# Presentation: 103208

## Orbital Debris MitigationSafe Disposal Planning Begins at Concept Design

- Scott Hull
- Josephine San
- GSFC Code 591

## Agenda

- Overview of NPD 8710.3 and NSS 1740.14, 	Scott Hull  And Reentry Analysis Basics
- GSFC Safe Disposal Planning 	Josephine San
- Design for Demise Examples	Scott Hull
- Current Status	Scott Hull

## Overview of DocumentationAnd Reentry Analysis Basics

- Scott Hull / 591
- NASA/GSFC

## NASA Policy

- Debris assessment shall be done for all missions at mission PDR and CDR
- Design for safe disposal at the end of the mission
- Notify other government agencies when NASA related hardware reenters
- Promote international cooperation on debris related issues

## Applicable Documents

- NPD 8710.3A
- Recently revised
- Requires an ODA to be written
- Invokes NSS 1740.14
- NSS 1740.14 (to be replaced by NS 8719.14)
- Guidelines for debris mitigation
- Evaluation instructions
- GSFC ISO Documents
- Debris Mitigation
- Controlled Reentry
- Reentry Survivability

## NPD 8710.3A ResponsibilitiesProgram/Project Manager

- Ensuring implementation of NSS1740.14
- Ensuring that an ODA has been performed
- Coordinating the ODA results with NASA HQ
- Ensuring that environmental assessment is performed
- Designing for end of mission disposal and submitting an end of mission plan to Code S/Y/U
- Communicating with DOD before significant orbit changes

## NPD 8710.3A ResponsibilitiesNASA Headquarters

- Code S/Y/U
- Approving ODA reports
- Reviewing the cost analysis if applicable
- Approving the end of mission plan
- Code Q
- Establishing policies
- Providing guidelines and standards
- Reviewing ODA reports and end of mission plans
- Providing software tools for evaluating orbital debris
- Coordinating NASA reentry information within the agency
- Code I
- Coordinating international agreements
- Developing procedures for coordinating information on significant reentries with other US government agencies
- Coordinating pre-reentry press releases with the National Security Council and the White House Office of Science and Technology Policy
- Code P
- Coordinating pre-reentry press releases

## NPD 8710.3A ResponsibilitiesJSC Orbital Debris Program Office

- Maintaining the orbital debris environment models
- Providing technical guidance on ODA issues
- Providing technical review of ODA reports
- Reviewing end of mission plans
- Providing technical and policy guidance to all NASA HQ offices and centers
- Maintaining a list of reentry predictions
- Updated every six months
- Sent to Code Q
- Promoting the use of international guidelines

## Orbital Debris Assessment (ODA)Report Review Process

- Program/Project Manager sends report to Code S/Y/U
- Code S/Y/U forwards it to Code Q
- Code Q forwards it to JSC-ODPO
- JSC-ODPO review comments sent back through Code Q to Code S/Y/U
**Code S/Y/U Associate Administrator makes the final decision** whether to accept the ODA and disposal plans

## What is in an ODA?

- Executive Summary
- Section 1: Introduction
- Section 2: Spacecraft/Mission Description
- Section 3: Operational Debris
- Section 4: Accidental Explosions and	           Intentional Breakups
- Section 5: On-orbit Collision Risk
- Section 6: Postmission Disposal
- Section 7: Reentry Survivability
- Conclusion

## ODA Conclusions

- Assessment was performed per NPD 8710.3A
- Overall findings
- All applicable guidelines were met
- All but X, Y, and Z were met
- Table of findings is recommended
- Include all guidelines
- Indicate whether each is Met, Not Met, or Not Applicable, and any necessary comments
- Always include the DCA and casualty odds

## NSS 1740.14 Guidelines

- Basically follows the report structure
- Report doesn’t necessarily call out all of the guidelines, though
- 14 guidelines, 7 sections
- Table of findings helps to prevent holes
- Most heavily scrutinized are 4-2, 5-1, 5-2, 6-1, 6-4, and 7-1

## NSS 1740.14 Guideline 4-2

- Accidental Explosions Postmission
- Risk to other spacecraft
- “All on-board sources of stored energy will be depleted when they are no longer required for mission operations or postmission disposal.”
- Proposed change: Recommendation to perform propellant depletion burns to reduce orbit lifetime.

## NSS 1740.14 Guideline 6-1

- Disposal from orbits passing through LEO (choose one)
- 6-1 a. Atmospheric reentry
- Orbit decay < 25 years after end of mission
- Uncontrolled reentry
- Controlled reentry
- 6-1 b. Maneuver to a storage orbit
- 	Perigee > 2500 km, Apogee < 35,288 km
- 6-1 c. Direct retrieval
- Proposed changes:
- Orbital lifetime < 30 years
- Specific language on controlled reentry
- Perigee > 2000 km, Apogee < 35,588 km

## NSS 1740.14 Guideline 6-4

- Reliability of Postmission Disposal
- Applies to both spacecraft and upper stages
- Identify all credible failure modes
- Probability of success _>_ 0.99
- Proposed change: Reliability of _>_ 0.90 acceptable if _not_ performing controlled reentry.

## NSS 1740.14 Guideline 7-1

- Risk from Surviving Debris
- Only applies to atmospheric reentry
- Function of spacecraft construction and materials chosen
- Debris Casualty Area _<_ 8 m2
- Complex simulation
- Proposed changes: Reentry risk _<_ 1 in 10,000 considering inclination and year of reentry; casualty threshold (> 15J) added officially

## Debris Casualty Area (DCA)

- The DCA is the portion of the Earth surface on which a person is likely to be injured by a piece of falling debris.
- When an object survives, a 0.3m “man-border” is essentially added to the circumference of the object

## Reentry Process

- Atmosphere entry: 122 km altitude
- Appendages breakoff
- Catastrophic breakup: Typically ~78 km
- Some recent evidence for lower breakup on larger spacecraft
- Object burnup: Generally ~80 to 55 km
- Cooling / survival: Below ~50 km

## Reentry Terms

## Effort Spent on Reentry Simulation

## Component Modeling

- Spacecraft components need to be modeled as one of four shapes:
- Sphere	Cylinder	Box	Flat Plate
- Choice is based on preserving surface area and cross-sectional area
- Many real components are difficult to model

## Component ModelingExample - Washer

- Circular top view resembles cylinder
- Side view resembles a box
- If tumbling, sweeps out a sphere
- If cut and straightened, flat plate results
- JSC recommends using a flat plate model

## Ablation

- An object is said to have ablated (demised) when it has fully melted
- Heat of Ablation
- HAblat = Mass x [Cp x (Tmelt – T init) + HFusion]
- Heat Balance Equation
- qnet = qconv + qrad + qox – qrr
- 	 qconv = average aerodynamic heating
- 	 qrad   = gas cap radiation heating
- 	 qox   = oxidation heating
- 	 qrr     = reradiative cooling

## DAS Software Overview

- Debris Assessment Software
- Written by JSC ODPO
- Very useful for evaluating Guidelines 5, 6, and 7
- Current version is 1.5.3
- Stand-alone software
- Downloadable from JSC ODPO web site
- Web-based interface
- Available to to GSFC domains only at this time
- Version 2.0 to be released soon

## DAS SoftwareGuideline 7 (slide 1 of 2)

- Program Variables
- Breakup Altitude
- Object Inputs (saved in a text file)
- Name, Shape, Dimensions, Mass, Material
- Materials Inputs
- Only uses Specific Heat, Heat of Fusion, and Melt Temp
- Synthetic Materials
- Allows an assembly to be modeled with two masses
- Aero mass – total mass of the assembly
- Thermal mass – mass of the container/ structure
- Web-interface version accepts inputs from Excel

## DAS SoftwareGuideline 7 (slide 2 of 2)

- Evaluation Results
- Simulation Output
- Repeats input information
- Demise Altitude
- Debris Casualty Area
- DCA Total
- Output can be saved or printed
- Easy to make small changes and re-run

## ORSAT SoftwareInputs

- All contained in one input file per run
- Start / Stop altitudes
- Parent object shape, dimensions, mass, material, trajectory
- Fragment object shapes, dimensions, masses, materials
- Separate file for each new material
- If three objects with that material, three files

## ORSAT SoftwareInputs

- Additional capabilities over DAS
- Directly entered thermal masses (sort of)
- More detailed analysis
- Up to 15 nodes per object
- Multiple material layers per object
- Oxidation heating, Radiative cooling
- Ability to scale heating factors
- Parametric studies
- Specified trajectory

## ORSAT SoftwareSimulation Routine

- Same basic routine as DAS /MORSAT
- Five simultaneous modules
- Trajectory: velocity and path of the object
- Atmosphere: environment around the object
- Aerodynamics: drag experienced by the object
- Aerothermodynamics: heating of the object
- Thermodynamics: response of the object to heat
- Continuous calculations at small time intervals
- Concludes when object either completely melts or reaches the stop altitude
- Software goes on to next object

## ORSAT SoftwareOutputs

- As many as nine detailed output files:Detailed Output	Basic Output	Trajectory Detailed Heating	Basic Heating	AerodynamicsDetailed Temperature	Temperature	Atmosphere
- Any or all can be disabled
- Basic Output file information
- Time, Altitude, Heating Rate, Demise Factor
- If object demises: Demise Altitude
- If object survives: Impact Velocity, DCA, Impact Energy, Maximum Demise Factor

## Safe Disposal Planning GSFC Practical Guidelines

- Josephine San/591
- NASA/GSFC

## Practical Guidelines - Content

- Objectives
- Background
- Concept Design Phase – Safe Disposal Planning begins at Concept Design
- Preliminary and Critical Design Phases – Design Considerations and Planning to Successfully Achieve Safe Disposal
- Operation and End-of-Mission Phases – Implementation of End-of-Mission Plan

## Objectives and Bases

- Objectives
- To Provide Practical Guidance in Compliance With NPD 8710.3 and NSS 1740.14 (to Be NASA Standard 8719.14)
- To Assist Projects and Engineers in the Planning of Safe Disposal
- To Prevent Reinventing the Wheel
- Bases
- NPD 8710.3 and NSS 1740.14
- Experiences From CGRO, TRMM, ERBS, LandSat
- Experiences From GLAST, GPM

## Background - Procedures and Guidelines 

- Orbital Debris Mitigation PG
- Provide Practical Guidelines on Orbital Debris Analysis
- Discuss Design Process Flow to Decide on A Safe Disposal Method
- Address Design Considerations, Necessary Analysis and Planning to Achieve Safe Disposal Through Concept, to Preliminary and Critical Design Phases
- Status: In the Process of AETD Review, and Will Be Ready for Projects and Code 300 Review by the End of the Month
- End-of-Mission Planning PG
- Discuss Necessary Planning for Safe Disposal at the End of the Mission
- Provide Guidance on the Development and Implementation of the End-of-mission Plan
- Serve As a Template for End-of-mission Plan
- Status: Ready for Peer Review by the End of the Month

## Background - Procedures and Guidelines (cont.)

- Guidance, Navigation and Control Safe Disposal PG
- Provide Guidance to Assist GN&C Flight Dynamic Engineers in the Mission Planning and End-of-Mission Operation Planning for Safe Disposal
- Status: In the Process of Developing
- Reentry Survivability Analysis Work Instruction
- Provide Detailed Instructions on Reentry Survivability Analysis Using Debris Analysis Software (DAS) and Object Reentry Survivability Analysis Tool (ORSAT)
- Clarify Details of NSS 1740.14
- Establish a Standard Approach for All GSFC Reentry Analysis
- Status: Ready to Submit to ISO

## Safe Disposal Methods

- Controlled Reentry Method
- Maneuver the Spacecraft at the End of Mission to a Disposal Orbit With a Perigee Altitude Low Enough to Control the Location of the Reentry and Ground Impact Point
- Is Applicable to a Spacecraft which Reenters Earth Atmosphere (Usually Spacecraft at or Passing Through Low Earth Orbit Altitude), and Does Not Meet the 1 in 10,000 Casualty Risk Guideline
- Orbit Raising or Lowering Method
- Maneuver the Spacecraft to a Storage Orbit by Raising or Lowering Its Final Orbit at the End of Mission; Is Applicable to Spacecraft With Perigee Above 2000 Km
- At the End of Mission, Lower the Final Perigee So That It Will Meet the Orbit Life Time Guideline; Is Applicable to Spacecraft With Perigee Below 2000 Km (Uncontrolled Reentry)
- Passivation
- Put Spacecraft in Passive State With No Energy Source
- Is Applicable to a Spacecraft which Meets the NSS Safe Disposal Guidelines
- Direct Retrieval
- By Shuttle or Other Means

## Concept Design Process FlowFor Selection of Safe Disposal Method

**No**

**Need Orbit Maneuver**
**To Meet 25 Year Orbit Life**
**Or to Remove Spacecraft**** **
**From Crowded Area?**

**Re-entry**
**Survivability **
**Analysis using DAS**

**Redesign to Reduce Debris Casualty Risk?**

**Controlled**
**Re-entry Method**

***Casualty risk < 1 in 10,000***

**Yes**

***Casualty risk  > 1 in 10,000***

**Re-entry**
**Survivability**
**Analysis **
**Using ORSAT**

***Casualty risk  >  1 in 10,000***

**Orbit Lowering/**
**Raising Method**

**Spacecraft**
**Passivation Method**

**Yes**

**No**

- Spacecraft With Perigee < 2000 km, and reenter Earth  starts here

- Spacecraft With Perigee > 2000 km, starts here

## Methods to Reduce Debris Casualty Risk

- Design for Demise (D4D)
- Alternative Design for Components Made of High Melting Point, Specific Heat or Heat of Fusion, Such As Titanium, Beryllium, Stainless Steel
- Composite Tank Design Utilizing Easily Demisable Material
- Hybrid Design Using Low Melting Point, High Density Materials for Reaction Wheel Flywheels
- Design a Spacecraft Such That It Will Achieve Orbit Safely but Will Burn up Upon Reentry
- Possible Alternative for Adhesives or Fasteners
- Reduce Area to Mass Ratio
- Reduce Impact Energy Below Required Level by Breaking up Large but Thin Components to Smaller Segment

## Controlled Reentry - Cost

- Material, Design and Development Costs
- Full Cost for Hardware to Meet High Probability of Success
- Propulsion System
- Structure to Support  Propulsion System
- ACS Components to Support Controlled Re-entry
- Incremental Cost for Hardware to Meet High Probability of Success Including Power, Communication, Thermal, and C&DH Systems
- Full Cost for Attitude Controller Design and Development Including Delta V Control Mode for Long Duration Burn, Delta H Mode to Achieve Low Perigee Control, and Mode Transitions
- Full Cost for Reentry Software, Including Fault Management for Controlled Re-entry System, Flight Software for ACS Reentry Controlled Algorithm, and Ground Software for Testing, Simulation, and Re-entry Operation Support
- Full Cost for Improved End-of-life Fuel Depletion Computation Method

## Controlled Reentry – Cost (cont.)

- All Full Costs Will Become Incremental Cost for Missions which Require a Propulsion System for Orbit Maintenance
- More Propellant, Larger Tank, and Higher Force Level Thrusters
- ACS Components Sized to Support Controlled Reentry
- I & T Cost for Safe Disposal Segment
- Incremental Cost for Missions Required Propulsion System for Orbit Maintenance Already
- Operational cost
- Managing and Planning
- Implementation, Training, and Simulation
- Carrying Out Final Reentry

## Concept Design Phase - Design Considerations

- Controlled Reentry
- Perform Trades on the Minimum Apogee and Perigee to Ensure the Success of Final Burns and the Debris Footprint Confidence
- Propellant
- ACS Actuation Authority
- Thermal Control at Lowest Perigee
- Be Sure Low Battery State of Charge Will Not Be the Trigger Point for Reentry
- Passivation
- Design a Mission With Orbit Lifetime Less Than 25 Years
- Design All Subsystems Such That They Can Be Passivated at the End of Mission
- Put Battery in Permanently Discharge State – Disconnect Solar Array
- Purge All Fuel, Power Down Wheels, Gyros, and Communication System
- Orbit Raising/lowering
- Maneuver to Storage Orbit: Incremental Cost to Meet the High Probability of Success
- Lower Perigee to Reduce Orbit Life: Trade on Lowest Perigee
- Design All Subsystems Such That They Can Be Passivated at the End of Mission

## Preliminary/Critical Design Phase – Design Considerations, Necessary Analysis and Planning

- Redo Orbital Debris Analysis and Reconsider Safe Disposal Method If Necessary
- Refine Design and Perform Analysis to Verify Design for Safe Disposal
- As a Good Practice, Outline a End-of-Mission Plan by PDR and Produce a Draft by CDR
- Controlled Reentry
- Refine Propellant Budget and End-of-life Fuel Mass Estimation Method
- Design Delta V and Delta H Mode, and Lay Out Mode Transition Sequence
- Develop Failure Detection and Correction (FDC) Logic
- Develop Failure Modes and Perform Failure Effect Analysis

## Operation and End-of-Mission Phase –Implementation of Safe Disposal Plan

- Perform Orbital Debris Analysis if not Done Already
- Evaluate Spacecraft Hardware and Software
- Propose or Re-Evaluate Viable Safe Disposal Options
- Perform Risk Analysis
- Evaluate Ground and Network System Readiness
- Complete End-of-mission Plan Including Nominal and Contingence Plans and Procedures
- Prepare for Reviews if Necessary
- Implement Safe Disposal Plan at the End of Mission

## End-of-Mission Planning

- Management
- Manpower Estimation, Assign Roles and Responsibilities, Prepare for Anomaly Investigation
- External Interfaces Including Space Command, NIMA (Coast Guard, Airline), Public Affairs, HQ, ISS/JSC and State Department
- Disposition of Ground Hardware and Software
- Plan to Continue Reentry Prediction If Needed
- The First Two Items Are Especially Critical for Controlled Reentry
- Trigger Points
- Nominal Trigger Point Around Which Safe Disposal Plan Is Designed, E.G. Fuel Level
- Off Nominal Trigger Points With Different Criticality Level
- Constituent and Actions Associated With Each Trigger Point

## End-of-Mission Planning (cont.)

- System Evaluation and Risk Analysis
- Ground Based System Evaluation Including Ground System and Network Support
- Spacecraft State of Health Including Instrument, Bus Hardware and Software
- Assign Trigger Level to Each Critical Component
- Perform Risk Analysis for Each Failure
- Documentation Management
- Configuration Management for Procedures, Timelines
- Final Engineering Report

## Implementation of End-of-Mission Plan

- Nominal Plans, Procedures, and Timeline Script
- Orbit Raising/lowering Option
- Maneuver Plan, Maneuver Plan Implementation Procedure, Procedure for Final Jettison of Propellant
- Plan to Coordinate Ground, Network and FDF Support
- Plan and Procedure for Lowering the Orbit by Other Means
- Sequence Plan to Shutdown Hardware, To Put Battery in Permanent Discharge State
- Timeline Scripts for on Consol Operation
- Passivation Option
- Plan to Coordinate Ground, Network and FDF Support
- Procedure for Final Jettison of Propellant If Needed
- Sequence Plan to Shutdown Hardware, To Put Battery in Permanent Discharge State
- Timeline Scripts for on Console Operation

## Implementation of End-of-Mission Plan (cont.)

- Nominal Plans, Procedures, and Timeline Script (Cont.)
- Controlled Reentry Option
- Plan to Coordinate Ground, Network and FDF Support
- Mission Design for Controlled Reentry Shall Be Simple and Robust, It Shall Use the Spacecraft As Close to Its Original Design As Possible
- Some of the End Products From Mission Design Are Maneuver Plan, Operation Sequence Plan, Mode Transition Plan, Plan to Characterization Burns
- Implementation Procedures for All These Plans
- Develop Burn Commit and Abort Criteria

## End-of-Mission Planning (cont.)Implementation of End-of-Mission Plan

- Contingence Plans
- Event Fault Tree and Probability of Success
- Debris Field Error Analysis and Effective Delta V Reserve Allocation
- Contingency Handling Flow
- Contingency Plans for Most Likely and Combination of Most Likely Failures
- Training and Simulation Planning
- Plans to Train Support Personnel
- Plans to Verify Scripts, Procedures and Contingency Plans
- Plans to Simulate Interaction Between Teams

## Design for Demise (D4D) Examples

- Scott Hull / 591
- NASA/GSFC

## Design for Demise (D4D)

- An effort to create alternate designs with the intent of ensuring complete demise during reentry
- Generic designs for perennial survivors
- Mission-specific designs for surviving components
- Methods
- Different material
- Multiple materials
- Different shape
- New technology

## Design for Demise (D4D)Examples

- Reaction Wheel Flywheels (GPM, New Missions)
- Often made with Stainless Steel or Titanium
- High torque wheels
- Almost always survive reentry
- Alternate Designs
- Large diameter Aluminum flywheels
- Composite flywheel
- Aluminum with demiseable counterweights on rim

## Design for Demise (D4D)Examples

- Propellant / Pressure Tanks (GPM, New Missions)
- Most traditional tanks are made from Titanium or Stainless Steel
- As you can see, Titanium and Stainless Steel tanks often survive!

## Design for Demise (D4D)Examples

- Propellant / Pressure Tanks - Alternate Designs
- Aluminum Tanks
- Composite Tanks
- Al, SS, or even Ti liner for hermeticity
- Graphite composite overwrap for strength
- External Heat Sources
- Passively initiated pyrotechnics
- Burn to provide intense heat, not explode

## Design for Demise (D4D)Examples

- Batteries (GPM, New Missions)
- Typical NiMH cells are pressure vessels
- Inconel, Nickel, or Stainless Steel
- Result: Cells barely demise or survive
- Due to high quantity, DCA can be very large (~10 m2)
- Lithium Ion Batteries
- Low pressure operation
- Aluminum case
- Result: Cells demise

## Design for Demise (D4D)Examples

- Instrument Attach Flexures (GLAST)
- Original design
- 4 Titanium “boomerang” with flat plates as legs
- Result: Flexures survived reentry
- DCA: 0.63 m2 each, 2.61 m2 total
- Modified design
- Legs converted to square cross-section
- Result: ORSAT simulation showed flexures demise
- DCA=0

## Design for Demise (D4D)Examples

- Tungsten Converter Foils (GLAST)
- Original design
- 1024 Thin flat plates ~4” square
- Result: Foils survive with impact energy of 24 J
- DCA: 0.47 m2 each, 484 m2 total
- Modified design
- 2048 Thin flat plates ~4”  x 2”
- Result: Foils survive with impact energy of 12 J
- Below the casualty threshold, DCA =0

## Design for Demise (D4D)Examples

- Optical Bench Struts (GLAST)
- Original design
- 8 Titanium tubes
- Good thermal isolation and CTE
- Result: Survived reentry
- DCA: 0.47 m2 each, 3.75 m2 total
- Modified design
- Material changed to graphite composite
- Maintained thermal properties
- Result: ORSAT simulation showed struts demise

## Current Status (slide 1 of 2)

- Orbital Debris Colloquia
- Most recent was 3/20/2002 at GSFC
- Next colloquium is 11/4-5/2003 at JSC
- NPD 8710.3A
- Updated and reissued 1/27/2003
- NSS 1740.14
- Updates proposed by JSC
- To be discussed 11/5/2003
- Will be reissued as NS 8719.14

## Current Status (slide 2 of 2)

- DAS Software
- Current version is 1.5.3
- Web interface is to be available soon to GSFC domains
- Version 2.0 to be discussed 11/5/2003
- ORSAT Software
- Current version is 5.8 (only at JSC)
- GSFC has version 5.5
- Projects being supported
- GLAST, TRMM, GPM, HST, SDO, SNOE, Swift, NPP, EXIST
- ReEntry Breakup Recorder (REBR)
- Cooperative effort with Aerospace Corp
- Will record temperature, accelometer, integrity data during actual reentries

## Mir Reentry