Space Situational Awareness



Space situational awareness (SSA) is the knowledge, characterization, and practice of tracking space objects and their operational environment. SSA data is used to predict conjunctions between objects and warn space operators of potentially dangerous close approaches to enable collision avoidance maneuvers. Debris from fragmentation events, meteor storms, or other natural events might also affect operations. SSA is foundational to all space safety and realtime space traffic coordination activities and is a critical component of Space Domain Awareness (SDA), which is the ability of decisionmakers to understand, as completely as necessary, their current and predicted operational environments.

The Aerospace Corporation has been deeply involved in all aspects of SSA as it has been practiced by the U.S. government, including the acquisition and operation of the Space Surveillance Network’s (SSN’s) radars and telescopes. We have been instrumental in developing the processes and algorithms of orbit determination, propagation, conjunction prediction and collision probability estimation that are used operationally by the U.S. Space Force, as well as the maintenance of the catalog of space objects. 

SSI experts educate the space industry in the practical details of turning observations from sensors into knowledge of orbits. Risks to space operators go beyond objects we can see and track, the focus of most SSA efforts. Our goal is to examine the space environment holistically, to understand both the debris that can’t be tracked connect the analysis of the present with practical assessments of the future. Some examples of this include:

  • For decades, Aerospace’s Center for Orbital and Reentry Debris Studies (CORDS) has honed models of the untrackable debris environment to quantify unseen risks now and in the future. The Aerospace Debris Environment Projection Tool (ADEPT) models the future environment under multiple scenarios and provides insight into the effects of various behaviors and policies on future debris generation, collision frequencies, and satellite operating conditions. Results from ADEPT help craft policies and norms of behavior that achieve desired outcomes.
  • We directly managed and provided public access to the unclassified space object catalog derived from SSN data as part of pilot commercial and foreign entity support (CFE) from 2003 through 2006. Aerospace created and handed over a functioning system to a contractor for continuing operations.
  • We have deep experience with current catalog maintenance and sensor processing. We help manage the SSN Metrics Improvement Project Team, and we developed a process for catalog covariance corrections. We lead multiple efforts in managing new observations for difficult-to-track objects and new observations, and we have developed techniques aimed at tracking rendezvous and proximity operations and minimizing observation cross-tagging. We have deep expertise in the algorithms of operational orbit propagators.
  • We have created prototype tools for daily SSA analysis. These include daily prediction of all-on-all close approaches, automatic detection of maneuvers, a space weather dashboard, and tools for SSA big data mining.


Independent Assessments

Aerospace, working cooperatively with the Naval Research Laboratory, assessed for the Air Force Research Laboratory state-of-the-art uncorrelated track (UCT) processing tools critical to maintaining a catalog of space objects and efficiently tracking debris after fragmentation events. The assessment covered a wide range of orbital altitudes and techniques, including radar and telescope observations; evaluations included testing against real-world cases. 


Standards and Best Practices

The U.S. Space Force maintains a set of standards for astrodynamic algorithms to process SSN data. Aerospace recently rewrote the government’s SGP4 orbit model to improve accuracy and extend its range of applicability. Aerospace worked with the U.S. government to define changes to the two-line element (TLE), used to define satellite orbits in the U.S. Air Force SSN catalog, to accommodate this new model. SGP4 is the most widely used propagator worldwide, and TLEs are the most commonly used format for orbit data. The new propagator will be included as a new astrodynamics standard.


Research and Development

SSI conducts research in a variety of areas to find practical solutions to new challenges for maintaining accurate information on space object orbits. It is critical to have an accurate understanding of all satellite orbits by integrating data from more sensors, including those of U.S. allies. Incorporating external data poses new challenges with no guaranteed improvement in tracking. Aerospace has supported government exercises examining satellite tracking data from foreign sensors to determine the effects and benefits of incorporating that data into U.S. space object catalog maintenance.

Orbit propagation accuracy is critical to determining the utility of tracking data for safety tasks, such as collision avoidance. At the request of the government, Aerospace extensively modified the orbit models inside the SGP4 propagator. These modifications provide one to two orders of magnitude improvement in accuracy as well as extending the model’s applicability to cislunar space.

Aerospace has long researched independent GPS-based active transponders and has been drastically reducing their required size, weight, and power. In addition, we are actively working with the Combined Space Operations Center (CSpOC) to incorporate this type of data into the space surveillance catalog.

Uniquely identifying and determining orbits for launches with many payloads is difficult, especially shortly after deployment. Aerospace modified the government’s breakup processor to identify the orbits of individual fragments after a breakup event. This tool is designed to quickly separate and catalog the satellites from multi-payload launches. 

When a fragmentation event occurs in space, hundreds or thousands of trackable fragments can be generated as well as tens of thousands (or more) untrackable but mission-ending fragments. Even for trackable fragments, it can take days to weeks to catalog them. During that time, they are an invisible hazard to satellites. Aerospace developed the tools needed to model the generation of debris from satellite and upper-stage fragmentation events and the associated risk to satellites. This capability is regularly called on by the government when on-orbit breakups occur.


Policy and Strategy

Space situational awareness depends on the collection and interpretation of data. There are a number of issues associated with collecting data from the range of available sources including government, commercial and international sensors. Standard methods and formats of data transfer must be developed and agree upon. SSI is helping develop the common understanding and language needed for effective space situational awareness.

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