Title: Development and Execution of EndofMission Operations. Case Study of the UARS and ERBS EndofMission P
1Development 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
2Agenda
- 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
3INTRODUCTION
- 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.
4NMI 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
5ERBS
- 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
6ERBS Observatory Status
7ERBS Observatory Status
8ERBS 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
9Implementing 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
10Implementing ERBS End-of-Mission Plan
11Implementing 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
12ERBS 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
13ERBS 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
14ERBS Yaw Anomaly
15ERBS 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
16Coarse Roll And Pitch Angles, Momentum Wheel
Speed And Scanwheel Speeds
17Final 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
18Final Fuel Depletion
Day 1 (DAY 286) of the Final Depletion
19Final Fuel Depletion
Day 2 (DAY 287) of the Final Depletion
Final Depletion Burn Summary Total Number of
burns TOTAL BURN TIME 70 516 Min
20Passivation
- 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.
21Lessons
- 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
22Upper 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)
23UARS
- 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
24UARS 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
25UARS 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
26Retrograde Burning
- Spacecraft must be flying in reverse to perform
retrograde maneuvers
27UARS Observatory Status
28Implementing 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
29Implementing 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
30Implementing UARS End-of-Mission Plan
31UARS Mission Calendar(Sept)
32UARS Mission Calendar(Oct)
33UARS 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
34UARS 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
35UARS/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
36Possible Maneuver Times
37UARS 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
38UARS Final Burn
39Natural Decay after Last burn
40UARS 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
41Lessons
- 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 43ERBS 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).
44ERBS 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
45Implementing 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.
46Details 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
47Contingency 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
48UARS 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
49UARS 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
50Implementing 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
51End 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
52UARS 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
53UARS Fuel Remaining Issues
54UARS 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 .