IAC-12-A6.4.3-15021

Debris Mitigation Capability and Capacity to Reduce Orbital Debris

Hugh Lewis (University of Southampton, UK)Hedley Stokes (PHS Space Ltd, UK)

Adam White (University of Southampton, UK)

63rd International Astronautical Congress, Naples, Italy1st - 5th October 2012

Introduction

• The EC is funding a small consortium to undertake a collaborative FP7 project called ACCORD (Alignment of Capability and Capacity for the Objective of Reducing Debris)

• The aim of the project is to support on-going R&D efforts by providing a coherent mechanism for communicating the efficacy of current debris mitigation practices and identifying opportunities for improving the implementation of such measures

• To achieve this aim the project is divided into the following main tasks:

– Surveying the capability of industry to implement debris mitigation measures, and identifying associated challenges

– Quantifying the capacity of mitigation measures to reduce debris creation

– Combining capability and capacity indicators within an environmental impact rating system to quantify the ability of a spacecraft to implement debris mitigation measures, whilst take into account the environmental effectiveness of those measures

– Disseminating the findings

Task #1:

Surveying the Capability to Implement

Debris Mitigation Measures

Approach to Debris Mitigation Survey

• The aim of the survey is to assess how well debris mitigation measures have been adopted across the industry

• Two questionnaires have been designed to collect data from a wide range of organizations involved in the manufacture and operation of spacecraft during the past decade

• One questionnaire focuses on debris mitigation measures relating to spacecraft design, and the other one addresses operations-related matter

• In constructing the questionnaires, the main mitigation measures from a variety of published guidelines and standards were synthesized

• To date the questionnaires have been sent to ~40 companies and agencies either directly or through associations comprising multiple members

• All responses to the questionnaires have been entered into a spreadsheet database, which is accessible only by the ACCORD project team

Survey Analysis: Use of Guidelines and Standards• Over the past decade or so a

variety of debris mitigation guidelines and standards have been published. Although these are broadly similar, there are variations in the detail

• The survey reveals that some long-standing documents, such as the IADC Space Debris Mitigation Guidelines, are less likely to be used in the future

• One possible explanation is that there will be a shift towards the newly-emerging ISO debris-related standards (which are designed to be applied within a customer / supplier contractual arrangement)

Survey Analysis: Preventing Debris Release• One of the key debris mitigation

requirements in the design of a spacecraft is to prevent or limit release of debris during normal operations

• Most of the organizations surveyed are already implementing design measures to prevent or limit the release of MROs and solid products from pyrotechnic devices. The implementation of such measures has little impact on the spacecraft design

• Most respondents do not currently implement measures to limit the release of surface ejecta in the design of their spacecraft since this is not a requirement in applicable standards. That said, some organizations stated that they expect to include ejecta considerations in future spacecraft.

Survey Analysis: Avoiding Accidental Break-ups • The break-up probability of a spacecraft can

also be calculated periodically during its mission life. 50% of operators surveyed either do this now or plan to do it in the future

• The remaining 50% stated that they had no plans to perform this calculation. However, it should be noted that all of the operators monitor the condition of a satellite during its life to detect any malfunctions which could lead to an accidental break-up

• One respondent offered the following observation: “We examine and limit the likelihood, but we have found that quantitative calculations are not very meaningful. Qualitative design measures are more effective indicators”

• There is an expectation that manufacturers should assess the probability of accidental break-up of a spacecraft or, at the very least, identify any internal failure modes which might lead to its break-up. The results from the survey confirm that, to a large extent, this is the case.

Survey Analysis: Post-Mission Disposal (1) • To ensure the removal of spacecraft from

the Protected Regions at end of life implies that they must have a reasonably high probability of successful post-mission disposal. A conditional probability of at least 0.9 is a common expectation.

• One respondent pointed out that the main element in calculating the probability was to assure that there was sufficient propellant for performing the disposal manoeuvre

• Another noted that the probability calculation “is not harmonized across prime contractors, and methods/data sources vary from project to project.”

• 25% of the operators advised that they had encountered circumstances where their spacecraft had insufficient propellant to accomplish the desired disposal manoeuvre

• Almost 90% of manufacturers surveyed have calculated the probability of successful disposal and the remainder expect to do so

• There is some variation about whether propellant gauging uncertainty, and/or passivation should be included

Survey Analysis: Post-Mission Disposal (2)

• Almost 80% of manufacturers confirmed that they had designed LEO spacecraft to be de-orbited according to the 25-year “rule”

• However, not everyone has considered uncertainty in the orbit lifetime prediction, which can ultimately lead to spacecraft remaining in orbit longer than 25 years

• Just over 60% of operators have disposed of GEO spacecraft according to the IADC re-orbit equation, and the same percentage has done so for the 100-year “rule”

• All of the GEO operators said they had done one or the other. The IADC equation is not applied systematically by operators

Survey Analysis: Impact of Mitigation on Design

• Most manufacturers consider post-mission disposal to have the biggest cost impact on spacecraft design

• The second most expensive measure is impact protection. This is also considered to be the most technically challenging

• The impact of mitigation measures on spacecraft operations is not as pronounced

• Again, post-mission disposal has the biggest cost impact. However, collision avoidance has the second highest cost impact and the greatest technical impact

Task #2:

Quantifying the Capacity of Mitigation Measures to Reduce

Debris Creation

Measuring Capacity of Mitigation Measures

• Use projections into the future to understand the effectiveness of key mitigation measures:

– Preventing debris release

– Avoiding accidental and intentional break-ups

– Prevention of collisions

– Post-mission disposal

• Compared with a non-mitigation projection

• Simulated using the DAMAGE debris model– Objects 10 cm from MASTER-2009

– 200-year projection (2009 to 2209)

– LEO and GEO considered separately

– Each mitigation measure analysed separately• 100% compliance (success)

DAMAGE Results

• Debris spatial density on 1 May 2209 (objects 10 cm)

LEO

DAMAGE Results

• Debris spatial density on 1 May 2209 (objects 10 cm)

GEO

DAMAGE Results

• The capacity of mitigation measures to reduce debris in LEO

DAMAGE Results

• The capacity of mitigation measures to reduce debris in GEO

GEO

Conclusions• Within the EC FP7 ACCORD project, the capability of industry to implement debris mitigation

measures has been surveyed, and the capacity of mitigation measures to reduce debris creation has been quantified

• One of the more significant capability challenges is the need to provide adequate propellant for post-mission disposal and collision avoidance purposes

• Some variations in implementation have also been observed, suggesting that further standardization might be beneficial. These include the calculation of the probability of successful disposal, and the risk threshold at which collision avoidance manoeuvres should be performed

• Possible areas for further research have been identified, including the need for improved risk assessments relating to collision avoidance and impact protection (and the data to support these)

• DAMAGE results have added to an evidence base that demonstrates the importance of post-mission disposal measures to the sustainable use of near-Earth space. Given that the implementation of this measure has relatively large impacts on the design and operation of spacecraft, such evidence is needed to encourage continued compliance

• In addition, the DAMAGE results have quantified the long-term benefits that arise from the implementation of all of the mitigation measures together, especially in the LEO regime. Here, the roles of passivation, preventing debris release and post-mission disposal in reducing different population types (i.e. intact objects and fragments) have been identified.

Acknowledgements

• The authors are grateful to the European Commission for funding this work under the Seventh Framework Programme (Project No. 262824)

• We also wish to extend our gratitude to those organizations that have kindly given of their time in providing information for the debris mitigation survey

• In addition, our thanks go to Holger Krag and Heiner Klinkrad (ESA) for permission to use the MASTER 2009 population data in our simulations