005 - Re-entry Event ID
Purpose
This design document proposes a design for Re-entry Event IDs.
Context and scope
One of the key responsibilities for Monitor Space Hazards is to present reports on re-entry events to users across the UK government and internationally. To enable clear distinction between different re-entry events, we need to provide a unique identifier for each event.
Each report will include data provided in JSON files by the UK Space Agency’s (UKSA) Orbital Analysis team about the event in question. The Orbital Analysis team will include the event’s unique identifier in the JSON file. This unique identifier will then be used to refer to the event throughout Monitor Space Hazards and form the heading of the report on the event.
Goals and non-goals
The goal of this Design Doc is to articulate a design for the structure of the Re–entry Event ID, not the data flow.
Goals
- Develop a unique re-entry event identifier that can be easily and independently matched by the UKSA Orbital Analysis team
- Ensure the ID is time sortable so re-entry events naturally sort by most recent
- Ensure IDs fit into 64-bits for smaller indexes and better storage
- Ensure generation of the IDs is easily implemented without involving additional infrastructure or components.
- A human readable form of ID or unique label is highly desired for interpersonal communication
The actual design
Prior to the digitisation of UKSA’s re-entry service, each re-entry event was given a unique ID in the format RE-YYYY-XX in which YYYY represents the year of the event and XX reflects the number of re-entry reports that have been produced that year. For example, the third re-entry report produced in 2023 would have the event ID RE-2023-03.
These event IDs were easily and independently generated by the UKSA Orbital Analysis team and time sortable. However, they contain limited information about the event in question and were inconsistent with the event IDs already being used for conjunction events.
Therefore, we have developed a new Re-entry Event ID which reflects existing Conjunction Event IDs and contains more information about the event in question.
Standard re-entry event ID
RE-YYYYMMDD-[NORAD ID] whereby the date will be the opening of the re-entry window.
There will also be a second variant of RE-YYYYMMDD-UK[NORAD ID] when a dummy NORAD ID needs to be assigned by the orbital analysts.
Alternatives considered
We considered two alternatives to the Re-entry Event ID selected.
Maintaining the existing ID system The existing event ID took the format RE-YYYY-XX in which YYYY represents the year of the event and XX reflects the number of re-entry reports that have been produced that year. As outlined above, this was discounted as it contains little information about the event beyond the year in which it occurred and was inconsistent with the existing IDs for conjunction events.
Developing an ID related to the re-entering objects NORAD ID We also considered developing an ID related to the re-entering objects NORAD ID, taking the format RE-YYYY-XXXXX in which YYYY represents the year of the event and XXXXX reflects the object’s NORAD ID. However, this option was discounted because in some edge cases different parts of an object (with a single NORAD ID) would re-enter the Earth’s atmosphere in two separate events. If these events occurred within the same year, the two event IDs would not be unique using this system.