5 - ISS Jettison Policy Overview.pdf

ISS Jettison Policy and Approval Process Overview

Charles Gray May 2024

Page No. 2

Agenda

• ISS Jettison Introduction

• ISS Jettison Policy

– Jettison Candidate Criteria / Jettison Rationale

– Jettison Review and Approval Process

– Jettison Policy Requirements

• Lessons Learned

NRCSD Deployer jettisoning 2 3U Cubesats

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What is a jettison?

• A jettison is the release of any object from the ISS or an ISS visiting vehicle while in free flight

– Jettison can be performed by a crewmember during EVA or by robotic systems like the Space Station Remote Manipulator System (SSRMS), JAXA Small Satellite Orbital Deployer (JSSOD), NanoRacks Cubesat Deployer (NRCSD), Cyclops, Kaber, etc.

– After a jettison, ISS no longer controls the orbit of a jettisoned object

• At the current ISS altitude, jettisoned objects generally continue to orbit the Earth for a few months to a few years before ultimately re-entering the Earth’s atmosphere (depending on solar activity and ballistic properties of the candidate)

J-SSOD Deployer jettisoning 3 1U Cubesats

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Jettison Criteria / Rationale

• To be considered for jettison from ISS, an object must meet at least one of the following criteria:

– The object poses a safety issue for the ISS or for return onboard an ISS Visiting Vehicle (contamination, materials degradation, etc.).

– The object negatively impact ISS utilization, return manifest or on-orbit stowage manifests.

– The object represents an Extravehicular Activity (EVA) timeline savings large enough to reduce the sum of the risks of EVA exposure time and the orbital environment’s hazardous debris population, compared to the sum of such risks without a jettison.

– The object is designed for jettison.

SSRMS “static release” jettison of HTV EP9

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The ISS Jettison Review Process

• Prior to approving any jettison, the ISS Program goes through a thorough review process to ensure that the object is safe to jettison:

– Can the object be jettisoned safely, either via crew during EVA or robotically?

– Does the object pose a risk of collision with the ISS or any visiting vehicles after jettison?

– Is the object trackable on-orbit?

– Do any parts of the object pose a risk of inuring anyone on the ground?

– How will the object change the orbital debris environment?

• The ISS program weighs the risks of all the above against the benefit of jettison for every single jettison event. Approval to jettison any object must be acquired from all International Partners, so all the approval boards are multilateral

– Jettison of hardware not originally intended for jettison is only approved if the jettison candidate and jettison plan can be shown to be a lower risk alternative when compared to alternate disposal options

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The Jettison Review and Approval Process

• The VIPER team within OM3 is responsible for managing the analysis and approval process for all ISS jettison candidates, including coordination with multiple teams:

– TOPO helps characterize re-contact risk with ISS and ISS visiting vehicles

– MAGIK helps estimate jettison structural clearance cones

– ODPO helps characterize risk to the ground population

– Payload Developer or hardware provider coordination to gather details on jettison candidate ballistic properties and to gather inputs for re-entry modelling

• The nominal approval process involves reviews of jettison analysis at multiple boards

– VIPER/SPARC Panel (VSP), Multilateral Systems Engineering & Integration Control Board (MSEICB), the Safety Review Panel (SRP), and (if necessary) the Space Station Program Control Board (SSPCB) and/or Space Station Control Board (SSCB – multilateral)

– For late-breaking contingencies or as a last minute update if minor assumptions have changed, we also have the Increment Mission Management Team (IMMT, focused on real-time efforts and also multilateral)

• The ISS Jettison Policy (Partner Program Directive 1011) is our guiding document, it explains what requirements a jettison candidate must meet to be approved and the approval process itself

Page No. 7

Jettison Policy Requirements: Trackability

• Trackability

– The jettison candidate(s) shall be trackable by the Space

Surveillance Network (SSN).

– Verification: Jettison candidates must either conform to the dimensions detailed in the Expedited Approval Criteria or be confirmed trackable by Trajectory Operations and Planning Officer (TOPO) in consultation with United States Space Command

(USSPACECOM).

– Expedited Approval Criteria: Objects with a cross sectional area on each of three orthogonal sides greater than that of a sphere with a diameter 10 cm (78.5 cm2) are considered trackable by the SSN and will meet Requirement 4.1-1.

Cyclops deployer jettisoning LONESTAR satellite

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Jettison Policy Requirements: Limit Generation of Orbital Debris

• Limit Generation of Orbital Debris

– Candidates with stored energy systems (batteries, pressurized volumes, propellant systems, etc.) shall be passivated by End of Mission (EOM) to prevent fragmentation or generation of additional orbital debris

– If the jettison candidate cannot or will not be passivated, the PD will provide analysis that the risk of fragmentation is acceptably low

– For EVA based jettisons, bundle multiple jettison candidates together when possible

– Verification: Payload developers shall provide an EOM passivation plan to NASA explaining planned methods of fragmentation. The internal NASA standard for accepting no further mitigation of fragmentation risks is a maximum 1/1,000 chance of fragmentation over the remaining life.

– Expedited Approval Criteria: CubeSats that are 3U in size or smaller with orbital lifetimes less than 25 years are considered to meet this requirement per guidance received from NASA’s Orbital Debris Program Office (ODPO).

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Jettison Policy Requirements: Structural Clearance

• ISS Structural Clearance

– All objects planned for jettison shall verify that they do not contact any ISS structure during jettison

– For EVA based jettisons (crew), we need a large clearance cone (30° half-angle minimum) to be sure that the crew doesn’t accidentally hit ISS structure soon after jettison. The object is also reviewed for EVA control (i.e., is it “handle-able”)

– Verification: Coordination with the EVA office to confirm the planned jettison location and direction. The 30° half-angle clearance can be verified via MAGIK analysis, or a comparable visualization and modelling software.

– For candidates to be jettisoned robotically, the clearance cone must be larger than the worst case accuracy of the jettison mechanism, as defined by the robotics deploy mechanism system owner and implementing ISS robotics team and safety team

– Verification: Robotics analysis of the jettison location and direction which identifies the available jettison clearance cone (distance from jettison vector to ISS structure) as well as the worst-case half-angle accuracy of the jettison mechanism.

Astronaut Franklin R. Chang-Diaz works with a grapple fixture during an ISS EVA

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Jettison Policy Requirements: Re-Contact

• Limit Risk of Re-Contact with the ISS

– All objects planned for jettison shall verify safe relative motion with the ISS

– The jettison candidate shall clear the 200 meter ISS Keep Out Sphere (KOS) within 1 orbit and maintain a positive departing rate while in the KOS

– In the nominal jettison scenario, the jettisoned object’s return time to the vicinity of ISS shall be no less than 30 days from the jettison date. ISS reboosts or avoidance maneuvers will not be considered in this analysis.

– In the worst-case contingency jettison scenario, the jettisoned object’s return time to the vicinity of ISS shall be no less than 10 days from the jettison date. ISS reboosts or avoidance maneuvers will not be considered in this analysis.

– Verification: Verified by TOPO relative motion analysis or comparable Payload Developer relative motion analysis. Relative motion analysis will assume 0.05 m/s for EVA jettison (to cover “drop” cases).

The dV assumed for robotic jettisons will be based on individual system capability, and agreed to by the ISRP, robotic jettison mechanism system owner, and implementing robotics team.

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Jettison Policy Requirements

• Data Sharing

– The mission operations team for propulsive jettison candidates shall have a Space Situational

Awareness (SSA) Sharing Agreement in place with 18SPCS

– The mission operations team must provide owner/operator generated ephemerides to 18SPCS for space catalog maintenance when an orbit-adjusting event is planned

– The mission operations team for propulsive jettison candidates shall sign an agreement with NASA that documents a data exchange process between the TOPO office and the satellite mission operations team to maintain ISS safety

– Verification: Payload developers will provide to NASA proof of an SSA Sharing agreement with USSPACECOM. Details on registering satellites can be found at space-track.org

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• Responsible and Safe Space Operator

– Operators of propulsive satellites should demonstrate that they are Responsible and Safe Space Operators while on orbit by demonstrating the following:

• The jettison candidate successfully demonstrates that it can maneuver to a commanded attitude within an acceptable margin of error based on system limitations.

• The jettison candidate successfully demonstrates that it can hold a commanded attitude within an acceptable margin of error based on system limitations through the duration of a translational maneuver.

• The jettison candidate successfully demonstrates that it can achieve a commanded delta-velocity within an acceptable margin of error based on system limitations.

• The mission operations team for the jettison candidate successfully demonstrates that they can output state vectors that compare reasonably to an independent source (ex. Tracked orbit determination solution from 18SPCS)

• The mission operations team for the jettison candidate successfully demonstrates that they can output predicted post-burn state vectors that, when compared to actual burn performance, are sufficiently accurate for collision avoidance analysis.

• The mission operations team for the jettison candidate has an approved Collision Avoidance process in place, which should include data sharing, daily notification criteria, debris avoidance maneuver (DAM) criteria, and Translational maneuver Go/No-Go criteria based on conjunctions on the predicted post-burn trajectory.

• The jettison candidate secures commands that result in translational maneuvers (i.e. data encryption, preamble).

– Verification: During the Safety Review process, the propulsive candidate must provide a plan to demonstrate the Responsible and Safe Space Operator criteria on orbit. Following the first on orbit maneuver, satellite operators will provide NASA with proof that the satellite has met the aforementioned criteria to be considered a Responsible and Safe Space Operator.

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• Limit Risk of Re-Contact with the ISS

– Propulsive candidates shall operate such that they do not impact ISS operations

– If a propulsive jettison candidate has not met the

RSSO or the satellite loses the ability to meet those criteria, prior to planning any on-orbit maneuvers the satellite’s missions operations team shall verify that they do not pose a collision hazard to the ISS or ISS Visiting Vehicles

• TOPO analysis and input shall be required for a Go/No-

Go prior to orbit modifying events

– If a propulsive jettison candidate has met the RSSO criteria, the jettison candidate shall not enter the ISS Conjunction Notification Volume (CNV) within 5 days of a planned burn

Cyclops deployer jettisoning SpinSat satellite

Page No. 16

Lessons Learned: Re-entry Risk Characterization

• NASA calculates re-entry risk with tools developed by the NASA Orbital Debris Program Office (ODPO)

– The Object Reentry Survival Analysis Tool (ORSAT) is used for detailed re-entry analysis and is time intensive

– Debris Assessment Software (DAS) is a simplified, conservative model that is publicly available and helpful for simple re-entry analyses

• Typically, items that do not show ground casualty risk violation in DAS are considered to meet the NASA Std. 8719.14 requirement, and failure in DAS generally results in the more detailed ORSAT analysis

• Both ORSAT and DAS require detailed input assumptions to be accurate –

– Total mass (including and excluding fluids)

– Three orthogonal illustrations with dimensions indicated

– Orbital inclination

– Year of re-entry

– Detailed parts list with materials, mass, dimensions, shapes, thicknesses, and nesting details (how components are assembled and may shield one another during natural atmospheric re-entry). Specification of components composing at least 90% of the total mass is desired

• Lessons Learned: The level of detail required for this analysis can be difficult to acquire from hardware owners who may not be invested in the jettison review and approval process, or in some cases may not even be actively supporting the program

– Maintenance of detailed materials database (with drawings) for all hardware that could be jettisoned is recommended, and program-level support in the data gathering process is recommended to prevent delays in the analysis process

Page No. 17

Lessons Learned: Jettison Direction Accuracy and dV Requirements

• In 2008, ISS Program reviewed and approved jettison of the Early Ammonia Servicer (EAS) via EVA. At the time EAS was the most massive ISS jettison candidate to date, and the ISS Jettison Policy had not yet been formalized. Crew was advised to make an effort to generate as much dV as possible to improve separation from ISS. Unfortunately, the jettison candidate was released outside the intended jettison cone, resulting in higher re-contact risk and need for ISS reboost

• Lessons learned:

– Jettison accuracy via EVA, particularly with large cumbersome candidates, cannot be guaranteed to be high. Jettison review and assessment should account for a large possible error in jettison direction to avoid structural collision in the event that the candidate obstructs crew visibility, is difficult to handle during EVA, or crew cannot adequately orient themselves into ideal jettison direction

– Jettison speed should not be required to be high for a successful jettison. Dropped items on-orbit can happen! Plus, in an effort to perform jettison with higher dV, it’s easy for crew to inadvertently sacrifice jettison accuracy

– Reinforcing communication between analysts, EVA and flight control personnel, and EVA crew is paramount to ensure the parameters for safe jettison are commonly understood and trained for. This and other challenging EVA jettisons demonstrate the need for all parties to know the constraints and variables involved, and their clear conveyance between Program approval and ops execution.

Page No. 18

Lessons Learned: Working with Providers to Ensure Safe Novel Operations

• Small satellites deployed from ISS (and in general across the industry) increasingly feature a variety of design elements that could pose hazards to Station not previously accounted for in the jettison requirements space, including propulsion systems and drag-increasing devices (balloons, parachutes, booms, etc.)

– These features could introduce a translational maneuvering capability to the satellite, which

– can increase risk of conjunction with the ISS if left uncontrolled.

To standardize the process to control this risk of collision, while still enabling the safe mission execution of these innovative satellites, the Propulsive Jettison Candidate Criteria (Data Sharing and Responsible and Safe Space Operator requirements) were added t the ISS Jettison Policy in 2021

• Lessons learned:

– In order to best serve industry while managing risk to the crew and the orbital environment at large, the

ISS Jettison Policy must grow with the small satellite industry, with each analysis and deploy campaign yielding potential improvements to the process and stakeholder coordination – not only for the next campaign, but with applicability and adaptability for future applications in LEO and beyond.