ISO an IEC maintain t erminolo ical data ases for use in s an ardization at the folowing ad r s es: — IECEle tro edia: a aia le at ht p:/ www .ele tro edia .org — ISO Onlnebrow sing plat
Overview of ISO debris-related standards
The requirements, recommendations, and best practices for mitigating debris generation and preventing other debris related problems are examined in this clause.
Figure 1 shows a general diagram of major ISO documents related to debris.
Figure 1 — Structure of major debris related standards for orbital stages
ISO debris-related standards for launch vehicles as of 2016
ISO Standards have been established to mitigate space debris Readers should verify the latest list of these standards at http://www.iso.org/iso/store.htm, particularly for sections 4.3 to 4.5.
(1) ISO 24113:2011, Space systems — Space debris mitigation requirements
(2) ISO 27852:2011, Space systems — Estimation of orbit lifetime
(3) ISO 16699:2015, Space systems — Disposal of orbital launch stages
(4) ISO 20893, Space systems — Prevention of break-up of orbital launch stages
Spacecraft related ISO standards
(1) ISO 16127:2014, Space systems — Prevention of break-up of unmanned spacecraft
(2) ISO 16164:2015, Space systems — Disposal of satellites operating in or crossing LEO
(3) ISO 26872:2010, Space systems — Disposal of satellites operating at geosynchronous altitude
Other ISO standards
The following ISO Standards are not specific to space debris mitigation However, they are considered pertinent:
(1) ISO 27875:2010, Space systems — Re-entry safety control for unmanned spacecraft and launch vehicle orbital stages
(2) ISO 14300-1:2011, Space systems — Programme management – Part 1: Structuring of a project
(3) ISO 14300-2:2011, Space systems — Product assurance — Policy and principles
(4) ISO 14623:2003, Space systems — Pressure vessels and pressurized structures - Design and operation
(5) ISO 27025:2010, Programme management —Quality assurance requirements
(6) ISO 10795:2011, Space systems – Programme management and quality –Vocabulary
(7) ISO/TR 16158:2013, Space systems — Avoiding collisions among orbiting objects: Best practices, data requirements, and operational concept
Other documents
The following documents are referenced to understand the background of the ISO documents:
The Space Debris Mitigation Guidelines, outlined in Annex IV of A/AC.105/890 and endorsed by the United Nations General Assembly through Resolution A/RES/62/217 on March 6, 2007, provide essential protocols for minimizing space debris and ensuring the sustainable use of outer space.
(2) IADC Space Debris Mitigation Guidelines, IADC-02-01, Revision 1, September 2007, available at http:// www iadc -online org/ index cgi ?item = docs _pub
(3) Support Document to the IADC Space Debris Mitigation Guidelines, IADC-04-06, Issue 1, 5 October
2004, available at http:// www iadc -online org/ index cgi ?item = docs _pub
Abbreviated terms
CFRP Carbon-Fiber-Reinforced Plastic
CNES Centre National d’Etudes Spatiales
COPUOS: Committee on the Peaceful Uses of Outer Space
Cr Solar Radiation Pressure Coefficient
DAS Debris Assessment Software (NASA)
DRAMA Debris Risk Assessment and Mitigation Analysis (ESA) e Eccentricity
Ec Expected number of casualties
EOMDP End-of-Mission (Operation) Disposal Plan
FMEA Failure Mode and Effect Analysis
IADC Inter-Agency Space Debris Coordination Committee
ISO International Organization for Standardization
JAXA Japan Aerospace Exploration Agency
JSpOC Joint Space Operations Center (USA)
LEGEND LEO-to-GEO Environment Debris model
MASTER Meteoroid and Space Debris Terrestrial Environment Reference
MMOD Micro-Meteoroid Orbital Debris
ORDEM Orbital Debris Engineering Model
SDMP Space-Debris-Mitigation Plan
STELA Semi-analytic Tool for End of Life Analysis (CNES)
STSC Scientific and Technical Subcommittee (UNCOPUOS)
USSTRATCOM United States Strategic Command
TR Technical Report (a type of ISO document)
5 Requirements in ISO Standards and system-level methodologies for complying with the requirements
General
To accomplish comprehensive activities for debris mitigation work, the following steps are considered:
(1) Identifying debris related requirements, recommendations, and best practices.
(2) Determining how to comply with requirements, recommendations, and best practices.
(3) Applying debris mitigation measures early and throughout development and manufacturing to assure sound debris mitigation capability in the final product.
(4) Applying appropriate QA and qualification programs to ensure compliance with debris mitigation requirements.
This clause outlines methodologies for implementing comprehensive actions at the system level, with additional details for subsystem and component actions found in Clause 8 Key subjects of focus are highlighted.
(1) Limiting the release of objects into the useful orbital regions.
(3) Proper disposal during the end of operation.
(4) Minimization of hazards on the ground from re-entering debris.
(5) Collision avoidance for manned or man-able systems.
(6) Quality, safety, and reliability assurance.
Refrain from releasing objects
Requirements
ISO 24113, 6.1, requires avoiding the intentional release of space debris into Earth orbit during normal operations:
Spacecraft and launch vehicle orbital stages must be engineered to prevent the release of space debris into Earth's orbit during standard operations Any space debris that is released, except as specified in section (2), should remain outside the Geostationary Orbit (GEO) protected area, and its presence in the Low Earth Orbit (LEO) protected region must be restricted to a maximum duration of 25 years post-release.
To ensure the protection of Earth's orbital regions, pyrotechnic devices must be engineered to prevent the release of combustion products larger than 1 mm Additionally, solid rocket motors should be designed and operated to avoid discharging solid combustion products into the Geostationary Orbit (GEO) protected area Furthermore, when designing and operating solid rocket motors, it is essential to implement strategies that minimize the risk of releasing solid combustion products that could contaminate the Low Earth Orbit (LEO) protected region.
The following classes of released objects are of concern from an orbital debris mitigation standpoint:
(1) Objects released as directed by mission requirements (ISO 24113, 6.1.1)
(2) Mission-related objects, such as yo-yo de-spinners and fasteners under the responsibility of designers (ISO 24113, 6.1.1)
(3) Combustion products from pyrotechnic devices (ISO 24113, 6.1.2.1)
(4) Combustion products from solid motors (ISO 24113, 6.1.2.2)
ISO 24113, section 6.1.1.2, specifies that if objects must be released despite the stipulations in section 6.1.1.1, their orbital lifetime in Low Earth Orbit (LEO) and potential interference with Geostationary Orbit (GEO) must be minimized A common example of this scenario is the support structure used in missions with multiple payloads.
Work breakdown
Table 2 shows the work breakdown as delineated in ISO 24113 to prevent the release of debris.
Table 2 — Work breakdown for preventing the release of debris
To prevent the creation of space debris, it is essential to implement preventive design measures that avoid the release of objects (ISO 24113, 6.1) Designers must also address potential design issues that could lead to unintentional releases and take corrective actions during the design process In cases where object release is unavoidable, it is crucial to estimate the orbital lifetime of these objects and ensure compliance with the relevant guidelines.
To prevent unexpected object releases in future missions, it is essential to conduct a thorough investigation and implement corrective actions.
Identification of released objects and design measures
As ISO 24113 states, launch vehicle designers shall avoid intentional release of space debris objects
If there are unavoidable reasons (such as, for example, serious technical problems), such objects are identified and their orbital lifetimes estimated and minimized.
To comply with ISO 24113, 6.1.1, the release of specific objects should be avoided, including nozzle closures for propulsion devices and certain igniters for solid motors that are ejected into space post-ignition, especially if they have orbital lifetimes exceeding 25 years Additionally, clamp bands that secure the spacecraft and launch vehicles, as well as structural elements supporting the upper spacecraft in multi-payload launches, should not be released.
[Remark: Usually allowed if release is unavoidable and the object’s orbit lifetime will be short; in which case the disposal orbit of these elements complies with ISO 24113, 6.1.1.2.]
(2) Combustion products from pyrotechnic devices
Adequately designed devices are selected to avoid the release of combustion products It is possible to apply parts that trap all combustion products larger than 1 mm inside for segregation.
(3) Combustion products from solid motors
ISO 24113 mandates that solid motors must not produce slag in a Geostationary Orbit (GEO) While the generation of slag is not explicitly banned in Low Earth Orbit (LEO), it is advisable to implement strategies to minimize its release One effective approach is to design nozzles that prevent the formation of pockets upstream, which can trap melting metals Additionally, utilizing propellants free of metals, such as aluminum, can further mitigate slag production.
The orbital lifetime of released objects is evaluated according to ISO 27852, which outlines acceptable analysis methodologies based on the orbit regime Various simplified tools may be permissible for estimating long-term orbital lifetimes, contingent upon the specific orbit regime and the requirements set forth by ISO 27852.
— NASA Debris assessment software (DAS) https:// orbitaldebris jsc nasa gov/ Mitigation/ das html);
— ESA DRAMA (an account at https:// sdup esoc esa int must be created to obtain a license before downloading); or
— CNES STELA (https:// logiciels cnes fr/ content/ stela ?language = en).
Break-up prevention
Requirements
ISO 24113 requires that break-ups be prevented as specified in ISO 24113, 6.2:
(1) Intentional break-ups a) In Earth orbit, intentional break-up of a spacecraft or launch vehicle orbital stage shall be avoided.
The probability of an accidental break-up of a spacecraft or launch vehicle orbital stage must not exceed \$10^{-3}\$ until the end of its operational life To assess this probability, all known failure modes related to the release of stored energy must be quantitatively evaluated, excluding external factors like impacts from space debris and meteoroids Additionally, during the disposal phase, it is essential for the spacecraft or launch vehicle to safely deplete or neutralize all remaining on-board stored energy in a controlled manner.
While ISO 16127 specifically addresses the prevention of S/C break-ups, it also provides useful information and procedures for preventing launch vehicle break-up (ISO 20893).
Work breakdown
Table 3 shows the work breakdown as delineated in ISO 24113 to prevent orbital break-up.
Table 3 — Work breakdown for preventing orbital break-ups
Preventive measures Identification of sources of breakup Identify components that may cause fragmentation during or after operation.
Design measures (1) Develop preventive designs to limit the probability of acciden- tal break-up during operation no greater than 10 −3 Confirm it with FMEA.
(2) Provide functions to prevent break-ups after disposal.
A self-destruct system must be developed to avoid accidental destruction due to miscommands or solar heating Additionally, risk detection and monitoring are essential during operation to ensure compliance with flight safety requirements.
After passing the flight safety range, some parameters are mon- itored to ensure performance, and functions for completing the mission and disposal actions, including controlled re-entry, are conducted.
During the operation phase, it is crucial to implement preventive measures to avoid break-ups This includes the removal of energy sources such as residual propellants and high-pressure gas, or ensuring that these sources are designed to be safe, preventing any potential break-ups after operations have concluded.
Identification of the sources of break-up
The following launch vehicle subsystem elements can potentially cause break-ups:
— propulsion sub-systems and associated components (Rocket engines and solid motors, tanks, tank pressurizing systems, valves, piping, etc.);
— pressure vessels and other equipment (such as pneumatic control systems, etc.); and
— self-destruct systems for range safety.
Design measures
The following aspects are to be incorporated into launch vehicle design.
Missions that involve intentional break-ups that can potentially eject fragments into outer space are prohibited unless required to prevent potential loss of human life after re-entry
(2) Avoiding accidental break-ups during operation
Per ISO 24113, the probability of accidental break-up must be no greater than 10 −3 until its EOL.
The ISO 16127 standard focuses on preventing the break-up of unmanned spacecraft, offering valuable guidance for spacecraft (S/C) design Its Annex A outlines a procedure for estimating break-up probability, providing engineers with essential instructions for managing complex subsystems, including liquid rocket engines.
To avoid accidental detonations of self-destruct charges, it is advisable to deactivate the Command Destruct Receivers after exiting range safety zones, thereby preventing explosions caused by miscommands.
(3) Preventing break-ups that occur after the end of operation
To prevent fragmentation in propulsion systems and their components, it is essential to manage residual propellants effectively Detailed guidelines for each subsystem or component can be found in Clause 8.
— Burning residual propellants to depletion.
— Venting residual propellant until its amount is insufficient to cause a break-up by ignition or pressure increase from tanks and lines. b) High pressure fluids
— Venting pressurized systems c) Range safety systems
— Prevention from inadvertent commands, thermal heating, or radio frequency interference
Monitoring during operations
ISO 16127, section 4.3.1, mandates the monitoring of critical parameters to identify symptoms that may result in mission failure, loss of orbit, or compromised attitude control It also stipulates that immediate action must be taken upon detection of any such symptoms However, for launch vehicles, this is often impractical due to their limited operational capabilities for terminating flight, aside from range safety measures.
Preventive measures for break-up after mission completion
After separation of payloads, the major sources of break-ups (examples listed in 5.3.3) should be mitigated (vented or operated in safe mode) according to ISO 16127, 4.4.
To minimize the risk of accidental breakups due to over-pressurization or chemical reactions, it is essential to thoroughly deplete residual propellants and other fluids, including pressurants, through methods such as depletion burns or venting At the end of End-of-Mission (EOM) passivation, opening fluid vessels and lines to the space environment can significantly lower the chances of a future explosion.
Disposal manoeuvres at the end of operation
Requirements
ISO 24113, 6.3 requires removing an S/C or launch vehicle orbital stage from the protected regions after EOM as follows:
The probability of successfully disposing of a spacecraft or launch vehicle orbital stage must be at least 0.9 at the time of disposal This probability is assessed as a conditional probability, taking into account the success of the mission Additionally, the timing for the start and end of the disposal phase should be selected to ensure that all disposal actions are completed within a timeframe that meets the aforementioned probability requirement.
Spacecraft and launch vehicle orbital stages operating in the Geostationary Orbit (GEO) protected region must execute controlled disposal maneuvers to transition to an orbit entirely outside this region, as defined by ISO 24113 After completing these maneuvers, the spacecraft must achieve an orbital state that meets at least one of the following criteria: an initial eccentricity of less than 0.003 and a minimum perigee altitude above the geostationary altitude, ensuring compliance with disposal regulations.
∆H = 235 + 1 000 Cr A/m ã the orbit has a perigee altitude sufficiently above the geostationary altitude that long-term perturbation forces do not cause the spacecraft to enter the GEO protected region within
Spacecraft and launch vehicle orbital stages operating in the Low Earth Orbit (LEO) protected region must limit their post-mission presence to a maximum of 25 years, as defined by ISO 24113 After mission completion, removal from the LEO protected region should be achieved through preferred methods: first, by retrieving the vehicle for a controlled re-entry to safely recover it on Earth; second, by maneuvering it for a targeted re-entry with a defined impact footprint to minimize human risk; third, by adjusting its orbit to ensure a shorter orbital lifetime; fourth, by deploying a device to enhance orbital decay; fifth, by allowing natural orbital decay; or sixth, by maneuvering it to a higher orbit to prevent re-entry into the LEO protected region for at least 100 years.
ISO 26872 outlines specific requirements and procedures for the disposal of Geostationary Earth Orbit (GEO) missions, ensuring compliance with the overarching standards set by ISO 24113 Additionally, ISO 16699 details the requirements and procedures for the disposal of launch vehicle orbital stages in Low Earth Orbit (LEO) missions.
Work breakdown
Table 4 shows the work breakdown as delineated in ISO 24113 to protect orbital regions:
Table 4 — Work breakdown for the preservation of the LEO-protected region
Preventive meas- ures Estimate the orbital lifetime and define a disposal plan
Estimate the orbital lifetime after payload separation, and define a disposal maneuver plan.
Disposal planning One of the following methods is applied (ISO 16699):
(2) Maneuvering to reduce the orbital lifetime
(3) Augmenting its orbital decay by deploying a device
(4) Allowing its orbit to decay naturally
(5) Maneuvering it to an orbit with a perigee altitude sufficiently above the LEO protected region
To ensure the effective removal of orbital stages from protected orbit regions, it is essential to implement disposal functions and utilize various resources, such as the main engine's restart capability, secondary propulsion systems, and independent thrusters.
Action in opera- tion phase Disposal sequence Disposal operations are executed in the proper sequence.
LEO mission
5.4.3.1 Estimate the orbital lifetime and define a disposal plan
For Low Earth Orbit (LEO) missions, ISO 16699, section 5.3 outlines the necessary planning and documentation for disposal maneuvers Additionally, ISO 27875 provides detailed steps and tools for estimating orbital lifetime The accuracy of these analyses relies heavily on the chosen algorithm; however, high-precision algorithms can take several hours to complete, making them unsuitable for early mission phases when operational plans are not yet finalized Therefore, it is crucial to select appropriate tools during the design phase, taking into account the certainty of the planned orbit and disposal timing.
There are a number of tools available to calculate the orbital lifetime, for instance:
(1) ISO 27852 introduces “STELA” available via the CNES freeware server As of August 2016, the latest version is 3.0, and it can be downloaded from https:// logiciels cnes fr/ STELA.
NASA has been providing the Debris Assessment Software (DAS) since April 2012, with the latest version being v 2.0.2 This software offers comprehensive analysis functions for various debris-related issues, including orbital lifetime analysis For more information, visit the official NASA website.
(3) ESA provides the DRAMA tool available at https:// sdup esoc esa int/ web/ csdtf/ home.
(4) Other viable Commercial Off-The-Shelf (COTS) toolkits exist to determine orbit lifetime.
ISO 16699 provides more detailed requirements and guidance for the orbital stages An EOMDP is required The process of developing it is described in detail in Clause 7 of ISO 16699.
5.4.3.3 Disposal function and resources to transition to disposal orbit
(1) It is recommended to provide liquid propellant engines with a re-start function to perform a disposal manoeuver after payload separation.
(2) In some cases, other propulsion devices, including attitude control thrusters, can be used.
5.4.3.4 Reliability of accomplishing disposal maneuver
ISO 24113 mandates that the conditional probability of successful disposal must exceed 0.9 (ISO 24113, 6.3.1.12) This requirement restricts the duration of spacecraft (S/C) remaining in orbit post-mission termination, often only for housekeeping purposes to monitor health.
The time interval between the end of mission (EOM) and the completion of disposal maneuvers for orbital stages is typically short, lasting only a few days at most However, the re-ignition of an engine after an extended ballistic phase, which is necessary to reach the designated impact zone, poses challenges such as propellant settling and thermal issues, significantly reducing the likelihood of mission success.
GEO mission and other high-elliptical orbit missions
Detailed requirements and procedures for GEO S/C are defined in ISO 26872 The concept of disposal methods for launch vehicle orbital stages is not considerably different from those for the S/C.
There are several methods to launch a GEO S/C, and the typical methods would be the following:
High Elliptical GTO is characterized by a perigee altitude that is within or near the Low Earth Orbit (LEO) protected region, while the apogee altitude approaches Geostationary Orbit (GEO) To transition the spacecraft to GEO, the apogee kick propulsion system is activated.
(2) Direct injection: The orbital stages reach the circular orbit near GEO The S/C is transferred to GEO with the S/C control function.
(3) Other elliptical orbit: the apogee altitude is higher than GEO, and the perigee altitude is inside or near the LEO protected region
In the case of the “High elliptical GTO” mentioned in 5.4.4.1 (1), orbital stages left in GTO after payload injection generally pose a risk to both GEO and LEO protected regions.
It is desirable to place the perigee altitude as low as possible to limit orbital lifetime to shorter than
According to ISO 27852, section 5.6, estimating the lifetime of a Geostationary Transfer Orbit (GTO) is challenging, and it is advisable to specify the maximum lifetime based on the intended perigee altitude along with its probability For instance, if the perigee is set at 200 km, the expected lifetime would be less than 25 years, with a probability of 90%.
Customers of launch services typically aim to set the perigee altitude as high as possible This strategy helps minimize propellant usage during the apogee kick maneuver and prevents orbital decay, especially when utilizing electrical propulsion systems.
Reducing the orbital lifetime to under 25 years is challenging, leading to orbital stages being maintained at a low apogee altitude This ensures they do not interfere with the protected region of Geostationary Orbit (GEO), even when accounting for long-term perturbations.
The re-start function in the main engine of orbital stages allows for the adjustment of apogee and perigee altitudes Reducing the apogee altitude helps avoid interference with the GEO protected region, although it does not significantly shorten the orbital lifetime Conversely, lowering the perigee altitude is a more effective method for reducing orbital lifetime, but it requires a longer duration to prevent GEO interference.
The orbital elements of a Geostationary Transfer Orbit (GTO) are significantly influenced by tidal perturbations from the gravitational forces of the sun and moon By effectively managing the Right Ascension of the Ascending Node (RAAN) through careful selection of the lift-off time, it is possible to substantially decrease the orbital lifetime.
In certain missions, the perigee altitude may reach several thousand kilometers, where natural forces are insufficient to reduce the orbit Consequently, the apogee altitude is set 200 km below the geostationary orbit (GEO) altitude.
In direct injection scenarios, the orbital stage and payloads are usually deployed directly into or close to the GEO protected area Subsequently, the payloads execute maneuvers to reach their designated operational orbit within GEO, while the orbital stage remains outside the GEO protected region.
Missions that inject payloads into elliptical orbits, rather than geostationary orbits, will be subject to the same requirements as Geostationary Transfer Orbit (GTO) missions according to ISO 24113 This includes the implementation of specific measures to ensure compliance and safety.
An elliptic orbit is characterized by an apogee altitude that is lower than the Geostationary Orbit (GEO) area and a perigee altitude that exceeds the Low Earth Orbit (LEO) area As long as these objects pose no risk to the protected regions of GEO and LEO for a minimum of 100 years, there will be no recommendations for their management.
— Very high elliptic orbit: if the apogee altitude is higher than the GEO area, and circularization above the GEO altitude is not reachable, this orbit should be avoided.
Ground safety from re-entering objects
Requirements
ISO 24113, section 6.3.4 mandates that ground safety from re-entering objects must be ensured by establishing a maximum acceptable casualty risk for the re-entry of spacecraft and launch vehicle orbital stages, in accordance with guidelines from approving agents Compliance with this maximum acceptable casualty risk is required for all re-entries of spacecraft or launch vehicle components.
ISO 27875 outlines the procedures for evaluating, mitigating, and managing the risks associated with space vehicles, including the spacecraft and launch vehicle orbital stages, during their re-entry into the Earth's atmosphere and subsequent impact It is important to note that ISO 27875 does not provide specific quantitative criteria for estimating the expected number of casualties (Ec), as this is determined by relevant regulatory authorities.
ISO 24113, section 6.3.4, refers to "casualty risk," typically interpreted as the risk of human casualties However, ISO 2787 expands this definition to include other risks, such as environmental pollution Consequently, "casualty risk" should be viewed as a broader concept, encompassing the comprehensive "re-entry risk" as defined by approving agents.
Work breakdown
ISO 27875 indicates the risk assessment procedure Table 5 shows the work breakdown as delineated in ISO 24113 to assure ground safety from re-entry.
Table 5 — Work breakdown related to ground safety from re-entry
Preventive measures Identification of re- quirements Identify the re-entry safety requirements imposed contractually, voluntarily, or by national or international authorities.
Hazard analysis to esti- mate the casualties Hazard analysis should be conducted to estimate the expected number of casualties and the pollution on the ground.
Design measures (1) Design should be conducted to limit the casualty risk to be set in accordance with norms issued by approving agents.
(2) Prevent environmental pollution on the ground.
If the anticipated number of casualties exceeds the established threshold, a controlled re-entry must be organized in accordance with ISO 27875 To facilitate this process, it is essential to notify all potentially affected countries, utilizing the NOTAM and NMs systems for effective communication.
Action in operation phase C o nduc t co ntro l le d re-entry and Monitoring (1) Conduct controlled re-entry as planned.
(2) Monitor the re-entry procedure and take adequate action in abnormal situations.
Preventive measures
The initial step involves identifying the re-entry safety requirements set by contracts, voluntary guidelines, or national and international authorities According to ISO 27875, the risk assessment procedure is outlined, although it does not specify quantitative requirements as of 2016.
[Information]: Many of the world’s space agencies apply 0,0001 as the limit of the expected number of casualties.
According to ISO 27875, sections 5.2 and 5.5, it is essential to identify safety requirements and evaluate hazard risks using recognized processes, methods, tools, models, and data Subsequently, the assessed risk must be analyzed to ascertain the need for implementing risk reduction measures.
If the anticipated casualties surpass the established criteria despite design enhancements, the impact area must be managed in accordance with ISO 27875, section 6.2 The system concept can be greatly influenced by the application of controlled re-entry, necessitating timely decisions to ensure they are incorporated into the system specifications.
Currently, there is a lack of agreement on standard analysis tools, algorithms, and conditions for assessing thermal properties of materials Additionally, there is no unified distribution model for human populations or predictive models for future scenarios, nor are there established equations to calculate casualties from object impacts These variables largely rely on the technical judgment and management decisions of various organizations.
Several national agencies have created re-entry survivability analysis tools for their specific needs Notable examples include NASA's Debris Assessment Software (DAS) and ESA's DRAMA tool, both of which provide rough estimations for analysis However, these tools are not intended for precise calculations, and official values are determined using tools authorized by the relevant organizations.
To minimize risks during controlled re-entry, it is crucial to design objects for easy disintegration This approach considers the failure rates of related functions and the potential casualties associated with natural re-entry scenarios Prioritizing designs that facilitate safe demise can significantly enhance safety outcomes.
Generally, the following methods are recommended for the design phase, but some of them can be limited to the orbital stages.
Materials with high melting temperatures, specific heat, and heat of fusion, like titanium and beryllium, are often substituted with alternatives that promote demise Notably, titanium propellant tanks and high-pressure bottles have been discovered intact on the ground post-re-entry In contrast, aluminum alloy tanks demonstrate superior thermal characteristics that enhance their demise during re-entry.
(2) Multiple materials, thinner wall thickness, etc.
In certain cases, a single durable material can be substituted with several materials that are less resilient, yet still preserve structural integrity For instance, a balance weight can be constructed using multiple metal plates rather than a single, solid mass.
If there is enough structural margin, and if it is possible to reduce wall thickness without changing the dimensions, the material can undergo demise more readily.
(3) Exposure to the ablation environment
Components exposed to the ablation environment are more susceptible to failure Propellant tanks or high-pressure bottles that are positioned to face the atmosphere during re-entry are particularly vulnerable However, this atmospheric exposure presents challenges during the orbital phase, as it compromises protection against thermal effects and debris impacts.
5.5.3.3.2 Prevention of environmental pollution on the ground
Efforts are also be made to avoid polluting the environment with toxic substances (including radioactive materials) as required in ISO 27875, 5.4.
5.5.3.3.3 Specific design for controlled re-entry in subsystem level
Subsystem engineers play a crucial role in controlled re-entry, focusing on propulsion, power, guidance, and communication systems, while also considering ground station support Identifying uninhabited regions, like vast ocean areas, is essential for managing the impact of surviving fragments Consequently, the choice to implement a controlled re-entry method is determined early in the design and development process, prior to finalizing system specifications.
A controlled re-entry may extend operation time and increase exposure to radiation Consequently, all systems must be qualified for this extended duration and adhere to radiation hardness design standards.
Risk detection: Notification
ISO 27875, (6.4) defines these notifications in case of a planned re-entry event.
Countermeasures: Controlled re-entry and Monitoring
In the case that controlled re-entry is planned, it is recommended to monitor the progress and confirm the consequences.
Collision avoidance
There are no definite requirements for collision avoidance in ISO 24113 However, the UNCOPUOS space debris mitigation guidelines indicate the following practice:
Guideline 3: Limit the probability of accidental collision in orbit
When designing spacecraft and launch vehicle stages, it is crucial to estimate and minimize the risk of accidental collisions with known objects during both the launch phase and orbital lifetime If orbital data suggests a possible collision, it is advisable to either adjust the launch timing or execute an orbital avoidance maneuver.
To prevent collisions during the launch of a vehicle, it is essential to coordinate the lift-off time to avoid known objects This coordination ensures that there are no collisions until the Joint Space Operations Center (JSpOC) can accurately determine the orbital characteristics of the vehicle's stages and any other released objects.
To enhance safety, it is crucial to avoid collisions with manned or man-able systems, such as the International Space Station (ISS), whose operational plans are known Given the insufficient dispersion of flight trajectories to guarantee the avoidance of all potential collisions, it is advisable to adjust lift-off times or flight paths when conflicts arise with significant spacecraft.
The global criteria and procedures for collision avoidance in space launches remain undefined It is essential for launch service providers to ensure that each stage of the launch vehicle, along with the payload and any separated objects, avoids collisions for a specified period, such as two days post-lift-off This precaution allows the Joint Space Operations Center (JSpOC) to accurately determine the orbital characteristics of the launch stages and all associated objects.
Estimating the probability of flight trajectories intersecting with the International Space Station (ISS) over a few days is challenging due to the limited analysis time and reliance on the updated ISS operation plan For vehicles with significant trajectory dispersion, identifying launch windows becomes particularly difficult Although there is no explicit requirement for this process, the provided recommendations serve as best practices, with ISO/TR 16158 offering valuable support for these analyses.
Reliability and QA
It is important to ensure sufficient reliability and quality ISO 16127, 5.1 contains the requirements for reliability and quality control to prevent failures that could lead to a break-up event.
The methodology for assessing break-up probability and the probability of successful disposal are provided in ISO 24113, 6.2.2 and 6.3.1.
In the development of space systems, there is always a trade-off between cost reduction and quality/reliability Project management typically involves adjusting quality assurance levels based on the mission's importance However, it is crucial to recognize that low-quality orbital stages can lead to debris in space, posing risks to other space operators.
ISO 27025 provides the QA system, and the wider scope of product assurance, QA, and dependability assurance are defined in ISO 14300-2.
6 Debris-related work in the development lifecycle
General
A typical phased planning of the development lifecycle is illustrated in Figure 2, according to ISO 14300-1.
In the initial stages of the orbital lifecycle, it is essential to prioritize the preservation of the orbital environment during the system concept phase, ensuring this focus is maintained throughout both development and operational processes.
Concept of debris-related work in each phase
The following debris-related activities are considered in each phase:
The Mission Requirement Analysis Phase (pre-phase A) involves the preliminary definition of launch performance aligned with the launch service business strategy, while also identifying debris mitigation requirements, design specifications, and regulatory constraints.
The Feasibility Phase (Phase A) involves exploring various concepts to achieve defined objectives related to performance, cost, and schedule, as outlined in ISO 14300-1, 8.2.3 During this phase, key debris-related specifications are established and documented in both a functional and a technical specification Critical aspects such as the re-entry control function and design reliability are considered, significantly influencing system design and overall costs.
The Definition Phase (phase B) outlines the overall concept of the launch vehicle system, as established at the conclusion of the feasibility phase in accordance with ISO 14300-1, section 8.2.4 This phase incorporates all significant debris mitigation strategies that influence the system's functions, performance, resource allocation, and reliability, which are detailed in the System Level Technical Specification.
The Development Phase (phase C) involves creating a comprehensive study of the selected proposal following the definition phase, as outlined in ISO 14300-1, 8.2.5.3.1 This phase aims to achieve a qualified design for the mass production of deliverable products essential for system operation and support, while also establishing all debris mitigation design and operational procedures.
The Production Phase (Phase D) involves the manufacturing and delivery of products to customers, commonly exemplified by launch service providers This phase concludes with the qualification of the product design and production processes.
In the routine production process following qualification, a pre-shipment review is essential to verify the configuration and quality before launching site operations This review ensures that the vehicle's detailed configuration and mission profile are established for each launch mission based on thorough mission analysis, confirming aspects such as flight trajectory, propellant allocation, and disposal sequence.
During the Utilization Phase (phase E), the final launch preparations at the launch site include confirming the lift-off time This step is crucial to mitigate collision risks between manned mission systems, ensuring a safe and successful lift-off.
(7) During the Disposal Phase (phase F), after injection of payload, disposal manoeuvers and break-up prevention procedures are conducted.
Throughout all phases, the characteristics of debris are identified and integrated into the design, culminating in effective disposal Each phase concludes with a review of its outputs to ensure quality and coherence.
Clause 5 outlines debris-related measures that influence design and solution options, while Clause 8 offers insights into subsystems and component-level considerations A typical phased planning of the development lifecycle is illustrated in Figure 2, in accordance with ISO 14300-1.
When a mission is integrated within a qualified launch vehicle system, certain review processes can be streamlined For instance, a Preliminary Mission Analysis (PMAR) may serve as a substitute for a Preliminary Design Review (PDR), a Final Mission Analysis (FMAR) can take the place of a Critical Design Review (CDR), and a Launch Readiness Review (LRR) can replace a Qualification Review (QR).
Figure 2 — Typical Phased Planning of the Development Lifecycle
Phase C: Development phase Phase D: Production phase
Phase E: Utilization phase Phase F: Disposal phase
2) Clarify debris related design phi- losophy and input into the system requirements & specification *4
1) Mass and Propellant allocation *4 (in- cluding that for disposal manoeuver, controlled re-entry, etc.)
1) Transfer debris-mitigation plan to operators *1
2) Fix the procedure to terminate the operation *1 (with guarantee the propellant for disposal).
1) Disposal action, which is con- ducted automatically *1 (including disposal manoeuver, break-up prevention, controlled re-entry)
Quality assurance 1) Clarify QA design philosophy *4
2) Define QA program including parts program *4
1) Confirm the probabilities for success- ful disposal and non-break-up and other probabilities required for the launching state or the mission requirements *1 Limiting of debris generation
1) Clarify debris-mitigation design philosophy *1 1) Fix the design to limit releasing objects, limit their orbital lifetime, etc *1
2) Identify the energy sources of break-up and design to prevent them *1
1) Monitor critical parameters to check symptoms of critical malfunctions *4
2) Terminate operation in the proper sequence *1
1) Design a propulsion subsystem for the planned disposal manoeuver *1 1) Remove orbital stages to avoid interference with protected re- gions *1
1) Clarify re-entry safety concept *3
2) Define re-entry survivability analysis method *3
3) Determine whether to apply con- trolled re-entry or not *3
1) Design a propulsion subsystem and attitude control system for controlled re-entry, if needed *1
Collision avoidance 1) Clarify avoidance procedures for
COLA (Collision Avoidance for new launch) *2
1: Complying with the requirement of ISO STDs (24113, 27875, etc.), or recommendations induced from them.
2: Best practices recommended by UN Guidelines (and IADC Guidelines referenced by the UN Guidelines).
3: Instructions given by the authorities, which are addressed in ISO STDs.
4: Management work conducted according to general project management, reliability and QA program, Safety program, etc.
01 7 – A ll r ig ht s r es er ve d
Mission Requirements Analysis Phase (pre-phase A)
General
The primary objective of this phase is to define the concept of a launch vehicle, particularly in relation to debris-related concerns.
(1) Identify the debris-mitigation requirements in ISO Standards, national regulations, etc.
(2) Identify safety, reliability, and quality requirements to ensure the ability to conduct debris- mitigation measures, including prevention of the fragmentation caused by malfunctions, etc.
Debris-related works
The article identifies the debris-mitigation requirements outlined in ISO 24113, while also considering any relevant regional and national regulations related to debris Ultimately, a comprehensive set of requirements is established.
ISO 24113 (2016) focuses solely on reducing debris generation and does not cover collision avoidance However, the UN Debris Mitigation Guidelines advise estimating and limiting the likelihood of accidental collisions with known objects during the launch phase of systems Additionally, they recommend adjusting the launch time if available orbital data suggests a potential collision.
Feasibility phase (phase A)
The output of this phase is reflected in the system requirements document (specifications) This document is reviewed during the “system requirement definition review (SRR).”
The various possible concepts are studied to meet the defined objectives Mission requirements, debris- related requirements, and other regulatory rules are taken into account.
The following aspects are considered:
(1) The requirements regarding not releasing objects provide normative content for the selection of types of propulsion systems (solid, hybrid, or liquid).
(2) Break-up preventive requirements provide normative content for the safety design concept (impact on mass allocation due to tank design, safety factors, and margins, etc.) and reliability design.
(3) Disposal requirements provide normative content for the basic configuration of staging structure and the allocation of function for each stage.
(4) Re-entry safety requirements provide normative content for the design of associated sub-systems related to controlled re-entry, including the radiation hardness design for avionics.
Definition phase (phase B)
Work in phase B
The output of this phase is reflected in the “system specifications” and “subsystem specifications (draft).” They are reviewed during the SDR.
In this phase, the system requirements are defined in a reference functional specification and a preliminary technical specification at the system level as specified in ISO 14300-1.
In this phase, key configurations such as physical, functional, and performance characteristics, along with the operational and verification concepts, are established It is crucial to finalize the decision on implementing a re-entry control function, as this choice significantly impacts the project's functional and performance attributes, and must be made by the end of this phase.
The concept to comply with ISO 24113 should be defined in the “space-debris-mitigation plan (SDMP)” as defined in ISO 24113, Clause 7.
Work procedure
Low reliability can lead to significant issues, including malfunctions and fragmentation that negatively impact the orbital environment To address these concerns, a mission assurance philosophy is established to enhance reliability and mitigate risks.
In system design, it is essential to incorporate debris mitigation measures by considering the allocation of propellant for disposal and controlled re-entry maneuvers Reliability is also a key factor, as the probability of break-up during operation must be assessed Additionally, the planning of controlled re-entry involves a thorough examination of the maneuver sequence and the propulsion subsystem's function and performance, alongside a comprehensive evaluation of the entire system, including ground control and monitoring systems, by the conclusion of this phase.
Development phase (phase C)
In this phase, the system specifications are allocated at the component and part levels In the specifications, the functional and performance requirements are defined to satisfy the SDMP.
During the above procedure, the following are considered:
Again, reliability and QA for orbital stages are essential not only for mission completion, but also for the safety of the other operating S/C in orbit (See ISO 16127, 5.1).
(2) Break-up prevention and safety control
The primary reasons for break-ups include the failure of the propulsion subsystem and the rupture of high-pressure vessels To mitigate these risks, it is crucial to implement effective design strategies, such as preventing the mixing of bi-propellants and ensuring a robust structural design.
(3) Prevent the release of parts
ISO 24113, section 6.1, specifies that orbital stages must be engineered to prevent the release of objects that could contribute to orbital debris, including items like clamp bands, nozzle closures, combustion-related products, and igniters for solid motors, during standard operations.
(4) Disposal after the end of operation
During the design phase, sufficient propellant is allocated to carry out the disposal manoeuver.
Safety assurance from ground impact after re-entry is governed by ISO 27875, which estimates and limits the expected number of casualties while preventing ground pollution In cases of significant risk, a controlled re-entry is planned, involving the design of a re-entry trajectory with control maneuvers, error analysis, and predictions of the footprint of surviving objects This process necessitates a propulsion subsystem that meets specific objectives, adequate propellant, and specialized avionics designs, such as radiation hardness Additionally, ground support systems, including tracking and control systems, are essential for successful implementation.
Production phase (phase D)
Qualification review
In the qualification process, the final design and manufacturing procedures are verified through testing and design evaluation or demonstration.
The following items are reviewed at the QR:
(1) List of parts that are designed to separate or be released;
(2) List of sources of break-up energy;
(3) A monitoring system for detecting critical malfunctions that may cause break-up as far as technically feasible;
(4) A disposal operation plan and data to be transferred to the operation phase;
(5) Ground casualty expectations if the orbital stages are disposed of by orbit decay;
(6) If controlled re-entry is planned, review of the operation plan; and
(7) Plan for notifying air traffic and maritime traffic authorities, in the case of controlled re-entry.
Launch service
Following qualification, launch vehicles enter routine service Each launch mission undergoes mission analysis tailored to its specific requirements, defining the system configuration and validating the hardware to ensure readiness for operations at the launch site.
Utilization phase (phase E)
Lift-off times are carefully planned to ensure that the release of orbital stages, payloads, and other objects does not jeopardize the safety of manned or man-capable systems.
[Information 2]: Debris mitigation measures are conducted according to the programmed sequence of events.
Disposal Phase (phase F)
Disposal actions are automatically conducted as follows:
(1) At the end of operation, the planned disposal manoeuvers defined in the SDMP are conducted If a controlled re-entry is planned, it is most likely conducted with ground support.
[Information 1]: Notification for controlled re-entry is given to the relevant nations, air traffic authorities, and maritime authorities.
After disposal maneuvers are completed, residual energy, including propellant and high-pressure fluids, must be removed in accordance with ISO 16127, pending the publication of ISO 20893 This process is essential unless the mechanical strength of the system guarantees that no break-up will happen until the residual fluids are safely depressurized.
[Information 2]: If there is potential risk that orbital stages can have interference with payloads by the venting force, the following item is considered:
When conducting the venting of residual fluids, it is crucial to evaluate the impact of surrounding devices, such as antennas, on the venting streams to prevent any unwanted disturbances to the orbital stage.
System design
After establishing the maximum payload mass for the injection orbit and identifying the geodetic conditions of the launch sites and tracking stations, the system concept of the launch vehicle is analyzed Additionally, the impact of the "debris mitigation design philosophy" on the system concept is evaluated.
(1) Constitution of stages is defined to minimize interference with protected orbital regions, ground casualties, probability of break-ups, etc.
(2) Orbital stages are given functions for disposal manoeuvers or controlled re-entry, if required, for missions that require such actions.
Solid propulsion systems that produce slag are not advisable for upper stages targeting geostationary orbit (GEO) To mitigate this issue, either the propellant must be modified to prevent slag generation, or the nozzle design should be adjusted to eliminate submerged nozzles.
(4) Orbital stages, whose re-entry hazards do not comply with restrictions, are given functions for controlled re-entry.
Mission analysis for each launch mission
For each launch mission, mission analysis, which includes the following debris related items, is conducted and reviewed before the pre-shipment review.
(1) Re-confirmation of physical characteristics of payloads and their injection orbits;
The development of the flight profile and sequence of events includes essential debris mitigation measures, such as disabling command destruct receivers, ensuring payload separation to avoid collisions, executing orbit change maneuvers for disposal, venting residual fluids, and planning for controlled re-entry if necessary.
(4) Propellant allocation, including consumption for disposal manoeuver or controlled re-entry.
8 Subsystem / Component design and operation
General
Scope
In the design phases (B, C, and D), the requirements outlined in Clause 6 of ISO 24113 and associated standards are transformed into design requirements, which are then assigned to the design specifications for systems, subsystems, or components These specifications provide essential support to engineers involved in the design of each subsystem.
The following subsystems are mentioned in this clause:
(6) Range safety subsystem (the same as the Self-destruct subsystem).
Debris-mitigation measures and subsystem-level actions for realizing them
Clause 3 of ISO 24113 outlines system-level design concepts, while this clause offers a detailed allocation of functions and performance for each subsystem Table 7 illustrates the connections between the requirements in the ISO Standards and the suggested actions for each subsystem.
Table 7 — Debris-related technology and design of affected subsystem
Name of debris-related technology Subsystem
Power supply Communication Structure Range safety
Releasing of parts, slags, etc -
(a) Fasteners, clamp bands, etc Yes
(b) Slag from solid motors Yes
(d) Support structures for mul- ti-payloads launching Yes
(a) Explosion of engines, propel- lant tanks, etc Yes
(b) Rupturing of high pressure vessels Yes
(d) Unintentional activation of self-destruct devices for range safety system
3 Disposal from protected regions Yes Yes Yes Yes
(a) Re-entry control Yes Yes Yes Yes
(b) Improvement of demisability Yes Yes
(c) Avoidance of toxic material Yes
Propulsion subsystem
Debris-related design
This clause applies to the main (and Vernier) engines (motors), attitude control thrusters, ullage thrusters (or motors), etc.
The items to be considered are shown in Table 7.
Table 7 — Debris-related measures in the propulsion subsystem
Mitigation measures Propulsion sub-system
Propellant tank Pressure vessels Valve, piping Solid motor
Refrain from releasing objects Yes - - - - Yes (slag)
Break-up prevention Yes Yes Yes Yes Yes Yes
Disposal maneuver Yes Yes Yes - - -
Ground safety Yes - Yes Yes - -
Re-entry control Yes Yes Yes - - -
Considerations for propulsion subsystems
To refrain from releasing objects, the following items are considered, per ISO 24113:
When designing solid motors, it is crucial to ensure that igniters and nozzle closures are not released, particularly for long-duration orbital missions Solid motors, which include metal components and submerged nozzles, often produce and expel slag, making them unsuitable for Geostationary Transfer Orbit (GTO) or near Geostationary Orbit (GEO) Additionally, their use in Low Earth Orbit (LEO) should be minimized.
(2) Auxiliary propulsion systems (ullage motors, retro motors, etc.) should not be separated, especially when they are injected into a long-lived orbit.
ISO 24113 requires the probability of fragmentation during operation to be 0,001 or smaller except for such external factors as collision with debris.
The following are typical modes of fragmentation relating to the propulsion subsystem:
(1) Failures of engine or thrusters (failures of combustion related elements, turbo-pumps, turbines, heaters of thrusters, etc.);
Explosions can occur when a homogeneous mixture of fuel and oxidizer is present, particularly in propellant tank designs that combine fuel and oxygen tanks with only a common bulkhead for separation Defects in this bulkhead may lead to dangerous mixtures of propellants, resulting in catastrophic explosions.
(3) Rupture of highly pressurized tanks or vessels caused by defects of tank structure, failures of regulators, valves, etc.;
(4) Certain types of gas jet thrusters can cause fragmentation due to cold-start induced by the failure of the heater for the catalyst bed;
Following the end of mission (EOM) and the injection of payloads, residual propellants and high-pressure gases are vented or relieved in accordance with ISO 24113, section 6.2, and ISO 16127 As outlined in section 8.2.3.1, the effective venting and relieving of these residual fluids depend on the coordinated operation of various components, including engines, tanks, pressure vessels, valves, and piping.
[Information]: Complete depletion of fluids is sometimes impossible in complicated propulsion systems ISO 16127, (5.3.2.1) shows the tailoring guidance for such cases.
When disposal maneuvers require greater forces than those achievable through passivation, it becomes necessary to activate the main engines or auxiliary propulsion systems This may also involve using independent devices specifically designed for these functions.
The following characteristics are designed to comply with disposal manoeuver requirements:
(1) Re-start functions of the main engines or auxiliary propulsion systems, which are available after payload separation is designed;
(2) Mission is designed to keep a sufficient amount of propellant for disposal manoeuvres;
(3) Tanks are designed to allow a safe and reliable re-start function of main engines or auxiliary propulsion systems; and
(4) Electric power subsystem and other subsystems support disposal manoeuvres.
8.2.2.4 Ground safety and re-entry control
Propulsion subsystems consist of various elements that endure re-entry, such as liquid engine components, stainless steel or titanium propellant tanks, titanium pressure vessels, large valves, motor cases, and solid motor nozzles Despite design efforts aimed at reducing the number of surviving objects during re-entry, if the casualty count remains above acceptable levels, a controlled re-entry is implemented.
When a controlled re-entry is planned:
(1) The propulsion system used for the final burn is designed to have enough thrust to provide enough delta velocity within a short period.
In cases where controlled re-entry requires more time than a standard disposal operation, radiation hardness design is implemented for electronic devices and avionics.
Considerations for component design
Engine reliability is crucial for maintaining a break-up probability below 0.001, as mandated by ISO 24113 Ensuring adequate reliability and quality is essential, as highlighted in section 5.7 Additionally, ISO 16127, section 5.1 outlines the necessary requirements for reliability and quality control to avert failures that may result in a break-up event.
When assessing the break-up probability of complex systems, such as large engine systems, it is often challenging to isolate this probability from other potential failures According to ISO 16127, specifically in sub-Clause A.3 of Annex-A, if the break-up event occurs at the system level and is indicative of one or more underlying failures, the break-up probability should be evaluated indirectly through the system's overall reliability.
For effective disposal maneuvers, an engine re-start function is essential In the absence of this feature, auxiliary propulsion systems, such as low thrust engines, play a crucial role in supporting these maneuvers.
8.2.3.1.2 Gas jet thrusters (and other low thrust engines or motors)
Low thrust engines or motors can be designed for various purposes including attitude and trajectory control, acceleration for propellant settling before re-start, retro thrust to avoid collision, etc.
Certain gas jet thrusters may experience fragmentation during cold starts if the catalyst bed heater fails These thrusters are only utilized when their design ensures this failure mode is prevented, or when Fault Detection, Isolation, and Recovery (FDIR) techniques are implemented to avoid cold start conditions.
Design of propellant tanks takes into consideration the following debris mitigation aspects:
(1) Tank volume can be defined considering the propellant consumption for disposal manoeuvres and controlled re-entry, if required.
To enhance ground safety during the re-entry of tanks, it is crucial to choose materials that are likely to disintegrate upon re-entry While large stainless steel tanks have been discovered intact on Earth, smaller titanium tanks and pressure vessels have also survived Consequently, replacing large tanks with aluminum alternatives is recommended, and for smaller tanks, using an aluminum skin reinforced with composite materials or other easily demisable substances is advisable.
To prevent explosions from propellant mixing, especially in two-liquid propulsion systems prone to auto-ignition, it is crucial to design tank arrangements that avoid liquid mixture Additionally, unreliable and non-robust common bulkhead tanks should be avoided.
[Information 1]: If the design of a small tank does not include a venting mechanism (in the case of small tanks with bladders, etc.), a sufficient safety margin is provided (as per ISO 16127, 5.3.2).
Tanks featuring a common bulkhead for homogeneous propellants pose significant risks due to several factors Firstly, tiny debris can penetrate both the tank skin and the common bulkhead, leading to potential failures Additionally, an imbalance of pressure between the outer and inner tanks may compromise the integrity of the common bulkhead Lastly, aging and erosion of the bulkhead caused by one of the propellants can result in an unintended mixture of the propellants, further increasing the risk of hazardous situations.
In designing a venting mechanism, it is crucial to consider the pressure gradient when venting residual liquid propellants from tanks to prevent boiling and potential rupture Additionally, during venting at specific pressure drops, adiabatic expansion may lead to freezing around the venting lines, necessitating careful design and operation to avoid flow blockage.
A main tank experienced a rupture after operations concluded, likely due to increased pressure from the evaporation of leftover cryogenic propellant To prevent such incidents, tanks are fitted with pressure relief mechanisms, and residual propellant is vented at the end of operations.
For orbital stages remaining in space for extended durations, such as several years, high-pressure vessels and propellant tanks are engineered to either safely relieve pressure post-operation or maintain safety margins that prevent rupture until the bleed valve connected to the pressure regulators sufficiently lowers the internal pressure.
If the pressure vessels are made of titanium, they can survive re-entry.
8.2.3.1.5 Design of valves and piping
In design of valves and piping, the following points are considered:
(1) It is desirable to have a mechanism to vent and minimize residual propellants after the end of operations
NOTE Some propellant can be allowed to become trapped in lines as long as the amount is insufficient to cause a break-up by ignition or pressure increase.
The failure rate of valves and pressure regulators is meticulously managed to ensure that the likelihood of tank or vessel fragmentation remains below 0.001 for the entire system.
(3) Venting lines are designed to prevent blockage from freezing propellants (ISO 16127, 5.3.2)
[Information]: Venting or relieving is not meant to pose adverse effects on payloads or orbital stages.
8.2.3.1.6 Design of engine control avionics
If a controlled re-entry is planned, the radiation hardness design is considered.
Solid motors with aluminum propellants and submerged nozzles can produce and release slag in orbit To prevent contamination of the GEO protected region, ISO 24113 advises against using these motors for GTO or GES direct-injection missions Additionally, ISO 24113 promotes the advancement of technologies that minimize slag generation for LEO missions.
Defects in solid rocket motor propellant ingots can lead to catastrophic break-ups Implementing non-destructive inspection techniques on these ingots is essential to determine their integrity and prevent potential failures.
Certain igniters are designed to be ejected after ignition, but they are unsuitable for high altitudes where they may remain in orbit for extended periods, exceeding 25 years Additionally, nozzle closures cannot be ejected at high altitudes to ensure they stay in orbit for a prolonged duration.
Guidance and control subsystem
Debris-related designs
The measures taken into consideration for this subsystem are shown in Table 9.
Table 9 — Debris-related measures in the Guidance and Control subsystem
Major components Attitude monitoring sensors, etc Other electronic circuit
Considerations for the guidance and control subsystem
The guidance and control subsystem plays a crucial role in executing disposal maneuvers by determining orbit and attitude, controlling the thrust vector, and carrying out the maneuvers themselves These activities are typically performed as part of the mission sequence within the launch program.
For a successful controlled re-entry, the guidance and control system must accurately determine the vehicle's position, velocity, and attitude until the maneuver point is reached Support from ground-based ranging systems or data from other operational spacecraft can enhance the effectiveness of the guidance and control system.
Controlled re-entry can require a longer duration of operation time.
Electric power-supply subsystem
Debris related design
The items taken into consideration for the power-supply subsystem are shown in Table 10:
Table 10 — Debris-related measures in the power-supply subsystem
Mitigation measures Power-supply subsystem
Break-up prevention Yes Yes -
Considerations for power subsystems
The battery is the only source of break-up energy in this subsystem Batteries are designed and manufactured as described in 8.4.3.1.
8.4.2.2 Disposal manoeuver and controlled re-entry
Disposal maneuvers and controlled re-entry rely on a combination of propulsion, power, guidance and control, and communication subsystems The battery capacity is specifically designed to sustain the entire duration of these operations.
Consideration in component design
Batteries serve as the sole energy source for break-ups in this subsystem, necessitating their careful design and manufacturing to ensure all electrical and mechanical aspects are optimized, preventing any abnormal internal pressure increases or structural fractures.
Launch vehicles lack built-in power generation, so batteries must be designed with sufficient capacity to ensure disposal maneuvers and controlled re-entry, even under worst-case scenarios.
Batteries tend to survive re-entry They are assessed in the survivability analysis to calculate Ec.
During controlled re-entry, avionics experience prolonged exposure to radiation compared to missions that end at payload separation Therefore, radiation hardness design is essential for scenarios where controlled re-entry may occur.
Communication subsystem
Debris-related designs
The communication subsystem consists of the telemetry transmitter, radar transponder, and other communication equipment Measuring and data transmission equipment is included in this category in this document.
Items to be considered for this subsystem are shown in Table 11.
Table 11 — Debris-related measures in the communication subsystem
Mitigation measures Communication sub- system
Major components Tele-communication Measuring systems
Re-entry control Yes Yes Yes
Design of communication subsystem
NOTE There are no specific requirements added to the normal functions to support disposal manoeuvers.
For a controlled re-entry, additional functions and performance can be required as follows:
(1) Since longer durations of operation periods are necessary for controlled re-entry, adding to the normal operation, radiation hardness design can be required.
To ensure the successful initiation of controlled re-entry and to monitor the conditions during the re-entering trajectory, a measuring function is implemented to assess the health of the associated functions as needed.
The command line is engineered to stay active, allowing it to receive commands from the ground for both the initiation and termination of re-entry functions.
Considerations for component design
To ensure flight safety and verify essential functions, this subsystem measures and transmits key parameters and significant event signals to the ground control center It also encompasses the necessary parameters and event signals to confirm the successful execution of disposal maneuvers and the venting of any residual fluid, when feasible.
If a controlled re-entry is planned, this subsystem is used to support determination to proceed to a controlled re-entry manoeuver or cancel it, if designed to do so.