Van Allen Probes Spacecraft Operations July 29, 2015 Kristin Fretz

2 Van Allen Probes Summary  Both observatories continue to operate nominally  Spacecraft, ground system, and instruments are continually monitored and anomalies are tracked  Trending reviews held every 6 months with subsystems and instruments reporting on:  Last review held on June 9, 2015; no new concerns indicated by a review of current trending data  Engineering team continues to support project science in evaluating changes to orbits and spacecraft operations  Subsystem or instrument performance  Overview of major subsystem/instrument activities  Anomalous behaviors (address any open ARs)  Changes in nominal operating conditions  Trends that could impact future operations

3 Ground & Operations Highlights  Average Daily Data Return  Average daily return for the past year  SCA: 13.9Gbits  SCB: 13.9Gbits  Consistently exceeding 5.9Gb data per day requirement from each spacecraft  Regular Activities  Decouple operations allows independent operation of the spacecraft and instruments  Non-critical real time contacts unattended; ground system executes Contact Plan  Critical event contacts are staffed (e.g., precession maneuvers every 3 weeks)  Monitor spacecraft, instruments, and ground system for anomalies  Ground HW replacement plan in place; moved to new RAID system in Dec  Currently no full GSW updated scheduled

4 Spacecraft Highlights (1 of 3)  G&C/Propulsion  All trended parameters are behaving within limits  Both spacecraft require a spin down maneuver; targeting August 20  Monitor propellant usage and provide estimates of predicted end of life Spacecraft Predicted LifeSCASCB Remaining useable propellant – June 2015 (kg)39.4 ± ± 0.81 Holdout for disposal (kg)* Available for extended mission (kg) Avg. prop usage per maneuver (kg)** Nominal SC life expected in orbit (years)*** Uncertainty in predicted life estimate (+/-years) Estimated nominal EOMMay-19June-19 Current Estimate (June 2015) * Based on 20.9 yr, 2-burn disposal maneuver; passivation waiver required ** Average propellant usage per maneuver between 2015 and 2019 *** Assumes 19 E-W precession maneuvers/year  Mission Design/Navigation  Routinely perform 1-week and 2-week comparisons of prediction accuracy  All trajectory requirements are currently being satisfied  Monitor for potential conjunctions (0 high interest events in the last 6 months)  Designing science related orbit changes as needed

5 Spacecraft Highlights (2 of 3)  Telecommunications  All data (except SSPA supply current) are within expected limits  SSPA trend shows excessive decrease in DC current draw  Assuming trend continues, the mission meets requirements (2.8-dB margin at end of 8 yrs)  Thermal  All trended parameters behaving within expected limits  Temperatures not expected to increase since material properties not expected to degrade  IEM/FSW  All trended parameters behaving within expected limits  Monitor and track SBC corrected error counts, SSR total error counts, single event upsets, etc.

6 Spacecraft Highlights (3 of 3)  PDU/PGS  All trended parameters behaving within expected limits  Completed extended mission analysis of power systems operations through Nov  Adequate power system margins through the extended mission  Solar Array has sufficient capabilities to complete the extended mission (solar array degradation less than predicted)  Battery cycle and calendar life are predicted to meet the extended mission  Autonomy/FM  All key parameters are within expected limits  Continually monitor LVS, Software LVS, and LBSOC thresholds  Adjusted in accordance with eclipse seasons  Work with PGS Subsystem to determine when degradation of battery or SA will require fine adjustments of thresholds

7 On-Going Work  As understood by the engineering team, the #1 science goal is to maximize mission lifetime  GOAL: Operate through early 2019  Any changes to the orbit are evaluated by engineering team  Propellant is the limiting item for mission life  EOL power analysis shows sufficient power through Nov  Radiation analysis on worst case part predicts total dose of 20krad in Feb  Evaluated various orbit changes for science team:  Lapping Events  Continue to evaluated on a case-by-case basis  Typically use 40-70g propellant  N-S Maneuver  Science team decided to eliminate N-S maneuvers after December 2014  Decreases mission life by 1-2 months/maneuver  Lower Sun Offset Angle / Widen E-W Component  Science team decided remain at 19°north sun offset angle component  Lowering N-S component would result in shadowing of EFW booms  Apogee Maneuver  Science team decided to adjust apogees of both spacecraft by 70km  Decreases mission life by 1-2 months

8 Deorbit Maneuver  Looking at adjusting de-orbit strategy to conserve propellant for a longer life and possibly adjust orbit of one spacecraft  Requirements  Must deorbit within 25 years  Passivate battery and propulsion system  Multiple maneuver strategy  Next to last burn would meet 25 year requirement  Last burn would use ‘Propellant Uncertainty’ to shorten orbit lifetime  Working with Scott Hull (GSFC) to revise plan  Would require a waiver to NASA-STD A Process for Limiting Orbital Debris

9 Summary  Both observatories continue to operate nominally  No new concerns indicated by a review of current trending data  Engineering team continues to support project science in evaluating changes to orbits and spacecraft operations for extended mission  Radiation effects analyzed; less severe than predicted  EOL power analysis completed; sufficient power exists  Rework end of mission plan; possible changes to deorbit strategy to extend propellant life  Questions?