Event parameter (Conjunctions)

Primary and secondary objects: The primary and secondary object distinction is taken from Space Track conjunction data messages (CDMs). This means that the primary object will not always be your own satellite.

Probability of collision: The probability of a collision as calculated by Space-Track or the UKSA. The method of calculation is shown in each event page under the ‘Probability of collision calculations' accordion.

Time of closest approach: The time, in UTC, that the distance between two objects is predicted to be the smallest.

Miss distance: The Consultative Committee for Space Data Systems (CCSDS) describes the miss distance as "the norm of the relative position vector. It indicates how close the two objects are at the time of the predicted encounter."

Monitor Space Hazards uses the RTN coordinate framework to describe miss distances. Radial is the unit vector in the radial direction pointed outward from the centre of the central body. Transverse or in-track is the unit vector perpendicular to the radial vector in the direction of the spacecraft velocity. Normal or cross-track is the unit vector normal to the satellite’s inertial orbit plane (in the direction of the satellite’s angular momentum) that completes the right-hand coordinate frame.

Total miss distance is the exact distance between the two objects in 3D space. It is the combination of the vectors of radial, in-track and cross-track distance.

Event history: The event history includes all updates to an event over time. This will include all CDMs and UKSA data.

Event parameter (Re-entries)

Object: The space object re-entering the Earth's atmosphere.

Risk to the UK: Risk thresholds assigned by the UKSA to re-entering objects based on their probability of re-entry over the UK. Risk levels are 'Low', 'Medium', and 'High'.

Probability of re-entry over the UK: The percentage chance that the object re-enters over the UK or any of its Overseas Territories 

Re-entry time window worldwide: The window of time in which the object is expected to re-enter the Earth's atmosphere

UK overflight time: The specific times within the Re-entry worldwide time window where the object is expected to pass over the UK or its Overseas Territories.

Expected survivability to ground: A qualitative assessment made by the UKSA's Orbital Analysis team based on their knowledge and analysis of the re-entering object

Licensing country: Country where the re-entering object was first licensed and registered

Event history: The event history includes all updates to an event over time. This will include all TIPs and UKSA Reports.

Data sources

Ephemeris: Ephemerides are cartesian vectors providing position and velocity, and optionally accelerations. More information about ephemerides and .oem files can be found at the CCSDS recommended standard for orbit data message.

Monitor Space Hazards provides a user-friendly system to help identify which CDMs contain SPECIAL ephemeris data.

Special ephemeris files represent a possible new orbit which assume a manoeuvre such as orbit raising, relocation, or COLA, will occur and are submitted to Space-Track for planning purposes using SPECIAL in the ephemeris file name.

Operational ephemeris files denote the current operational plan for the satellite (this may include manoeuvres which have been confirmed and are about to be committed). 

By labelling which CDMs include SPECIAL information, users can easily access the data they need to plan their operations.

TIP: Tracking and Impact Prediction message generated by Space-Track. Provides information on re-entering objects, including predicted re-entry time, predicted coordinates of re-entry, and time of next update.

SSN: The United States space surveillance network.

ESA DISCOS: The European Space Agency’s Database and Information System Characterising Objects in Space.

TLE (two line elements): A two-line element set is a data format encoding a list of orbital elements of an Earth-orbiting object for a given point in time, the epoch.

Data received: The timestamp in UTC of when the data source was received.

Observations: The number and timespan of observations of the objects are shown to reflect the reliability of the data.

Object information

All object information within Monitor Space Hazards is sourced from Space-Track's satellite catalogue. UKSA orbital analysis is supplemented with wider data sources listed in 'Conjunction analysis process and sources'. Any fields that are 'pending' are yet to be connected to a source.

NORAD ID: An object in space's catalogue number, assigned by the United States' Space Command. Unknown objects are given an ID in the 80,000s.

Object type: This can be payload, rocket body, or unknown.

Manoeuvrability: This is based upon data that operators provide to Space-Track. Note that this information may be out-of-date or inaccurate.

Further definitions can be found in the Terms of Service.