abbreviated terms
| CCSDS | Consultative Committee for Space Data Systems |
| CDM | Conjunction Data Message |
| SSA | Space Situational Awareness |
| SSR | Space Sustainability Rating |
| SST | Space Surveillance and Tracking |
| TLE | Two-Line Elements |
OVERVIEW
This section covers the essential capabilities that satellite operators should have, to improve their ability to identify, respond to, and mitigate collisions. The methodology groups the capabilities in four categories, with a number of items of increasing value in each category.
1. Orbital State Knowledge
Rationale: Cooperative tracking often results in smaller covariances, as do more frequent tracking and improved information about planned satellite manoeuvres (e.g. by characterising the manoeuvre uncertainties).
The SSR gives additional credit for better orbit determination, more frequently updated orbit determinations, and better characterized/validated covariance estimation. This could help spur better orbit determination capabilities, especially for small satellites that might otherwise lack it. In the absence of an industry-wide standard for covariance estimation, knowing you have well-characterized the realism of your covariance information helps other operators determine whether to trust provided covariance estimates.
The accuracy which can be achieved on the orbital state knowledge, in any spatial direction, is orbit-regime dependent and can be influenced by the chosen technologies. A top-level distinction between coarse and accurate is to be made, which can be assessed by the SSR issuer.
2. Collision Avoidance: Availability to Coordinate
Rationale: Operators should be credited for maintaining service availability to coordinate with other operators for collision avoidance and being reachable for collision avoidance purposes with high availability.
3. Collision Avoidance: Capability to Coordinate
Rationale: Operators should be credited for maintaining staff with expertise to meaningfully resolve the potential event, namely:
a) Ability to accept and interpret common data formats including conjunction data messages (CDMs) and other Consultative Committee for Space Data Systems (CCSDS) standards;
b) Ability to review various sources of SSA information and determine the level of risk posed by a conjunction and whether a manoeuvre is indicated, not-indicated, or if further information is needed;
c) Ability to develop manoeuvre plans to mitigate a conjunction, screen manoeuvre plans from other operators for safety; and ability to task new non-routine manoeuvres for your satellites and confirm execution. Documented procedures help prevent human and technical errors during critical safety of flight operations.
4. Collision Avoidance: Manoeuvre capability
Rationale: Operators should be credited for implementing capabilities to avoid collisions. A relatively low thrust level implemented within a few revolutions can greatly enhance spaceflight safety and will be rewarded as part of the rating.
Table 1: Scoring Rubric for Collision Avoidance Capability
| Orbital State Knowledge (during normal operations) | Rely on a third party public SSA provider for state information (e.g. space-track.org TLE) | Operator maintained orbital position state knowledge of object [*] |
Maintain orbital state knowledge of object to < 10 km in any direction Update orbit determination for the operated satellite when a manoeuvre or other event induces a change to its orbit that would cause the operator’s state estimation to be worse than the required orbital state knowledge Characterize/validate covariance of your orbit determination |
Maintain orbital state knowledge of object to within < 1 km in any direction Update orbit determination for the operated satellite when a manoeuvre or other event induces a change to its orbit that would cause the operator’s state estimation to be worse than the required orbital state knowledge Characterize/validate covariance of your orbit determination |
| Collision Avoidance: Availability to Coordinate | Not able to coordinate | Able to coordinate in response to emergencies (but not necessarily on a routine basis) | Able to coordinate during set hours per day | Has a system for routine conjunction assessment and capability to respond to concerns 24 hours per day via human or computer system capable of supporting near-immediate coordination and reaction for urgent issues |
| Collision Avoidance: Capability to Coordinate |
Operator has no dedicated process for conjunction screening, assessment, or mitigation The operator may be unable to or chose not to ever manoeuvre in response to conjunctions |
Has the capability to be contacted in case of close approach or another high-risk event Operator regularly screens orbits and planned manoeuvres against public catalogues and/or information from SSA sharing organizations and/or third-party SSA providers |
Operator is capable of interpreting conjunction data messages and other common formats, to determine risk and generate/screen mitigating manoeuvres Operator has a system for automated routine conjunction assessment |
Has documented procedures for collision screening, assessment, and mitigation Regularly screens operational spacecraft and planned manoeuvres against SSA sharing organization catalogue |
| Collision avoidance: manoeuvre capability | No maneuver capabilities | Any maneuver capabilities (including differential drag) | Reaction (at least ∆v=1 cm/s) within 6 orbital revolutions | Reaction (at least ∆v=1 cm/s) within 1 orbital revolution |
|
(BONUS) Maintaining orbital state knowledge after the end of normal operations |
Maintain orbital state knowledge until spacecraft is placed into a graveyard orbit or is disposed of through atmospheric re-entry | Maintain orbital state knowledge to 10 km until spacecraft is placed into a graveyard orbit or is disposed of through atmospheric re-entry | Maintain orbital state knowledge to 1 km until spacecraft is placed into a graveyard orbit or is disposed of through atmospheric re-entry |
Scoring Guidance: Entities can receive credit for any box where they satisfy all criteria contained in the box. If an operator is able to fulfil multiple boxes in a single row, those point values are added. During the scoring process, the total number of points earned by the entity are divided by the total possible points. The normalized point total is an input to the full SSR calculation.