Launch Screening
A screening is a Conjunction Assessment (CA) process to predict close approaches between Resident Space Objects (RSOs).
A launch screening is a screening processed by Satcat Launch for the explicit purpose of identifying close approaches between the trajectory of a launch vehicle on its path from Earth's surface to its target orbit with other objects in the space environment.
📚 Learn more about Conjunction Assessment
Ephemeris Data
An ephemeris is a timeseries data file of predicted state information about an object. Ephemeris contains information about an asset's position and velocity, and may include uncertainty data.
Screenings work by comparing the ephemeris from a set of primary objects against the ephemeris from a set of secondary objects, which is typically a catalog of all on-orbit RSOs. Launch screenings are processed on Satcat Launch servers, and screenings can be configured to use a launch provider's own predictive ephemerides and/or catalog ephemerides from third party sources.
Form 22 is the Launch Screening Request form required by the US Department of Defense for launch screenings performed by 18/19 SDS.
Throughout the Satcat Launch documentation, parameters which correspond to fields on Form 22 may be marked to clarify for users who are familiar with the 18/19 SDS process, e.g.: (Form 22: Item 4)
Launch Ephemeris
A launch ephemeris (Form 22: Item 5) is a file describing the planned trajectory that the launch vehicle intends to follow. Launch screening in Satcat Launch begins with the user uploading one or more launch ephemerides. Launch ephemeris that is used as a secondary in a screening will only be considered at the nominal launch time contained in the file.
Satcat Launch specifically accepts the CALIPER Trajectory Covariance V2.0 launch ephemeris file format, which requires velocity terms in each state data record, and lower triangular position covariance.
Hard Body Radius (HBR)
When uploading each launch ephemeris, the Hard Body Radius (HBR) of the object whose trajectory the ephemeris file describes must be included. The HBR of an object is the radius of the smallest sphere which circumscribes the object. This value is used when computing the Probability of Collision (Pc).
Some conjunction assessment systems, including the Form 22 launch screening system operated by 18/19 SDS, express the object size as the RCS in units of area instead of the HBR in units of distance.
Multiple Stages
Most launch missions are comprised of multiple separating stages or objects whose trajectories diverge as the mission progresses. However, each launch ephemeris uploaded to Satcat Launch must represent the trajectory of a single discrete object with a constant HBR value. Launch missions with multiple stages, whether launch vehicle separations or fallback trajectories (ex: tension rods or failed relight plans), must submit each individual trajectory as a separate launch ephemeris file.
For each uploaded launch ephemeris added as a primary to the launch screening, Satcat Launch will screen the trajectories of all mission stages over the same launch options.
Catalog Data
A catalog is a large set of ephemerides describing the trajectories of a set of objects in the space domain over a given time interval. Only one catalog may be used as a secondary data source in a screening job, and a catalog may not be used as a primary data source.
The catalog type indicates the data source from which its ephemerides were generated. Satcat Launch maintains operational catalogs of the following types:
- Special Perturbations (SP), or High-Accuracy Catalog (HAC)
This catalog is maintained by 18 SDS via the Space Surveillance Network (SSN) and is distributed by 18/19 SDS without covariance data. This means that Probability of Collision (Pc) computations that use SP catalog data are based solely upon the uncertainty of the primary object when present.
If both the primary and secondary data do not contain uncertainty, conjunction Pc cannot be calculated.
Learn more about Probability of Collision
Use of the SP Catalog requires your organization to have a Data Sharing Agreement with 18/19 SDS.
Coverage
When performing a screening with gamut, it is important that the primary and secondary ephemeris data overlap in time. The coverage of a primary is the amount of the primary ephemeris which overlaps in time with the secondary ephemerides. Satcat Launch reports both the coverage of each individual primary, and the average coverage of the screening considering all its primaries.
Satcat Launch reports coverage at three discrete levels:
- ✅
FULL, when the primary data fully overlaps in time with the secondary data - ⚠️
PARTIAL, when the primary data partially overlaps in time with the secondary data - ❌
NO_OVERLAP, when the primary data does not overlap in time with the secondary data at all
Satcat Launch also reports the coverage ratio, a number between 0 and 1 which represents the fraction of the primary ephemeris data's time interval which overlaps with the secondary data.
In general, screenings performed for operational use should have FULL coverage, so that all data points supplied in the primary ephemeris are considered during screening. By default, Satcat Launch ensures that screenings have FULL coverage, and screenings with PARTIAL or NO_OVERLAP coverage will be rejected at validation and present the user with an error message.
The launch window set on a screening will impact the coverage of its primaries, because the launch window determines the time at which the primary launch ephemerides are considered.
If a screening has NO_OVERLAP or PARTIAL coverage in Satcat Launch, it could be because the configured launch window places the primary ephemeris data outside the usable time interval of the configured secondary data.
Strict Coverage
Satcat Launch provides an optional strict coverage configuration parameter (enabled by default) which can be disabled to allow a screening to be performed even with PARTIAL coverage. When this setting is enabled, if a screening has PARTIAL coverage, the screening will pass validation and the screening will consider the overlap between the configured primary and secondary ephemeris data. Screenings with NO_OVERLAP coverage will be rejected at validation regardless of the strict coverage setting.
Disabling strict coverage can be useful when uploading very long ephemerides, but is generally discouraged for most operational use cases.
Launch options
Each launch option is a potential time at which a vehicle may launch and begin its ascent into orbit. By identifying the conjunctions along the trajectory that begins at each launch option, Satcat Launch quickly determines which launch options will pose a significant safety risk to the launch vehicle.
Launch options in Satcat Launch are defined using a launch window, which is described as:
- The Start Time - the earliest launch time being considered (Form 22: Item 2)
- The End Time - the latest launch time being considered (Form 22: Item 2)
- The Cadence - the amount of time between each Launch Option (Form 22: Item 4)
Launch options example
- Start Time 2023-01-01 12:00:00
- End Time 2023-01-01 16:00:00
- Cadence 10 seconds
- = 1441 Launch options
[(4 h x 3600 sec/h window) / 10 sec cadence] + 1 inclusive window endpoint = 1441
Conjunction Results
A conjunction is a close-approach event between a launch vehicle and an object in the space domain. For a given screening, a conjunction is reported for each instance at which the miss distance between primary and secondary objects violates the screening's threshold radius.
Conjunction results will include identifying data, including primary and secondary NORAD_ID, the Time of Closest Approach (TCA), the Miss Distance, and the launch time of the mission which will result in the conjunction. If uncertainty data was included with one or both of the primary and secondary data, then the Probability of Collision (Pc) will also be reported.