This invention relates to a method and a system for writing fiber Bragg gratings having apodized spectrum on optical fibers. The analog processing circuit is communicatively coupled to receive data from an inertial measurement unit and from at least one obstacle-detection sensor. A portion of the unconverted oil is then converted to lower boiling point hydrocarbons in the next reactor, once again creating a mixture of unconverted oil, hydrogen, converted oil, and slurry catalyst.