Situational Awareness: a Cornerstone of Operational Excellence in Space

Abstract

O perating in space is, at best, a risky business. Given that it is fraught with peril, the goal of operational excellence is not just a nice-to-have objective; it becomes a mandatory, albeit unwritten, requirement. Does this mean we have to command our spacecraft flawlessly or that every maneuver imparts an exactly predictable amount of delta-V? Obviously not, but it does mean striving to be error free in commanding and trying to reduce the variance of our maneuvers as much as possible. It is an attitude in our behavior as much as it is an exactitude in our performance. A number of factors, training, experience, education, and so forth, contribute to our behavior and performance, but the one that provides the essential foundation is maintenance of situational awareness.Situational awareness is woven into the very fabric of operational excellence. By recognizing the similarities and differences between situations for which you have trained and those you have not, you are able to deal with new operational challenges. Being aware of your spacecraft state as well as its future state may well help you avoid a catastrophic commanding error. As an example, consider that you are about to send an innocuous command to your spacecraft for one of its instruments. You can tell from telemetry that the instrument's sequence engine (portion of memory dedicated to sequences for this instrument) is empty with nothing executing at the time. However, a check of your spacecraft sequence of events alerts you to the fact that, in the time it takes for your command to reach the spacecraft (a light time), a different sequence to ramp up the voltage in the instrument will begin to execute in that sequence engine. Both sequences occupying the same engine will cause a sequence collision. A collision usually results in a safe mode entry which, under the right conditions, can have unintended and undesirable consequences. Fortunately, by maintaining situational awareness and checking the sequence of events, you can delay your command until the sequence engine is actually empty, avoiding a sequence collision and perhaps significantly grave consequences. In addition to understanding current and future states of the spacecraft, it is essential to understand and communicate about the interactions of flight and ground states and systems.The interactions of the attitude control and navigation teams supporting a spacecraft intended to orbit another planet provide an excellent case study of the need to maintain situational awareness of interactions and what can happen when you do not. The navigation team is responsible for determining the spacecraft trajectory, designing maneuvers to maintain its course and inserting it into an orbit around the planet. A major input to their calculations comes from the tracking data they receive. This includes range information, Doppler data and delta-differenced one-way ranging (DDOR) to name a few. However, there are forces at work on the spacecraft that are hard to model with just radiometric data, such as non-gr...