EN 16603-60-20:2014

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
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

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
EN reference Reference in text Title EN 16601-00-01 ECSS-S-ST-00-01 ECSS system – Glossary of terms
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

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

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

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

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

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

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
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).
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

Hence, with this understanding, the figure and the associated time definitions also apply to this sensor configuration. SIST EN 16603-60-20:2014

Integration Processing Output Integration time Optical Head 1 Sample Time Latency Time data is first available PROCESSING Optical Head 2 PROCESSING OUT Data is accessed
OUT Data
Flow Time
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. SIST EN 16603-60-20:2014

Detector BRF Z axis Light cone for Full Cone Field of View Light cone for Half-Rectangular Field of View Full Cone Field of View Half Rectangular Field of View
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 will produce an image on the Detector array that is then used by the star sensor NOTE
This Field of View is determined by the optics 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 SIST EN 16603-60-20:2014

Solar System
Body Detector ZBRF ASPECT ANGLE (in plane of diagram) MEA SEA EEA
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. In general, the bandwidth is the lowest of the cut-off frequencies implied by the above factors. 3.2.7 Most common terms
3.2.7.1 correct attitude attitude for which the quaternion absolute measurement error (AMEq defined in D.2.2) is lower than a given threshold SIST EN 16603-60-20:2014

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. 3.2.7.5 image output time time required to output the detector image 3.2.7.6 statistical ensemble set of sensors (not all actually built) 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. 3.2.7.7 maintenance level of attitude tracking total time within a longer defined interval that attitude tracking is maintained (i.e. without any attitude acquisition being performed) 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. 3.2.7.8 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
This covers the case where the stars in the FOV are changing, such that the star tracks maintained evolve with time. 3.2.7.9 night sky test test performed during night time using the sky as physical stimulus
for the star sensor. The effect of atmospheric extinction should be taken into account and reduced by appropriate choice of the location for test SIST EN 16603-60-20:2014

The time period is specified with a probability of n% - if not quoted, a value of 99 % is assumed. 3.2.7.14 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 SIST EN 16603-60-20:2014

Star magnitude takes into account spectral considerations. This is also referred to as instrumental magnitude. 3.2.7.17 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 Errors 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: ()usincVθ=ε where: V
is the magnitude of the absolute linear velocity V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 V vector and the star direction n nVnVu∧∧= 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 associated metrics is the MDE (see Annex B.5.11 for the mathematical definition). The detailed contributors to the relativistic error are given in Annex G. SIST EN 16603-60-20:2014

error on the knowledge of the orientation of the BRF including:
• the initial alignment measurement error between the Alignment Reference Frame (ARF) and the sensor Boresight Reference Frame (BRF) (on ground calibration)
• the Alignment Stability Error (Calibration to Flight )witch
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 1 The bias can be for the BRF Z-axis directional or the rotational errors around the BRF X, Y- axes.
NOTE 2 For definition of directional and rotational errors see B.5.14 and B.5.17. NOTE 3 Due to its nature, the bias metric value is the same whatever the observation area is. NOTE 4 The associated metrics is the MME (see Annex B.5.7 for the mathematical definition). The detailed contributors to the bias are given in Annex G. 3.2.8.3
FOV spatial error error on the measured attitude quaternion due to the individual spatial errors on the stars NOTE 1 This error has a spatial periodicity, whose amplitude is defined by the supplier. It ranges from a few pixels up to the full camera FOV. NOTE 2 FOV spatial errors are mainly due to optical distortion. These errors can be converted to time domain using sensor angular rate. Then, from temporal frequency point of view, they range from bias to high frequency errors depending on the motion of stars on the detector. They lead to bias error in the case of inertial pointing, while they contribute to random noise for high angular rate missions. NOTE 3 The associated metrics is the MDE (see Annex B.5.11 for the mathematical definition). The detailed contributors to the FOV spatial error are given in Annex G. 3.2.8.4 pixel spatial error Measurement errors of star positions due to detector spatial non uniformities (including PRNU, DSNU, dark current spikes, FPN) and star centroid computation (also called interpolation error) NOTE 1 Because of their ‘spatial’ nature – these errors vary with the position of stars on the detector – they are well captured by metrics working in the angular domain. The pixel spatial errors are then well defined as the errors on the measured attitude SIST EN 16603-60-20:2014

NOTE 1 Temporal noise is a white noise. NOTE 2 The associated metrics is the RME (see Annex B.5.8 for the mathematical definition). The detailed contributors to the temporal noise error are given in Annex G.
3.2.8.6 thermo elastic error deviation of BRF
versus MRF for a given temperature variation of
the mechanical interface of the optical head of the sensor and thermal power exchange with space NOTE 1 The detailed contributors to the thermo elastic error are given in Annex G. NOTE 2 The associated metrics is the MDE (see Annex B.5.11 for the mathematical definition). FOV spatial error. 3.2.9 Star sensor configurations 3.2.9.1 fused multiple optical head configuration more than one Optical Head, each with a Baffle, and a single Electronic Processing Unit producing a single set of outputs that uses data from all Optical Heads
3.2.9.2 independent multiple optical head configuration more than one optical head, each with a baffle, and a single electronic processing unit producing independent outputs for each optical head
3.2.9.3 integrated single optical head configuration single optical head plus baffle and a single electronic processing unit contained within the same mechanical structure SIST EN 16603-60-20:2014
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