRAJECT. GNC
COMPRESSION
VIDEO/IMAGE
COMMUNICATIONS, TM/TC INTERFACE
COMMUNICATIONS, TM/TC INTERFACE
MANAGEMENT
PROCESSINGCONTROL PROCESSING
PRIMARY
SENSORS
TRAJECTORY
SENSORS
ACTUATORS
ATTITUDE
GROUND
SEGMENT
SEGMENT
SPACE
MISSION & VEHICLE
GUIDANCE NAVIGATION &
SUPPORTING
ANALYSIS
&
SIMULATIONS
General control concept ina GEO servicing scenario
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PART 2
VERIFICATION & VALIDATION PRIOR TO FLIGHT,
CONCEPTS AND TOOLS
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PART 2
VERIFICATION & VALIDATION PRIOR TO FLIGHT,
CONCEPTS AND TOOLS
ISSUES ADDRESSED:
• GENERAL VERIFICATION ISSUES OF SPACE PROJECTS
• VERIFICATION & VALIDATION OF RV-CONTROL SYSTEMIN THE DEVELOPMENT PHASES
• STIMULATION FACILITIES FOR NAVIGATION
• VERIFICATION OF CAPTURE IN THE DOCKING PROCESS
• VALIDATION OF SIMULATION MODELS
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GENERAL VERIFICATION ISSUES FOR SPACE
TECHNIQUES & TECHNOLOGY
PHYSICAL CONDITIONS OF ORBITAL FLIGHT CANNOT BEREPRODUCED ON GROUND IN ALL ASPECTS (0-g, ORBITAL DYNAMICS).
• A MAJOR PART OF THE VERIFICATION TASKSCANNOT BE PERFORMED BY DIRECT PHYSICAL TESTINGPRIOR TO THE REAL MISSION.
VERIFICATION HAS TO RELY ON TOOLS AND FACILITIES, CONTAININGMATHEMATICAL MODELLING OF
• SPACECRAFT KINEMATICS AND DYNAMICS,
• ACTUATORS, SENSORS, COMMUNICATION EQUIPMENT etc.,
• EFFECTS OF ORBITAL ENVIRONMENT ON SENSORS, ACTUATORS etc.,
• CONTACT DYNAMICS OF 2 BODIES IN SPACE (2 x 6 DOF).
VALIDATION OF THESE MATHEMATICAL MODELS w.r.t. PROPERTIESAND EFFECTS OF THE REAL WORLD IN ORBIT IS ONE OF THE ESSENTIALTASKS OF THE VERIFICATION PROCESS.
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GENERAL RVD VERIFICATION ISSUES (cont’d)
AS A CONSEQUENCE,USING DEDICATED TOOLS AND FACILITIES,FOR THE VERIFICATION OF RV-SYSTEMS AND ITEMS,IT HAS TO BE DEMONSTRATED PRIOR TO ORBITAL OPERATIONSTHAT BOTH
• SYTEM AND ITEMS TO BE FLOWN IN ORBIT ARE VERIFIEDCONCERNING THE FUNCTION AND PERFORMANCEAS NECESSARY FOR THEIR PARTICULAR MISSION.
AND
• TOOLS AND FACILITIES USED FOR VERIFICATION AREVALIDATED FOR THEIR PARTICULAR VERIFICATION TASK.
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THE AIM OF VERIFICATION AND VALIDATION
VERIFICATION AND VALIDATION ARE TASKS, WHICH BY NATURE WILLALWAYS BE LIMITED IN THEIR EXTENT.
THERE WILL NEVER BE A 100% VERIFCATION OR VALIDATION !
IT WILL BE IMPOSSIBLE TO CHECK ALL POTENTIAL VALUES ANDCOMBINATIONS OF PARAMETERS OR ASPECTS.
THE ISSUE OF VERIFICATION AND VALIDATION CAN, THEREFORE,
• NEVER BE THE ACHIEVEMENT OF AN ABSOLUTE PROOF, BUT
• RATHER THE ACHIEVEMENT OF THE HIGHEST POSSIBLECONFIDENCE LEVEL THAT SYSTEMS, ITEMS OR FUNCTIONS WILLPERFORM AS REQUIRED UNDER REAL WORLD CONDITIONS.
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DEFINITION OF VERIFICATION AND VALIDATION
VERIFICATION IS DEFINED AS THE PROOF THAT
• AN ITEM, FUNCTION OR PROCESS WORKS AND PERFORMSACCORDING TO ITS SPECIFICATION.
VALIDATION IS DEFINED AS THE PROOF THAT
• AN ITEM, FUNCTION OR PROCESS WILL PERFORM AS EXPECTED, OR
• THE DESCRIPTION OF THE BEHAVIOUR OF AN ITEM, FUNCTION ORPROCESS BY MATHEMATICAL MODELLING WILL MATCH THE BEHAVIOUR
UNDER REAL WORLD CONDITIONS.
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DEFINITION OF DEMONSTRATION
DEMONSTRATION IS THE PROOF IN FRONT OF WITNESSESTHAT A FEATURE BEHAVES AS IT IS EXPECTED TO BEHAVE.
THIS CAN INCLUDE :
• DEMONSTRATION OF THE FEASIBILITY OF A CONCEPT,
• DEMONSTRATIONS RELATED TOVERIFICATION & VALIDATION OF ITEMS,
• DEMONSTRATION OF OTHER ISSUES, e.g.CAPABILITIES IN GENERAL.
DEMONSTRATIONS CONCERNING RVD ISSUES CAN RANGE FROM
• SIMULATIONS,
• VIA PHYSICAL TESTS,
• UP TO DEMONSTRATION FLIGHTS IN ORBIT.
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PART 2
VERIFICATION & VALIDATION PRIOR TO FLIGHT,
CONCEPTS AND TOOLS
• GENERAL VERIFICATION ISSUES OF SPACE PROJECTS
• VERIFICATION & VALIDATION OF RV-CONTROL SYSTEMIN THE DEVELOPMENT PHASES
• STIMULATION FACILITIES FOR NAVIGATION
• VERIFICATION OF CAPTURE IN THE DOCKING PROCESS
• VALIDATION OF SIMULATION MODELS
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WHAT NEEDS TO BE VERIFIED FOR RVD ?
FOR THE PARTICULAR MISSION TASK OF RENDEZVOUS + DOCKING,PROPER FUNCTION AND PERFORMANCE OF THE FOLLOWING FEATURESMUST BE VERIFIED:
• THE ALGORITHMS OF THE ONBOARD- AND GROUND SYSTEMS CON-TROLLING THE RVD PROCESS,
• THE CONTROL SOFTWAREIN WHICH THESE ALGORITHMS ARE IMPLEMENTED,
• THE SENSORS REQUIRED FORTRAJECTORY AND REL. ATTITUDE CONTROL,
• THE FUNCTION AND PERFORMANCE OF THEINTEGRATED SYSTEM,
• THE SUCCESSFUL CAPTURE OF THEDOCKING OR BERTHING INTERFACES
• THE PROPER INTERACTION OF REMOTE CONTROL FUNCTIONS(GROUND OR TARGET STATION) WITH THE ONBOARD SYSTEM.
MANY OTHER ITEMS OR FEATURES OF THE CHASER SPACECRAFT AREALSO INVOLVED, BUT ARE NOT SPECIFIC TO THE RENDEZVOUSCONTROL SYSTEM.SUCH ITEMS OR FEATURES ARE NOT CONSIDERED HERE, AS THEY AREPART OF THE NORMAL SPACECRAFT VERIFICATION PROCESS.
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VERIFICATION AND VALIDATION
IN THE DEVELOPMENT PHASES
THE METHODS OF VERIFICATION HAVE TO BE CHOSEN ACCORDING TOTHE ISSUES WHICH ARE AT STAKE IN THE PARTICULAR PROJECT PHASE:
FEASIBILITY PHASE:
• ARE MISSION CONCEPT AND REQUIREMENTS FEASIBLE ?
DESIGN PHASE:
• IS THE PRELIMINARY DESIGN ABLE TO REALISE THE CONCEPT ANDTO FULFIL THE REQUIREMENTS ?
DEVELOPMENT PHASE (QUALIFICATION):
• DOES THE DESIGN IMPLEMENTATION IN H/W AND S/W FULFIL THEFUNCTION AND PERFORMANCE REQUIREMENTS FOR THE MISSION ?
FLIGHT ITEM MANUFACTURE PHASE:
• DO THE FLIGHT ITEMS ”AS BUlLT” CORRESPOND FULLY, i.eIN PHYSICAL ASPECTS, IN FUNCTION AND IN PERFORMANCE, TOTHE ONES QUALIFIED ?
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VERIFICATION IN THE DEVELOPMENT PHASES (cont’d)
IN THE FOLLOWING CHARTS THE VERIFICATION STEPS OF A RENDEZVOUSCONTROL SYSTEM IN THE DEVELOPMENT LIFE CYCLE WILL BE SHOWNON THE EXAMPLE OF THE GNC SYSTEM.
THE DEVELOPMENT OF THE MVM- AND FDIR-FUNCTIONS WILL STARTSEPARATELY. IT WILL BE MERGED WITH THE GNC, WHEN THECOMPLETE RV-CONTROL SOFTWARE WILL BE INTEGRATED.
RVD-SPECIFIC EQUIPMENT, SUCH AS SENSORS, WILL BE DEVELOPEDIN PARALLEL AND THEIR PERFORMANCE WILL FIRST BE VERIFIEDBY STATIC TESTS IN THEIR OWN TEST FACILITIES.THEREAFTER, THEY WILL BE VERIFIED IN THE DYNAMIC MEASUREMENTENVIRONMENT ON STIMULATION FACILITIES (see below).
EVENTUALLY THEY WILL BE MERGED INTO THE COMPLETERV-CONTROL SYSTEM FOR FUNCTIONAL TESTINGAT THE END OF THE DEVELOPMENT PHASE.
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VERIFICATION IN THE FEASIBILITY STUDY PHASE
WHAT NEEDS TO BE VERIFIED IS THE FEASIBILITY OF :
• TRAJECTORY AND ATTITUDE STRATEGY,
• TOTAL DELTA-V REQUIREMENT,
• THRUSTER CONFIGURATION, THRUST LEVEL,
• PROPELLANT BUDGET,
• NAVIGATION PERFORMANCE
WHAT TOOLS ARE REQUIRED:
• TRAJECTORY SIMULATIONS w/o MODELLING OF THE GNC LOOP,
• SIMULATIONS WITH SIMPLIFIED GNC AND S/C MODELLING.
AT START, THRUST LEVEL, PROPELLANT BUDGET etc. WILL BE DERIVEDFROM THE DELTA-V RESULTS BY APPLYING EMPIRICAL FACTORS,
NAVIGATION PERFORMANCE ESTIMATED FROM AVAILABLE SENSOR DATA.
A SIMULATION WHICH MODELS THE COMPLETE GNC LOOP OR THE OTHERAUTOMATIC FUNCTIONS IS NOT YET REQUIRED.
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VERIFICATION IN THE DESIGN PHASE
WHAT NEEDS TO BE VERIFIED:
• FEASIBILITY OF THE DESIGN CONCEPTS FOR GNC, MVM AND FDIR,
• FEASIBlLITY OF REQUIRED PERFORMANCE FOR GNC,
• FEASIBILITY OF DESIGN IMPLEMENTATION WITH THE ENVISAGEDHARDWARE,
• PROBABILITY OF CAPTURE WITH THE GIVEN CAPTURE INTERFACEDESIGN
WHAT TOOLS ARE REQUIRED:
CLOSED LOOP SIMULATIONS WITH GNC/MVM ALGORITHMS RUNNINGAGAINST MODELLED ENVIRONMENT
IN THE FIRST STEPS OF DESIGN, GNC, MVM AND FDIR ALGORITHMS WILLBE DESIGNED AND ANALYSED SEPARATELY.
LATER, GNC- AND MVM ALGORITHMS WILL HAVE TO BE MERGED INTO APROTOTYPE CONTROL SOFTWARE.
FOR FIRST VERIFICATION OF CAPTURE ALL FEATURES WILL BEMODELLED IN A SINGLE SIMULATION S/W.
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VERIFICATION IN THE EARLY DESIGN PHASE
GNC ALGORITHMS WILL FIRST BE TESTED IN SIMULATIONS, IN WHICH
• SPACECRAFT DYNAMICS AND DISTURBANCES,
• SENSORS,
• ACTUATORS
• DATA MANAGEMENT etc. H/W AND S/W
ARE MODELLED GLOBALLY ACCORDING TO THEIR BEHAVIOUR, RATHERTHAN TO THEIR DETAILED DESIGN.
LATER, THESE MODELS WILL SUCCESSIVELY REPLACED BY MODELSREPRESENTING THE ACTUAL DESIGN.
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CLOSED LOOP GNC SIMULATION, SINGLE PLATFORM
(EARLY GNC ALGORITHMS AND BEHAVIOUR MODELS)
ALGORITHMS
ACCORDING TO BEHAVIOUR
SIMPL. THRUSTER MODELS
ACCORDING TO BEHAVIOUR
SIMPLIFIED SENSOR MODELS
GNC ALGORITHMS TO BE DEVELOPED
ALGORITHMS
ALGORITHMS
ALGORITHMS
SIMULATION COMPUTER
DYNAMICS
DYNAMIC
MODELS
DISTURBANCE
ATTITUDE
SENSOR
MODELS
MODELS
THRUSTER
MODELS
NAVIGATION
FILTERCONTROLLER
THRUSTER
MANAGEMENT
MODEL
GPS
MODEL
RVS
RECEIVERMEASUREMENT
ENVIRONMENT
GUIDANCE
MODEL
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VERIFICATION IN THE FINAL DESIGN PHASE
WHAT TOOLS ARE REQUIRED (cont’d):
IN A NEXT STEP GNC, MVM AND FDIR DESIGNS HAVE TO BE MERGED,TO ESTABLISH A FIRST PROTOTYPE OF AN RV ONBOARD CONTROLSOFTWARE.
IT HAS THAN TO BE VERIFIED IN A CLOSED LOOP SIMULATION THATTHIS FIRST PROTOTYPE OF A RENDEZVOUS CONTROL SOFTWAREWILL WORK PROPERLY AND WILL PROVIDE THE REQUIREDPERFORMANCE IN THE ENVIRONMENT OF THE SIMULATED ONBOARDSYSTEM.
FOR THIS PURPOSE THE SIMULATION MUST INCLUDE DETAILEDMODELS OF THE ONBOARD SYSTEM, i.e. OF
• THE DATA MANAGEMENT AND COMMUNICATION ARCHITECTURE
• THE ACTUAL DESIGN OF THE EQUIPMENT (SENSORS, THRUSTERS)
(THIS IS IN CONTRAST TO THE GLOBAL BEHAVIOUR SIMULATION OF THEEQUIPMENT IN STEP 1)
THIS SIMULATION IS STILL ALL S/W (NO H/W IN THE LOOP) AND DOESNOT NEED TO RUN IN ’REAL TIME’.
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CLOSED LOOP GNC SIMULATION, SINGLE PLATFORM
(FINAL GNC ALGORITHMS AND DESIGN REPRESENTATIVE MODELS)
DESIGN REPRESENTATIVE
ALGORITHMS
DESIGN REPRESENTATIVE
GNC ALGORITHM SOFTWARE
FOR ALL GNC MODES
ALGORITHMS
FINAL ALGORITHMS
MEASUREMENT
ALGORITHMS
ENVIRONMENT
MODELS
IMPROVED
SENSOR MODELS
THRUSTER MODELS
ALGORITHMS
SIMULATION COMPUTER
DYNAMICS
DYNAMIC
MODELS
DISTURBANCE
ATTITUDE
SENSOR
MODELS
MODELS
MEASUREMENT
ENVIRONMENT
THRUSTER
MODEL
GUIDANCE
NAVIGATION
FILTERCONTROLLER
THRUSTER
MANAGEMENT
MODEL
GPS
RECEIVER
MODEL
RVS
MODELS
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MERGING OF GNC, MVM AND FDIR IN O/B COMPUTER
DESIGN REPRESENTATIVE
S/W CODES/W CODES/W CODE
including:
OPERATING SYSTEM S/W
GENERAL SERVICES S/W
S/W CODE
SENSOR MODELS
GUIDANCE
NAVIGATIONFILTER
CONTROLLERTHRUSTER
MANAGEMENT
AUTOMATIC FDIR
AUTOMATIC MVM
GNC
MODESSENSOR ACTUA−
TOR H/WH/W
FAILURE DETECTION, ISOLATION& RECOVERY SYSTEM
MISSION & VEHICLE MANAGEMENT(MODE SWITCH./ EQU’PT ASSIGNM.)
MODE/EQU’PT SWITCHING COMMANDS
DYNAMICS
DYNAMIC
MODELSDISTURBANCE
THRUSTER
MODELMODEL
GPS RECEIVERMODEL
ATTITUDESENSOR MODELS
GNC COMPUTER H/W
GNC SOFTWARE
MVM & FDIR SOFTWARE
ENVIRONMENT SIMULATION COMPUTER
RVS MODEL
MODELS
MEASUREMENTENVIRONMENT
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VERIFICATION IN THE DEVELOPMENT PHASE
WHAT NEEDS TO BE VERIFIED:
1. PROPER FUNCTION AND PERFORMANCE OF COMPLETERV-CONTROL SYSTEM IMPLEMENTED IN H/W AND S/W.
2. FUNCTION AND PERFORMANCE OF THE NAVIGATION H/W AND S/WIN A REALISTIC MEASUREMENT ENVIRONMENT.
3. PROPER FUNCTION OF THE ONBOARD SYSTEM TOGETHER WITHTHE REMOTE CONTROL FUNCTIONS (GROUND/SPACE).
WHAT TOOLS ARE REQUIRED:
FOR POINT 1:REAL TIME SIMULATIONS WITH THE DATA MANAGEMENT H/W (COM-PUTER AND DATA BUS) IN THE LOOP.(see CLOSED LOOP SIMULATION W. O/B COMPUTER) .
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CLOSED LOOP GNC SIMULATION WITH O/B
COMPUTER
MVM & FDIR S/W
S/W CODE
DESIGN REPRESENTATIVE
SENSOR MODELS
S/W CODE
also including:
OPERATING SYSTEM S/W
S/W CODE
S/W CODEGENERAL SERVICES S/W
ENVIRONMENT SIMULATION COMPUTER
DYNAMICS
DYNAMIC
MODELSDISTURBANCE
THRUSTER
MODELMODEL
GUIDANCE
NAVIGATIONFILTER
CONTROLLERTHRUSTER
MANAGEMENT
RVS MODEL
MODEL
ATTITUDE
SENSOR MODELS
GNC COMPUTER H/W
MODELS
MEASUREMENTENVIRONMENT
GPS RECEIVER
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VERIFICATION IN THE DEVELOPMENT PHASE
WHAT TOOLS ARE REQUIRED (cont’d):
FOR POINT 2(FUNCTION AND PERFORMANCE OF THE NAVIGATION H/W AND S/WIN A REALISTIC MEASUREMENT ENVIRONMENT):
SIMULATIONS WITH PHYSICAL STIMULATION, PROVIDING AREALISTIC MEASUREMENT ENVIRONMENT TO THE SENSOR H/W, i.e.
• MOTION AND ILLUMINATION TO THE OPTICAL RV-SENSORACCORDING TO THE REAL MOTION OF THE S/C AND TOPOTENTIAL DISTURBANCES (SUN IN FOV, REFLECTIONS)
• R/F DATA INPUT TO THE GPS RECEIVERS ON CHASER ANDTARGET SIDE ACCORDING TO GPS SATELLITE CONSTELLATION ANDPOSITION + ATTITUDE OF THE TWO VEHICLES(see next chart).
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CLOSED LOOP GNC SIMULATION WITH
REAL-TIME GNC S/W AND SENSOR H/W
The GNC function in the O/B-computer may be replaced by a real-time simulation.
GENERAL SERVICES S/Wstimulation
including:
MVM & FDIR S/W
FACILITY
OPERATING SYSTEM S/W
NAVIGATION
FILTER
GUIDANCE
SIMULATIONPHYSICAL
TRAJECTORY
MEASUREMENT
ENVIRONMENT
SENSOR HARDWARE
STIMULATION
ONBOARD COMPUTER
SENSOR
ATTITUDE
MODELS
SENSOR
DYNAMIC
MODELS
DISTURBANCE
THRUSTER
MODEL
ENVIRONMENT SIMULATION COMPUTER
MEAS. STATE
CALCULATION
MEASUREMENT
STATE
CONTROLLERMANAGEMENT
THRUSTER
DYNAMICS
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VERIFICATION IN THE DEVELOPMENT PHASE
WHAT TOOLS ARE REQUIRED (cont’d):
CLOSED LOOP SIMULATION WITH ONBOARD SYSTEM AND THEREMOTE CONTROL FUNCTIONS ON GROUND AND IN THETARGET STATION IN THE LOOP (incl. HUMAN OPERATORS).
GENERAL REMARKS:
NOTE 1: ALTHOUGH IT IS HIGHLY DESIRABLE TO INCLUDE AS MUCH ASPOSSIBLE REAL H/W IN THE SIMULATION, IT IS NOT POSSIBLE TO TESTTHE ONBOARD SYSTEM WITH THE ACTUATOR HARDWARE IN THE LOOP.
NOTE 2: THE TOOLS OF THE DESIGN PHASE WILL ALSO BE NEEDED INTHE DEVELOPMENT PHASE TO DESIGN, ANALYSE AND VERIFY THE MANYSMALLER AND LARGER DESIGN CHANGES DURING DEVELOPMENT.
NOTE 3: SIMULATIONS WITH GROUND- AND SPACE SEGMENT IN THELOOP WILL ALSO GO THROUGH SEVERAL STEPS OF INCREASINGINVOLVEMENT OF ACTUAL H/W AND S/W.
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VERIFICATION IN THE FLIGHT ITEM
MANUFACTURE PHASE
WHAT NEEDS TO BE VERIFIED:
• FUNCTION/PERFORMANCE OF ITEMS/SYSTEM MANUFACTURED FORFLIGHT IN COMPARISON WITH QUALIFICATION RESULTS OF THEDEVELOPMENT PHASE.
WHAT TOOLS ARE REQUIRED:
• IT WILL NOT BE NECESSARY TO REPEAT ALL TEST FORQUALIFICATION.
• H/W ITEMS WILL BE TESTED INDIVIDUALLY IN THEIR OWNACCEPTANCE TEST PROGRAMME
• THE RV-CONTROL S/W WILL IN ADDITION TO COMPREHENSIVES/W TESTING BE ACCEPTANCE TESTED IN THE REAL TIMESIMULATION WITH THE DATA MANAGEMENT H/W IN THE LOOP
• TESTS OF SENSOR H/W FOR SENSITIVITY TO MEASUREMENTENVIRONMENT NOT NECESSARY FOR ACCEPTANCE.SENSITIVITY IS CONSIDERED TO BE DESIGN DEPENDENTRATHER THAN MANUFACTURE DEPENDENT.
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VERIFICATION IN THE FLIGHT ITEM
MANUFACTURE PHASE (cont’d)
WHAT NEEDS TO BE VERIFIED:
• FUNCTIONING OF COMPLETE CHAIN
AN END- TO-END TEST WITH ALL H/W AND S/W IN THE LOOP(ONLY FUNCTION - NOT PERFORMANCE) NEEDS TO BE PERFORMED ONSPACECRAFT LEVEL DURING ACCEPTANCE OF THE VEHICLETO VERIFY PROPER FUNCTIONING OF THE COMPLETE CHAIN.
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PART 2
VERIFICATION & VALIDATION PRIOR TO FLIGHT,
CONCEPTS AND TOOLS
• GENERAL VERIFICATION ISSUES OF SPACE PROJECTS
• VERIFICATION & VALIDATION OF RV-CONTROL SYSTEMIN THE DEVELOPMENT PHASES
• STIMULATION FACILITIES FOR NAVIGATION
• VERIFICATION OF CAPTURE IN THE DOCKING PROCESS
• VALIDATION OF SIMULATION MODELS
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STIMULATION FACILITIES FOR RENDEZVOUS SENSORS
TO VERIFY FUNCTION AND PERFORMANCE OF THE NAVIGATIONH/W AND S/W, STIMULATION FACILITIES ARE REQUIRED, WHICH
• PROVIDE THE PROPER MEASUREMENT INPUTS TO THESENSOR SYSTEM ACCORDING TO THE REAL FLIGHT CONDITIONS,
• PROVIDE THE REALISTIC WORST CASE DISTURBANCESACCORDING TO THE MEASUREMENT ENVIRONMENT OFTHE REAL WORLD.
VALIDATION OF THE SYSTEMATIC PART OF THE STIMULATION, i.e.THE SIGNAL THAT THE SENSOR RECEIVES ACCORDING TO POSITION ANDATTITUDE OF THE VEHICLES, IS GENERALLY STRAIGHT FORWARD.
VALIDATION OF THE UNSYSTEMATIC PART OF THE STIMULATION,i.e. THE MODELLING OF THE DISTURBANCES DUE TO THEMEASUREMENT ENVIRONMENT, IS DIFFICULT AND REQUIRES A LOT OFPRACTICAL IN-FLIGHT EXPERIENCE.
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CLOSED LOOP GNC SIMULATION WITH
REAL-TIME GNC S/W AND SENSOR H/W
For the test of optical sensors the onboard computer may not be necessary.
The dynamic input to the facility may be read from a file.
GENERAL SERVICES S/Wstimulation
including:
MVM & FDIR S/W
FACILITY
OPERATING SYSTEM S/W
NAVIGATION
FILTER
GUIDANCE
SIMULATIONPHYSICAL
TRAJECTORY
MEASUREMENT
ENVIRONMENT
SENSOR HARDWARE
STIMULATION
ONBOARD COMPUTER
SENSOR
ATTITUDE
MODELS
SENSOR
DYNAMIC
MODELS
DISTURBANCE
THRUSTER
MODEL
ENVIRONMENT SIMULATION COMPUTER
MEAS. STATE
CALCULATION
MEASUREMENT
STATE
CONTROLLERMANAGEMENT
THRUSTER
DYNAMICS
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RGPS VERIFICATION SETUP
SENSOR H/WSTIMULATOR GNC FUNCTION
CHASER POSITION
TARGET POSITION
GUIDANCE
FUNCTION
CONTROL
FUNCTION
DISTUR−
BANCES
GYROS(MODEL)
GPS SAT’S
POSITION RECEIVERH/W
GPS−LAB FUNCTIONS
RECEIVER
ORBITAL
STATE
RV SYSTEM SIMULATOR FUNCTIONS
STIMULATOR
NAVIGATION
FILTER
RV CONTROL SOFTWARE (CHASER)TARGET GPS−
CHASER GPS−
H/W
GPS SAT’S
POSITION
STIMULATOR
S/C
DYNAMICS &
KINEMATICS
DISTUR−
DISTUR−
BANCES
TARGET
ORBITAL STATE
CHASER
BANCES
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STIMULATION FACILITY FOR OPTICAL SENSORS: EPOS
(This figure shows the old EPOS facility with a gantry robot type of motion system)
Gantry Robot 6 DOF, Target Mount 3 DOF, Illumination System 4 DOF
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STIMULATION FACILITY FOR OPT. SENSORS: EPOSx
(EPOSx is based on a 500m flow dynamics test facility for shape analysis of ships)
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PART 2
VERIFICATION & VALIDATION PRIOR TO FLIGHT,
CONCEPTS AND TOOLS
• GENERAL VERIFICATION ISSUES OF SPACE PROJECTS
• VERIFICATION & VALIDATION OF RV-CONTROL SYSTEMIN THE DEVELOPMENT PHASES
• STIMULATION FACILITIES FOR NAVIGATION
• VERIFICATION OF CAPTURE IN THE DOCKING PROCESS
• VALIDATION OF SIMULATION MODELS
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VERIFICATION OF CAPTURE IN THE DOCKING
PROCESS
TO ACHIEVE SUCCESSFUL CAPTURE, THE FOLLOWING TASKS HAVE TOBE ACHIEVED:
1. THE GNC SYSTEM OF THE CHASER VEHICLE MUST GUIDE ITSCAPTURE INTERFACES INTO THAT OF THE TARGET VEHICLEWHITHIN CERTAIN LATERAL AND ANGULAR ALIGNMENTBOUNDARIES AND MAX. LINEAR AND ANGULAR RATES.
2. WITHIN THIS RANGE OF CONTACT CONDITIONS THE DOCKINGMECHANISM MUST SUCCESSFULLY CAPTURE ITS INTERFACES ONTHE OTHER SIDE, SUCH THAT NO ESCAPE IS POSSIBLE.
3. AFTER INITIAL CAPTURE, THE MECHANISM MUST BRING INTOPOSITION AND ALIGN THE INTERFACES IN SUCH AWAY THATENGAGEMENT OF THE STRUCTURAL LATCHES CAN COMMENCE.
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VERIFICATION OF CAPTURE IN THE DOCKING
PROCESS (cont’d)
THE VERIFICATION OF THE FIRST TASK IS PART OF THEGNC PERFORMANCE VERIFICATION, DISCUSSED BEFORE.
IF IT CAN BE SHOWN THAT
1. THE GNC IS ABLE TO BE WITHIN CERTAIN PERFORMANCEBOUNDARIES AT CONTACT,
2. THE MECHANISM IS ABLE TO CAPTURE WITHIN THAT RANGE OFCONTACT CONDITIONS,
TASKS 1 (GNC) AND 2 (CAPTURE) CAN BE VERIFIED INDEPENDENTLYOF EACH OTHER, i.e. THERE IS NO NEED FOR A COMBINED TEST.
VERIFICATION OF TASK 3 (STRUCTURAL LATCHING) CAN ANYWAYBE DONE INDEPENDENTLY OF TASK 2.
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COMPUTER SIMULATION OF CAPTURE(USED IN THE EARLY PROJECT PHASES)
FRONT−ENDS
KINEMATICS
TO SPACECR.
TARGET
DYNAMICS
DYNAMICS
CHASER
relative forcesINITIAL
CONDITIONS
rel. motion
rel. attitude
rel. position
relative position, attitude and rates of spacecraft
position & attitude
of front−ends
relative
SIMULATION COMPUTER
KINEMATICS
& LATCHES
TORQUES
FORCES &
RELATIVE
SYSTEM:
ATTENUATION
MODEL:
CAPTURE
KINEMATICS
RELATIVE
SPACECRAFT
POINT & TIME
CONTACT
RELATIVE
FRONT−ENDS:
DOCK. MECH.
initiation of capturecapture criteria
fulfilled: yes / no
& torques
relative position,
attitude & rates
INITIAL CONDITIONS WILL BE OBTAINED FROM GNC SIMULATIONS
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VERIFICATION OF CAPTURE INTERFACES
IN THE DEVELOPMENT PHASE CAPTURE HAS TO BE VERIFIED WITH
• THE HARDWARE OF THE CAPTURE MECHANISM (DOCK. OR BERTH.)
• THE ACTUAL DYNAMIC CONDITIONS AT CONTACT.
THE RELATIVE MOTION CONDITIONS OF THE TWO VEHICLESAT CONTACT IN TERMS OF
• CONTACT VELOCITY VECTOR
• LATERAL MISALIGNMENT
• ANGULAR MISALIGNMENT
WILL BE OBTAINED FROM THE RESULTS OF THE GNC SIMULATION.
THE DYNAMIC REACTION OF THE TWO SPACECRAFTAFTER CONTACT WILL BE DETERMINED BY SIMULATION.
IN THE TEST THE RESULTING RELATIVE MOTION HAS TO BE EXECUTEDBETWEEN THE TWO HALVES OF THE CAPTURE INTERFACES.
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CAPTURE VERIFICATION FACILITY
INITIAL CONDITIONS
6 DOF
FORCE &
TORQUE
CHASER
DYNAMICS
TARGET
DYNAMICS
RELATIVE
MOTION
TABLE
POSITION
LINEAR
ACTUATOR
EXTENSION
STEWART PLATFORM
ACTUATORS
LINEAR
FORCE SENSORS
ATTENUATION SYSTEM
DOCKING I/F CHASER
DOCKING I/F TARGET
TEST ITEM
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PART 2
VERIFICATION & VALIDATION PRIOR TO FLIGHT,
CONCEPTS AND TOOLS
• GENERAL VERIFICATION ISSUES OF SPACE PROJECTS
• VERIFICATION & VALIDATION OF RV-CONTROL SYSTEMIN THE DEVELOPMENT PHASES
• STIMULATION FACILITIES FOR NAVIGATION
• VERIFICATION OF CAPTURE IN THE DOCKING PROCESS
• VALIDATION OF SIMULATION MODELS
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VALIDATION OF SIMULATION MODELS
IN LATER STAGES OF DEVELOPMENT, SIMULATION MODELSOF EQUIPMENT MAY BE REPLACED BY THE EQUIPMENT ITSELF.
SOME FEATURES AND ITEMS, HOWEVER, HAVE TO BE REPRESENTEDALWAYS BY MATHEMATICAL MODELS, AS THEIRPHYSICAL REPRESENTATION IS NOT POSSIBLE ON GROUND.
SUCH FEATURES AND ITEMS ARE:
• THE ORBITAL DYNAMICS,
• THE DYNAMIC DISTURBANCES,
• THE BEHAVIOUR OF THE ACTUATORS.
OTHER FEATURES, SUCH AS THE MEASUREMENT ENVIRONMENTOF THE SENSORS, ARE IN SOME SIMULATIONS REPRESENTEDBY MATHEMATICAL MODELS, IN OTHERS BY PHYSICALSTIMULATION TOOLS.
ALL THESE MODELS AND STIMULATION TOOLS NEED TO BEVALIDATED IN ORDER TO BE USED FOR VERIFICATION PUPOSES.IT MUST BE SHOWN THAT THE MODELS AND TOOLS REPRESENTTHE REALITY TO THE EXTENT NECESSARY FOR THEPARTICULAR VERIFICATION TEST.
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CLOSED LOOP SIMULATION WITH O/B COMPUTER
(repeated)
THE MODELS OF THE ENVIRONMENT SIMULATION MUST BE VALIDATED
MVM & FDIR S/W
S/W CODE
DESIGN REPRESENTATIVE
SENSOR MODELS
S/W CODE
also including:
OPERATING SYSTEM S/W
S/W CODE
S/W CODEGENERAL SERVICES S/W
ENVIRONMENT SIMULATION COMPUTER
DYNAMICS
DYNAMIC
MODELSDISTURBANCE
THRUSTER
MODELMODEL
GUIDANCE
NAVIGATIONFILTER
CONTROLLERTHRUSTER
MANAGEMENT
RVS MODEL
MODEL
ATTITUDE
SENSOR MODELS
GNC COMPUTER H/W
MODELS
MEASUREMENTENVIRONMENT
GPS RECEIVER
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MODELS IN GNC SIMULATION
CHASER
TARGET
C.O.M.
MODEL
ON CHASER
GRAVITY FIELD
CHASER DYNAMICS
TARGET DYNAMICS
MEASUREMENT ENVIRONMENT ANDMODEL
MODEL
PROPULSION
THRUSTER &
ACCOMM. MODEL
MODEL
MODEL (J2)
SENSOR MODELS
MODEL
MODEL
ATTITUDE
ORBIT
ORBIT
ATTITUDE
COMMANDS
GNC
POSITION
RAW DATA
ABSOLUTE
ATTITUDE
POSITION
RAW DATA
RANGE, LOS
REL. ATTITUDE
MODEL
GPS RECEIVER
GPS RECEIVER
MODEL
MODELS
KINEMAT. MODEL
MODEL
RV−SENSOR
DRIVE ELECTR’CS
MODEL
MODELS
(INTEGRATION)
(INTEGRATION)
DYNAMICS
(INTEGRATION)
GYRO ASSEMBLY
MODEL
TARGET PERTURBAT.
CHASER ACTUATION
AIRDRAG
PLUME IMPINGEM.
& MEAS. ENVIRONM.
GPS CONSTELLATION
GPS CONSTELLATION
& MEAS. ENVIRONM.
RVS ACCOMMODAT.
DOCKING PORT,
TARGET POSITION
DYNAMICS
TARGET ATTITUDE
CHASER ATTITUDE
DYNAMICS
CHASER POSITION
DYNAMICS
(INTEGRATION)
SLOSH./FLEX.
SUN/EARTH−SENS.
GRAV. GRADIENT
MODEL (J2)
GRAVITY FIELD
CHASER PERTURBAT.
TARGET ATTITUDE
CONTROL MODEL
MODEL
AIRDRAG
TARGET PATTERN
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VALIDATION OF SIMULATION MODELS (cont’d)
SUCH VALIDATION CAN BE ACHIEVED BY COMPARISON OF:
• THE OUTPUT OF A MODEL OR COMPLETE SIMULATIONWITH DATA DERIVED FROM REAL SPACE MISSIONS,
• THE OUTPUT OF A MODEL OR COMPLETE SIMULATIONWITH PHYSICAL TEST DATA,
• MATHEMATICAL MODELS OR SIMULATIONSWITH ACCORDING MODELS OR SIMULATIONSWHICH ARE ALREADY VALIDATED,
• MATHEMATICAL MODELS OR SIMULATIONSWITH ONES GENERATED BY INDEPENDENT SOURCES.
IT HAS TO BE STRESSED THAT A 100% VALIDATION WILL NEVER EXIST !THE QUESTIONS TO BE ASKED MUST BE ALWAYS:
• VALIDATION w.r.t. WHAT FEATURE, TO WHAT EXTENT ?
• IS IT SUFFICIENT FOR THE PURPOSE OF THE PRESENT VERIFICATIONTASK ?
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CONCLUSIONS
VERIFICATION AND VALIDATION ARE NOT CONSTRAINED TO APARTICULAR PHASE AT THE END OF A PROJECT.
ON THE CONTRARY,VERIFICATION TASKS START AT THE VERYBEGINNING OF A PROJECT ANDCONTINUES IN EACH OF THE PROJECT PHASES.
AT EACH STEP OF THE PROJECT DEVELOPMENT SEQUENCESOMETHING CAN GO WRONG.
THE TASK OF VERIFICATION IS TO ENSURE THAT POSSIBLE MISTAKESIN CONCEPT, REQUIREMENTS, DESIGN AND MANUFACTUREARE DETECTED AS EARLY AS POSSIBLE.
THE METHODS OF VERIFICATION HAVE TO BECHOSEN ACCORDING TO THE ISSUES WHICH ARE AT STAKEIN THE PARTICULAR PROJECT PHASE.
WHERE IN THE FEASIBILITY PHASE OF A PROJECT GENERIC TOOLSCAN BE USED, WITH THE PROGRESSING PROJECT,SIMULATION MODELS MUST MORE AND MOREREPRESENT THE ACTUAL DESIGN OF ITEMS AND SYSTEMS USED.
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DEVELOPMENT LIFE CYCLE OF A SPACE PROJECT
VALIDATION W.R.T. REAL WORLD VERIFICATION W.R.T. SPECIFICATION
THE INTENDED
SPACE OPERATION
Includes
System, Ops., Safety etc.
Subsystem, Equipment
Subsystem, EquipmentDevel., Manufact. & Verific.
THE REAL WORLD
Customer’s Ideaof the Reality
Mission Requirements
Specifications
System Integration &Qualification
In−Orbit Operation
MISSION DEFINITION
PHASE
CONCEPT DEFINITION
PHASE
(Phase A)
DESIGN PHASE
(Phase B)
DEVELOPMENT,
QUALIFICATION &
FLIGHT ITEM MANUF.
PHASE
(Phase C/D)
OPERATIONAL
PHASE
Mission Concept,
Requirements
System Level
Preparation
Specifications
of Concept and
Requirements
by the Customer
Industrial
Contract
Development &
System Verification
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