EN 16603-60-20:2020

SLOVENSKI STANDARD
01-november-2020
Nadomešča:
SIST EN 16603-60-20:2014
Vesoljska tehnika - Terminologija v zvezi s senzorji za zaznavanje zvezd in
specifikacija lastnosti
Space engineering - Star sensor terminology and performance specification
Raumfahrttechnik - Terminologie und Leistungsspezifikation für Sternensensoren
Ingénierie spatiale - Specification des performances et terminologie des senseurs
stellaires
Ta slovenski standard je istoveten z: EN 16603-60-20:2020
ICS:
01.040.49 Letalska in vesoljska tehnika Aircraft and space vehicle
(Slovarji) engineering (Vocabularies)
49.140 Vesoljski sistemi in operacije Space systems and
operations
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 16603-60-20
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2020
ICS 01.040.49; 49.140
Supersedes EN 16603-60-20:2014
English version
Space engineering - Star sensor terminology and
performance specification
Ingénierie spatiale - Terminologie et spécification des Raumfahrttechnik - Terminologie und
performances des capteurs stellaires Leistungsspezifikation für Sternensensoren
This European Standard was approved by CEN on 20 May 2020.

CEN and CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for
giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical
references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to
any CEN and CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN and CENELEC member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN and CENELEC members are the national standards bodies and national electrotechnical committees of Austria, Belgium,
Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia,
Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.

CEN-CENELEC Management Centre:
Rue de la Science 23, B-1040 Brussels
© 2020 CEN/CENELEC All rights of exploitation in any form and by any means Ref. No. EN 16603-60-20:2020 E
reserved worldwide for CEN national Members and for
CENELEC Members.
Table of contents
European Foreword . 5
Introduction . 7
1 Scope . 8
2 Normative references . 9
3 Terms, definitions and abbreviated terms . 10
3.1 Terms from other standards . 10
3.2 Terms specific to the present standard . 10
3.3 Abbreviated terms. 29
3.4 Nomenclature . 30
4 Functional requirements . 31
4.1 Star sensor capabilities . 31
4.1.1 Overview . 31
4.1.2 Cartography . 32
4.1.3 Star tracking . 33
4.1.4 Autonomous star tracking . 33
4.1.5 Autonomous attitude determination . 34
4.1.6 Autonomous attitude tracking . 35
4.1.7 Angular rate measurement . 35
4.1.8 (Partial) image download. 36
4.1.9 Sun survivability . 37
4.2 Types of star sensors . 37
4.2.1 Overview . 37
4.2.2 Star camera . 37
4.2.3 Star tracker . 37
4.2.4 Autonomous star tracker . 38
4.3 Reference frames . 38
4.3.1 Overview . 38
4.3.2 Provisions . 38
4.4 On-board star catalogue . 38
5 Performance requirements . 40
5.1 Use of the statistical ensemble . 40
5.1.1 Overview . 40
5.1.2 Provisions . 41
5.2 Verification methods . 42
5.2.1 Overview . 42
5.2.2 Provisions for single star performances . 42
5.2.3 Provisions for attitude performances . 42
5.2.4 Provision for tests . 42
5.3 <> . 43
5.4 General performance requirements . 43
5.5 General performance metrics . 45
5.5.1 Overview . 45
5.5.2 Bias . 45
5.5.3 Thermo elastic error . 46
5.5.4 FOV spatial error . 46
5.5.5 Pixel spatial error . 47
5.5.6 Temporal noise . 48
5.5.7 Aberration of light . 49
5.5.8 Measurement date error . 50
5.5.9 Measured output bandwidth . 50
5.6 Cartography . 50
5.7 Star tracking . 51
5.7.1 Additional performance conditions . 51
5.7.2 Single star tracking maintenance probability . 51
5.8 Autonomous star tracking . 51
5.8.1 Additional performance conditions . 51
5.8.2 Multiple star tracking maintenance level . 52
5.9 Autonomous attitude determination . 52
5.9.1 General . 52
5.9.2 Additional performance conditions . 52
5.9.3 Verification methods . 53
5.9.4 Attitude determination probability . 53
5.10 Autonomous attitude tracking . 54
5.10.1 Additional performance conditions . 54
5.10.2 Maintenance level of attitude tracking . 55
5.10.3 Sensor settling time . 56
5.11 Angular rate measurement . 56
5.11.1 Additional performance conditions . 56
5.11.2 Verification methods . 56
5.12 Mathematical model . 57
5.13 Robustness to solar events . 57
5.13.1 Additional robustness conditions . 57
5.13.2 Continuity of tracking during a solar event . 58
5.13.3 Ability to solve the lost in space problem during a solar event . 59
5.13.4 Flux levels . 59
Bibliography . 88

Figures
Figure 3-1: Star sensor elements – schematic . 13
Figure 3-2: Example alignment reference frame . 15
Figure 3-3: Boresight reference frame . 16
Figure 3-4: Example of Inertial reference frame . 16
Figure 3-5: Mechanical reference frame . 17
Figure 3-6: Stellar reference frame . 18
Figure 3-7: Schematic illustration of reference frames . 18
Figure 3-8: Schematic timing diagram . 20
Figure 3-9: Field of View . 22
Figure 3-10: Aspect angle to planetary body or sun . 23
Figure 4-1: Schematic generalized Star Sensor model . 32

Figure B-1 : Rotational and directional Error Geometry . 65
Figure F-1 : Angle rotation sequence . 76
Figure H-1 : Example of detailed data sheet . 82

Tables
Table C-1 : Minimum and optional capabilities for star sensors . 69
Table G-1 : Contributing error sources . 78
Table I-1 : Command table . 84
Table I-2 : Telemetry table . 86

European Foreword
This document (EN 16603-60-20:2020) has been prepared by Technical
Committee CEN-CENELEC/TC 5 “Space”, the secretariat of which is held by
DIN.
This standard (EN 16603-60-20:2020) originates from ECSS-E-ST-60-20C Rev. 2.
This European Standard shall be given the status of a national standard, either
by publication of an identical text or by endorsement, at the latest by February
2021, and conflicting national standards shall be withdrawn at the latest by
February 2021.
Attention is drawn to the possibility that some of the elements of this document
may be the subject of patent rights. CEN [and/or CENELEC] shall not be held
responsible for identifying any or all such patent rights.
This document supersedes EN 16603-60-20:2014.
The main changes with respect to EN 16603-60-20:2014 are:
• Update of several definitions in clause 3.2 including update of some of
the Figures.
• Update of list of Abbreviated term in clause 3.3.
• Addition of the Nomenclature in clause 3.4
• Addition of a standard set of core commands and telemetry (or
functional interfaces) prepared in the context of SAVOIR initiative in
clauses 4.1.5, 4.1.6, 4.1.7 and Annex I.
• Clause 5.1.1 rewritten.
• Addition of new clause 5.13 “Robustness to solar events” addressing
robustness and performance in presence of solar events.
• Heading of clauses 5.2, 5.2.3, 5.4 updated.
• Addition of new clauses
• 5.2.4 “Provision for tests”;
• 5.9.4.1 “Probability of correct attitude determination”;
• 5.9.4.2 “Probability of false attitude determination”;
• 5.9.4.3 “Probability of invalid attitude solution”
• Update of Clause 5 and Annex B and Annex G to be fully consistent with
the Control Performance Standard ECSS-E-ST-60-10 and to remove
irrelevant duplications.
This document has been prepared under a standardization request given to
CEN by the European Commission and the European Free Trade Association.
This document has been developed to cover specifically space systems and has
therefore precedence over any EN covering the same scope but with a wider
domain of applicability (e.g. : aerospace).
According to the CEN-CENELEC Internal Regulations, the national standards
organizations of the following countries are bound to implement this European
Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia ,
Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United
Kingdom.
Introduction
In recent years there have been rapid developments in star sensor technology,
in particular with a great increase in sensor autonomy and capabilities. This
Standard is intended to support the variety of star sensors either available or
under development.
This Standard defines the terminology and specification definitions for the
performance of star sensors (in particular, star trackers and autonomous star
trackers). It focuses on the specific issues involved in the specification of
performances of star sensors and is intended to be used as a structured set of
systematic provisions.
This Standard is not intended to replace textbook material on star sensor
technology, and such material is intentionally avoided. The readers and users of
this Standard are assumed to possess general knowledge of star sensor
technology and its application to space missions.
This document defines and normalizes terms used in star sensor performance
specifications, as well as some performance assessment conditions:
• sensor components
• sensor capabilities
• sensor types
• sensor reference frames
• general performance conditions including temperature, radiation,
dynamic and stray light
• sensor performance metrics
This document also defines a standard core of functional interfaces which help
to harmonize the majority of commands and telemetry necessary to operate star
sensors.
Scope
This Standard specifies star sensor performances as part of a space project. The
Standard covers all aspects of performances, including nomenclature,
definitions, and performance requirements for the performance specification of
star sensors.
The Standard focuses on:
• performance specifications (including the impact of temperature,
radiation and straylight environments);
• robustness (ability to maintain functionalities under non nominal
environmental conditions).
Other specification types, for example mass and power, housekeeping data and
data structures, are outside the scope of this Standard.
This Standard also proposes a standard core of functional interfaces defined by
unit suppliers and avionics primes in the context of Space AVionics Open
Interface aRchitecture (SAVOIR) initiative.
When viewed from the perspective of a specific project context, the
requirements defined in this Standard should be tailored to match the genuine
requirements of a particular profile and circumstances of a project.
This standard may be tailored for the specific characteristics and constraints of a
space project in conformance with ECSS-S-ST-00.

Normative references
The following normative documents contain provisions which, through
reference in this text, constitute provisions of this ECSS Standard. For dated
references, subsequent amendments to, or revision of any of these publications,
do not apply. However, parties to agreements based on this ECSS Standard are
encouraged to investigate the possibility of applying the more recent editions of
the normative documents indicated below. For undated references, the latest
edition of the publication referred to applies.

EN reference Reference in text Title
EN 16601-00-01 ECSS-S-ST-00-01 ECSS system – Glossary of terms
EN 16603-60-10 ECSS-E-ST-60-10 Space engineering – Control performance
EN 16603-60-30 ECSS-E-ST-60-30 Space engineering – Satellite attitude and orbit
control system (AOCS) requirements

Terms, definitions and abbreviated terms
3.1 Terms from other standards
a. For the purpose of this Standard, the terms and definitions from ECSS-S-
ST-00-01, ECSS-E-ST-60-10 and ECSS-E-ST-60-30 apply.
NOTE Additional definitions are included in Annex B.
3.2 Terms specific to the present standard
3.2.1 Capabilities
3.2.1.1 aided tracking
capability to input information to the star sensor internal processing from an
external source
NOTE 1 This capability applies to star tracking,
autonomous star tracking and autonomous
attitude tracking.
NOTE 2 E.g. AOCS.
3.2.1.2 angular rate measurement
capability to determine, the instantaneous sensor reference frame inertial
angular rotational rates
NOTE Angular rate can be computed from successive star
positions obtained from the detector or successive
absolute attitude (derivation of successive
attitude).
3.2.1.3 autonomous attitude determination
capability to determine the absolute orientation of a defined sensor reference
frame with respect to a defined inertial reference frame and to do so without
the use of any a priori or externally supplied attitude, angular rate or angular
acceleration information
3.2.1.4 autonomous attitude tracking
capability to repeatedly re-assess and update the orientation of a sensor-defined
reference frame with respect to an inertially defined reference frame for an
extended period of time, using autonomously selected star images in the field
of view, following the changing orientation of the sensor reference frame as it
moves in space
NOTE 1 The Autonomous Attitude Tracking makes use of a
supplied a priori Attitude Quaternion, either
provided by an external source (e.g. AOCS) or as
the output of an Autonomous Attitude
Determination (‘Lost-in-Space’ solution).
NOTE 2 The autonomous attitude tracking functionality
can also be achieved by the repeated use of the
Autonomous Attitude Determination capability.
NOTE 3 The Autonomous Attitude Tracking capability
does not imply the solution of the ‘lost in space’
problem.
3.2.1.5 autonomous star tracking
capability to detect, locate, select and subsequently track star images within the
sensor field of view for an extended period of time with no assistance external
to the sensor
NOTE 1 Furthermore, the autonomous star tracking
capability is taken to include the ability to
determine when a tracked image leaves the sensor
field of view and select a replacement image to be
tracked without any user intervention.
NOTE 2 See also 3.2.1.9 (star tracking).
3.2.1.6 cartography
capability to scan the entire sensor field of view and to locate and output the
position of each star image within that field of view
3.2.1.7 image download
capability to capture the signals from the detector over the entire detector Field
of view, within a single integration, and output all of that information to the
user
NOTE See also 3.2.1.8 (partial image download).
3.2.1.8 partial image download
capability to capture the signals from the detector over the entire detector Field
of view, within a single integration, and output part of that information to the
user
NOTE 1 Partial image download is an image download (see
3.2.1.7) where only a part of the detector field of
view can be output for any given specific ‘instant’.
NOTE 2 Partial readout of the detector array (windowing)
and output of the corresponding pixel signals also
fulfil the functionality.
3.2.1.9 star tracking
capability to measure the location of selected star images on a detector, to
output the co-ordinates of those star images with respect to a sensor defined
reference frame and to repeatedly re-assess and update those co-ordinates for
an extended period of time, following the motion of each image across the
detector
3.2.1.10 sun survivability
capability to withstand direct sun illumination along the boresight axis for a
certain period of time without permanent damage or subsequent performance
degradation
NOTE This capability can be extended to flare capability
considering the potential effect of the earth or the
moon in the FOV.
3.2.2 Star sensor components
3.2.2.1 Overview
Figure 3-1 shows a scheme of the interface among the generalized components
specified in this Standard.
NOTE Used as a camera the sensor output can be located
directly after the pre-processing block.
BAFFLE
OPTICAL
HEAD
OPTICAL SYSTEM
DETECTOR
PRE-PROCESSING
MEMORY
PROCESSOR
CAMERA
OUTPUT
PROCESS OUPUT
Figure 3-1: Star sensor elements – schematic
3.2.2.2 baffle
passive structure used to prevent or reduce the entry into the sensor lens or
aperture of any signals originating from outside of the field of view of the
sensor
NOTE Baffle design is usually mission specific and
usually determines the effective exclusion angles
for the limb of the Earth, Moon and Sun. The Baffle
can be mounted directly on the sensor or can be a
totally separate element. In the latter case, a
positioning specification with respect to the sensor
is used.
3.2.2.3 detector
element of the star sensor that converts the incoming signal (photons) into an
electrical signal
NOTE Usual technologies in use are CCD (charge
coupled device) and APS (active pixel sensor)
arrays though photomultipliers and various other
technologies can also be used.
3.2.2.4 electronic processing unit
set of functions of the sensor not contained within the optical head
NOTE Specifically, the sensor electronics contains:
• sensor processor;
• power conditioning;
• software algorithms;
• onboard star catalogue (if present).
3.2.2.5 optical head
part of the sensor responsible for the capture and measurement of the incoming
signal
NOTE As such it consists of
• the optical system;
• the detector (including any cooling equipment);
• the proximity electronics (usually detector
control, readout and interface, and optionally
pixel pre-processing);
• the mechanical structure to support the above.
3.2.2.6 optical system
system that comprises the component parts to capture and focus the incoming
photons
NOTE Usually this consists of a number of lenses, or
mirrors and filters, and the supporting mechanical
structure, stops, pinholes and slits if used.
3.2.3 Reference frames
3.2.3.1 alignment reference frame (ARF)
reference frame fixed with respect to the sensor external optical cube where the
origin of the ARF is defined unambiguously with reference to the sensor
external optical cube
NOTE 1 The X-, Y- and Z-axes of the ARF are a right-
handed orthogonal set of axes which are defined
unambiguously with respect to the normal of the
faces of the external optical cube. Figure 3-2
schematically illustrates the definition of the ARF.
NOTE 2 The ARF is the frame used to align the sensor
during integration.
NOTE 3 This definition does not attempt to prescribe a
definition of the ARF, other than it is a frame fixed
relative to the physical geometry of the sensor
optical cube.
NOTE 4 If the optical cube’s faces are not perfectly
orthogonal, the X-axis can be defined as the
projection of the normal of the X-face in the plane
orthogonal to the Z-axis, and the Y-axis completes
the RHS.
Z
ARF
Y
ARF
X
ARF
Sensor
Optical
Cube
Figure 3-2: Example alignment reference frame
3.2.3.2 boresight reference frame (BRF)
reference frame where:
• the origin of the Boresight Reference Frame (BRF) is defined
unambiguously with reference to the mounting interface plane of the
sensor Optical Head;
NOTE In an ideally aligned opto-electrical system this
results in a measured position at the centre of the
detector.
• the Z-axis of the BRF is defined to be anti-parallel to the direction of an
incoming collimated light ray which is parallel to the optical axis;
• X-BRF-axis is in the plane spanned by Z-BRF-axis and the vector from
the detector centre pointing along the positively counted detector rows,
as the axis perpendicular to Z-BRF-axis. The Y-BRF-axis completes the
right handed orthogonal system.
NOTE 1 The X-axes and Y-axes of the BRF are defined to lie
(nominally) in the plane of the detector
perpendicular to the Z-axis, so as to form a right
handed set with one axis nominally along the
detector array row and the other nominally along
the detector array column. Figure 3-3 schematically
illustrates the definition of the BRF.
NOTE 2 The definition of the Boresight Reference Frame
does not imply that it is fixed with respect to the
Detector, but that it is fixed with respect to the
combined detector and optical system.

Incoming light ray that
will give a measured
position at the centre of
the Detector.
Z
BRF
Optics
Y
BRF
Detector
X
BRF
Figure 3-3: Boresight reference frame
3.2.3.3 inertial reference frame (IRF)
reference frame determined to provide an inertial reference
NOTE 1 E.g. use the J2000 reference frame as IRF as shown
in Figure 3-4.
NOTE 2 The J2000 reference frame (in short for ICRF – Inertial
Celestial Reference Frame at J2000 Julian date) is
usually defined as Z IRF = earth axis of rotation
(direction of north) at J2000 (01/01/2000 at noon
GMT), X IRF = direction of vernal equinox at J2000,
Y IRF completes the right-handed orthonormal
reference frame.
Z at J2000 Julian date
IRF
Y
IRF
Earth
Ecliptic Plane
ϒ
X
IRF
X-axis in direction of
vernal equinox
Equatorial Plane
Figure 3-4: Example of Inertial reference frame
3.2.3.4 mechanical reference frame (MRF)
reference frame where the origin of the MRF is defined unambiguously with
reference to the mounting interface plane of the sensor Optical Head
NOTE 1 E.g. the Z-axis of the MRF is defined to be
perpendicular to the mounting interface plane. The
X- and Y-axes of the MRF are defined to lie in the
mounting plane such as to form an orthogonal
RHS with the MRF Z-axis.
NOTE 2 Figure 3-5 schematically illustrates the definition
of the MRF.
NOTE 3 For Fused Multiple Optical Head configurations,
MRF should be discussed and agreed between
supplier and customer.
Z
MRF
Y
MRF
Mounting Interface
X
Spacecraft Body
MRF
Figure 3-5: Mechanical reference frame
3.2.3.5 stellar reference frame (SRF)
reference frame for each star where the origin of any SRF is defined to be
coincident with the Boresight Reference Frame (BRF) origin
NOTE 1 The Z-axis of any SRF is defined to be the direction
from the SRF origin to the true position of the
selected star Figure 3-6 schematically illustrates the
definition of the SRF. Figure 3-7 gives a schematic
representation of the reference frames.
NOTE 2 The X- and Y- axes of the SRF are obtained under
the assumption that the BRF can be brought into
coincidence with the SRF by two rotations, the first
around the BRF X-axis and the second around the
new BRF Y-axis (which is coincident with the SRF
Y-axis).
Selected star
Z
BRF
Z
SRF
nd
2 rotation
Y
SRF
Y
BRF
st
1 rotation
Detector
X
BRF
X
SRF
Figure 3-6: Stellar reference frame

Z
BRF
Z
SRF
Z
ARF IRF Axes
Sensor
Z
MRF
Optical
Y
BRF
Cube
X
BRF
Mounting Plate
Spacecraft Body
Figure 3-7: Schematic illustration of reference frames
3.2.4 Definitions related to time and frequency
3.2.4.1 integration time
exposure time over which photons were collected in the detector array prior to
readout and processing to generate star positions or attitude
NOTE 1 Integration time can be fixed, manually adjustable
or autonomously set.
NOTE 2 Figure 3-8 illustrates schematically the various
times defined together with their inter-
relationship. The figure includes data being output
from two Optical Heads, each of which is
separately processed prior to generation of the
sensor output. Note that for a Fused Multiple
Optical Head sensor; conceptually it is assumed
that the filtered output is achieved via sequential
processing of data from a single head at a time as
the data is received. Hence, with this
understanding, the figure and the associated time
definitions also apply to this sensor configuration.
Figure 3-8: Schematic timing diagram
3.2.4.2 measurement date
date of the provided measurement
NOTE 1 In case of on board filtering the measurement date
can deviate from individual measurement dates.
Sample Time
Data
Optical
Flow
Head 1
Integration time
Integration
Optical Head
Processing
PROCESSING PROCESSING
Time data is
Output first available
OUT OUT
Data is
accessed
Latency
Time
NOTE 2 Usually the mid-point of the integration time is
considered as measurement date for CCD
technology.
3.2.4.3 output bandwidth
maximum frequency contained within the sensor outputs
NOTE 1 The bandwidth of the sensor is limited in general
by several factors, including:
• integration time;
• sampling frequency;
• attitude processing rate;
• onboard filtering of data (in particular for
multiple head units).
NOTE 2 The output bandwidth corresponds to the
bandwidth of the sensor seen as a low-pass filter.
In general, the bandwidth is the lowest of the cut-
off frequencies implied by the factors listed in
NOTE 1.
3.2.5 Field of view
3.2.5.1 half-rectangular field of view
angular region around the Boresight Reference Frame (BRF) frame Z-axis,
specified by the angular excursions around the BRF X- and Y-axes between the
BRF Z-axis and the appropriate rectangle edge, within which a star produces an
image on the Detector array that is then used by the star sensor
NOTE 1 This Field of View is determined by the optical
system and Detector design. This is schematically
illustrated in Figure 3-9.
NOTE 2 In the corners, the extent of the FOV for this
definition exceeds the quoted value (see Figure
3-9).
Half Rectangular
Field of View
Light cone for
Half-Rectangular
Field of View
Light cone for Full
BRF Z axis Cone Field of View
Full Cone Field
of View
Detector
Figure 3-9: Field of View
3.2.5.2 full cone field of view
angular region around the Boresight Reference Frame (BRF) frame Z-axis,
specified as a full cone angle, within which a star produces an image on the
Detector array that is then used by the star sensor
NOTE This Field of View is determined by the optical
system and Detector design. This is schematically
illustrated in Figure 3-9.
3.2.5.3 pixel field of view
angle subtended by a single Detector element
NOTE Pixel Field of View replaces (and is identical to) the
commonly used term Instantaneous Field of View.
3.2.6 Angles of celestial bodies
3.2.6.1 aspect angle
half-cone angle between the Boresight Reference Frame (BRF) Z-axis and the
nearest limb of a celestial body
Z
BRF
Solar System
Body
MEA
EEA
ASPECT ANGLE
SEA
(in plane of diagram)
Detector
Figure 3-10: Aspect angle to planetary body or sun
3.2.6.2 exclusion angle (EA)
lowest aspect angle of a body at which quoted full performance is achieved
NOTE 1 The following particular exclusion angles can be
considered:
• The Earth exclusion angle (EEA), defined as the
lowest aspect angle of fully illuminated Earth
(including the Earth atmosphere) at which
quoted full performance is achieved, as shown
schematically in Figure 3-10.
• The Sun Exclusion Angle (SEA), defined as the
lowest Aspect Angle of the Sun at which
quoted full performance is achieved, as shown
schematically in Figure 3-10.
• The Moon Exclusion Angle (MEA) is defined as
the lowest Aspect Angle of the Full Moon at
which quoted full performance is achieved, as
shown schematically in Figure 3-10.
NOTE 2 The value of any EA depends on the distance to
the object.
3.2.7 Most common terms
3.2.7.1 correct attitude
attitude for which the quaternion absolute measurement error is lower than a
given threshold
3.2.7.2 false attitude
attitude which is an incorret attitude
3.2.7.3 false star
signal on the detector not arising from a stellar source but otherwise
indistinguishable from a star image
NOTE This definition explicitly excludes effects from the
Moon, low incidence angle proton effects etc.,
which can generally be distinguished as non-stellar
in origin by geometry.
3.2.7.4 image output time
time required to output the detector image
3.2.7.5 statistical ensemble
set of not actually built sensors on which the performances are assessed by use
of statistical tools on a set of observations and observation conditions
NOTE 1 The statistical ensemble is defined on a case-by-
case basis, depending on the performances to be
assessed.
NOTE 2 See 5.1 and Annex E for further details.
3.2.7.6 maintenance level of attitude tracking
total time within a longer defined interval that attitude tracking is maintained
with a probability of 100 % for any initial pointing within the celestial sphere
NOTE This parameter can also be specified as Mean Time
between loss of tracking or probability to loose
tracking per time unit.
3.2.7.7 multiple star tracking maintenance level
total time within a longer defined interval that at least ‘n’ star tracks are
maintained with a probability of 100 %
NOTE 1 This covers the case where the stars in the FOV are
changing, such that the star tracks maintained
evolve with time.
NOTE 2 During this time interval no attitude acquisition is
performed.
3.2.7.8 night sky test
test performed during night time using the sky as physical stimulus for the star
sensor.
NOTE The effect of atmospheric extinction is generally
taken into account and reduced by appropriate
choice of the location for test.
3.2.7.9 probability of correct attitude determination
probability that a correct attitude solution is obtained and is flagged as valid,
within a defined time from the start of attitude determination with the sensor
switched on and at the operating temperature
NOTE 1 Time periods for other conditions, like recovery
after the Sun entering the FOV or a cold start, can
be defined as the time needed to reach the start
time of the attitude determination. The total time
needed is then the sum of the time needed to reach
the start time of the attitude determination and the
time period related to this metric.
NOTE 2 Attitude solution flagged as valid means that the
obtained attitude is considered by star sensor
suitable for use by the AOCS. The validity is
independent of accuracy.
NOTE 3 Correct attitude solution means that stars used to
derive the quaternion have been correctly
identified, i.e. error on delivered measurement is
below a defined threshold.
3.2.7.10 probability of false attitude determination
probability that not correct attitude solution is obtained, which is flagged as
valid, within a defined time from the start of attitude determination with the
sensor switched on and at the operating temperature
3.2.7.11 probability of invalid attitude solution
probability that an attitude solution, that can be either correct or not correct, is
obtained and it is flagged as not valid, within a defined time from the start of
attitude determination with the sensor switched on and at the operating
temperature
NOTE 1 The value of the Probability of Invalid Attitude
Solution is 1-(Probability of Correct Attitude
Determination + Probability of False Attitude
Determination).
NOTE 2 Invalid attitude solutions include cases of silence
(i.e. no attitude is available from star sensor).
3.2.7.12 sensor settling time
time period from the first quaternion output to the first quaternion at full
attitude accuracy, for random initial pointing within a defined region of the
celestial sphere
NOTE The time period is specified with a probability of
n% - if not quoted, a value of 99 % is assumed.
3.2.7.13 single star tracking maintenance probability
probability to be maintained by an existing star track over a defined time period
while the tracked star is in the FOV
3.2.7.14 star image
pattern of light falling on the detector from a stellar source
3.2.7.15 star magnitude
magnitude of the stellar image as seen by the sensor
NOTE Star magnitude takes into account spectral
considerations. This is also referred to as
instrumental magnitude.
3.2.7.16 validity
characteristics of an output of the star sensor being accurate enough for the
purpose it is intended for
NOTE E.g. use by the AOCS.
3.2.8 Error sources
3.2.8.1 aberration of light
Error on the position of a measured star due to the time of propagation of light,
and the linear motion of the STR in an inertial coordinate system
NOTE 1 The Newtonian first order expression of the
rotation error for one star direction is:

where:
V is the magnitude of the absolute linear velocity
of the spacecraft w.r.t. to an inertial frame
c is the light velocity (299 792 458 m/s)
θ is the angle between the vector and the star

direction
NOTE 2 For a satellite on an orbit around the Earth, the
absolute velocity is the vector sum of the relative
velocity of the spacecraft w.r.t the Earth and of the
velocity of the Earth w.r.t the Sun.
NOTE 3 For an Earth orbit, the magnitude of this effect is
around 25 arcsec (max). For an interplanetary
spacecraft the absolute velocity is simply the
absolute velocity w.r.t. the sun.
NOTE 4 The detailed contributors to the relativistic error
are given in Annex G.
3.2.8.2 bias
error on the knowledge of the orientation of the BRF including the initial
alignment measurement error and the alignment stability error
NOTE 1 The initial alignment measurement error is
between the Alignment Reference Frame (ARF)
and the sensor Boresight Reference Frame (BRF) as
measured during on ground calibration.
NOTE 2 The Alignment Stability Error (Calibration to
Flight) is the change in the transformation between
the sensor Mechanical Reference Frame (MRF) and
the sensor Boresight Reference Frame (BRF)
between the time of calibration and the start of the
in-flight mission.
NOTE 3 The bias can be for the BRF Z-axis directional or
the rotational erro
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