Section 12.0 Guidance, Navigation & Control Samuel J. Placanica GN&C Lead Engineer ST5 PDR June 19-20, Space Technology “Tomorrow’s Technology Today” GSFC

ST5 PDR June 19-20, 2001 GSFC Agenda Requirements Documentation Components Operational Modes Mission Planning Attitude Determination Dynamic Simulator Risk Mitigation

ST5 PDR June 19-20, 2001 GSFC General System Requirements (1 of 2)  Spin stabilized spacecraft control. (MRD ) –Utilize attitude design techniques to maintain spin stabilization control –Spin-to-transverse inertia ratio greater than 1.2  Provide ground-based attitude determination and maneuver planning capabilities. (MRD ) –Utilize sun sensor and magnetometer data in conjunction with standard sun position and geomagnetic field (IGRF-2000) reference models  Provide the capability to perform spin axis attitude maneuvers and orbit adjustment maneuvers. (MRD ) –Magnitude of attitude maneuvers calculated on the ground and based upon attitude determination results and mission planning –Initiated by either real-time or stored program commands –Uses the Cold Gas Micro Thruster System

ST5 PDR June 19-20, 2001 GSFC General System Requirements (2 of 2)  Implement a pre-programmed autonomous Sun Acquisition Mode (SAM). (MRD ) –GN&C will provide to Flight Software an algorithm document which presents the SAM control equations  Passively control spacecraft nutation. (MRD ) –Nutation will be dissipated using a ring-like shaped damper which will be fully filled with silicone oil  A Dynamic Simulator (DS) shall be designed to simulate a realistic orbital environment on the ground and emulate the functionality and performance needed for spacecraft level GN&C and science validation requirements. (MRD ) –Based upon SMEX/Triana DS heritage –Tenth order magnetic field model –Includes science event modeling

ST5 PDR June 19-20, 2001 GSFC Specific Requirements (1 of 2)  Spin Rate Operation Range –Perform autonomous SAM following launch vehicle release; spin rate greater than 20 rpm –20 rpm ± 10% following magnetometer boom and antenna deployments  SAM Performance –Maintain the sun to within 5 degrees of the normal to the solar panels –Spin rate knowledge: ± 10% (3 sigma) –Spin axis pointing knowledge: ± 5 degree (3 sigma) –Limit thruster actuation for any single SAM activity  Nominal Spacecraft Operation Performance –Maintain spin axis to be within 5 deg (3 sigma) of the ecliptic pole –Spin rate knowledge: ± 3% (3 sigma) –Spin axis pointing knowledge: ± 1 deg (3 sigma)

ST5 PDR June 19-20, 2001 GSFC Specific Requirements (2 of 2)  Provide the capability for a full 540 deg attitude maneuver –Includes margin for worst case precession maneuver scenario  Nutation Control –Time constant less than 60 minutes –Steady-state nutation angle less than 0.5 degrees –Maximum nutation angle due to launch vehicle release is to be less than 10 degrees  Spacecraft relative separations between 100 and 1000 km at apogee  All spacecraft to have the same orbital period  No constellation station keeping is required  Comply with NASA Safety Standard regarding orbital debris

ST5 PDR June 19-20, 2001 GSFC Documentation GN&C Subsystem SpecificationST Preliminary GN&C Algorithms DocumentST Preliminary Magnetometer System SpecST Baseline Magnetometer System SOWST Baseline Magnetometer Mechanical ICDDraft Magnetometer Electrical ICDDraft Sun Sensor SpecificationST Preliminary Sun Sensor Statement of WorkST Preliminary Sun Sensor ICDDraft Attitude Determination andDraft Maneuver Planning Document Dynamic Simulator Users GuideDraft Nutation Damper Spec and ICDDraft Document Number Status

ST5 PDR June 19-20, 2001 GSFC /8 inch Damper AssemblyGD Draft 5/8 inch TubeGD Draft Fill Adapter for 5/8 inch TubeGD Draft Tube ClampGC Draft Test StandGD Draft Configuration Damper FillGD Draft Drawings Nutation Damper DrawingsNumberStatus

ST5 PDR June 19-20, 2001 GSFC Magnetometer Science-grade device provided by UCLA Component includes sensor head, electronics and interface cable Dynamic range –0 to 64,000 nT over two range bands Resolution –1 to 2 nT in 64,000 nT field –0.1 to 0.2 nT in 1000 nT field Sample rate –16 three-axis measurements per second Data will also be used for ground-based attitude determination activities

ST5 PDR June 19-20, 2001 GSFC Magnetometer Total mass: ~ kg –Electronics unit: ~ kg –Electronics chassis: ~ kg –Sensor head: ~ kg –Interface cable: ~ kg Total power: W –Electronics unit: W –Sensor head: W Volume/Length (cm) –Electronics chassis : 10 x 10 x 12 –Sensor head: 4 x 4 x 6 –Interface cable: 100 max Thermal operating environment –Electronics unit: -20 to +40 deg C –Sensor head: -20 to +40 deg C –Interface cable: -100 to +40 deg C Thermal survival environment –Electronics unit: -40 to +50 deg C –Sensor head: -40 to +50 deg C –Interface cable: -130 to +80 deg C

ST5 PDR June 19-20, 2001 GSFC Sun Sensor Accuracy: ± 0.25 deg Resolution: ± deg Volume (estimated): 74 cm 3 Mass (estimated): 0.16 kg Power (estimated): W Thermal environment –Operating: -20 to +50 deg C –Survival: -40 to + 60 deg C Radiation –100 Krad (Si) Total dose, SEU and latch-up immune Manufactured by Adcole Corp. 4 π steradian field of view (spinning) Will provide sun elevation and sun pulse data

ST5 PDR June 19-20, 2001 GSFC Nutation Damper (1 of 2) Passive device will damp nutation induced by both launch vehicle release and thruster firings GSFC in-house design and fabrication Fully-filled with silicone oil Will be mounted inside spacecraft along a wall Performance and environmental testing will be performed

ST5 PDR June 19-20, 2001 GSFC Nutation Damper (2 of 2) Size: 18 cm x 18 cm Tubing material: Aluminum Alloy 6061-T6 –0.625 inch outer diameter –0.035 inch wall thickness Fill adapter material: Aluminum Alloy 6061-T6 Fluid: Fully filled with Dow Corning 200 Silicone –5 centistoke viscosity at 25 deg C Mass (best current estimate): kg Power: None Thermal –Operating:-20 to +50 deg C –Survival:-40 to +60 deg C

ST5 PDR June 19-20, 2001 GSFC Operational Modes (1 of 2) Standby Mode –Used during nominal spacecraft operations –No thruster activity Sun Acquisition Mode (SAM) –Can remain in mode for indefinite amount of time –Uses on-board flight software to process sun sensor data –SAM control logic will issue the appropriate commands to the cold gas thruster to orient spacecraft into a power positive attitude –Activation methods: Autonomously entered following launch vehicle release On cold CPU reset, initialization will boot spacecraft CPU into SAM Ground command

ST5 PDR June 19-20, 2001 GSFC Operational Modes (2 of 2) Maneuver Mode –Spacecraft spin axis is processed to a pre-determined orientation –Required prior to a delta V in order to orient the spacecraft spin axis along the velocity vector –Ground-based processing of sun sensor and magnetometer data results in thruster fire commands which are uploaded to the spacecraft and executed in open-loop fashion Delta V Mode –Required to maneuver the three spacecraft into a mission orbit constellation in order to demonstrate inter-spacecraft communications/crosslink capabilities –Ground command

ST5 PDR June 19-20, 2001 GSFC System Block Diagram Sun Sensor C&DH Card Cold Gas Micro Thruster System Thruster Commands Magnetometer Sun Sensor And Mag Telemetry Ground Station Attitude/Orbit Determination Develop Thruster Cmds SAM FSW Telemetry Processing Standby Mode SAM Maneuver & Delta V Modes No Command

ST5 PDR June 19-20, 2001 GSFC Rhumb Line Precession (1 of 2)  First used thirty years ago on Early Bird and still frequently employed to reorient spinning spacecraft.  A constant heading angle   is maintained throughout the maneuver.  The heading angle is computed based on the known initial orientation and the desired final orientation.

ST5 PDR June 19-20, 2001 GSFC Rhumb Line Precession (2 of 2) Heading angle is used to compute a phase angle from the sun presence signal Phase angle is used with the estimated spin rate to compute a time delay between sun presence and the thruster pulse Orientation in the Spin Plane at Sun PresenceOrientation in the Spin Plane at Thruster Pulse

ST5 PDR June 19-20, 2001 GSFC Thruster and C&DH Interface Digital Sun Sensor Sun Elevation Sun Presence Clock Sun Presence Time Thruster Delay Time Thruster Pulse Width Thruster Enable Flight Software C&DH Sun Presence Thruster Delay Time Thruster Pulse Width Sun Presence Spacecraft Spin Period 0 1 Time Flight software sends the Delay Time, Pulse Width and Enable flag to C&DH C&DH produces the thruster commands in the form of a pulse train that repeats at the spin period in Sun Acquisition and Maneuver Modes and at 2 Hz in Delta V Mode

ST5 PDR June 19-20, 2001 GSFC Sun Acquisition Mode Block Diagram Filter Sun Elevation Threshold Comparison With Hysterisis Thruster Enable Flag If pos then   = 270° If neg then   = 90° Sun Presence Time Spin Rate Estimation Thruster Delay Calculation Thruster Delay Time Compute Variance

ST5 PDR June 19-20, 2001 GSFC Mission Planning Constellation - Formation defined as inter-spacecraft distances greater than 100 km and less than 1000 km at apogee Lifetime - 3 months, 6 month goal On-board maneuvers to final configuration Orbit Debris mitigation - NASA NSS Orbit Determination - 10 km knowledge All spacecraft in same orbit plane, identical periods Delta V required to deploy from geosynchronous transfer orbit no greater than 1.6 m/s No provision for orbit maintenance

ST5 PDR June 19-20, 2001 GSFC Orbit Characteristics Assumptions –Launch November 2003 –Nominal Orbit: from empirical survey of launch vehicle histories 200 x 38,000 km altitude (Period: 10.5 hours) 28 deg inclination perigee at descending node (typical LV injection for GTO) apogee sun side (noon) Eclipse History –30 minutes max eclipse, 143 days from launch Lifetime - nominal scenario –+2 sigma solar flux = 1.1 years, meets 6 month goal

ST5 PDR June 19-20, 2001 GSFC Lifetime Estimate for Initial 200 x 38,000 km Orbit 25 kg30 kg20 kg Preliminary

ST5 PDR June 19-20, 2001 GSFC Lifetime Estimate - Perigee Variation 200 km 215 km 225 km 250 km Preliminary

ST5 PDR June 19-20, 2001 GSFC Attitude Determination Shall accurately determine rate and attitude of the spacecraft for both the normal on-orbit mode and the orbit and attitude adjustment modes The ground-based Attitude Determination System (ADS) will reuse components from the MultiMission Spin-Axis Support System (MSASS) MSASS is a Matlab-based attitude determination system which has been used to support several GSFC missions, including FAST, Wind, and Polar ADS will utilize magnetometer and sun sensor telemetry data GN&C will provide hardware and analysis tools to support two redundant strings in the mission operation control center

ST5 PDR June 19-20, 2001 GSFC Dynamic Simulator (1 of 2) Simulator core simulates single spacecraft Simulator core code is hosted in a single PC-compatible Simulator core code is a ‘C’ program running under Linux Interface is through commercial PCI plug-in cards (via custom hardware as needed) ASCII text configuration files are used extensively to allow rapid re- configuration as needed Internal data is stored in a mnemonic-driven database Simulator core is derived from SMEX/Triana heritage code (especially Triana and FAST) One copy of simulator to be built for each of three test environments (Flight S/W, C&DH S/W, and FlatSat – no testing at spacecraft level intended)

ST5 PDR June 19-20, 2001 GSFC Dynamic Simulator (2 of 2) Simulator can be configured for “open loop” operation (i.e., sensor data is static regardless of actuators and dynamics, and interfaces can be tested in this fashion) Simulator can be configured for “mixed loop” operation (i.e., sensor data reflects the response of the dynamics to constant actuation regardless of actual commands, and interfaces can be tested in this fashion) Simulator can be configured for “closed loop” operation (i.e., sensor data reflects the response of the dynamics to the actuator commands received) Regardless of loop configuration, individual sensors and actuators can be disconnected from the simulator and actual hardware substituted (it will not then be “in the loop”) No simulation of GPS or inter-spacecraft signals intended

ST5 PDR June 19-20, 2001 GSFC Risk Mitigation Risk: Magnetometer electronics parts availability -Mitigation: GSFC will assist UCLA in parts procurement Risk: Sun sensor shock environment -Mitigation: Adcole will perform analysis and redesign to strengthen the sun sensor in the areas of recticle hold-down and recticle/solar cell separation Risk: Rapidly decaying orbit -Mitigation: Provide larger delta V capacity Acquire higher perigee altitude due to launch vehicle insertion Accommodate through system-level design