Space engineering - Star sensor terminology and performance specification

This Standard specifies star tracker performances as part of a space project. The Standard covers all aspects of performances, including nomenclature, definitions, and performance metrics for the performance specification of star sensors.
The Standard focuses on performance specifications. Other specification types, for example mass and power, housekeeping data, TM/TC interface and data structures, are outside the scope of this Standard.
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.

Raumfahrttechnik - Terminologie und Leistungsspezifikation für Sternensensoren

Ingénierie spatiale - Specification des performances et terminologie des senseurs stellaires

Vesoljska tehnika - Terminologija na področju senzorjev za zaznavanje zvezd in tehnične specifikacije

Standard EN 16603-60-20 določa zmogljivost sledilnika zvezd kot del vesoljskega projekta. Standard zajema vse vidike zmogljivosti, vključno z nomenklaturo, opredelitvami in meritvami uspešnosti za tehnične specifikacije zmogljivosti zvezdnih senzorjev. Standard se osredotoča na tehnične specifikacije. Druge vrste specifikacije, na primer za maso in moč, vzdrževalni podatki, vmesniki TM/TC in podatkovne strukture, ne sodijo v področje tega standarda. Gledano z vidika določenega konteksta projekta naj bi se zahteve iz tega standarda prilagodile tako, da se ujemajo z izvirnimi zahtevami posameznega profila in okoliščinami projekta. Ta standard se lahko prilagodi posameznim lastnostim in omejitvam vesoljskega projekta v skladu s standardom ECSS-S-ST-00.

General Information

Status
Withdrawn
Publication Date
09-Sep-2014
Technical Committee
Drafting Committee
Current Stage
9960 - Withdrawal effective - Withdrawal
Completion Date
19-Aug-2020

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Raumfahrttechnik - Terminologie und Leistungsspezifikation für SternensensorenIngénierie spatiale - Specification des performances et terminolodie des senseurs stellairesSpace engineering - Star sensor terminology and performance specification49.140Vesoljski sistemi in operacijeSpace systems and operationsICS:Ta slovenski standard je istoveten z:EN 16603-60-20:2014SIST EN 16603-60-20:2014en,fr,de01-november-2014SIST EN 16603-60-20:2014SLOVENSKI

STANDARD
SIST EN 16603-60-20:2014
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 16603-60-20
September 2014 ICS 49.140
English version
Space engineering - Star sensor terminology and performance specification

Ingénierie spatiale - Specification des performances et terminolodie des senseurs stellaires

Raumfahrttechnik - Terminologie und Leistungsspezifikation für Sternensensoren This European Standard was approved by CEN on 1 March 2014.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels © 2014 CEN/CENELEC All rights of exploitation in any form and by any means reserved worldwide for CEN national Members and for CENELEC Members. Ref. No. EN 16603-60-20:2014 E SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 2 Table of contents Foreword .................................................................................................................... 5 Introduction ................................................................................................................ 6 1 Scope ....................................................................................................................... 7 2 Normative references ............................................................................................. 8 3 Terms, definitions and abbreviated terms ............................................................ 9 3.1 Terms from other standards ...................................................................................... 9 3.2 Terms specific to the present standard ..................................................................... 9 3.3 Abbreviated terms................................................................................................... 28 4 Functional requirements ...................................................................................... 30 4.1 Star sensor capabilities ........................................................................................... 30 4.1.1 Overview ................................................................................................... 30 4.1.2 Cartography .............................................................................................. 31 4.1.3 Star tracking .............................................................................................. 32 4.1.4 Autonomous star tracking .......................................................................... 32 4.1.5 Autonomous attitude determination ........................................................... 33 4.1.6 Autonomous attitude tracking .................................................................... 34 4.1.7 Angular rate measurement ........................................................................ 34 4.1.8 (Partial) image download........................................................................... 35 4.1.9 Sun survivability ........................................................................................ 35 4.2 Types of star sensors ............................................................................................. 36 4.2.1 Overview ................................................................................................... 36 4.2.2 Star camera .............................................................................................. 36 4.2.3 Star tracker ............................................................................................... 36 4.2.4 Autonomous star tracker ........................................................................... 36 4.3 Reference frames ................................................................................................... 37 4.3.1 Overview ................................................................................................... 37 4.3.2 Provisions ................................................................................................. 37 4.4 On-board star catalogue ......................................................................................... 37 5 Performance requirements .................................................................................. 39 SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 3 5.1 Use of the statistical ensemble ............................................................................... 39 5.1.1 Overview ................................................................................................... 39 5.1.2 Provisions ................................................................................................. 39 5.2 Use of simulations in verification methods .............................................................. 40 5.2.1 Overview ................................................................................................... 40 5.2.2 Provisions for single star performances ..................................................... 40 5.2.3 Provisions for quaternion performances .................................................... 40 5.3 Confidence level ..................................................................................................... 40 5.4 General performance conditions ............................................................................. 41 5.5 General performance metrics ................................................................................. 42 5.5.1 Overview ................................................................................................... 42 5.5.2 Bias ........................................................................................................... 42 5.5.3 Thermo elastic error .................................................................................. 43 5.5.4 FOV spatial error ....................................................................................... 44 5.5.5 Pixel spatial error ...................................................................................... 45 5.5.6 Temporal noise ......................................................................................... 45 5.5.7 Aberration of light ...................................................................................... 46 5.5.8 Measurement date error ............................................................................ 47 5.5.9 Measured output bandwidth ...................................................................... 47 5.6 Cartography ............................................................................................................ 47 5.7 Star tracking ........................................................................................................... 47 5.7.1 Additional performance conditions ............................................................ 47 5.7.2 Single star tracking maintenance probability ............................................. 48 5.8 Autonomous star tracking ....................................................................................... 48 5.8.1 Additional performance conditions ............................................................ 48 5.8.2 Multiple star tracking maintenance level .................................................... 48 5.9 Autonomous attitude determination ........................................................................ 49 5.9.1 General ..................................................................................................... 49 5.9.2 Additional performance conditions ............................................................ 49 5.9.3 Verification methods .................................................................................. 50 5.9.4 Attitude determination probability .............................................................. 50 5.10 Autonomous attitude tracking ................................................................................. 51 5.10.1 Additional performance conditions ............................................................ 51 5.10.2 Maintenance level of attitude tracking ....................................................... 52 5.10.3 Sensor settling time ................................................................................... 53 5.11 Angular rate measurement ..................................................................................... 53 5.11.1 Additional performance conditions ............................................................ 53 SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 4 5.11.2 Verification methods .................................................................................. 53 5.12 Mathematical model ................................................................................................ 54 Bibliography ............................................................................................................. 84

Figures Figure 3-1: Star sensor elements – schematic ...................................................................... 12 Figure 3-2: Example alignment reference frame ................................................................... 14 Figure 3-3: Boresight reference frame .................................................................................. 15 Figure 3-4: Example of Inertial reference frame .................................................................... 15 Figure 3-5: Mechanical reference frame ............................................................................... 16 Figure 3-6: Schematic illustration of reference frames .......................................................... 17 Figure 3-7: Stellar reference frame ....................................................................................... 17 Figure 3-8: Schematic timing diagram .................................................................................. 19 Figure 3-9: Field of View ....................................................................................................... 21 Figure 3-10: Aspect angle to planetary body or sun .............................................................. 22 Figure 4-1: Schematic generalized Star Sensor model ......................................................... 31 Figure B-1 : AME, MME schematic definition ........................................................................ 61 Figure B-2 : RME Schematic Definition ................................................................................ 62 Figure B-3 : MDE Schematic Definition ................................................................................ 63 Figure B-4 : Rotational and directional Error Geometry ........................................................ 64 Figure F-1 : Angle rotation sequence .................................................................................... 79 Figure H-1 : Example of detailed data sheet ......................................................................... 83

Tables

Table C-1 : Minimum and optional capabilities for star sensors ............................................ 69 Table D-1 : Measurement error metrics ................................................................................ 71 Table D-2 : Star Position measurement error metrics ........................................................... 71 Table E-1 : Minimum number of simulations to verify a performance at performance confidence level PC to an estimation confidence level of 95 % ........................... 76 Table G-1 : Contributing error sources ................................................................................. 80

SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 5 Foreword This document (EN 16603-60-20:2014) has been prepared by Technical Committee CEN/CLC/TC 5 “Space”, the secretariat of which is held by DIN. This standard (EN 16603-60-20:2014) originates from ECSS-E-ST-60-20C Rev. 1. 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 March 2015, and conflicting national standards shall be withdrawn at the latest by March 2015. 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 has been prepared under a mandate 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, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 6 Introduction In recent years there have been rapid developments in star tracker 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 trackers (in particular, autonomous star trackers). It focuses on the specific issues involved in the specification of performances of star trackers and is intended to be used as a structured set of systematic provisions. This Standard is not intended to replace textbook material on star tracker technology, and such material is intentionally avoided. The readers and users of this Standard are assumed to possess general knowledge of star tracker 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 • sensor metrics

SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 7 1 Scope This Standard specifies star tracker performances as part of a space project. The Standard covers all aspects of performances, including nomenclature, definitions, and performance metrics for the performance specification of star sensors. The Standard focuses on performance specifications. Other specification types, for example mass and power, housekeeping data, TM/TC interface and data structures, are outside the scope of this Standard. 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.

SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 8 2 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

SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 9 3 Terms, definitions and abbreviated terms 3.1 Terms from other standards For the purpose of this Standard, the terms and definitions from ECSS-S-ST-00-01 apply. 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 SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 10 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, at one instant (i.e. 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, at one instant (i.e. within a single integration), and output part of that information to the user NOTE 1 Partial image download is an image downloads (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. SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 11 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 could 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. SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 12

BAFFLE OPTICAL HEAD OPTICAL SYSTEM PROCESSOR PROCESS OUPUT DETECTOR MEMORY CAMERA OUTPUT PRE-PROCESSING

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) SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 13 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. SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 14 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.

Optical Cube XARF YARF ZARF Sensor

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 SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 15 Detector, but that it is fixed with respect to the combined detector and optical system.

Optics Detector ZBRF YBRF XBRF Incoming light ray that will give a measured position at the centre of the Detector.

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.

Ecliptic Plane Equatorial Plane XIRF
YIRF
ZIRF at J2000 Julian date X-axis in direction of vernal equinox
ϒ Earth
Figure 3-4: Example of Inertial reference frame
SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 16 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 For Fused Multiple Optical Head configurations, the interface plane of one of the Optical Heads may be nominated to define the MRF. The orientation is to be defined. NOTE 2 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 3 Figure 3-5 schematically illustrates the definition of the MRF.

YMRF XMRF Spacecraft Body Mounting Interface ZMRF
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 gives a schematic representation of the reference frames. Figure 3-7 schematically illustrates the definition of the SRF. 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).

SIST EN 16603-60-20:2014
EN 16603-60-20:2014 (E) 17
ZMRF Optical Cube Spacecraft Body ZBRF Sensor YBRF XBRF ZARF ZSRF
Mounting Plate IRF Axes
Figure 3-6: Schematic illustration of reference frames
YSRF XSRF XBRF Detector Selected star ZSRF ZBRF YBRF 1st rotation 2nd rotation
Figure 3-7: Stellar reference frame SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 18 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 the output (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. SIST EN 16603-60-20:2014

EN 16603-60-20:2014 (E) 19

Integration Processing Output Integration time Optical Head 1 Sample Time Latency Time data is fir

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