Recovering NEOSSat following major attitude control system failures Feb 14, 2018 Satellite Operations and Infrastructure

Acknowledgments

Near Earth Objects Surveillance Satellite NEOSSat NESS (CSA) HEOSS (DND-DRDC) Near Earth Space Surveillance  NESS High Earth Orbit Space Surveillance  HEOSS Launched 25 February 2013 PSLV C-20

NEOSSAT Missions HEOSS (High Earth Orbit Space Surveillance): Demonstrate military utility of microsatellite platform Gather metric observations of resident space objects in support of space situational awareness research & development NESS (Near-Earth Space Surveillance): Discovery, tracking and study of asteroids, especially interior to Earth orbit, comets and other astronomical objects

NEOSSat Architecture Architecture: Team: 730 km Sun-Synchronous Orbit 75kg micro-satellite based on MOST space telescope 15-cm aperture Maksutov telescope, with 0.8⁰ field-of-view Sensors: 1024 x 1024 E2V CCDs (star tracker and science) 3-axis stabilization w/ pointing accuracy ~2 arcseconds Coarse Sun Sensor (CSS) Magnetometer (MAG) Custom Star Tracker along payload boresight 3 rate sensors 4 reaction wheels 3 torque rods for momentum dumping 2 GPS receivers for orbit determination Team: Funded by CSA and DRDC Built by Microsat Systems Canada Inc (MSCI) Operated by CSA and SED in multi-mission control centre

NEOSSAT Modes Key Operational Modes: Support Modes: “Fine Point”: aka “Star Stare” mode characterize satellite/asteroid motion through streaks in images good for imaging astronomical targets “Fine Slew”: aka “Track Rate” mode track moving space objects by matching their speed (stars appear as streaks) Support Modes: “Coarse Point” with CSS and MAG to provide initial pointing for star tracker acquisition enables transition to “fine” modes “Rate Slew” to quickly move target-to-target

Activities pre-failure NESS (University of Calgary) Delivered astrometry of known NEOs to Minor Planet Centre (MPC) Obtained observatory code (C53) Comet observations at ~34⁰ solar elongation during eclipse period Other experiments/studies Limiting magnitude ~19 in Fine Point for 100s exposures, after post-processing HEOSS (DRDC) Routine tasking of resident space objects Metric observations demonstrating residuals within 3” spec

Magnetometer Failure Failure Signature Impact Severity: Critical Magnetometer became very noisy and unreliable Impact Satellite could not achieve/maintain Coarse Point, let alone Fine states All mission activities suspended due to lack of satellite controllability Severity: Critical Investigation: Attempts to recalibrate / reset magnetometer and/or control parameters were unsuccessful Ultimate conclusion was that failure was permanent Recommendation: Find an alternate coarse attitude determination strategy for NEOSSat

Health and Safety Satellite Status Maintaining thermal profile Unable to perform closed-loop control, NEOSSat was tumbling in space Ability to communicate with satellite nominal (two TTC receivers) Command and telemetry capabilities fully operational Shutter closed to prevent damage to payload CCD Battery temperatures are key health parameters monitored in telemetry Maintaining thermal profile When tumble is such that +Z face is constantly seeing the Sun, battery temperatures rise above safety limits In that situation, operators would command reaction wheels directly to “flip” the satellite to create a more favorable tumble Strategy successfully maintained health and safety as software patches were planned for a return to nominal operations

Software Update #1: “Sun Point” mode With no realistic option for hardware on-orbit servicing, software updates were the only option to recover flight operations OPS-8 Flight Software New “Sun Point” control mode, to control the Sun vector in body frame Satellite still free to rotate around Sun vector (not fully constrained) Rate sensors used to minimize satellite rotation / tumbling Augmented GPS logs, providing details on contributing GPS space vehicles Satellite Status “Sun Point” parking allowed thermal control without operator intervention Allowed opening of shutter to take image exposures and get attitude truth Post-processed attitude truth and new GPS logs allowed evaluation of new strategies to recover coarse attitude determination with available sensors

Software Update #2: GPS Attitude Sensor Team evaluated various strategies to replace failed magnetometer Strategies attempted to get more information from existing equipment, such as rate sensors, sun sensors, star tracker, GPS, torque rods, etc. Ultimately, GPS-based attitude sensor was selected for implementation Proposed by Magellan Aerospace, based on Alexrad et al. literature Augmented GPS logs and Flatsat facility allowed offline validation of strategy Ref: “Single GPS Antenna Attitude Vector Pair - NEOSSat Recovery”, Eagleson et al. OPS-9 Flight Software MSCI incorporates GPS attitude sensor into attitude control flight software Satellite Status After improvements to the coarse sun sensor and a few other software patches, CSS + GPS produced sufficient accuracy to re-achieve “Fine Point”

But before Fine Point was achieved…

Failure #2: Torque Rod Controller Failure Signature All commands to torque rod controller would time-out Impact Unable to command torque rods for perform desaturation Increase in overall satellite momentum during “Sun Point” control Eventual wheel saturation Severity: Critical Investigation: Attempts to power cycle or rewrite controller were unsuccessful Ultimate conclusion was that failure was permanent Recommendation: Find a new desaturation strategy for NEOSSat

Health and Safety Satellite Status Maintaining thermal profile Closed-loop control could only be performed for short intervals before wheel saturation would occur GPS attitude sensor not yet available, so “Sun Point” was still highest operational mode achievable However, it could not be used constantly due to momentum build-up while counteracting disturbance torques, leading to eventual wheel saturation Command and telemetry capabilities fully operational Maintaining thermal profile “Sun Point” used intermittently for thermal control; tumbling otherwise Momentum build-up would be gradually dissipated during tumbling periods In low-momentum situations, “Sun Point” to maintain battery temperatures In high-momentum situations, “Flip” was used instead

Software Update #3: DESAT Team evaluated strategies to recover satellite controllability in parallel to implementing the GPS attitude sensor for attitude determination Reaction wheels could be used for slews as long as momentum was available Conservation of momentum: wheels can only transfer momentum, not dump Ultimately, the satellite’s own residual dipole was key to the solution Earlier, body-fixed residual dipole had been discovered as a disturbance force Selected concept: new control mode orienting the satellite to optimize the desaturation effect of the residual dipole  never before proposed or demonstrated Ref: “A Novel Reaction Wheel Desaturation Method Using Satellite Residual Dipole”, Sekhavat et al. OPS-10 Flight Software MSCI successfully implements “DESAT” mode Enables return to routine “Fine” operations, with desaturation between tasks OPS-10 (flight) Momentum dumping

NEOSSat Activities Post-Recovery HEOSS Satellite Tracking (DRDC) Failed GEOs Maneuvering Special events Close Approach SSA Experiments … HEOSS Target: Mar 31

NEOSSat Activities Post-Recovery Photometry Investigations Tabby’s Star Unexplained brightness dimming events, first discovered by Kepler space telescope in Sep 2015 Beta Pictoris / Hill’s sphere transit Proposed by Bishop’s/J. Rowe, timely opportunity to observe exoplanet Hill’s sphere influence using photometry KIC 8462852

NEOSSat Activities Post-Recovery Astronomy Images Trifid Nebula: Jun 24, 2017 Lagoon Nebula: Jun 30, 2017 Eagle Nebula: July 14, 2017

NEOSSat Activities Post-Recovery Near-Earth Objects Asteroid 2012 TC4 Oct 11, 2017 Asteroid 1989VB, July 29, 2017 Asteroid 2012 TC4, Oct 12, 2017

2012 TC4 Close Approach Observation Timeline NASA-led global observation campaign, to practice strategies in the event of a real asteroid collision threat + characterize asteroid’s orbit for future passes Note: all dates are year 2017 2012 TC4 Direction of Motion Oct-11 05:46 First NEOSSat Detection Oct-12 03:00 TC4 peak brightness Lunar Orbit 2017-Oct-12 04:54 Last confirmed NEOSSat observation Oct-12 05:41 TC4 closest approach (~44,000 km altitude) Oct-12 06:18 -NEOSSat attempts observations on following orbit -Sun safety shutter closes -No observations after this time 2012-TC4 on sunward of Earth. Undetectable to NEOSSat NEOSSat can track at spefific event times (Sapphire can’t). Above shows Skynet 5A inserting itself next to NSS-6, SES-12. Notice the short positional shift of the objects between the two images relative to NSS-6 and SES-12. Sun Direction

Conclusions Recovery Effort Outcomes: Mission Outcomes: Innovative software techniques to save an operational mission Improved resiliency for space assets New applications for GPS New desaturation technique Mission Outcomes: Demonstrated utility and potential for microsatellite platforms NEOSSat contributing to space situational awareness for Canada New space-based science applications

Thank you!