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Title: Development and Execution of EndofMission Operations. Case Study of the UARS and ERBS EndofMission P


1
Development and Execution of End-of-Mission
Operations.Case Study of the UARS and ERBS
End-of-Mission PlansJ. Hughes, J. Marius, M.
Montoro, M. Patel and D. Bludworth, NASA Goddard
Space Flight Center, Greenbelt,, MD
2
Agenda
  • Introduction
  • NMI Guidelines
  • ERBS Disposal Assessment
  • ERBS Observatory Status
  • ERBS Decommissioning Method
  • Implementing ERBS End-of-Mission Plan
  • ERBS Burn Plan Summary
  • Yaw Maneuver Anomaly
  • Passivation
  • UARS Status and Disposal Assessment
  • UARS Observatory Status
  • UARS Disposal Method
  • Implementing UARS End-of-Mission Plan
  • UARS Burn Plan Summary
  • COLA Collision Avoidance
  • Passivation

3
INTRODUCTION
  • Case study of the development and execution of
    End-of-Mission plans
  • Earth Radiation Budget Satellite (ERBS)
  • Upper Atmosphere Research Satellite (UARS).
  • Goals of the End-of-Mission Plans
  • minimize the time the spacecraft remains on orbit
  • minimize the risk of creating orbital debris.
  • Both of these Missions predate the NASA
    Management Instructions (NMI) that directs
    missions to provide for safe mission termination.
  • Ultimately the End-of-Mission operations were
    about risk mitigation.

4
NMI Guidelines
  • NASA policies and guidelines for End of Mission
    disposal of spacecraft are covered by
  • NPD 8710.3B and the associated NASA Safety
    Standard Guidelines and Assessment Procedures
    for Limiting Orbital Debris (NSS 1740.14).
  • Depleting on-board energy sources after
    completion of mission.
  • Limiting orbit lifetime after mission completion
    to 25 years or maneuvering to a disposal orbit.
  • Limiting the generation of debris associated with
    normal space operations.
  • Limiting the consequences of impact with existing
    orbital debris
  • Limiting the risk from space system components
    surviving re-entry as a result of post-mission
    disposal

5
ERBS
  • Deployed from the Space Shuttle Challenger during
    Shuttle Mission STS-41G on October 5, 1984.
  • scheduled mission life of 2 years.
  • The mission was to investigate the earth
    radiation budget
  • Thermal equilibrium that exists between the Sun,
    the Earth and space.
  • Earth Radiation Budget Experiment (ERBE)
  • Measure total solar irradiance, reflected solar
    radiation and Earth/atmosphere radiation.
  • ERBE-Scanner (ERBE-S)
  • ERBE-Non-Scanner (ERBE-NS).
  • Stratospheric Aerosol and Gas Experiment II (SAGE
    II).
  • Monitors the radiation energy of the atmosphere
    by determining the amount and global distribution
    of stratospheric aerosols, constituents such as
    nitrogen dioxide and ozone, and the natural
    background formed by ambient constituents

6
ERBS Observatory Status
7
ERBS Observatory Status
8
ERBS Decommissioning Method
  • Plan was developed to address safety first and
    spacecraft technical constraints
  • Plan timeline was very success oriented
  • The EOM plan was designed to achieve all
    passivation goals in a safe manner and meet all
    the objectives defined.
  • Perform fuel Venting operations with thrusters
    normal to velocity vector

9
Implementing ERBS End-of-Mission Plan
  • Developed Comprehensive timeline to execute the
    EOM
  • Defined Organizational Roles and Responsibilities
  • Ensure all activities are performed in accordance
    with GSFC and NASA policies and regulations
  • Vent propellant on current orbit
  • Identify procedures required to execute the EOM
  • Products and Analysis for Orbit Determination
  • Analysis for Attitude Control
  • Power Analysis
  • Command sequences and FOT activities
  • Identify Risk and Mitigation factors
  • Develop Contingency Plan
  • Reviews HQ, Peer, CAM, Project approval
  • Execute EOM Plan

10
Implementing ERBS End-of-Mission Plan
11
Implementing ERBS End-of-Mission Plan
  • All Burns were started during day since power was
    a major concern
  • Burn supports scheduled as Critical Supports
  • For the full orbit burns - DSN-Canberra supports
    were scheduled during the spacecraft eclipse to
    assess the health and performance of the
    spacecraft during the venting operations
  • The planned End of Mission activities
    wereDemonstration Burn 08 September 2005 1610
    - 1640Confidence Burn 13 September 2005-09-13
    1130 - 1630Depletion Burn 1 16 September
    1130 - 1630Depletion Burn 2 20 September
    1130 1630 Spacecraft Passivation 21
    September 1230 - 1830

12
ERBS Burn Plan Summary Fuel Remaining
  • Estimates of propellant loading
  • 175 22 lbm
  • Telemetry uncertainty in pressure reading bounds
    error ( 4.0 psia)
  • Bookkeeping uncertainty of 9.5 lbm

13
ERBS Yaw AnomalyYaw Preparation
  • During Depletion Burn I a change in thruster
    performance was seen
  • Attitude excursion indicated a loss of efficency
    in one of the pairs of thrusters
  • Post burn simulation indicated a 15 thrust
    reduction with original command load
  • Spacecraft tumbled in simulation

14
ERBS Yaw Anomaly
15
ERBS Yaw Anomaly Code 500 Review
  • To ensure that everything was done to ensure a
    safe yaw maneuver the ERBS EOM Team had Code 500
    review their preparations. Satisfied that prudent
    care had taken the yaw was executed.
  • Load was to account for the thruster imbalance
  • At the start of the yaw the thrust that was still
    15 lower than the previous burn
  • Spacecraft tumbled in flight just like in
    simulation

16
Coarse Roll And Pitch Angles, Momentum Wheel
Speed And Scanwheel Speeds
17
Final Fuel Depletion
  • Since the performance of the Propulsion system
    was changing, the EOM Team decided to perform
    small incremental burns until depletion
  • Block commands of different durations
  • 2 Min ? 6 Min
  • 4 Min ? 8 Min
  • 10 Min
  • Smaller burn durations were designed to allow the
    S/C to recover from small excursions
  • Maintained attitude control for entire depletion
    operation

18
Final Fuel Depletion
Day 1 (DAY 286) of the Final Depletion
19
Final Fuel Depletion
Day 2 (DAY 287) of the Final Depletion
Final Depletion Burn Summary Total Number of
burns TOTAL BURN TIME 70 516 Min
20
Passivation
  • Most of the remaining fuel had been removed from
    the propulsion system.
  • The Tank Pressure 40 psi (bladder pressure was
    80psi)
  • Affects on spacecraft attitude had greatly
    diminished.
  • It was decided to and passivate the spacecraft as
    planned and leave the thrusters open when the
    Spacecraft was terminated.
  • The Thruster valves would close when the bus
    voltage dropped below 12 volts.
  • Ensure the EPS system the following remains power
    negative
  • Leave Catbed Heaters ON
  • Leave Survival Heaters ON
  • Leave Instruments ON
  • Disable all (4) Commandable Solar Array Circuits
  • Change C/D Level to CD 4 (C/D 1.10 _at_ 5 C
    harder to reach 100 SOC)
  • Disable SPRU VT Reset signal
  • Put in -5 Amp Mode
  • Disable Command Storage Memory
  • Perform final tape recorder playback.
  • Disable Command Storage Memory
  • Turn RF transmitter OFF.

21
Lessons
  • Prepare early All EOM analyses needs to be done
    early and before crunch time.
  • Consistently Inconsistent Dont except a
    changing system to act the same way twice
  • Be Adaptable Develop flexibility in executing
    the plan

22
Upper Atmosphere Research Satellite
  • Primary purpose of UARS was to illuminate and
    quantify processes
  • that control stratospheric ozone, its
    distribution and variability
  • in the present atmosphere
  • Ten science instruments (constituents, solar
    flux, winds, particles)

23
UARS
  • The Upper Atmospheric Research Satellite was
    deployed from the Space Shuttle Discovery
    (STS-48) on September 15, 1991.
  • Research and exploration of the upper reaches of
    the atmosphere.
  • UARS was placed in a 585 km orbit with a 57º
    inclination.
  • Suite of 10 Instruments
  • Conceived to be retrieved by the shuttle

24
UARS Five Science Accomplishments
  • Demonstrated the dominance of human-made
    chlorofluorocarbons in atmospheric chlorine
    amounts
  • Quantified the role of chlorine in polar ozone
    loss for both the Antarctic and the Arctic
  • Quantified the transport of gases in the
    stratosphere and mesosphere
  • Quantified the ultraviolet flux variation for
    more than a solar cycle (14 years)
  • Quantified the influence of solar particles
    (protons electrons) on the stratosphere and
    mesosphere
  • gt1000 publications in journals

25
UARS Disposal Assessment
  • Launched prior to the NASA EoM directives
  • The NASA guidelines preferred method
  • Lower orbit perigee
  • Deplete all onboard hydrazine fuel
  • Discharge Batteries
  • Lifetime Analysis
  • Using existing fuel to lower the orbit, the worst
    case UARS lifetime projection is reduced to less
    than 5 years from the minimum achievable
    elliptical orbit.
  • Debris Assessment
  • This debris estimate is based on a Johnson Space
    Center Office For Orbital Debris analysis using
    the Object Reentry Survivability Analysis Tool
    (ORSAT) program

26
Retrograde Burning
  • Spacecraft must be flying in reverse to perform
    retrograde maneuvers

27
UARS Observatory Status
28
Implementing UARS End-of-Mission Plan
  • Developed Comprehensive timeline to execute the
    EOM
  • Defined Organizational Roles and Responsibilities
  • Ensure all activities are performed in accordance
    with GSFC and NASA policies and regulations
  • Lower Perigee as Much as Possible
  • Identify procedures required to execute the EOM
  • Products and Analysis for Orbit Determination
  • Analysis for Attitude Control
  • Power Analysis
  • Command sequences and FOT activities
  • Identify Risk and Mitigation factors
  • Develop Contingency Plan
  • Reviews HQ, Peer, CAM, ORR, Project approval
  • Execute EOM Plan

29
Implementing UARS End-of-Mission Plan
De-Orbit Burn 1 09/29
De-Orbit Burn 2 10/04
De-Orbit Burn 3 10/06
De-Orbit Burn 4 10/12
Yaw to reverse Flight 09/17
De-Orbit Burn 5 10/18
De-Orbit Burn 6 10/20
De-Orbit Burn 7 10/22
Yaw to Forward Flight 10/25
30
Implementing UARS End-of-Mission Plan
31
UARS Mission Calendar(Sept)
32
UARS Mission Calendar(Oct)
33
UARS Burn Summary
  • Series of calibration burns were performed to
    test new mode
  • Lower perigee through a series of 8 burns
  • Original calculations was based on 6 burns _at_ 90
    efficiency
  • Required Burns to occur over 2 reverse flight yaw
    cycles
  • Issues with fuel remaining calculations occurred
    after Burn 5
  • Priority COLA Assessments required as UARS
    approached the ISS orbit

34
UARS Fuel Remaining Issues
  • After Burn 5 the Fuel Remaining calculations
    varied
  • Range of 43.4 to 68.5 lbs
  • Remaining burn time was uncertain which made
    predicting burn unreliable
  • Multiple post-burn ephemeredes were generated to
    cover the range
  • Range of burn times allowed for one more full (18
    min burn)
  • Lower range of uncertainty had a burn time of
    17.65 minutes
  • Burn 6 was completed nominally
  • Range of burn time left UARS in the International
    Space Station (ISS) orbit range
  • Final Burns were to be Apogee Lowering Burns to
    eliminate the uncertainty of burning close to the
    ISS
  • ISS Wanted at least 3 days to respond to an
    imminent close approach
  • Due to the uncertainty Burn 7 and 8 would be
    performed as far from the ISS as possible

35
UARS/ISS COLA Issues
  • COLA is required by NASA for any orbit change of
    1 km.
  • Cheyenne Mountain Operations Center (CMOC) was
    briefed on the UARS Burn plan once UARS was
    within 30 km of the ISS orbit
  • All operations were reviewed by the GSFC Debris
    Avoidance Working Group (DAWG)
  • Burn days was chosen to provide maximum response
    time for the ISS
  • Screening ephemeredes were delivered prior to
    each manuver
  • Ephemeredes delivered by 1200 p.m. had a
    turnaround of 600 p.m. the same day.
  • COLA Waive off Criteria
  • The Burn will be waived off if the weight of
    evidence makes it safer not to burn then to Burn
  • Volume of concern violation
  • Additional analysis on accuracy for predicted
    results
  • No-Burn Case yields safer results
  • Recommendations of the Debris Avoidance Working
    Group

36
Possible Maneuver Times
37
UARS Final Burns
  • Burn 7 an apogee lowering maneuver and was
    extended to 24 minutes to cover the range of
    uncertainty
  • Burn 7 completed nominally to everybodies
    complete surprise (except the ERBS Guys)
  • Post Burn analysis suggested that the tanks were
    almost dry.
  • Lost Fuel
  • In 1996 the tank pressure fell by 4 psi and
    remained steady afterward.
  • This was known to the EOM team and treated as
    lost fuel (Bladder bubble, bad strain gauge, etc)
  • Adding this lost fuel back into the equation it
    was concluded that Burn 8 would last
    approximately 2 minutes
  • Burn 8 an apogee lowering maneuver was commanded
    off after 98 seconds
  • Tank pressure dropped off rapidly indicting the
    tanks were dry

38
UARS Final Burn
39
Natural Decay after Last burn
40
UARS Passivation
  • Power off non-vital components
  • NBTR-B Power OFF
  • Platform Sun Sensor (PSS)
  • Solar Array Drive Electronics (SADDE)
  • SSPP Gimbal Drive Electronics (GDE)
  • Power off Instruments
  • Turn on EPS load
  • Primary heaters (335W) Thermostat controlled
  • Secondary ATK heaters (94.5W) Thermostat
    controlled
  • Alignment heaters on ( A B master)
  • All alignment heaters (110W) no thermostat
    control
  • MPS MACS heaters (105W 166W) Thermostat
    controlled
  • Set VT Level to VT-1
  • Set Constant Current mode to .75A
  • Disable Attitude Control
  • Power off Magnetic Torque Rods,Earth Sensor 2 off
    (ESA-2), TAM 1 2 off
  • Reaction Wheels off (Roll, Pitch, Yaw, Skew)
  • Fine Sun Sensor off (FSS)
  • Gyros off

41
Lessons
  • Always communicate Make sure all possible
    stakeholders are aware of your plans and
    precautions
  • Sweat the small stuff Something seemingly
    insignificant may play a big role in the end
  • One at a time Attempting to do UARS and ERBS at
    the same time with the same team added complexity
  • Guidelines are not Requirements Getting the
    optimum results may not be worth the additional
    risk

42
  • Backup Slides

43
ERBS Disposal Assessment
  • Launched prior to the NASA EoM directives
  • The NASA guidelines preferred method
  • Lower orbit perigee
  • Deplete all onboard hydrazine fuel
  • Discharge Batteries
  • Orbit Lowering Maneuvers (90) would have been
    very risk due to component failures
  • ERBS will perform an uncontrolled return to the
    earth in approximately 16 years.
  • Several analyses of ERBS reentry were performed
    by GSFC to determine the Debris Casualty Area
    (DCA).

44
ERBS Decommissioning Method Background
  • On July 8, 2005, NASA HQ informed the ERBS
    Project Science Office at Langley Research Center
    to terminate the mission by the end of FY 05.
  • ESMO was officially informed of this decision on
    July 12, 2005
  • Mission Director started to organize and plan for
    spacecraft decommissioning and end of mission
    activities
  • Organized a Mission Operations Working Group
    consisted of
  • FOT
  • Power Branch
  • FDF
  • Ball Aerospace
  • LRC Science Office
  • Debris Avoidance Working Group (DAWG)
  • Network Support
  • Other Support personnel
  • Evaluated Decommissioning Options
  • Developed End of Mission Plan

45
Implementing ERBS End-of-Mission Plan
  • The ERBS Flight Operations Team
  • One offline engineer
  • Four console operators
  • Student Interns from the Capitol College
  • Space Operations Institute (SOI) supplement the
    FOT on a limited basis
  • The console operators cover four shifts at a
    level of one operator per shift.
  • The offline engineer performs the planning and
    scheduling functions for the mission
  • End of Mission Activity
  • the offline engineer will lead the console
    operations
  • operators - double up to support the End of
    mission activities.
  • SOI Interns - available to assist as needed.

46
Details of Burn Plan
  • Test burn, 20 minutes
  • checks thrusters, command loads, modulation
    prediction
  • Confidence Burn, 5 hours
  • use same 20 minute block repeatedly
  • duration limited by people consideration
  • Depletion Burn 1, 5 hours
  • Depletion Burn 2, to depletion or stop at 5
    hours
  • No anomalous thrusting when tanks go dry
  • Thruster temperature and attitude stability
    indicate empty tanks
  • no need to know when it occurs
  • Normal pointing uses wheels, depletion doesnt
    effect this

47
Contingency Plans
  • Risks
  • thruster malfunction - wild tumble, recovery
    questionable
  • memory hit - pitch excursion
  • command load error - wild tumble, recovery
    questionable
  • Criteria
  • RW spin speed outside 1000 to 3000 RPM range
  • attitude errors greater than 10 deg
  • memory hit causing temporary thruster loss
  • power problems
  • loss of telemetry capability
  • Action
  • disable NORMAL and BLOCK memory, turn thrusters
    off
  • correct momentum with thruster A pulse only for
    memory hit

48
UARS Background
  • UARS Project Science Office was instructed in
    July 2005 by senior managers at NASA Headquarters
    to terminate the mission by the end of December
    2005
  • ESMO was officially informed of this decision on
    July 8
  • Mission Director started to organize and plan for
    spacecraft decommissioning and end of mission
    activities
  • Organized a Mission Operations Working Group
    consisted of
  • FOT Honeywell
  • Power Branch
  • GNCS/FDS
  • SGT
  • Science Office
  • Debris Assessment Group
  • Debris Avoidance Working Group/Cheyenne Mountain
  • Network Support
  • General Dynamics
  • Evaluated Decommissioning Options
  • Developed End of Mission Plan

49
UARS EOM Procedure
  • The EOM procedures for UARS to meet EOM
    requirements include
  • De-orbiting activities by lowering perigee
  • These activities do NOT result in a "controlled
    re-entry"
  • There is not enough hydrazine aboard to
    accomplish that purpose. 
  • The lowering the orbit will result in an
    "uncontrolled re-entry" of the UARS around 2010.
  • Terminate Science Operations HALOE turn off in
    mid December
  • Depleting on-board energy sources after
    completion of mission
  • Passivate Spacecraft
  • Discharging Batteries
  • Disable OBC

50
Implementing UARS End-of-Mission Plan
  • The UARS Flight Operations Team
  • Three Off-Line engineers
  • One Mission Planner
  • Four Flight Ops Directors 3 On-Line Evaluator /
    Mission Planner
  • End of Mission Activity
  • UARS lead Engineer led the End-Of-Mission console
    activities
  • Mission Planner worked with the FD Maneuver Team
    to schedule burn operations
  • Mission Director provided go /no-go for EOM
    activities
  • FD Operations monitored maneuvers in real-time
  • All Activities were closely coordinated with
    Cheyenne Mountain Operations Center

51
End Of Mission Planning
  • Phase 1 July 8 September 22
  • EOM Planning
  • Approvals and direction
  • Reviews
  • Phase 2 September 1-22
  • FSW Change for 4-thruster burn
  • Test Plan
  • Simulation
  • Test Burns
  • Phase 3 September 29- October 20
  • De-orbiting
  • Phase 4 October 20- December 15
  • Continue HALOE observations
  • Phase 5 December 16-20
  • Passivation

52
UARS Burn Summary
  • Plan was developed to address safety first and
    spacecraft technical constraints
  • Plan timeline was keyed to the direction of
    flight and was very success oriented
  • Perigee lowering burns scheduled for October and
    December
  • 18-minute burns.
  • Burn at Apogee 10 min
  • 5 minutes around maneuvers must fall within
    TDRSS views from either TDRS-E, TDRS-W and/or
    TDRS-275.
  • Minimum TDRSS view periods need to be 28 minutes

53
UARS Fuel Remaining Issues
54
UARS Final Burns
  • Uncertainty in the amount of fuel available of
    approximately 25 lbs (Peak)
  • Final UARS orbit lowering maneuvers will
  • Lower the perigee to nearly that of ISS
  • Possibly deplete the fuel (lower estimate of
    remaining fuel)
  • All results of predicted maneuvers are
    completely uncertain.
  • Goal
  • Maintain large separation with ISS for nominal
    burn
  • Maximize response time in the event that the burn
    duration is not as expected
  • Perform Burn immediately following time of
    closest approach (1 or 2 orbits). This will
    ensure that the minimum reaction time before the
    next time of close approach is 60 hours (69 hours
    if ISS orbit raised)
  • Period of close approach were 2.72 days 65 (hrs)
    after burns .
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