I was wondering how a rocket adjusts its position to ensure it takes the desired path. What sensors, or generally technology, are used to gain data on the rocket's position, where it is heading and the rocket's orientation?

Additionally, is processing of the data from the sensors required before feeding the data to the output devices or actuators of the rocket? For example the engine or the fins in order to adjust the rocket's position. If so what processing occurs?


2 Answers 2


Traditionally, just an inertial measurement unit. More recently GPS has come into play as an additional sensor to better nail down the state.

Yes, a great deal of processing takes place to convert the data from the sensors into a filtered state, comparing that state to the desired state at that moment in time, and coming up with various commands, kept within their limits, to guide the vehicle back to the desired trajectory, as well as deciding when to cut off burns and stage.

  • $\begingroup$ Addendum: Shuttle, in addition to IMUs, used Rate Gyro Units. $\endgroup$ Commented Sep 29, 2016 at 18:03

Astronauts need to know 2 things; the attitude the ship is in, and where the ship is. Internal guidance can store both of these types of information with gyros and accelerometers, but it has to be updated. So whereas the Apollo had an internal gyroscope that tracked the attitude, it was updated / corrected with star sightings by an astronaut. Where the ship is, is tricker because it is not in a place, it is in a vector, and that changes constantly from one moment to the next. A computer model of movement predicts it's trajectory and that needs to be updated as it drifts. In earth orbit, the ship can be tracked from the ground where there are more people and many antennas to triangulate between. Beyond earth (and GPS) like a trip to Mars, astronomical observation of the planets would have to be done to update the trajectory information.


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