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HUBBLE SPACE TELESCOPE PROGRAM
Sixth European Conference on Space Debris
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Space Shuttle STS- 31 Deployment of HST on
April 25, 1990
AN EARLY STUDY OF DISPOSAL OPTIONS FOR THE HUBBLE SPACE TELESCOPE
Thomas Griffin, Scott Hull, Joy Bretthauer, Stephen LeeteNASA Goddard Space Flight Center
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Purpose for the Study
Known Reentry Risk
– HST has no propulsion system; orbit is constantly decaying
– Uncontrolled reentry in 2040 +/- ~10 years
– Risk to the ground population is ~ 0.004 (about 1:250)
Disposal Options
– Controlled reentry is one obvious option to study
– Are there other disposal options available?
Study Topics
– Are there practical options to controlled reentry for the disposal of HST, and what are the costs and benefits to each in terms of risk to both the public and the shared orbital environment?
– What is the necessary schedule for successful disposal of HST?
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Wide Field Planetary Camera 2COSTARGyrosSolar Arrays
Launch!
Imaging SpectrographNear Infrared CameraFine Guidance Sensor
GyrosAdvanced ComputerFine Guidance Sensor
Advanced CameraSolar ArraysPower Control UnitNICMOS Cooling System
GyrosWide Field Camera 3Cosmic Origins SpectrographBatteriesFine Guidance SensorSTIS RepairACS RepairNew Outer Blanket LayerSoft Capture Mechanism
SM1
SM2
SM3A
SM3B
SM4 DisposalMission
Hubble Servicing Missions
Hubble Servicing Missions
1990 1993 1997 1999 2002 2009 ~2024 3
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NASA / ESA Partnership
NASA and ESA have been partners in HST for over 30 years
Together, ESA and NASA have forged a four decade long Partnership that has revolutionized the Astronomy Community.
Original ESA/NASA HST Memorandum of Understanding was signed in 1977
This relationship will continue through the Disposal of the Observatory
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HRSDM Foundations and Lessons
In March 2004, a design effort was undertaken to perform the Hubble Robotic Servicing and De-orbit Mission (HRSDM)
Within one year, a full mission was designed through PDR
– Rendezvous and capture HST
– Change out two science instruments and spacecraft bus hardware
– Detach Servicing Module, leaving the Deorbit Module on HST
– Controlled reentry some years later
Much of the background research and planning is still applicable
– Tumble rates
– Rendezvous and capture techniques
– Propulsion system sizing
This effort spawned the current Satellite Servicing efforts at GSFC
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Orbit Decay Profile for HST
HST tumble rates are acceptable above 500 km
Earliest credible date for reaching 500 km is 2024
Disposal decisions do not need to be made immediately
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Orbit Change Options Considered
Drag Enhancement
– Can accelerate the reentry of HST
– Insufficient control to positively determine the reentry location
– Methods included balloon, mist, sail, tether
Laser Nudging
– Insufficient thrust to make substantial orbit changes
Intentional Breakup
– Makes the reentry risk worse unless all resulting particles are very small
Propulsion
– Chemical propulsion – monopropellant and bipropellant
– Electric propulsion
– Electrodynamic tether
– All are feasible, and have potential applications for HST disposal
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Disposal Options Considered
Option 1: Controlled Reentry
– Bipropellant propulsion to 50 km perigee and ocean reentry
– Removal from orbit at least 6-10 years before natural decay
– High profile event, with great consequences for anomalies
Option 2: Boost to 1200 km
– Highest practical altitude for chemicalpropulsion
– Very low existing debris density
– Long-term stable orbit
– Incompatible with existing guidelines
Option 3: Boost to 2000 km
– Electric propulsion or electrodynamic tether
– Longer time to reach the final orbit
– Naturally circular resulting orbit, meets existing guidelines
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Feasible Options Identified
HUBBLE SPACE TELESCOPE PROGRAM
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mk_overview.ppt
Collision Risks (>10 cm)
Inherent Collision Risks
– Since launch, HST has accumulated ~0.00200
– By 2024, risk estimated as 0.00300
Option 1: Controlled Reentry
– Additional large object risk is zero
Option 2: Boost to 1200 km
– Risk during orbit raising is near zero, including conjunction assessment
– Collision risk during storage estimated as ~0.00007 per year
Option 3: Boost to 2000 km
– Risk during orbit raising is near zero, including conjunction assessment
– Collision risk during storage estimated as ~0.00001 per year
Collision risks estimated using DAS 2.0.2 (ORDEM2000)
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Reentry Risks
Do Nothing: Uncontrolled Reentry
– Reentry risk is estimated as 0.004323 for reentry in 2031 (1:230)
Option 1: Controlled Reentry
– If successful, reentry risk is zero
– End-to-end risk is 0.000111 (1:9000), 39X reduction in overall risk
Option 2: Boost to 1200 km
– If successful, reentry risk is zero
– End-to-end risk is 0.000111 (1:9000), 39X reduction in overall risk
Option 3: Boost to 2000 km
– If successful, reentry risk is zero
– End-to-end risk is 0.000376 (1:2650), 11.5X reduction in overall risk
End-to-end risks include the reliability of the launch, rendezvous, and orbit change
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Conclusions
There are feasible disposal options for HST, in addition to controlled reentry
Each of the disposal options carries a different set of advantages, disadvantages, and challenges
Drag enhancement, intentional breakup, and laser nudging were all found to be impractical approaches for the disposal of HST
A decision on the ultimate HST disposal method and design can be delayed at least five years without reducing its success
Disposal Option Advantages DisadvantagesUncontrolled Reentry Zero cost Unacceptable public risk1) Controlled Reentry Lowest cost, Short time
Meets all disposal requirementsMature technologyAccepted approach
Sensitive to errorsHigh visibility
2) Boost to 1200 km Short timeLow costInsensitive to errors
Violates NASA requirements and International agreements
Higher collision risk3) Boost to 2000 km Meets all disposal requirements
Insensitive to errorsLongest timeHighest costTechnology maturity
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Questions
Please feel free to email questions to
Scott.Hull@NASA.gov
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