464-ACS-ICD-0067
Revision G
Solar Dynamics Observatory (SDO)
Attitude Control System (ACS)
Coordinate System Document
464-ACS-ICD-0067
Revision G
Effective Date: September 23, 2008
Prepared By: Kristin Bourkland/591
CHECK THE SDO MIS AT https://sdomis.gsfc.nasa.gov
TO VERIFY THAT THIS IS THE CORRECT VERSION PRIOR TO USE.
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CM FOREWORD
This document is a Solar Dynamics Observatory Project (SDO) signature controlled document. In accordance with SDO Project Office Configuration Management Procedures, all proposed changes shall be submitted on a SCoRe change request in the SDO Management Information System (MIS).
Questions or comments concerning this document should be addressed to:
SDO Configuration Management Office
Mail Stop 464
Goddard Space Flight Center
Greenbelt, Maryland 20771
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REVIEWED/APPROVED BY:
M. Vess
S. Himes
P. Mule
***Signatures are available on-line at: https://sdomis.gsfc.nasa.gov***
Solar Dynamics Observatory (SDO) Attitude Control System (ACS) Coordinate System Document
DOCUMENT CHANGE RECORD Sheet:1of 1
REV/ VERLEVEL / DESCRIPTION OF CHANGE / APPROVED
BY / DATE
APPROVED
Rev (-)
Rev C
Rev D
Rev E
Rev F
Rev G / SDO Attitude Control System (ACS) Coordinate System Document as per SDO-SCoRe-0257
Released following approval of SDO-CCR-0525 and SDO-SCoRe-0789. The description of changes made for Revisions A, B, and C is listed on the following pages within the Revision Log…as per approval of SDO-SCoRe-0789
Revision D as per approval of SDO-SCoRe-1349
Revision E as per approval of SDO-SCoRe-1657
Revision F as per approval of SDO-SCoRe-2118 and SDO-CCR-0857.
Revision G as per approval of SDO-SCoRe-2307. / W. Morgenstern
W. Morgenstern
W. Morgenstern
W. Morgenstern
W. Morgenstern
M. Vess / 12/29/05
04/25/2006
05/08/2007
06/18/2007
02/13/2008
09/23/2008
Solar Dynamics Observatory Attitude Control System Coordinate System Document
REVISION LOG (For ACS Tracking) Sheet: 1 of 1
REV/ VERLEVEL / DESCRIPTION OF CHANGE / APPROVED
BY / DATE
APPROVED
A
B / Initial Release
Add description of “A” and “B” CSS sensor locations.
Correction in CSS rotation description.
Addition of Thruster diagrams.
Replace sensor and actuator diagram.
Alter HGA diagrams to match naming convention.
Change HGA description to include elevation and azimuth.
Change CSS diagrams.
Include Guide Telescope transformation matrix.
Add documentation to GT diagram.
Remove thruster diagrams.
Fix IRU diagram to match naming convention.
Fix IRU GyroA matrix.
Change IRU A, B, C to IRU 1, 2, 3.
Change IRU software numbering.
Alter CSS diagrams.
Change ST rotations.
Change ST description to accommodate chosen sensor.
Fix typo in RWA diagram labeling.
Change HGA section to include a comparison of all gimbal naming conventions.
Fix typo in CSS rotation matrix.
Change ST rotation matrix to incorporate new rotation angles.
Define difference in ST1 and ST2.
Redefine ST axis descriptions.
Updated ST axis descriptions and added additional “clocking” rotation.
Fixed spelling error
Replaced dimensional diagram with newer version
Add star tracker location and orientation picture
Add DSS orientation picture
C
D
E
F
G
H / Change IRU picture to one provided by Paul Mason.
Add line of description to IRU transformation.
Updated ST alignments to match new configuration.
Replace spacecraft pictures with current configuration.
Change IRU drawing from ABC to 123.
Delete mass property table in thruster section.
Update picture in Figure 4.
Change description of DSS alignment to account for rotation of DSS mount.
Add mapping of RT address and A-STR serial number to ST section.
Add solar array serial numbers to solar array section.
Add table of CSS serial numbers.
Correct signs in HGA figure 9.
Correct DSS directions in Figure 13.
Update thruster location table to correct for the switch of A and B thrusters.
Fix typos in HGA alpha and beta descriptions.
Add serial numbers to thruster section.
Change Figure 13 showing corrected DSS location on spacecraft.
Added the IRU serial numbers to each box in Figure 16
Updated the prime and redundant Table 4 to reflect the use of the first two IRU boxes for the prime rates. Change is in response to SDO-CCR-0857.
Updated IRU alignment descriptions and numbers using Mechanical data collected 03/20/2008.
Updated ST alignments using Mechanical data (04/22/2008).
Updated DSS Head alignment using Mechanical data (05/2008).
Updated THR position & alignment using Mech data (03/15/2008).
Reorganized IRU information to reflect use in FSW
Corrected THR information. / W. Morgenstern
W. Morgenstern
W. Morgenstern
P.
Mason
S. Starin
S. Starin / 04/26/06
05/08/07
06/18/07
01/07/08
06/10/08
09/23/08
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Table of Contents
1.0 Purpose of Document 1-1
2.0 Coordinate Frame Defintions 2-1
2.1 Geocentric Inertial Frame (GCI) 2-1
2.2 Solar North Referenced Frame (SNR) 2-1
2.3 Spacecraft Body Coordinate System (BCS) 2-3
3.0 Hardware Components 3-1
3.1 Deployables 3-1
3.1.1 Solar Arrays 3-1
3.1.2 High Gain Antennas 3-2
3.2 Sensors 3-5
3.2.1 Coarse Sun Sensors 3-5
3.2.2 Digital Sun Sensors 3-7
3.2.3 Star Trackers 3-9
3.2.4 Inertial Reference Units 3-12
3.2.5 Guide Telescope 3-15
3.3 Actuators 3-17
3.3.1 Reaction Wheels 3-17
3.3.2 Thrusters 3-19
4.0 References 4-1
List of Figures
Figure 1. SDO Spacecraft 1-1
Figure 2. SDO Stowed Configuration 1-2
Figure 3. SDO Deployed Configuration 1-3
Figure 4. SDO Commanded Axes and Target Sun 1-4
Figure 5. SNR Coordinate Frame Definition 2-2
Figure 6. SDO's Sensors and Actuators 3-1
Figure 7. High Gain Antenna Local Frames 3-2
Figure 8. Stowed Configuration: Spacecraft and HGA dishes (not to scale) 3-3
Figure 9. Deployed Configuration: Spacecraft and HGA dishes (not to scale) 3-3
Figure 10. SDO CSS Locations 3-5
Figure 11. "A" and "B" CSS Sensors 3-6
Figure 12: DSS coordinate system and sun angles6 3-8
Figure 13: DSS orientation on spacecraft 3-9
Figure 14: Star Tracker location and orientation 3-11
Figure 15. SDO IRU—Kearfott TARA 1T 3-12
Figure 16. SDO IRU Assembly with Coordinate Systems 3-13
Figure 17. SDO IRU System Location 3-13
Figure 18. Guide Telescope Coordinate System and Sun Vector Measurement 3-16
Figure 19. Guide Telescope Numbering5 3-17
Figure 20. SDO RW Numbering and Locations 3-18
Figure 21. SDO RW Pyramidal Configuration. Positive spin matches RWA vendor’s definition of positive axes. 3-18
Figure 22. Thruster Positions and Spacecraft Coordinate Frame 3-19
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List of Tables
Table 1: CSS Serial Numbers 3-6
Table 2. CSS Boresight Vectors 3-6
Table 3. SDO IRU Channel Axes, Spacecraft Axes, and Software Numbering 3-14
Table 4. SDO IRU Prime and Redundant 3-14
Table 5. RWA Spin Axes in the Spacecraft Body Frame 3-18
Table 6. Nominal Thruster Location and Performance 3-20
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1.0 Purpose of Document
This document gives an overview of the Solar Dynamics Observatory (SDO) coordinate reference frames and their relation to the spacecraft and geocentric inertial reference frames. In addition, this document defines the coordinate transformations between the SDO Attitude Control System (ACS) hardware components and the spacecraft coordinate system.
A three-view drawing of the SDO spacecraft is shown in Figure 1.
Figure 1. SDO Spacecraft
Figure 2 shows the stowed configuration of the spacecraft, where the solar arrays and High Gain Antennas (HGAs) have not yet been deployed. The various spacecraft modules are labeled in the diagram.
Figure 2. SDO Stowed Configuration
The deployed spacecraft configuration is shown in Figure 3, with the main instruments and hardware labeled.
Figure 3. SDO Deployed Configuration
Figure 4 shows the commanded configuration of the spacecraft. In the default science attitude, the spacecraft x-axis points towards the Sun, and the z-axis aligns the HGAs and Solar North.
Figure 4. SDO Commanded Axes and Target Sun
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2.0 Coordinate Frame Defintions
Three right-handed, orthogonal coordinate systems are used for SDO. All vectors referred to below are unit length vectors.
2.1 Geocentric Inertial Frame (GCI)
The Geocentric Inertial frame (GCI) is an Earth-centered frame in which the xGCI axis points to the vernal equinox, the zGCI axis points to the North Celestial Pole (parallel to the Earth's spin axis), and the yGCI axis is the cross product yGCI = zGCI ´ xGCI. This frame is mean of J2000.
2.2 Solar North Referenced Frame (SNR)
The Solar North Referenced frame (SNR) is a body-centered frame in which the vector to the Sun is always [1 0 0]. This frame represents the desired body attitude, or commanded attitude. The SNR frame rotates in the GCI frame at approximately 1°/day. The xSNR axis points from the spacecraft to the Sun, and the ySNR axis is defined as the cross product of the solar north pole, zH, and xSNR , or ySNR = zH ´ xSNR. The zSNR axis completes the orthogonal frame: zSNR = xSNR ´ ySNR. See Figure 5 for a pictorial representation.
Figure 5. SNR Coordinate Frame Definition
The Solar North Reference Frame is defined by:
where is the vector from the Earth to the Sun, is the vector from the Earth to the Spacecraft, and is the unit vector in the direction from the spacecraft to the Sun.
The Sun’s spin axis in the direction of the Sun's north pole, , (also known as the Solar North Pole unit vector), can be described in the Geocentric Inertial (GCI) frame using the following equation:
where and are right ascension and declination, respectively. From the inclination of the Sun and the longitude of the ascending node, the position of the Sun north pole is1
= 286.1300 deg, = 63.8700 deg
.
2.3 Spacecraft Body Coordinate System (BCS)
The body coordinate system (BCS) is centered at the spacecraft center of mass. The xBCS axis is parallel to the spacecraft centerline, and is directed from the propulsion module to the instruments. The zBCS axis is parallel to the High Gain Antenna booms, directed from the centerline to the star tracker mounting location. The yBCS axis completes the triad yBCS = zBCS ´ xBCS and is pointed along the solar arrays. (See Figure 3.)
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3.0 Hardware Components
The hardware components fall into three categories: deployables, sensors, and actuators. A detailed display of the locations of the actuators and sensors can be found in Figure 6.
Figure 6. SDO's Sensors and Actuators
3.1 Deployables
3.1.1 Solar Arrays
SDO has two solar arrays that will be deployed after separation. After deployment, these arrays will remain in a fixed position.
The solar arrays have attach points on the +y and –y faces of the spacecraft. While in the stowed position, the tips of the arrays are pointed in the –x direction, with the panel faces pointing in +y and –y. Upon deployment, the panels are positioned with their tips pointing towards +y and –y, and with their faces in the +x direction. See Figure 1 and Figure 2.
The +y solar array has a serial number of 2062540-002, and the –y solar array has a serial number of 2062540-001.
3.1.2 High Gain Antennas
SDO has two High Gain Antennas (HGA) located on the +z and –z face of the spacecraft bus. These will be referred to as the (+) and (-) antennas, and parameters referring to them will appear with a (+) or (-) superscript to indicate to which antenna the parameters apply. Where no (+) or (-) symbol is used, the reference applies to both antennas. The two HGAs are defined to have identical local dish frames, denoted by subscript “D”, as shown in Figure 7. The local zD-axis points along the HGA boom and away from the spacecraft bus, the local xD-axis points along the boresight of the dish, and the local yD-axis completes the triad. The dish frame is fixed to the antenna dish but rotates with respect to the spacecraft.
Figure 7. High Gain Antenna Local Frames
Schematics of spacecraft plus HGA assemblies for the stowed and deployed configurations are shown in Figure 8 and Figure 9, respectively. The subscript “B” denotes the spacecraft body frame in these figures. An additional gimbal reference frame (GR) is introduced in the deployed configuration. The gimbaled reference frame (GR) is fixed with respect to the body frame and co-aligns with the antenna dish frame (D) when the HGA booms are first deployed.
Figure 8. Stowed Configuration: Spacecraft and HGA dishes (not to scale)
Figure 9. Deployed Configuration: Spacecraft and HGA dishes (not to scale)
The rotation matrix from body to +z GR frame is given by
whereas the rotation matrix from body to –z GR is
While the GR frames remain fixed with respect to the spacecraft body frame, the dish frames move with the antennas. Each of the antennas is articulated by two gimbals – the inner, or azimuth, gimbal rotates about the spacecraft z-axis; the outer, or elevation, gimbals are attached to the antennas and rotate about the spacecraft y-axis if the inner gimbal rotations are zero. Consequently, the rotation of the dish frame with respect to the GR frame can be described by two sequential Euler rotations about the 3 and then 2 axis. The rotation matrix that transforms from GR to antenna dish frame can then be computed as
where a is the inner gimbal angle, and b is the outer gimbal angle. When these two angles are at their zero positions, the GR frames coincide with the antenna dish frames. Note that the above rotation matrix from GR to the dish frame is the same for both +z and –z face HGAs, but there are two sets of gimbal angles that can be changed, one for each HGA. We will use (a+b+) and (a –b –) to indicate the gimbal angles for +z and –z face HGAs, respectively. The rotation matrices from spacecraft body to the two antenna dish frames are computed below: