Q: What is GNC and what is it used for?
A: GNC is the subsystem responsible for guidance, navigation and control of a satellite in space. Guidance determines the desired position and orientation trajectories of spacecraft in the constellation. Navigation estimates the current state by fusing measurements from multiple sensors. Control commands actuators according to tuned algorithms that ensure the desired state is closely tracked.
Q: What kinds of software are involved with GNC?
A: Software is used on each spacecraft, starting from the collection and processing of sensor measurements to the allocation of commands to individual actuators. High-fidelity simulation software is needed to predict the behavior of spacecraft in the constellation, allowing GNC engineers to tune and verify their designs and commands before they are used on spacecraft in orbit.
Q: What types of hardware are associated with GNC?
A: GNC relies on a range of dedicated hardware such as gyroscopes, sun sensors and magnetometers used to determine the orientation and position of the spacecraft with respect to references like the sun and locations on Earth. At the other end of the GNC chain are actuators, such as reaction wheels and magnetorquers, whose role is to generate torques that compensate for external disturbances and keep the spacecraft pointed in the desired direction.
Q: How has evolving technology changed GNC?
A: There has been a dramatic increase in processing power and storage capacity as well as miniaturization of hardware components. The commercial-off-the-shelf version of some GNC sensors are tiny micro-electro-mechanical systems (MEMS) devices that can be integrated directly within printed circuit boards. Much of the GNC hardware interfaces are increasingly being standardized, allowing prices to decrease significantly and making integration of satellites approachable for small companies and universities.
From a software standpoint, more sophisticated GNC algorithms are being used on board while machine learning algorithms are increasingly finding applications within GNC. This is especially true as the number of spacecraft increases and large constellations need to be designed and managed.
Q: What are some examples of how GNC works for different applications?
A: GNC plays a crucial role in spacecraft and launchers and is also vital to most transport applications: cars and trucks that are becoming increasingly autonomous, manned and unmanned aircraft, trains, etc. Control has been used extensively for decades in many other industrial applications to drive all sorts of robots, machines and to regulate factories and power plants. High-tech consumer electronics, like smartphones and smart watches, are also packed with sensors and software that uses estimation algorithms like the ones used to predict the attitude and orbits of spacecraft.