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How aware are we?

Our current space surveillance network (SSN) is a patchwork of sensors that has been cobbled together from many different programs and funding sources during the past 60 years for a variety of purposes.  If we were to write a requirements document today for a sensor network to provide adequate space situational awareness (SSA) to enable reliable space traffic management (STM), it would look very different.

As we all know, the ability to determine an object’s position at any moment in its orbit is predicated upon how accurately its position and velocity was determined, and when. The more recent and accurate the measurement, the greater the certainty of its position. In the limit, if an object is constantly tracked, its position is known, and if tracked long enough, its future position can be projected with the highest accuracy possible.

The less frequent and accurate the measurement of any object, the greater the uncertainty of its position at any future time. Also, the further in time the projection is made from its last measurement, the higher the uncertainty of its position. Consequently, given a requirement for a certain level of position certainty for the objects in orbit, it should be fairly straightforward to calculate the required number, location, and duration of observations by the SSN to meet that requirement.

The addition of new, more capable sensors (i.e. Space Fence) is expected to add hundreds of thousands of new, smaller, and harder to track objects to the current catalog. This requires an SSN far more capable than we have today to achieve an acceptable level of performance for future STM needs.


My questions to those in the know:

  1. What is an acceptable level of position uncertainty? Is this dependent on object size and orbit? Are the objects in the current catalog monitored according to any tracking priority?
  2. Given the current catalog, how many more observations and over what period of time are required to provide this level of certainty? What percentage of high-priority objects meet this level of position uncertainty today?
  3. What is the criteria for adequate SSA?
  4. How many more sensors, where located, and of what type are needed today to meet this observation requirement?
  5. Given the expected growth of the catalog from new, more accurate sensors, what is the expected additional observations of these newly catalogued, smaller objects to maintain this level of position certainty? How many more sensors and what type will be required to meet this evolving need?
  6. Is there a critical level of observations below which SSA is lost? How will this change over time with the anticipated launch of mega constellations?


The evolving space ecosystem in low earth orbit requires us to know the answers to these questions.