Attitude Control System (ACS).ppt

1、Attitude Control System (ACS),Eric Holmes, Code 591 Joe Garrick, Code 595 Jim Simpson, Code 596 NASA/GSFC August 16-17, 2005,Lunar Reconnaissance Orbiter (LRO) ACS Subsystem Document Tree,Level 2 431-RQMT-000004 LRO Mission Requirements Document 431-PLAN-000131 Lunar Reconnaissance Orbiter Spacecraf

2、t Performance Assurance Implementation Plan 431-OPS-000042 Lunar Reconnaissance Orbiter Concept and Operations Document 431-SPEC-000012 LRO Mechanical Systems Specification 431-SPEC-000091 Lunar Reconnaissance Orbiter General Thermal Subsystem Specification 431-ICD-000018 LRO Power Subsystem Electro

3、nics Electrical Interface Control DocumentLevel 3 431-SPEC-000162 Lunar Reconnaissance Orbiter Guidance, Navigation and Control Attitude Control System Specifications 431-SPEC-000063 Flight Dynamics Specification 431-RQMT-000113 LRO Pointing and Alignment Specifciation 431-PROP-000017 LRO Propulsion

4、 Subsystem SOW and Specification 431-ICD-000008 Lunar Reconnaissance Orbiter Electrical Systems Interface Control Document 431-RQMT-000045 Lunar Reconnaissance Orbiter Radiation Requirements 431-RQMT-000092 Lunar Reconnaissance Orbiter Thermal Math Model Requirements,This list reflects the ACS hardw

5、are complement needed to meet requirements and with selective redundancy ensure minimal risk,The LRO ACS will utilize the hardware needed to implement the general and derived requirements stated in this ACS Specifications document. - IRU shall provide 3-axis angular rate and delta angle information

6、to the ACS. - 8 CSS total to allow for as much spherical coverage as possible and for redundancy. - 2 STs to ensure the ACS onboard knowledge is maintained during occultations. - 4 reaction wheels for momentum storage and attitude control. - 8, 5 lbf (TBD) for attitude/orbit/momentum unloading - 2,

7、20 lbf (TBD) for orbit insertion/maintenance - Engine Valve Driver (EVD) electronics for thruster control - The ACS will interface with other spacecraft hardware electronics,ACS-3.2.12.1 ACS-3.2.13.7 ACS-3.2.14.2 ACS-3.2.15.1 ACS-3.2.16.1,MRD-084 MRD-085 MRD-087,Control modes reflect pointing and fu

8、nctional requirements for the different phases of the mission,The LRO ACS will implement the necessary control modes to meet all pointing requirements during all phases of the mission. - Sun Acquisition: coarse sun pointing for anomalous conditions - Observing: science taking mode - Delta-H: momentu

9、m unloading - Delta-V: orbit insertion, orbit adjusts and station keeping maneuvers.,ACS-3.2.4.1 ACS-3.2.5.1 ACS-3.2.6.1 ACS-3.2.7.1,MRD-088 MRD-089 MRD-091,ACS needs to ensure proper pointing throughout lifetime,LRO ACS will be responsible for maintaining the proper spacecraft attitude throughout t

10、he mission lifetime,MRD-084,Requirement,Paragraph,Concept/Compliance,Level 3: Requirements,Level 2 Req.,Lunar Reconnaissance Orbiter (LRO) ACS Subsystem Level 2 Flow Down Key Requirements,Accuracies needed to maintain velocity vector that will meet orbit maintenance requirements during burns,The LRO

11、 ACS shall meet the pointing, knowledge and stability requirements associated with all thruster modes. Knowledge (Resolution) 5.0 deg, per axis, (3s) Accuracy (Control) 0.1 deg, per axis, (3s) Stability N/A,ACS-3.1.5.2,MRD-049 MRD-087 MRD-092,Represents needed ACS and Mechanical allocations for poin

12、ting accuracies,The LRO ACS shall meet the pointing, knowledge and stability requirements at the instrument interface associated with the Observing Mode. Knowledge (Resolution) 60.0 arcsec, per axis, (3s) Accuracy (Control) 30.0 arcsec, per axis, (3s) Stability 5 arcsec, per axis, over 1 msec. 10 ar

13、csec, per axis, over 100 msec.20 arcsec, per axis, over 4 sec.,ACS-3.1.4.3,MRD-049,The LRO ACS will compute and provide HGA and Solar Array gimbal commands. -The ACS shall ensure commanding of the HGA to an accuracy of TBD degrees. -The ACS shall be responsible for commanding the Solar Array to an i

14、ndex position -The ACS shall ensure that the Solar Array tracks the sun to an accuracy of 5 degrees.,ACS-3.1.13.3 ACS-3.1.14.4 ACS-3.2.17.1 ACS-3.2.18.1,MRD-015 MRD-016 MRD-049 MRD-084,Requirement,Paragraph,Concept/Compliance,Level 3: Requirements,Level 2 Req.,Lunar Reconnaissance Orbiter (LRO) ACS

15、Subsystem Level 2 Flow Down Key Requirements,ACS will determine and track pointing commands and slewing profiles for HGA and Solar Array,Lunar Reconnaissance Orbiter (LRO) ACS Subsystem Level 2 Flow Down Key Requirements,Need to keep frequency of science interruptions to a manageable level,The ACS s

16、hall implement hardware and software capable of managing momentum for periods of no less than 2 weeks over the life of the mission.,ACS-3.1.10.4,MRD-017,Control system design practices that have long been used by GN&C will be employed here,All ACS control modes shall meet stability margins in accord

17、ance with established GN&C design practices with a single set of gains for the entire range of inertias over the mission lifetime, from Beginning of Life (BOL) to End of Life (EOL).,ACS-3.1.3.1,Requirement to keep spacecraft in a power positive and thermally protected pointing,The LRO ACS shall meet

18、 the pointing, knowledge and stability requirements associated with the Sun Acquisition Mode. Knowledge (Resolution) N/A Accuracy (Control) 15 deg from targeted sun line, RSS (3s) Stability N/A,ACS-3.1.7.1,MRD-090,Requirement,Paragraph,Concept/Compliance,Level 3: Requirements,Level 2 Req.,Prolonged

19、sun exposure can damage science instruments,The ACS shall ensure sun avoidance of science instruments to within 30 degrees of nadir (+Z axis ), or shall ensure the sun passes through their boresights with a rate of no less than 0.1 deg/sec.,ACS-3.1.12.1,MRD-052,Lunar Reconnaissance Orbiter (LRO) ACS

20、 Subsystem Level 2 Flow Down Key Requirements,ACS will monitor status and react appropriately to anomalies,The ACS subsystem shall provide an onboard means of failure detection and correction (FDC) for anomalous conditions.,ACS-3.2.11.1,Use method that will ensure capability to null residual rates t

21、o allow transition to initial pointing.,Nulling of tip-off rates and residual despin rates will be initiated autonomously after separation, using thrusters or wheels. Wheels shall be able to handle up to 2.0 deg/sec, per axis.,ACS-3.1.10.1 ACS-3.2.3.1,MRD-005 MRD-006 MRD-026 MRD-027,Yaw maneuver to

22、keep sun on warm side of spacecraft and minimize science interruption,The LRO ACS shall provide a 180 yaw maneuver during the Observing Mode and shall take no more than 20 minutes.,ACS-3.1.15.6 ACS-3.1.15.7,MRD-018,Requirement,Paragraph,Concept/Compliance,Level 3: Requirements,Level 2 Req.,Separatio

23、n,CSS Sun Acquire (with and w/o gyros),Nadir Pointing (Primary Mission),Inertial Pointing,Offset Pointing,Delta-H,Delta-V,Thruster Modes,Observing Mode,Power On / Reset,LRO GN&C Nominal Control Mode Flow,Command Only Transition,Autonomous Transition,Autonomous (Post Separation Sequence, Thrusters),N

24、o transitions between Thruster Modes,Any Observing Sub-Mode can be commanded to any other Observing Sub-Mode,= Command-Only Transition,= Autonomous (Post Separation) Transition,= Autonomous (Nominal) Transition,Autonomous (Post Separation Sequence, wheels),All Modes (FDC Corrective Action),Note that

25、 autonomous transition paths can also be commanded, but command-only paths cannot occur autonomously,Momentum Level?,LRO Top Level Block Diagram,Lunar Reconnaissance Orbiter (LRO) ACS Subsystem Preliminary Verification Approach,Components All sensors and actuators, are expected to have been previous

26、ly qualified Acceptance testing required of all components (mechanical, thermal, and electrical)Subsystem Subsystem verification at the spacecraft level will be performed using a combination of functional and performance tests augmented by analysis and simulation Dynamic simulator to perform hardwar

27、e in the loop testing,Lunar Reconnaissance Orbiter (LRO) ACS Summary,LRO ACS driving requirements are defined Pointing performance and ACS functional requirements have been defined Preliminary architecture has been identified which will satisfy driving requirements ACS control modes have been define

28、d which will satisfy driving requirements Interfaces between the propulsion system and the following subsystems have been defined at Level 3 and are being developed at Level 4: Mechanical Thermal C&DH Propulsion Electrical Power FSWACS subsystem ready to proceed PDR Performance and Functional Requirements Understood Sufficient to Size Actuators Sufficient to Proceed with Hardware Procurements Sufficient to Develop Controller Algorithms,